Bio 181 Plant Lab Questions

Which generation corresponds with which parts of a seed?

(1) The outer seed coat is diploid tissue derived from the ovule wall of the parent plant (sporophyte); the pulpy interior of the seed is (2) the remnant of the haploid female gametophyte, which surrounds (3) the diploid embryo, which is the next generation of sporophyte.

difference between rhizoids and true roots

A rhizoid is one cell thick but several-to-many epidermal cells long. A root hair is made up of a single, elongated epidermal cell.

What are some advantages of being a big and tall land plant, including advantages for nutrition and reproduction?

Advantages of being big and tall include greater ability to capture sunlight for photosynthesis (less shading by other plants) and better dispersal of spores (ferns), pollen, seeds and fruits. Being bigger enables the plant to make more of everything: branched and longer roots penetrate farther and deeper into the soil for increased uptake of water and minerals and provide more cells in which to store photosynthates. A large root system also physically supports a larger shoot system, containing more leaves for photosynthesis and more reproductive structures (e.g., fern fronds with sporangia, gymnosperm cones and angiosperm flowers), thereby increasing the number of individuals in each generation.

Which of the fern fronds that you examined for #15 have indusia? Examine the prepared slide of indusia and associated sporangia at this station. How do you think indusia might also function in spore dispersal?

An indusium (flat, plate-like structure on opposite side of sorus from leaf surface) protects the developing sporangia and also helps to disperse spores farther away from plant by preventing them from falling straight down underneath the leaf.

antheridia and archegonia How do you tell them apart? What is produced in these structures? How many of each type? How does fertilization occur and from which of these structures will the sporophyte develop?

Antheridia and archegonia are produced at the tips of the moss gametophyte. One antheridium produces many sperm while each archegonium produces just one egg. The sporophyte will develop by mitotic divisions of the fertilized egg, which is enclosed in the archegonium.

(liverworts) slightly-elevated, flat-topped stalked structures attached to the flat parts of the gametophyte; these are reddish (especially in the center). What are they and what is their ploidy level? What is dispersed from them? What is the ploidy level of the cells that are dispersed?

Antheridiophores are haploid. The antheridia are on these and they produce sperm, which is haploid.

(liverworts) taller stalked structures that are bright green and rounded with fingerlike projections rather than flat-topped. What are these and what is their ploidy level? How and where does fertilization occur? What happens after fertilization? How does the stalked structure function to aid dispersal? What is ultimately dispersed from them?

Archegoniophores are haploid and contain the archegonia, each of which produces one egg. Sperm get splashed by rain drops from the antheridia onto the archegoniophores, then swim up and under to the base of the finger-like projections to fertilize an egg in an archegonium. After fertilization, the egg develops by mitosis into a diploid, eggplant-shaped sporophyte, which stays attached to the underside of the fingerlike projections. Meiosis occurs within the interior of the sporophyte capsule, to create haploid spores. Elevation of the archegoniophores by their long stalks off the flat, leafy surface of the gametophyte facilitates the subsequent dispersal of spores through the air.

(liverworts) Are the gemmae cups a means of sexual or asexual reproduction?

Asexual reproduction; they and the discs of cells they contain are all haploid. Water droplets from rain showers splash the small discs out of the gemmae cups, and the discs will divide by mitosis into a new liverwort gametophyte after landing in a suitable place.

Are mosses or liverworts more dependent on water?

Both clades rely on water for sperm to swim to eggs in the archegonia, so both will be in moist environments. However, because the pores are always open in liverworts, they are a constant route of water loss from the plant. Since mosses can close their openings when they are not undergoing photosynthesis, they will lose less water.

What are the individual flowers of the sunflower? Which type of flower gives rise to the sunflower fruits (and seeds therein)?

Each "sunflower" is an inflorescence (a cluster of many small flowers on a single stem) that consists of two types of flowers. Ray flowers are located around the edge and have a single, fused showy yellow petal, whereas disk flowers are in the middle of the head, are less showy but have all the classic flower parts - sepals, petals, anthers and a single (bifurcated) pistil. The sunflower seed develops from the ovule, and the seed is encased in a dry "fruit", which is the hard shell that surrounds the seed. The ovary wall of each disk flower gives rise to the "fruit."

