Exam 2 Study Guide
What are the characteristics of shade leaves?
-large leaves -long internodes -leaves green -thin cuticle -leaves thin -chloroplasts evenly distributed between the palisade and spongy mesophyll layers
What are the characteristics of sun leaves?
-small leaves -short internodes -leaves and/or stems often with red pigmentation -thick cuticle -leaves thick -most of chloroplasts found in the palisade layer
What are the seven differences between photosynthesis and respiration.
1. Photosynthesis stores energy in sugar molecules, whereas respiration releases energy from sugar molecules. 2. Photosynthesis uses carbon dioxide and water, whereas respiration releases carbon dioxide and water. 3. Photosynthesis increases the weight of a plant, whereas respiration decreases weight. 4. Photosynthesis occurs only in light, while respiration can occur in either light or dark. 5. Photosynthesis occurs only in cells containing chlorophyll, whereas respiration occurs in all living cells. 6. Photosynthesis produces oxygen in green organisms, whereas respiration utilizes oxygen (aerobic respiration). 7. Photosynthesis produces ATP with light energy, whereas respiration produces ATP with energy released from sugar.
What are the functions of plant leaves?
1. Photosynthesis. The process of producing food, known as photosynthesis, mainly occurs in the leaves of most angiosperms. This process essentially involves the absorption of light mainly by the chlorophyll pigments and the absorption of carbon dioxide via the stomatal pores in the leaves. As a result of the cleavage of the water molecule during photosynthesis, oxygen is generated and released to the atmosphere. 2. Transpiration. Plants lose a large volume of water through the leaves in the form of vapor. The exit of water is through the stomata and the cuticle, but stomatal transpiration is largely more dominant than cuticular transpiration. It is estimated that the loss of water via stomata through the process of transpiration exceeds 90 percent of the water absorbed by the roots. Transpiration may be advantageous to the plant because of its cooling effect resulting from the expenditure of a portion of the plant's heat energy in converting liquid water to water vapor. There is wide support also that transpiration pull is responsible for the continuous ascent of water and nutrients from the roots to the topmost parts of trees. But this process can be a disadvantage to the plant if transpiration loss exceeds the rate of water absorption through the roots. 3. Food Storage. The leaves serve as food storage organ of the plant both temporarily and on long-term basis. Under favorable conditions, the rate of photosynthesis may exceed that of translocation of photosynthates toward other organs. During the daytime, sugars accumulate in the leaves and starch is synthesized and stored in the chloroplasts. At nighttime, the starch is hydrolyzed to glucose and respired or converted to transportable forms like sucrose.
What are the 3 functions of transpiration?
1. cools plants 2. allows for absorption of minerals and ions 3. transporting materials from the soil to leaves
Describe pericycle.
A core of tissues, referred to collectively as the vascular cylinder, lies to the inside of the endodermis. Most of the cells of the vascular cylinder conduct water or food in solution, but lying directly against the inner boundary of the endodermis is an important layer of parenchyma tissue known as the pericycle. This tissue, which is usually one cell wide, may in some plants be a little wider. The cells of the pericycle may continue to divide even after they have matured. Lateral (branch) roots and part of the vascular cambium of dicots arise within the pericycle.
What is opposite leaf arrangement?
A pair of leaves is attached at a node.
What is the difference between simple and compound leaves?
A simple leaf blade is undivided. The blade of a compound leaf is divided into several leaflets.
What is alternate leaf arrangement?
A single leaf is attached at a node.
What are shade leaves?
A single tree may have leaves that appear similar, but close inspection may reveal important differences. For example, because leaves in the shade receive less total light needed for photosynthesis, they tend to be larger than their counterparts in the sun. In addition, since they receive less intense sunlight and heat, they are thinner and have fewer well-defined mesophyll layers and fewer chloroplasts (Fig. 7.11). They also do not have as many hairs.
What is ATP?
Adenosine triphosphate, a molecule that contains three phosphates held together by high energy bonds. When the third phosphate is cleaved, leaving adenosine diphosphate (ADP), energy is released to drive anabolic reactions. Energy is required to add a third phosphate to ADP to form ATP; the energy comes from catabolic reactions and is stored in the newly formed bond.
Describe aerial roots.
Aerial roots are a type of adventitious root. They grow not from root tissue, but from the plant's stem or leaf tissues. Because they're exposed to the air, they're more likely to dry out and are usually found in plants that live in wet environments, like tropical rain forests. Some aerial roots even have chlorophyll (the plant chemical that helps to convert the sun's energy into food for the plant) and can photosynthesize. Plants with underground roots have little reason to have chlorophyll since they are not exposed to the sun.
Why do most roots grow towards gravity?
Amyloplasts in plants allow them to perceive gravity and grow accordingly (gravitropism). Amyoplasts are specialized plastids that contain starch granules and settle downwards in response to gravity. These plastids can be found in specialized cells of the root cap.
What are stomata?
An important feature of leaves is the presence of stomata or stomates (sing. stoma). Each stoma consists of a tiny pore surrounded by two specialized, sausage-shaped epidermal cells called guard cells. These tiny pores open and close to regulate the passage of gases and water to and from the leaves. Stomata are located mostly on the undersides of leaves, but they are also present on the epidermis of other plant organs such as the stems, flowers and fruit.
Are photosynthesis reactions anabolic or catabolic?
Anabolic. Energy is stored by constructing carbohydrates by combining carbon dioxide and water.
What is anabolism?
