Kwashiorkor
Many protein rich foods are expensive. Protein deficiency is common in developing countries such as Ghana and Sudan because:
- There are food shortages
- There is little rain – bad crops
- They are over-populated
- There are few animals
- There is a limited investment in agricultural techniques
- There are very few jobs and those which are available have low wages
- Any animals that they have may die out – no medication or vets
Protein deficiency is called Kwashiorkor. It is particularly dangerous for children because they would die quicker because they need so much more protein and the mother stops producing it in her breast milk due to famine and lack of protein for her body.
Children with Kwashiorkor are short and underweight. They may look fat as they have swollen abdomens due to fluid accumulation. They are weak as their muscles are under developed.
Obesity and Anorexia
When we eat too much energy containing foods we get heavier and become mal-nourished because we are getting too much of something and this is not a balance.
When we eat too little we lose weight but gain weight in the long run and we become mal-nourished because we are getting too little of something and this is not a balance.
If we eat as much energy as we use up, we don’t gain or lose weight.
Obesity
This is a type of mal-nourishment. It increases the risk of:
- Arthritis
- High blood pressure
- Type 2 diabetes
- Heart disease
- Breast cancer
- Bowel disease
- Under active thyroid
Anorexia
Anorexic people are severely mal-nourished. They are usually weak and lethargic and anaemic. Anaemic = vitamin deficiency. They would have a short concentration span due to low brain activity. It can cause an over active thyroid.
Can be triggered by:
- Low self esteem
- Poor self image
- Desire for perfection
- Pressure from peers or media
BMI (Body Mass Index)
This can be used as a guide to check that your body weight is approximately correct. It is calculated using the formula:
BMI = Mass in kg/ (height in metres) squared
BMI is not very accurate because muscles can weigh a lot and can therefore raise the BMI. This could make the person seam obese, although they are perfectly healthy.
Malaria
Malaria is the 3rd biggest killer. It is caused by a protozoan called Plasmodium which is a parasite. Symptoms include:
- Shivering
- Sweating
- Pain in the limbs and muscles
- Feeling tired
- Anaemia – not enough minerals – feel tired
- Pale face
A parasite is an organism which lives in or on another living organism – the host.
Humans and other animals are the hosts for plasmodium.
Plasmodium lives in red blood cells and liver cells. It feeds on haemoglobin – a protein molecule with iron in it which carries oxygen around the body.
Mosquitoes are the vector for Malaria – they pass it on – causing the Plasmodium to go from one person to another.
VECTOR – carrier of pathogen from one organism to another
HOST – the living organism in which the parasite is living
PARASITE – an organism which lives in or on another living organism
Prevention of Malaria
- Tablets/ medicine e.g. quinine
- Sterilize male mosquitoes – so that they can’t reproduce
- Use mosquito nets
- Insect repellent/ insecticides – kill mosquitoes
- Wear long sleeves and trousers
Getting Malaria:
- Female anopheles mosquito bites, injecting saliva and plasmodium
- Reaches the liver and multiplies inside
- Released into blood stream where they multiply and burst red blood cells
- Travels in the blood stream, reaching every organ and slowly shutting them down
- Another non-infected mosquito can now bite and collect the plasmodium, and pass it on to someone else.
- Before it can get passed on, the plasmodium needs to mature and change inside the mosquito’s body.
Adult mosquitoes live in bushes – so if bushes are cut down, mosquitoes will have nowhere to live.
Male mosquitoes breed in stagnant waters – smelly, dirty, still waters – lakes, puddles, ponds.
After mating, the female lays eggs on the surface of any available water.
The eggs hatch into larvae which need to rise to the surface to breathe air.
In the water, the larvae change to pupae. Adults emerge from the pupae and fly off to bite people.
To prevent malaria, insect-eating fish can be released into the water to eat the eggs and children. Pouring oil onto the surface of the water means that the adults can’t emerge and they can’t breathe.
It is important to isolate people with malaria so that another mosquito can’t bite them and thus pass on malaria again.
Cancer
Cancer is a disorder which occurs when body cells continue to divide uncontrollably. A tumour is a mass of cells.
