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

What is phototropism of auxins and how does it effect growth

Answer 20

When IAA moves to the more shaded parts of the shoots and roots so there is uneven growth. The IAA elongate causing the shoot to bend towards the light or can be inhibited so the root bends away from the light.

Question 20

What is geotropism of auxins and how does it effect growth

Answer 20

IAA moves to the underside of shoots and roots so that there is uneven growth. The IAA elongate causing the shoot to bend upwards or can be inhibited so the root bends downwards.

Question 21

How to carry out the practical to see how plant shoots respond to light

Answer 21

1) Take nine wheat shoots and plant in individual pots in the same type of soil, roughly the same height

2) Cover the tips of three with a foil cap, leave three without and wrap the last three at the base with foil so only the tip is exposed

3) Set the shoots in front of a light source at the same distance and leave for 2 days

4) After the experiment the shoots with exposed tips should have grown towards the light source, the covered tip should grow still straight up and the covered base should have the tip grow towards the light

5) Growth should be recorded in mm and the direction

Question 22

How to carry out the practical to investigate geotropism

Answer 22

1) Line three petri dishes with moist cotton wool with the same volume of water

2) Space out 10 cress seeds on the surface and push into wool

3) Tape a lid onto each dish and wrap in foil

4) Place in a constant warmish temperature place

5) Prop one dish at a 90 degree angle and label. Place another at a 45 degree angle and label. Place the last on a flat, horizontal surface and label.

6) Leave the seed for 4 days

7) Observe the results and the angle placed at the shoots have all grown away from gravity

Question 23

What is an apical bud

Answer 23

The shoot tip at the top of a flowering plant

Question 24

What is apical dominance

Answer 24

When auxins stimulate growth of the apical bud and inhibit the growth of side shoots from lateral buds - the apical bud is dominant over the lateral buds

Question 25

Why is apical dominance good

Answer 25

It prevents side shoot from growing which saves energy and prevents them from competing with the shoot tip for light. This means that a plant in an area where there are lots of other plants, the plant can still grow tall very fast, past the smaller plants to reach sunlight.

Question 26

What happens if you remove the apical bud

Answer 26

The plant won't produce any auxins, so the side shoots will start growing by cell division and elongation

Question 27

What happens if you replace the apical bud with a source of auxin

Answer 27

Side shoot development is inhibited, and proves apical dominance is controlled by auxins

Question 28

How does auxin concentration change through the plant

Answer 28

They become less concentrated further from the apical bud. If a plant is very tall then the bottom will have a low auxin concentration

Question 29

How to investigate the role of auxins in apical dominance

Answer 29

1) Plant 30 plants of a similar age, height and weight in pots 2) Count and record the number of side shoots growing from each main stem 3) For 10 plants remove the tip of the shoot and apply with a paste with auxins 4) For another 10 plants, remove the tip of the shoot and apply a paste without auxins 5) Leave the last 10 as they are 6) Let each group grow for 6 days in the same conditions such as light intensity, water etc 7) After 6 days count the number of side shoots from each plant, work out an average and create a table

Question 30

What are gibberellins produced in and used for

Answer 30

Produced in young leaves and seeds to stimulate seed germination, stem elongation, side shoot formation and flowering

Question 31

How do gibberellins impact stem elongation

Answer 31

They stimulate the stem of the plants to grow by stem elongation to help plants to grow tall. They do not inhibit growth in any way

Question 32

How do gibberellins impact seed germination

Answer 32

By triggering the breakdown of starch into glucose in the seed. The plant embryo in the seed can then used the glucose to begin respiring and release the energy it needs to grow. Gibberellins can be inhibited by the hormone abscisic acid.