EXAM 3

How does the behavior of Anolis lizards in the Dominican Republic change over elevation?

Anolis lizards in the Dominican Republic bask more frequently at high elevation than they do at low elevation.

Early angiosperm embryos undergo a series of general changes as a seed matures. Summarize this sequence; then describe the structural differences that develop in the seeds of monocots and eudicots.

As a seed matures, the embryo inside it develops a root-shoot axis with a root apical meristem at one end and a shoot apical meristem at the other end. Depending on the plant group, one or two cotyledons also develop. In monocots, a single large cotyledon develops and stores endosperm; protective tissues arise around the root and shoot apical meristems. In eudicots, two endosperm-storing cotyledons form. Near the micropyle, the radicle (embryonic root) attaches to the cotyledon at a region called the hypocotyl. Beyond the hypocotyl is the epicotyl, which has the shoot apical meristem at its tip and often bears a cluster of tiny foliage leaves, the plumule. At germination, when the root and shoot first elongate and emerge from the seed, the cotyledons are positioned at the first stem node with the epicotyl above them and the hypocotyl below them.

What is a mycorrhiza, and why are mycorrhizal associations so vital to many plants?

As described in this chapter and in Section 28.3, a mycorrhiza is a symbiotic association between a fungus and plant roots. Most plants form mycorrhizal associations, which facilitate the plant's ability to extract soil nutrients such as nitrogen and phosphorus. As with plant roots, mineral ions enter fungal hyphae by way of transport proteins. Some of the plant's sugars and nitrogenous compounds nourish the fungus, and as the root grows, it takes up a portion of the minerals that the fungus has secured. In some types of mycorrhizae the fungus actually lives inside cells of the root cortex.

What role do properties of water play in the transport of xylem sap?

As water evaporates from mesophyll cell walls into leaf air spaces, surface tension in the water film remaining at air-water interfaces pulls the film inward, producing a curved meniscus. This curved shape signals the development of a negative pressure potential—and, hence, a lower water potential—in a cell's water. Because the water potential in neighboring cells now is comparatively higher, some of water moves out by osmosis, replacing that lost at the start of transpiration. As the loss and replacement of water continues from cell to cell in mesophyll, eventually replacement water is pulled osmotically out of small xylem veins in the leaf, which in turn withdraw water from larger veins, and so on. The cohesion of water molecules maintains the pull ever farther from the air-water interface, a pull that extends through the xylem all the way down to a plant's roots.

What processes move large quantities of carbon from an organic compartment to an inorganic compartment?

Respiration, excretion, leaching, and the burning of fossil fuels move large quantities of carbon from an organic compartment to an inorganic compartment of an ecosystem.

Summarize the various ways that chemical signals reaching plant cells are converted to changes in cell functioning.

Two general types of signal response pathways convert chemical signals into altered plant cell activity. Some plant hormones and growth factors bind to receptors at the target cell's plasma membrane. Others cross the plasma membrane and bind to receptors inside the cell. Second messengers enhance the cellular response.

Explain how nastic movements differ from tropic movements.

Unlike tropisms, nastic movements occur in response to nondirectional stimuli, such as mechanical pressure resulting from an insect brushing against hairlike sensory structures in the leaves of a Venus flytrap plant.

Describe the components of vascular cambium and their roles in secondary growth in stems, including the development of tissues such as bark, cork, and wood.

Vascular cambium consists of two types of cells—fusiform initials and ray initials. Fusiform initials are derived from cambium inside the vascular bundles and give rise to secondary xylem and phloem cells. Secondary xylem forms on the inner face of the vascular cambium, and secondary phloem forms on the outer face. Ray initials are derived from the parenchyma cells between vascular bundles. Their descendants form spoke-like rays of parenchyma cells—horizontal channels that carry water sideways through the stem. As the mass of secondary xylem inside the ring of vascular cambium increases, it forms hard tissue known as wood. Bark encompasses all of the living and nonliving tissues between the vascular cambium and the stem surface. It includes the secondary phloem and the periderm, the outermost portion of bark that consists of cork, cork cambium, and secondary cortex.

According to the equilibrium theory of island biogeography, what are the effects of an island's size and its distance from the mainland on the number of species that can occupy it?

According to the equilibrium theory of island biogeography, large islands will harbor more species than small islands, and islands that are close to the mainland will harbor more species than those that are farther away.

Some flowers have distinctive patterns that only reflect ultraviolet light and therefore are invisible to humans. Which statement about such markings is NOT correct? A The ultraviolet patterns repel birds and bats from the flowers. B Flowers with ultraviolet patterns usually appear yellow or orange to humans. C The ultraviolet patterns are highly visible and attractive to bees. D The ultraviolet patterns often form a conspicuous central bull's eye or identify the best landing sites.

A

Starting from the outside and moving in toward the center, which gives the correct order of tissues in the stem of a young tree? A primary phloem, secondary phloem, secondary xylem, primary xylem B primary xylem, secondary xylem, secondary phloem, primary phloem C secondary phloem, primary phloem, primary xylem, secondary xylem D secondary phloem, primary xylem, secondary xylem, primary phloem E primary phloem, secondary xylem, secondary phloem, primary xylem

A

Which graph, A, B, C, or D, depicts the principle of competitive exclusion?

A

Which statement is NOT true about primary plant growth? A Only woody plants show primary growth. B Primary growth increases the length of the plant. C The ground meristem is a primary meristem that produces ground tissue. D The procambium is a primary meristem that produces primary vascular tissue. E The protoderm is a primary meristem that produces the more mature dermal tissue.

A

How does a climax community differ from early successional stages?

A climax community differs from earlier successional stages in having taller, longer-lived vegetation, generally higher species richness, and a buffered physical environment under the vegetation.

What do the three patterns of dispersion imply about the relationships between individuals in a population?

A clumped pattern of dispersion implies that individuals in the population help each other or that some vital resource in the environment also has a clumped distribution. A uniform pattern of dispersion implies that individuals in the population repel each other. A random pattern of dispersion does not imply either positive or negative interactions among individuals in the population.

What is a homeobox gene? Give at least two examples of plant tissues such genes might govern in a species such as A. thaliana.

A homeobox gene is a regulatory gene in the genome of an organism that encodes a transcription factor. In A. thaliana, homeobox genes govern the development of the root and shoot tissue systems, as well as of floral organs.

Compare and contrast the functions of a land plant's root and shoot systems.

A land plant's shoot system consists of its photosynthetic tissues and organs—stems, leaves, and buds. Stems are frameworks for upright growth and favorably position leaves for light exposure and flowers for pollination. Leaves increase a plant's surface area and thus its exposure to sunlight. Buds eventually extend the shoot or give rise to a new, branching shoot. The shoot system of a flowering plant also includes flowers and fruits. Parts of the shoot system store carbohydrates manufactured during photosynthesis. The root system usually grows below ground. It anchors the plant, and sometimes structurally supports its upright parts. It also absorbs water and dissolved minerals from soil and stores carbohydrates.

What statistics are usually included in a life table?

A life table usually summarizes statistics about the agespecific survival rates, age-specific mortality rates, and age-specific fecundity of a population.

What factors affect a plant's ability to absorb minerals from the soil?

A plant's ability to absorb soil minerals depends partly on cation exchange, in which one cation, usually , replaces a soil cation. As enters the soil solution, it displaces adsorbed mineral cations attached to clay and humus, freeing them to move into roots. Anions in the soil solution, such as nitrate , sulfate , and phosphate , generally move more readily into root hairs. Soil pH also affects the availability of some mineral ions because chemical reactions in very acidic (low pH) soils can trigger chemical reactions that bind various mineral cations in compounds that are insoluble in soil water.

Explain the sequence of events in a flowering plant that begins with formation of a pollen tube and culminates with the formation of a diploid zygote and the 3n cell that will give rise to endosperm in a seed.

A pollen grain that lands on a compatible stigma absorbs moisture and germinates a pollen tube, which burrows through the stigma and style toward an ovule. Chemical cues from the two synergid cells help guide the pollen tube toward the egg. Before or during these events, the pollen grain's haploid sperm-producing cell divides by mitosis, forming two haploid sperm. When the pollen tube reaches the ovule, it enters through the micropyle and an opening forms in its tip. The two sperm are released into the cytoplasm of a disintegrating synergid. Next double fertilization occurs: typically, one sperm nucleus fuses with the egg to form a diploid (2n) zygote. The other sperm nucleus fuses with the central cell, forming a cell with a triploid (3n) nucleus. Tissues derived from the 3n cell are called endosperm.

How does a population viability analysis assist in the development of a conservation plan for a species?

A population viability analysis allows a conservation biologist to identify the minimum population size that is likely to survive both predictable and unpredictable environmental change. It therefore specifies how many individuals must be conserved for the continued survival of the population and species.

What is the difference between a population's size and its density?

A population's size is simply the number of individuals it contains. Its density is the number of individuals per area or volume of habitat occupied.

What is a time lag?

A time lag is a delay in a population's response to a changing environment. It may cause a population's size to oscillate around its carrying capacity.

Select all the correct choices A Most animals have the ability to move fairly freely B Plants contain chlorophyl and can make their own food C Plant and animal cells have vacuoles for storing water D Plants give off oxygen and take in carbon dioxide given off by animals E Plants give off carbon dioxide and take inoxygen

A,B,D

These photos of the drone fly and honeybee represent which ecological concept? (select all that apply). answerable question reference Multiple answers: You can select more than one option A Protective coloration B Commensalism C Mullerian mimicry D Batesian mimicry

A,D

Summarize the mechanism by which associations with bacteria supply nitrogen to plants such as legumes.

Associations with bacteria supply nitrogen to certain types of plants, such as legumes. The host plant provides organic molecules that the bacteria use for cellular respiration, and the bacteria supply that the plant uses to produce nitrogenous molecules. In legumes the nitrogen-fixing bacteria reside in root nodules. Usually, a single species of nitrogen-fixing bacteria colonizes a single legume species, drawn to the plant's roots by chemical attractants (mainly flavonoids) that the roots secrete. By way of exchanged molecular signals, bacteria then are able to penetrate a root hair and form a colony inside the root cortex. Each cell in a root nodule may contain several thousand bacteria (now called bacteroids). The plant takes up some of the nitrogen fixed by the bacteroids, and the bacteroids use some compounds produced by the plant.

