Plant Growth and Development Test

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Plant Growth and Development Test - 83

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Question 1

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Directions For Questions

A series of experiments were performed by Charles Darwin and his son Francis on phototropism (growth toward light) of the coleoptile (the cap that covers the first leaves of new seedlings of grass). The treatments they used are described.

Treatment	Growth Toward Light
I. Coleoptile.	Allowed
II. Tip of coleoptile cut off.	Prevented
III. Opaque cap placed over coleoptile tip.	Prevented
IV. Coleoptile cut halfway through.	Allowed
V. Transparent cap placed over coleoptile tip.	Allowed
VI. Opaque sleeve placed over base of coleoptile	Allowed

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What conclusion can be drawn from the comparison of treatments I and II?

Growth is promoted by cutting off the tip

The tip is the site of sensing light

The tip is the site of auxin synthesis

The tip is necessary for the response to light

There is a range of response to a single treatment

Solution

As can be seen from the experiments, when the tip of the coleoptile is cut off, the growth towards the light is prevented while the intact coleoptile responds to the light. This shows that the tip is necessary for the response to light.

Question 2
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Ethylene gas is a plant hormone that regulates plant growth, development and response to environmental stress. It is produced from leaves, roots, stems, flowers, and fruits, and it plays a major role in fruit ripening, flowering, and abscission (the natural shedding of leaves, flowers, and fruits). Like many hormones, ethylene functions via an intracellular signal transduction pathway illustrated in Figure 1 above:

Figure 1. Signal transduction pathway of ethylene in plant cells. Key: 1. Ethylene Gas 2. Plasma Membrane 3. Receptor Protein 4. Endoplasmic Reticulum 5. Constitutive Triple Response Protein Kinase 1 (CTR1) 6. Ethylene Insensitive 2 protein (EIN2) 7. Ethylene Insensitive 3 protein (EIN3) 8. DNA 9. mRNA 10. Enzyme production.

In the absence of ethylene gas, a receptor protein activates the CTR1 protein kinase, which represses EIN2 function. Recent studies with plants genetically engineered to have reduced gene expression of an ethylene receptor (Tieman, et al. 1999) showed an increase in ethylene sensitivity, including accelerated fruit ripening and flower aging.

Which statement best explains how the ethylene response is regulated in plants?

A
In the presence of ethylene gas (1), the ethylene receptors (3) activate CTR1 (5), resulting in the release of the EIN2 (6). EIN3 (7) can then continue the transduction pathway by acting as a transcription factor to mediate the expression of the particular genes involved.

B
This pathway involves negative regulation by ethylene receptor proteins (3) because CTR1 (5) actively represses the release of EIN2 (6) in the absence of ethylene (1) but the response is activated when ethylene (1) is present or when the number of ethylene receptors (3) is reduced.

C
In the absence of the hormone, ethylene receptors (3) activate CTR1 (5), resulting in the release of the EIN2 (6). EIN3 (7) can then continue the transduction pathway by acting as a transcription factor to mediate the expression of the particular genes involved.

D
When ethylene (1) binds to its receptors (3) the EIN2 (6) is activated, which represses CTR1 (5) and allows for the transcriptional response to ethylene (1). It the absence of ethylene (1), EIN2 (6) is repressed and this causes CTR1 (5) to be activated, shutting down the transcriptional response to ethylene (1).

Solution

Ethylene response is a negative regulation by ethylene receptor proteins because, In the absence of ethylene gas, a receptor protein activates the CTR1 protein kinase, which represses EIN2 function. Recent studies with plants genetically engineered to have reduced gene expression of an ethylene receptor (Tieman, et al. 1999) showed an increase in ethylene sensitivity, including accelerated fruit ripening and flower aging.

So the correct option is 'This pathway involves negative regulation by ethylene receptor proteins (3) because CTR1 (5) actively represses the release of EIN2 (6) in the absence of ethylene (1) but the response is activated when ethylene (1) is present or when the number of ethylene receptors (3) is reduced.'
Question 3
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Ethylene gas is a plant hormone that regulates plant growth, development and response to environmental stress. It is produced from leaves, roots, stems, flowers and fruits, and it plays a major role in fruit ripening, flowering and abscission (the natural shedding of leaves, flowers and fruits). Like all hormones, ethylene functions via an intracellular signal transduction pathway, which is illustrated in Figure 1 above.
Figure 1. Signal transduction pathway of ethylene in plant cells. Key: 1. Ethylene Gas 2. Plasma Membrane 3. Receptor Protein 4. Endoplasmic Reticulum 5. Constitutive Triple Response Protein Kinase 1 (CTR1) 6. Ethylene Insensitive 2 protein (EIN2) 7. Ethylene Insensitive 3 protein (EIN3) 8. DNA 9. mRNA 10. Enzyme production
What is the MOST direct evidence that the ethylene gas signaling mechanism functions to mediate gene expression?

