Deck 19: Plant Hormones and Growth Responses

Question 1

Plant growth responses are regulated by

A) change in hormone levels.
B) changes in sensitivity of plant tissues to hormones.
C) environmental stimuli.
D) genetic factors.
E) All of the answers are correct.

Answer 1

All of the answers are correct.

Question 2

Auxins, gibberellins, cytokinins, abscisic acid and ethylene are

A) five main groups of plant hormones.
B) five metabolic toxins commonly used in commercial herbicides.
C) toxic compounds produced by plants to deter predators.
D) five lesser plant hormones.
E) compounds used to ripen fruit.

Answer 2

five main groups of plant hormones.

Question 3

Phototropism is a phenomenon whereby

A) a plant's growth is directed by light.
B) a plant's growth is dependent on light.
C) people living close to the poles become listless, depressed and sometimes aggressive due to deprivation of natural light.
D) plant growth is dependent on environmental factors.
E) all the animals in a food web eat plants.

Answer 3

a plant's growth is directed by light.

Question 4

Which of the following affects plant growth and development?

A) Day length
B) Gravity
C) Temperature
D) Soil nutrients
E) All of the answers are correct

Question 5

Which of the following plant hormones are used in tissue culture to promote cell enlargement and division?

A) Abscisic acid and auxin
B) Gibberellins and auxin
C) Cytokinin and ethylene
D) Cytokinin and auxin
E) Auxin and ethylene

Question 6

In the 1920s Friedrich Went, a plant physiologist from the Netherlands, proposed the existence of

A) acetic acid.
B) indole-3-acetic acid.
C) auxin.
D) amyloplasts.
E) cytokinins.

Question 7

Which of the following growth responses is found in plant cells exposed to auxins?

A) Increased respiration rate.
B) Increased ATP-ADP ratio.
C) Decreased membrane potential.
D) Decreased K⁺ uptake.
E) Increased Ca²⁺ uptake.

Question 8

Phototropism in plants is the

A) bending of the coleoptile away from a light source.
B) bending of the coleoptile towards a light source.
C) bending of the rhizoid in the direction of the force of gravity.
D) straight growth of the stem.
E) growth of roots towards a light source.

Question 9

The plant hormone, indole-3-acetic acid (IAA) is synthesised from

A) an amino acid.
B) gibberellin.
C) a polysaccharide.
D) meualonic acid.
E) acetic acid.

Question 10

Amyloplasts contain

A) auxin.
B) plastids.
C) root cap cells.
D) starch granules.
E) gibberellin.

Question 11

The compound known as 2,4-D

A) is a synthetic gibberellin.
B) is a synthetic auxin.
C) promotes roots in tissue culture.
D) is responsible for dwarfism.
E) is an essential plant hormone.

Question 12

In gravitropism, the plant root bends. This bending

A) occurs in the root cap.
B) occurs in the zone of elongation.
C) is mediated by gibberellins.
D) is a response to darkness.
E) involves the uptake of Ca²⁺ from the soil.

Question 13

IAA produces a phototropic response in plants

A) by promoting an increase in the number of cells in a section of stem or coleoptile.
B) only when present in high concentrations in a section of stem or coleoptile.
C) by promoting cell elongation in a section of stem or coleoptile.
D) by promoting an increase in the number of cells and an elongation of the cells of the stem or coleoptile.
E) by increasing cell division in the apical tip.

Question 14

IAA is thought to be involved in apical dominance through

A) promoting the production of a growth-suppression factor.
B) promoting the growth of lateral buds.
C) promoting the growth of the apical bud.
D) diffusing down from the apical bud and inhibiting the growth of lateral buds.
E) All of the answers are correct.

Question 15

The plant hormones known as cytokinins are synthesised in the

A) shoots.
B) stems.
C) coleoptiles.
D) roots.
E) apical buds.

Question 16

Synthetic growth retardants

A) reduce vegetative plant growth.
B) reduce overall plant growth.
C) increase plant growth.
D) reduce bud growth.
E) reduce root growth.

Question 17

In addition to stem elongation, gibberellins are thought to be involved in

A) regulation of axillary bud growth.
B) apical dominance.
C) leaf senescence.
D) breaking seed dormancy and stimulating germination.
E) extensive root growth.

Question 18

In barley, gibberellin is produced in the embryo and

A) directly breaks down endosperm starch into smaller molecules.
B) regulates the production of amylase there.
C) regulates production of abscisic acid in the endosperm.
D) moves to the aleurone layer where it suppresses gene transcription.
E) regulates production of amylase in the endosperm via GAMYB.