Benign tumour – stops growing and doesn’t spread – like a mole
Malignant tumour – grows quickly and can spread around the body internally
Cancer can be caused by:
- Diet
- Genetics
- Burnt food – e.g. toast
- Smoking – lung cancer
- UV light/ sun – cause mutation in DNA – skin cancer
Reduce Risks by:
- Don’t smoke and drink lots of alcohol
- Avoid sun beds
- Eat 5-a-day and have a balanced diet
The government may need to know about cancer statistics so they can make campaigns to reduce cancer patients and educated people on lifestyle. They would need to know so that they spend money on the serious types.
E.g. lung cancer has decreased because there was such a big effort to stop smoking.
E.g. melanoma (skin cancer) has increased because more people want to look tanned and wear very exposing clothes.
Examples of cancer: Breast cancer, Lung cancer, Skin cancer
Testing New Drugs
A placebo is a fake decoy drug. It looks like the drug, but doesn’t contain the active ingredient. If someone believes they are taking a drug, they can sometimes get better just because they thought they were taking medicine. – Psychology
Single-blind trial: The idea was to remove any bias the patient may have regarding their treatment. If the treatment was effective, the benefit should show up clearly in the treated group compared to the control group. The doctors knew whether the patient was taking a placebo or the drug.
It was realized the researchers could be biased too. Observer bias could lead researchers to the results that they were expecting to find.
Double-blind trial: In the double-blind trial neither the patient nor the researchers administering the treatment know who is being treated and who is in the placebo control group. Patients are randomly assigned to one of the groups independently of the researchers, and the actual treatment they receive is coded so that no one knows whether it is real or placebo. This ensures that all possible biases that could be introduced to the trial by the researchers or the patients are eliminated.
Disease
Our immune system is made up of white blood cells. There are 2 types – lymphocytes and phagocytes.
Infectious diseases are caused by the toxins that pathogens produce.
There are 4 types of pathogens:
- Protozoa - Malaria
- Virus – flu, cold, AIDS – these are all infectious – can be passed on easily
- Fungus – Athlete’s Foot
- Bacteria - TB
Cystic fibrosis, sickle-cell anaemia, Huntington’s disease – passed from parent to child – inherited disorders
Symptoms are caused when the microorganisms damage our body cells or produce toxins.
An antigen is a substance on the surface of a pathogen or a toxin that a pathogen has produced. Antibodies are chemical that go into the blood and lock themselves onto the specific antigen. Each pathogen has its own antigen; therefore the B lymphocytes take several days to produce the necessary antibodies. The B lymphocytes can become memory cells so that next time the pathogen invades, it is a quicker process. Antibodies kill bacteria and neutralize toxins. This is an immune response.
The skin is thick and strong. This makes it hard for pathogens to get through. When the skin is damaged, the blood forms a clot to seal the wound and prevent pathogens getting in.
Our stomachs protect us against bacteria because we have hydrochloric acid in our stomachs along with protein digesting enzymes which kill bacteria.
Cilia and mucus in the trachea and bronchi trap pathogens sweep them away from the lungs. White blood cells patrol the surface of the alveoli and kill any bacteria they find.
Phagocytes – they move up to the bacteria and attach themselves with specific hooks like antibodies. Then they engulf the bacteria and release an enzyme called pseudopodia which digests the bacteria and absorbs the products.
Lymphocytes – there are B and T lymphocytes. The B lymphocytes make specific antibodies to lock onto and destroy each pathogen and its toxins by neutralizing them. Some of the B cells become memory cells. The T lymphocytes produce chemicals to destroy the infected cell. The T cells activate the B cells.
Immunity
There are 2 types of immunity: active and passive.
Active Immunity – the body makes its own antibodies due to either infectious disease or vaccination.
Passive Immunity – immunity due to receiving antibodies from someone else e.g. from mother to baby via breast milk.
Passive immunity give faster protection but active immunity can protect for a lot longer.
Vaccinations
Vaccines are a small amount of dead or weakened pathogen. The antigens trigger the B cells to make antibodies and the memory cells remember them, without making the person ill. The vaccinated person is now immune to this pathogen. If the same pathogen re-infects the person, the antibodies will be produced very quickly.
Antibiotics
E.g. Amoxicillin, penicillin, streptomycin, erythromycin
Antibiotics are chemicals made by microbes which kill or stop the growth of bacteria and fungi but NOT viruses and they have no effect on protozoan.