Which plant hormones promote growth and which inhibit it?

Auxins, gibberellins, cytokinins, and brassinosteroids all promote the growth of plant parts, and ethylene stimulates cell division in seedlings. Strigolactones interact with other hormones, including auxin and cytokinins, to modify the development of roots and shoots as environmental conditions shift. In particular, strigolactones regulate lateral branching in shoots and roots. Abscisic acid is the major growth-inhibiting plant hormone. ABA also triggers plant responses to various abiotic environmental stresses, including cold snaps and drought.

Abscisic acid (ABA) is synthesized in the roots in response to decreased soil water potential. ABA then translocates to the leaves, where it rapidly alters the osmotic potential of guard cells. What effect would this have on the stomata and the process of transpiration? A The stomata would open thereby increasing the rate of transpiration. B The stomata would close thereby decreasing the rate of transpiration. C The stomata would close thereby increasing the rate of transpiration. D The stomata would open thereby decreasing the rate of transpiration.

B

Which of the following statements is false? A Negative water potential draws water into the root hairs. Cohesion and adhesion draw water up the xylem. Transpiration draws water from the leaf. B Negative water potential draws water into the root hairs. Cohesion and adhesion draw water up the phloem. Transpiration draws water from the leaf. C Water potential decreases from the roots to the top of the plant. D Water enters the plants through root hairs and exits through stoma.

B

What microorganisms drive the global nitrogen cycle, and how do they do it?

Bacteria, cyanobacteria, and fungi drive the global nitrogen cycle through their activities in nitrogen fixation, ammonification, nitrification, and denitrification.

How does Earth's spherical shape influence temperature and air movements at different latitudes?

Because of Earth's spherical shape, sunlight striking the planet's surface is more concentrated near the equator than at the poles. As a result, temperatures are higher at low latitudes. The concentrated sunlight near the equator heats the atmosphere, causing air masses near the equator to rise, establishing three circulation cells in the Northern Hemisphere and three in the Southern Hemisphere.

What data must ecologists collect before constructing a simulation model of an ecosystem?

Before constructing a simulation model of an ecosystem, ecologists must collect data about the population sizes of important species, the average energy and nutrient content of each, the food webs in which they participate, the quantity of food each species consumes, and the productivity of each population; the ecosystem's energy and nutrient gains and losses caused by erosion, weathering, precipitation, and runoff; and seasonal and annual variations in these factors.

How do extinction rates today compare with the background extinction rate evident in the fossil record?

By one estimate, extinction rates today may be 1,000 times greater than the background extinction rate evident in the fossil record.

Animals trapped and digested by "carnivorous" plants are used primarily as a source of A Carbon B Potassium C Nitrogen D An energy supplement for small plants growing in shady areas

C

If a pollen grain generates only one sperm cell instead of two, then after pollination A No pollination would take place B The seeds would lack either embryos or endosperm, and would germinate C The seeds would lack either embryos or endosperm, and is nonviable. D The seed would develop two endosperms

C

The term that would best fit in the empty box below with the question mark would be: answerable question reference A Dead inorganic matter B Plants C Dead organic matter D Primary consumers E Fast food

C

The worldwide intrinsic rate of human population growth (r) is currently 1.3%. In the United States, r = 0.6%. How will the U.S. population change relative to the world population? A The world population will grow, while the population of the United States will decline. B The world population will grow, while the population of the United States will remain the same. C Both the world and the U.S. populations will grow, but the world population will grow more rapidly. D The world population will decline, while the U.S. population will increase.

C

Tropical climates are warmer than temperate climates because A temperate climates have more mountains and thus more snow causing the landmasses to warm slower. B tropical climates have more vegetation and thus can absorb more heat. C tropical climates receive the sun's rays at an almost perpendicular angle; since Earth is a sphere, the temperate climates receive the sun's rays at a much steeper incidence thus spreading the radiation over a broader area. D tropical climates receive the sun's rays at a much steeper incidence thus spreading the radiation over a broader area and causing the tropics to be warmer while the temperate climates receive the sun's rays at an almost perpendicular angle, which causes some areas to be warm and other areas to be cold.

C

When an apical meristem cell divides, one daughter cell is called the initial and the other is called the derivative. What are the fates of these cells? A Both the initial and the derivative remain part of the apical meristem B Both the initial and the derivative are used to form primary meristems C The initial remains part of the apical meristem, and the derivative is used to form primary meristems D Enough with the plants already

C

What is carrying capacity? Is it a property of a habitat or of a population?

Carrying capacity is the maximum number of individuals in a population that an environment can support. The carrying capacity is thus a property of the environment with reference to a particular population.

What organisms are responsible for the synthesis of organic compounds in hydrothermal vent and cold seep communities, and how do they differ from those in the photic zone?

Chemoautotrophic bacteria are the primary producers of hydrothermal vent communities and cold seep communities. Unlike photosynthetic organisms of the photic zone, they use hydrogen sulfide and other molecules, instead of sunlight, as an energy source for their chemosynthetic activity.

To what two broad categories of activities do children devote their energy budget?

Children spend most of their energy on growth and maintenance.

Why are conservation biologists especially concerned about the rapid rate of deforestation in the New World tropics?

Conservation biologists are especially alarmed about deforestation in the New World tropics because these forests harbor many species in imminent danger of becoming extinct.

What criteria do conservation biologists use to identify sites where extinctions are imminent?

Conservation biologists identify a site as one where extinction is imminent if it houses 95% or more of the individuals in an endangered species and it has definable boundaries that encompass distinctive habitats.

What are the differences between cryptic coloration, aposematic coloration, and mimicry? Can a mimic ever have aposematic coloration?

Cryptic coloration makes an organism inconspicuous, allowing it to blend in with its surroundings. Aposematic coloration makes an organism highly conspicuous, advertising its unpalatability. Mimicry allows one organism, the mimic, to resemble another species, the model; models are usually unpalatable or poisonous. A mimic will have aposematic coloration if it resembles an aposematic model.

Plant cells selectively pump different ions in and out of the cell in order to maintain and use a difference in electrical charge between the inside and outside of the cell, called a membrane potential. Why is this membrane potential important? A It maintains a low pH inside the cell. B The membrane potential generates electrical currents for internal communication in the plant. C It maintains an equal amount of ions inside and outside a cell. D These ion movements are a potential source of energy that can perform cellular work E Many of these ions are used as food by the plant

D

What is the main determinant of biome distribution? A Elevation B Vegetation type C Ocean currents D Climate E Weather

D

Which of the following is not an important part of the cohesion-tension mechanism of water transport model of xylem flow? A Water evaporates from the walls of the mesophyll. B Water molecules are adhesive. C Water molecules are strongly cohesive. D The interior surface of a xylem cell is strongly hydrophobic. E Transpiration allows the escape of water vapor from a plant through stomata in the leaf surface.

D

Which one of the following expressions from the logistic equation: dN/dt = rN ((K - N)/K) represents the FRACTION of unused resources remaining for use by the population? A N-K B K C rN D (K - N)/K

D

What is the direct stimulus for phototropism? For gravitropism?

Directional light of blue wavelengths is the direct stimulus for phototropism (an example of photomorphogenesis). The most widely accepted scientific explanation for gravitropism is the sinking of amyloplasts in cells surrounding vascular bundles in response to gravity. Sinking amyloplasts may provide a mechanical stimulus that triggers a gene-guided redistribution of IAA. The changing auxin gradient in turn adjusts a plant's growth pattern.

How does the availability of dissolved oxygen vary from the headwaters of a stream to the mouth of a river?

Dissolved oxygen concentration is usually high in the headwaters of a stream, gradually diminishing as water flows into a river.

Explain why dormancy is an adaptive response to a plant's environment.

Dormancy is an adaptive response because it attunes a plant's growth to the most favorable environmental conditions for survival.

Why do dry conditions occur at and S latitude?

Dry conditions prevail at and S latitudes because sinking air masses warm as they descend, causing them to absorb water from the land.

Transpiration is supported by which of the following critical factors? A Root pressure B Capillarity action C Cohesion D Evaporation E All of the above

E

What causes seasonality of the climate in the temperate zone?

Earth's fixed tilt on its axis causes seasonal variation in the amount of sunlight striking the temperate zone as the planet orbits the Sun.

Why would you often find more species living in an ecotone than you would in the communities on either side of it?

Ecologists find more species living in an ecotone than in the communities on either side of it because ecotones contain species from both neighboring communities as well as species that are adapted to transitional environmental conditions.

How can the concept of ecosystem services be used to foster conservation of threatened habitats and species?

Economists can determine the economic values of specific ecosystem services and convince local governments that it is economically beneficial to preserve ecosystems and the services they provide.

Why is energy lost from an ecosystem at every transfer from one trophic level to the trophic level above it?

Energy is lost from an ecosystem at every transfer between trophic levels because some of the energy is not assimilated, because organisms use some of the energy they assimilate for maintenance costs, and because biological processes are never 100% efficient.

How does an ion enter a root hair and then move to the xylem?

Epidermal cells of root hairs actively transport most mineral ions into root epidermal cells. These ions travel inward via the transmembrane pathway. Other ions may be dissolved in apoplastic water. They ultimately travel to the xylem in the symplast after crossing into and through endodermal cells of the Casparian strip. Once an ion reaches the stele, it enters the xylem.

Which marine environments experience the largest fluctuations in salinity (salt concentration) over time?

Estuaries experience the largest fluctuations in salinity over time.

Which marine regions receive abundant energy input from sunlight?

Estuaries, the intertidal zone, and the upper layer of the oceanic pelagic zone receive substantial energy inputs from sunlight.

Give examples of how some hormones have both promoting and inhibiting effects on growth in different parts of the plant at different times of the life cycle.

Ethylene is a good example of a hormone that can stimulate or inhibit growth at various stages of the plant life cycle. In seedlings, it simultaneously slows elongation of the stem and stimulates cell divisions that increase stem girth. In mature plants of deciduous species, it governs senescence (including fruit ripening) and the abscission of flowers, fruits, and leaves. Studies of brassinosteroids have revealed that this family of steroid hormones has different effects in different tissues—for example, promoting the elongation of vascular tissue and pollen tubes, but inhibiting elongation in roots.

