Plant responses and hormones

Question 1

What are the three ways plants respond to changes in their environment?

Answer 1

• grow towards light to maximise light absorption for photosynthesis
• sense gravity so roots and shoots grow in the right direction
• climbing plants have a sense of touch so they can climb to find sunlight

Question 2

What are the two toxic chemical defences to herbivory?

Answer 2

1) Alkaloids - deter or kill herbivores
2) Tannins - deter herbivores

Question 3

What are two examples of pheromones that plants release in response to herbivory?

Answer 3

• alarm pheromones alert nearby plants to produce chemicals such as tannins
• Pheromones which can attract parasitic wasps to kill caterpillars by laying eggs in them

Question 4

What is one example of a plants physical response to being touched?

Answer 4

Mimosas leaves quickly fold up when it is touched to protect against herbivory and knock off small insects

Question 5

What is a tropism?

Answer 5

The response of a plant to a stimulus coming from a particular direction

Question 6

What is positive tropism?

Answer 6

Growing towards the stimulus

Question 7

What is negative tropism?

Answer 7

Growing away from the stimulus

Question 8

What is phototropism?

Answer 8

The growth of a plant in response to light

Question 9

In regards to phototropism, what are shoots and roots?

Answer 9

Shoots are positively phototropic and roots are negatively phototropic

Question 10

What is geotropism?

Answer 10

The growth of a plant in response to gravity

Question 11

In regards to geotropism, what are shoots and roots?

Answer 11

Shoots are negatively geotrophic and roots are positively geotrophic

Question 12

What is hydrotropism? Give an example of a positively hydrotrophic plant part.

Answer 12

Plant growth in response to water - roots are positively hydrotrophic

Question 13

What is thermotropism?

Answer 13

plant growth in response to temperature

Question 14

What is thigmotropism?

Answer 14

Plant growth in response to contact with an object

Question 15

What a growth hormones in plants?

Answer 15

Chemicals that speed up or slow down plant growth

Question 16

Where are growth hormones produced in plants?

Answer 16

Growing regions - Shoot tips and leaves

Question 17

What does gibberellin do?

Answer 17

Stimulates seed germination, stem elongation, side shoot formation, and flowering

Question 18

What do auxins do?

Answer 18

Stimulate the growth of shoots by cell elongation

Question 19

What is the problem with a high concentration of auxins?

Answer 19

It will inhibit growth in the roots

Question 20

Where does IAA move in the shoots and roots in phototropism?

Answer 20

In the shoots, it moves to the shaded side and in the roots, it moves away from the light

Question 21

Where does IAA move in the shoots and roots in geotropism?

Answer 21

In the shoots, it will move to the shaded side so the shoot can grow upwards and in the roots it will continue to grow down

Question 22

What would be the result of placing a cap on a shoot?

Answer 22

It will not move towards the light, and it will grow upwards

Question 23

What would be the result of placing foil around a shoot, but not on the tip?

Answer 23

The tip would bend towards the light, but not the rest of the shoot

Question 24

What is apical dominance?

Answer 24

The prevention of the growth of sides shoots from lateral buds, so the shoot tip continues to grow

Question 25

How does inhibiting side growth lead to apical dominance?

Answer 25

Energy isn’t used up growing sides shoots, so the plant can grow tall very fast

Question 26

Which hormone, auxins, or gibberellins, can inhibit plant growth?

Answer 26

Auxins

Question 27

What are gibberellins inhibited by and why?

Answer 27

Abscisic acid to prevent seed germination

Question 28

What does auxins and the gibberellins being synergistic mean? Give an example.

Answer 28

They work together to have a really big effect - Plant growing tall

Question 29

What does auxins and gibberellins being antagonistic mean? Given an example.

Answer 29

They oppose each other’s actions - gibberellins stimulate side shoot growth, but auxins inhibit it

Question 30

What are deciduous plants?

Answer 30

Plants that lose their leaves in the winter

Question 31

What does plants losing their leaves in the winter do?

Answer 31

Helps them to conserve water during cold parts of the year as soil may be frozen and there is less light for photosynthesis

Question 32

What is leaf length triggered by?

Answer 32

The shortening of the days in the autumn

Question 33

How is leaf loss controlled?

Answer 33

Auxins inhibit leaf loss - less auxin produced = leaf loss

Ethene stimulates leaf loss - stimulates cells in abscission layer to expand and break the cells walls = leaf falls off

Question 34

Why do plants need to close their stomata?

Answer 34

To reduce water loss through transpiration

Question 35

What makes guard cells open and close stomata?

Answer 35

Guard cells full of water - turgid - pore is open

Guard cells lose water - flaccid- pore is closed

Question 36

What does abscisic acid do to somata?

Answer 36

Triggers their closure by binding to receptors and allowing calcium ions to enter and cause other channels to open, raising the water potential so water leaves via osmosis

Question 37

How is ethene used commercially?

Answer 37

Ethene ripens fruit by breaking down cells walls so bananas are transported before ripe and exposed to Ethene on arrival

Question 38

What are the two ways auxins are used commercially?

Answer 38

1) used in selective weed killers to make weeds grow too fast - can’t get enough water and nutrients
2) used as rooting hormones so cuttings can be cut and grown quickly and cheaply