B1- Biology- B2.1 - B2.7 (Coordination and Control)

Key Points

• The nervous systems use electrical impulses to allow you to react quickly to your surroundings and co-ordinate what you do.
• Cells called receptors detect stimuli (Changes in the environment)
• Like all animal cells, light receptor cells have a nucleus, cytoplasm and cell membrane
• Impulses from receptors pass along sensory neurons to the brain or spinal cord (CNS). Impulses are sent along motor neurons from the brain (CNS) to the efector organs.

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Sense organs detect stimuli

• You have 5 sense organs (Eyes, ears, nose, tounges and skin)
• They all contain different receptors. Receptors are a group of cells which are sensitive to a stimulus. They change stimulus energy (light energy) to electrical impulses
• A stimulus can be light, sound, pressure, pain,chemical, change in position/ tempratur

CNS- Is where all the information from the sense organs is sent and where reflexes and actions are coordinated. It consists of the brain and the spinal cord only. Neurones (nerve cells) transmit the information (as electrical impulses) very quickly to and from the CNS. Instructions from the CNS are sent to the effectors (muscles and glands) which respond accordingly

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Examiners Tip

Make sure you are clear that 'motor' means movement. 'Motor' means movement. 'Motor neurons' stimulate the muscles to contract.

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Examiners Tip 2

Be careful to use the terms neuron and nerve correctly

Talk about impulses (not messages) travelling along a neuron

Key Points

• Some responses to stimuli are automatic and rapid and area called 'refex actions.'
• Reflex actions run everyday bodily functions to help avoid danger`
• Neurons transmit information very quickly to and from the brain and you brain decides how to respond to a stimulus. But reflexes are quicker

Synapses connect Neurones

• The connection between two neurones is called a synapse
• The nerve signal is transferred by chemicals which diffuse across the gap
• Those chemicals then set off a new electrical signal in the next neurone

Reflexes help prevent injury

• Reflexes are automatic responses to a certain stimuli. They help reduce the chance of injury
• For example, if someone shines a bright light at you, your pupils get smaller to reduce the light entering the eye to prevent damage 
• Or if you get a shock, your body automatically releases the hormone adreneline before you can decide if you are shocked or not

Most reflex actions can be shown as follows:

• Stimulus -> Receptor -> Coordinator -> Effector -> Response
• Stimulus -> Receptor -> Sensory Neuron -> Relay Neuron -> Motor Neuron -> Effector -> Response

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Examiner's Tip

Make sure you know the correct sequence of links from the receptor to the effecctor

Key Points

• Hormones control the release of an egg from the ovary and the build-up of the lining of the womb in the menstural cycle.
• Some of the hormones involved are FSH from the pituitary gland and oestrogen from the ovary

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Hormones are chemical which travel in the blood to activate target cells (Learn this)

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• Hormones are chemicals released directly into the blood. They are carried in blood plasma to other parts of the body, but only affect paticular cells (target cells) in particular places. Hormones control things in organs and cells that need constant adjustment
• Hormones are produced in and secreted by various glands. 
• The Pituitary Gland- Produces many important hormones including FSH and LH which are involved in the menstural cycle
• Ovaries- Produce Oestrogen, which is involved in the menstural cycle.

Hormones and nerves do similar jobs, but there are differences

• Nerves- Very fast action, Act for a short time on a preicise area
• Hormones- Slower action, Act for a longer time in a more general way

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Is it hormonal or nervous?

• If the response is really quick, its probably nervous. Some information needs to be passed to effectors quickly, so its no good using hormones as they're too slow
• But if the response lasts for a long time its probably hormonal. For example, if you're shocked the hormone adreneline is released. You can tell its a hormonal response because you feel a bit wobbly afterwards

The Menstural Cycle- Monthy release of an egg from a womans ovaries, and the build up and breakdown of lining in the uterus

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The Menstural Cycle has 4 stages

• Stage 1- Day 1 is where the bleeding starts. The uterus lining breaks down for about 4 days
• Stage 2- The lining in the uterus builds up again from day 4 to day 14, into a thick spongy layer full of blood vessels, ready to recieve a fertilised egg.
• Stage 3- An egg is released from the ovary at day 14
• Stage 4- The wall is then maintained for about 14 days, until day 28. If no fertilised egg has landed on the uterus wall by day 28, the spongy lining starts to break down again and the whole cycle starts again.