Anabolism refers to chemical reactions in which simpler substances are combined to form more complex molecules. Anabolic reactions usually require energy. Anabolic reactions build new molecules and/or store energy.
Explain pressure flow hypothesis (mass flow hypothesis) of transport of organic solutes in plants.
At present, the most widely accepted theory for movement of substances in the phloem is called the pressure-flow (or mass-flow) hypothesis. According to this theory, food substances in solution (organic solutes) flow from a source, where water enters by osmosis (e.g., a food-storage tissue, such as the cortex of a root or rhizome, or a food-producing tissue, such as the mesophyll tissue of a leaf). The water exits at a sink, which is a place where food is utilized, such as the growing tip of a stem or root. Food substances in solution (organic solutes) are moved along concentration gradients between sources and sinks. First, in a process called phloem-loading, sugar, by means of active transport, enters the sieve tubes of the smallest veinlets. This decreases the water potential in the sieve tubes, and water then enters these phloem cells by osmosis. Turgor pressure, which develops as this osmosis occurs, is responsible for driving the fluid through the sieve-tube network toward the sinks. As the food substances (largely sucrose) in solution are actively removed at the sink, water also exits the sink ends of sieve tubes, and the pressure in these sieve tubes is lowered, causing a mass flow from the higher pressure at the source to the lower pressure at the sink. Most of the water diffuses back to the xylem, where it then returns to the source and is transpired or recirculated. The pressure-flow hypothesis explains how nontoxic dyes applied to leaves or substances entering the sieve tubes, such as viruses introduced by aphids, are carried through the phloem.
Are cellular respiration reactions anabolic or catabolic?
Catabolic. Energy from chemical bonds is released by breaking down carbohydrates, producing carbon dioxide and water.
What is catabolism?
Catabolism refers to chemical reactions that result in the breakdown of more complex organic molecules into simpler substances. Catabolic reactions usually release energy that is used to drive chemical reactions.
Describe the regulation of transpiration.
Changes in turgor pressure take place when osmosis and active transport between the guard cells and other epidermal cells bring about shifts in solute concentrations. While photosynthesis is occurring in the guard cells, they expend energy to acquire potassium ions from adjacent epidermal cells, leading to the opening of the stomata. When photosynthesis is not occurring in the guard cells, the potassium ions leave, and the stomata close. With an increase in potassium ions, the water potential in the guard cells is lowered, and the osmosis that takes place as a result brings in water that makes the cells turgid. The departure of potassium ions also results in water leaving, making the cells less turgid and causing the stomata to close. Stomata will close when water stress occurs. There is evidence that the hormone abscisic acid is produced in leaves subject to water stress and that this hormone causes membrane leakages, which induce a loss of potassium ions from the guard cells and cause them to deflate. The stomata of most plants are open during the day and closed at night. However, the stomata of a number of desert plants are open only at night when there is less water stress on the plants. This conserves water but makes carbon dioxide needed for photosynthesis inaccessible during the day. Such plants convert the carbon dioxide available at night to organic acids, which are stored in cell vacuoles. The organic acids are then converted back to carbon dioxide during the day when photosynthesis occurs (Fig. 9.14). A specialized form of photosynthesis called CAM photosynthesis uses the carbon dioxide released from the organic acids. CAM photosynthesis is discussed in Chapter 10. Other desert plants have their stomata recessed below the surface of the leaf or stem in small chambers. These chambers, called stomatal crypts, often are partially filled with epidermal hairs, which further reduce water loss by slowing down air movement. Similar recessed stomata are found in the leaves of pine trees, which have little water available to them in winter when the soil is frozen (see Fig. 7.12). A few tropical plants that occur in damp, humid areas (e.g., ruellias; see also Fig. 4.13b) have stomata that are raised above the surface of the leaf, while plants of wet habitats generally lack stomata on submerged surfaces. Although light and carbon dioxide concentration affect transpiration rates, several other factors play at least an indirect role. For example, air currents speed up transpiration as they sweep away water molecules emerging from stomata. Humidity plays an inverse but direct role in transpiration rates: high humidity reduces transpiration, and low humidity accelerates it. Temperature also plays a role in the movement of water molecules out of a leaf. The transpiration rate of a leaf at 30°C (86°F), for example, is about twice as great as it is for the same leaf at 20°C (68°F). The various adaptive modifications of leaves and their surfaces and the availability of water to the roots also may play important roles in influencing the amount of water transpired. Leaf modifications are discussed in Chapter 7. If a cool night follows a warm, humid day, water droplets may be produced through structures called hydathodes at the tips of veins of the leaves of some herbaceous plants. This loss of water in liquid form is called guttation (Fig. 9.15). Minerals absorbed at night are pumped into the intercellular spaces surrounding the vessels and tracheids of the xylem. As a result, the water potential of the xylem elements is lowered, and water moves into them from the surrounding cells. In the absence of transpiration at night, the pressure in the xylem elements builds to the point of forcing liquid water out of the hydathodes in the leaves. Although the droplets resemble dew, the two should not be confused. Dew is water that is condensed from the air, while guttation water is literally forced out of the plant by root pressure. As the sun strikes the droplets in the morning, they dry up, leaving a residue of salts and organic substances, one of which is used in the manufacture of commercial flavor enhancers (e.g., the monosodium glutamate in products such as Accent®). In the tropics, the amount of water produced by guttation can be considerable. In taro plants, used by the Polynesians to make poi, a single leaf may produce as much as a cupful (about 240 milliliters) of water overnight through guttation.
