Plant hormones

Học bằng cách chơi

Trả lời những câu hỏi này để kiếm năng lượng, rồi câu cá và khám phá. Không cần tài khoản.

Dành cho nhà giáo dục: slide bài học, ghi chú ôn tập sẵn dùng cho Plant hormones (Science, Biology) — dùng trong bài giảng của bạn, hoặc chạy chủ đề như một hoạt động lớp học tương tác để người học chơi như một trò chơi trực tiếp.

Ghi chú bài học

Tropisms: Growth Responses in Plants

Plants need to grow in response to light so leaves can absorb light for photosynthesis.
Plants need to grow in response to gravity so shoots grow upwards and roots grow downwards.
A directional growth response to light is called phototropism.
A directional growth response to gravity is called gravitropism or geotropism.
Growth towards a stimulus is a positive tropism; growth away from a stimulus is a negative tropism.
Shoots show positive phototropism (grow towards light) and negative gravitropism (grow away from gravity).
Roots show negative phototropism (grow away from light) and positive gravitropism (grow towards gravity).

Auxins: The Growth Hormone

Auxins are plant hormones that coordinate and control growth responses such as phototropism and gravitropism.
Auxins are produced in the tips of shoots and roots and diffuse to cells behind the tips.
In shoots, auxin promotes cell elongation; more auxin means more elongation and more growth.
In roots, auxin inhibits cell elongation; more auxin means less elongation and less growth.
Unequal distributions of auxin cause unequal growth rates in roots and shoots.
Auxin distribution in shoots is affected by both light and gravity; in roots it is mainly affected by gravity.

Phototropism: How Shoots Bend Towards Light

When light comes from all directions, auxin is distributed evenly and cells grow at the same rate.
When light comes mainly from one side, auxin concentrates on the shaded side of the shoot.
Auxin on the shaded side makes cells elongate faster than cells on the lit side.
This unequal growth causes the shoot to bend and grow towards the light.
Positive phototropism in shoots is the result of auxin accumulating on the shaded side.

Gravitropism: How Shoots and Roots Respond to Gravity

If a shoot or root is placed on its side, auxin accumulates on the lower side due to gravity.
In shoots, the lower side grows faster than the upper side, so the shoot grows upwards.
In roots, the lower side grows slower than the upper side, so the root grows downwards.
This shows that the same hormone can have opposite effects in shoots and roots.

Other Plant Hormones (Higher Tier)

Gibberellins are important in initiating seed germination.
Gibberellins also have a role in inducing flowering and the growth of fruit.
Ethene is a gas released by plants that controls cell division and ripening of fruits.
The mechanisms of how gibberellins and ethene work are not required.

Required Practical: Investigating Light or Gravity

Aim: to investigate the effect of light or gravity on the growth of newly germinated seedlings.
Set up two petri dishes with damp cotton wool and seedlings; place one on a clinostat and the other on its side.
A clinostat rotates slowly and cancels out the effect of gravity.
Place both dishes in a light-proof box so seedlings are in complete darkness; this controls the effect of light.
Record the direction of growth of shoots and roots, and measure length as well as making labelled drawings.
Expected results: on the support, roots grow downwards and shoots grow upwards; on the clinostat, roots and shoots grow straight outwards with no gravitropic response.

Commercial Uses of Auxins

Auxins can be used as selective weed killers that affect broad-leaved weeds but not narrow-leaved grasses and cereals.
Selective weedkillers disrupt the growth of weeds, causing them to die, reducing competition for space and nutrients.
However, once applied, their spread cannot be controlled and they could affect other plant species negatively.
Auxins are sold as rooting powders; dipping cuttings in them encourages rapid root development.
Auxins are also used in tissue culture to promote growth and produce clones of desirable plants.

Commercial Uses of Ethene and Gibberellins

Ethene is used in the food industry to control ripening of fruit during storage and transport.
Transporting unripe fruit is better because ripe fruit is softer and more easily damaged.
Ethene production can be inhibited to delay ripening, or ethene gas can be released to speed up ripening.
Gibberellins can be used to end seed dormancy and promote seed germination.
Gibberellins can promote flowering regardless of weather conditions.
Gibberellins can increase fruit size and produce seedless fruit when applied to unpollinated flowers.

