Human Biology

Gaseous Exchange

Lungs:

During inhalation, the external intercostal muscles contracts and the internal relaxes which pushes the ribs up and out. Apart from this, the diaphragm contracts, pulling the diaphragm down and flat. All this creates a high volume in the chest (thorax) and therefore low pressure. This causes air to be pulled into the lungs as there is higher pressure outside. During exhalation, the opposite happens meaning the ribs are pulled down and in and the diaphragm goes back to a dome shape. This creates high pressure which pulls the air out of the lungs.

Lung capacity - the volume of air the lung takes in different phases of the respiratory cycle. This can be measured with a spirometer.

1. Vital capacity - maximum lung capacity
2. Tidal volume - normal volume of air in the lungs during quiet breathing.

When the brain detects a too large or too little concentration of oxygen or carbon dioxide in the blood it changes the breathing rate to change the amount of air it takes in. e.g. if there is too much carbon dioxide, the breathing rate rises to breathe out the carbon dioxide.

Diseases from smoking:

1. Emphysema - chemicals from cigarettes damage the elastic tissue in the lungs, reducing the surface area of the alveoli and, therefore, the speed and amount of oxygen it absorbs.
2. Lung cancer - carcinogenic chemicals in cigarette tar causes cancer.
3. Bronchitis - cigarette smoke paralyses cilia in the trachea meaning phlegm and microbes enter the lungs, this can cause infections.
4. Heart disease - nicotine in the cigarettes leads to the hardening and narrowing of blood vessels. This can lead to heart attacks.
5. Lethargy - cigarette smoke contains carbon monoxide which means less oxygen are carried around the body
6. Nervousness - cigarettes contain nicotine which is addictive so withdrawal symptoms occur when one is not smoking.

Investigating the effects of exercise on breathing:

1. Breath into a double bubbler with limewater or bicarbonate indicator for twenty seconds.
2. Do vigorous exercise for three minutes.
3. Repeat step one with a new double bubbler. 

After exercise, the limewater is usually more cloudy and the indicator should be more yellow. This is because your breathing is more concentrated in carbon dioxide and also because the breathing rate is high after exercise.

Effects of exercise:

1. Muscles need more energy so breathing rate increases to supply more oxygen for respiration and to oxidise carbon dioxide.
2. Heart rate increases to pump more oxygen around the body and faster.
3. Arterioles widen to stop blood pressure from increasing.
4. Blood diverted from inactive organs (e.g. stomach/liver) towards muscles through vasodilation and constriction

Benefits of regular exercise:

1. Improves body posture, muscle tone and weight loss.
2. Strengthen bones and muscles.
3. Improves endurance, flexibility and overall fitness.
4. Less risk of coronary diseases by lowering blood pressure.
5. Lowers the heart rate and relaxes blood vessels.

Internal Transport

The Blood Contains…

• Plasma
• Red blood cells (erythrocytes)
• White blood cells (lymphocytes and phagocytes)
• Platelets

Sickle Cell Anaemia:

This is a disease where the genetic code for the production of haemoglobin has mutated. This causes the haemoglobin when the oxygen concentration is low, to become sickle shaped. Effects of this are:

1. The sickle cells stick together to form blockages in the capillaries causing severe pain, especially in the joints. This is known as sickle cell crisis.
2. A stroke may occur because of this as there is reduced supply of blood to the brain.
3. The sickle shape means less oxygen can be carried. They also often burst and are destroyed by the spleen at a higher rate than normal cells. This causes anaemia.

Haemophilia:

This is caused by a mutation in a gene which produces chemicals needed to form clots. This means that the person infected would often need a blood transfusion after minor injuries and would need injections of the missing clotting factor every time they are injured.

Plasma transports hormones from the glands to organs of the body, nutrients such as glucose, amino acids, proteins and lipids from the gut to cells, urea to the kidneys, carbon dioxide (90%) and heat energy from muscles and the liver to organs that produce less hear maintaining an even body temperature.

