Auxin

Question 1

What are auxins?

Answer 1

A family of hormones in plants that help with plant growth. They change the rate of elongation in cells, controlling how long they become.

Question 2

What is phototropism?

Answer 2

A response in which parts of a plant grow towards or away from the direction in which light is coming

Question 3

What is gravitropism?

Answer 3

A response in which parts

of a plant grow towards or away from gravity

Question 4

Where are auxins made?

Answer 4

In the tips shoot tip

Question 5

What is the effect of auxin on shoots?

Answer 5

Cells in shoots will grow more

Question 6

What is the effect of auxin on roots?

Answer 6

Cells in roots grow less

Question 7

How does a shoot grow towards light?

Answer 7

1. Light causes auxin to move to the shaded side
2. Shaded side contains more auxin
3. Auxin stimulates cell growth and shaded side grows longer.
4. Root bends towards light.

Question 8

How is a root pulled down by gravity?

Answer 8

1. A root is placed horizontally
2. This causes the bottom side to contain more auxin than the top side.
3. Cells at the bottom side grow less than cells at the top side.
4. Root bends in the direction of the force of gravity

Question 9

What do Darwin and Darwin’s experiments tell us about the tip of a shoot?

Answer 9

It is the part of the shoot responding to light

Question 10

Explain the role of auxin in controlling shoot growth

Answer 10

– auxin made in shoot tip (only)
– auxin spreads through the plant from the shoot tip
– auxin is unequally distributed in response to light and gravity
– auxin stimulates cell elongation

Question 11

What are phototropism and gravitropism examples of?

Answer 11

The chemical control of plant growth

Question 12

Why is a positive phototrophic response important?

Answer 12

Shoots need to grow upwards away from gravity and towards light to allow leaves to absorb light for photosynthesis

Question 13

Why do roots need a gravitropic response?

Answer 13

Roots need to grow downwards into the soil in the direction of gravity to anchor the plant and absorb water and minerals from the soil.

Question 14

How does a clinostat cancel out the effect of light coming from one direction?

Answer 14

It revolves slowly and repeatedly so shoots are evenly exposed to light

Question 15

What else can be cancelled by a clinostat?

Answer 15

The effect of gravity

Question 16

Why do weeds compete with crops like barley and wheat?

Answer 16

Barley and wheat have narrow leaves, while weeds have broad leaves

Question 17

What can synthetic auxins be used as?

Answer 17

Selective weedkillers

Question 18

Example of a selective weed killer

Answer 18

2,4 - D

Question 19

What do synthetic auxins in selective weed killers do to weeds?

Answer 19

They increase the growth rate of weeds by increasing the rate of cell division

Question 20

How do weeds die due to selective weedkillers?

Answer 20

The weeds cannot provide enough food through photosynthesis to maintain the growth rate, so they die

Question 21

Advantage of selective weedkillers

Answer 21

Allow more space, nutrients and water for crop plants

Question 22

Disadvantage of selective weedkillers

Answer 22

Can lead to eutrophication if they wash into lakes