Soil microorganisms consume nitrogen-containing organic compounds, and mineralize nitrogen in the process, even after their own nitrogen demands are satisfied. Why don't these microorganisms stop breaking down nitrogenous organic compounds once their demand for nitrogen is met?

Even after microorganisms satisfy their N requirements, they continue to consume nitrogen-containing organic compounds because they need the carbon in these compounds to fuel metabolism and growth.

Why do fecundity and the amount of parental care devoted to each offspring exhibit an inverse relationship?

Fecundity and the amount of parental care devoted to each offspring exhibit an inverse relationship because organisms that produce few offspring can devote substantial time and energy to each, whereas those that produce many offspring can devote only minimal time and energy to each.

Trace the development of a female gametophyte, beginning with the megasporocyte in an ovule of a flower's ovary. Which structures are diploid and which haploid?

Female gametophytes develop inside ovules in a flower's carpels. They arise by the following steps: In an ovule, a diploid megasporocyte divides by meiosis, forming four haploid megaspores. Three (usually) of these megaspores disintegrate. The remaining megaspore undergoes three rounds of mitosis without cytokinesis. The result is a single large cell with eight nuclei arranged in two groups of four. One nucleus in each group migrates to the center of the cell. After the cell undergoes cytokinesis, a cell wall forms around these two polar nuclei, forming a large "central cell." A wall also forms around each of the remaining nuclei, and three of them, including an egg cell, cluster near the micropyle. The result is an embryo sac containing seven cells and eight nuclei. This sac is the mature female gametophyte.

How can field experiments demonstrate conclusively that two species compete for limiting resources?

Field experiments can demonstrate that two species are competing for limiting resources if the removal of one species increases population size or density in the other or if the addition of a potential competitor decreases the population size or density of the other.

Describe three modes of asexual reproduction that occur in flowering plants.

Flowering plants may reproduce asexually (vegetatively) by fragmentation, in which cells in a piece of the parent plant dedifferentiate and then regenerate a whole plant; by apomixis, in which a diploid embryo develops from an unfertilized egg or from diploid cells in ovule tissue; or by the production of structures such as rhizomes or suckers from a nonreproductive plant part, typically meristem tissues in a bud on a root or stem.

What is the biological role of flowers, and what fundamental developmental shift must occur before an angiosperm can produce a flower?

Flowers are specialized for reproduction. Before an angiosperm can produce a flower, biochemical signals (triggered in part by environmental cues such as day length and temperature) travel to the apical meristem of a shoot. In response, cells there change their activity: instead of continuing vegetative growth, the shoot is modified into a floral shoot that will give rise to floral organs.

Which plant chemical defenses are general responses to attack, and which are specific to a particular pathogen?

General plant responses to attack include mobilization of jasmonates and salicylic acid, systemin (in tomato), the hypersensitive response, PR proteins, and bioactive compounds called phytoalexins. Defenses against feeding herbivores include structural features such as spines and leathery leaves and compounds such as alkaloids and phenolics. Plants respond to specific threats by way of pattern recognition receptors and effector-triggered immunity. The former include receptors that can recognize PAMPs—pathogen-associated molecular patterns, which often are proteins associated with an invader's cell wall or flagellum. Detection launches a complex web of signals that culminate in the cell's response, such as changes in gene expression that lead to the synthesis of phytoalexins. Some plant immune responses are triggered by bacterial virulence effectors—proteins produced by pathogenic bacteria that can bypass a plant cell's pattern recognition receptors. Effector-triggered immunity is an inducible mechanism in which resistance proteins encoded by so-called R genes (for "resistance") trigger an immediate defense response in the plant.

Which view of communities suggests that they are just chance assemblages of species that happen to be adapted to similar abiotic environmental conditions?

Gleason's individualistic view of communities suggests that they are just chance assemblages of species that happen to be adapted to similar abiotic environmental conditions.

What effect is global warming likely to have on the geographical distributions of organisms?

Global warming will likely cause the geographical distributions of species to shift or expand to higher latitudes and to higher elevations.

What is the difference between gross primary productivity and net primary productivity?

Gross primary productivity is a measure of the total amount of solar energy converted into chemical energy by the producers in an ecosystem. Net primary productivity is the amount of chemical energy that remains after deducting the producers' maintenance costs from the gross primary productivity.

How have humans sidestepped the controls that regulate populations of other organisms?

Humans have sidestepped the controls that regulate the populations of other organisms by expanding their geographical range to include a wide variety of habitats, by increasing the carrying capacity through agricultural production, and by decreasing their death rate through the introduction of medical care and improved sanitation.

Which type of survivorship curve is characteristic of humans in industrialized countries? Explain your answer.

Humans in the industrialized countries exhibit Type I survivorship curves because they provide lots of care to their offspring, thus reducing infant and childhood mortality to low levels.

How do environmental conditions affect transpiration?

Humidity, air temperature, and wind all affect transpiration. Relative humidity is a measure of the amount of water vapor in air. The less water vapor in the air, the more evaporates from leaves because the water potential is higher in the leaves than in the dry air. Rising air temperature at the leaf surface also speeds evaporation and hence transpiration. Although evaporation cools the leaf a little, the amount of water lost can double for each rise in air temperature. Air moving across the leaf surface carries water vapor away from the surface and so makes a steeper gradient. Together these factors explain why on extremely hot, dry, breezy days, the leaves of some plants must completely replace their water each hour.

Why is humus an important component of fertile soil?

Humus is important in soil because it generally contains nutrient-rich organic material and because it absorbs water, which contributes to the water-holding capacity of soil.

What would happen if part of an apical meristem were removed?

If part of an apical meristem were to be removed, hormonal signals would prompt the remaining meristematic cells to give rise to replacement cells.

What are some of the practical applications of deciphering signals that mediate pollen-tube guidance?

If pollen-tube growth and guidance are defective, seeds are not produced. Around 80% of the world's staple food is derived from seeds of crop plants, so studying this process is very important agriculturally. By understanding pollen-tube guidance signals, we are equipping ourselves with knowledge that could help us to:\ improve seed yield; regulate interspecies hybridizations, and thereby generate novel plant hybrids; and contain pollen spreading from genetically modified crops—a possibility that will reassure concerned public and regulatory agencies.

Germination begins when a seed imbibes water. What are the next key biochemical and developmental events that bring an angiosperm's life cycle full circle?

Imbibition causes the seed coat to split, and water and oxygen move more easily into the seed. Metabolism switches into high gear as cells divide and elongate to produce the seedling. Enzymes that were synthesized before dormancy become active; other enzymes are produced as the genes encoding them begin to be expressed. The increased gene activity and enzyme production mobilize the seed's food reserves in cotyledons or endosperm. Nutrients released by the enzymes sustain the developing seedling sporophyte until its root and shoot systems are established.

What environmental factors influence rates of primary productivity in terrestrial and aquatic ecosystems?

In terrestrial ecosystems, primary productivity may be influenced by the availability of light, water, and nutrients and by the environmental temperature. In aquatic ecosystems, primary productivity is often limited by the joint availability of light and nutrients in the same place.

Explain two key differences in how the apoplastic and symplastic pathways route substances laterally in roots.

In the apoplastic pathway, water and dissolved substances do not pass through living root cells but instead move through the continuous network of adjoining cell walls and air spaces. When apoplastic water and solutes reach the endodermis, however, they must detour around the impermeable Casparian strip and pass through cells to move into the stele. The symplastic pathway passes through living cells. Water that diffuses into root cells moves in this pathway from cell to cell through plasmodesmata.

Explain the key steps in the cohesion-tension mechanism of water transport in a plant.

In the cohesion-tension mechanism, water transport begins as water evaporates from the walls of mesophyll cells inside leaves and into the intercellular spaces. This water vapor escapes by transpiration through open stomata. As water molecules exit the leaf, they are replaced by others from the mesophyll cell cytoplasm. The water loss gradually reduces the water potential in a transpiring cell below the water potential in the leaf xylem. Water from the xylem in the leaf veins then follows the gradient into cells, replacing the water lost in transpiration.

In the generalized compartment model of biogeochemical cycling, how do we classify the compartments where nutrients accumulate?

In the generalized compartment model of biogeochemical cycling, nutrient pools are classified as available or unavailable and as organic or inorganic.

What agricultural practices contribute to the disruption of the nitrogen cycle?

Irrigation, the use of synthetic nitrogen-containing fertilizers, the harvesting of crops, and the rearing of livestock contribute to the disruption of the nitrogen cycle.

What are keystone species, and how do they influence species richness in communities?

Keystone species are those that have a substantial effect on community structure even if their populations are not very dense. Keystone species may either increase or decrease species richness in the communities they occupy.

Cuticle A , Lower epidermis G , Spongy mesophyll F , Xylem E , Palisade mesophyll C , Upper epidermis B , Phloem D

Leaf picture

Explain the general function of leaves and how leaf anatomy supports this role in eudicots and monocots.

Leaves are organs specialized for photosynthesis. In both eudicots and monocots, the leaf blade provides a large surface area for absorbing sunlight and carbon dioxide. Many eudicot leaves have a broad, flat blade attached to the stem by a petiole. Unless a petiole is very short, it holds a leaf away from the stem and helps prevent individual leaves from shading one another. In most monocot leaves, such as those of rye grass or corn, the blade is longer and narrower and its base simply forms a sheath around the stem.

Summarize the gene-guided developmental program that produces a leaf.

Leaves arise through a developmental program that begins with gene-regulated activity in meristematic tissue. Hormones or other signals may arrive at target cells via the stem's vascular tissue, activating genes that regulate development. Small phloem vessels penetrate a young leaf primordium almost immediately after it begins to bulge out from the underlying meristematic tissue, followed by xylem. A growing primordium becomes coneshaped (wider at its base than at its tip). Rapid mitosis in a particular plane in cells along the flanks of the cone (perpendicular to the surface in eudicots and parallel to the surface in monocots) produce the leaf blade that is characteristic of the particular species. Leaf tip cells typically are the first to stop dividing. By the time a leaf has expanded to its mature size, mitosis has ended and the leaf is a fully functional photosynthetic organ.

Describe the steps in primary growth of a leaf and the structures that result from the process.

