Homeostasis 3

Question 1

Why do plants produce hormones?

Answer 1

To coordinate and control growth and responses to light (phototropism) and gravity ( geotropism).

Question 2

What does unequal distributions of auxin cause?

Answer 2

Unequal growth rates in plant roots and shoots.

Question 3

What is auxin?

Answer 3

A plant hormone that controls growth near the tips of roots and shoots.

Question 4

Where is auxin produced?

Answer 4

The tips.

It moves backwards to stimulate the cell elongation process which occurs in the cells just behind the tips.

Question 5

What happens if the tip of a shoot is removed?

Answer 5

No auxin will be available and so the shoot may stop growing.

Question 6

What does auxin do?

Answer 6

-Promote growth in the shoot

-Inhibit growth in the root

Question 7

Phototropism

Answer 7

The growth of plant shoots towards the light.

Question 8

Why do shoots bend towards the light?

Answer 8

-When a shoot tip is exposed to light, more auxin accumulates on the side that’s in the shade than that’s in the light.

-This makes the cells grow (elongate) faster on the shaded side, so the shoot bends towards the light

Question 9

Geotropism

Answer 9

The growth of plant roots towards gravity.

Question 10

Negative geotropism

Answer 10

The growth of plant shoots away from gravity.

Question 11

Negative phototropism

Answer 11

The growth of plant roots away from the light.

Question 12

Why do roots grow downwards, towards gravity?

Answer 12

-When a root is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side.

-In roots, extra auxin inhibits growth.

-So, the cells on the top side of the root elongate faster and the root bends downwards

Question 13

Why do shoots grow upwards, away from gravity?

Answer 13

-When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side.

-In shoots, extra auxin promotes growth

-This causes the lower side to grow faster, bending the shoot upwards.

Question 14

What are gibberellins important in?

Answer 14

Initiating seed germination.

Question 15

What does ethene control?

Answer 15

Cell division and ripening of fruits.

Question 16

What are auxins useful for?

Answer 16

Controlling plant growth:

-Killing weeds
-Growing from cuttings with rooting powder
-Growing cells in tissue culture

Question 17

Auxins in weed killers

Answer 17

-A too high concentration of auxin can kill a plant

-They negatively affect the growth of broad-leaved plants (weeds) by disrupting their normal growth patterns and killing them

-But they spare narrow-leaved grasses and cereals (crops)

Question 18

What happens if we add rooting powder containing auxins to cuttings?

Answer 18

The cuttings will grow roots rapidly and start growing as new plants.

This enables growers to produce lots of clones of useful plants very quickly.

Question 19

How can auxins promote growth in tissue culture?

Answer 19

-Tissue culture can be used to grow clones of a plant from a few of its cells

-Hormones such as auxins need to be added to the growth medium (along with nutrients) to stimulate the cells to divide and form both roots and shoots

Question 20

Plant growth hormones are used in…

Answer 20

…agriculture and horticulture.

Question 21

What is ethene used for commercially?

Answer 21

It is used in the food industry to control ripening of fruit during storage and transport.

Question 22

What is ethene?

Answer 22

A gas produced by ageing parts of a plant.

It influences the growth of the plant by controlling cell division.

It also stimulates enzymes that cause fruit to ripen.

(Some fruit will produce more ethene as it ripens)

Question 23

How is ethene used in food ripening?

Answer 23

-Fruit is picked while it’s still unripe

-So, it’s firmer and less easily damaged

-Ethene gas is added to the fruit during transport

-So, it will be perfectly ripe as it reaches the shelves of a supermarket

Question 24

How can the effects of ethene be stopped?

Answer 24

-Using chemicals that react with ethene to remove it from the air

-Adding chemicals to fruits that limit the amount of ethene that can be produced or block its effect

(this delays ripening on supermarket shelves)

Question 25

How can gibberellins be used?

Answer 25

-To end seed dormancy

-To promote flowering

-To increase fruit size

Question 26

What is gibberellin?

Answer 26

A type of plant hormone that stimulates seed germination, stem growth, and flowering.

Question 27

What is seed germination?

Answer 27

When a seed starts to grow into a plant.

Question 28

What is seed dormancy?

Answer 28

Seeds not germinating until they’ve been through certain conditions (e.g. a period of cold or dryness).

Question 29

How can gibberellins be used to control seed dormancy?

Answer 29

They are used to treat seeds, making them germinate at times of the year they wouldn’t normally.

It also helps to ensure all the seeds in a batch germinate at the same time.

Question 30

How can gibberellin be used to induce flowering?

Answer 30

-Some plants require certain conditions to flower, such as longer days or low temperatures.

-If these plants are treated with gibberellin, they will flower without any change in their environment

-It can also be used to grow bigger flowers

Question 31

How can gibberellin be used to grow larger fruit?

Answer 31

Gibberellin can be added to fruits that do not grow large (e.g. to seedless grapes which do not grow as large as seeded grapes) to make them match the normal varieties.

Question 32

Where will auxins always diffuse to?

Answer 32

The shaded part of a plant.