Describe abscission.
During the spring and summer the leaves have served as factories where most of the foods necessary for the tree's growth are manufactured. This food-making process takes place in the leaf in numerous cells containing chlorophyll, which gives the leaf its green color. This extraordinary chemical absorbs from sunlight the energy that is used in transforming carbon dioxide and water to carbohydrates, such as sugars and starch. Along with the green pigment are yellow to orange pigments, carotenes and xanthophyll pigments which, for example, give the orange color to a carrot. Most of the year these colors are masked by great amounts of green coloring. But in the fall, because of changes in the length of daylight and changes in temperature, the leaves stop their food-making process. The chlorophyll breaks down, the green color disappears, and the yellow to orange colors become visible and give the leaves part of their fall splendor. At the same time other chemical changes may occur, which form additional colors through the development of red anthocyanin pigments. Some mixtures give rise to the reddish and purplish fall colors of trees such as dogwoods and sumacs, while others give the sugar maple its brilliant orange. The autumn foliage of some trees show only yellow colors. Others, like many oaks, display mostly browns. All these colors are due to the mixing of varying amounts of the chlorophyll residue and other pigments in the leaf during the fall season. As the fall colors appear, other changes are taking place. At the point where the stem of the leaf is attached to the tree, a special layer of cells develops and gradually severs the tissues that support the leaf. At the same time, the tree seals the cut, so that when the leaf is finally blown off by the wind or falls from its own weight, it leaves behind a leaf scar. Most of the broad-leaved trees in the North shed their leaves in the fall. However, the dead brown leaves of the oaks and a few other species may stay on the tree until growth starts again in the spring. In the South, where the winters are mild, some of the broad-leaved trees are evergreen; that is, the leaves stay on the trees during winter and keep their green color.
What is the function of enzymes?
Enzymes regulate metabolic activities.
What sort of products are plants the sources of?
Food, perfumes, dyes, beverages, lumber, paper, clothing, medicines, coal and oil, and alternate energy sources.
Describe plasmolysis.
If you place turgid carrot and celery sticks in a 10% solution of salt in water, they soon lose their rigidity and become limp enough to curl around your finger. The water potential inside the carrot cells is greater than the water potential outside, and so diffusion of water out of the cells into the salt solution takes place. If you were to examine such cells with a microscope, you would see that the vacuoles, which are largely water, had disappeared and that the cytoplasm was clumped in the middle of the cell, having shrunken away from the walls. Such cells are said to be plasmolyzed. This loss of water through osmosis, which is accompanied by the shrinkage of protoplasm away from the cell wall, is called plasmolysis (Fig. 9.5). If plasmolyzed cells are placed in fresh water before permanent damage is done, water reenters the cell by osmosis, and the cells become turgid once more.
Describe osmosis.
In plant cells, osmosis is essentially the diffusion of water through a semipermeable membrane from a region where the water is more concentrated to a region where it is less concentrated. Osmosis ceases if the concentration of water on both sides of the membrane becomes equal. Water enters a cell by osmosis until the osmotic potential is balanced by the resistance to expansion of the cell wall. Water gained by osmosis may keep a cell firm, or turgid, and the turgor pressure that develops against the walls as a result of water entering the vacuole of the cell is called pressure potential. Water has entered the cell by osmosis, and turgor pressure is pushing the cell contents against the cell walls. Osmosis is the primary means by which water enters plants from their surrounding environment. This loss of water through osmosis, which is accompanied by the shrinkage of protoplasm away from the cell wall, is called plasmolysis. Osmosis is the diffusion of water through a semipermeable membrane. Water moves from a region of higher water potential (osmotic potential and pressure potential combined) to a region of lower water potential when osmosis is occurring. Osmosis is the primary means by which plants obtain water from their environment. Plasmolysis is the shrinkage of the cytoplasm away from the cell wall as a result of osmosis taking place when the water potential inside the cell is greater than outside. These changes, which involve potassium ions, result from osmosis and active transport between the guard cells and the adjacent epidermal cells.
Where do the final two major stages in aerobic respiration, the citric acid (Krebs) cycle and electron transport, take place?
In the mitochondria. The processes are controlled by enzymes.
What are nodes?
Lateral buds and leaves grow out of the stem at intervals called nodes.
Describe lateral roots.
Lateral roots extend horizontally from the primary root (radicle) and serve to anchor the plant securely into the soil. This branching of roots also contributes to water uptake, and facilitates the extraction of nutrients required for the growth and development of the plant.
Describe lateral roots.
Lateral roots extend horizontally from the primary root (radicle) and serve to anchor the plant securely into the soil. This branching of roots also contributes to water uptake, and facilitates the extraction of nutrients required for the growth and development of the plant. Many different factors are involved in the formation of lateral roots. Regulation of root formation is tightly controlled by plant hormones such as auxin, and by the precise control of aspects of the cell cycle. Such control can be particularly useful: increased auxin levels, which help to promote lateral root development, occur when young leaf primordia form and are able to synthesise the hormone. This allows coordination of root development with leaf development, enabling a balance between carbon and nitrogen metabolism to be established.
Describe thorns.
Like grape and other tendrils, many spinelike objects arising in the axils of leaves of woody plants are modified stems rather than modified leaves. Such modifications should be referred to as thorns to distinguish them from true spines.
What are mycorrhizae and root nodules in plants?
