Why do plants produce plant hormones?
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Why do plants produce plant hormones?
Plants produce hormones in order to coordinate and control growth responses.
Define the term phototropism.
Phototropism is the directional growth of plants in response to light, allowing shoots to grow towards light to optimise photosynthesis.
Define the term geotropism (or gravitropism).
Geotropism, also known as gravitropism, is the directional growth response of plants in relation to gravity; roots grow downwards and shoots grow upwards.
True or False?
Unequal distribution of auxin results in uneven growth in plant shoots and in plant roots.
True.
Auxin distributes itself unevenly in shoots due to the direction of light, and in roots due to the direction of gravity. This uneven auxin distribution results in uneven growth.
What effect does auxin have on cells in the shoots of plants?
Auxin stimulates cell elongation in plant shoots.
How does auxin distribution in response to light lead to phototropism?
Auxin accumulation on the shaded side of a shoot causes cells on the shady side to elongate at a faster rate than cells on the light side; this leads to bending of the shoot towards the light.
True or False?
Auxin inhibits the growth of cells in plant roots.
True.
Auxin accumulates on the lower side of plant roots, inhibiting cell growth and causing roots to bend downwards towards gravity.
What role do gibberellins have in seeds? (Higher Tier Only)
Gibberellins initiate seed germination.
True or False?
In an investigation into the effect of gravity on newly germinated seedlings the dependent variable is the direction of gravity.
False.
In an investigation into the effect of gravity on newly germinated seedlings the dependent variable is the length and/or direction of growth of newly grown roots and shoots.
The direction of gravity is the independent variable in this investigation.
Which variables need to be controlled in an investigation into the effect of light on newly germinated seedlings?
Variables that need to be controlled in an investigation into the effect of light on newly germinated seedlings include:
direction of gravity
temperature
water availability / how damp the cotton wool is
type / size / age of seedlings
Why is a clinostat used to investigate the effect of light or gravity on newly germinated seedlings?
A clinostat is used to investigate the effect of light or gravity on newly germinated seedlings because it cancels out the effects of gravity.
When investigating light this means that the variable of gravity can be controlled so that it does not affect results
When investigating gravity this means that it is possible to study seedling growth in the presence and absence of gravity
True or False?
Auxins can be used in agriculture as a weedkiller. (Higher Tier Only)
True.
Auxins can be used as weedkillers in agriculture; this is because they cause broad-leaved weed species to die while allowing narrow-leaved crop species to grow normally.
How can auxins aid the production of new plants? (Higher Tier Only)
Auxins can aid the production of new plants when it is added to:
rooting powder that encourages plant cuttings to grow new roots
cells in a tissue culture to promote growth
True or False?
Ethene prevents fruit ripening. (Higher Tier Only)
False.
Ethene causes fruit ripening. In the food industry the ripening of fruits can therefore be slowed by inhibiting ethene production.
How are gibberellins used in the plant growing industry? (Higher Tier Only)
Gibberellins can be used to:
initiate seed germination by ending seed dormancy
promote flowering
increase fruit size