A
The reception of ethylene gas (1) occurs on the endoplasmic reticulum (4), resulting in the release of EIN2 (6) by CTR1 (5). Binding of EIN2 on the nuclear membrane allows EIN3 (7) to bind to a regulatory gene resulting in the transcription and translation of enzymes involved in plant cell growth and regulation.

B
The reception of ethylene gas (1) occurs on the plasma membrane (2), which triggers the release of EIN2 (6) by CTR1 (5). EIN2 binds to the nuclear membrane which activates EIN3 (7) to function as a transcription factor in the transcription and translation of enzymes involved in plant growth and regulation.

C
Ethylene (1) binds to a receptor on the endoplasmic reticulum (4), resulting in the release of EIN2 (6) by CTR1 (5). EIN 2 binds to the nuclear membrane which triggers the transcription and translation plant proteins necessary for plant growth and regulation.

D
Ethylene (1) binds to a receptor on the endoplasmic reticulum (4), resulting in the release of EIN3 (7), which functions as a transcription factor in the expression of enzymes involved in plant growth and regulation.

Solution

The reception of ethylene gas occurs on the endoplasmic reticulum which triggers Constitutive Triple Response Protein Kinase 1 (CTR1) to release EIN2 and EIN2 binds on the nuclear membrane allows EIN3, EIN3 will initiate to transcription and translation of enzymes involved in plant growth and regulation.
So the correct option is 'The reception of ethylene gas (1) occurs on the endoplasmic reticulum (4), resulting in the release of EIN2 (6) by CTR1 (5). Binding of EIN2 on the nuclear membrane allows EIN3 (7) to bind to a regulatory gene resulting in the transcription and translation of enzymes involved in plant cell growth and regulation.'
Question 4
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To test the effect of an auxin on plant growth, the auxin was dissolved in a gelatin block. Several plant seedlings were prepared and growth was measured every five days.
Plant
Growth after 5 days
Growth after 10 days
1
15 mm
29 mm
2
4 mm
9 mm
3
5 mm
10 mm
4
14 mm
31 mm
5
8 mm
20 mm

Based on the results of the experiment, one can conclude that the tip of the plant contains

A
Gelatin

B
Water

C
Auxin

D
Paste

E
Nothing significant

Solution

Growth rate in intact plant 1 is 3 mm per day which is reduced in plant 2 upon removal of tip to 1 mm per day. The growth rate is resumed to 3 mm per day upon application of auxin as in plant 4. This means plant tip contain auxin and removal of tip resulted in truncated growth.
Therefore, the correct answer is option C.
Question 5
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Two different plants associated with the discovery of two different phytohormones having common biosynthetic precursor exhibit one of the following character each.
I- Versatile anthers
II- Compound spadix
III- Pentalocular ovary
IV- Trifoliate compound leaves
The correct answer is:

A
II and III

B
I and III

C
II and IV

D
I and IV

Solution

Auxin was discovered from the grass Phalaris belonging to family-Poaceae. It is characterized by versatile anthers. Abscisic acid was discovered from cotton (Malvaceae). Cotton contains trifoliate compound leaves. The mevalonic acid in involved is the synthesis of both.
Thus, the correct answer is the option (D).
Question 6
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To test the effect of an auxin on plant growth, the auxin was dissolved in a gelatin block. Several plant seedlings were prepared and growth was measured every five days.
Plant
Growth after 5 days
Growth after 10 days
1
15 mm
29 mm
2
4 mm
9 mm
3
5 mm
10 mm
4
14 mm
31 mm
5
8 mm
20 mm
Which of the following plants in the experiment acted as a control?

