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A-Level Biology - OCR A > 5.1.5 Plant Responces > Flashcards

5.1.5 Plant Responces Flashcards

1
Q

What do plants react to?

A

Chemicals.
Gravity.
Pressure.
Light.
Moisture.
Infection.
Temperature.
Oxygen.
Carbon Dioxide Concentration.
Disease.
Physical Disruption.
Sound.
Touch.

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2
Q

What happens when a plant detects a change?

A

They pick up electrochemical signals from the environment.

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3
Q

What is a Tropism?

A

Directional growth response of plants in response to a stimuli.

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4
Q

What is phototropism?

A

Response to light

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5
Q

What is an example of phototropism?

A

Plants grow towards the light to maximise photosynthesis.

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6
Q

What is geotropism?

A

Response to gravity

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6
Q

Skip

A

To delete

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6
Q
A
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7
Q

What is an example of geotropism?

A

Roots grow towards the pull of gravity - positive geotropism.
Shoots grow away from the pull of gravity - negative geotropism.

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8
Q

What is chemotropism?

A

Response to chemicals

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9
Q

What is an example of chemotropism?

A

Pollen tubes grow down the style, attracted by chemicals, towards the ovary where fertialisation takes place.

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10
Q

What is Thigatropism?

A

Response to touch

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11
Q

What is an example of thigmatropism?

A

Climbing plants detect support and wrap around it.

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12
Q

What is hydrotropism?

A

Responce to water/moisture

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13
Q

What is an example of hydrotropism?

A

Roots grow towards water

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14
Q

What is a positive tropic responce?

A

If the plant responds towards the stimulus

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15
Q

What is a negitive tropic responce?

A

if a plant responds away from a stimulus

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16
Q

What is an advantage of positive and negative tropism?

A

Roots grow towards gravity - positive geotropism.
Shoots grow away from gravity - negative geotropism.

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17
Q

When is a response not a tropism?

A

When the response is immediate. As it is not a growth response

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18
Q

What are non directional responses known as?

A

Nastic responses/movements.
or Trigomonasty

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19
Q

What is the difference between nastic movements and tropisms?

A

nastic responses are more rapid and are caused by local biochemical signals

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20
Q

What are the plant responces to biotic stresses?

A

Tannins.
Alkaloids.
Pheromones.

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21
Q

What are tannins?

A

Chemicals stored within the vacuole. They are fatal to insects and deters herbiovores.
They are toxic and have a bitter taste.

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22
Q

Where are tannins used?

A

In roots they prevent infiltration by pathogenic microorganisms

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23
Q

What are alkaloids?

A

Nitrogenous compounds derived from amino acids.

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24
Q

How do alkaloids protect against biotic stress?

A

Have a bitter taste to deter animals from eating the plant. Some can be toxic.

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25
Q

What is an example of where alkaloids are used?

A

In growing tips and flowers and peritoneal cell layers of stems and roots.

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26
Q

What are pheromones?

A

Chemicals released by an individual to affect another

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27
Q

What do pheromones do?

A

Can control other chemical defenses in plants by switching genes on and off that produce chemicals that deter insects. So they act as hormones

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28
Q

What are examples of the use of pheromones?

A

Ethene released by plants causes ripening of fruit in nearby plants and causes leaf loss. Oxides of ethene are toxic to insects.

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29
Q

What is a plants responce to freezing?

A

Some plants produce a chemical that prevents ice crystals forming inside it.

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30
Q

What is a plants response to drought?

A

Closing stomata or loosing leafs to prevent water loss by transpiration

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31
Q

What are some abiotic stresses experianced by plants?

A

Freezing.
Drought.
Salinity of soil water.
Presence of heavy metals.

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32
Q

What are plant hormones?

A

Hormones that act within plants. They work in the same way as animal hormones but are made by cells in a variety of cells rather than specific endocrine glands.

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33
Q

How are hormones moved in plants?

