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Biology mod 5 Communication, homeostasis and energy > 5.1.5 plant responses > Flashcards

5.1.5 plant responses Flashcards

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1
Q

Why do plants needed specialised responses that differ from animals?

A

Plants cannot run away from predators or move to shaded areas from the sun etc.

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2
Q

What is a tropism?

A

A growth movement of a plant in response to a directional stimulus.

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3
Q

What is a positive tropism?

A

Growth towards the stimulus.

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4
Q

What is a negative tropism?

A

Growth away from the stimulus.

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5
Q

List some different types of tropisms.

A

-Phototropism
-Geotropism
-Hydrotropsim
-Thigmotropism
-Chemotropism

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6
Q

What is phototropism a response to?

A

Light

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7
Q

What is geotropism a response to?

A

Gravity

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8
Q

What is hydrotropsim a response to?

A

Water/moisture.

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9
Q

What is thigmotropism a response to?

A

Touch

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10
Q

What is chemotropism a response to?

A

Chemicals.

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11
Q

Purpose of phototropism?

A

To ensure that plants get access to as much light as possible to maximise photosynthesis.

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12
Q

Are shoots positively or negatively phototrophic?

A

Positively.

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13
Q

Are roots positively or negatively phototrophic?

A

Negatively

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14
Q

Purpose of geotropism.

A

Ensures germinating seeds grow in the right direction.

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15
Q

Are shoots positively or negatively geotrophic?

A

Negatively

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16
Q

Are roots positively or negatively geotrophic?

A

Positively.

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17
Q

What direction do shoots grow in in response to geotropism?

A

Upwards

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18
Q

In what direction do roots grow in response to geotropism?

A

Downwards.

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19
Q

Purpose of hydrotropism.

A

Roots grow towards damper areas of soil which increases their access to water.

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20
Q

Purpose of thigmotropism?

A

Important in climbing plants as provides them with certain advantages e.g greater access to light in dense rainforests.

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21
Q

What is herbivory?

A

The consumption of plants by herbivores.
Plants have adaptations to this.

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22
Q

State some examples of chemical responses to herbivory?

A

-Alkaloids
-Tannins
-Pheromones

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23
Q

What are alkaloids?
How do these deter herbivores?

A

Chemicals with bitter tastes, noxious smells or poisonous characteristics which affect the metabolism of the herbivore which can result in death.

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24
Q

Give an example of a plant which produces alkaloids.

A

Tobacco plants produce the alkaloid nicotine.

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25
Q

What are tannins and how do they prevent herbivory?

A

Bitter-tasting chemicals which discourages animals from eating them.

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26
Q

Example of a plant which produces tannins.

A

Rhubarb produces the tannin Gallic acid.

27
Q

What are pheromones? How can they prevent herbivory?

A

Chemicals released by one member of a species that affect the physiology or behaviour of another member of the same species. Some plants release alarm pheromones into the air in response to herbivore grazing which can cause nearby plants to detect these chemicals and produce chemical defences such as tannins themselves.

28
Q

What are nastic movements?

A

When a plant folds in response to touch as it will protect the leaves from herbivores.

29
Q

What is abiotic stress?

A

Anything that is harmful and natural but non-living.

30
Q

Give some examples of abiotic stress.

A

Freezing
Drought
Increased soil water salinity
High winds
lack of water/excess water

31
Q

Give some examples of how plants react to abiotic stress.

A

Leaf loss
Stomatal control
Preventing freezing
Abscission
Daylight sensitivity

32
Q

How do plants use leaf loss to respond to abiotic stress such as temperature changes?

A

Tress will lose their leaves in countries that have cold winters. When it gets cold and daylight hours decrease, the rate of photosynthesis will decrease so it is more energy efficient for plants to lose their leaves as leaves require a lot of ATP to be maintained.

33
Q

How do plants use stomatal closure to respond to abiotic stress such as temperature changes?

A

The evaporation of water out of open stomata provides a cooling effect to a plant. The opening and closing can be controlled by ABA in response to temperature stress.

34
Q

How do plants use antifreeze chemicals to respond to abiotic stress?

A

Some plants e.g carrots produce natural antifreeze proteins that at low temperatures bind to ice crystals that lower the temperature that water freezes at, stopping more ice crystals from growing.

35
Q

How do plants use abscission to respond to abiotic stress E.g reduced light levels?

A

When light levels decrease, ethene switches on genes for enzymes that digest and weaken the cell wall at the abscission zone. This can cause the leaf to seperate from the plant, leaving a waterproof scar behind to protect the rest of the plant.

36
Q

What is a coleoptile?

A

A sheath that surrounds the young growing shoot of grass plants.

37
Q

What is IAA?

