B1B edexcel

Biology topic 3 and 4 summary 

HideShow resource information
  • Created by: Dementia
  • Created on: 13-11-11 22:50

Nervous System

Stimulus: a change in environment which you may need to react to

Receptors: groups of cells which are sensitive to a stimulus (they change the stimulus energy from light energy to electrical impulses)

5 senses: eyes, ears, nose, tongue and skin: contain different receptors

When a stimulus is detected by receptors in the sense organs information is sent through electrical impulses along the neurones to the CNS.

CNS contains brain and spinal cord only + peripheral nervous system (PNS) = all the nerves going into and out of the CNS. The gaps between the neurones are synapses.

CNS co ordinates the response to the stimulus + sends instructions along various neurones to the effectors (muscle and gland) to respond

Stimulus, receptor, sensory neurone, spinal cord, brain, spinal cord, motor neurone, effecter, response

1 of 11


Cerebrum: Memory and Thinking (the largest part of the brain)

Cerebellum: Movement and the senses are at the back of the brain

·         A stroke is when the brain has poor oxygen and dies (often by blood clot). Consists of loss in brain functioning and sufferers lose some control of one side of their body. 

·         Tumours form when cells grow uncontrollably, some are cancerous and can spread to other organsSymptoms depend on its size and location, and treatment is with drugs and surgery

·         Parkinson’s disease is due to loss of neurones in the brain which controls movement. Causes lack of muscle control: shaking, stiff muscles and slow movements. Drugs can help control disease.

·         Epilepsy is when an area of the brain becomes excited when it shouldn’t.  The most serious type of this is grand mal epilepsy is when they get epileptic fits and lose consciousness and convulse- muscles contract randomly. Can be controlled with drugs or sometimes surgery. 

2 of 11

Voluntary and reflex actions

Voluntary responses – the conscious part of your brain can make decisions quickly and electrical impulses travel along the neurones

Involuntary reflexes are faster because you don’t have to think about it + they are automatic

Reflex actions save you from injuries

Receptors, sensory neurone, spinal cord, relay neurone, motor neurone, effecter, and response

Reaction Time: how quickly you respond to a stimulus

3 of 11

Examples of Reflex Actions

Iris reflex: In bright light the pupil is smaller because the circular muscle contracts, in the dim light pupil is larger as the radial muscle contracts

This happens because the light damages the retina so an involuntary reflex takes place

Accommodation: brain works out whether it’s a distant or close object

To look at distant objects the ciliary muscles relaxes + the suspensory ligaments tighten = lens goes thin

Near objects the ciliary muscle contracts which loosens the sensory ligaments = thicken lens

4 of 11


Red blood cells (RBC) carry oxygen from the lungs to all the cells in the body. They have a doughnut shape to give them a large surface area for absorbing oxygen. RBC contains a substance called haemoglobin which contains lots of iron, this combines with oxygen to create oxyhaemoglobin. In the body tissues the reverse happens to release oxygen to the cells. RBC’s don’t have a nucleus so there’s enough space for the haemoglobin. A lack of iron in a diet could lead to a type of anaemia, where blood can’t carry enough oxygen.  

White blood cells (WBC) can change shape according to the unwanted microorganisms to destroy it. WBC produces antibodies to fight microorganisms and antitoxins to neutralise any toxins created by microbes. A low number of WBC could increase the risk of getting an infection but a high number could mean you have an infection, or even leukaemia (cancer of WBC). 

5 of 11

Blood 2

Platelets are small fragments of cells which help blood clot. To stop all your blood pouring out, the platelets help the blood clot at the wound + to stop microbes getting in. Lack of platelets can cause excessive bleeding and bruising.

Plasma is a pale yellow liquid that carries everything in the blood: Red and white blood cells + platelets, Nutrients like glucose and amino acids (absorbed from the gut + taken to the body cells), CO2- waste product formed in every cell which is transported in the blood to the lungs where it’s removed, Urea- a waste product formed in the liver (blood transports it to the kidney to be removed), also carries hormones and Antibodies + Antitoxins.