Nodules and mychorrhizae are both examples of symbiotic relationships where both the plants and the organisms involved benefit. The plants benefit by getting nutrients which they could not get normally through the roots. Often nodules and mychorrhizae occur in poor soils that do not have alot of nutrients. Nodules are a symbiotic relationship between a bacterium of the genus Rhizobia and the plant. The bacterium actually infects the root and produces the nodules. The bacterium takes nitrogen in the atmosphere and chemically transforms it in to ammonia which the plant can then absorb. Nitrogen is needed to make plant proteins. The plant in return provides the bacteria with energy in the form of carbohydrates (sugars lke glucose). Mycorrhizae are a type of fungus which infect the roots of a plant. The fungus is like microscopic threads and they are numerous. The fungus has a large surface area because the threads are so thin and there are so many of them. The large surface area allows the fungus to efficiently absorb water and nutrients which are transferred to the plant roots. In return, the plants provides the fungus with a steady source of energy (sucrose or glucose).
Describe imbibition.
Osmosis is not the only force involved in the absorption of water by plants. Colloidal materials (i.e., materials that contain a permanent suspension of fine particles) and large molecules, such as cellulose and starch, usually develop electrical charges when they are wet. The charged colloids and molecules attract water molecules, which adhere to the internal surfaces of the materials. Because water molecules are polar, they can become both highly adhesive to large organic molecules such as cellulose and cohesive with one another. As discussed in Chapter 2, polar molecules have slightly different electrical charges at each end due to their asymmetry. This process, known as imbibition, results in the swelling of tissues, whether they are alive or dead, often to several times their original volume. Imbibition is the initial step in the germination of seeds.
Why are humans and animals dependent on plants?
Plants convert the sun's energy into energy that is usable to plants and to animals. In the process, plants produce oxygen and remove carbon dioxide in the air we breathe.
Describe the process of abscission of leaves in plants.
Plants whose leaves drop seasonally are said to be deciduous. In temperate climates, new leaves are produced in the spring and are shed in the fall, but in the tropics, the cycles coincide with wet and dry seasons rather than with temperature changes. Even evergreen trees shed their leaves; they do so a few at a time, however, so that they never have the bare look of deciduous trees in their winter condition. The process by which the leaves are shed is called abscission. Abscission occurs as a result of changes that take place in an abscission zone near the base of the petiole of each leaf. Sometimes the abscission zone can be seen externally as a thin band of slightly different color on the petiole. Hormones that apparently inhibit the formation of the specialized layers of cells that facilitate abscission are produced in young leaves. As the leaf ages, hormonal changes take place, and at least two layers of cells become differentiated. Closest to the stem, the cells of the protective layer, which may be several cells deep, become coated and impregnated with fatty suberin. On the leaf side, a separation layer develops in which the cells swell, sometimes divide, and become gelatinous. In response to any of several environmental changes (such as lowering temperatures, decreasing day lengths or light intensities, lack of adequate water, or damage to the leaf), the pectins in the middle lamella of the cells of the separation layer are broken down by enzymes. All that holds the leaf on to the stem at this point are some strands of xylem. Wind and rain then easily break the connecting strands, leaving tiny bundle scars within a leaf scar, and the leaf falls to the ground.
What processes are involved in metabolism?
Respiration, photosynthesis, digestion, and assimilation.
What is another term for netted venation?
Reticulate venation.
Describe active transport.
Return for a moment to our two rooms with the tennis balls. Suppose that, besides the 100 tennis balls, we drop in 50 slightly underinflated basketballs; these basketballs are also extraordinary in having perpetual-motion motors that propel them in any direction at 12 mph. They should also become randomly distributed throughout the room shortly after they are introduced. Assume, however, that the hole in the wall (which is large enough for the passage of a tennis ball) is not quite large enough to allow a basketball to pass through freely. The basketballs will then remain in the first room. However, if we were to install a mechanical arm next to the hole in the second room, and if this arm could grab basketballs that come near the hole and squeeze them through in one direction, basketballs would be transported into the second room through the expenditure of energy. The basketballs obviously would gradually accumulate in the second room in greater numbers. Plants expend energy to move substances, too. Plant cells generally have a larger number of mineral molecules and ions than exist in the soil immediately next to the root hairs. If it were not for the barriers imposed by the semipermeable membranes, these molecules and ions would move from a region of higher concentration in the cells to a region of lower concentration in the soil. Most molecules needed by cells are polar, and those of solutes may set up an electrical gradient across a semi-permeable membrane of a living cell. To pass through the membrane, molecules require special embedded transport proteins (see Fig. 3.7). The transport proteins are believed to occur in two forms: one facilitating the transport of specific ions to the outside of the cell and the other facilitating the transport of specific ions into the cell. The plants absorb and retain these solutes against a diffusion (or electrical) gradient through the expenditure of energy. This process is called active transport. Recent evidence suggests that this process involves an enzyme complex and what has been referred to as a proton pump. The pump involves the plasma membrane of plant and fungal cells and sodium and potassium ions in animal cells. Both pumps are energized by special energy-storing ATP molecules (discussed in Chapter 10). Mangroves, saltbush, and certain algae thrive in areas where the water or soil contains enough salt to kill most vegetation. Such plants accumulate large amounts of organic solutes, including the carbohydrate mannitol and the amino acid proline. The organic solutes facilitate osmosis, despite the otherwise adverse environment (Fig. 9.8). The leaves of some mangroves also have salt glands through which they excrete excess salt.
List all the human uses of plants.
