Chapter 31 - Plant Growth

Question 1

Recall that in many plants, if the shoot apical meristem is removed, axillary buds become active and new lateral branches form. What is this an example of?

Answer 1

apical dominance

Question 2

A houseplant is growing on your windowsill. Every Sunday, without fail, your roommate turns the plant 180 degrees. When you ask your roommate why she does that, her reply is simply, “I want straight plants.” Does this method produce straight plants?

Answer 2

Yes. Rotating the plant will even out the growth of the plant toward the light by changing where the light hits the plant every week.

Question 3

Turgor pressure, which causes cells to expand, results in a force applied uniformly to the entire cell wall. How is it that plant cells are often observed to expand in a particular direction—for example, increasing their length but not their girth?

Answer 3

Cellulose molecules individually resist extension, and so the cell wall stretches more readily in directions perpendicular to the dominant orientation of cellulose molecules .

Question 4

Within the stem of a vascular plant, where would you expect to find the cells that are the MOST mature?

Answer 4

at the base of the stem near the soil

Question 5

In seed plants, branches grow out from _____, which are meristems that form at the base of each leaf

Answer 5

axillary buds

Question 6

Flowering is triggered by the production of _____, which triggers the transition from apical meristem to floral meristem identity.

Answer 6

florigen

Question 7

The highly productive varieties of wheat and rice that were developed in the Green Revolution produce lots of seeds. Given that evolutionary fitness is measured in terms of reproductive success (for which total seed production is a good proxy), why might natural selection have failed to produce these highly productive varieties on its own, without the work of human plant breeders?

Answer 7

Green Revolution crops have reduced stem elongation and thus are poor competitors for sunlight compared to wild plants

Question 8

A researcher creates a mutant pea plant in which cytokinins are over expressed and gibberellic acid is under expressed. What is the MOST likely phenotype of this mutant pea plant?

Answer 8

The pea plant would be shorter with more branches compared to wild-type plants

Question 9

Which of the following is NOT one of the major plant hormones?

Answer 9

calcitonin

Question 10

The condition in which shoot apical meristems suppress the growth of axillary buds is called:

Answer 10

apical dominance

Question 11

A botanist is studying the growth rings of a redwood tree. She notices that three concentric rings are very thin compared to the surrounding growth rings. What can she deduce from the presence of these thin growth rings?

Answer 11

The tree may have experienced a drought or had limited access to nutrients during that time period

Question 12

Vascular cambium is one of two lateral meristems; the other is cork cambium. A plant grows in diameter primarily through divisions of the vascular cambium. If you pull a small piece of bark off a tree, and then look at the bark’s inside surface, what tissue are you looking at (ignore any remaining cells of vascular cambium that may be left)?

Answer 12

phloem

Question 13

Roots are capable of which types of growth?

Answer 13

both primary and secondary growth

Question 14

Root hairs are MOST abundant:

Answer 14

near the root tip.

Question 15

The hormone responsible for cell differentiation, particularly xylem and phloem, in the roots is:

Answer 15

auxin.

Question 16

If you were to dissect a root, the layers from outside to inside would be:

Answer 16

epidermis → cortex → endodermis → phloem → xylem

Question 17

You have a really leafy houseplant that completely shades the soil in the pot where it is growing. You notice that the tips of some roots are starting to break through the surface of the soil (likely these are new roots growing from the pericycle of an existing root just beneath the surface). If you do nothing, what would you expect to happen to the growth of these roots and why?

Answer 17

The roots will grow downward back into the soil because the statoliths are being redistributed due to gravity and that will change the direction of growth

Question 18

If a plant stem is exposed to sunlight only on its right side, what happens and why?

Answer 18

The stem will bend to the right, as auxin collects on the LEFT side of the plant, causing cells to elongate

Question 19

Abscisic acid is produced in the _____ of roots in drying soils and promotes root _____.

Answer 19

root cap; elongation

Question 20

Phytochrome prevents seeds of some plants from germinating when they are in deep shade by the:

Answer 20

absorption of far-red wavelengths by Pfr.

Question 21

Gravitropism is a result of:

Answer 21

auxin concentration and the movement of starch-filled organelles called statoliths

Question 22

A photoreceptor in seeds detects the ratio of red to far-red light, preventing seeds from germinating when:

Answer 22

they are in the shade of another plant.

Question 23

Short-day plants flower in the _____ leaving enough time to complete seed development before _____.

Answer 23

late summer; winter

Question 24

Vascular cambium is capable of producing:

Answer 24

secondary xylem and phloem.

Question 25

Many plants are able to detect day length because they have:

Answer 25

photoreceptors.

Question 26

Auxin:

Answer 26

is transported from developing leaves to differentiated vascular tissue.

Question 27

The root apical meristem is covered by a _____ that protects the meristem as it grows through the soil.

Answer 27

root cap

Question 28

Plants grow toward the light because:

Answer 28

auxin concentration on the shaded side increases.

Question 29

In a study of Arabidopsis thaliana researchers determined that, with respect to the protein product responsible for triggering flowering:

Answer 29

transcription was high and in sync with the light period when day-lengths were long.

Question 30

At the tip of each branch, the _____ surround(s) the shoot apical meristem.

Answer 30

leaf primordia

Question 31

Auxin has no net charge under the _____ conditions _____ a cell.

Answer 31

acidic; outside

Question 32

Which of the following statements does not describe a function of the vascular cambium?

Answer 32

New cells produced by vascular cambia result in an increase in stem length.