Negative Feedback + Plants Flashcards
Where are the adrenal glands located
The adrenal glands are located at the top of the kidneys
When is adrenaline produced
During times of fear or stress the adrenal glands produce the hormone adrenaline.
The adrenaline is released into the blood
What are the main effects of adrenaline
One of the main effects of adrenaline is to increase the heart rate.
Explain why one of the main effects of adrenaline is to increase the heart rate
Because the heart is beating faster, more oxygen and glucose are delivered in the blood to the brain and muscles
Both oxygen and glucose are needed for aerobic respiration
This prepares the body to either fight or run away (for ‘fight’ or ‘flight’)
This is called ‘fight’ or ‘flight’
Where is the thyroid gland found
The thyroid gland is found in the base of the neck
What hormone does the thyroid gland release
The thyroid gland releases the hormone thyroxine
Two main effects of thryoxine
Thyroxine stimulates the body’s basal metabolic rate. (metabolism is the sum of all the reactions in a cell or the body)
–> Thyroxine makes the body’s chemical reactions take place at a faster rate
Thyroxine plays an important role in growth and in development
How is the level of thyroxine in the blood controlled
The level of thyroxine in the blood is controlled by negative feedback
Describe how the levels of thyroxine in the blood are controlled (negative feedback loop)
The level of thyroxine in the blood is monitored by the brain
When the thyroxine level falls, this is detected by the brain. The pituitary gland releases the hormone TSH into the bloodstream
TSH triggers the thyroid gland to release more thyroxine into the blood
The increased level of thyroxine is now detected by the brain
This now prevents the pituitary gland from releasing TSH
As the TSH level falls, the thyroid gland releases less thyroxine
–) If the level of thyroxine falls, events are triggered which cause the level of thyroxine to increase
If the level of thyroxine becomes too high, events are triggered to bring it back down
This is called a negative feedback cycle
examples of negative feedback cycles in the body
In the control of blood glucose
Menstrual cycle
Control of body temperature
What is phototropism
Plants produce hormones to coordinate and control growth and responses to light
(THE RESPONSE OF A PLANT TO LIGHT, CONTROLLED BY AUXIN)
What is phototropism caused by
Unequal distributions of auxin which cause unequal growth rates in plant roots and shoots.
Describe the experiments scientists carried out to find out how phototropism works
Get some plant shoots.
Shine light from one side only.
The shoots grow towards the light
Scientists wondered whether this is controlled by hormones
First the scientists removed the very tips of the shoots
They found that now the shoots did not grow towards the light
Scientists suggested that shoot tips produce a plant hormone. This hormone is called auxin.
The scientists then covered the tips of the shoots with foil to block out the light
The shoots did not grow towards the light. This tells us that the tips are sensitive to light
The scientists then used foil to cover the lower parts of the shoots
In this case, the shoots grew towards the light as normal.
This tells us that the lower parts of shoots are not sensitive to light
Where do plant shoots grow towards
Plant shoots grow towards the light (an away from gravity)
What hormone do shoots use to help them grow towards the light
shoots use the hormone auxin to grow towards the light
How do shoots use the hormone auxin to grow towards the light
Describe how plants use hormones to respond to light
The hormone, auxin is produced at the very tip of the shoot
In shoots, auxin triggers (stimulates) cell growth
Light causes auxin to concentrate on the darker side of the shoot tip
Auxin now spreads down the shoot
Cells on the darker side grow faster than cells on the lighter side
This causes the shoot to grow towards the light
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Unequal distributions of auxin cause unequal growth rates in plant roots and shoots.
Where do plant roots grow towards
Plant roots grow towards the force of gravity (called gravitropism or geotropism)
What is gravitropism (or geotropism)
The response of a plant to gravity
What hormone do roots use to help them grow towards gravity
plant roots use the hormone auxin to
grow towards the force of gravity
Describe how plants use hormones to respond to gravity
How do roots use the hormone auxin to grow towards the force of gravity
The hormone auxin is produced in the root but gravity causes the auxin to concentrate on the lower side
In roots, auxin inhibits cell growth
So the lower side now grows more slowly than the upper side
This causes the roots to grow towards the force of gravity
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Unequal distributions of auxin cause unequal growth rates in plant roots and shoots.
Name other chemicals (apart from auxin) plants use to regulate their behaviour
Ethene
Gibberellins (HORMONE)
Describe the role of gibberellins
Gibberellins are important in starting the germination of seeds
Gibberellins are important in initiating seed germination.
Describe the role of ethene
The chemical ethene controls cell division and the ripening of fruits
Where are plant hormones used in:
Plant growth hormones are used in agriculture and horticulture.
