Negative Feedback + Plants

Question 1

Where are the adrenal glands located

Answer 1

The adrenal glands are located at the top of the kidneys

Question 2

When is adrenaline produced

Answer 2

During times of fear or stress the adrenal glands produce the hormone adrenaline.
The adrenaline is released into the blood

Question 3

What are the main effects of adrenaline

Answer 3

One of the main effects of adrenaline is to increase the heart rate.

Question 4

Explain why one of the main effects of adrenaline is to increase the heart rate

Answer 4

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’

Question 5

Where is the thyroid gland found

Answer 5

The thyroid gland is found in the base of the neck

Question 6

What hormone does the thyroid gland release

Answer 6

The thyroid gland releases the hormone thyroxine

Question 7

Two main effects of thryoxine

Answer 7

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

Question 8

How is the level of thyroxine in the blood controlled

Answer 8

The level of thyroxine in the blood is controlled by negative feedback

Question 9

Describe how the levels of thyroxine in the blood are controlled (negative feedback loop)

Answer 9

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

Question 10

examples of negative feedback cycles in the body

Answer 10

In the control of blood glucose
Menstrual cycle
Control of body temperature

Question 11

What is phototropism

Answer 11

Plants produce hormones to coordinate and control growth and responses to light

(THE RESPONSE OF A PLANT TO LIGHT, CONTROLLED BY AUXIN)

Question 12

What is phototropism caused by

Answer 12

Unequal distributions of auxin which cause unequal growth rates in plant roots and shoots.

Question 13

Describe the experiments scientists carried out to find out how phototropism works

Answer 13

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

Question 14

Where do plant shoots grow towards

Answer 14

Plant shoots grow towards the light (an away from gravity)

Question 15

What hormone do shoots use to help them grow towards the light

Answer 15

shoots use the hormone auxin to grow towards the light

Question 16

How do shoots use the hormone auxin to grow towards the light

Describe how plants use hormones to respond to light

Answer 16

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

____________________
Unequal distributions of auxin cause unequal growth rates in plant roots and shoots.

Question 17

Where do plant roots grow towards

Answer 17

Plant roots grow towards the force of gravity (called gravitropism or geotropism)

Question 18

What is gravitropism (or geotropism)

Answer 18

The response of a plant to gravity

Question 19

What hormone do roots use to help them grow towards gravity

Answer 19

plant roots use the hormone auxin to
grow towards the force of gravity

Question 20

Describe how plants use hormones to respond to gravity
How do roots use the hormone auxin to grow towards the force of gravity

Answer 20

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

_________________________
Unequal distributions of auxin cause unequal growth rates in plant roots and shoots.

Question 21

Name other chemicals (apart from auxin) plants use to regulate their behaviour

Answer 21

Ethene
Gibberellins (HORMONE)

Question 22

Describe the role of gibberellins

Answer 22

Gibberellins are important in starting the germination of seeds

Gibberellins are important in initiating seed germination.

Question 23

Describe the role of ethene

Answer 23

The chemical ethene controls cell division and the ripening of fruits

Question 24

Where are plant hormones used in:

Answer 24

Plant growth hormones are used in agriculture and horticulture.

Question 25

Uses of auxins (in agriculture (growing food crops) and horticulture (growing plants for gardens)

Answer 25

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

Question 26

Uses of gibberellins (in agriculture (growing food crops) and horticulture (growing plants for gardens)

Answer 26

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

Question 27

Where is the chemical ethene used a lot in

Answer 27

The chemical ethene is used a lot in the food industry

Question 28

Uses of the chemical ethene

Answer 28

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.)

Question 29

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

Answer 29

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

Question 30

Describe the results for this experiment (Describe how to investigate the effect of light intensity on the height of seedlings)

Answer 30

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

Question 31

Describe how to investigate the effect of gravity on seedlings

Answer 31

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

__________________________________

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

Question 32

https://bam.files.bbci.co.uk/bam/live/content/zsrcmsg/medium
Describe and explain what has happened

Answer 32

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

Question 33

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

Answer 33

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