Antibiotic Resistance – the antibiotic is no longer effective
Can be caused by:
- Taking antibiotics unnecessarily
- Not finishing the course
When treated with antibiotics:
- 95% of bacteria are killed, 5% have genetic differences because of constant mutation so they survive and reproduce
- Try a different antibiotic – same thing happens
- Eventually forms a superbug as it becomes resistant to most antibiotics e.g. MRSA
Mutation – a random spontaneous change in DNA
The Eye
We can detect changes in the environment (stimuli) by using our senses.
Our sense organs are part of our nervous system. Stimuli are detected by receptor cells in the sense organs. There are different types of receptor cells e.g. for pain, temperature etc.
Information from our sense organs is taken to the central nervous system by nerve cells called neurons.
1. The eye is the sensory organ of sight and responds to light.
- Circular muscle contracted
Radial and circular muscles are antagonistic. When one is relaxed, the other is contracted and vice versa.
Monocular and Binocular Vision
Focusing and Accommodation
The light needs to come into focus on the retina for us to be able to see clearly.
The cornea does most of the refraction; the lens just does the fine focusing.
When we look at a close object, the lens is thick. The ciliary muscles are contracted and the suspensory ligaments are relaxed. When we look at a distant object, the lens is thin. The ciliary muscles are relaxed and the suspensory ligaments are contracted.
When the lens is thick it refracts more light than when it is thin. It changes shape using the suspensory ligaments and ciliary muscles.
Focusing the Light
- The light rays are refracted as they pass into the eye
- The cornea’s curved shape means it acts like a convex lens, refracting the light inwards.
-
The image on the retina is upside down because the light rays crossed over on the way into the eye. The brain sees the image the right way up.
Eye defects
Short-sightedness: you can see close object clearly, but objects at a distance are blurry.
- Light rays come to focus before the retina – eyeball too long/ lens too thick
- Can be corrected by wearing a concave lens so that the light rays are diverging
Long sightedness: you can see distant objects clearly but close objects are blurry.
- Light rays come to focus behind the retina – eyeball too short/ lens too thin
- Can be corrected by wearing a convex lens so that the light rays are converging
As we age, our lenses become less elastic. They can’t stretch and relax as easily as they used to. Elderly people often have problems focusing on distant and close objects.
Long and short sightedness can be corrected by:
- Corneal surgery – re-shape the surface of the cornea with a laser to allow light to focus well
- Different lenses in glasses – concave for short sightedness and convex for long sightedness
- Contact lenses – same as glasses but without the frame
Testing Vision
We use a Snellen chart to test our sight.
Colour blindness: there are several types of light receptor cells in the retina:
- Some are called RODS – for seeing in the dark – sensitive to dim light
- Some are called CONES – for seeing colours – sensitive to bright light
- There are 3 cones – one red, blue and green – primary colours in light
Some people only have 2 types of cones. They have red-green colour blindness which is an inherited condition.
The Nervous System
The central nervous system (CNS) consists of the brain and spinal cord. It is very well protected.
The peripheral nervous system (PNS) connects all the body parts to the CNS – limbs etc.
Nerve cells are called neurones. Lots of neurones group together to form nerves. Nerves carry electrical impulses around the body to and from the CNS.
Neurones are specialised cells. They are adapted to carry electrical impulses very fast. They are very long and have an insulating layer (myelin sheath). They have branched endings called dendrites.
Neurones – carry information between receptors, CNS and effectors
Effectors – muscles and glands
Myelin Sheath – insulates the neurone from neighbouring cells and increases the speed of transmission of a nerve impulse.
Sensory neurones – carry electrical impulses from receptors to the CNS. The cell body in a sensory neurone is in the middle and the nerve fibres extend on either side.
Motor neurones – carry electrical impulses from CNS to effectors.
Synapses and Reflexes
Synapse: connects neurones:
- Neurones pass impulses to each other but they don’t actually touch each other, there are gaps between them.
- The gap between two adjacent neurones is called the synapse
In the nerve ending of presynaptic neurones, there are hundreds of tiny vesicles containing a chemical called transmitter substance (neurotransmitter). When an impulse reaches the nerve ending, vesicles fuse with the cell membrane and empty the transmitter substance into the synaptic cleft. The transmitter substance diffuses across the synaptic cleft and binds with the receptor molecules in the next neurone. This triggers an electrical impulse in the next neurone.
Whenever there is a connection between 2 neurones, one of them has the vesicles and the other has the receptors because the impulse can only go in 1 direction. The vesicles are in the presynaptic neurone and the receptors are in the post-synaptic neurone.