Uses of auxins (in agriculture (growing food crops) and horticulture (growing plants for gardens)
Auxins are used as weedkillers for example in gardens
Auxins are used as rooting powders
Auxin is used for promoting cell growth in tissue culture
Uses of gibberellins (in agriculture (growing food crops) and horticulture (growing plants for gardens)
Gibberellins can be used to end seed dormancy (they can force a seed to germinate earlier than it normally would)
Gibberellins can also be used to encourage plants to flower
Gibberellins can be used to make fruit grow larger
Where is the chemical ethene used a lot in
The chemical ethene is used a lot in the food industry
Uses of the chemical ethene
Ethene is used in the food industry to control ripening of fruit during storage and transport
e.g. fruits such as bananas are usually harvested before they are ripe
These are then transported long distances and can be stored before they are needed
Ethene is then used to trigger (stimulate) the bananas to ripen just before they are sold in the UK.
or
Chemicals which block ethene’s effect on fruit can be used to delay ripening while the fruit is in storage. Chemicals can also be used which remove ethene from the air. (ethene is a gas which is produced by aging parts of the plant. It influences the growth of the plant by controlling cell division and stimulates enzymes which causes fruit to ripen.)
Describe how to investigate the effect of light intensity on the height of seedlings
Describe how to investigate the effect of light or gravity on the growth of newly germinated seedlings
The independent variable is the light intensity
The dependent variable is the height of the seedlings
First place cotton wool in three petri dishes and then soak them with equal volumes of water
The volume of water is a control variable
Then place ten mustard seeds in each dish
Another control variable is the type of seed
Next we leave the dishes in a warm place and allow the seeds to germinate
Ensure that the seeds are watered every day with the same volume of water
After a few days, the seeds will germinate
At this point, we need to make sure that the three dishes have the same number of seedlings
This is because the number of seedlings is another control variable
- remove any extra seeds if necessary.
(e.g. if only 8 seeds germinate in one of the dishes but ten seeds germinate in both of the other dishes. in this case we need to remove two seedlings from the dishes (which are in the same respective position) which contain ten seedlings, so that all three dishes now contain eight seedlings.
Next use a ruler to measure the height of each seedling
We need to hold the stems to make sure that they are straight - to ensure measurements are accurate
However, we need to be careful not to damage the seedlings
Now we place the three dishes in different conditions
One dish is placed in full sunlight for example on a very bright window sill
One dish is placed in partial light for example at the back of the lab
One dish is placed is placed in darkness for example in a cupboard
We then measure the height of each seedling every day for at least five consecutive days and record the results in a table
When the experiment is finished, we calculate a mean seedling height for each day.
compare the mean heights in the three different locations.
Diagrams can also be drawn to show the effects of different light intensities on the seedlings
Describe the results for this experiment (Describe how to investigate the effect of light intensity on the height of seedlings)
The height of the seedling is similar for both full sunlight and partial light
That is because chlorophyll is very efficient at absorbing light energy
So plants do not need full sunlight to grow
The seedlings have grown towards the light source
This is due to phototropism
The seedlings which were in the dark have grown the longest
This is because seeds usually germinate underground and they grow rapidly to reach the light
If we keep seedlings in the dark, then they continue to grow rapidly, trying to reach the light
The leaves of the seedlings are small and yellow
That is because once the seedlings have used all their energy stores, they cannot carry out photosynthesis in the dark
Describe how to investigate the effect of gravity on seedlings
The dependent variable is the height of the seedlings
First place cotton wool in a petri dish dishes and then soak it with water
Then place ten mustard seeds in each dish
Another control variable is the type of seed
Next we leave the dishes in a warm place and allow the seeds to germinate
Ensure that the seeds are watered every day with the same volume of water
After a few days, the seeds will germinate
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In this case, a dish of seedlings is placed on its side in the dark.
(In the dark so that light doesn’t have an effect on the direction in which the seedlings grow)
(on its side because if they were placed normally (and not on their side, with the roots down), we wouldn’t be able to know if the roots have grown downwards because of gravitropism or because they were already pointing down in the first place)
To know whether the roots have grown in the particular direction due to gravity or because they were like to start off with.
The seeds have grown upwards, against the direction of gravity and the roots have grown downwards towards the direction of gravity
This is due to gravitropism
https://bam.files.bbci.co.uk/bam/live/content/zsrcmsg/medium
Describe and explain what has happened
Seedling A
The tips have been removed
No auxin is produced
The stems do not grow longer
No light reaches the tips
Equal concentration of auxin on both sides
The stems grow evenly and longer on both sides
More light reaches one side of the tips
Greater concentration of auxin on the shaded side
The cells on the darker side of the stems grow longer, causing the plant to grow towards the light
Control variables for experiment
Describe how to investigate the effect of light intensity on the height of seedlings
Describe how to investigate the effect of light or gravity on the growth of newly germinated seedlings
Number of seeds - use the same number of seeds in each dish
Type of seed - use seeds that all come from the same packet
temperature - keep your petri dishes in a place where the temperature is stable (i.e. away from heat sources and draughts)
- the temperature they are kept at
water - use a measuring cylinder to add the same amount of water for each dish
the amount of water in the cotton/soil