Red Blood Cells:

White Blood Cells:

White blood cells prevent diseases. Around 70% of these cells are phagocytes which produce extensions of their cytoplasm called pseudopodia to enclose the foreign organism in a vacuole. Enzymes then break them down. Phagocytes essentially consume them. 25% of these cells are lymphocytes. They are used to make antibodies which stick to the antigens on microorganisms to kill or make it easier to kill it. This is because antibodies make pathogens group together making them easier to kill. Some lymphocytes also produce memory cells which make us immune to diseases.

Platelets:

Exposure to air stimulates the platelets and damaged tissue to produce chemicals. This causes the soluble protein fibrinogen to change into an insoluble fibre of a protein called fibrin. Fibrin forms a network across the wound, trapping the red blood cells and forming a clot. This prevents further loss of blood and entry of pathogens. The clot will develop into a scab which protects the damaged tissue while the new skin grows.

Blood Groups: 
Each person either is in blood group A, B, O or AB. This is dictated by what antigens are located on your red blood cells. Blood group A will have antigen A, blood group B will have antigen B, blood group AB will have both antigen A and B and blood group O will have neither antigen. This is important for blood transfusion as you also have antibodies in the blood which cause the red blood cells with a particular antigen to agglutinate (clump together) and die. For example, if you are blood group A, you will have antibody B meaning only group A or group O blood can be transfused to you. Group O is called the universal donor as it has neither antigen A or B meaning it will never agglutinate. Group AB is  called the universal recipient as it has neither antibody A or B meaning all blood groups can be transfused to the patient.

Transplants:

Transplants are dangerous because of organ rejection. This is where the lymphocytes recognise the antigen on the new cells to be foreign and produces antibodies to destroy them. This can be prevented through tissue typing to keep the antigens as close as possible to the ones already inside the body. This can be achieved by using organs from relatives. Organ rejection can also be prevented through the use of immunosuppressive drugs which stop the immune system from damaging the foreign organ.

Heart:

How the heart works:

1. Blood enters the atria.
2. The walls of the atria contract, raising pressure and forcing open the bicuspid and tricuspid valves. 
3. When the ventricles fill with blood, the ventricles contract, raising pressure and closing the valves.
4. The ventricles continue to contract and raise pressure. This forces the semilunar valves (pulmonary valve and aortic valve) to open.
5. Blood flows into the aorta which carries blood to parts of the body and the pulmonary artery which carries blood to the lungs.
6. High pressure in the aorta and pulmonary artery closes the semilunar valves and the process restarts.

Heart attacks are caused when the coronary artery is blocked completely meaning the heart muscles will stop contracting. This blockage is usually caused by a build-up of fat called an atheroma. Many factors can make heart attacks more likely:

1. Heredity
2. Permanent high blood pressure/hypertension puts more strain on the heart muscles as it has to work harder to pump blood.
3. Diet - a diet rich in fats raises cholesterol. High cholesterol and fats create the atheroma which can block the coronary arteries.
4. Smoking - nicotine constricts blood vessels, raises blood pressure, speeds up the heart rate and increases blood cholesterol.
5. Stress - hormones released during stress constricts blood vessels, raising blood pressure.
6. Lack of exercise - regular exercise reduces blood pressure and strengthens the heart.

Heart rate:

Your heart rate increases during exercise to supply oxygen needed for the increased need for aerobic respiration to release more energy to be supplied to the muscle. This occurs as the aorta and the carotid artery detects extra carbon dioxide from the exercise and sends a signal to the medulla in the brain. The medulla sends impulses along the acceleration nerve. When carbon dioxide production slows, the medulla sends impulses along the decelerator nerve.

Arteries: 

• Used to carry food away from the heart.
• Small lumen (central cavity).
• Thick wall with thick muscle fibres and elastic tissue.

Vein:

• Used to carry blood to the heart.
• Large lumen (central cavity).
• Thin wall with little muscle fibres and elastic tissue.
• Have valves which prevent the back-flow of blood.