Reflexes
A reflex action is a fast, automatic and protective response to a stimulus. They are not controlled by the brain. E.g. knee jerk reflex, pupil reflex, withdrawing hand from hot plate.
Reflex arcs reduce the time between detecting a stimulus and reacting to it. It is quicker because the information does not need to go to the brain first. It is not sent to the brain to process before the effectors are activated.
Stimulus – Receptor – Sensory neurone – CNS – Motor neurone – Effectors - Response
E.g. Pain receptors in the finger send electrical impulses through the sensory neurone to the CNS then the motor neurone which tells the effectors to move the finger away. The relay neurone goes through the CNS.
The nervous system allows very quick responses because of the electrical responses it uses.
We also have cranial reflex arcs. These are reflex arcs that have the relay neurone in the brain rather than the spinal cord, but they are still automatic and not under conscious control.
E.g. pupil size – automatically adjusts to the light
In some cases the brain can modify a reflex response e.g. keeping hold of a hot plate.
Drugs and You
- A drug is a chemical which altars the way your brain and body works. They can alter your metabolism as well as your behaviour. A metabolism is to do with how fast chemical reactions take place within your body. Drugs normally affect the nervous system and most affect the synapse.
- Drugs can be beneficial or harmful. Beneficial drugs include: morphine, codeine and antibiotics. Most drugs are prescribed by a doctor because you need to know how much and what to take so that you don’t make the drug harmful by overdose or interfering it with another medication. There can also be nasty side effects.
- Some drugs are legal and used for recreation e.g. caffeine, nicotine, alcohol. They can be called social drugs. Some athletes take performance enhancing drugs such anabolic steroids. These can have bad side effects e.g. mood swings and worn out muscles.
- As a drug alters the way your body works, you can become tolerant to them. This means you need to increase the dosage of the drug to get the initial desired effect. Eventually, your body may not function normally without the drugs. This is called addiction. Heroin and cocaine are particularly addictive. If you stop taking a drug you are addicted to, you will experience withdrawal symptoms. These are different for each drug, but can include: nausea, hallucinations, vomiting, shaking and cravings.
People who want to stop taking drugs may need rehabilitation. This can involve going to a special clinic. The staff help support the patients and stop them from taking drugs they are addicted to. After a while the withdrawal symptoms start to fade and the patient can cope without the drug.
Stimulants and depressants act on synapses. Stimulants cause more transmitter substance to be release. Depressants block the receptors in the next neurone to stop the impulses.
Illegal Drugs
Alcohol
There are many reasons why people drink alcohol. Alcohol is a depressant. You can become tolerant to it and eventually become dependent on it. If you don’t drink ay, you will get withdrawal symptoms.
Binge drinking is particularly harmful. This is when you get drunk on purpose – drinking for the sake of being drunk.
Alcohol should be drunk with food so that it can absorb some of it; otherwise it goes straight into the stomach and can damage its lining.
The Effects of Alcohol
Short term:
- Vomiting
- Dizziness
- Loss of control over body and balance
- Loss of muscle and limb control
- Increased reaction times
- Violent behaviour
- Blurry eyes – impaired vision
- Impaired judgement
- Slurred speech
- Drowsiness
- Loss of mental control
- Increased blood flow to the skin – you feel warm but are losing core body heat
- Unconsciousness or a coma
Long term:
- Brain damage – brain cells shrink and dehydrate
- Weight gain
- Liver disease – the liver breaks down alcohol and toxins into harmless substances. Too much alcohol and destroy the liver cells and cause liver disease. It takes the liver roughly 1 hour to break down 1 unit of alcohol
- Memory loss
- Depression
- Can damage foetus
- Increased risk of heart disease and diabetes
- Cancer of liver, mouth, throat and oesophagus
If a baby is born to an alcoholic mother, its brain is a lot smaller and underdeveloped which can lead to problems in the future from which it may not be able to recover.
Alcohol consumption is measured in units. One unit is equivalent to 10ml of pure alcohol. Regulations apply when driving because dizziness, loss of control over body and balance, loss of muscle and limb control, increased reaction times, blurry eyes – impaired vision, impaired judgement, drowsiness and loss of mental control can affect the safety of those on the road.
Recommended allowance: men – 21 units/ week, women – 14 units/ week
This is not very accurate because different people have livers of different strengths and may react differently to different amounts of alcohol.