Roots have been important sources of food for humans since prehistoric times, and some, such as the carrot, have been in cultivation in Europe for at least 2,000 years. A number of cultivated root crops involve biennials (i.e., plants that complete their life cycles from seed to flowering and back to seed in two seasons). Such plants store food in a swollen taproot during the first year of growth, and then the stored food is used in the production of flowers in the second season. Among the best-known biennial root crops are sugar beets, beets, turnips, rutabagas, parsnips, horseradishes, and carrots. Other important root crops include sweet potatoes, yams, and cassava. Cassava (Fig. 5.18), from which tapioca is made, forms a major part of the basic diet for millions of inhabitants of the tropics. With a minimum of human labor, it yields more starch per hectare (about 45 metric tons, the equivalent of 20 tons per acre) than any other cultivated crop. Minor root crops, including relatives of wild mustards, nasturtiums, and sorrel, are cultivated in South America and other parts of the world. Several well-known spices, including sassafras, sarsaparilla, licorice, and angelica, are obtained from roots. Sweet potatoes are used in the production of alcohol in Japan. Some important red to brownish dyes are obtained from roots of members of the Madder Family (Rubiaceae), to which coffee plants belong. Drugs obtained from roots include aconite, ipecac, gentian, and reserpine, a tranquilizer. A valuable insecticide, rotenone, is obtained from the barbasco plant, which has been cultivated for centuries as a fish poison by primitive South American tribes. When thrown into a dammed stream, the roots containing rotenone cause the fish to float but in no way poison them for human consumption. In tobacco plants, nicotine produced in the roots is transported to the leaves.
Describe osmosis.
Solvents are liquids in which substances dissolve. Although the cytoplasm of living cells is bounded by membranes, it is now well known that water (a solvent) moves freely from cell to cell. This has led scientists to believe that plasma, vacuolar, and other membranes have tiny holes or spaces in them, even though such holes or spaces are invisible to the instruments presently available. It also has led to the construction of models of such membranes (see Fig. 3.7). Membranes through which different substances diffuse at different rates are described as semipermeable. All plant cell membranes appear to be semipermeable. In plant cells, osmosis is essentially the diffusion of water through a semipermeable membrane from a region where the water is more concentrated to a region where it is less concentrated. Osmosis ceases if the concentration of water on both sides of the membrane becomes equal. Although the previous simple definition of osmosis serves our purposes, plant physiologists prefer to define and discuss osmosis more precisely in terms of potentials. It is possible to prevent osmosis by applying pressure. Just enough pressure to prevent fluid from moving as a result of osmosis is referred to as the osmotic pressure of the solution. In other words, osmotic pressure is the pressure required to prevent osmosis. The osmotic potential (represented by ψs) of a solution is a measure of the potential of water to move from one cell to another as influenced by solute concentration. Water enters a cell by osmosis until the osmotic potential is balanced by the resistance to expansion of the cell wall. Water gained by osmosis may keep a cell firm, or turgid, and the turgor pressure that develops against the walls as a result of water entering the vacuole of the cell is called pressure potential (represented by ψp). The release of turgor pressure can be heard each time you bite into a crisp celery stick or the leaf of a young head of lettuce. When we soak carrot sticks, celery, or lettuce in pure water to make them crisp, we are merely assisting the plant in bringing about an increase in the turgor of the cells (Fig. 9.4). Figure 9.4(a) A turgid cell. Water has entered the cell by osmosis, and turgor pressure is pushing the cell contents against the cell walls. (b) Water has left the cell, and turgor pressure has dropped, leaving the cell flaccid. The vacuole has disappeared. ×200. The water potential (represented by ψw) of a plant cell is essentially its osmotic potential and pressure potential combined (ψw = ψs + ψp). If we have two adjacent cells of different water potentials, water will move from the cell having the higher water potential to the cell having the lower water potential. Osmosis is the primary means by which water enters plants from their surrounding environment. In land plants, water from the soil enters the cell walls and intercellular spaces of the epidermis and the root hairs and travels along the walls until it reaches the endodermis. Here it crosses the differentially permeable membranes and cytoplasm of the endodermal cells on its way to the xylem. Water flows from the xylem to the leaves, evaporates within the leaf air spaces, and diffuses out (transpires) through the stomata into the atmosphere. The movement of water takes place because there is a water potential gradient from relatively high soil water potential to successively lower water potentials in roots, stems, leaves, and the atmosphere.
Describe contractile roots.
Some herbaceous dicots and monocots have contractile roots that pull the plant deeper into the soil. The contractile part of the root may lose as much as two-thirds of its length within a few weeks as stored food is used and the cortex collapses.
Describe root hairs.
Some of the epidermal cells in the region of maturation develop root hairs; the root hairs greatly increase the absorptive surface of the root.
Describe buttress roots.
Some tropical trees growing in shallow soils produce huge, buttresslike roots toward the base of the trunk, giving them great stability.
Differentiate between monocot leaves and dicot leaves.
