exam 3 questions Flashcards
(49 cards)
Why are vascular plants better able to sustain photosynthesis than are bryophytes?
Vascular plants are better able to sustain photosynthesis than bryophytes because they are able to take up water from the soil through their roots and to limit rates of water loss from their leaves. As a result, they can remain hydrated and continue to photosynthesize, even when the air is quite dry. In contrast, bryophytes rely on surface moisture for hydration and are unable to control their water loss. When their surfaces are dry, these plants lose water rapidly, drying out to a point where they are no longer able to carry out photosynthesis (as well as other forms of metabolism).
Why do plants transpire?
Transpiration is the loss of water vapor from the leaves through evaporation. It is a consequence of acquiring COz from the atmosphere. As COz diffuses into a leaf to reach the photosynthetic cells, water vapor evaporates from surfaces within the leaf and diffuses out through stomata. Plants cannot completely seal themselves off against water loss, because doing so would prevent them from obtaining the COz needed for photosynthesis. Thus, transpiration is an unavoidable by-product of acquiring COz by diffusion from the atmosphere.
because when co2 diffuses into the leafto reach the photosynthetic cells, water vapor evaporates and diffuses through the stomata.
How is the statement that water is transported through the xylem without requiring any input in energy by the plant both correct and incorrect?
The statement is correct in that the negative pressures that pull water from the soil result from the evaporation of water from leaf cells, and the energy for evaporation comes from the heating of the leaf by the sun. It is incorrect in that water transport in the xylem is possible only because of structures within the plant, notably the xylem conduits, and also the roots and the stem. The plant must expend energy to produce these structures.
it is correct because evaporation results from heat energy from the sun hitting the leaves which then causes evaporation which then causes the negative pressure that allows the water to flow up through the xylem. the statement is incorrect because water transport through the xylem is possible because of the structures in the plant like the xylem conduits, roots and stem.
How is phloem able to transport carbohydrates from the shoot to the roots, as well as from the roots to the shoot (but not at the same time)?
The carbohydrates in phloem move from source to sink due to a difference in turgor pressure. In sources, a high concentration of sugars in sieve tubes causes water to flow in by osmosis, increasing turgor pressure. In sinks, sugars are transported out of sieve tubes and used by surrounding cells. The withdrawal of sugar from sieve tubes causes water to flow out of the sieve tube, by osmosis, thereby lowering the turgor pressure. It is the difference in turgor pressure between sources and sinks that drives the movement of phloem sap through sieve tubes. Sources can be actively photosynthesizing leaves, or any organ with a large amount of stored carbohydrates. Carrots are examples of roots with large amounts of stored carbohydrates. In contrast, sinks are organs that require an import of carbohydrates to meet their growth and respiratory needs. Examples of sinks include young leaves, developing fruits, and most roots.
How are the xylem and the phloem similar? How are they different?
Similarities: Transport in both xylem and phloem is driven by differences in pressure. In both, transport occurs through elongated cells.
Differences: In xylem, flow is from roots to leaves; pressures are less than zero; conduit cells are dead at maturity; the driving force results from transpiration; and the material transported is mostly water (with small amounts of nutrients and other solutes). In phloem, flow is from sources to sinks; pressures are greater than zero; conduit cells are alive but highly modified at maturity; the driving force results from osmosis; and the material transported is phloem sap, which contains a large amount of sugars.
Why is phloem necessary to produce roots?
Phloem transports sugars and other nutrients to non-photosynthetic organs, such as the roots.
What are four adaptations of roots that enhance the uptake of nutrients from the soil?
Four adaptations of roots that enhance the uptake of nutrients from the soil are (1) root hairs of the epidermis, (2) the ability of endodermal cells to control which nutrients enter the vascular system, (3) the beneficial association of mycorrhizal fungi, and (4) the beneficial association of bacteria in the root nodules of some plants, such as legumes.
In what ways are spores similar to gametes, and in what ways do spores and gametes differ?
Both spores and gametes are unicellular and haploid. Gametes are short-lived and require hydration; they must fuse with another gamete to form a new individual. In contrast, spores can be long-lived and can survive exposure to air because of the presence of sporopollenin, a tough, resistant covering that allows spores to withstand environmental stresses such as ultraviolet radiation and desiccation. A spore, once dispersed, can grow into a new individual.
In what ways is fern reproduction similar to moss reproduction? In what ways is fern reproduction different from moss reproduction?
Both mosses and ferns exhibit alternation of a haploid (gametophyte) generation and a diploid (sporophyte) generation, the release of swimming sperm, and the dispersal of spores. In mosses, the sporophyte is completely dependent on the gametophyte. In contrast, in ferns, the sporophyte is only initially dependent on the gametophyte and eventually becomes free-living
How do the male and female gametophyte generations differ in seed plants?
The male gametophyte develops within the spore wall, forming pollen.