Units = Volume (ml) x ABV (%) divided by 1000.
Reaction times:
In the UK, the legal limit for alcohol in the blood when driving is 80mg/ 100cm cubed. 1 unit increases the blood alcohol by 20 mg/ 100cm cubed so this means someone can have 4 units before driving.
Smoking
Tobacco comes from the leaves of the tobacco plant, Nicotiana. It has been used for hundreds of years as a recreational drug.
Smoking mainly affects the respiratory system. Air is supplied to the lungs through a network of tubes.
These tubes lead to the alveoli which are tiny air sacs. Gas exchanges take place here. Carbon dioxide is removed and Oxygen takes its place.
The trachea, bronchi and bronchioles have a highly specialised cell layer lining them called the ciliated epithelium. The alveoli don’t have a ciliated epithelium. They are made of flattened cells which are very thin – making them great for gas exchanges.
The cilia brush away dust and bacteria. It goes to the mouth where it is swallowed and destroyed by the hydrochloric acid in the stomach.
There are over 4000 different chemicals in tobacco smoke. 4 of them are dangerous:
- Nicotine
- Carbon monoxide
- Tar
- Particulates
Carbon monoxide is a poisonous gas. It binds to the haemoglobin in red blood cells more easily and more tightly than oxygen does. This decreases the oxygen carrying capacity in the blood. Less oxygen is delivered to the tissues, leading to heart disease because the heart has to work harder.
Nicotine is a stimulant. It makes the blood vessels narrower. It increases blood pressure and puts strain on the heart. It increases the risk of a stroke and a heart attack.
Tar is a carcinogen – a cancer causing substance. It damages the lungs, paralyses the cilia and causes lung cancer. It also causes cells to reproduce quicker, causing a tumour.
Particulates are tiny particles of carbon and other materials. They can accumulate in lung tissue and cause irritation. They can also get trapped and block small airways. White blood cells secrete enzymes to try to remove particulates but they damage the alveoli.
Cigarette smoke paralyses the cilia. This causes the smokers to produce more mucus, which eventually accumulates in the lungs. Excess mucus can’t be moved out of the lungs so smokers need to cough to try and remove it. This is called smokers’ cough.
Disease caused by smoking:
- Cancer – throat, mouth, lungs, oesophagus, bladder
- Bronchitis – inflammation of the bronchi – narrower tube
- Emphysema – weakened and collapsed air sacs with excess mucus
Bronchitis – the build up of mucus means bronchi and bronchioles can become infected more easily. Bronchitis is inflammation in the bronchi. Smokers can get long lasting bronchitis called chronic bronchitis.
Emphysema – a constant coughing because chemicals in the smoke have damaged the alveoli. The alveoli can burst and get destroyed. This reduces the surface area of the lungs and therefore, less oxygen is able to pass into the blood with each breath.
Smoking during pregnancy isn’t good because the nicotine and CO can cross the placenta and harm the baby. The baby is like to be born early, with a low birth rate and suffer from diseases later in life.
Sample Answer: Describe how smoking cigarettes damages human health:
Smoking mainly affects the respiratory system. There are over 4000 different chemicals in tobacco smoke. 4 of these are very dangerous. Nicotine narrows the blood vessels, increasing blood pressure and straining the heart which could lead to heart attacks or strokes. Tar damages the lungs, paralyses the cilia and causes lung cancer. Particulates can accumulate in lung tissue and cause irritation. They can block small airways. Carbon monoxide is poisonous. It displaces oxygen in the blood by binding to the haemoglobin in red blood cells. This decreases the oxygen carrying capacity in the blood. The heart has to work harder to supply enough oxygen to the tissues and this can lead to heart disease. Smokers produce more mucus because the cilia are paralysed by the smoke. The excess mucus can’t be removed so it accumulates in the lungs. Smokers have to cough to try and remove this mucus and this is called Smokers’ Cough. The build up of mucus means that the bronchi and bronchioles can get inflamed and infected more easily. Inflammation in the bronchi is called bronchitis but smokers can get chronic bronchitis which is a long lasting form of bronchitis. Emphysema is a constant coughing because the chemicals in the smoke have damaged the alveoli. The alveoli can burst and reduce the surface area of the lungs and therefore less oxygen can pass to the blood with each breath.
