plant hormones

Question 1

positive gravitropism

definition

Answer 1

when a root grows in the direction of the force of gravity

Question 2

negative gravitropism

definition

Answer 2

when the stem grows against the force of gravity

Question 3

auxins

definition

Answer 3

Plant hormones that control cell elongation.

Question 4

diffusion

definition

Answer 4

The movement of molecules from an area of higher concentration to an area of lower concentration.

Question 5

dormancy

definition

Answer 5

Hibernation for seeds which stops when they germinate.

Question 6

ethene

definition

Answer 6

The simplest alkene, consisting of two carbon atoms joined by a double bond, surrounded by four hydrogen atoms.

Question 7

geotropism

definition

Answer 7

Growth of plant roots downwards as a result of gravity.

Question 8

germination

definition

Answer 8

The process where seeds sprout and begin to grow.

Question 9

gibberellin

definition

Answer 9

A plant hormone involved in germination, flowering and fruit formation.

Question 10

hydrocarbon

definition

Answer 10

A compound that contains hydrogen and carbon only.

Question 11

photosynthesis

definition

Answer 11

A chemical process used by plants to make glucose and oxygen from carbon dioxide and water, using light energy. Oxygen is produced as a by-product of photosynthesis. Algae subsumed within plants and some bacteria are also photosynthetic.

Question 12

phototropism

definition

Answer 12

Growth of plant shoots towards the light.

Question 13

plant hormones

definition

Answer 13

Substances that can modify or control the growth of plants.

Question 14

stimulus

definition

Answer 14

Any change in the environment that can be detected by receptors in an organism.

Question 15

tropism

definition

Answer 15

Plant growth response to light, gravity or water.

Question 16

Why have plants developed tropisms?

Answer 16

In order to survive, plants require light and water for photosynthesis. They have developed responses called tropisms to help ensure they grow towards adequate sources of light and water.

Question 17

There are two main types of tropisms:

Answer 17

• positive tropisms - the plant grows towards the stimulus

- negative tropisms - the plant grows away from the stimulus

Question 18

What is phototropism?

Answer 18

Phototropism is the growth of plant shoots towards the light.

Question 19

Responses to stimuli of different parts of the plant

Answer 19

• In the plant stem, responses to light are known as a positive phototropism, which means the stem grows towards the light.
• In the plant root, responses to light are known as a negative phototropism, which means the root grows away from the light.

Question 20

Auxins

What are they

Answer 20

Auxins are a family of plant hormones. An example of a specific auxin is IAA, which is known as Indole acetic acid.

Question 21

Where are auxins made?

Answer 21

They are mostly made in the tips of the growing stems and roots, which are known as apical meristems, and can diffuse to other parts of the stems or roots.

Question 22

Unequal distribution of auxins

Answer 22

Unequal distribution of auxin can cause unequal growth rates in plants and shoots. Auxins change the rates of elongation in plant cells and control growth of stems and roots.

Question 23

Stems and roots respond differently to high concentrations of auxins:

Answer 23

• cells in stems grow more

- cells in roots grow less

Question 24

Phototropisms

Answer 24

In a stem, the shaded side contains more auxin and grows longer, which causes the stem to grow towards the light. The plant does NOT bend towards the light. It grows because the auxin causes the cells to elongate on the shaded side, so this side grows more. This unequal growth of the two sides, results in the growth of the stem towards the light.

If lit from above, the plant will grow upwards.

Question 25

Gravitropisms

Answer 25

Phototropism is a response to the stimulus of light, whereas gravitropism (also called geotropism) is a response to the stimulus of gravity.

Question 26

Plants responses to gravity:

Answer 26

- when the stem grows against the force of gravity, this is known as a negative gravitropism - when a root grows in the direction of the force of gravity, this is known as a positive gravitropism

Question 27

Gravitropism | What happens when a root is placed horizontally?

Answer 27

In a root placed horizontally, the bottom side contains more auxin and grows less - causing the root to grow in the direction of the force of gravity.

Question 28

Gravitropism | What happens when a stem is placed horizontally?