Leaves develop on the sides of the shoot apical meristem. Initially, meristem cells near the apex divide and their derivatives elongate. The resulting bulge enlarges into a thin, rudimentary leaf, or leaf primordium. As the plant grows and internodes elongate, the leaves become spaced at intervals along the length of the stem or its branches. Leaf tissues typically form several layers. Uppermost is epidermis, with cuticle covering its outer surface. Just beneath the epidermis is mesophyll, which is composed of loosely packed parenchyma cells that contain chloroplasts. Leaves of many plants, especially eudicots, contain two layers of mesophyll. Palisade mesophyll cells contain more chloroplasts and are arranged in compact columns with smaller air spaces between them, typically toward the upper leaf surface. Spongy mesophyll, which tends to be located toward the underside of a leaf, consists of irregularly arranged cells with a network of air spaces that enhance the uptake of carbon dioxide and release of oxygen during photosynthesis and account for 15% to 50% of a leaf's volume. Below the mesophyll is another cuticle-covered epidermal layer. Except in grasses and a few other plants, this layer contains most of the stomata through which water vapor exits the leaf and gas exchange occurs. Vascular bundles form a network of veins throughout the leaf.

How does biodiversity serve as a storehouse of genetic information that is potentially useful to humans?

Living systems are a storehouse of potentially useful genetic information because naturally occurring compounds may prove to be useful in the treatment of disease, in the manufacture of new products, or in agriculture.

What is Earth's main reservoir for phosphorus, and why is it recycled at such a slow rate from that reservoir?

Marine sediments are Earth's main reservoir for phosphorus, which is recycled slowly after geological uplifting and erosion make it available to producers.

How do ecologists use mathematical models in their research?

Mathematical models are useful in ecological research because they help scientists formalize hypotheses about the relationships between variables and because they allow researchers to simulate the effects of changing variables before investing time and resources in experiments or observational studies.

Explain what meristem tissue is, and name and describe the roles of the basic types of meristems in forming the plant body.

Meristem tissue is self-perpetuating embryonic tissue. Apical meristems, at the tips of shoots and roots, gives rise to a young plant's stems, buds, roots, and other primary tissues. In plants that show secondary growth, cylinders of lateral meristem tissue give rise to (often woody) secondary tissues that increase the diameter of older stems and roots.

How do moderately severe and moderately frequent disturbances influence a community's species richness?

Moderately severe and moderately frequent disturbances increase a community's species richness by creating opportunities for r-selected species to colonize the habitat while allowing populations of K-selected species to persist.

Compare the two general types of root systems.

Most eudicots have a taproot system—a single main root, or taproot, that is adapted for storage and smaller branching lateral roots. As the main root grows downward, its diameter increases, and the lateral roots emerge along the length of its older, differentiated regions. Grasses and many other monocots develop a fibrous root system in which several main roots branch to form a dense mass of smaller roots. Fibrous root systems are adapted to absorb water and nutrients from the upper layers of soil, and tend to spread out laterally from the base of the stem.

Briefly describe how mountains influence local precipitation.

Mountains affect local precipitation because rising air masses on the windward side of a mountain cool adiabatically and release moisture. When the air masses descend on the leeward side of a mountain, they warm and absorb moisture, causing a rain shadow.

What ecosystem services do naturally occurring organisms provide to humans?

Naturally occurring organisms provide many ecosystem services, such as the sequestration of carbon dioxide, fixation of nitrogen into forms that plants can absorb, recycling of nutrients within ecosystems, and the retention of water in ecosystems.

Distinguish between nitrogen fixation, ammonification, nitrification, and denitrification.

Nitrogen fixation refers to the incorporation of atmospheric nitrogen into compounds, especially nitrate , which plants can readily take up. Ammonification is a process in which soil bacteria known as ammonifying bacteria break down decaying organic matter and convert it to ammonium . In nitrification, nitrifying bacteria oxidize to . Inside root cells, absorbed is converted by a multistep process back to . In this form, it is rapidly used to synthesize organic molecules, mainly amino acids. In denitrification, soil bacteria convert nitrites or nitrates first into nitrous oxide and then into molecular nitrogen that escapes to the atmosphere. Because denitrification removes nitrates from the soil, it reduces the amount of nitrogen available to plant roots.

Why are oligotrophic lakes better for recreational purposes than eutrophic lakes?

Oligotrophic lakes are better than eutrophic lakes for recreational purposes because the water in oligotrophic lakes is clear, whereas the water in eutrophic lakes is often clogged with strands of algae and cyanobacteria.

How is the scientific literature on interspecific competition potentially "biased"?

On the one hand, the ecological literature may overestimate the importance of competition because ecologists are more likely to study and publish papers on interactions in which competition is important than on interactions in which it is not. On the other hand, the literature may underestimate the importance of competition because, if strong competition between species cannot persist for long periods of time, we are unlikely to find populations competing strongly in nature.

What are the consequences of the overexploitation of fish populations?

Overexploitation of fish populations typically causes fishes to reach reproductive maturity at a smaller size and younger age, decreases population sizes, and sometimes leads to the extinction of populations.

Give some examples of how relative lengths of dark and light can influence flowering.

Photoperiod length is a factor in the seasonal flowering of many angiosperms. Spinach and irises are examples of long-day plants, which flower in spring when the period of daylight extends at least 9 to 16 hours. Chrysanthemums and potatoes are examples of short-day plants, which flower as day length becomes shorter than some critical period, a condition that occurs naturally in the fall.

Peregrine falcons are predatory birds that have been introduced into many North American cities, where they feed primarily on pigeons. The pigeons eat mostly vegetable matter. To what two different trophic levels do pigeons and peregrine falcons belong?

Pigeons, which eat grain and other vegetable matter, are included in the second trophic level, primary consumers. Peregrine falcons, which feed on pigeons and other birds, are in the third trophic level, secondary consumers.

hormone that promotes lengthening of plant stems by cell division and cell elongation gibberellins, hormone that prompts seeds and buds to break dormancy gibberellins, hormone that promotes growth of a floral stalk (internode growth or bolting) in plants such as cabbages gibberellins

Plant hormone

hormone that promotes genetically programmed death and recycling (senescence and leaf abscission) ethylene, a hormone gas that ripens fruit ethylene

Plant hormone associated with action

Summarize the switching mechanism that operates in plant responses to changes in photoperiod.

Plant responses to changes in photoperiod rely on different chemical forms of the blue-green pigment phytochrome. Daylight converts the inactive phytochrome to an active form . When light levels fall, reverts to . This switching mechanism helps regulate light-related processes such as photosynthesis.

What are the two main categories of the essential elements plants need? Give several examples of each.

Plants require relatively large amounts of macronutrients, such as nitrogen, sulfur, potassium, and calcium, and trace amounts of micronutrients, such as iron, chlorine, zinc, nickel, and copper.

Describe two examples of the life phases of long-lived plant species.

Plants that live for many years may spend part of their lives in a juvenile phase, and then shift to a mature, or adult phase. The differences between juveniles and adults often are reflected in leaf size and shape, in the arrangement of leaves on the stem, or in a change from vegetative growth to a reproductive stage. Most woody plants must attain a certain size before their meristem tissue can respond to the hormonal signals that govern flower development.

Do all plants require the same basic nutrients in the same amounts? Explain.

Plants vary in their nutritional requirements. For example, leafy plants require more nitrogen and magnesium than other plant types do, and alfalfa, a grass, requires significantly more potassium than lawn grasses do. An adequate amount of an essential element for one plant also may be toxic for another. For these reasons, the nutrient content of soils is an important factor determining which plants grow well in a given location.

Explain the steps leading to the formation of a mature male gametophyte, beginning with microsporocytes in a flower's anthers. Which structures are diploid and which haploid?

Pollen grains are the mature male gametophytes. They arise by the following steps: Spores that give rise to male gametophytes are produced in a flower bud's anthers. Diploid microsporocytes inside an anther's pollen sacs undergo meiosis; eventually each one produces four small haploid microspores. Microspores then divide by mitosis. One of the two resulting nuclei divides again by mitosis, yielding a three-celled immature gametophyte: two haploid sperm cells and a third cell that will control the development of a pollen tube after pollen lands on a receptive stigma. A mature male gametophyte consists of the pollen tube and sperm cells.

Do you think pollen-tube guidance signals from different plant species will be similar?

Pollen-tube guidance signals are likely to be species specific. Because they are involved in mating, it is likely that these signals ensure that successful pollination, and consequently fertilization, occur only within compatible species. It is also likely that the later the guidance event, the more specific is the guidance signal. For example, the guidance signal from an ovule is likely more selective and specific than those that mediate early interactions between a pollen tube and stigma.

How does a population bottleneck increase the likelihood that a species will become extinct?

Population bottlenecks—large, temporary reductions in a population's size—inevitably foster genetic drift, thereby reducing a population's genetic variability, which increases its likelihood of becoming extinct.

Describe the various tissues that arise in a root system and their functions.

Primary root growth produces a system of vascular pipelines extending from root tip to shoot tip. The root procambium produces cells that mature into the root's xylem and phloem. Ground meristem gives rise to the root's cortex, its ground tissue of starch-storing parenchyma cells that surround the stele. In many flowering plants, the outer root cortex cells give rise to an exodermis, a thin band of cells that may limit water losses from roots and help regulate the absorption of ions. The innermost layer of the root cortex is the thin endodermis, which helps control the movement of water and dissolved minerals into the stele. Between the stele and the endodermis is the pericycle, which gives rise to lateral roots. In some cells in the developing root epidermis, the outer surface extends into root hairs.

What is the difference between primary succession and secondary succession?

Primary succession occurs in places without soil; secondary succession occurs after a disturbance has destroyed vegetation.

Why is salicylic acid considered to be a general systemic response to damage?

Salicylic acid (SA) is considered to be a general systemic response to damage because experiments show that when a plant is wounded, soon thereafter SA can be detected in a variety of its tissues.

Which terrestrial biomes are renewed by periodic fires?

Savannas, chaparral, and temperate grasslands are renewed by periodic fires.

Explain how and where secondary growth typically occurs in plants.

Secondary growth processes add girth to roots and stems over two or more growing seasons. In plant species that have secondary growth, older stems and roots become more massive and woody through the activity of two types of lateral meristems. One of these meristems, the vascular cambium, produces secondary xylem and phloem. The other, the cork cambium, produces cork, a secondary epidermis that is one element of bark.