Homeostasis
Homeostasis is keeping everything in the body constant e.g. temperature, glucose levels
It is maintaining a constant internal environment, so everything that goes into the body has to be balance by what goes out – inputs balance outputs
This is an automatic process which uses nerves and hormones.
We need to keep the following things at constant levels so that we function properly:
-
Temperature – (36-38)
- Blood glucose – (4-7)
- Oxygen levels
- Water levels
- Salt levels
- Carbon dioxide levels
Enzymes are biological catalysts which control every reaction that occurs inside our cells. Without enzymes (which wouldn’t function if they were affected by e.g. salt levels) our cells would not function. Homeostasis maintains the ideal conditions at which enzymes work best.
Body temperature
- Ideally 37 - this is the best temperature for enzymes to work in
-
This is also known as our core temperature. Our extremities are cooler.
Animals which can keep their body temperature constant are said to be homoeothermic. They are usually warm-blooded mammals.
If the body’s temperature falls below 32, you develop hypothermia. Reactions in the body slow down because enzymes can’t work properly. Your pulse rate goes down. You could die.
Hyperthermia is when the body’s temperature is above 40. You could get heat stroke and become dehydrated. Enzymes become denatured (damaged) and they lose their 3D structure. You could die.
The body temperature is carefully monitored by the brain. If it deviates from 37, mechanisms are activated to reverse the change. In order to maintain a constant temperature: heat gain = energy loss.
The skin is the organ which is largely responsible for reversing temperature changes. Temperature receptors detect the external temperature.
Negative Feedback
The hypothalamus is the area of the brain which constantly monitors blood temperature, blood glucose levels, blood C02 levels and water levels. This is part of the negative feedback system which maintains a constant internal environment.
When it’s cold, the body reduces heat loss by:
- Respiration in cells releases energy as heat
- Shivering and exercise (muscles contracting) generates heat because muscles need to respires more to contract more
- Vasoconstriction – capillaries beneath the skin constrict so they go a bit deeper and they carry warm air around the body
- Wearing more clothes insulates the body
- Hairs on the limbs stand up and trap a layer of air over the skin
Muscle cells respire more to produce more energy to heat the body. They don’t need energy to respire.
Vasoconstrictions – there are small arterioles/ little capillaries/ little blood vessels that carry blood to the skin. They get narrower (Vasoconstriction) when you get cold. Less blood flows to the skin surface so less heat is lost by radiation. You look paler because the blood is now deeper inside the body.
When it’s hot, the body loses heat by:
- Vasodilatation – arterioles supplying the skin get wider. This brings more blood near to the surface of the skin. More heat is lost by radiation, and this is why you look flushed and red.
- Sweating – the water in sweat evaporates. This uses heat from the skin to change from a liquid to a gas.
- Wearing fewer clothes so that there is less insulation.
Endocrine Glands and Controlling Blood Sugar Levels
Hormones are chemical messengers which are secreted by an endocrine gland. Hormones travel in the blood to the target organ or cell.
Hormones regulate the functions of many organs and cells and coordinate many processes in the body.
The body usually reacts slowly to hormones and they coordinate long-term body changes e.g. growth. Adrenaline is an exception.
Insulin
This is a hormone produced by the pancreas. It lowers blood sugar levels. Cells need a constant supply of glucose to make energy (respiration). Glucose affects osmosis.
If there is too much glucose in the blood:
- The pancreas secretes insulin
- This travels in the blood to the liver
- The liver takes in extra glucose and stores it as glycogen
- Body cells can absorb some glucose
If there is too little glucose in the blood:
- The pancreas stops secreting insulin
- The liver doesn’t convert glucose into glycogen
- Body cells don’t absorb glucose
- The pancreas makes a different hormone called glucagon which causes glycogen to break down into glucose and then the glucose is released into the blood.
If the pancreas doesn’t make enough insulin it causes a disease called diabetes. There are 2 types of diabetes.
People with diabetes regularly test their blood to check their glucose levels. Diabetes sufferers can also control their high blood sugar level by exercising. Exercise uses up some of the extra glucose in the blood. The amount of insulin a person needs to inject will be different each day depending on diet and exercise. If blood sugar levels are low, the patient should sit down and take glucose pills/ gel. Hypoglycaemia – low, hyperglycemias - high
Controlling Plant Growth
Plants can respond to stimuli in their environment. This is called sensitivity. They make plant hormones which control and coordinate:
- Growth of shoots and roots
- Flowering
- Ripening of fruits
The differences between plants and humans are:
- Plants don’t have endocrine glands
- Their hormones don’t travel in the blood stream
Tropisms – growth responses by plants to particular stimuli, which can be positive or negative. If the tropism is positive, the plant will grow towards the stimuli. If the tropism is negative, the plant will grow away from the stimuli.