Environmental Impact of Plant Hormone Use

Using hormones as weed killers can have a negative effect on biodiversity.
Many plants classed as weeds are a food source and habitat for other organisms.
Destroying weeds can therefore have negative effects on other organisms in the ecosystem.

Slide

Step through every slide for this topic — plus flashcards and revision notes — with a free account.

ĐĂNG KÝ — MIỄN PHÍ ĐĂNG NHẬP

Câu hỏi luyện tập

Xem trước miễn phí — 8 trên 56 câu hỏi. Đăng ký để xem tất cả.

1.Which plant hormone is responsible for controlling phototropism and gravitropism?
Easy
- AAuxin
- BGibberellin
- CEthene
- DOestrogen
2.What is phototropism in plants?
Easy
- AGrowth stimulated by light
- BGrowth due to photosynthesis
- CGrowth inhibited by light
- DGrowth stimulated by temperature
3.Plant roots respond to gravity by growing downwards. What is this response called?
Easy
- APositive gravitropism
- BNegative geotropism
- CPositive phototropism
- DNegative gravitropism
4.What effect would positive gravitropism have on a plant?
Easy
- ARoots would grow towards gravity
- BRoots would grow away from gravity
- CShoots would grow away from gravity
- DShoots would grow sideways
5.What happens to the cells in plant shoots in response to auxins?
Easy
- AElongate
- BThe cell cycle is stopped
- CMitosis is increased
- DShorten
6.Which gas acts as a plant hormone?
Easy
- AEthene
- BEthane
- CMethane
- DCarbon dioxide
7.A gardener wishes to remove all the dandelions (a type of weed) from their lawn without damaging the grass. They purchased a selective weedkiller which contained a synthetic plant hormone. Which hormone would most likely be in the weedkiller?
Medium
- AAuxin
- BOestrogen
- CGibberellin
- DEthene
8.A plant is grown near a fixed light source. The plant is then rotated by 180°. Predict the direction of growth of the plant shoots over the next 48 hours.
Medium
- AThe shoots will bend towards the new light direction
- BThe shoots will continue growing in the original direction
- CThe shoots will grow straight upwards
- DThe shoots will grow away from the light

