5.1.5 Plant Hormones And Growth In Plants

Question 1

What do cytokinins do?

Answer 1

They promote cell division in roots and shoots therefore:

• cytokinins = more mitosis
• more mitosis = more cells
• more cells = plant growth

Question 2

What do giberellins do?

Answer 2

Promote seed germination. Within the seed, once it’s watered, it will absorb that water and it stimulates giberelins production in embryo. This acts as a transcription factor, turning on sections of dna, allowing it to be transcribed into rna and then translated into proteases and amylases. Thee break down food stores. The broken down glucose is then used in respiration and the amino acids are used to make proteins that develops it into a seedling

Question 3

What does abscisic acid do?

Answer 3

It’s responsible for stomata closure and opening. When water becomes limiting, we need stomata to close, so roots synthesise ABA, which is transported to the leaves of the plant. ABA them binds to complimentary receptors of the plasma membrane of the guard cells. This decreases the ionic concentration of the guard cells. Due to ionic concentration decreased, water potential inside guard cells decreases. Water moves out of the cell by osmosis. This results in reduction of turgor pressure and stomata close

Question 4

What does auxin do (IAA)

Answer 4

• causes shoots to bend towards light and roots towards gravitational pull.
• It’s involved in apical dominance which is where the plant aims to grow as high as possible as quickly as possible.
• Auxin inhibits ethene

Question 5

How do auxins enable phototropism

Answer 5

Auxins are made in shoot tip and diffuse down the shoot tip but the sunlight breaks down the auxin. So shaded side will have a high auxin conc. this promotes cell division on the shaded side, causing it to bend towards the light.

In shoots however, the auxin will build up on the side that has the most gravitational pull. However in the roots, auxin inhibits cell division. So the side furthest away from the gravitational pull will grow more and will bend towards gravity

Question 6

Role of Ethene

Answer 6

Leaves get lost during winter as more energy needed to keep them. So due to the increase in darkness and shorter daylight hours, less auxin gets made. Due to less auxin being made, ethene can now be produced as it is not being inhibited anymore. This stimulates the cells in the abscission zone to be produce enzymes that digest and weaken the end of the lear petiole. Leaf will fall and fatty deposits where leaf was to prevent entry of pathogens