Key facts about co-ordination and control
The nervous system, made up of the brain and spinal cord, coordinates responses to stimuli by sending nerve impulses between receptors and effectors.
Reflex actions are rapid, automatic responses that follow a short pathway through the spinal cord without conscious thought to protect the body.
Hormones are chemical messengers carried in the blood that act more slowly than the nervous system but have longer-lasting effects.
Blood glucose levels are controlled by insulin, and problems with this system can lead to diabetes and long-term health complications.
The nervous system
The brain and The part of central nervous system of a mammal which runs inside its backbone form the central nervous system (CNS).
The CNS controls and coordinates responses between Organ, tissue or cell that detects a stimulus. and The organ, tissue or cell that produces a response..
- Stimuli are changes in our environment that we respond to and are detected by receptors.
- A nerve cell/neurone carries information in the form of nerve impulses from the receptor to the coordinator.
- The coordinator – brain or spinal cord – determines whether or not to respond to the stimulus.
- A neurone carries information from the The central nervous system, it determines the correct response to a stimulus. to an effector.
- An effector is a muscle or gland that can bring about a response.
Reflex actions
Voluntary actions require conscious thought and take more time due to thinking.
Reflex actions happen quickly without conscious thought, protecting the body from harm, for example, pulling your hand away from a hot surface.
Reflex arc
A reflex action is fast because it follows a short pathway with only three neurones and two synapses:
- Sensory neurone: carries impulse from the receptor to the spinal cord (coordinator).
- Association neurone: connects the sensory neurone to the motor neurone.
- Motor neurone: sends impulses from the spinal cord to an effector (muscle or gland) to cause a response.
A synapse is the gap between two neurones. There is one between the sensory and association neurones and one between the association and motor neurones.
Watch: Explaining reflex actions and voluntary actions
What are hormones?
Hormones are chemical messengers.
They are:
- released by glands
- travel in the blood
- carried to target organ or organs
Compared to the nervous system, hormones are much slower and act over a longer period – sex hormones such as testosterone and oestrogen act over years.
An example of a human hormone is:
- Insulin – controlling blood glucose concentrations
How does insulin work?
After eating a meal, blood glucose levels increase.
Pancreas monitors blood glucose concentration.
Pancreas produces insulin in response to increasing blood glucose concentration.
Insulin causes the liver to reduce blood glucose concentration by:
- increasing glucose absorption from the blood
- respiring the absorbed glucose
- converting excess glucose to glycogen which is stored in the liver and muscles
Diabetes
Diabetes occurs when someone cannot control their blood glucose levels.
This happens because they either don’t produce enough insulin or none at all.
Symptoms:
- glucose in the urine – blood glucose concentration is so high that some is filtered out by the kidneys and passed into the urine
- high blood glucose levels
- being thirsty
- the need to go to the toilet a lot
- lethargy – feeling tired / having low energy
What are the differences between Type 1 and Type 2 diabetes?
| Type 1 diabetes | Type 2 diabetes | |
|---|---|---|
| Develops | develops usually early in life | a progressive disease linked to poor diet/lack of exercise/obesity |
| Effect | pancreas stops producing insulin | pancreas gradually produces less insulin |
| Treatment | insulin injections / diet - reduce carbohydrate intake | diet - reduce carbohydrate intake / increase exercise to lose weight / insulin injections |
What are the long term effects of diabetes?
- eye damage/blindness
- heart disease
- stroke
- kidney damage
These complications are due to high blood glucose concentrations damaging the capillaries that supply that part of the body.
Why is the number of people with Type 2 diabetes increasing?
- Obesity: poor diet and less exercise lead to weight gain, which raises the risk of Type 2 diabetes.
- Aging population: older people are more likely to develop Type 2 diabetes.
- Less activity: modern, less active lifestyles contribute to the problem.
- Better diagnosis: better awareness and improved medical testing so more people being diagnosed.
- Genetics predisposition: family history makes some people more likely to get Type 2 diabetes.
Plant hormones
Plants need to respond to the world around them just like we do, and for them, two of the most important things are gravity and light.
They need to figure out which way is up and which is down, and they need to know where the light is so they can photosynthesise. So how do they do that?
Well, mainly they use hormones. In particular, a group of plant hormones called auxins.
Auxin controls growth in the meristems near the tips of the shoots and roots causing shoot cells to grow more and root cells to grow less.
So… the pattern of auxin distribution around the plant is really going to change the way it grows.
If a plant tip had loads of auxin on the left side and hardly any on the right, the left side would grow way more than the right and we'd end up with a very lopsided plant.
It looks weird but it does happen, and it's a really important process.
Plants need to respond differently to light depending on where it’s coming from to help them maximise photosynthesis.
When light falls evenly on the shoot, the auxin spreads evenly through the shoot tip – and it grows steadily up.
But when a shoot tip is exposed to light from just one side auxin diffuses away from the light to the shady side.
So the cells on the shady side elongate and grow faster, and the shoot grows towards the light.
This response is called positive phototropism.
You get the opposite, negative phototropism too - think of the roots, they're negatively phototropic because they grow away from light.
The other major factor that determines how plants organise their growth is, of course, gravity…
When a root starts to grow out of a seed it needs to turn down WHICHEVER way the seed’s been planted…
How does it do it? Yep you bet, auxin.
The auxin sinks to the lower side of the root in response to gravity
But remember, auxin in roots slows down the rate of growth – so the cells on the lower side grow more slowly and this creates a downward bend, which, if you're a root, is just the sort of bend you want.
If a shoot starts growing sideways, gravity again causes an unequal distribution of auxin with more on the lower side of the tip.
This has the opposite effect to the roots, making the cells grow faster and bending the shoot upward.
The way plants respond to gravity is called 'gravitropism'.
Roots are positively gravitropic so they grow downwards, and shoots are the opposite - negatively gravitropic.
Auxin is really important in another way too it affects the overall shape of the plant.
See, it's essential that the central shoot grows more quickly, and stays stronger, than the side branches that grow out of it.
And that's all down to good old auxin.
Plant growth and development is controlled by plant hormones.
Auxin is a plant hormone that causes shoots to grow towards light. This is known as The response of a plant to light..
Phototropism
- Plant responds to unidirectional light (eg plant on a windowsill)
- Plant shoot bends towards light
- Advantage of this response: - more light – more Chemical reaction that happens in plant cells. It converts carbon dioxide and water into glucose and oxygen in the presence of light. The glucose can then be used for a number of processes including growth. - more growth
How does a shoot bend towards unidirectional light?
- Plant hormones that control cell elongation. is produced at the tip of the shoot and moves down the shoot.
- Light coming from one side causes the uneven distribution of auxin – more on the shaded side.
- Auxin causes cells on the shaded side to elongate faster – this is known as differential growth.
- This causes the stem to bend towards light.
Test your knowledge
More on Body systems
Find out more by working through a topic
- count2 of 2