The big difference that most people note about monocots and dicots is the formation of the plants' veins on leaves. However, there are many different things that separate monocots from dicots. In fact, monocots differ from dicots in four structural features: their leaves, stems, roots and flowers. Within the seed lies the plant's embryo; it is here that the first difference between the two types can be seen. Whereas monocots have one cotyledon (vein), dicots have two. This small difference at the very start of the plant's life cycle leads each plant to develop vast differences. Once the embryo begins to grow its roots, another structural difference occurs. Monocots tend to have "fibrous roots" that web off in many directions. These fibrous roots occupy the upper level of the soil in comparison to dicot root structures that dig deeper and create thicker systems. Dicot roots also contain one main root called the taproot, where the other, smaller roots branch off. The roots are essential to the plant's growth and survival, therefore encouraging a deeper and more extensive root system that can help increase the health of the plant. As the monocots develop, their stems arrange the vascular tissue (the circulatory system of the plant) sporadically. This is extremely unique compared to dicots' organized fashion that arranges the tissue into a donut-looking structure (see figure). The way a stem develops is important to note. Stems are in charge of supporting the entire plant and help position it to reach as much sunlight as possible. The vascular tissue within the stem can be thought of as a circulatory system for bringing nutrients to each portion of the plant. The differences don't end there. Both monocots and dicots form different leaves. Monocot leaves are characterized by their parallel veins, while dicots form "branching veins." Leaves are another important structure of the plant because they are in charge of feeding the plant and carrying out the process of photosynthesis. The last distinct difference between monocots and dicots are their flowers (if present). Monocot flowers usually form in threes whereas dicot flowers occur in groups of four or five.
In aerobic respiration, what are the two major stages following glycolysis?
The citric acid (Krebs) cycle and electron transport.
What is metabolism?
The collective product of all biochemical reactions in an organism.
Describe diffusion.
The differing intensity of odors discussed earlier involves molecules behaving somewhat like the tennis balls. Through their random motion, molecules tend to become distributed throughout the space available to them. Accordingly, if perfume molecules are kept in a bottle, they will become distributed throughout the bottle, but if the stopper is removed, they will eventually become dispersed throughout the room, even if there is no fan or other device to move the air. This movement of molecules or ions from a region of higher concentration to a region of lower concentration is called diffusion (Fig. 9.2). Molecules that are moving from a region of higher concentration to a region of lower concentration are said to be moving along a diffusion gradient, while molecules going in the opposite direction are said to be moving against a diffusion gradient. When the molecules, through their random movement, have become distributed throughout the space available, they are considered to be in a state of equilibrium. The rate of diffusion depends on several factors, including pressure, temperature, and the density of the medium through which it is taking place. Except within the area immediately surrounding the source, unaided diffusion requires a great deal of time because molecules and ions are infinitesimally small. Something that is less than a millionth of a millimeter in diameter is going to take a long time to move just 1 millimeter, even though the amount of movement may be great in proportion to the size of the particle concerned. In gases, there is a great deal of space between the molecules and correspondingly less chance of the molecules bumping into each other and thus being slowed down. Accordingly, gas molecules occupy a space that becomes available to them relatively rapidly, while liquids do so more slowly, and solids are slower yet. Large molecules move much more slowly than small molecules. If you added a tiny drop of a dye (which has relatively large molecules) to one end of a bathtub of water without disturbing the water in any way, it would take years for the dye molecules to diffuse throughout the tub and reach a state of equilibrium. In nature, however, wind and water currents distribute molecules much faster than they ever could be distributed by diffusion alone.
What happens if glucose molecules undergo glycolysis without enough oxygen available to complete aerobic respiration?
The hydrogen released during glycolysis is simply transferred from the hydrogen acceptor molecules back to the pyruvic acid after it has been formed, creating ethyl alcohol in some organisms, and lactic acid or similar substances in others. A little energy is released during either fermentation or true anaerobic respiration, but most of it remains locked up in the alcohol, lactic acid, or other compounds produced.
What are internodes?
The intervals on the stem between the nodes.
What are the difference between sun and shade leaves?
The large leaves of the shade shoot provide a larger area for trapping light energy for photosynthesis in a place where light levels are low. Plants subjected to low light intensity often grow rapidly producing long internodes (the part of the stem between each leaf). Rapid growth may help the shoot to reach light. Pupils can relate this to work they may have done comparing the growth of plants/seedlings in the light and dark. The small leaves of the sun plants will provide less surface area for the loss of water through transpiration. Evaporation rates will be high where leaves are exposed directly to the sun Various things may cause the colour difference in the leaves e.g. sun leaves may have a thicker cuticle and several layers of palisade cells with the chloroplasts concentrated in them. There may also be a difference in the amounts of different pigments in the leaf. Anthocyanin pigments are produced in the stems and leaves of the sun shoots. These red pigments help to protect the chlorophyll from excess ultra-violet radiation.
Why are leaves important?
The leaves may be considered as the most important life-giving part of the plant body. The carbohydrate that is produced in the leaves in the process of photosynthesis sustains animal life, both directly and indirectly. This organic compound contains the energy which the plant obtains from the sun, the same energy that powers animal and human life. Likewise, the oxygen that plant leaves give off is essential to the continuing existence of animals and other aerobic organisms.
Describe spines.
The leaves of many cacti and other desert plants are modified as spines. This reduction in leaf surface correspondingly reduces water loss from the plants, and the spines also tend to protect the plants from browsing animals. In such desert plants, photosynthesis, which would otherwise take place in leaves, occurs in the green stems. Most spines are modifications of the whole leaf, in which much of the normal leaf tissue is replaced with sclerenchyma, but in a number of woody plants (e.g., mesquite, black locust), it is the stipules at the bases of the leaves that are modified as short, paired spines.
Explain in detail the cohesion-tension theory of water movement in plants.