Thêm câu hỏi

9.In an experiment, a plant pot is attached to a clinostat and rotated slowly on its side in a darkened room. What is the expected result after two days?
Medium
- AThe shoot grows straight outwards in the direction it was placed
- BThe shoot grows upwards
- CThe shoot grows downwards
- DThe shoot bends towards the centre of the clinostat
10.A plant shoot is illuminated from one side. Which image best represents how auxins will start to accumulate in the shoot tip in response to light?
Medium
- AAuxin accumulates on the shaded side
- BAuxin accumulates on the illuminated side
- CAuxin is evenly distributed throughout
- DAuxin accumulates at the very tip only
11.A scientist investigated the effects of gibberellins on flowering in plants. The plants were grown in identical environmental conditions but half were treated with gibberellins. The results showed that treated plants flowered earlier. What conclusion can the scientist make about gibberellins?
Medium
- AGibberellins promote flowering
- BGibberellins inhibit flowering
- CGibberellins have no effect on flowering
- DGibberellins only affect seed germination
12.Which of the following is a commercial use of gibberellins?
Medium
- AEnd seed dormancy
- BDelay fruit ripening
- CAct as a selective weedkiller
- DPromote root growth in cuttings
13.A student investigated the effect of light direction on cress seedling growth. Group A (light from left) bent towards the light; Group B (light from above) grew straight upwards; Group C (no light) grew straight upwards but yellow. The student concluded 'Light always makes seedlings grow towards it.' Evaluate this conclusion.
Hard
- AThe conclusion is not fully supported because Group C grew straight upwards without light
- BThe conclusion is fully supported by all groups
- CThe conclusion is wrong because seedlings never grow towards light
- DThe conclusion is supported because Group C grew towards the light
14.Which of the following statements about auxins are correct? (select all that apply)
Medium
- AAuxins are produced in the tips of shoots and roots
- BAuxins promote cell elongation in shoots
- CAuxins inhibit cell elongation in roots
- DAuxins are gases that control fruit ripening
- EAuxins cause cells to divide rather than elongate
15.Which of the following are commercial uses of plant hormones? (select all that apply)
Medium
- ASelective weedkillers containing auxins
- BRooting powders containing auxins
- CEthene to control fruit ripening
- DGibberellins to end seed dormancy
- EAuxins to inhibit root growth in cuttings
16.Phototropism is a plant's growth response to gravity.
Easy
True or false?
17.Auxins are produced in the tips of shoots and roots.
Easy
True or false?
18.In roots, a higher concentration of auxin leads to more cell elongation and faster growth.
Easy
True or false?
19.Ethene is a gas that controls cell division and the ripening of fruits.
Easy
True or false?
20.Gibberellins are important in initiating seed germination.
Medium
True or false?
21.Shoots show a positive gravitropic response and a negative phototropic response.
Medium
True or false?
22.Match each plant response to the correct part of the plant.
Medium
- Phototropism
- Gravitropism
- Geotropism
- Response to light
- Response to gravity
- Another name for response to gravity
23.Match each plant hormone to its function.
Medium
- Auxin
- Gibberellin
- Ethene
- Controls phototropism and gravitropism
- Initiates seed germination
- Controls fruit ripening
24.Place the steps in the correct order to describe how auxin causes a shoot to bend towards light.
Medium
- Auxin is produced in the shoot tip
- Auxin diffuses to the shaded side of the shoot
- Cells on the shaded side elongate more
- The shoot bends towards the light
25.Order the steps to describe how a root responds to gravity when placed on its side.
Medium
- Auxin accumulates on the lower side of the root
- Auxin inhibits cell elongation on the lower side
- The upper side grows faster than the lower side
- The root bends and grows downwards
26.Which of the following statements about the distribution of auxin in shoots and roots are correct? (select all that apply)
Medium
- AAuxin is produced in the tips of shoots and roots.
- BAuxin diffuses to the cells behind the tip.
- CIn shoots, a higher auxin concentration causes less cell elongation.
- DIn roots, a higher auxin concentration causes less cell elongation.
- EAuxin distribution in roots is primarily affected by light.
27.Which of the following are effects of gibberellins? (select all that apply)
Hard
- AEnd seed dormancy
- BPromote flowering
- CInhibit fruit growth
- DIncrease fruit size
- EControl fruit ripening
28.Match each plant hormone with its commercial use.
Medium
- Auxin
- Ethene
- Gibberellin
- Rooting powder
- Control fruit ripening
- End seed dormancy
29.Match each plant response with the correct description.
Medium
- Phototropism
- Gravitropism
- Positive tropism
- Growth in response to light
- Growth in response to gravity
- Growth towards the stimulus
30.Place the steps in the correct order to describe how auxin causes a shoot to bend away from gravity when placed on its side.
Medium
- Auxin accumulates on the lower side of the shoot due to gravity.
- Cells on the lower side elongate more than cells on the upper side.
- The shoot bends and grows upwards.
31.A plant shoot is placed on its side in the dark. Which side of the shoot will have the higher concentration of auxin?
Medium
- AThe upper side
- BThe lower side
- CThe shaded side
- DThe side facing the light
32.Which of the following best explains why a shoot bends towards light?
Medium
- AAuxin accumulates on the shaded side, causing cells there to elongate more.