Capillaries:

• Carry blood through organs and between cells.
• Capillary walls are one cell thick and allow substances to diffuse in or out.

Pulse:

A pulse occurs when the aorta stretches the wall of the aorta because of high pressure. When the ventricle of the heart relaxes, the stretched section of the aorta recoils, increasing the pressure inside it and thereby creating a wave of stretching followed by constrictions along the aorta and through the arterioles. There is no pulse in veins as it is too far away for the wave to reach.

Tissue Fluid:

This surrounds the capillaries and is the liquid that leaks out of the capillaries under high pressure. It is like blood plasma except lacking in protein which is too large to pass through the capillary walls. Tissue fluid forms a pathway for diffusion of substances between the capillaries and cells.

Circulation System:

Homeostatic Mechanisms

Organisms are able to respond to changes in their environment by adapting their internal body conditions. Homeostasis is the maintenance of a constant internal condition. Examples of homeostasis are osmoregulation, thermoregulation and the regulation of the composition of the blood.

Skin:

Functions:

1. Protection
2. Waterproof barrier
3. Thermoregulation

Thermoregulation:

1. Sweat glands release sweat when the internal temperature is too high. The evaporation of sweat uses heat energy of the skin. This takes away heat energy.
2. Vasodilation occurs when the body is too warm. The shunt vessel constricts and the capillaries widen meaning more blood flows through the surface of the skin and so more heat is lost through the radiation of heat. Vasoconstriction occurs when you are too cold. The opposite occurs meaning less heat is lost through radiation.
3. Hair erector muscles relax to flatten the hair when it is warm. This means less trapped air is present and therefore, there is less insulation. The opposite occurs when it is cold.
4. Adrenaline is used to raise metabolism meaning more energy is released and so more heat is also released.
5. Shivering - more respiration occurs in muscles meaning more heat is released.

Excretion: the removal of metabolic waste created in cells such as urea, carbon dioxide and water. The lungs, kidneys and skin are all organs of excretion.

Renal/Urinary system: 

Function:

The urinary system is used to create, store and remove urine which in turn removes wastes such as urea. Blood flows to the kidneys which separates it into the components of urine: water, urea, some salts. The urine then moves down the ureters and is stored in the bladder until the two sphincter muscles relax where it then exits the body.

The components and various concentrations of urine may vary depending on the amount of water and salt intake and whether you have kidney failure or diabetes.

Kidneys: the kidney is involved in both excretion and osmoregulation. 

Nephron: there are millions of these in each kidney and they are the main areas of the kidney where filtration occurs.

Ultrafiltration is the separation of smaller molecules such as glucose, water, urea, oxygen, salts, and amino acids from the blood at the glomerulus in high pressure. 

Selective reabsorption is where molecules in the glomerular substrate are retaken by the capillaries at the proximal convoluted tubule. It is selective as only some molecules such as glucose, amino acids and some salts are retaken. 

Water is reabsorbed into the blood both through selective reabsorption and through osmosis at the collecting ducts. The latter is controlled by ADH (anti-diuretic hormone). When the hypothalamus detects the blood is too concentrated, it tells the pituitary gland to release ADH which travels via the bloodstream to the kidneys. ADH makes the collecting ducts more permeable to water meaning more water is absorbed. This is how the kidneys act in osmoregulation.

Transplant:

If the kidneys were to fail, without a kidney transplant or dialysis you would die very quickly as the blood will become full of urea, which is toxic. Dialysis is where a machine is used to artificially create a kidney as it essentially performs the job of the kidneys.

Problems:

• Risk of surgery
• Difficulty in finding donors and tissue matching.
• Use of immunosuppressants means the chance of infection is high. 
• Chance of organ rejection.

Advantages:

• Relatively cheaper than dialysis.
• Dialysis takes a long time (around thirty hours a week).
• Dialysis may cause damage to arteries and veins.
• Dialysis has a high chance of infection.
• A transplant is a permanent solution.
• A transplant will mean that urea concentration will remain constant while under dialysis it will spike up and down.