The major mechanism for long-distance water transport is described by the cohesion-tension theory, whereby the driving force of transport is transpiration, that is, the evaporation of water from the leaf surfaces. Water molecules cohere (stick together), and are pulled up the plant by the tension, or pulling force, exerted by evaporation at the leaf surface. Water will always move toward a site with lower water potential, which is a measure of the chemical free energy of water. By definition, pure water has a water potential of 0 MegaPascals (MPa). In contrast, at 20 percent relative humidity, the water potential of the atmosphere is -500 MPa. This difference signifies that water will tend to evaporate into the atmosphere. The water within plants also has a negative potential, indicating water will tend to evaporate into the air from the leaf. The leaves of crop plants often function at -1 MPa, and some desert plants can tolerate leaf water potentials as low as -10 MPa. The water in plants can exist at such low water potentials due to the cohesive forces of water molecules. The chemical structure of water molecules is such that they cohere very strongly. By the cohesion-tension theory, when sunlight strikes a leaf, the resultant evaporation first causes a drop in leaf water potential. This causes water to move from stem to leaf, lowering the water potential in the stem, which in turn causes water to move from root to stem, and soil to root. This serves to pull water up through the xylem tissue of the plant.
Describe prickles.
The prickles of roses and raspberries, however, are neither leaves nor stems, but are outgrowths from the epidermis or cortex.
What is the 'mid rib?'
The single middle prominent vein, or primary vein.
Describe tendrils.
There are many plants whose leaves are partly or completely modified as tendrils. These modified leaves, when curled tightly around more rigid objects, help the plant in climbing or in supporting weak stems. As the tendrils develop, they become coiled like a spring. When contact with a support is made, not only does the tip curl around it but the direction of the coil reverses; sclerenchyma and collenchyma cells then develop in the vicinity of contact. The sclerenchyma cells provide rigid support, while the collenchyma cells impart flexibility. This makes a very strong but flexible attachment that protects the plant from damage during high winds. The tendrils of many other plants (e.g., grapes) are not modified leaves but develop instead from stems.
Taproot v. fibrous root system?
There are two main types of roots according to origin of development and branching pattern in the angiosperms: taproot system and fibrous system. Generally, plants with a taproot system are deep-rooted in comparison with those having fibrous type. The taproot system enables the plant to anchor better to the soil and obtain water from deeper sources. In contrast, shallow-rooted plants are more susceptible to drought but they are quick to absorb surface and irrigation water and thus have the ability to respond quickly to fertilizer application. In order to enhance the development of more lateral roots in taprooted plants, pruning of the taproot is practiced, as in plant nurseries. The practice is also a standard procedure with bonsai trees. The primary root which develops from a radicle and becomes dominant is called a taproot, as in carrot. Roots that develop from other roots are generally called lateral roots; those that arise from other plant organs rather than the root, such as from stems or leaves, are called adventitious roots. A taproot system is one in which the primary root becomes the main root of the plant with minimal branching consisting of secondary, smaller lateral roots. The taproot system occurs in dicot plants and is one of the basis of distinguishing these plants from the monocots which have fibrous roots. In plants having a taproot system, the trunk-like primary root develops directly from the embryonic root called radicle and grows downward into the soil. From this taproot, lateral roots develop which may initially grow horizontally then turn downward. These roots repeatedly form finer roots which terminate in a root tip with a minute, dome-shaped, protective root cap at the tipmost part. As the root grows, it pushes its root cap forward, probing the soil and absorbing water and nutrients mainly through fine root hairs. The root hairs are extensions of the epidermis which develop in the region of differentiation. These plant organs are short-lived and constantly replaced. In grasses and other monocots including lilies and palm plants, the root system is a fibrous root system consisting of a dense mass of slender, adventitious roots that arise from the stem. A fibrous root system has no single large taproot because the embryonic root dies back when the plant is still young. The roots grow downward and outward from the stem, branching repeatedly to form a mass of fine roots.
Explain in detail the cohesion-tension theory of water movement in plants.
This theory however describes the movement of water from roots to the leaves of a plant. Because of osmosis water from soil reach the xylem of roots of a plant. Water molecules are bonded to each other by hydrogen bonding, hence water form a string of molecules during its movement toward xylem. The water molecules stick together and get pulled up by the force called tension. This force is exerted because of the evaporation at the surface of the leaf. The theory is based on the following features: Cohesive and adhesive properties of water molecules to form an unbroken continuous water column in the xylem. Transpiration pull or tension exerted on this water column. Xylem vessels are tubular structures extending from roots to the top of the plants. Cells are placed one above the other, with their end walls perforated forming a continuous tube. These are supported by xylem tracheids which are characterised by having pores in their walls .one end of xylem tube is connected with the root hairs via pericycle, endodermis and cortex and another end is connected with the sub stomatal cavity in the leaves via mesophyll cells. This tube is filled with water. The water is filled inside the xylem capillaries and due to cohesion and adhesion properties of water, it forms a continuous water column. The water column cannot be broken or pulled away from the xylem walls because of cohesion and adhesion of water. An important factor which can discontinue the water column is the introduction of air bubbles in the xylem. Copeland (1902) believed that air bubbles enter into the xylem which breaks the tensile strength of water column, but Scholander et al. (1957) have shown that the air does not block the entire conducting system. Even if air bubbles were introduced, the individual water columns were unbroken and continuous with each other both in the vertical and lateral directions through the pits present in the cell wall.
Describe turgor pressure in plants.