What are you eating when you eat popcorn (available in the lobby)?

Exploded endosperm!

(fern) What is produced inside the antheridia? Where do they go? What guides them there?

Fern antheridia produce sperm, similar to mosses and other non-vascular plants. What differs between ferns and mosses is that the fern gametophyte is much reduced in size and short- lived compared to the sporophyte generation. Sperm emerge from the antheridia and swim into the archegonia of a (usually) different gametophyte, guided there by chemotaxis, in which they swim up a gradient of chemicals that are released by the egg.

Why is it advantageous for these species of trees to rely on fire to open the female cones in order to disperse their seeds? (serotinous cones)

Fire will burn up the understory of tall grasses, shrubs, small trees, etc., greatly decreasing competition for sunlight and water after the seeds from the serotinous cones are released.

How does the placement of the stomata within sunken "stomatal crypts" and long epidermal hair-like trichomes, which extend into the crypts help reduce evaporative water loss from the leaf?

First, the crypts are on the underside of the leaf and somewhat protected from the direct rays of the sun. Second, having openings into the leaf buried in a crypt reduces the airflow over their surfaces, which reduces evaporative water loss. Trichomes help to maintain high humidity inside the stomatal crypts, further reducing diffusion of water vapor out of the leaf.

What major clades of plants can undergo secondary growth?

Gymnosperms and non- monocot angiosperms

Moss life cycle

Haploid 1.gametophytes (haploid) 2. sperm leaves antheridium in water to archegonium 3. travels towards egg in archegonium 4. fertilization Diploid 5.embryo 6. sporophyte 7. sporangium 8. meiosis Haploid 9. ungerminated spores 10. germinating spore 11. bud, protonema, rhizoid 12. Gametophyte

How does movement of water (and dissolved solutes) and sugars in a plant contrast with the movement of the same materials in mammals?

In plants, water and solutes are moved by unidirectional mass flow systems. Xylem sap is drawn from the root to the shoot by the interplay of cohesion and tension between water molecules and the evaporation of water out of the stomata in the leaves. Sugars are actively uploaded into the phloem from leaf (source) cells, creating a pressure gradient driving movement to other parts of the plant (roots and growing tip sinks). In animals, there is a single mass flow circulation system for the transport of solutes and gases. The blood system circulates around all tissues, and the system depends on pressure differences created by muscle action (hearts that act as pumps) rather than the osmotic pressure or potential energy of evaporating water in plants.

How does the plant produce a pressure difference within the phloem, causing sugars to be moved from leaf to root (or vice versa in the spring)?

In the leaf, source sugars are pumped (using cellular active transport mechanisms) into phloem cells lowering the water potential of the cell contents and causing water to enter by osmosis, and thus increasing the pressure. In the root (sink), sugar is removed from the phloem, raising the water potential causing water to exit by osmosis and thus reducing the pressure. These two processes cause a pressure difference to exist across the phloem, with the gradient in pressure driving sap movement by mass flow. Sugars can also flow upwards from source leaves to developing shoots and flowers by the same mechanism.

What happens in the megasporangium? What does a megaspore develop into? How does a sperm nucleus reach the unfertilized egg in each ovule?

In the megasporangium (contained within each ovule), meiosis occurs to form four haploid cells. However, because of asymmetric cell divisions during each meiotic division, only one of the haploid cells - the megaspore - will develop further. The megaspore divides by mitosis to form a small, multicellular female gametophyte, and one cell of the female gametophyte develops into an egg. After a pollen grain lands on a scale, a pollen tube grows towards the ovule at the base of the scale. The sperm nucleus will travel through the pollen tube to the unfertilized egg (contained within the female gametophyte).

Differences in roots between monocots and eudicots

In the roots of monocots, a central core of relatively undifferentiated cells (the pith) is surrounded by concentric rings of bundles of xylem and then bundles of phloem. In eudicots, the xylem is at the very center of the root; when viewed in cross-section, the xylem usually has a star-shaped structure, with smaller bundles of phloem surrounding the points of the star.

Notice the small microstrobili (male cones) at the tips of the branch. Male cones contain microsporangia. What important process occurs in these sporangia? What is produced?