Answer 28

The opposite happens in a stem. When a stem is placed horizontally, the bottom side contains more auxin and grows more - causing the stem to grow upwards against the force of gravity.

Question 29

What is germination?

Answer 29

Germination is the beginning of plant growth, and the plant will continue to grow if the correct conditions are available.

Question 30

What are plant hormones used in?

Answer 30

There are many types of plant hormones. They are used in agriculture and horticulture to have a specific effect.

Question 31

Auxins

Answer 31

Auxins were the first class of plant hormones to be discovered. Their main function is to help plants grow and auxin stimulates plant cells to elongate. The apical meristem of a plant is one of the main places where auxin is produced. The apical meristem is also the location that all other parts of a plant grow from - the stem, leaves, and flowers.

Question 32

Auxins are one specific group of hormones that are used:

Answer 32

- as weed killers | - as rooting powders

Question 33

Weed killers

Answer 33

Selective weed killers kill some plants, but not others. This can be useful for getting rid of dandelions in a lawn without killing the grass. The selective weed killer contains a growth hormone that causes the weeds to grow too quickly and die. Because the weeds have broader leaves, the weed killer is absorbed in larger quantities by the weeds than it is by the grass. Selective weed killers can reduce biodiversity within treated areas due to specific plants being killed. Rooting powder contains plant hormones to promote growth. A small potted plant bring dipped in rooting powder Plant cuttings can be dipped in hormone rooting powder before planting. Synthetic plant hormones are used to control plant growth. For example, rooting powder contains growth hormones that make stem cuttings develop roots quickly.

Question 34

Other plant hormones | Gibberellins

Answer 34

Gibberellins are a group of plant hormones responsible for growth and development. They are important for initiating seed germination. Low concentrations can be used to increase the speed of germination, and they stimulate cell elongation so plants grow taller. They are naturally produced by barley and other seeds.

Question 35

Gibberellins can be used to:

Answer 35

end seed dormancy promote flowering increase fruit size

Question 36

Seed dormancy | Gibberellins

Answer 36

Seed dormancy must be broken for seeds to germinate, and this can be done by using gibberellins.

Question 37

Gibberellins | Flowering

Answer 37

Gibberellins can promote flowering, which can result in more financially profitable flowers to sell due to the increased speed of flower growth. More attractive flowers and larger specimens are also produced. Flowering also has an impact on the rate of fruit growth. Gibberellins are used in the production of seedless fruit such as seedless grapes, which are normally sprayed with gibberellin to increase the size of each grape.

Question 38

Controlling fruit ripening

Answer 38

Some hormones slow the ripening of fruits and others speed it up. These hormones and their inhibitors are useful for delaying ripening during transport or when fruit is displayed in shops. Ethene is a plant hormone which causes fruit to ripen.

Question 39

Controlling fruit ripening | Ethene

Answer 39

Ethene is used routinely within the food industry to provide controlled ripening during storage and transport or when fruit is displayed in shops, in sealed packages. Bananas are picked when they are green and unripened. Ethene is a hydrocarbon gas and it speeds up ripening in bananas and other fruit. The effect of ethene released from bananas is clearly visible if you keep them in a bowl with other fruit, as it causes other fruits to ripen very quickly.

Question 40

Which plant hormone is found in rooting powder?

Answer 40

Auxin

Question 41

Which plant hormone ripens fruit?

Answer 41

Ethene

Question 42

How can plant hormones be used to control fruit ripening?

Answer 42

Plant hormones can speed up or slow down ripening

Question 43

What is a phototropism?

Answer 43

A response to light

Question 44

Where are auxins made in the plant?

Answer 44

Auxins are made in the growing tip of a stem or root. Only cells in the tips of roots or shoots can make auxins.

Question 45

Which side of a stem contains more auxin?

Answer 45

The shaded side of a stem contains more auxin. This makes the cells elongate, causing the stem to grow towards the light.

Question 46

What happens to make a root grow in the direction of the force of gravity?

Answer 46

When a root grows in the direction of the force of gravity, its top side grows more than its bottom side. This is because the top side contains less auxin, making it grow longer.