F215:04:01 Why plants respond to the environment Flashcards
What is a tropism?
a directional growth response in which the direction of the response is determined by the direction of the external stimulus (away or towards the stimuli)
What are the 3 things plants respond to?
Biotic components of their environment
Abiotic components of their environment
External stimuli
Why do plants need to actively respond to external components?
To avoid stress
To avoid being eaten
To survive long enough to reproduce
What are the 4 types of tropism?
- Photortropism
- Geotropism
- Chemotropism
- Thigmotropism
What is phototropism?
Where shoots tend to grow towards the light which enables them to photosynthesise
(they are positively phototrophic)
What is geotropism?
Where the roots grow towards the pull of gravity
This anchors the plant in the soil and helps to take up water (to remain turgid, as a raw material for photosynthesis and to help cool the plant), and the uptake of minerals e.g. nitrates that are needed for the synthesis of amino acids
Why is geotropism vital?
This anchors the plant in the soil and helps to take up water (to remain turgid, as a raw material for photosynthesis and to help cool the plant), and the uptake of minerals e.g. nitrates that are needed for the synthesis of amino acids
Why is phototropism vital?
growing towards light enables them to photosynthesise
What is chemotropism?
On a flower, the pollen tubes grow down to the style towards the ovary where fertilisation can take place (attracted by chemicals)
How do pollen tubes know where to grow towards the ovary?
They are attracted by chemicals
Why is chemotropism vital?
It aids reproduction in plants
What is thigmotropism?
shoots of climbing plants, such as ivy, wind round other plants or solid structures to gain support
Why is thigmotropism vital?
To gain support from other plants/solid structures
What co-ordinates a plants response to environmental stimuli?
hormones, but are often known as plant growth regulators because unlike animal hormones, they are not produced in endocrine glands but by cells in a variety of tissues in the plant
Whats the difference between tropic and trophic?
tropic: a growth response towards or away from a stimulus
trophic: connected with how living things feed
What is the difference between negative and positive tropic responses?
positive is towards the stimulus
negative is away from the stimulus
Why are plant hormones often known as plant growth regulators?
because unlike animal hormones, they are not produced in endocrine glands but by cells in a variety of tissues in the plant
How do plants ensure hormones only act upon the correct tissues?
- When the hormone reaches the target cells, they bind to receptors on the plasma membrane.
Specific hormones have specific shapes which can only bind to specific receptors with complimentary shapes of particular cells
Name the 3 methods hormones are transported round a plant
- active transport
- diffusion
- mass flow in the phloem sap or in the xylem vessels
What is synergy?
(The fact that some hormones have different effects on different tissues, and) some can amplify each others’ hormones effects
What is antagonism?
(The fact that some hormones have different effects on different tissues, and) some can even cancel out each other’s effecrs
What are the 3 things hormones can influence in a plant?
cell division
cell elongation
cell differentiation
Name the main 5 plant hormones
Auxins Cytokinins Gibberellins Abscisic acid Ethene
What effect do Auxins have on plants?
They promote cell elongation, inhibit the growth of side shoots and inhibit leaf abscission (leaf fall)
What is leaf abscission?
leaf fall
What effect do cytokinins have on plants?
they promote cell division
What effect do gibberellins have on plants?
They promote seed germination and the growth of stems
What effect does abscisic acid have on plants?
It inhibits seed germination and growth
causes stomatal closure when the plant is stressed by low water availablility
What effect does Ethene have on plants?
it promotes fruit ripening
Apart from tropism, what other responses to plants make to environmental stimuli?
nasties (nastic responses) that are non-directional responses
Give an example of thigmonaty
Mimosa pudica (a sensitive plant) responds to touch with a sudden drooping of the leaves
What are nasties/nastic responses?
non-directional responses
How might thigmonastic responses in plants help them to survive?
The response of sensitive plants may make it more difficult for herbivores to eat its leaves
Explain how such a response as thigmonastism might have evolved?
Variation in extent of response between individuals
Those with the most pronounced response are less likely to be eaten as their leaves droop more quickly and hence are more likely to survive longer and reproduce
After many generations, eventually the whole population will respond more dramatically
What does it mean to photoperiod?
When plants in temperate zones respond to day length
What influence does photoperiod have on plants?
It influences their flowering
Some are short-day plants, which flower in the autumn and spring
Some are long-day plants which flower in the summer
What has research shown about photoperiod plants?
that it is the length of darkness that is really crucial as short-day plants need a long period without light each night
Suggest how flower growers can make plants flower out of their normal season
Impose an artificial day length using artificial lights
Suggest why research into photoperiodism could be beneficial in agriculture to help increase the yield from food crops
Finding out which day length promotes flowering enables growers to manipulate the day length to encourage sustained flowering
Fertilisation of flowers leads to fruit and seed production, hence more flowering gives a higher yield
Suggest why plant growth regulators are called hormones, even though they arent produced in endocrine glands
They are chemical messengers that can be transported away from their site of manufacture to act in other parts (target cells or tissues) of the plant
When they reach their target cells, they bind to receptors on the plasma membrane
Explain why only certain tissues in a plant will respond to a particular plant hormone/growth regulator substance
Specific hormone molecules have specific shapes which can only bind to specific receptors with complementary shapes on the membranes of particular cells
Ethene is a gas, ripe fruit produces it, and bananas produce a lot of it. Why is it not advisable to place a vase of cut flowers next to a fruit bowl containing bananas?
Because the flowers release ethene in gaseous form, which causes the banana to ripen and may cause them to become over ripe
Describe Ethene and how it works etc
Its a gas
It is produced by flowers, stems, leaves and ripe fruit
Bananas produce a lot of it