- When a plant responds to light, it is called phototropism.
- When a plant responds to gravity, it is called geotropism.
- When a plant responds to moisture, it is called hydrotropism.
Different parts of the plant will respond differently to these stimuli.
How do Shoots Bend?
Auxin is a plant hormone which controls photo and geo tropism. It is made by the growing tips of shoots and roots. The Auxin diffuses (in solution) to the area of cell elongation, just behind the tip, making the cell elongate.
If the light is unidirectional (from one side only), the Auxin moves away from the light and accumulates in the shaded side of the shoot. Here, it causes the cells to elongate – so the shoot bends towards the light.
Auxin changes the elasticity of the cell walls and this allows the cells to elongate.
Variations
These can be determined by genes, the environment or both.
Almost every cell in out body has a nucleus which holds genetic information.
Inside the nucleus there are 46 long coiled chromosomes. Chromosomes are made up of DNA.
DNA – Deoxyribose Nucleic Acid (also DeoxyriboNucleic Acid)
46 chromosomes come from the egg and sperm (23 from each) and combine to form a unique baby with unique genes.
Genes are sections of long strings of DNA which codes for 1 characteristic.
Each chromosome has hundreds of genes along its length.
Different species have different numbers of chromosomes:
- Dogs – 78 chromosomes – (39 pairs) / nucleus
- Horses – 64 chromosomes – (32 pairs) / nucleus
- Chimpanzees – 48 chromosomes – (24 pairs) / nucleus
- Humans – 46 chromosomes – (23 pairs) / nucleus
Every cell in the body has the same number of chromosomes except for red blood cells and gametes.
Gametes are sex cells – sperm in men and eggs in women.
Causes of Variation
- Genes
- Mutation – change in gene
- Environment
- Formation of Gametes
- Fertilisation
Mutation is a change in the gene. They sometimes happen spontaneously without an external cause. A mistake can happen when DNA is copied before the cells divide.
Sometimes, mutations are caused by environmental factors such as:
- Chemicals in cigarette smoke (Tar)
- UV in sunlight
- Ionising radiation such as X-rays and gamma rays
- Chemicals used for dying materials
When a mutation happens, it creates a different version of the gene. Different versions of a gene are called Alleles.
Alleles still code for the same characteristic but produce a slightly different version of that characteristic.
Gametes are sex cells – sperm in men and eggs in women. When cells in the ovaries or testes divide in a special way it is called Meiosis.
Gamete formation produces genetic variation because just before the cells divide, they line up in pairs and the chromosomes in each pair swap pieces with each other, making them different from the original chromosomes.
When the members of each pair of chromosomes separate they do so randomly. Therefore each egg and sperm is different.
Gametes join together at fertilisation. It’s random, so any sperm can fuse with any egg.
Variation and Inheritance Glossary
Boy or Girl
Somatic (body) cells have 23 pairs of chromosomes. The 23rd pair determines the sex of the person. Females have XX chromosomes and males have XY chromosomes. Hermaphrodites have YY chromosomes.
Genetic diagrams can be used to find the chance that sexual reproduction will produce a male or a female. There are 2 ways of showing how chromosomes can cross:
A Punnett Square:
50% chance of a girl and 50% chance of a boy.
XX XY
XX XY XX XY
Inherited Disorders
Chromosomes come in pairs, one from the mother and one from the father.
Homologous refers to the 2 chromosomes you inherit from your parents.
Rules for genetic Diagrams
- Show the phenotypes and genotypes of the parents
- Use a capital letter to represent the dominant allele and a lower case letter to represent the recessive allele
- Put gametes in circles
- Show all the possible combinations of the alleles during fertilisation
- Put an X to show mating
Monohybrid Cross
This is used to study the inheritance of a characteristic from 1 generation to the next.
A monohybrid cross to show how brown eye colour is inherited:
Parents’ Phenotypes: Brown eyes X Blue eyes
Parents’ Genotypes: BB X bb
Gametes’ Genotypes: B b