Meiosis, to produce spores - in this case microspores. Recall that all seed plants (angiosperms + gymnosperms) are heterosporous and produce two types of spores (megaspores and microspores). Each diploid microspore progenitor cell will produce four haploid microspores by meiosis.

describe the structural and mutualistic relationship that exists between plant roots and the filamentous fungal hyphae in the mycorrhizae

Mycorrhizae, a fungus-plant association, are thought to have facilitated the invasion of land by plants because the fungus increased the surface area for absorption of nutrients from the poor soil that existed in terrestrial environments. Today, almost all plants roots have mycorrhizae containing fungal hyphae. Hyphae are long, branching filamentous structures, by which multicellular fungi grow vegetatively into their environment. Hyphae consist of one or more cells surrounded by a tubular cell wall (Wikipedia). In the endomycorrhizae seen in lab, the fungal hyphae penetrate the cell walls and form an arbuscular (tangled, tree- like) network between the cell walls and cell membranes of the plant cells; in ectomycorrhizae, the fungal hyphae wrap around the outside of the plant roots. In both cases, the fungal hyphae extend into the soil and take up water and nutrients like phosphorus and nitrogen for the plant, and in return the fungal cells receive fixed carbon (sugar) resulting from the plant's photosynthesis.

What is the significance of the subsequent double fertilization event (i.e., what part of the female gametophyte does each sperm nucleus fuse with & what do these cells become)?

One sperm nucleus fuses with the egg to form the diploid zygote, which divides by mitosis to form the embryo (which will develop into the next generation of sporophyte following seed germination). The second sperm nucleus fuses with the two polar nuclei to form a triploid cell, which divides by mitosis to create the endosperm. Triploid endosperm provides a rich nutritive supply for development of the embryo upon seed germination.

Describe the relationships among the following: fruits, ovules, ovaries and seeds.

Ovules and ovaries are pre-fertilization. Seed and fruits are post-fertilization. Seeds are mature ovules and fruit are mature ovaries.

What is another, more common name for the male gametophytes of seed plants?

Pollen. The nucleus of each of the haploid microspores formed by meiosis divides 1-2 times by mitosis without any accompanying cytokinesis to form a multinucleate pollen grain.

How do stomata differ from the pores you observed last week in the leaf-like tissue of the liverwort gametophyte? When are the stomata usually open? Closed?

Pores - like stomata - function in gas exchange (take in carbon dioxide from the atmosphere and release oxygen). But pores are always open, so the plant is continually losing water by evaporation through the pores. The guard cells of stomata can close the opening into the leaf, reducing evaporative water loss. Stomata are usually open during the day, to allow CO2 to enter the leaf for photosynthesis. However, the stomata will close on hot days or when water availability is limited. The stomata of most plants also close in the absence of sunlight.

Why might wilting be a useful survival mechanism for plants in times of water stress?

Reduction in cell volume causes the cells to become flaccid and to wilt. In guard cells, this causes the stomata to close and therefore reduce transpiration rate. There will now be less leaf area exposed to radiation from the sun, reducing leaf temperature. The collapsed leaf will also tend to trap moist air and reduce the concentration gradient of water vapor between the inside of the leaf and surrounding air, causing a reduction in transpiration rate.

examples of edible roots, stems, leaves, flowers

Roots: carrots, beets, radishes Stems: asparagus (lower parts), potatoes (sprouts = stems of new plants) and ginger (rhizomes - underground stems) Leaves: onions (green and yellow), lettuce, spinach, parsley, kale, cabbage Flowers: artichokes, broccoli

Can you distinguish sepals from petals? Why or why not? Make sure to dissect the ovary to find the parallel columns of ovules. Where are the male gametophytes (pollen) and female gametophytes produced?

Sepals are the outermost whorl in the flower, they are lowest on the stem. The three petals are internal to the three sepals (these numbers are typical for monocots). They look similar to each other (sepals are petal-like); this, of course, suggests that the sepals may function in attraction. Breeders select for petaloid sepals as it makes for a more colorful flower. Female gametophytes are produced inside ovules within an ovary. Male gametophytes (pollen grains) are produced within anthers. Same general process to make each as in the conifers.

