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Edexcel Biology Gcse > plant hormones > Flashcards

plant hormones Flashcards

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1
Q

positive gravitropism

definition

A

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

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2
Q

negative gravitropism

definition

A

when the stem grows against the force of gravity

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3
Q

auxins

definition

A

Plant hormones that control cell elongation.

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4
Q

diffusion

definition

A

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

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5
Q

dormancy

definition

A

Hibernation for seeds which stops when they germinate.

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6
Q

ethene

definition

A

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

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7
Q

geotropism

definition

A

Growth of plant roots downwards as a result of gravity.

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8
Q

germination

definition

A

The process where seeds sprout and begin to grow.

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9
Q

gibberellin

definition

A

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

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10
Q

hydrocarbon

definition

A

A compound that contains hydrogen and carbon only.

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11
Q

photosynthesis

definition

A

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.

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12
Q

phototropism

definition

A

Growth of plant shoots towards the light.

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13
Q

plant hormones

definition

A

Substances that can modify or control the growth of plants.

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14
Q

stimulus

definition

A

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

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15
Q

tropism

definition

A

Plant growth response to light, gravity or water.

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16
Q

Why have plants developed tropisms?

A

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.

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17
Q

There are two main types of tropisms:

A
  • positive tropisms - the plant grows towards the stimulus

- negative tropisms - the plant grows away from the stimulus

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18
Q

What is phototropism?

A

Phototropism is the growth of plant shoots towards the light.

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19
Q

Responses to stimuli of different parts of the plant

A
  • 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.
20
Q

Auxins

What are they

A

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

21
Q

Where are auxins made?

A

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.

22
Q

Unequal distribution of auxins

A

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.

23
Q

Stems and roots respond differently to high concentrations of auxins:

A
  • cells in stems grow more

- cells in roots grow less

24
Q

Phototropisms

A

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.

25
Q

Gravitropisms

A

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

26
Q

Plants responses to gravity:

A
  • 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
27
Q

Gravitropism

What happens when a root is placed horizontally?

A

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.

28
Q

Gravitropism

What happens when a stem is placed horizontally?

A

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.

29
Q

What is germination?

A

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

30
Q

What are plant hormones used in?

A

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

31
Q

Auxins

A

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.

32
Q

Auxins are one specific group of hormones that are used:

A
  • as weed killers

- as rooting powders

33
Q

Weed killers

A

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.

34
Q

Other plant hormones

Gibberellins

A

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.

35
Q

Gibberellins can be used to:

A

end seed dormancy
promote flowering
increase fruit size

36
Q

Seed dormancy

Gibberellins

A

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

37
Q

Gibberellins

Flowering

A

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.

38
Q

Controlling fruit ripening

A

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.

39
Q

Controlling fruit ripening

Ethene

A

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.

40
Q

Which plant hormone is found in rooting powder?

A

Auxin

41
Q

Which plant hormone ripens fruit?

A

Ethene

42
Q

How can plant hormones be used to control fruit ripening?

A

Plant hormones can speed up or slow down ripening

43
Q

What is a phototropism?

A

A response to light

44
Q

Where are auxins made in the plant?

A

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

45
Q

Which side of a stem contains more auxin?

A

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

46
Q

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

A

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.

Edexcel Biology Gcse (36 decks)

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