Would a single large nature preserve or several small preserves experience greater edge effects?

Several small preserves would collectively experience more edge effects than one large preserve of the same total size.

Topsoil A, Parent material C, Subsoil B

Soil horizons in a grassland.

How do solute potential and pressure potential contribute to water potential?

Solute potential reflects the presence (if any) of dissolved substances in a solution. It is always a negative value. Pressure potential reflects the effects of physical pressure. It can be either a negative or positive value. Solute potential and pressure potential combine to yield water potential—a statement represented by the equation . {$}= {$s} + {$p}

How might natural selection favor a carnivore that spends more time and energy capturing large prey than small prey?

Some carnivores spend more time and energy capturing large prey than small prey because large prey provides a larger return on their investment of time and energy in the hunt.

What factors may promote the maintenance of high species richness in tropical communities?

Some explanations of the high species richness in the tropics suggest that the benign climate and historically low levels of severe disturbance have fostered more rapid rates of speciation. Other explanations suggest that the year-round availability of food resources and complex food webs allow more species to coexist in tropical regions.

How do these two life phases differ in structure and function?

Sporophytes produce spores that give rise to gametophytes. Gametophytes then may produce gametes; male gametophytes produce sperm, and female gametophytes produce eggs. In all seed plants the sporophyte is much larger and longer-lived than the gametophyte, and the gametophyte is protected within sporophyte tissues for all or part of its life. Gametophytes also are dependent upon the sporophyte for their nutrition.

Describe the functions of stems and stem structure, and list the basic steps in primary growth of stems.

Stems have four main functions: (1) they provide mechanical support for body parts involved in growth, photosynthesis, and reproduction; (2) they house the vascular tissues (xylem and phloem), which transport products of photosynthesis, water and dissolved minerals, hormones, and other substances throughout the plant; (3) they often are modified to store water and food; and (4) they have specific stem regions that contain meristematic tissue, which gives rise to new cells of the shoot. A plant stem is divided into modules, each consisting of a node, where leaves are attached, and an internode, the space between nodes. New primary growth occurs in buds—a terminal bud at the apex of the main shoot, and lateral buds, which produce branches (lateral shoots), in the leaf axils. Meristem tissue in buds gives rise to leaves, flowers, or both. In eudicots, most primary growth in a stem's length occurs directly below the shoot apical meristem. When a meristematic cell divides, one of its daughter cells becomes an initial, a cell that remains as part of the meristem. The other daughter cell becomes a derivative, which typically divides once or twice and then enters on the path to differentiation. As derivatives differentiate, they give rise to three primary meristems: protoderm, procambium, and ground meristem. These primary meristems produce cells that differentiate into specialized cells and tissues. In eudicots, the primary meristems are also responsible for elongation of the plant body. Each primary meristem occupies a different position in the shoot tip. Outermost is protoderm, which gives rise to the stem's epidermis. Inward from the protoderm, the ground meristem gives rise to ground tissue (mostly parenchyma). Procambium, which produces the primary vascular tissues, is sandwiched between ground meristem layers. In most plants, inner procambial cells give rise to xylem and outer procambial cells to phloem. The developing vascular tissues become organized into vascular bundles that are wrapped in sclerenchyma and thread lengthwise through the parenchyma. In the stems and roots of most eudicots and some conifers, the vascular bundles form a stele (vascular cylinder) that vertically divides the column of ground tissue into an outer cortex and an inner pith.

How and when do stomata open and close?

Stomata open and close in response to changing environmental cues, such as light levels (detected via blue-light receptors), concentration in the air spaces inside leaves, and the amount of water available to the plant. Stomata open when hydrogen ions are pumped out of guard cells, setting up the symport of and into the guard cells through ion channels. Water then follows by osmosis. Stomata close when pumping in guard cells ceases and moves out of guard cells, with water again following by osmosis.

How might disturbances from storms allow coral reefs to be rejuvenated by the recruitment of young individuals?

Strong storms allow coral communities to be rejuvenated through the recruitment of new individuals because they scour the seafloor, removing existing coral colonies from the community. These openings provide spaces where coral larvae may settle and initiate the growth of new colonies.

Why are studies of ecosystems more "inclusive" than studies of populations?

Studies of ecosystems are more "inclusive" than studies of populations because ecosystems include the populations of many different species.

Why do you think the mathematical models describing population growth introduced in this chapter are not considered biological laws?

The "ideal" conditions under which the equations predict growth simply never exist, as is clear, for example, from the growth of populations illustrated in the chapter (see growth of Thrips imaginis). Therefore, unlike a law such as the law of gravity, population growth cannot simply be predicted by applying the logistic or exponential equation for population growth. The mathematical growth models are constructed after basic observations define the variables of the models.

What categories does the IUCN use to designate the status of species and higher taxa?

The IUCN designates the conservation status of species and higher taxa in the following categories: least concern, near threatened, vulnerable, endangered, critically endangered, extinct in the wild, and extinct. Some species and higher taxa are omitted from consideration because of insufficient data.

Is the Pine Bush habitat in New York State an example of preservation, mixed-use conservation, or restoration?

The Pine Bush habitat in the state of New York is an example of conservation through preservation.

How has the establishment of the Royal Chitwan National Park in Nepal been a successful conservation effort? How do conservation biologists measure its success?

The Royal Chitwan National Park has been judged a success because local residents benefit from the park's existence and therefore support it, and because populations of many animals, including tigers and rhinoceroses, have increased within its borders.

What are the advantages and disadvantages of relying on conceptual models that describe ecosystem function?

The advantage of using conceptual models of ecosystem function is that they are a simplification of the processes that determine ecosystem function in nature. The disadvantage of these models is that they do not include data on the processes that carry nutrients and energy out of one ecosystem and into another; neither do they include the details of exactly how specific ecosystems function. Thus, conceptual models do not provide precise predictions about potential changes in ecosystem function.

How does the age structure of a population influence its future population growth?

The age structure of a population influences its future population growth by determining how many individuals will reach reproductive age in the future. Populations with a bottom-heavy age structure (that is, with many young children) will experience rapid population growth when children alive today reach sexual maturity. Populations with a more even age structure will not experience a dramatic future increase in population size.

How does the composition of a soil affect a plant's ability to take up water?

The amount of water that is available in soil to be taken up by plant roots depends primarily on the relative proportions of different soil components. Water moves quickly through sandy soils, whereas soils rich in clay and humus tend to hold the most water.

How is the original stimulus transferred from cells in one part of a leaf to cells elsewhere?

The answer lies in the polarity of charge across cell plasma membranes, leaflet triggers an action potential—a brief reversal in the polarity of the membrane charge. When an action potential occurs at the plasma membrane of a pulvinar cell, the change in polarity causes potassium ion channels to open, and ions flow out of the cell, setting up an osmotic gradient that draws water out as well. As water leaves by osmosis, turgor pressure falls, pulvinar cells become flaccid, and the leaflets move together. Later, when the process is reversed, the pulvinar cells regain turgor and the leaflets spread apart.

Explain how the apoplastic, symplastic, and transmembrane pathways route substances in plant tissues.

The apoplastic pathway is an extracellular route that passes through a continuous network of adjoining cell walls and air spaces. The symplastic pathway is a plantwide compartment that consists of the protoplasts of living plant cells, which are connected by plasmodesmata. Water in the transmembrane pathway diffuses short distances, moving across plasma membranes or entering cells through membrane aquaporins.

What is the difference between the benthic and pelagic provinces of the ocean?

The benthic province of the ocean includes all of the bottom sediments. The pelagic province includes all of the water.

What is the source of nutrients and energy for the benthos of the oceanic zone?

The benthos of the oceanic zone receives nutrients and energy from the detritus sinking from the upper layers of water.

What human activities release the most into the atmosphere?

The combustion of fossil fuels and wood is the human activity that releases the most into the atmosphere.

How does the construction of a dam disrupt the lives of river-dwelling organisms?

The construction of dams changes the water flow in rivers, leading to changes in the physical structure of the river and the species that inhabit it; disrupting the environmental cues that trigger successful reproduction of organisms; inhibiting the free movement of migrating animals through all parts of the river system; and opening the habitat to invasion by species that originated elsewhere.

Given data on environmentally induced heritable changes in flax, how might plant scientists need to modify their thinking about the role of the environment as a mutagen, rather than simply as a selective agent?

The data indicate that the environment can direct higher rates of mutations to particular regions of the genome, and therefore mutating and selecting plants simultaneously might provide a better frequency of adaptive mutations. Because plants are sessile, do they need mechanisms that enable the generation of diversity in the face of chronic stress growth conditions for evolution? If so, partitioning of the plant genome into regions that are protected from change (because they are essential) and variable regions (in which changes have phenotypic effects but are not lethal) is important. Using the information might permit the more rapid breeding of stress tolerant crops.

What are the cellular components and functions of the dermal tissue system?

The dermal tissue system serves as a skinlike protective covering for the plant body. Cells of the epidermis are tightly packed and cover the primary plant body. They secrete a cuticle that coats all plant parts except the very tips of the shoot and most absorptive parts of roots. Some epidermal cells become modified for specialized functions. Examples include guard cells, which form stomata; root hairs, which absorb water and minerals; and hairlike trichomes, which function in defense against herbivory or secrete sugars that attract pollinators.

How can you tell whether an environmental factor causes density-dependent or density-independent effects on a population?

The effects of density-dependent factors get stronger (that is, they affect a larger percentage of the individuals in the population) as the population's density increases. The effects of density-independent factors do not change (that is, they affect the same percentage of the individuals in a population) as the population's density changes.

Are the effects of infectious diseases on populations more likely to be density-dependent or density-independent?

The effects of infectious diseases are usually densitydependent effects because disease-causing pathogens spread more quickly through dense populations of the organisms they infect.

What factors cause the seasonal overturns in lakes?

The factors that cause seasonal overturns in lakes include seasonal changes in environmental temperature, variations in wind velocity, and the fact that water is densest at 4 deg.

How does genome reconfiguration differ from mutation systems that normally operate in plants?

The genome reorganization occurs in a specific subset of the genome and reproducibly occurs under the same stress conditions. Therefore, it is not random, but the mechanism by which these regions of the genome are recognized is currently unknown. Most mutation systems are assumed to be random within the genome, although there is evidence that transposons do have preferential sites.