Following pollination, the male gametophyte produces a pollen tube that penetrates the tissues of the ovule to deliver male gametes to the egg. The female gametophyte grows to fill the entire sporangium, which remains attached to the sporophyte. Seed plant gametophytes are never free-living, all of the resources that fuel the growth of both the male and female gametophytes come from the sporophyte generation
What are two advantages of seeds over spores in terms of the probability that the next sporophyte generation will become successfully established?
Compared with spores, seeds can store more resources and exhibit dormancy, both of which aid in the successful establishment of the next generation.
What are the names and functions of the structures in each whorl of a flower?
A flower consists of four whorls of organs. From outside in, they are the sepals, petals, stamens, and carpels. The sepals protect developing flowers, the petals commonly attract pollinators; the stamens produce pollen, and the carpel protects the ovules inside that develop into seeds following fertilization.
The often colorful petals attract pollinators. The sepals do not play a direct role in fertilization, but rather protect the flower during its development.
Contrast the investments that angiosperms and gymnosperms make and the structures that they produce to enhance pollination.
Gymnosperm pollen and ovules are produced in separate structures, and pollen is carried to the female structure by the wind. Angiosperms often produce pollen and ovules in one structure, the flower. Some angiosperms take advantage of the wind to disperse their pollen, but more common is the use of animal pollinators.
Because the sites of pollen and ovule formation are near each other in a flower, a pollinator can deliver pollen to one plant and take up pollen to carry to another plant in a single visit. Pollen is captured on the sticky or feathery stigma at the top of the ovary-containing carpel. Many angiosperms invest in rewards such as nectar or attractants such as scent to lure pollinators.
From which flower structure(s) is a fruit derived?
A fruit forms from the ovary that encloses the seeds. In some plants, it also forms from other parts of the flower, including the petals and sepals.
From which flower structure(s) is a fruit derived?
A fruit forms from the ovary that encloses the seeds. In some plants, it also forms from other parts of the flower, including the petals and sepals.
Describe two ways that plants can reproduce asexually. How does each of these methods help to disperse offspring?
Plants are able to reproduce asexually by apomixis (formation of seeds without fertilization) and by vegetative reproduction (when a plant spreads horizontally and develops new upright shoots). Seeds formed by apomixis spread just like seeds produced sexually. Vegetative reproduction allows new shoots to spread, and sometimes break off, far from the parent plant.
What are three functions of the shoot apical meristem?
The shoot apical meristem is the site of cell division and, therefore, the source of all the cells that make up a stem. It also initiates leaves and produces new meristems, which allow stems to branch.
Name one role of the plant hormone auxin. How is auxin is transported within a plant?
Auxin is responsible for guiding the development of vascular connections between leaves and stem. It also causes shoots to elongate and causes branching to be suppressed, among other functions.
Auxin is transported by polar transport, which is the coordinated movement across many cells in a particular direction. Auxin can exit cells only through PIN proteins, so the placement of PIN proteins on the basal side of each cell will cause auxin to flow from the tip to the base of a plant. Auxin can also be carried in the phloem.
Why do plants have two types of lateral meristem?
One of a plant’s lateral meristems produces new vascular tissues; the other maintains an outer protective layer.
Why does a plant that has a vascular cambium also have a cork cambium?
Cork, produced by cork cambium, protects the stem of the plant against herbivores, mechanical damage, desiccation, and, in some cases, fire. The plant needs this protection because as the activities of the vascular cambium increase the plant’s diameter, the epidermis formed during primary growth eventually ruptures.
Why does the vascular cambium form a continuous sheath that runs from near the tips of the branches to near the tips of the roots, whereas the cork cambium is discontinuous in both space and time?
The vascular cambium forms a continuous sheath from root to tip, as a result, it produces xylem and phloem along the length of the plant. The xylem and phloem must form a continuous transport pathway between roots and leaves if they are to function efficiently. Cork cambium is discontinuous in both space and time, however, because it is relatively short-lived. The cork cambium eventually becomes cut off from its source of carbohydrates, the phloem. A new cork cambium forms when the distance between the original cork cambium and the active phloem grows too large. In many cases, cork cambium forms in patches rather than as a continuous layer.
How is root development similar to and different from stem development?
Both roots and stems grow from apical meristems, and both have regions of cell division, elongation, and differentiation. However, root apical meristems are covered by a root cap, the root has a single vascular bundle in the center, and branching occurs by the formation of new meristems from the pericycle; all of these features are different from those seen in stems.
What are three structural differences between roots and shoots that allow roots to grow through the soil?
Roots are typically much thinner than stems, allowing them to grow around particles in densely packed soil. The root apical meristem is also protected by a root cap as the root grows through the soil. Finally, the root apical meristem does not produce any lateral organs such as leaves.
How would you tell whether an isolated piece of a plant came from the shoot or from the root?
You can identify a root in several ways. First, does it have a root cap surrounding the apical meristem? Second, are there thin projections, root hairs, growing from the zone of maturation? Third, how big is the tissue in relation to the rest of the plant (roots are typically thinner)? Fourth, is the tissue able to photosynthesize and therefore green in color (root tissue is not usually green)?