Oral rehydration method: this is one of the medications used to prevent dehydration. It is water containing several salts and glucose.

It is vitally important to rehydrate after vomiting or diarrhoea. This is because if you are dehydrated then there is less water to transport vitamins, minerals and glucose and also less water to remove metabolic waste such as carbon dioxide. It is also needed for cell turgidity. As a result, the oral rehydration method is often used following vomiting or diarrhoea.

Liver:

Functions: 

1. Produces bile which is used to emulsify fats and to neutralise foods in the duodenum to allow enzymes to work at optimum pH.
2. Regulates blood sugar. When glucose levels are too high the liver converts glucose to glycogen while the opposite occurs if glucose levels are low
3. It controls amino acids concentration. Urea is a byproduct of the breakdown of amino acids.
4. The above is an example of detoxification where the liver breaks down toxic substances into less toxic ones. Alcohol is another example of this.

Effects of alcohol:

On liver:

1. It causes fat deposits to develop in the liver as metabolism of alcohol needs oxygen, this means more respiration.
2. After continued excessive drinking the liver may become inflamed causing alcoholic hepatitis which can result in liver failure and death.
3. Excessive alcohol can permanently scar and damage the liver, resulting in liver cirrhosis and an increased risk of liver cancer.

On the nervous system:

1. Cells of the central nervous system are affected by alcohol.
2. After excessive alcohol, a syndrome called blackout may occur where a person may appear to be functioning in an alert state while not recalling the events afterwards.
3. Impaired reaction times and motor co-ordination as vision and hearing are affected.
4. Neuropathy where there are alternating feelings of pain, burns, numbness and weakness in hands and feet.

On your behaviour:

1. People have less control over their actions as less oxygen is supplied to their brains. The person is, therefore, more likely to commit crimes or does things that they wouldn't normally do or would be irresponsible.

Reproduction and Heredity

The process of fertilisation involves the fusion of a male and female gamete (sex cell) to produce a single cell called a zygote.

Reproductive System:

Male:

Sperm is stored and created in the testes. During intercourse, it travels along the sperm duct in the penis and mixes with secreted liquid from the seminal vesicle to form semen. One ovum is released into the fallopian tube each month and when it is in the tube a sperm can fertilise it.

Female:

Menstruation:

Hormones are very important for this process. First the follicle stimulating hormone (FSH) stimulates the growth of the follicle containing an ovum. At the same time, FSH stimulates the release of oestrogen which begins the re-thickening of the uterus lining and also slows the release of FSH and stimulates the release of LH (luteinizing hormone). When LH is at its peak, ovulation occurs where the ovum is shed by the ovary. If sexual intercourse occurs, what is left of the follicle forms a structure called the corpus lute. This releases progesterone which completes the thickening of the uterus walls and inhibits production of FSH and LH, stopping any further ovulation. If the egg is not fertilised then the corpus luteum breaks down and the lining of the uterus is shed through menstruation. Progesterone is also used during pregnancy to stop menstruation. It is produced by the placenta.

Definitions:

• Genes - a small section of DNA that determines a particular feature by instructing cells to produce a particular protein are called genes.
• Alleles - an alternative form of a gene which gives rise to differences in inherited characteristics.
• Dominant - a feature will always have two alleles. If one allele’s characteristic is present while the other is not then it is said to be dominant.
• Recessive - if one allele is dominant then the other is said to be recessive.
• Homozygous - contains two copies of one allele (e.g. TT, aa).
• Heterozygous - contains two different alleles (e.g.Tt, Aa).
• Genotype - describes the alleles each cell has for a certain feature.
• Phenotype - a feature that results from the genotype.
• Codominance - if two alleles are expressed in the same phenotype.
• Diploid cells - cells with chromosomes in homologous pairs are said to be diploid.
• Haploid cells - cells with chromosomes not in a homologous pair is said to be haploid.