How does the global hydrologic cycle maintain its balance?

The global hydrologic cycle maintains its balance because the amount of water returned to the atmosphere by evaporation and transpiration is equal to the amount that falls as precipitation. Runoff from the land maintains the balance between terrestrial and marine components of the cycle.

What is the greenhouse effect, and how does an increase in atmospheric concentration affect it?

The greenhouse effect refers to the tendency of certain gases, called greenhouse gases, to foster the accumulation of heat in the lower atmosphere by hindering the escape of infrared heat into space. enhances the greenhouse effect because it is one of the greenhouse gases.

Describe the defining features, cellular components, and functions of the ground tissue system.

The ground tissue system makes up most of the plant body. It includes three types of structurally simple tissues—parenchyma, collenchyma, and sclerenchyma—each of which is composed mainly of one type of cell. Parenchyma makes up most of a plant's primary tissue and typically has air spaces between its cells, which are alive at maturity and can continue to divide. Subgroups of parenchyma cells are specialized for photosynthesis, secretion, and storage (of starch). Collenchyma is flexible ground tissue that contains cellulose. Its cells remain alive and metabolically active at maturity. They provide mechanical support for parenchyma and often collectively form strands or a sheathlike cylinder under the dermal tissue of growing shoot regions and leaf stalks. Cells of sclerenchyma are dead at maturity, but they develop thick secondary walls while alive that typically are lignified and provide additional support and protection in mature plant parts.

What factors have increased the likelihood of desertification in southern Florida?

The growing human population in south Florida has increased the likelihood of desertification there by withdrawing groundwater for agricultural, recreational, and residential uses faster than it is replenished.

Using sucrose as your example, summarize how a substance moves from a source into sieve tubes and then is unloaded at a sink. What is this mechanism called, and why?

The mechanism of pressure flow moves sucrose from a source (such as a leaf or stem) into sieve tubes. Pressure builds up at the source end of a sieve tube system as sucrose enters sieve tubes at sources and water follows by osmosis. Under high pressure, sucrose moves by bulk flow toward a sink (plant parts that take up sucrose as metabolic fuel), where the sugar is unloaded.

How does the prediction of the exponential model of population growth differ from that of the logistic model?

The model of exponential population growth predicts unlimited population growth over time, generating a J-shaped curve of population size versus time. The logistic model predicts that population growth slows down as the population approaches its carrying capacity, generating an S-shaped curve of population size versus time.

What plant growth forms are common in tropical forests?

The plant growth forms found in tropical forests include a canopy of tall trees, an understory of shorter trees and shrubs, an herb layer, vinelike lianas, and epiphytes.

How can the presence of predators influence an ecosystem's productivity?

The presence of predators can influence an ecosystem's productivity by consuming herbivores and thereby changing the population dynamics of the herbivores and the plants they eat. These effects can reverberate through an ecosystem in a trophic cascade.

Describe the zones of primary growth in roots.

The root apical meristem and the actively dividing cells behind it form the zone of cell division. Cells in the center of the root tip become the procambium; those just outside the procambium become ground meristem; and those on the periphery of the apical meristem become protoderm. The zone of cell division merges into the zone of elongation, where most of the increase in a root's length occurs. Above the zone of elongation, cells may differentiate further and take on specialized roles in the zone of maturation.

What is the difference between species richness and relative abundance?

The species richness of a community is the number of species it contains. Relative abundance refers to the commonness or rarity of species in the community.

How do the three hypotheses about the causes of ecological succession view the role of population interactions in the successional process?

The three hypotheses about the underlying causes of succession differ in how they view the role of population interactions. The facilitation hypothesis specifies no particular role for population interactions. The inhibition hypothesis suggests that the species already present prevent other species from joining a community. The tolerance hypothesis suggests that as environmental conditions within the community change during succession, only species that can compete strongly under the changing conditions will persist.

Considering life table data, why do you think population ecologists often "ignore" evolutionary change? How can molecular biology be used to incorporate evolution into population level studies?

The time scales for most population studies are too short to consider selection, genetic drift, or mutation. Molecular studies allow population biologists to measure changes in gene frequencies at the time scales of single generations and before those changes are manifested in noticeable changes in fecundity or survival (or morphology and behavior).

What are the two "alternating generations" of plants?

The two alternating generations of plants are the sporophyte (spore-producing) and gametophyte (gameteproducing) generations.

What are the two basic mechanisms of morphogenesis in plants? Describe the patterns of cell division by which a plant part grows longer and adds girth.

The two basic mechanisms of plant morphogenesis are oriented cell division and cell expansion. Oriented cell division establishes the general shape of a plant organ, and cell expansion enlarges the cells in a developing organ in particular directions. They increase in circumference (girth) when new cell walls form parallel to the nearest plant surface (such as the surface of a stem or tree trunk) or when cell walls form at right angles both to the nearest surface and to the transverse plane.

What environmental factor has caused the demise of vulture populations throughout South Asia?

The use of the anti-inflammatory drug diclofenac on livestock has decimated vulture populations in South Asia. Diclofenac is highly toxic to birds, and the vultures ingest it when they feed on the carcasses of livestock.

In what ways is stomatal functioning important to a plant's ability to manage water loss?

Through their ability to open and close, stomata help regulate water loss by plants and the uptake of carbon dioxide for photosynthesis.

What is totipotency, and how does tissue culture exploit this property of plant cells?

Totipotency is the capacity of fully differentiated cells to dedifferentiate, return to an unspecialized embryonic state, and then develop into a fully functional mature plant. Plant tissue culture procedures trigger the development of a mass of dedifferentiated cells (a callus), some of which regain totipotency and develop into plantlets.

Compare and contrast translocation and transpiration.

Translocation is the long-distance transport of substances in plants. The term generally applies to the transport of organic compounds, mainly sucrose, in phloem. Transpiration is the evaporation of water from a plant's aerial parts, mainly leaves. This water moves from roots upward to aerial parts in the xylem.

In which terrestrial biomes are the trees usually evergreen?

Trees are usually evergreen in tropical rainforest, temperate rainforest, and taiga.

Which terrestrial biomes occur in habitats that receive the most rainfall?

Tropical rainforest and temperate rainforest are the terrestrial biomes that receive the most rainfall.

Which terrestrial biomes have the tallest vegetation? Which ones have the shortest?

Tropical rainforests and temperate rainforests have the tallest vegetation. Arctic and alpine tundra have the shortest vegetation.

What is water potential, and why is it important with respect to plant cells?

Water potential is potential energy stored in water. It is the driving force for osmosis, which in turn is responsible for the movement of water into and out of plant cells, including root cells.

Given what you have learned about the effects of climate change on species' distributions, in which types of habitats or geographical regions should we witness the most dramatic loss of species in the near future?

We should expect to see the loss of species in mountaintop habitats because the species have no cooler habitats into which they can migrate. We would also expect to see the loss of polar species, especially those that depend on sea ice, the extent of which is shrinking rapidly.

How is the hypersensitive response integrated with other chemical defenses?

While the hypersensitive response is under way, SA also is synthesized and operates in other defensive chemical pathways in a plant. This effect includes the synthesis of PR (pathogenesis-related) proteins that attack pathogenic cells.

What are the functions of the vascular tissues xylem and phloem?

Xylem and phloem are the tissues of the vascular tissue system. The two types of xylem cells, called tracheids and vessel members, both develop thick, lignified secondary cell walls and die at maturity. The empty cell walls of abutting cells serve as pipelines for water and minerals. The conducting cells of phloem, called sieve tube members, form sieve tubes that conduct solutes, mainly sugars made during photosynthesis, throughout a plant.

Active transport in plant root cells requires that those cells have access to O2. Normally there is enough O2 available in air pockets in the soil, but flooded soil has very little O2. Thus, unless they have special adaptations, plants in flooded soil effectively have no active transport in their roots. Which of the following should you expect to occur for trees without special adaptations to flooding after several days in flooded soil? a. wilting of their leaves b. excess uptake of water and minerals in the xylem only c. excess uptake of water and minerals in the xylem, and excess water pushed out at the margins of their leaves d. excess water pushed out at the margins of their leaves only e. bursting of leaf cells due to excess water flow

a

Aquaporins are ____. a. channel proteins for water b. channel proteins for solutes c. carrier proteins for solutes d. carrier proteins for water e. carrier proteins for water and solutes

a

Evidence of the hypersensitive response in plants can be seen as _____. a. dead brown spots on leaves b. the presence of heat-shock proteins c. leaf abscission d. the presence of secondary metabolites e. formation of galls on leaves or stems

a

Guard cells contain chloroplasts. a. True b. False

a

Hydroponic culture is the process of ____. a. growing plants in pure water mixed with carefully measured amounts of specific minerals b. irrigation of dry areas to improve mineral absorption by plants c. irrigation of dry areas to prevent crop plants from wilting d. growing plants with specific hydrocarbons added to the soil to test the effect on plant growth e. growing plants in ponds and lakes to improve their access to water, allowing the plants to place more resources into the shoot system

a

If you want all of the orange trees in your orchard to uniformly flower and set fruit, you should spray ____ on your plants. a. auxins b. salicylic acid c. cytokinins d. ethylene e. brassinosteroids

a

Imagine that you own a nursery and you want to reduce the chance that plants you ship will suffer from shipping damage. You should you apply ____ to the plants before shipping. a. abscisic acid b. gibberellins c. ethylene d. oligosaccharins e. cytokinins

a

In herbaceous plants, the stress-related closing of stomata is regulated by ____. a. abscisic acid b. ion concentrations in the xylem c. CO2 concentration d. sunlight e. O2 concentration

a

In the internal leaf structure, the structure labeled "3" is ____. a. spongy mesophyll b. a stoma c. a vascular bundle d. palisade mesophyll e. epidermis

a

Loading of most carbohydrates produced by photosynthesis into companion cells at a source occurs by ____. a. active transport b. osmosis c. diffusion of water from the xylem d. suction from unloading at a sink e. proton pumping

a

Stomata generally open in response to ____. a. a drop in CO2 concentration in leaf air spaces b. the release of abscisic acid by the roots c. an increase in CO2 concentration in the leaf air spaces d. exposure to red light e. a drop in O2 concentration in leaf air spaces