- BAuxin accumulates on the lit side, causing cells there to elongate more.
- CAuxin is evenly distributed, causing cells to grow at the same rate.
- DAuxin inhibits cell elongation on the shaded side.
33.A shoot tip is removed from a young plant and the cut tip is placed on a block of agar. The agar block is then placed on one side of the cut shoot, which is kept in the dark. What is the expected result after several days?
Medium
- AThe shoot grows straight upwards because light is absent
- BThe shoot bends towards the side with the agar block
- CThe shoot bends away from the side with the agar block
- DThe shoot stops growing because the tip has been removed
34.A student places a germinated bean seedling horizontally in a dark box. After 3 days, the root has grown downwards and the shoot has grown upwards. Which statement best explains the root's response?
Medium
- AAuxin accumulates on the lower side and stimulates cell elongation in root cells
- BAuxin accumulates on the lower side and inhibits cell elongation in root cells
- CAuxin accumulates on the upper side and stimulates cell elongation in root cells
- DAuxin is evenly distributed and root cells elongate at the same rate
35.A clinostat is used in plant growth experiments to cancel out the effect of gravity.
Easy
True or false?
36.A farmer wants to transport unripe bananas to a supermarket and then ripen them quickly on arrival. Which of the following methods would be appropriate? (select all that apply)
Medium
- ATreat the fruit with ethene gas during transport to speed up ripening
- BAdd chemicals that prevent ethene production during transport to delay ripening
- CReact ethene in the air around the fruit with substances that remove it during transport
- DRelease artificially produced ethene gas when the fruit reaches the supermarket
- EApply gibberellins to the fruit to delay ripening during transport
37.A student sets up an experiment with two groups of bean seedlings. Group A is grown in normal light from above. Group B is grown with a light source from the right side only. After 5 days, the mean shoot length in Group A is 45 mm and in Group B is 42 mm. Which conclusion is best supported by these results?
Hard
- ALight from one side reduces the overall growth of shoots
- BLight from one side causes shoots to bend towards the light but does not stop growth
- CLight from one side causes shoots to bend away from the light
- DLight from one side has no effect on shoot growth or direction
38.A gardener takes cuttings from a rare plant and wants to produce many identical plants quickly. They dip the cut ends into a powder before planting. Which hormone does the powder contain and why?
Medium
- AGibberellin, to promote flowering in the cuttings
- BAuxin, to encourage rapid root development
- CEthene, to stimulate cell division in the stem
- DAuxin, to inhibit root growth and prevent rotting
39.Place the steps in the correct order to describe how auxin causes a shoot to bend towards unilateral light.
Medium
- Light is detected by the shoot tip
- Auxin is produced in the shoot tip
- Auxin diffuses to the shaded side of the shoot
- Cells on the shaded side elongate more than cells on the lit side
- The shoot bends towards the light
40.A student investigates the effect of gravity on seedling growth. They place one petri dish on a support on its side and another on a clinostat, both in a lightproof box. After two days, what is the expected result for the seedlings on the clinostat?
Medium
- ARoots grow downwards and shoots grow upwards
- BRoots and shoots both grow straight outwards in the direction they were placed
- CRoots grow upwards and shoots grow downwards
- DRoots and shoots do not grow at all
41.A plant shoot grows 42 mm in 7 days. Calculate the mean growth per day in mm.
Medium
42.In an experiment, the mean length of shoots in Group A was 42 mm and in Group B was 38 mm. Calculate the difference in mean length in mm.
Medium
43.Complete the sentence using the correct term.
Easy
The plant hormone responsible for phototropism and gravitropism is called ____.
44.Complete the sentence using the correct terms.
Medium
In shoots, auxin ____ cell elongation, while in roots, auxin ____ cell elongation.
45.Name the plant hormone responsible for controlling phototropism.
Easy
46.Name the plant hormone responsible for both phototropism and gravitropism.
Medium
47.In an experiment, a shoot grows 72 mm in 6 days. Calculate the mean growth per day in mm.
Medium
48.Complete the sentence about the effect of auxin on shoot cells.
Medium
In shoots, auxin promotes cell ____.
49.Describe the biological mechanism that results in a shoot bending towards the light.
Hard
50.Explain the role of auxins in coordinating the response of a seedling when it is placed on its side in the dark.
Hard
51.A student investigated gravitropism using bean seedlings. Explain why it is important to place the seedlings in a dark room.
Hard
52.Describe how a suitable control could be set up for an investigation into gravitropism using bean seedlings.
Medium
53.Explain why a root and a shoot respond differently when placed on their sides in the dark. Include reference to auxin distribution and cell elongation in your answer.
Hard
54.A plant shoot grows 42 mm in 7 days. Calculate the mean growth per day in mm.
Medium
- A6 mm/day
- B5 mm/day
- C8 mm/day
- D7 mm/day
55.In an experiment, the mean length of shoots in Group A was 42 mm and in Group B was 38 mm. Calculate the difference in mean length in mm.
Medium
- A5 mm
- B4 mm
- C6 mm
- D3 mm
56.In an experiment, a shoot grows 72 mm in 6 days. Calculate the mean growth per day in mm.
Medium
- A13 mm
- B12 mm
- C11 mm
- D14 mm

