Plant Hormones

Question 1

What is tropism?

Answer 1

When the movements are the results of stimuli coming mainly from one direction, the response is called tropism.

Question 2

What do plants need for photosynthesis?

Answer 2

Plants need light and water for photosynthesis.

Question 3

What is positive tropism?

Answer 3

Positive tropism is when the plant moves towards the stimulus.

Question 4

What is negative tropism?

Answer 4

Negative tropism is when the plant moves away from the stimulus.

Question 5

What is phototropism?

Answer 5

Phototropism is growth in response to the direction of light.

Question 6

What is geotropism?

Answer 6

Geotropism is growth in response to the direction of gravity.

Question 7

What happens in positive phototropism?

Answer 7

Positive phototropism happens in the stem tip. Here growth is towards the light and it does this to get maximum light for photosynthesis.

Question 8

What happens in negative phototropism?

Answer 8

Negative phototropism happens in the root tip. Here growth is away from the light and it does this for the less chance of drying out.

Question 9

What happens in positive geotropism?

Answer 9

Positive geotropism happens in root tip. Here growth is towards gravity and it does this for the higher chance of finding moisture.

Question 10

What happens in negative geotropism?

Answer 10

Negative geotropism happens in the stem tip. Here growth is away from gravity and it does this for the higher chance of finding light.

Question 11

What is auxin?

Answer 11

Auxin is a plant hormone responsible for controlling the direction of growth of root tips and stem tips in response to different stimuli including light and gravity.

Question 12

Where is auxin made?

Answer 12

Auxin is made at the tips of stems and roots.

Question 13

What does auxin do and where is it produced?

Answer 13

Auxin is produced in the tip of growing shoots.
If the tips are removed from growing shoots they cannot produce auxin, so phototropism cannot occur.
If the tips are covered, light cannot break down the auxin, so phototropism cannot then occur either.

Question 14

What happens in shoots?

Answer 14

In shoots, auxin is more concentrated in tissues on the side where light is least intense. The cells here grow more quickly than those on the brightly lit side. In this way, the shoot grows towards the brightest light.

Question 15

What happens in roots?

Answer 15

In roots where the concentration of auxin is high, the cells of the tissues grow more slowly. Auxin is more concentrated on the underside of roots, so the cells of the tissues of the underside grow more slowly than those on the upper side causing the roots to grow again.

Question 16

How can we used weedkillers?

Answer 16

Selective weedkillers kill some plants but not others. This can be useful for getting rid of dandelions in a lawn without killing the grass, or getting rid of thistles in a field without killing the wheat plants. The selective weedkiller contains growth hormone that causes the weeds to grow too quickly. The weedkiller is absorbed in larger quantities by the weeds than the beneficial plants.

Question 17

How can we use rooting powder?

Answer 17

Rooting powder makes stem cuttings quickly develop roots. Rooting powder contains growth hormones.

Question 18

How can we control fruit ripening?

Answer 18

Some hormones slow the ripening of fruits and others speed it up. These hormones and their inhibitors are useful for delaying ripening during transport or when fruit is displayed in shops.

Question 19

How can we used dormancy?

Answer 19

Dormancy stops seeds germinating until conditions are ideal for growth. Hormones can be used to remove the dormancy of a seed so it can germinate at all times of year. Buds and flowers can also be naturally dormant. Hormones can also be used to make plants grow bushier, make them flower or control the growth of hedge plants.

Question 20

What is ethene gas used for?

Answer 20

Ethene gas is used to ripen fruit just before it’s delivered to shops.

Question 21

How is herbicide used?

Answer 21

Herbicide contains plant hormone that stimulates the growth of plant stems. This is because the rate of root growth does not keep pace with the stem, the roots are not able to absorb enough water to support the growing plant and it dies. Herbicides only affect the weeds because they are broad-leaved and absorb more herbicide than narrow-leaved crop plants.

Question 22

How can growers produce seedless fruits?

Answer 22

Growers can produce seedless fruits by smearing the plant’ female sex organs with auxin paste, this then stimulates the development of the fruit. However, the egg cells within the female sex organs have not been fertilised so seeds are not produced.