a

Studies of a soybean plant (Glycine max) and the bacterium Bradyrhizobium japonicum have shown that the tip of a root hair curls toward the bacterium in response to ____. a. nod gene products produced by the bacterium b. nitrogen fixation by the bacterium c. nod gene products produced by soybean roots d. a flavonoid produced by the bacterium e. a flavonoid released by soybean roots

a

Sucrose moves into a cell against its concentration gradient at the same time that protons move into the cell along their concentration gradient. This is an example of ____. a. symport b. active transport c. passive diffusion d. facilitated diffusion e. antiport

a

Suppose you are culturing tobacco callus in a Petri dish at a 10:1 ratio of auxin to cytokinin. To promote only shoot development you would ____. a. increase the cytokinin ratio b. reduce the auxin level significantly and increase the cytokinin level slightly c. grow the tobacco in the light d. increase the auxin ratio e. grow the tobacco in the dark

a

The ability of roots to absorb mineral ions and water is maximized by _____. a. producing large quantities of root hairs throughout the life of the plant b. producing a single type of ion channel that is able to take up many types of ions c. producing chemicals that deter infection by mycorrhizal fungi d. producing deep taproots in arid regions e. increasing the diameter of roots as they age, to accommodate more nutrients

a

The chemical message system that stimulates a plant to develop flowers begins with the expression of the _____ gene. a. vernalization b. FT c. CO d. CONSTANS e. AP1

a

The loss of water vapor from aboveground plant parts is called ____. a. transpiration b. root pressure c. sublimation d. passive transport e. evaporation

a

The uptake of water and mineral ions from the soil occurs primarily at the ____. a. root hairs b. endodermis c. pericycle d. root cap e. quiescent center

a

When an apical meristem cell divides, one daughter cell is called the initial and the other is called the derivative. What are the fates of these cells? a. The initial remains part of the apical meristem, and the derivative is used to form primary meristems. b. Both the initial and the derivative remain part of the apical meristem. c. The initial is used to form primary meristems, and the derivative remains part of the apical meristem. d. The initial is used to form primary meristems, and the derivative is used to form secondary meristems. e. Both the initial and the derivative are used to form primary meristems.

a

Which characteristic is not true for an essential element? a. Occasionally, it can be functionally replaced by another element. b. It may be contained in plant seeds in high enough quantities to sustain the adult plant. c. It is necessary for normal growth and reproduction. d. It may play only one role in plant metabolism. e. It may be required in only trace amounts

a

A plant responds to changes in photoperiods by activation of _____, which drives _____ to stimulate cellular responses to light. a. cryptochromes; PR proteins b. phytochromes; calcium-binding proteins c. red light; blue light d. transcription factors; abscisic acid e. phytochromes; auxins

b

Animals trapped and digested by "carnivorous" plants such as the cobra lily are used primarily as ____. a. food for bacteria and fungi that grow symbiotically with the plant roots b. a nutrient supplement in nutrient-deficient environments c. an energy supplement during winter months d. an energy supplement for small plants growing in shady areas e. a carbon source for the plant

b

Apical dominance is maintained by ____. a. sugars produced in the leaves b. hormones released by the terminal bud c. water transported from the roots d. sugars produced in the lateral buds e. hormones released by the lateral buds

b

During daylight hours, primarily ____. a. Pfr is converted to Pr b. Pr absorbs red light and is converted to Pfr c. Pfr absorbs far-red light and is converted to Pr d. Pfr absorbs red light and is converted to Pr e. Pr absorbs far-red light and is converted to Pfr

b

If nitrifying bacteria were not present in a soil, plants would ____. a. take up nitrogen for their use mainly as NH3 b. take up nitrogen for their use mainly as NH4+ c. take up nitrogen for their use mainly as N2 d. not survive because they could not get useful nitrogen e. take up nitrogen for their use mainly as NO3-

b

In a living plant cell in a living plant, you would expect the cytoplasm to be ____. a. slightly more positively charged than the fluid outside the cell b. slightly more negatively charged than the fluid outside the cell c. much more negatively charged than the fluid outside the cell d. much more positively charged than the fluid outside the cell e. essentially the same charge as the fluid outside the cell

b

In systemic acquired resistance, the regulatory protein NPR-1 moves from the cytoplasm to the cell nucleus, apparently in response to a buildup of ____ in the cytoplasm. a. jasmonates b. salicylic acid c. brassinosteroids d. ethylene e. oligosaccharins

b

In the internal leaf structure, the item labeled "5" is ____. a. epidermis b. a vascular bundle c. a stoma d. spongy mesophyll e. palisade mesophyll

b

In vascular plants, water and dissolved minerals are transported from roots to the stems and leaves by ____. a. parenchyma b. xylem c. sclerenchyma d. collenchyma e. phloem

b

Statoliths, particles that move in the direction gravity pulls them, are typically ____ in plants. a. nuclei b. amyloplasts c. calcium carbonate crystals d. hormones e. vacuoles

b

Suppose two living plant cells are in contact with each other so that water, but not solutes, can pass between them. The cells have the same water potential. One cell has yP = 0.3 MPa and yS = -0.5 MPa, while the other cell has yS = -0.3 MPa. What is the yP of the second cell? a. yP = 0 MPa b. yP = 0.1 MPa c. yP = -0.8 MPa d. yP = 0.8 MPa e. yP = 0.5 MPa

b

The Casparian strip of the endodermis stops water from the ____ before it reaches the stele. a. apoplastic, transmembrane, and symplastic pathways b. apoplastic pathway only c. transmembrane pathway only d. transmembrane and symplastic pathways e. symplastic pathway only

b

The ____ prevents important substances in the xylem from leaking into the root cortex. a. primary xylem b. endodermis c. root hairs d. tonoplasts e. pericycle

b

The innermost layer of the root cortex, known as the ____, is a selectively permeable barrier that helps control the movement of water and dissolved minerals. a. pericycle b. endodermis c. root hairs d. root cap e. quiescent center

b

The plant hormone ____ is primarily responsible for helping break the dormancy of seeds and buds. a. cytokinin b. gibberellin c. jasmonate d. ethylene e. auxin

b

The principal driving force for guttation is ____. a. upward pressure as sugar is forced into the roots b. root pressure c. pumping by the xylem cells d. passive transport e. sunlight

b

The root apical meristem is surrounded and protected by a structure called the ____. a. pericycle b. root cap c. root hairs d. endodermis e. quiescent center

b

The synthesis of ____ is triggered when cells bind systemin. a. cytokinin b. jasmonate c. gibberellin d. auxin e. brassinosteroids

b

To conserve nutrients, plants that drop their leaves in autumn _____. a. retain mineral ions in the leaves so when they fall, they will attract pollinators to the tree b. transport mineral ions from the leaves to the twigs and branches before the leaves fall c. transport chlorophyll from the leaves to the twigs and branches before the leaves fall d. convert mineral ions to ATP for winter storage in the bark e. assimilate excess mineral ions into glucose, which is then transported to the roots

b

Water particles adhere tightly to soil particles due to _____. a. hydrogen bonding with positive charges on soil particles b. hydrogen bonding with negative charges on soil particles c. the small spaces between particles through which gravity can draw the water d. ionic bonding with negative charges on soil particles e. adhesive properties of minerals in the soil

b

What is the yP of a living plant cell that has y = -0.2 MPa and yS = -0.4 MPa? a. yP = 0.5 MPa b. yP = 0.2 MPa c. yP = -0.2 MPa d. yP = 0.08 MPa e. yP = -0.6 MPa

b

When a plant has a hypersensitive response, production of ____ triggers effects such as the expression of PR proteins. a. ethylene b. salicylic acid c. cytokinin d. brassinosteroids e. oligosaccharins

b

Which tissue gives rise to secondary xylem and phloem? a. protoderm b. vascular cambium c. apical meristem d. ground meristem e. procambium

b

You might infer from packages of commercial fertilizer that which nutrients are most limiting to plant growth? a. hydrogen, phosphorus, and magnesium b. nitrogen, phosphorous, and potassium c. iron, magnesium, and nitrogen d. carbon, nitrogen, and phosphorous e. phosphorus, potassium, and calcium

b

A mutant soybean plant that is unable to produce leghemoglobin will most likely suffer from ____ deficiency. a. magnesium b. phosphorus c. nitrogen d. potassium e. oxygen

c

A researcher using hydroponic methods to determine if molybdenum is an essential plant nutrient would likely ____. a. grow plants from seed in a molybdenum-deficient environment to see if they grow properly b. add extra molybdenum to a complete nutrient solution to see if plant growth improves c. transfer healthy plants to a solution without molybdenum and observe their growth d. transfer unhealthy plants to a solution containing molybdenum to see if their growth improves e. grow seeds in solutions with varying molybdenum concentrations to see which grows best

c

After a plant has survived a microbial invasion, the rest of the plant is often less vulnerable to future infections. This is called ____. a. wound defense b. gene-for-gene recognition c. systemic acquired resistance d. hypersensitive response e. jasmonate response

c

At a source the phloem typically has a water potential that is ____ that in surrounding xylem. a. about the same as b. less negative than c. lower than d. higher than e. exactly the same as

c

At night, assuming no artificial lights, primarily ____. a. Pfr absorbs far-red light and is converted to Pr b. Pr absorbs red light and is converted to Pfr c. Pfr is converted to Pr d. Pr absorbs far-red light and is converted to Pfr e. Pfr absorbs red light and is converted to Pr

c

Each primary meristem occupies a different position in the shoot tip. Which primary meristem gives rise to primary vascular tissues? a. protoderm b. leaf primordium c. procambium d. ground meristem e. shoot apical meristem

c

Girdling is the process by which bark is removed from the entire circumference of a tree or branch. This is lethal to a tree because it prevents ____. a. water uptake b. photosynthesis c. sugar transport to roots d. water transport to leaves e. respiration

c

In response to increased carbon dioxide levels in the atmosphere over the past 200 years, stomata in leaves of some species have ____. a. increased in number b. become larger c. declined in number d. disappeared e. become smaller

c

In vascular plants, sugars are transported throughout the plant by ____. a. xylem b. sclerenchyma c. phloem d. collenchyma e. parenchyma

c

Individual plant cells typically gain or lose water mainly via ____. a. facilitated diffusion b. symport c. osmosis d. guttation e. bulk flow