Meiosis:

1. Each chromosome in the nucleus duplicates itself.
2. The cell divides into two as in mitosis.
3. The cell divides again to form four cells containing half the number of chromosomes. This results in the formation of genetically different haploid (half the number of chromosomes) cells that are not in homologous pairs.

A zygote is formed when two gametes (sex cells) formed through meiosis fuse to form a cell with a full chromosome count. Following this, mitosis duplicates the cell millions of times to form an embryo.

The embryo in the uterus develops a placenta which not only anchors the embryo to the uterus but also allows the embryo to obtain nutrients such as oxygen and glucose from the mother’s blood. It also allows the embryo to get rid of waste products such as urea and carbon dioxide. An embryo also is enclosed by a membrane called the amnion. This secretes amniotic fluid which protects the embryo from jolts and bumps.

Secondary Sexual Characteristics:

Boys: controlled by testosterone

• Growth of penis and testes.
• Growth of facial and body hair.
• Muscle development.
• Breaking of the voice.

Girls: controlled by oestrogen

• The breast develop.
• Menstruation starts.
• Growth of armpit and pubic hair.

Birth Process:

1. Cervix dilates to allow the baby to pass through. The muscles of the uterus contract strongly and rupture the amnion, allowing the amniotic liquid to escape. This is called the water break.
2. Strong contractions of the uterus push the baby head first through the cervix and vagina.
3. After the birth, the uterus continues to contract to push out the placenta and the amnion. This is called the afterbirth.

Breastfeeding:

Advantages:

• Perfect food for healthy growth of the baby.
• Contains antibodies which protect the baby against infection diseases.
• Forms an emotional bond between the mother and the baby.

Growth and development:

gametes—> zygote—> embryo—> foetus—> baby—> child —> adolescent —> puberty—> adult

Contraception:

Hormonal - oral contraceptive pill such as the combined pill (oestrogen and progesterone) or the mini pill (progesterone). The mini pill creates a thickening of the mucus in the cervix which acts as the barrier and the combined pill prevents the production of FSH and LH, preventing menstruation. Its advantage is that it has a low failure rate however it must be taken every day and at a certain time.

Barrier - uses a barrier to prevent sperm from reaching the ovum. Examples include the condom and femidom. The advantages are that they are easy to obtain and use and that they also protect against STI. However, they may slip off during intercourse.

Natural - withdrawal from intercourse or having intercourse during a “safe period” is easy however there is a high failure rate and women will also have to have a regular cycle and will need to keep track of it.

Inter-uterine - an IUD (inter-uterine device) or coil is inserted through the cervix into the uterus. It is a piece of plastic or copper that prevents a fertilised egg from implanting in the uterus. Its main advantage is that it has no effect on intercourse however it does have to be fitted by a doctor and cause heavy periods.

Sterilisation - a surgical process that prevents sperm from passing to the penis or eggs from passing to the uterus. In men, it is called a vasectomy and is where the sperm ducts are cut and tied under general anaesthetic. In women, a similar process occurs in the fallopian tubes and is called tubal ligations. Its advantage is that it has a very low failure rate while its disadvantages are that it is non-reversible and that it has to be performed by a doctor.

The nucleus of a cell contains chromosomes which contain DNA. A small section of DNA that determines a particular feature by instructing cells to produce a particular protein are called genes. In humans, the diploid number of chromosomes is 46 and the haploid number is 23.

ABO blood groups are determined by multiple alleles (more than two alleles) with each allele determining which antigens are on red blood cells. The alleles are: I^A, I^B, I^O

 I^A and I^B are codominant and I^O is recessive to both.

To show patterns of inheritance we often s a genetic diagram called a pedigree.

The sex of a person is determined by a pair of chromosomes, XY in a male and XX in a female. The overall ratio of male and female births is 1:1

This can be shown by this diagram:

There are certain diseases which are sex-linked. This means that they exist on the X chromosome and means that often boys are more susceptible to them. An example of this is a blood disorder called haemophilia. The allele for this is recessive and is “h”. It is only found on the X chromosome. A woman with the gene X^HX^h would not have haemophilia but would be a carrier.