A
Plant 1

B
Plants 2 and 3

C
Plant 5

D
Plant 1, 2 and 3

E
Plant 4 and 5

Solution

Plant 1 is intact plant and no external material is applied on it. It is serving as control. Plant 2 has only tip removed but nothing is applied. The experiment is about effect of auxin on growth of plant. Plant 2 will serve as control for the experimental plant on which auxin is applied on cut edge. Plant 3, 4 5 exhibit some exogenous application of auxin/gelatin or both. However, plant 3 will serve as control to show if the effect is due to auxin only or auxin + gelatin. Therefore, the correct answer is option D.
Question 7
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To test the effect of an auxin on plant growth, the auxin was dissolved in a gelatin block. Several plant seedlings were prepared and growth was measured every five days.
Plant
Growth after 5 days
Growth after 10 days
1
15 mm
29 mm
2
4 mm
9 mm
3
5 mm
10 mm
4
14 mm
31 mm
5
8 mm
20 mm
What proves that auxin is necessary for plant growth?

A
Plant 1 grew faster than Plants 2 or 3.

B
Plant 4 grew faster than Plants 2 or 3.

C
Plant 5 grew faster than Plant 1.

D
Plant 3 grew faster than Plant 2.

E
Plant 5 grew faster than Plant 4.

Solution

Growth rate in intact plant 1 is 3 mm per day which is reduced in plant 2 upon removal of tip to 1 mm per day. The growth rate is resumed to 3 mm per day upon application of auxin as in plant 4. This means plant tip contain auxin and removal of tip resulted in truncated growth. Also, comparing the growth rates, plant 4 exhibit 3.1 mm growth rate after auxin application while plants 2 and 3 (plants with removed tip) showed only 0.9 mm and 1 mm growth rate per day. This proves that auxin is necessary for plant growth.
Therefore, the correct answer is option B.
Question 8
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Ethylene gas is a plant hormone that regulates plant growth, development and response to environmental stress. It is produced from leaves, roots, stems, flowers and fruits, and it plays a major role in fruit ripening, flowering and abscission (the natural shedding of leaves, flowers and fruits). The biosynthesis of ethylene in plant cells occurs in a two-step biochemical pathway illustrated in figure below:
Figure : Ethylene biosynthesis starts when S-adenosyl-L-methionine (SAM) is converted to 1-aminocyclopropane-1-carboxylic acid (ACC) by the enzyme ACC synthase (ACS). ACC is then converted to ethylene by the enzyme ACC oxidase (ACO). The ACS and ACO genes are expressed in response to internal developmental cues and environmental stresses, such as wounding, flooding, drought, and pathogen attack.
Atta-Aly, Brecht and Huber (2000) researched ethylene feedback mechanisms in tomato and strawberry fruit tissues. Their studies revealed that immature fruit had a reduced concentration of ACC when exposed to ethylene gas, but ethylene application on mature fruit increased ACC oxidase (ACO) activity.
Which statement best explains how different plant tissues respond to ethylene gas?

A
Ethylene gas serves as a positive feedback signal in immature fruit and a negative feedback signal in mature fruit.

B
Exposure to ethylene gas results in a negative feedback loop in both immature and mature fruit.

C
Ethylene gas serves as a negative feedback signal in immature fruit and a positive feedback signal in mature fruit.

D
Exposure to ethylene gas results in a positive feedback loop in both immature and mature fruit.

Solution

Atta-Aly, Brecht and Huber (2000) researched revealed that immature fruit had a reduced concentration of ACC when exposed to ethylene gas, but ethylene application on mature fruit increased ACC oxidase (ACO) activity.
So the correct option is 'Ethylene gas serves as a positive feedback signal in immature fruit and a negative feedback signal in mature fruit.'
Question 9
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Ethylene is related with

A
Aerobic respiration

B
Climacteric phenomenon

C
Anaerobic respiration

D
Fermentation
Solution
- The climacteric is a stage of fruit ripening associated with increased ethylene production and a rise in cellular respiration.
- Apples, bananas, melons, apricots, tomatoes are climacteric fruits. In most of the plants, there is a sharp rise in the respiration rate near the end of the development of fruit, which sets in progress those changes which are involved in the ripening of fruit.
- This sharp rise in respiration is called as a climacteric rise or climacteric.
Thus, the correct answer is option B.
Question 10
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Cell division is initiated by

A
Cytokinin

B
Auxin

C
Gibberellin

D
ABA

Solution

The cytokinin hormones promote cell division and tissue growth, and depend upon the presence of auxins to determine the extent of their activity. When the ratio of cytokinins to auxins is relatively high, stem and leaf growth is stimulated.
So the correct option is 'Cytokinin'.