c

Jasmonates help plants defend against herbivores because they induce _____. a. rapid growth to replace leaves removed by herbivores b. production of thorns or spines c. production of chemicals that prevent insects from digesting the plant material d. increased production of indigestible fibers in leaves e. production of chemicals that attack an herbivorous insect's nervous system

c

Starting from the outside and moving in toward the center, which list gives the correct order of tissues in the stem of a young tree? a. primary xylem, secondary xylem, secondary phloem, primary phloem b. primary phloem, secondary xylem, secondary phloem, primary xylem c. primary phloem, secondary phloem, secondary xylem, primary xylem d. secondary phloem, primary phloem, primary xylem, secondary xylem e. secondary phloem, primary xylem, secondary xylem, primary phloem

c

Stomata open when K+ concentration in guard cells ____, followed by water ____ the guard cells by osmosis. a. decreases; leaving b. increases; leaving c. increases; entering d. increases H+; leaving e. decreases; entering

c

The ____ is self-perpetuating embryonic tissue typically found at the tips of shoots and roots. a. vascular tissue b. dermal tissue c. meristem d. protoderm e. ground tissue

c

The major cost to plants for having cuticle-covered epidermis in the shoot system to reduce water loss is reduced ____ uptake. a. oxygen b. calcium c. carbon dioxide d. nitrogen e. potassium

c

You have been studying the relationship between jackals and tigers in India: Until recently, the only relationship you have observed is that jackals will attach themselves to a particular tiger and follow it at a safe distance in order to feed on the big cat's kills. However, recently you observed a jackal alerting a tiger to a kill with a loud cry. If you continue to observe this alerting behavior, you might change the categorization of the jackal/tiger relationship from this (BLANK) to this (BLANK).

commensalism mutualism

According to the cohesion-tension mechanism of water transport, cohesion occurs because ____. a. evaporation removes water from the leaves b. waxy coatings on insides of xylem keep water molecules together in the xylem c. water is pushed into the xylem by bulk flow d. water molecules tend to form hydrogen bonds with each other e. water is pushed into the xylem by phloem pressure

d

An agar block filled with auxin is placed on top of a shoot that has had the shoot tip removed. The agar block is placed so that it covers only one side of the top of the shoot. You would expect the shoot to ____. a. grow straight up b. grow faster on the side away from the agar block c. grow faster on both the side away from the agar block and on the side with agar block d. grow faster on the side with the agar block e. stop growing

d

In seed plants, water-stressed roots produce _____, which stimulates K+ loss by guard cells, causing the stomata to close. a. a fatty acid b. an amino acid c. an organic acid d. the hormone abscisic acid (ABA) e. a nucleic acid

d

In the internal leaf structure, the structure labeled "4" is ____. a. palisade mesophyll b. epidermis c. a vascular bundle d. a stoma e. spongy mesophyll

d

Leaf chlorosis is not likely to be caused by a deficiency in ____. a. nitrogen b. zinc c. iron d. boron e. magnesium

d

Most mineral ions that plants need are moved into the ____. a. apoplast via facilitated diffusion b. apoplast via bulk flow c. transmembrane pathway via bulk flow d. symplast via active transport e. symplast via facilitated diffusion

d

Most plants absorb nitrogen mainly in the form of _____. a. nitrogen gas b. ammonia c. ammonium d. nitrate e. nitrite

d

Suppose a living plant cell has yP = 0.4 MPa and yS = -0.5 MPa. If the plant cell is placed into a beaker filled with a solution with y = yS = -0.9 MPa, then the cell should ____. a. take up water until it bursts b. take up water until within the cell yP = -yS c. take up water until its y = yS of the solution d. lose water until its y = y of the solution e. lose water until its yS = its yP

d

Symptoms of nitrogen deficiency in plants first appear in _____. a. seeds b. younger leaves c. the stem d. older leaves e. roots

d

The main form in which sugars are transported in the phloem sap is ____. a. lactose b. starch c. fructose d. sucrose e. glucose

d

The most common limit to plant growth is a lack of ____. a. carbon b. hydrogen c. oxygen d. nitrogen e. phosphorous

d

The movement of NH4+ ions into a cell down an electrochemical gradient created by H+ pumping is an example of ____. a. facilitated diffusion b. an ion pump c. passive diffusion d. secondary active transport e. passive transport

d

The plant hormone that triggers abscission of leaves in the fall is _____. a. a brassinosteroid b. abscisic acid c. jasmonate d. ethylene e. a phytochrome

d

Which factor has little effect on the rate of transpiration? a. air temperature b. air movement c. the amount of direct solar radiation d. daily fluctuations in atmospheric carbon dioxide concentrations e. relative humidity

d

A unique characteristic of plant cells is their ability to ____. a. form defensive compounds b. carry out cellular respiration c. protect themselves through movement d. photosynthesize e. continuously grow and generate new organs throughout their life cycle

e

According to the acid-growth hypothesis, auxin causes increased acidity in cell walls, which then activates ____ that disrupt(s) bonds between cellulose microfibrils, allowing cell expansion. a. AUX1 transporters b. an mRNA c. K+ ions d. a membrane potential e. proteins called expansins

e

Areas that receive heavy rainfall tend to have ____ soils, and arid regions tend to have ____ soils. a. pH-neutral; acidic b. acidic; pH-neutral c. pH-neutral; alkaline d. alkaline; acid e. acidic; alkaline

e

Check My Work If the y of surrounding soil is higher than that in living root epidermal cells, then water should ____. a. none of these accurately describe water movement b. leave the root cells, making them turgid c. enter the root cells, making them flaccid d. leave the root cells, making them flaccid e. enter the root cells, making them turgid

e

Consider a living plant cell in a living leaf that has a higher water potential than the fluids surrounding the cell. In such a situation there should be ____. a. no net flow of water into or out of the cell b. gain of water by the cell only if the cell's pressure potential is high enough c. gain of water by the cell only if the cell's pressure potential is low enough d. a net flow of water into the cell e. a net flow of water out of the cell

e

Imagine that you are a farmer who chose not to rotate your crops with soybeans even though the local extension agent recommended that you do so. Which deficiency symptom in your crops should indicate to you that the extension agent's advice was correct? a. purplish veins b. chlorosis and mottled or bronzed leaves c. pale green, rolled, or cupped leaves d. burned leaf edges and curled, mottled, or spotted older leaves e. chlorosis in older leaves and stunted growth

e

In some cases, when an insect begins feeding on a leaf the plant responds by activating a signaling pathway that results in the production of ____, which disrupt an insect's capacity to digest proteins. a. lipases b. chitinases c. gibberellins d. cytokinins e. protease inhibitors

e

In the internal leaf structure, the structure labeled "2" is ____. a. spongy mesophyll b. epidermis c. a stoma d. a vascular bundle e. palisade mesophyll

e

Rhizomes, tubers, corms, and stolons are examples of modified ____. a. flowers b. leaves c. roots d. bulbs e. stems

e

Stomata close when ____ guard cells and they become ____. a. active transport pumps H+ out of; turgid b. active transport pumps H+ into; flaccid c. active transport pumps H+ into; turgid d. active transport of H+ stops in; turgid e. active transport of H+ stops in; flaccid

e

The KN-1 gene in maize is normally expressed in ____. a. in primary meristems, where it maintains the undifferentiated state b. in apical meristems, where it initiates the process of differentiation c. in lateral meristems, where it initiates the process of secondary growth d. in primary meristems, where it initiates the process of differentiation e. in apical meristems, where it maintains the undifferentiated state

e

The growth-promoting substance that promotes stem elongation and bending toward light is produced primarily in ____. a. flowers and flower buds b. root tips, traveling to the stem in the phloem c. root tips, traveling to the stem in the xylem d. the center of the stem region where elongation or bending occurs e. the shoot tip

e

The hormones _____ are probably involved in breaking dormancy. a. ethylene and gibberellins b. brassinosteroids and jasmonates c. ethylene and brassinosteroids d. jasmonates and abscisic acid e. gibberellins and abscisic acid

e

The plant hormone ____ triggers plant responses to environmental stresses such as cold snaps, high salinity, and drought. a. jasmonate b. oligosaccharin c. ethylene d. cytokinin e. abscisic acid

e

The plant hormone structurally similar to adenine is ____. a. ethylene b. systemin c. brassinosteroid d. abscisic acid e. cytokinin

e

The surfaces of clay particles in soil ____. a. are generally hydrophobic b. release water to plants easily c. often bear positively charged ions d. acidify the soil e. often bear negatively charged ions

e

Water can move inside a root via the ____. a. transmembrane pathway only b. transmembrane and symplastic pathways c. apoplastic pathway only d. symplastic pathway only e. apoplastic, transmembrane, and symplastic pathways

e

When solutes are unloaded from phloem, water ____. a. is pumped out of the phloem by active transport b. is pumped into the phloem by active transport c. moves into the phloem by facilitated diffusion d. leaves the xylem by osmosis e. leaves the phloem by osmosis

e

Which statement is true regarding typical plant development? a. Plant bodies do not have a fixed final size, and final plant form is not influenced by the environment. b. Final plant form is not influenced by the environment, and growing tips and zones are present throughout a plant's life. c. Growing tips and zones are present throughout a plant's life, and final plant form is not influenced by the environment. d. Plant bodies have a fixed final size, and final plant form is influenced by the environment. e. Growing tips and zones are present throughout a plant's life, and plant bodies do not have a fixed final size.

e

Wood is composed of ____. a. both xylem and phloem b. primary phloem c. primary xylem d. secondary phloem e. secondary xylem

e

manganese micronutrient, carbon nonmineral macronutrient, arsenic not generally considered an essential nutrient, lithium not generally considered an essential nutrient, magnesium mineral macronutrient, calcium mineral macronutrient, gold not generally considered an essential nutrient, iron micronutrient, oxygen nonmineral macronutrient, zinc micronutrient, sulfur mineral macronutrient, potassium mineral macronutrient, chlorine micronutrient, nickel micronutrient

general plant nutritional requirement for each element

Gibberellins affect many processes in plants. In seeds embryos, gibberellins are believed to signal hydrolysis of the stored food reserves through inducing the synthesis of the enzyme α-amylase. What SPECIFIC food source are gibberellins targeting with the release of α-amylase?

starch