Plant responses

Question 1

How to plants increase their chance of survival when responding to changes in their environment

Answer 1

• Sensing the direction of light and growing towards it maximizing light absorption
• Sensing gravity so the roots and shoot grow in the correct direction
• Climbing plants have a sense of touch to reach sunlight

Question 2

What are the chemical defences that plants have to herbivory

Answer 2

Alkaloids = chemicals with bitter tastes, noxious smells or poisonous characteristics that deter or kill herbivores

Tannins = taste bitter and in some herbivores (cattle and sheep) they bind to proteins in the gut so the plant is hard to digest

Question 3

What signaling chemical do some plants in response to herbivory

Answer 3

Pheromones:
Some plants release alarm pheromones into the air in response to herbivore grazing causing nearby plants that detect these chemicals to start making chemical defences e.g tannins.

Question 4

How do some plants react to being touched to deter against herbivory

Answer 4

They might fold up as a signal spreads through the whole leaf to help knock off small insects or animals trying to eat it.

Question 5

How do plants respond to abiotic stress

Answer 5

Producing antifreeze proteins at low temperatures that bind to ice crystals and lower the temperature that water freezes at, stopping ice crystals from growing

Question 6

What is a tropism

Answer 6

The response of a plant to a directional stimulus

Question 7

What is a positive tropism

Answer 7

Growth towards the stimulus

Question 8

What is a negative tropism

Answer 8

Growth away from the stimulus

Question 9

What is phototropism and which parts of the plants react in what way to it

Answer 9

The growth of a plant in response to light
- Shoots are positively phototropic and grow towards light
- Roots are negatively phototropic and grow away from light

Question 10

What is geotropism and which parts of the plants react in what way to it

Answer 10

The growth of a plant in response to gravity
- Shoots are negatively geotropic and grow upwards
- Roots are positively geotropic and grow downwards

Question 11

What is hydrotropism

Answer 11

Plant growth in response to water

Question 12

What is thermotropism

Answer 12

Plant growth in response to temperature

Question 13

What is thigmotropism

Answer 13

Plant growth in response to contact with an object

Question 14

How do plants respond to some stimuli

Answer 14

Using growth hormones

Question 15

What are growth hormones

Answer 15

Chemicals that speed up or slow down plant growth

Question 16

Where are growth hormones produced

Answer 16

The growing regions or the plant (e.g shoot tips and leaves) and move to where they are needed in the other parts of the plant

Question 17

What do gibberellins 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 (cell walls become loose and stretchy so cells get longer). High concentrations inhibit growth in roots

Question 19

What is IAA

Answer 19

Indoleacetic acid is an auxin produced in the tips of shoots in flowering plants. It is moved (by diffusion and active transport for short distances, phloem for long distances) around the plant to control tropisms

Question 20

How is IAA distributed through the plant

Answer 20

Unevenly - it moves to the shaded parts of the roots and shoots due to phototropism and then elongate. It moves to the underside of shoots and roots due to geotropism so the plant grows upwards and the root down