A

Active transport.
Diffusion.
Mass Flow.

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34
Q

How do hormones interact with the target cell?

A

The target cell has receptors that are specific to that hormone.

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35
Q

What do cytokinins do?

A

Promote cell division.
Delay leaf senescence.
Overcome apical dominance.
Promote cell expansion.

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36
Q

What does abscisic acid do?

A

Inhibit seed germination and growth.
Causes stomatal closure when the plant is stressed by low water availability.
Produced in the roots in response to low water potential and gets translocated to the leaves.

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37
Q

What does auxin do?

A

Promotes cell elongation.
Inhibits the growth of side shoots.
Inhibits leaf abscission.

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38
Q

What do gibberellins do?

A

Promote seed germination and growth of stems

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39
Q

What does ethene do?

A

Promotes fruit ripening

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40
Q

What are deciduous plants?

A

Plants that loose leaves when very hot or dry (in order to reduce water loss), when the soil water is frozen, or no photosynthesis is taking place.

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41
Q

What is abscission?

A

The shedding of an old or mature organ from a plant.

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42
Q

How is leaf loss controlled by hormones?

A

An abscission layer forms at the bottom of the leaf or stalk. Its a layer of perenchima cells.
Ethene breaks down the abscission layer and causes the leaf to fall.

43
Q

Why does leaf loss only occur in mature leaves, not young ones?

A

Auxin is produced by young leaves to inhibit leaf loss by being insensitive to ethene. As the leaf matures the concentration of auxin decreases. allowing for leaf loss in response to ethene. Leading to leaf, fruit and flower drop.

44
Q

Where does growth occur in a plant?

A

Only occurs where there are groups of immature cells that are still able to divide and specialise - called meristems

45
Q

What are the different types of meristems?

A

Apical Meristems.
Lateral Bud Meristems.
Lateral Meristems.
Intercalory Meristems.

46
Q

What are apical meristems?

A

Meristem cells at the apices (apex) of roots and shoots to make them longer.

47
Q

What are lateral bud meristems?

A

Meristems in buds and side shoots to make them grow.

48
Q

What are lateral meristems?

A

Meristems that form a cylinder near the outside of roots and shoots and are responsible for roots and shoots getting wider.

49
Q

What are intercalary meristems?

A

Meristems located at nodes, where leaves and branches branch off the stem. These make the shoot longer.

50
Q

What hormones regulate plant growth?

A

Auxin

51
Q

Where is auxin produced in a shoot?

A

In the apical bud.

52
Q

What does auxin do in the shoot?

A

Moves down the stem and inhibits lateral bud growth.

53
Q

What happens if the apical bud gets removed?

A

The plant starts to develop side branches due to the reduction of auxin. Previouesly dormant cells become active.

54
Q

What is the aim of auxin in the apical bud?

A

Allow the shoot to grow towards the light before it grows out laterally - when it cant go any higher.

55
Q

How does abscisic acid controll plant growth?

A

It inhibits bud growth. High concentrations of auxin in the tip keeps abscisic acid high in the buds.

56
Q

How do cytokinins control plant growth?

A

They promote bud growth. If the tip is removed it overrides apical dominance and cytokinins are produced in the roots.
High levels of auxin create a sink for cytokinins at the apical shoot to promote growth. Once the tip is removed the cytokinins spread about the plant.

57
Q

What is IAA?

A

Indol-3-acetic acid

58
Q

What does Indol-3-acetic acid do?

A

Controls phototrophic mechanisms

59
Q

How does Indol-3-acetic acid work?

A

Produced in the meristems and causes genes to turn on and off, stimulating protein expansion - making cells more flexible by loosening cellulose fibers.
By making one side of the stem more flexible it can control the direction of growth.

60
Q

How does auxin cause the plant to change its direction of growth?