A carrier female and a healthy male have a 25% chance of a having a haemophiliac boy but no chance of a haemophiliac girl.

Another example of a sex-linked disease is red-green colour blindness.

The offspring formed through intercourse vary genetically because of the huge variation in sex cells. It is also because of the random nature of fertilisation where over a billion different sperms can fertilise one of the thousands of ova

Variation can be produced both by genes and by the environment. e.g. body mass, height, skin colour, intelligence.

Mutations are rare, random genetic changes to the genetic material that can be inherited.

Most mutations are harmful, some are natural and a few are beneficial.

Mutations that are beneficial can cause the mutant organism to increase in population through natural selection. An example of this is in bacteria that have mutated to be resistant to antibiotics. These bacteria live for longer and can, therefore, multiple more.

The chances of mutations can be increased by mutagens. Examples of these are ionising radiation such as ultraviolet light, X-rays and gamma rays and many different chemicals, both natural and man-made (e.g. benzene).

Disease

The general course of a disease:

1.Infection:

• Droplet infection - coughs, sneezes e.g. cold, influenza
• Drinking contaminated water - e.g. cholera, typhoid
• Eating contaminated food - e.g. polio, salmonella
• Direct contact - skin to skin contact e.g. athlete’s foot, ringworm
• Sexual intercourse - e.g. AIDS, syphilis, chlamydia
• Blood to blood contact - e.g. AIDS, hepatitis B
• Animal vectors - e.g. malaria, sleeping sickness

2. Incubation period:

The time between when a person is infected and when they first show symptoms. This occurs as the pathogen may need time to multiply for the effects to become large enough. It also may need time to reach its destination.

3.Sign:

A disease that can be seen by other people. It can be seen, heard or be measured (e.g. blood sugar). A sign is different from a symptom as a symptom does not have to be visible to other people as it is what the patient experiences.

Endemic disease - a disease that is always present in the population of a particular geographical area.

Epidemic disease - a widespread outbreak of a disease spreading over a large area and many people.

Pandemic disease - a worldwide outbreak of a disease e.g. Swine Flu (2009).

Pathogens:

Viruses:

Structure:

Reproduction:

A virus takes over the host cell and its genetic machinery and uses it to make more virus particles. The host dies after more viruses are reproduced and the viruses then spread to other cells in the body.

Diseases:

Influenza: transmitted through airborne droplets produced when a person sneezes or coughs. Influenza primarily affects the cells in the upper airways of the respiratory system. There is little that can be done to treat the disease although antibiotics can be used to combat the secondary bacterial infections. The disease can, however, be prevented 60-70% of the time through vaccinations. Staying away from infected people also prevents transmission.

Poliomyelitis: this is spread through animal vectors such as flies and also through contaminated water and food. There is no effective treatment but this can be prevented by a vaccine and/or a good hygiene so that flies do not make contact with human sewage or food and drink.

AIDS: this is spread through the HIV virus through sexual intercourse or blood to blood contact. There is no cure or vaccine. It can be prevented by not sharing needles or limiting the number of sexual partners.

Bacteria:

Structure:

Nutrition:

Most bacteria are heterotrophic meaning they live on other organisms and eat organic matter. Saprobes are bacteria that live off dead organic material while heterotrophic parasites are those that cause disease. Some bacteria are also autotrophic meaning they produce their own food through photosynthesis.

Reproduction:

Bacteria reproduce asexually by binary fission. This is where the DNA of a bacterium duplicates creating two daughter bacteria with the same genetic information as the parent bacterium.