How is the shape of the pine seeds well suited for their primary mode of dispersal?

Similar to the cones, seeds are larger than pollen and female cones protect and maintain the developing embryos until the seeds have matured. Winged seeds aid in dispersal by wind.

The cuticle is an acellular, waxy layer that prevents evaporative water loss through the underlying epidermis. Note that it is thicker on the upper surface of the leaf than the lower surface. Why does that make sense?

Since the top of the leaf is exposed to direct sunlight, a thicker cuticle will help prevent evaporative water loss through the epidermis and protect the DNA of the underlying cells against the damaging effects of ultraviolet radiation.

Are the spores of a fern produced by mitosis or meiosis?

Spores are ALWAYS produced by meiosis in ALL plants.

The products of meiosis in the sporophyte are called? Are they haploid or diploid? What will they develop into? With regard to the transition to land, what is the selective advantage of producing these cells in a structure that is elevated on a stalk?

Spores are haploid and they develop by mitosis into a new gametophyte after landing in a suitable location. It is advantageous to produce spores up & out of the water such that they can disperse to dry land. Examine peristome teeth on poster and SEM photos. They are curved into the interior of the spore capsule when it is closed and help to fling the spores out of the capsule as they unfurl and the capsule opens.

What is starch? Why is it in the roots?

Starch is a branched polymer of glucose and is the storage form of glucose in plant cells. The roots store glucose that is made during photosynthesis for use by the plant at times when it is unable to perform photosynthesis.

How does their structure relate to the mode of transportation of these pollen grains? Likewise, why might it be advantageous for a plant to produce male cones on the tips of their branches?

The flat, lobed pollen (looks like Mickey Mouse!) floats through the air. Conifer pollen is wind dispersed so it is also advantageous to have the male cones at the tips of branches, to enhance dispersal of the pollen by wind to another branch or tree.

determine if the fruit is a simple, multiple, aggregate or accessory fruit,

The fleshy parts of tomatoes, kiwis, cherries, peppers, cucumbers, zucchini, okra, oranges, peaches, mangos and coconuts are all simple fruits, derived from the walls of a single ovary at the base of a single flower. Some ovaries have only one ovule (giving rise to a single seed, such as the pit of a peach or cherry). Others have multiple ovules, giving rise to multiple seeds within the fruit (zucchini, okra, etc.). For fruits like okra and oranges that have 'sections', each section is derived from a different carpel within the ovary. Raspberries and blackberries are aggregate fruits, derived from a single flower with multiple ovaries (each with one ovule) and associated pistils (which become the little 'hairs' on each plumped-up section of the berry). Pineapples are multiple fruits: the ovaries of many separate flowers on a single inflorescence plump up and fuse together to form the fruit. The dry, brown 'true fruits' (what are commonly called the seeds) of strawberries are scattered over the surface of the berry; the red, fleshy part of a strawberry is considered an accessory fruit as it is derived from the receptacle tissue that supports the flower (and not the ovary wall). Apples and pears are also accessory fruits.

How are moss and liverwort gametophytes differ?

The liverwort Marchantia has an extremely flat morphology (thallus), whereas the moss gametophyte is more erect.

When you look at a large fern, what generation are you looking at? Is it haploid or diploid?

The mature plant is the sporophyte, which is diploid. Fronds - leaves function in photosynthesis and also hold the sporangia, so ultimately assist in spore dispersal Fiddlehead - newly-developing stem and frond Rhizomes - horizontal stems (usually underground), function to spread the plant horizontally; like all stems, function in water and nutrient transport Sori - clusters of sporangia, which is where spores are produced by meiosis

what are liverwort pores used for?

The pores are always open and function in gas exchange (take in carbon dioxide for photosynthesis from the atmosphere and release oxygen).

(Fern) What is the ploidy level of the prothallus? Which generation are you looking at?

The prothallus is haploid and is the gametophyte generation of a fern.

Compare the size of the fern prothallus to the equivalent generation in the mosses.

The prothallus is much smaller (relative to the size of the sporophyte) than the moss gametophyte.

What are the furry "rabbit's feet" in botanical terms? How do these function in reproduction? Is this an asexual or sexual process? What would the ploidy level be of offspring from such reproduction?