Question 19

Cytokinins are plant hormones that are thought to

A) stimulate cell elongation but not cell division.
B) be involved in control of lateral branch growth and leaf senescence.
C) be growth inhibitors.
D) stimulate root growth.
E) only occur in the flowering plants.

Question 20

Which plant hormone is known to be necessary for the development of seed dormancy?

A) Gibberellic acid.
B) Auxin.
C) Ethylene.
D) Abscisic acid.
E) Cytokinin.

Question 21

Which of the following statements about ethylene is true?

A) Its primary role is thought to be influencing plant responses to environmental stress.
B) Plants cannot grow without ethylene.
C) High auxin levels inhibit ethylene production.
D) Ethylene is used to retard ripening of stored fruit.
E) Ethylene production is controlled by cytokinin.

Question 22

Growth inhibitors in plants

A) have a role in mediating the plants' response to stressful environments.
B) cause coleoptiles to bend away from light.
C) include zeatin and alpha amylase.
D) are essential for fruit ripening.
E) mediate positive geotropism.

Question 23

In which one of the following processes in plants is abscisic acid NOT involved?

A) Drought resistance
B) Frost tolerance
C) Fruit ripening
D) Salinity tolerance
E) Closure of stomata

Question 24

Short-day plants flower in response to a

A) shortening of the photoperiod.
B) lengthening of the photoperiod.
C) lengthening of the dark period.
D) shortening of the dark period.
E) lengthening of day light.

Question 25

The critical factor inducing flowering in plants is

A) temperature.
B) time of sowing.
C) length of dark period.
D) length of sunlight.
E) Can be any of the answers.

Question 26

The photoperiod response in plants is detected by

A) the leaves.
B) the stems.
C) the apical buds.
D) chlorophyll molecules.
E) leaf stomata.

Question 27

Vernalisation is

A) the increase in plant growth rate correlating with increased temperature.
B) the metabolic changes for adaptation to low temperature.
C) the induction of flowering by low temperature.
D) the production of leaf pigments to enable them to detect changes in light.
E) the bending of plant stems in response to light.

Question 28

During the vegetative phase of 'short day' plants, the interruption of the dark period with a ten-minute period of light will

A) promote flowering.
B) have no effect.
C) cause etiolation of the stems.
D) inhibit growth at the apical bud.
E) negate the effect of the dark period.

Question 29

Which of the following processes in plants is influenced by a phytochrome reaction?

A) Seed germination
B) Internode elongation
C) Initiation of flowering
D) Chlorophyll synthesis
E) All of the answers are correct

Question 30

The plant hormone auxin has many effects on plant growth EXCEPT

A) it increases the respiration rate of the plant.
B) it increases the uptake of K+ ions by cells.
C) it increases the membrane potential of the cell.
D) it causes the uptake of hydrogen ions from the cell.
E) it stimulates the expression of new genes.

Question 31

Ethylene affects plant growth by reacting with a receptor which is located in the

A) nucleus, where it directly activates transcription factors.
B) plasma membrane where dimerisation causes autophosphorylation to initiate a signal transduction pathway.
C) intracellular as the ethylene may diffuse through the plasma membrane.
D) fruit, where it initiates ripening.
E) cytosol where it causes increased respiration.

Question 32

Stratification is

A) the prevention of seed germination after only light rain in some plants.
B) germination of seeds after exposure to red light.
C) genes switched on in response to environmental stress.
D) the period of cold which breaks dormancy and causes seed germination.
E) dehydration of the seed after development of the embryo.

Question 33

Brassinosteroids are

A) hormones involved in the differentiation of xylem.
B) plant steroid hormones that promote cell elongation.
C) control cell growth through a signal transduction pathway and protein phosphorylation.
D) active transcription factors which induce mRNA synthesis.
E) All of the answers are correct.

Question 34

The ability of plants to produce flowers seasonally is due to the phenomenon known as

A) signal transduction.
B) photoperiodism.
C) florigen.
D) vernalisation.
E) hormonal response.

Question 35

In germinating cereal seeds, the gibberellan GA₁ activates genes that

A) induce stem elongation.
B) control the synthesis of enzymes that convert sucrose to starch.
C) control the synthesis of enzymes that convert starch to sugar.
D) repress the stem development of the embryo.
E) induce root development.

