Plant Growth Factors (Indoleacetic acid IAA)

Question 1

Plants respond to changes in both their external and internal environments. What are three factors that plants respond to?

Answer 1

Light
Gravity
Water

Question 2

How do plants respond to light?

Answer 2

Shoots grow towards light, as they are positively phototropic because light is needed for photosynthesis

Question 3

How do plants respond to gravity?

Answer 3

The roots of a plant are sensitive to gravity and grow in the direction of its pull, being positively gravitropic. This allows the plant to be firmly anchored in the soil

Question 4

How do plants respond to water?

Answer 4

Almost all plant roots grow towards water, being positively hydrotropic. This is done so they can absorb it for use in photosynthesis and other metabolic processes, as well as for support

Question 5

What do plant growth factors do?

Answer 5

Plant growth factors exert their influence by affecting growth and some factors affect the tissues that release them rather than on a distant target organ

Question 6

Where are plant growth factors produced? Are plant growth factors produced in big or small quantities?

Answer 6

Plant growth factors are produced by cell located throughout the plant rather than in particular organs. They are produced in small quantities

Question 7

What is the main example used in AQA bio A level?

Answer 7

The indoleacetic acid (IAA)

Question 8

What does IAA control? Where is the indoleacetic acid made?

Answer 8

The indoleacetic acid can control cell elongation in shoots and inhibit the growth of cells in the roots. Additionally it is able to diffuse into other cells. Indoleacetic acid is formed in the tip/roots

Question 9

What is tropism?

Answer 9

Tropism is directional growth of a plant in response to a directional stimulus

Question 10

What happens when there is an even distribution of light in a shoot tip cell that has indoleacetic acid?

Answer 10

Shoot tip cells produce indoleacetic acid, when there is an even distribution of light, that is when the indoleacetic acid diffuses towards the shaded side of the shoot which causes cell elongation in the shoots so the cell grows upwards

Question 11

What happens when there is unilateral light on a shoot tip cell that has indoleacetic acid?

Answer 11

If there is light shining in one specific area of the shoot, the indoleacetic acid will always diffuse from the root tip to the most shaded side, making that side elongate and become longer

Question 12

Does the shaded side of the shoot elongate faster or the lighted side and what does this faster elongation cause?

Answer 12

The shaded side of the shoot elongates faster than the light side causing the shoot tip to bend towards the light

Question 13

What is the function of the roots and what are two things they do NOT do?

Answer 13

Roots anchor plants into soil and they do no need light because they do not photosynthesise

Question 14

What does a high concentration of indoleacetic acid result in for roots?

Answer 14

In roots, a high concentration of indoleacetic acid inhibits cell elongation which causes root cells to elongate more on the lighter side and makes the roots bend away from the light. This is described as the negative phototropism

Question 15

How does gravitropism affect shoots?

Answer 15

Indoleacetic acid will diffuse from the tips to the lower side of the shoot, as the indoleacetic acids diffuse towards the pull of gravity

Question 16

What is the effect of indoleacetic acid on roots?

Answer 16

Indoleacetic acid diffuses towards gravity which is on the lower side of the root. This causes the upper side to elongate and the roots to bend down towards gravity, anchoring the plant into the soil

Question 16

If a plant is vertical, what occurs?
If a plant is on its side, what occurs?

Answer 16

If a plant is vertical, the plant cells will elongate and cause the plant to grow upwards. If a plant is on its side, it will cause the shoot to bend upwards