A

Promotes active transport of H+ by ATPase enzymes on the plasma membrane and cell wall. This produces a low PH which provides optimal conditions for wall loosening enzymes (expansins) to work. The enzyme breaks bonds in the cellulose (the increase in hydrogen ions also disrupts hydrogen bonds between threads). This makes the walls less rigid, allowing the cell to expand as it takes in water.

61
Q

What THEORY suggests how auxin moves to the correct side of the plant?

A

Phototropin 1 and phototropin 2 are promoted in plants by blue light. This makes them very active on the light side of the plant, and decreasingly so on the shaded side. This redistributes the auxin through their effect on PIN proteins (a transmembrane protein) which move auxin between cells and around the shoot.

62
Q

What do gibberellins control?

A

Stem elongation and seed germination

63
Q

Where are gibberellins produced?

A

Young leaves, seeds and root tips.

64
Q

How do gibberellins work with auxin?

A

Synergistically - The combined action is greater than each individual effect combined.

65
Q

What is gibberellins a collective name for?

A

Gibberellic acids

66
Q

What are different gibberellic acids responcible for?

A

Stem growth

67
Q

What does GA1 control?

A

Dwarfism - the more GA1 a plant has the taller the plant is.

68
Q

What determins the concentration of GA1?

A

The Le Gene - it is responcible for converting GA20 into GA1.

69
Q

What happens if the Le Gene is not present?

A

GA20 cant be converted into GA1 so the plant will be a dwarf. Any other changes to the pathway will also mean that the plant will be a dwarf.

70
Q

How are gibberellins involved with seed germination?

A

When a seed absorbs water the embryo releases gibberellins. They travel to the endosperm region of the seed and cause the production of amylase. This converts starch in the seed into glucose - providing a substrate for respiration and protein synthesis.

71
Q

How does auxin work in the shoots of a seed?

A

Shoot auxin stimulates growth so the bottom of the shoot elongates faster and the shoot curves upwards.

72
Q

How does auxin work in the roots of a seed?

A

Root auxin inhibits growth so the top elongates faster meaning that the root curves downwards.

73
Q

What is the difference between shoot and root auxin?

A

The effect of auxin in the roots is in contrast to that in the shoots. In the roots it inhibits cell elongation. In the shoot it promotes it. Root and shoot cells in the zone of elongation exhibit different responses to the same concentration of auxin.

74
Q

Who conducted the first investigations into phototropism?

A

Darwin and Boysen-Jenson

75
Q

What type of light did the experiments by Darwin and Boysen-Jenson use?

A

Directional Light

76
Q

What did the investigations by Darwin and Boysen-Jenson prove?

A

Water and solutes need to be able to pass from the shoot tip to the rest of the shoot for phototropism to happen.

77
Q

Who continued the studies conducted by Darwin and Boysen-Jenson?

A

Went

78
Q

What type of light did Went use?

A

Undirected light

79
Q

What did Went’s investigations prove?

A

A chemical messenger (auxin) exists.

80
Q

What was the combined outcome of the experiments by Darwin, Boysen-Jenson and Went?

A

Shows that auxin is present. Light shining on one side of the shoot appears to cause auxin to be transported to the shaded side and causes the cells to elongate there quicker.

81
Q

How can you measure the change in the direction of growth of a plant?

A

Mark the plants shoot at regular intervals along the shoot. After the growth has occoured you can remeasure the new distances and compare them using standard deviation.

82
Q

What equipment is used to measure the effect of geotropism?

A

Using a kinostat

83
Q

How is a kinostat used to measure the effect of geotropism?

A

It rotates the plant to effectively negate the effect of gravity.
By placing the plant sideways you can negate the effect. Having another plant that doesn’t rotate will cause that one to be affected by gravity so you can observe the difference.

84
Q

How can auxin be used commercially?

A

Preventing fruit dropping.
Promoting fruit dropping.
Weed killer.
Seedless fruit.
Cuttings.

85
Q

How are auxins used to prevent fruit dropping?

A

Synthetic auxin prevents fruit drops in mangos, avocados and macadamia for example. Prevents the fruit abscission layer forming

86
Q

What is the advantage of preventing fruit drop?