Thẻ ghi nhớ

What is a tropism?

A directional growth response made by a plant in response to a stimulus such as light or gravity.

What is phototropism?

A plant's growth response to light. Growth towards light is positive phototropism; growth away from light is negative phototropism.

What is gravitropism (or geotropism)?

A plant's growth response to gravity. Growth towards gravity is positive gravitropism; growth away from gravity is negative gravitropism.

How do shoots respond to light and gravity?

Shoots show positive phototropism (grow towards light) and negative gravitropism (grow away from gravity, upwards).

How do roots respond to light and gravity?

Roots show negative phototropism (grow away from light) and positive gravitropism (grow towards gravity, downwards).

Where are auxins produced in a plant?

Auxins are produced in the tips of the shoots and the roots.

What effect do auxins have on cells in shoots?

Auxins promote cell elongation in shoots: more auxin causes more elongation and therefore more growth.

What effect do auxins have on cells in roots?

Auxins inhibit cell elongation in roots: more auxin causes less elongation and therefore less growth.

How does auxin cause a shoot to bend towards light?

Auxin concentrates on the shaded side of the shoot, causing cells there to elongate more. This unequal growth makes the shoot bend towards the light.

Why does a shoot placed on its side grow upwards?

Gravity makes auxin accumulate on the lower side. In shoots, more auxin means more cell elongation, so the lower side grows faster and the shoot bends upwards.

Why does a root placed on its side grow downwards?

Gravity makes auxin accumulate on the lower side. In roots, auxin inhibits cell elongation, so the lower side grows slower and the root bends downwards.

What is the role of gibberellins in seed germination?

Gibberellins initiate seed germination. A high concentration of gibberellin promotes germination, ending seed dormancy.

What is ethene and what does it control?

Ethene is a gas released by plants. It controls cell division and the ripening of fruits.

How are auxins used as selective weedkillers?

Auxins disrupt the growth of broad-leaved weeds while leaving narrow-leaved grasses and cereals (crops) unaffected.

What are rooting powders and how do they work?

Rooting powders contain auxins. Dipping plant cuttings in them encourages rapid root development, helping to produce clones cheaply.

How is ethene used in the food industry?

Ethene is used to control fruit ripening during storage and transport. Inhibiting ethene delays ripening; adding ethene speeds it up.

Give three commercial uses of gibberellins.

Gibberellins can be used to end seed dormancy, promote flowering regardless of weather, increase fruit size, and produce seedless fruit.

What is a clinostat and why is it used in plant growth experiments?

A clinostat is a machine that slowly rotates a plant on its side. It cancels out the effect of gravity so that gravitropism can be investigated.

Why must seedlings be placed in a light-proof box when investigating gravitropism?

To control the effect of light, so that any growth response observed is due to gravity alone.

In the required practical, what happens to roots and shoots when seedlings are placed on their side in the dark?

Roots (radicles) grow downwards (positive gravitropism) and shoots (plumules) grow upwards (negative gravitropism), regardless of their initial orientation.

What is the expected result for seedlings on a clinostat in the dark?

Roots and shoots grow straight outwards in the direction they were placed, showing no gravitropic response because the clinostat cancels gravity.

What is a common misconception about how auxin works?

Auxin causes cell elongation, not cell division. Also, high auxin promotes shoot growth but inhibits root growth.

Why is it important for shoots to grow upwards and roots downwards?

Shoots grow upwards to absorb sunlight for photosynthesis; roots grow downwards to anchor the plant and absorb water and minerals from the soil.

What is the difference between positive and negative tropism?

Positive tropism is growth towards the stimulus; negative tropism is growth away from the stimulus.

Unlock all 56 questions, flashcards & more

Tạo tài khoản miễn phí để xem mọi câu hỏi, slide, thẻ ghi nhớ và ghi chú ôn tập cho chủ đề này.

ĐĂNG KÝ — MIỄN PHÍ ĐĂNG NHẬP

Đề thi cũ

Luyện đề thi cũ cho chủ đề này sắp ra mắt.

Sắp ra mắt