Bio HW 35

How about in the year 2010?

3x

In the year 1915, the stomatal conductance of oak was approximately how many times higher than that of pine?

4x

Which term describes an area where sugars are used or stored?

A sink is an area where sugars are used or stored; typically, these are the roots and fruits of a plant.

Assuming that CO2 levels continue to increase with time, how likely are plants to be able to continue to adapt by adjusting stomatal conductance?

At some point, plants would likely reach a limit in their phenotypic flexibility; they would not be able to decrease the number of stomata any further without compromising CO2 uptake and decreasing photosynthesis.

what characterizes the rates of photosynthesis and transport in a plant on a dry cloudy day?

Both the photosynthesis and transpiration rates are low. On a cloudy day with low soil moisture, the photosynthesis rate is low and stomata are closed, so the transpiration rate is low.

Which of the following plant organs may act as a source for translocation of sugars inside a plant? See Section 35.4

Correct. Mature leaves photosynthesize, manufacturing sugars.

Which tissue acts as a filter on the water absorbed by root hairs?

Endodermal cells filter solutes from water and allow them to pass through to the vascular tissue.

Why is the transport of phloem sap considered an active process?

Energy is used to transport sucrose into companion cells near sources, against a concentration gradient.

True or false? The rate of sugar transport in a plant depends on the rate of photosynthesis, the rate of transpiration, and the difference in turgor pressure between the source and the sink.

False While the rate of photosynthesis and the difference in turgor pressure between the source and the sink do influence the rate of sugar transport in the phloem, the rate of transpiration does not; transpiration mainly influences the rate of water transport through the xylem.

True or false? Root pressure can move water a long distance up the xylem because of the higher water potential of the xylem in comparison to the water potential in the surrounding cells.

False, Root pressure can move water a short distance up the xylem because of the lower water potential of the xylem in comparison to the water potential in the surrounding cells.

The water potential of phloem sap is lowest in which of the following situations? See Section 35.4

Near leaves at the start of spring Correct. The water potential of phloem sap is lowest here because developing leaves are using sucrose faster than they are creating it.

Your friend claims that phloem always carries sugars down a plant. What, if anything, is wrong with that statement?

Phloem can carry sugars down a plant, but it can carry sugars up as well (e.g., if sugars are moving to flowers or fruits).

According to the pressure-flow hypothesis, what mechanism causes the movement of phloem sap from sources to sink tissues?

Pressure potential differences between source and sink These differences cause a flow of sugars in the phloem.

Which of the following statements about the distribution of sap throughout a plant is true?

The mechanism that explains the movement of sugars throughout a plant is called the pressure-flow hypothesis.

The amount of water that evaporates from stomata over a period of time is referred to as stomatal conductance, which is determined largely by the number of stomata in a given area of leaf surface. Researchers obtained specimens from preserved collections and measured stomatal conductance in leaves from oak trees and pine trees that grew at various times under different CO2 levels. The data are shown in the following graph. In general, is the maximum stomatal conductance rate in plants more or less than it was a century ago?

The plants have lower stomatal conductance now than they did a century ago.

What is the role of companion cells in the movement of sugars through plants?

They accumulate sucrose, which is then transferred to adjacent sieve-tube elements.

Which of the following statements about xylem transport is true?

Water and minerals move through the root cortex into the xylem and upward through the stem and into leaves. Water and minerals that are taken up in the soil are transported from roots to leaves by the xylem.

According to the pressure-flow hypothesis, which direction are sucrose and water flowing in the phloem when roots are sources and leaves are sinks? See Section 35.4

Water and sucrose flow up the stem. Sucrose flows from a higher pressure to a lower pressure via a flow of water obtained from the xylem.

A cell is placed in a solution that is hypotonic to the cell. Which of the following best describes movement of water in this situation?

Water will flow into and out of the cell, but the overall net movement will be into the cell.

What would happen if this cell were moved from pure water to a seawater solution? See Section 35.1 (Page)

Water would move out of the cell. Because the solute potential would be lower outside the cell, water would move in that direction.

When water moves from soil into the vascular tissues inside the root, it can take three possible pathways. Of these, the apoplastic route is _____. See Section 35.2 (Page) .

between cells and through cell walls Correct. Water can move through the apoplast but must enter the symplast at the endodermis to enter the xylem.

The transport of a water column up a very tall tree can be explained by _____.

cohesive and adhesive forces of the water column under evaporative tension Correct. The pull of evaporation, combined with the cohesive tendency of water to form hydrogen bonds, moves water.

Some plants growing in arid climates have small leaves and thick waxy cuticles on the upper epidermis. This is an adaptation for ____

decreasing water loss from leaves Correct. Plants in arid climates may also have stomata only on their lower leaf epidermis. The stomata may be in pits, protected from water loss by hairlike epidermal extensions called trichomes.

A mutant plant lacking the ability to pump protons out of leaf companion cells will be unable to do which of the following?

load sucrose into sieve cells