6 of 11


Hormones: Chemical messengers which travel in the blood to activate target cells. Hormones are chemicals produced in various glands (called endocrine glands). They are released directly into the blood; the blood then carries them to other parts of the body. The target cells (affected cells) have the right receptors to respond to that hormone. Hormones travel at the speed of blood and have long-lasting effects. 

Insulin: helps control blood sugar levels – produced in the pancreas

Oestrogen + Progesterone: help control the menstrual cycle and produced in the women’s ovaries

Hormones and nerves do very similar jobs but have their differences:

Nerves: very fast message, Act for a very short time, Acts on a very precise area and electrical message

Hormones: Slower message, Acts for a long time, Acts in a more general way and a chemical message

7 of 11

Insulin & Diabetes

Diabetes type 1 is a disease in which the pancreas doesn’t produce enough insulin (insulin reduces blood sugar level). The result is that a person’s blood sugar can rise to a level that can kill them. The problem can be controlled in two ways:

1) Avoiding food rich in carbohydrates and

2) Injecting Insulin into the blood at mealtimes. This will make the liver remove the glucose as soon as it reaches the blood from the gut, when the food is digesting. However, the person must make sure they eat sensibly after injecting as their blood sugar could drop dangerously.

Insulin used by diabetics used to come from cows and pigs when they were slaughtered: insulin was extracted from their pancreas and purified. They can’t produce enough insulin, to keep up with the demand and it’s also not quite the same as the human form, which means the immune system often attacks it. So bacteria are now genetically modified to include human insulin gene, producing a pure form of human insulin which isn’t rejected by the immune system.    

8 of 11

The Menstrual Cycle

Stage 1: Day 1 is when the bleeding starts & the uterus lining breaks down for four days.

Stage 2: The uterus builds into a thick spongy layer of blood vessels ready to receive fertilized egg.

Stage 3: Egg is developed and released

Stage 4: The wall is maintained for about 14 days. If no fertilized egg has landed on the uterus wall by day 28 the lining breaks down again.

Oestrogen and Progesterone

Oestrogen: causes the lining of the uterus to thicken and grow and it stimulates the release of the egg on day 14.

Progesterone: Maintains the lining of the uterus. When the level of progesterone falls, the lining breaks down.

9 of 11

Hormones & Fertility

Hormones are used to stop egg production in the ‘pill’. The pill contains both progesterone and oestrogen which acts by inhibiting the production of another hormone called LH (luteinizing hormone), the hormone which stimulates the release of an egg. If there’s no egg released, there’s no egg to be fertilized = no pregnancy.

Some women are infertile because they have low levels of hormone called FSH (Follicle stimulating hormone) which stimulates the ovaries to produce eggs. This can be taken to increase egg production in their ovaries. This also produces oestrogen which causes eggs to be released. But you have to take cautions of the dosage as you could get multiple births.

10 of 11

Hormones & Fertility

IVF (In Vitro Fertilization) is a treatment for couples who find it difficult to conceive. The process is the same as natural fertilization but it’s done outside the body. Sperm taken from the man is used to fertilize egg taken from the woman (fertility drugs). The embryo is then implanted back into the women. More than one embryo is usually implanted for a better chance of success.

Some people dislike this treatment as it’s not natural. IVF can cause health problems or discomfort for the woman. Multiple births are risky for the mother and babies and there’s a high risk of miscarriage. IVF makes it possible for women past natural age to give birth. However, children born to older mother are likely to suffer from a genetic disorder: Down syndrome. IVF means same-sex couples can have a baby with the help of donors or surrogate mother. Some people say this is unnatural and could cause psychological problems for the child. Many embryos are discarded during this process which is considered murder by some people.             

11 of 11


No comments have yet been made

Similar Biology resources:

See all Biology resources »