A

Less fruit drop promotes larger fruit growth

87
Q

How is auxin used to promote fruit dropping?

A

High levels of auxin causes fruit to drop

88
Q

What is an advantage of promoting fruit drop?

A

Allows fruit to be harvested at the same time.

89
Q

How is auxin used as a weed killer?

A

High concentrations cause rapid growth, expecially in the roots. This causes the tissue to become damaged and allows pathogens to enter and kill the plant.
Typically used on cereals and grasses as they are less effected by the auxin so dont die themselves.

90
Q

How is auxin used to produce seedless fruit?

A

Treating unpollinated plants with auxin promotes ovule growth, triggering automatic auxin growth and completing the development process.

91
Q

What does parthenocarpy mean?

A

grown without fertilisation - e.g. seedless fruit

92
Q

What name is given to fruit grown without fertilisation - e.g. seedless fruit?

A

Parthenocarpy

93
Q

How is auxin used for cutings?

A

Dipping cuttings in rooting powder encourages root growth.

94
Q

What is rooting powder made from?

A

Auxin and talcum powder

95
Q

How can cytokinin’s be used commercially?

A

Delaying leaf senescence.
Mass producing plants.

96
Q

How are cytokinin’s used to delay leaf senescence?

A

Prevents the yellowing of salad leaves, like lettuce, after they have been picked.
This extends the amount of time that they can be left unpicked - e.g. on the shelves

97
Q

How are cytokinins used in the mass production of plants?

A

Promotes bud and shoot growth from small pieces of tissue from the parent plant. Produces short shoots with lots of side branches which easily split into lots of small plants, each grown separately.

98
Q

What needs to be done to ethene so that it can be used commercially?

A

Ethene is a gas so cant be sprayed directly. 2-chloroethyl phosphoric acid is used. When sprayed in solution it is easily absorbed by plants to slowly release ethene within the plant.

99
Q

What are the uses of ethene?

A

Speed up the ripening of apples, tomatoes and citrus fruits.
Promotes fruit drop in cotton, cherry and walnuts.
Promotes female sex expression in cucumbers. This reduces the chance of self-pollination - which makes cucumbers taste bitter and reduces the yield.
Promotes lateral growth in some plants, yielding compact flowering stems.

100
Q

What are the commercial uses of gibberellins?

A

Fruit Production.
Brewing.
Sugar Production.
Plant Breeding.

101
Q

How are gibberellins used in fruit production?

A

They delay senescence in fruit. Extending the time they can be left on the shelf.

Act with cytokinins to elongate apples.

Can be used to produce seedless fruit.

Makes grapes less compacted and larger by elongating the stalks.

102
Q

How are gibberellins used in brewing?

A

During the germination of barley seeds, the aleurone layer of the seed produces amylase enzymes that break down starch into glucose. This is normally controlled by naturally occurring gibberellins. By adding more it speeds up the process.
Dying and grinding the seeds produces malt which is used in the brewing industry to make beer.

103
Q

How are gibberellins used in sugar production?

A

Spraying sugar cane with gibberellins promotes growth between the nodes - stem elongation. Sugar is stored in the parenchyma cells of internodes, meaning more sugar is available from each plant.

104
Q

How are gibberellins used in plant breeding?

A

Causes plants to mature faster tyhan usual - making them reproductivly active much quicker. This makes breeding easier as they can be bread much quicker.

Formation of seeds in biennial plants can be spread up so that they are produced in the first year.

105
Q

What are biennial plants?

A

Plants that only flower in their second year of life

106
Q

Why are gibberellins inhibited in plant breeding?

A

Spraying plants with gibberellin inhibitors keeps them short and stocky.
This helps prevent lodging where the plant gets pulled over due to an accumulation of rainwater on the plant. Lodging makes the plant harder to harvest.

A-Level Biology - OCR A (10 decks)

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