H.W. 7 Mastering Biology

If a long-day plant has a critical night length of 9 hours, which 24-hour cycle would prevent flowering?

14 hours light/10 hours dark

Select the correct mechanism of stomatal opening and closing. A) The radial orientation of cellulose microfibrils in the cell walls of guard cells causes them to bow outward and open the stomatal pore when turgid. B) The cell walls of guard cells are thickened on the side of the stomatal opening and the thinner walls bow outward when the guard cells become turgid, to close the stomata. C) Light stimulates proton pumps in the plasma membrane of the guard cells, causing them to lose K+ and become flaccid.

A. The radial orientation of cellulose microfibrils in the cell walls of guard cells causes them to bow outward and open the stomatal pore when turgid.

What is the physical basis of the phototropic response? Hints A) Cell elongation. B) Cell transport. C) Cell shortening. D) Photosynthesis.

A. cell elongation

Which of the following would tend to increase transpiration? A) higher stomatal density B) spiny leaves C) sunken stomata D) a rainstorm E) a thicker cuticle

A. higher stomatal density

How does auxin produce phototropism?

Auxin accumulates in cells on the side of the plant opposite the source of light and stimulates their elongation.

How does auxin produce gravitropism in a plant that is placed on its side?

Auxin accumulates on the lower surface of the root and inhibits elongation of cells in that region.

Which term describes the direction of auxin transport in a plant? Hints A) Bidirectional. B) Polar. C) Circular. D) Multidirectional.

B. Polar

Which of the following statements about xylem transport is true? A) Water and minerals enter the xylem by diffusion. B) Water and minerals move through the root cortex into the xylem and upward through the stem and into leaves. C) The xylem cells that conduct water and minerals are alive. D) All water transported by the xylem is used for photosynthesis in the leaves.

B. Water and minerals move through the root cortex into the xylem and upward through the stem and into leaves.

Which one of the following refers to the loss of water through the stomata in a plant's leaves? A) respiration B) transpiration C) osmosis D) guttation E) bulk flow

B. transpiration

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

Both the photosynthesis and transpiration rates are low.

Which of the following statements about hormones is true? Hints A) Hormones are produced at the sites where they are needed. B) Hormones are small inorganic molecules. C) Hormones can function at very low concentrations. D) Hormones are produced only in plants.

C. Hormones can function at very low concentrations.

Which of the following statements about the distribution of sap throughout a plant is true? A) The main component of phloem sap is glucose. B) The driving force for sugar movement is transpiration. C) The mechanism that explains the movement of sugars throughout a plant is called the pressure-flow hypothesis. D) Companion cells form the conducting tissue for sap.

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

Select the accurate statement about water potential. A) Free water moves from a region of lower water potential to a region of higher water potential. B) Adding solutes to water increases water potential. C) Water in a turgid cell has positive pressure potential.

C. Water in a turgid cell has positive pressure potential.

If a plant's stomata are closed and no transpiration is occurring, which of the following predictions is accurate? A) Without transpiration, the plant will be water deficient. B) Without transpiration, the plant's cells will become flaccid. C) Without transpiration, less water will be absorbed from the soil.

C. Without transpiration, less water will be absorbed from the soil.

Where does the majority of stem growth in a plant occur? Hints A) Lateral branches. B) Both the apical meristem and lateral branches. C) Axillary buds. D) Apical meristem

D. Apical meristem

Which tissue acts as a filter on the water absorbed by root hairs? A) Vascular tissue B) Cortex C) Epidermis D) Endodermis

D. Endodermis

Which term describes an area where sugars are used or stored? Hints A) Source B) Stomata C) Leaves D) Sink

D. Sink

Which of the following seedlings will probably bend toward light? Hints A) one whose tip is cut off and topped by a gelatin block containing no plant substances B) one whose tip is cut off C) one whose tip is separated from its base by aluminum foil D) one whose tip is separated from its base by a gelatin block E) one whose tip is covered with a black plastic cap

D. one whose tip is separated from its base by a gelatin block

In addition to transporting sugar, the phloem also _____. A) transmits electrical signals B) transports viral RNA throughout the plant C) transports plant RNA throughout the plant D) transports proteins throughout the plant E) All of the above

E. All of the above

Which of the following is a correct statement about a difference between xylem and phloem transport? A) Transpiration moves phloem sap but not xylem sap. B) Phloem carries water and minerals; xylem carries organic molecules. C) Active transport moves xylem sap but not phloem sap. D) Xylem sap moves from sugar source to sink, but phloem sap does not. E) Xylem sap moves up; phloem sap moves up or down.

E. Xylem sap moves up; phloem sap moves up or down.

Which of these plant hormones is not typically considered a growth-promoting substance? Hints A) auxin B) gibberellin C) brassinosteroids D) cytokinin E) abscisic acid

E. abscisic acid

True or false? Auxin is asymmetrically distributed in shoots because the auxin on the side of the plant facing the source of light is destroyed.

False

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

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

What do the relative widths of the stomatal openings in the treatment group indicate about plants 6-10?

Plants 6-8 are experiencing drought stress and have closed their stomata; plants 9 and 10 are starting to close their stomata.

When the experiment was run for 1 hour rather than 15 minutes, the results were about the same except that the stomatal openings of plants 9-11 were comparable in size to those of plants 6-8. What is the most likely explanation for this?

Plants 9-11 responded later because they were farther from plant 6, where the drought-stress message originated.

How do the widths of the stomatal openings of plants 6-10 compare with those of the other plants after plant 6 was osmotically shocked?

The stomatal openings of plants 6-8 are smaller than those of the other plants; those of plants 9 and 10 are intermediate in size.

What do the results of the control experiment indicate?

Water did not duplicate the effect of mannitol.

Movement of phloem sap from a source to a sink

depends ultimately on the activity of proton pumps.

A plant cell placed in a solution with a lower (more negative) water potential will _____.

lose water and plasmolyze

Plants must always compromise between _____ and _____.

maximizing photosynthesis ... minimizing water loss

The Pr form of the phytochrome pigment has maximum absorption in the _____ part of the spectrum.

red

Plant hormones act by directly affecting the activities of _____.

signal transduction pathways

Photosynthesis ceases when leaves wilt, mainly because

stomata close, preventing CO2 from entering the leaf.

A student is performing a chemical analysis of xylem sap. This student should not expect to find much _____.

sugar

Most plants flower when _____.

the nights are the right length

Why was it necessary to make sure that chemicals could not move through the soil from one plant to the next? In other words, why was it important for the plants to be in separate pots?

to ensure that mannitol did not move through the soil from plant 6 to other plants

Why was water added to plant 6 instead of mannitol in the control experiment?

to mimic the handling of the plants

Do the data indicate that the communication is via the shoot system or the root system?

via the root system, since plants 7 and 8 were affected but plants 4 and 5 were not

Do the data support the idea that plants can communicate their drought-stressed condition to their neighbors?

yes