CHAPTER SUMMARY

29.1 THE EVOLUTION OF LAND PLANTS FROM AQUATIC ANCESTORS INTRODUCED A MAJOR CHALLENGE FOR PHOTOSYNTHESIS: ACQUIRING CO2 WITHOUT LOSING EXCESSIVE AMOUNTS OF WATER.

29.2 LEAVES HAVE A WAXY CUTICLE THAT RETARDS WATER LOSS BUT INHIBITS THE DIFFUSION OF CO2, AND PORES, CALLED STOMATA, THAT REGULATE CO2 GAIN AND WATER LOSS.

29.3 XYLEM ALLOWS VASCULAR PLANTS TO REPLACE WATER EVAPORATED FROM LEAVES WITH WATER PULLED FROM THE SOIL.

29.4 PHLOEM TRANSPORTS CARBOHYDRATES AND SUPPORTS THE GROWTH AND RESPIRATION OF NON-PHOTOSYNTHETIC ORGANS SUCH AS STEMS AND ROOTS.

29.5 ROOTS EXPEND ENERGY TO OBTAIN NUTRIENTS FROM THE SOIL.

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Self-Assessment Question 1

Explain why vascular plants are better able to sustain photosynthesis than are bryophytes.

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Model Answer:

Vascular plants are better able to sustain photosynthesis than bryophytes because they are able to take up water from the ground through their root system instead of being dependent on the level of water on the surface. Bryophytes dry out when not enough water is available at the surface, and, as a result, they lose the ability to photosynthesize.

Self-Assessment Question 2

Explain why transpiration is best explained as a consequence of acquiring CO2 from the atmosphere, as opposed to temperature regulation, nutrient transport, or utilization of water as a substrate in photosynthesis.

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Model Answer:

Transpiration is the loss of water vapor from the leaves through evaporation. It is a consequence of acquiring CO2 from the atmosphere. As CO2 diffuses into the leaf through stomata, water vapor diffuses out at a faster rate. Thus, several hundred molecules of water are lost for every molecule of CO2 acquired for photosynthesis.

Self-Assessment Question 3

Draw and label the features of a leaf that are necessary to maintain a well-hydrated interior while still allowing CO2 uptake from the atmosphere.

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Self-Assessment Question 4

Diagram how the movement of solutes results in the opening and closing of stomata.

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Self-Assessment Question 5

Diagram how the enzyme PEP carboxylase allows CAM plants to reduce transpiration rates and C4 plants to suppress photorespiration.

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Self-Assessment Question 6

Contrast how transport is generated in xylem and in phloem.

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Model Answer:

Water transport in xylem is driven by an evaporative pump whose driving force is generated in the leaves. Thus, water moves from the roots to the leaves in xylem. In contrast, the transport of sap in the phloem can go in either direction, from tubers to young leaves or from leaves to roots, for example.

Phloem transport is driven by differences in turgor pressure. Water is drawn into the phloem by osmosis, in response to the active transport of sugar molecules into the phloem. The influx of water increases turgor pressure at the source. Water leaves the phloem when sugar molecules are transported out into the other plant tissues. The outflow of water reduces turgor pressure at the sink. Water flows from the region of high turgor pressure to the region of low turgor pressure.

Self-Assessment Question 7

Describe the structure of xylem conduits and sieve tubes in relation to their function.

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Model Answer:

Xylem conduits are basically hollow tubes made up of thick cell walls. There is no cytosol or internal organelles. Water is able to flow easily through the hollow tubes.

Phloem consists of sieve tubes that transport carbohydrates. They are also elongated, but they contain cytoplasm and a few organelles. The cytoplasm provides a medium in which to transport the carbohydrates, called phloem sap.

Self-Assessment Question 8

Explain why phloem is necessary to produce roots.

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Model Answer:

Phloem transports sugars and other nutrients to non-photosynthetic organs, like the roots.

Self-Assessment Question 9

List four adaptations of roots that enhance the uptake of nutrients from the soil.

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Model Answer:

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 like legumes.