Flashcards · Biology
Plant Adaptations and Hormones
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What is an adaptation?
A feature that helps an organism to survive in its environment.
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How are cactus leaves adapted?
They are reduced to spines, so there is a very small surface area for water loss.
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Why does a cactus have a thick cuticle?
To reduce the loss of water through the surface.
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Why do some desert plants open their stomata only at night?
It is cooler, so less water is lost.
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Why are stomata sunk in pits?
The pit traps humid air, which slows the diffusion of water vapour out.
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Why does marram grass roll its leaves?
To trap humid air around the stomata and reduce water loss.
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Where are the stomata of a water lily?
On the upper surface of the leaf.
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Why does a water lily have a thin cuticle?
Water is always available, so it does not need to prevent water loss.
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What do air spaces do in a water lily?
They keep the plant afloat and carry oxygen.
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Why do cushion plants grow low to the ground?
It is warmer and less windy, and the shape has a small surface area.
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What is a xerophyte?
A plant that is adapted to a very dry habitat.
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What does a small surface area to volume ratio do?
Reduces the rate of loss of water.
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Why do many cacti store water in their stems?
To survive the long periods between rain.
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How does the cuticle affect gas exchange?
A thick cuticle reduces it, so it is only thick where water loss is the main problem.
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Why do hairs on leaves reduce water loss?
They trap a layer of humid, still air next to the leaf surface.
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Common mistake about desert plants?
Saying they have no stomata. They have stomata, but fewer, and often open at night.
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What is a plant hormone?
A chemical that controls and coordinates growth and development in a plant.
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Where is auxin made?
In the tips of the shoots and roots.
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What does auxin do in a shoot?
Makes the cells elongate.
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What is a tropism?
A growth response to a stimulus from one direction.
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What is phototropism?
Growth in response to the direction of light.
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Where does auxin go in phototropism?
To the shaded side of the shoot.
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What happens to the shaded side of a shoot?
The cells elongate more, so the shoot bends towards the light.
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What is gravitropism?
Growth in response to gravity.
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Where does auxin collect in a shoot on its side?
On the lower side.
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Why does the shoot bend up?
The lower side grows faster.
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Why does the root bend down?
Auxin on the lower side slows its growth, so the upper side grows faster.
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What is positive phototropism?
Growth towards the light.
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Why is phototropism useful?
The leaves receive more light for photosynthesis.
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Why is gravitropism useful in a root?
It grows down to find water and to anchor the plant.
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What did Darwin show?
The tip detects light, as shoots with covered tips did not bend.
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Common mistake about auxin?
Saying that auxin makes the lit side grow. It moves to the shaded side.
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What is the independent variable in the phototropism investigation?
The direction of the light.
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What is the dependent variable?
The angle of bending of the shoots.
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What does a clinostat do?
Turns the seedlings slowly, so gravity acts on all sides equally.
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Why is a pot kept in the dark?
As a control, to show the growth without a direction of light.
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Why use a pot lit from above?
To show that the shoots grow straight with light from all around.
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What do roots do in a dish on its side?
Curve downwards.
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What do shoots do in a dish on its side?
Curve upwards.
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Why are the gravity dishes kept in the dark?
So that light does not affect the direction of growth.
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Name two control variables.
Any two from: type of seed, temperature, water, distance from lamp, time.
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How is the angle of bending measured?
With a protractor, on the seedling or on a photograph.
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How is the mean calculated?
Add all of the angles, and divide by the number of seedlings.
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Why use many seedlings?
To get a reliable mean, and to spot anomalies.
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Why can the lamp affect the results?
It can warm one side of the seedlings.
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Why wash hands after the investigation?
Mould may grow on damp seeds and cotton wool.
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Why is a photograph useful?
It gives a record, and can be used to measure the angle accurately.
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Common mistake about the dark pot?
Thinking it has no growth. The shoots grow, but straight and pale.
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Why are auxin weedkillers selective?
Broad-leaved weeds take them up and die, but narrow-leaved crops are not harmed.
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How do auxin weedkillers kill weeds?
They make the weed grow too fast and die.
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What does rooting powder contain?
A synthetic auxin.
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What does rooting powder do?
Makes cuttings grow roots quickly.
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What do gibberellins do to seeds?
End dormancy, so that they germinate.
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Why is it useful for seeds to germinate together?
The crop grows at the same rate and can be harvested at the same time.
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What do gibberellins do to flowers?
Bring on the formation of flowers.
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How are seedless grapes made?
They are sprayed with gibberellin so they grow without seeds and larger.
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What is ethene?
A gas made by plants, which makes fruit ripen.
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Why are bananas picked green?
They are firm, so they are not damaged in transport.
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How are green bananas ripened?
They are exposed to ethene gas.
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How can ripening be delayed?
Store the fruit cool, and remove the ethene.
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What is an advantage of using hormones in farming?
More uniform crops, more yield, or planned harvests.
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What is a disadvantage of weedkillers?
They can wash into streams and harm wildlife.
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What is a clone?
A genetically identical copy, such as a plant grown from a cutting.
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Common mistake about ethene?
Saying it is a solid. It is a gas, which is made by plants.