This thickness allows each stoma to be opened and closed by means of changes in the turgor of the guard cells. The stoma is closed when turgor pressure is low and open when turgor pressure is high. Changes in turgor pressures in the guard cells, which contain chloroplasts, take place when they are exposed to changes in light intensity, carbon dioxide concentration, or water concentration. The guard cells swell when turgor pressure in them increases and the stoma opens as the thinner outer walls stretch more than the thicker inner walls. The stoma closes when the turgor pressure in the guard cells decreases. Changes in turgor pressure take place when osmosis and active transport between the guard cells and other epidermal cells bring about shifts in solute concentrations. Water gained by osmosis may keep a cell firm, or turgid, and the turgor pressure that develops against the walls as a result of water entering the vacuole of the cell is called pressure potential (represented by ψp).
Describe endodermis.
This tissue, which may be many cells thick, is similar to the cortex of stems except for the presence of an endodermis at its inner boundary. The endodermis consists of a single-layered cylinder of compactly arranged cells whose walls are impregnated with lignin and suberin. An endodermis is rare in stems but so universal in roots that only three species of plants are known to lack a root endodermis. A core of tissues, referred to collectively as the vascular cylinder, lies to the inside of the endodermis.
What is whorled leaf arrangement?
Three or more leaves are attached at a node.
Describe transpiration.
Two guard cells and an opening called the stoma (plural: stomata) constitute the stomatal apparatus. These stomatal apparatuses, which often occupy 1% or more of the surface area of a leaf, regulate transpiration and gas exchange. Control of transpiration is, however, strongly influenced by the water-vapor concentration of the atmosphere. The guard cells bordering each stoma have relatively elastic walls with radially oriented microfibrils, making them analogous to pairs of sausage-shaped balloons joined at each end, each with a row of rubber bands around it. The part of the wall adjacent to the hole itself is considerably thicker than the remainder of the wall (Fig. 9.13). This thickness allows each stoma to be opened and closed by means of changes in the turgor of the guard cells. The stoma is closed when turgor pressure is low and open when turgor pressure is high. Changes in turgor pressures in the guard cells, which contain chloroplasts, take place when they are exposed to changes in light intensity, carbon dioxide concentration, or water concentration.
Why are veins important?
Veins consist of vascular tissues which are important for the transport of food and water. Leaf veins connect the blade to the petiole, and lead from the petiole to the stem. The two primary vascular tissues in leaf veins are xylem, which is important for transport of water and soluble ions into the leaf, and phloem, which is important for transport of carbohydrates (made by photosynthesis) from the leaf to the rest of the plant.
Describe pneumatophore roots.
Water, even after air has been bubbled through it, contains less than one-thirtieth the amount of free oxygen found in the air. Accordingly, plants growing with their roots in water may not have enough oxygen available for normal respiration in their root cells. Some swamp plants develop special spongy roots, called pneumatophores, which extend above the water's surface and enhance gas exchange between the atmosphere and the subsurface roots to which they are connected.
What is netted venation?
With netted venation veins are repeatedly branched to form a network or reticulum. The veins branch from the major midribs and split into smaller strands of veinlets. Reticulated venation is the most common venation pattern, and occurs in the leaves of nearly all dicots.
What is parallel venation?
With parallel venation the veins are arranged parallel to each other and are connected by smaller veins. Characteristic of monocots.
Is it possible for glucose molecules to undergo glycolysis without enough oxygen available to complete aerobic respiration?
Yes.
Which form of respiration cannot be completed without oxygen?
aerobic respiration (the most widespread form of respiration)
What is the equation for photosynthesis?
carbon dioxide + water +light energy = glucose + oxygen + water
What is the equation for respiration?
glucose + oxygen = energy + carbon dioxide + water
What is the equation for aerobic respiration?
glucose + oxygen are converted by enzymes to carbon dioxide + water + energy
Describe root hair.
root hair, or absorbent hair, the rhizoid of a vascular plant, is a tubular outgrowth of a trichoblast, a hair-forming cell on the epidermis of a plant root. As they are lateral extensions of a single cell and only rarely branched, they are invisible to the naked eye. They are found only in the region of maturation of the root. Just prior to the root hair cell development, there is a point of elevated phosphorylase activity. The function of root hairs is to collect water and mineral nutrients present in the soil and take this solution up through the roots to the rest of the plant. As root hair cells do not carry out photosynthesis they do not contain chloroplasts. Root hair cells are outgrowths at a tip of the plants roots. Root hair cells vary between 15 and 17 micrometres in diameter, and 80 to 1,500 micrometres in length.[1] They are found only in the zone of maturation, and not the zone of elongation, possibly because any root hairs that arise are sheared off as the root elongates and moves through the soil. Root hairs form an important surface over which plants absorb most of their water and nutrients. They are also directly involved in the formation of root nodules in legumeplants. They have a large surface area, which makes absorbing water during osmosis and minerals during active uptake more efficient. Also, root hair cells secrete acid (H+ from malic acid) which exchanges and helps solubilize the minerals into ionic form, making the ions easier to take up. Root hair cells can survive for 2 to 3 weeks and then die off,at the same time new root hair cells are continually being formed at the tip of the root. This way, the root hair coverage stays the same. When a new root hair cell grows, it excretes a poison so that the other cells in close proximity to it are unable to grow one of these hairs. This ensures equal and efficient distribution of the actual hairs on these cells.
List functions of roots.
•Absorption of water and dissolved minerals •Conduction of water and minerals •Anchorage and support •Storage of food reserve •Vegetative reproduction •Prevents soil erosion