Hormones control different stages- There are 3 main hormones involved: (Progesterone is also involved in the menstrual cycle

FSH (Follicle-Stimulating Homone)

• Produced by the Pituitary Gland
• Causes an egg to mature in the ovaries
• Stimulates the production of oestrogen in the ovaries

Oestrogen

• Produced in the ovaries
• Causes the pituitary to produce LH
• Inhibits the production of FSH
• Stimulates the release of a mature egg

LH (Luteninising Hormone)

• Produced by the pituiary gland
• Stimulates the release of an egg at around the middle of the menstural cycle

Key Points

• Hormones can be used to control fertility
• Oral contraceptives contain hormones, which stop FSH production so no eggs mature
• FSH can be used as a fertility drug for women, to stimulate eggs to mature in their ovaries. These eggs may be used in IVF treatments.

Hormones can be used to reduce fertility

• Oestrogen can be used to prevent the relase of an egg. - So it can be used as a method of contraception.
• Its sort of strange as oestrogen is normally used to stimulate the release of and egg. But if oestrogen is taken every day to keep the level permanently high, it inhibits the production of FSH and after a while, egg development and production stop and stay stopped
• Progesterone also reduces fertility by stimulating the production of thick cervical mucus which prevents sperm getting through to the egg
• The pill is an oral contraceptive first introduced in the 1950s and contained high oestrogen and progesterone levels.- Known as the combined oral contraceptive pill
• There were concerns with links between oestrogen and blood clots, so lower doses are now taken to lower the risk

Pros of the Pill

• Over 99% effective
• Reduced the risk of some types of cancer

Cons of the Pill

• Isnt 100% effective. Still a small chance of getting pregnant
• Side effects- Head ache, nausea, irregular bleeding
• Doesnt protect against STI's

FSH

Some women have levels of FSH to low to mature eggs. So no eggs are released and the woman cant get pregnant. The hormone FSH and LH can be injected to stimulate egg release in ovaries

Pros of FSH- Helps women get pregnant

Cons of FSH- Doesnt always work, have to have it done many times- expensive. Too many eggs could be stimulated- unwanted multiple pregnancys

IVF

Involved collecting eggs from the ovaries and fertilising them in a lab using the mans sperm. They are grown into embryos. Once the embryos are tiny balls of cells. one or two of them are transferred to the womans uterus to improve pregnancy chance. FSH and LH are given before hand to stimulate egg production. (So more than one egg can be collected)

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Pros of IVF

• Can give an infertile couple a child

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Cons of IVF

• Some women have bad reactions to the hormones- Vomitting, nausea, abdominal pain
• Increased risk of cancer
• Multiple births can happen

Key Points

• Plants are sensitive to light, moisture and gravity
• Plants response are brought about by plant hormones (Auxin)
• The responses of roots and shoots to stimuli are brought about by light and gravityare the results of unequal distribution of plant hormones
• We can use plant hormones as weed killers and as rooting hormones on cuttings
• Photropism is a plants response to light

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Auxin is a plant growth hormone

• It controls growth near the tips of shoots and roots
• Controls growth of a plant in response to light (phototrpism)
• Auxin is produced in the tips and moves backwards to stimulate cell elongation
• If the tip of the plant is removed, no auxin is avaliable and the shoot may stop growing
• Extra auxin promotes growth in the shoots but inhibits growth in the root- producing the desired results

• Shoots grow towards the light
• Shoots grow away from gravity- If a shoot grows sideways the auxins are on the lower side and therefore the tip grows upwards
• Roots grow towards gravity- If a root grows sideways it has more auxins on the lower side. Root bends downwards
• Roots grow towards moisture- More auxins are produced on the side with more misture. Roots bend towards the moisture

Homeostatsis- Constant internal environment

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Your body needs some things to be kept constant. For certain things to work properly you must keep things at the right level. Here are the bodily levels that need to be controlled

• Ion Content- Regulated by the kidneys
• Water Content- Lost through skin as sweat, lungs in breath, kidneys as urine
• Sugar Content- Insulin is released to maintain the right level of glucose
• Temprature- Controlled by the brain