The rabbit's feet are rhizomes, which are horizontal (usually underground) stems (not to be confused with the rhizoids of mosses and liverworts). Asexual reproduction can occur via fragmentation when the rhizomes (rabbit's feet) develop roots and shoots and break off from the main plant. The offspring would be diploid, the same as the parent plant.

How does the arrangement of vascular tissue change between the roots and stems in herbaceous eudicots? In herbaceous monocots?

The single, central cylinder of vascular tissue in herbaceous eudicot roots gives rise to a concentric ring of xylem and phloem bundles in the stems. In contrast, the more central concentric ring of xylem and phloem bundles in the roots of monocots gives rise to bundles of xylem and phloem that are dispersed throughout the width of the stems.

What evidence suggests that at least early in its development, the embryo (or young sporophyte) of a fern receives nutrients from the prothallus? What happens to the gametophyte of a fern (i.e., the prothallus) after the sporophyte begins to produce its own food? Which generation is dominant in ferns? Why?

The young sporophyte is initially attached to (and nutritionally dependent upon) the gametophyte, since it grows right out of the archegonium. Young sporophytes grow into adult ferns (such as the specimens in the laboratory), while the prothallus (gametophyte) eventually degenerates after the sporophyte begins to make its own food. The diploid, sporophyte is the dominant stage, as the majority of the life cycle is spent as a sporophyte and sporophytes are larger than gametophytes.

How are ferns better adapted to terrestrial life than mosses and liverworts?

They have true vascular tissue. Like mosses, also have leaf openings for gas exchange (stomata) that can open and close (more next week).

In what way are ferns no better adapted to terrestrial life than mosses or liverworts?

Thin, flat gametophyte with rhizoids and swimming sperm limit them to moist environments.

The Casparian strip prevents water and dissolved solutes from entering the vascular tissue via the apoplast route. Why is this advantageous to the plant?

This enables the cells that surround the stele to regulate the passage of water and dissolved minerals into and out of the vascular tissue. The Casparian strip is a barrier to the movement of water between cells. Water, and any dissolved solutes in it, therefore have to pass through the membranes of cells. This membrane transport allows the plant to regulate the quantities of materials entering the rest of the plant. The water-proof layer also helps retain water within the stem and roots when the soil is dry.

Why would many angiosperms have evolved the energetically-costly feature of enclosing their seeds in fleshy fruits?

To entice animals to eat the fruit, as this leads to a form of dispersal for the plants. Assuming some of the seeds contained within the yummy, fleshy fruit survive the trip through the animal's digestive tract, the seeds will then be excreted (in the feces), likely somewhere distant from the parent plant since animals move around.

Which of these tissue types - xylem or phloem - are made up of cells with extra thick cell walls and are dead at maturity? What might this suggest about another function of this tissue type in helping the fern grow tall?

Xylem cells are dead at maturity and have thick secondary cell walls in which ordered arrays of cellulose (linear polymer of glucose) are embedded in a meshwork of lignin, a complex, hydrophobic polymer. One should be able to compare the thickness of the cell walls in the two tissue types and notice how much thicker the cells walls are in xylem than in phloem. Xylem provides structural support for plants; it is the main component of wood

Describe the mechanism by which water (& dissolved solutes) are transported up the xylem.

Xylem sap is drawn from the root to the shoot by cohesion and tension between water molecules, with the driving force ultimately being the loss of potential energy as water changes from a liquid to vapor during evaporation. Thus, the column of water and dissolved minerals is essentially pulled up the stem as water evaporates out of the stomata in the leaves.

How does water and mineral travel up with rhizoids?

along the outside by capillary action

Dominant generation of mosses?

gametophyte, longer-lived part of the life cycle. sporophyte it physically attached, it is yellowish and is non-photosynthetic and therefore dependent on the gametophyte (green) for nutrition

meiosis (mosses)

occurs in the capsule or sporangium of the sporophyte to produce haploid spores. Stalk of sporophyte and outer wall of capsule remain diploid

rhizoids

simple projections from the epidermis, usually one cell thick, though many cells, anchor moss to substrate

stomata

which are openings into the leaf for gas exchange.