A

Indoleacetic acid (an auxin) which stimulates cell elongation in plants.

38
Q

Where are IAA molecules synthesised?

A

The meristem.

39
Q

How does IAA stimulate cell elongation?

A

IAA molecules activate proteins in cell walls known as expansins which losen the bonds between cellulose microfibrils therefore making cell walls more flexible.

40
Q

How does IAA cause phototrophism?

A

In shoots, IAA diffuses to the shaded side of the shoot so there is a high concentration there so cells elongate on the shaded side causing the plant to bend towards the light.
In roots, a high concentration of IAA inhibits elongation causing roots to elongate more on the lighter side and bend downwards away from the light.

41
Q

How does IAA cause geotropism?

A

IAA will diffuse from the upper side to the lower side of the shoot which causes plant cells to elongate on this side and the shoot grows upwards.
In roots, a high concentration of IAA results in a lower rate of cell elongation so the root bends downards at a slow rate.

42
Q

What is apical dominance?

A

When auxins (produced at the tip) cause the stem to grow upwards and stop lateral buds from growing.

43
Q

Why is apical dominance usually beneficial?

A

It is better for plants to grow towards the light as this ensures it has more energy for photosynthesis. Sideways growth is not as useful.

44
Q

Which hormone controls apical dominance?

A

auxins

45
Q

What happens if the apical bud in plants is removed?

A

Lateral buds will grow as the auxins have been removed.

46
Q

What are deciduous plants?

A

Plants which lose their leaves in very hot and dry environmental conditions in order to reduce water loss.

47
Q

Which hormones are involved in leaf loss?

A

Ethene
Auxins

48
Q

How do deciduous plants lose their leaves due to ethene?

A

A layer of cells called the abscission layer develops at the base of the leaf stalk and this layer of parenchyma cells is weak making it easy to break.
The plant hormone ethene stimulates the breakdown of cell walls in the abscission layer which causes the leaf to drop off.

49
Q

How can auxins also lead to leaf loss?

A

Usually, auxins inhibit leaf loss and are produced in young leaves which makes them insensitive to ethene. But, the concentration of auxins in leaves decreases as they age until lead loss can occur again due to ethene.

50
Q

Which hormone is involved in seed germination?

A

Gibberellins.

51
Q

Explain how gibberellins lead to seed germination?

A

When a seed is shed from the parent plant, it is in a state of dormancy. This allowed the seed to survive harsh conditions. When the conditions are right, the seed will start to absorb water and begin germination.
Gibberellin molecules diffuse into the aleurone layer and simulate the cells there to produce amylase. Amylase hydrolyses starch molecules in the endosperm which produces maltose molecules. The maltose is converted to glucose and transported to the embryo. The glucose can now be respired by the embryo and providing it with the energy needed to grow.

52
Q

What is an endosperm?

A

An endosperm- starch containing energy store surrounding the embryo of a seed.

53
Q

What is the aleurone layer?

A

A protein-rich layer on the outer edge of the endosperm.

54
Q

What hormone is involved in stomatal closure?

A

Abscisic acid (ABA).

55
Q

How does ABA lead to stomatal closure?

A

-Guard cells have ABA receptors on their cell surface membranes.
-ABA binds with these receptors on the cell surface membrane and inhibits proton pumps which stops the active transport of hydrogen ions out of the guard cells.
-ABA also causes calcium ions to move into the cytoplasm of the guard cells through the cell surface membranes. The calcium ions act as second messengers and:
Cause channel proteins to open that allow negatively charged ions to leave the guard cells.
This stimulates the opening of further channel proteins that allow potassium ions to leave the guard cells
*The calcium ions also stimulate the closing of the channel proteins that allow potassium ions to enter the guard cells.
The loss of ions increases the water potential of the guard cells.
Water leaves the guard cells by osmosis and the stomata of the guard cells close.

56
Q

State some commercial uses of plant hormones.

A

Selective weed killers
Rooting powders
Ripening

57
Q

Which plant hormone is used as a selective weed killer?

A

Auxin.

58
Q

Why plant hormone is used for rooting powder?

A

Auxin.

59
Q

Which plant hormone is used for fruit ripening?

A

Ethene.

60
Q

Why do we need selective weed killers?

A

They are designed to work on specific plants rather than normal weed killers which do not.

61
Q

How do auxins act as rooting powders.

A

The lower end of the cutting is dipped into powder before being planted in compost. Roots begin to grow shortly afterwards.

62
Q

Why do we need rooting powders?

A

To grow new roots.

63
Q

Why do we need to manually ripen fruit?

A

These plant can be unripe when harvested, transported, given ethene and then ripened to stop fruit being moudly by the time it is sold.

Biology mod 5 Communication, homeostasis and energy (8 decks)

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