3.4.5 Control Systems in Plants Flashcards
Why do flowering plants respond to changes in their environment?
Increases their chances of survival
Give examples of how flowering plants respond to changes in environment
- They sense direction of light and grow towards it to maximise light absorption for photosynthesis
- Sense gravity so roots and shoots grow in right direction
- Climbing plants have a sense of touch = find things to climb up and reach sunlight
What is tropism?
Response of plant to directional stimulus
How do plants respond to stimuli?
By regulating their growth
What is positive tropism?
Growth towards stimulus
What is negative tropism?
Growth away from stimulus
Name 4 types of tropisms
- Phototropism
- Gravitropism
- Hydrotropism
- Responds to water
- Chemotropism
- Responds to chemicals
What is phototropism?
Growth of plant in response to light
Describe how the shoots and roots respond to light
- Shoots are positively phototropic and grow towards light
- Roots are negatively phototropic and grow away from light
What is gravitropism (aka geotropism)?
Growth of plant in response to gravity
Describe how the shoots and roots respond to gravity
- Shoots are negatively gravitropic and grow upwards
- Roots are positively gravitropic and grow downwards
What do plants use to respond to directional stimuli?
growth factors
What are growth factors?
Hormone-like chemicals that speed up or slow down plant growth
Where are growth factors produced?
In growing regions of plant (e.g. shoot tips, leaves)
& move to where they’re needed in other parts of plant
What do auxins (growth factors) do?
- Stimulate growth of shoots by cell elongation
- Where cell walls become loose and stretchy so cells get longer
What does high concentrations of auxin result in?
Inhibits growth in roots
What is indoleacetic acid (IAA)?
Important auxin that’s produced in tips of shoots in flowering plants
Describe how IAA is moved around a plant
Moves by diffusion and active transport over short distances & via phloem over long distances
What does an uneven distribution of IAA mean?
There’s uneven growth of plant
Describe where IAA moves to control phototropism
IAA moves to more shaded parts of shoots and roots so there’s uneven growth
Phototropism
State what happens to IAA and its effect in a shoot
- IAA concentration increases on the shaded side
- cells elongate and the shoot bends towards the light
Phototropism
State what happens to IAA and its effect in a root
- IAA concentration increases on the shaded side
- Growth is inhibited so root bends away from light
Describe where IAA moves to control gravitropism
IAA moves to the underside of shoots and roots, so there’s uneven growth
Gravitropism
State what happens to IAA and its effect in a shoot
- IAA concentration increases on lower side
- cells elongate so shoot grows upwards
Gravitropism
State what happens to IAA and its effect in a root
- IAA concentration increases on the lower side
- growth is inhibited so the root grows downwards
Describe how bananas are artificially ripened before they are sold
- Placed in ripening rooms where temperature and humidity are raised optimum levels
- Ethene concentration is raised using a catalytic generator
- Rooms are airtight to prevent gases escaping
Describe the role of ethene in fruit ripening
Ethene switch on genes for enzymes responsible for changing colour (hydrolyses), softening fruit (pectinases), increasing sugar content (amylases)
Synthesis of these enzymes require ATP and hence linked to increased respiration rate
Describe the role of abscisic acid (ABA) on a plant
- Key role in plants response to environmental stress
- Closing the stomata in response to low soil water or high salinity
When is abscisic acid (ABA) needed? Describe how ABA is transported
When soil water is low, ABA is transported from roots where it is synthesised up to shoots via xylem
Describe how stomata open
- H+ are actively transported out of guard cells causing inside to become more negative
- Negative charge causes inward K+ gates to open and allows K+ to enter guards cells
- K+ lowers water potential and water moves in by osmosis
- Guard cells become turgid
Describe how abscisic acid (ABA) causes the stomata to close
- ABA binds to receptors = production of H2O2 and other reactive oxygen species (ROS)
- ROS then triggers an increase in Ca2+ in cytoplasm = Ca2+ enters from both outside the cell and from the vacuole
- ROS inhibits H+ pumps
- Rise in Ca2+ opens anion channels with Cl- and other negatively charged ions to leave
- This caused inward K+ channels to close and outward K+ channels to open = causing K+ to leave the guard cell
- Water then leaves guard cells via osmosis, so they become flaccid and close the stomata
Describe how you would investigate the effect of light intensity on the direction of shoot growth
- Place same amount of compost into each small transparent plastic containers (about 2 spatulas)
- Add same volume of water to each container
- Then add 10 cress seeds to each container, distribute them evenly
- Wrap black card around one container and leave a square hole in the card so light can pass through
- Leave both containers in sunlight for a day
- Then observe the results/measure the curvature (degrees) of the plant
Describe how you would investigate the effect of gravity on the direction of root growth
- Cut blotting paper to fit into a CD jewel case & place into case
- 6 cases in total
- Moisten bolting paper
- No surface water
- Place 4 seeds in middle of moist paper, evenly spaced from each other
- None of the seeds should be close to sides of paper
- Close CD case and repeat for each CD case
- Label each CD case and mark the 4 edges on the front side of each CD case: Up, Down, Left and Right
- Using modelling clay to hold them in place, set 2 CD cases upright each in their own shallow dish with Up on top edge
- Place 2 CD cases horizontally into 2 shallow dishes
- (Roots can’t grow in direction of gravity)
- Use modelling clay under the CD cases to lift them up
- (Any water added can drip into dish to dry)
- 2 CD cases set vertically in modelling clay on 2 more shallow dishes, label Up at top
- Rotate these CD cases 90° clockwise every 2 days
- Put all of your CD cases inside a dark cupboard
- Check seeds daily
- Add water using dropper
- Once roots start to grow measure angle of growth daily with protractor
- ‘Down’ = 0°, left = 90°, up = 180°, right = 270°
What does ABA do in plants cells besides closing stomatas? (linked to fruit development)
- ABA (is a hormone) that regulates the expression of genes that matures fruit and causes abscission (fruit to drop off)
- ABA increases while the fruit is maturing, causing some fruit to drop off
