A3. Responses in Plants Flashcards
Tropisms - Flowering plants, like animals, increase their chances of survival by responding to changes in their environment.
Examples - They sense the direction of light and grow towards it to maximise _____ ______________for photosynthesis.
They can sense ________, so their roots and shoots grow in the right direction.
Climbing plants have a sense of touch, so they can find things to climb and reach the sunlight.
They sense the direction of light and grow towards it to maximise light absorption for photosynthesis.
They can sense gravity, so their roots and shoots grow in the right direction.
Climbing plants have a sense of touch, so they can find things to climb and reach the sunlight.
A tropism is the response of a plant to a directional stimulus (a stimulus coming from a particular direction). Plants respond to stimuli by regulating their growth. A _________tropism is growth towards the stimulus, whereas a _______tropism is growth away from the stimulus.
A tropism is the response of a plant to a directional stimulus (a stimulus coming from a particular direction). Plants respond to stimuli by regulating their growth. A positive tropism is growth towards the stimulus, whereas a negative tropism is growth away from the stimulus.
Phototropism is the growth of a plant in response to light. Shoots are _________ phototropic and grow towards light. Roots are ___________ phototropic and grow away from light
Phototropism is the growth of a plant in response to light. Shoots are positively phototropic and grow towards light. Roots are negatively phototropic and grow away from light
Gravitropism
Gravitropism is the growth of a plant in response to gravity. Shoots are ________gravitropic and grow upwards. Roots are ___________ gravitropic and grow downwards
Gravitropism
Gravitropism is the growth of a plant in response to gravity. Shoots are negatively gravitropic and grow upwards. Roots are positively gravitropic and grow downwards
Auxins
Plants respond to directional stimuli using specific growth factors-these are __________-like chemicals that speed up or slow down plant growth. Plant growth factors are produced in the growing regions of the plant (e.g, ________and ____tips) and they move to where they’re needed in the other parts of the plant.
Plants respond to directional stimuli using specific growth factors-these are hormone-like chemicals that speed up or slow down plant growth. Plant growth factors are produced in the growing regions of the plant (e.g, shoot and root tips) and they move to where they’re needed in the other parts of the plant.
Figure 7: Effects of auxins on shoot growth
Growth factors called ______are produced in the tips of _______and diffuse __________to stimulate the cell just behind the tips to _________- this is where cell walls become loose and stretchy, so the cells get longer. If the tip of a shoot is removed, no auxin will be available and the shoot stops growing.
Auxins stimulate growth in shoots but high concentrations _________ growth in roots.
Growth factors called auxins are produced in the tips of shoots and diffuse backwards to stimulate the cell just behind the tips to elongate - this is where cell walls become loose and stretchy, so the cells get longer. If the tip of a shoot is removed, no auxin will be available and the shoot stops growing.
Auxins stimulate growth in shoots but high concentrations inhibit growth in roots.
Indoleacetic acid (IAA)
Indoleacetic acid (IAA) is an important auxin that’s produced in the tips of _______and ______in _____________plants. It’s moved around the plant to control tropisms-it moves by __________and ________ ____________ over short distances, and via the _________over long distances. This results in different parts of the plant having different concentrations of IAA. The uneven distribution of IAA means there’s uneven growth of the plant.
Indoleacetic acid (IAA) is an important auxin that’s produced in the tips of shoots and roots in flowering plants. It’s moved around the plant to control tropisms-it moves by diffusion and active transport over short distances, and via the phloem over long distances. This results in different parts of the plant having different concentrations of IAA. The uneven distribution of IAA means there’s uneven growth of the plant.
Example-phototropism
IAA moves to the more __________parts of the shoots and roots, so there’s uneven growth.
IAA concentration increases on the _________side - cells elongate and the shoot bends ________the light
IAA concentration increases on the _________side growth is inhibited so the root bends _____ from the light
IAA moves to the more shaded parts of the shoots and roots, so there’s uneven growth.
IAA concentration increases on the shaded side- cells elongate and the shoot bends towards the light
IAA concentration increases on the shaded side growth is inhibited so the root bends away from the light
Example-gravitropism
IAA moves to the ____________of shoots and roots, so there’s uneven growth.
IAA concentration increases on the _______side- cells elongate so the shoot grows ___________
IAA concentration increases on the _______side- growth is inhibited so the root grows ______________
IAA moves to the underside of shoots and roots, so there’s uneven growth.
IAA concentration increases on the lower side- cells elongate so the shoot grows upwards
IAA concentration increases on the lower side- growth is inhibited so the root grows downwards
Tip: Remember, root growth is ____________by high concentrations of IAA. The opposite is true in _______-high concentrations of IAA promote shoot growth.
Remember, root growth is inhibited by high concentrations of IAA. The opposite is true in shoots-high concentrations of IAA promote shoot growth.
Interpreting experimental data about IAA example
An experiment was carried out to investigate the role of IAA in shoot growth. Eight shoots, equal in height and mass, had their tips removed. Sponges soaked in glucose and either IAA or water were then placed where the tip should be. Four shoots were then placed in the dark (experiment A) and the other four shoots were exposed to a light source, directed at them from the right (experiment B)
After two days the amount of growth(in mm) and direction of growth was recorded. The results are shown in the table on the right.
explain the data…
The results show how the movement of IAA controls phototropism in plant shoots. In experiment A shoot A, the IAA diffused straight down from the sponge into the left-hand side of the shoot. This stimulated the cells on this side to elongate, so the shoot grew towards the right. In shoot B, the opposite occurred, making the shoot grow towards the left. In shoot C, equal amounts of IAA diffused down both sides, making all the cells elongate at the same rate.
In experiment B, the shoots were exposed to a light source. The IAA diffused into the shoot and accumulated on the shaded side (left-hand side) regardless of where the sponge was placed. Shoots A, B and C all grew towards the right because most IAA accumulated on the left, stimulating cell elongation there.