Question 36

The most important activity of abscisic acid is

A) to enable plants to adapt to drought.
B) to activate a transcription factor by autophosphorylation.
C) to stimulate cell division in tissue culture.
D) to promote the growth of lateral buds into branches.
E) to enable plants to survive growth in swamp-like conditions.

Question 37

A florist comes to you asking for advice on how he might be able to extend the shelf life of his stock. Using your knowledge of plant hormones, what would you suggest as a potential treatment?

A) Spraying them with cytokinin
B) Spraying them with auxin
C) Spraying them with gibberellic acid
D) Spraying them with abscisic acid
E) Spraying them with ethylene

Question 38

You have a bowl full of slightly under-ripe bananas that you decide to leave for a few days until they are ready to eat. After returning a few days later to eat a banana, you discover they are now black and over-ripe. Upon further investigation you also discover a very over-ripe banana at the bottom of the bowl that you had not previously noticed. How would you explain this observation?

A) The over-ripe banana released methylene which triggered rapid ripening in the other bananas.
B) The over-ripe banana released ethanol which triggered rapid ripening in the other bananas.
C) The over-ripe banana released cytokinins which triggered rapid ripening in the other bananas.
D) The over-ripe banana released auxins which triggered rapid ripening in the other bananas.
E) The over-ripe banana released ethylene which triggered rapid ripening in the other bananas.

Question 39

What phenotype is associated with PIN1 mutants?

A) Curled, needle-like leaves
B) Thin, elongated petioles
C) Naked, needle-like inflorescence stems
D) Thin, pointy roots devoid of lateral roots
E) Sepals and petals that are reduced in width such that they look thin and pointy

Question 40

It is hypothesised that auxin stimulates cell elongation, and therefore plant growth, by triggering the release of H⁺ inside cells and therefore acidifying the intracellular environment. What protein would need to be activated to achieve this, and where would it be located?

A) ATPase proton pump in the tonoplast
B) ATPase proton pump in the plasma membrane
C) Antiport transport protein in the nuclear membrane
D) Ion channel in the cell wall
E) Auxin binding protein in the plasma membrane

Question 41

In young seedlings, the development of which organs is affected when expression of the auxin binding protein (ABP) is inhibited?

A) Roots
B) Shoots
C) Cotyledons
D) Radicule
E) Both roots and shoots

Question 42

In a frost resistant plant, it was found that when exposed to cold, abscisic acid (ABA) levels were elevated. For this to occur, what must be the state of the phosphatase involved in ABA regulation?

A) Free (unbound)
B) Bound to the SnRK2 protein kinase
C) Bound to the ABA receptor
D) Activating (phosphorylating) downstream proteins in the ABA signalling pathway
E) Bound directly to gene sequences regulated by ABA

Question 43

You have been asked to assist in trying to regenerate a recently logged area of forest. One of the tasks in this role is to try to encourage the germination of native seeds already present in the soil seedbank that typically only sprout after a fire. How might you produce the desired result, without further damaging or disturbing the area of forest in question?

A) Set fire to the remaining plant material left behind after the logging
B) Dig up all the soil and manually retrieve seeds present before exposing them to wood smoke and replanting and germinating seeds
C) Apply kinophosphatidin to bind to butenolide recepetors
D) Use karrikin to induce seed germination
E) Spray the area with a mix of hormones including cytokinins, ABA and auxin

Question 44

At the end of a long day what is the relative level of CO and how does this in turn affect the expression of the FT gene and thus flowering?

A) CO levels are high. CO binds to the FT promoter, initiating transcription and thus inhibiting flowering.
B) CO levels are high. CO binds to and inhibits FT expression, resulting in the inhibition of flowering.
C) CO levels are high. CO binds to and inhibits FT expression, resulting in the promotion of flowering.
D) CO levels are high. CO binds to the FT promoter, initiating transcription and thus promoting flowering.
E) CO levels are low. CO is displaced from its inhibiting position on the FT promoter, resulting in the promotion of flowering.

Question 45

What is the effective temperature range for plant to respond to vernalisation, and for how long will a plant typically need to be exposed to this temperature range?

A) -1 $\degree$ C to 4 $\degree$ C for at least 4 weeks
B) 1 $\degree$ C to 9 $\degree$ C for at least 3 weeks
C) -1 $\degree$ C to 9 $\degree$ C for at least 4 weeks
D) 1 $\degree$ C to 9 $\degree$ C for at least 2 weeks
E) -1 $\degree$ C to 9 $\degree$ C for at least 6 weeks