Diseases:

• Typhoid: spread through contaminated water containing the bacteria Salmonella Typhi or flies transferring the bacteria from faeces to food. It can be treated with antibiotics such as penicillin and the oral rehydration method is useful in combating the effects. It can be prevented by a vaccine, better sanitization and better hygiene.
• Tuberculosis (TB): this is spread through droplet infection of a bacteria called mycobacterium tuberculosis. Long-term use of antibiotics can treat the illness but it can take up to 15 months to treat it. In that time, the bacteria may become resistant to the antibiotics meaning it will have to constantly be changed. It can be prevented through better standards of living as if people are less crowded then there is less chance of infection. Also, the vaccine BCG can be used although it only works for children.
• Gonorrhoea: spread through sexual intercourse. It can be treated with antibiotics although resistance to them are growing. It is prevented through the use of condoms or through avoiding sexual intercourse with someone infected with the disease.

Fungi:

Diseases:

• Thrush: transmitted through direct contact of the fungus candida Albicans. It is treated with anti-fungal drugs and prevented through a good hygiene.
• Athletes Foot: transmitted through direct contact it can once again be treated with anti-fungal drugs and prevented through a good hygiene.

Parasites:

Schistosomiasis (or Bilharzia): this is spread by the parasite Schistosome.

1. Larvae of the worms are released by freshwater snail.
2. The larvae swim in the water and penetrate the skin of people in the water.
3. The larvae develop in the body to adult worms, living inside the liver, intestine and bladder. They feed of red blood cells.
4. They mate and release eggs which pass out in faeces or urine to infect more snails.

Effects: Schistosomiasis is a long term illness (chronic). Symptoms are generally quite mild although in serious cases symptoms may include fever, chills, diarrhoea, severe rashes and blood in the urine. Organs may also become damaged and the liver, spleen and/or lymph nodes may become enlarged.

Prevention:

1. Treatment with drugs to kill the worms in the body.
2. Killing the freshwater snails through chemicals or introducing natural predators such as crayfish. This interrupts the life cycle.
3. Improving sanitisation also disrupts the cycle as it prevents faeces containing the worms from faeces and urine from entering the rivers and lakes and infecting the snails.
4. Health education needed to inform the villagers about the dangers of going into the river.

Malaria and Typhoid: spread through animal vectors. Malaria parasites are spread by mosquitos while typhoid bacillus is spread through houseflies.

Malaria:

1. Mosquitos feed on an infected person’s sex cells.
2. Fertilisation occurs in female mosquitos. The zygote develops into malarial parasites.
3. Infected mosquitos infect the person.
4. Parasites enter liver cells and change form. They rupture the liver cells, enters the blood stream and infects the red blood cells.
5. The red blood cells burst, releasing more parasites and sex cells.
6. The process repeats.

Prevention:

1. Use of insecticides to kill mosquitos and houseflies.
2. Draining swamps and rubbish dumps where mosquitos and houseflies gather.
3. Use of drugs to target the life cycle of the malarial parasites.
4. Stocking ponds with a fish called Tilapia which feed on mosquito larvae.
5. Using insect repellents, wearing long-sleeved shirts and sleeping under insect nets prevent bites from mosquitos.
6. Improving hygiene and sanitisation.

Defence:

Immunity: immunity can be...

• Natural - created through organic processes.
• Artificial - created through man-made intervention.
• Active - created through an immune response and so is in the long term.
• Passive - created without an immune response. Normally this only happens twice in our lives. First when we receive antibodies across the placenta and second through our mothers in colostrum and breast milk.

Vaccines:

These are a form of an artificial active immunity and works by injecting a person with an “agent” that carries the same antigens as a specific disease-causing microorganism. This can be achieved by injecting…

• An attenuated (weakened) strain of the actual microorganism (e.g. polio, TB and measles)
• Dead microorganisms (e.g. a whooping cough, typhoid)
• A modified toxin of the bacteria (e.g. tetanus)
• Just the antigen (e.g.influenza)
• Harmless bacteria, genetically engineered to carry the antigen of a different disease carrying microorganism.

The Antibody/Antigen reaction:

1. Lymphocytes recognise individual marker chemicals called antigens on the surface of the pathogens.
2. Lymphocytes’ receptor proteins bind with the antigens.
3. When it binds the lymphocytes to divide rapidly, producing millions of the same type of lymphocyte that is capable of recognising the microorganism.
4. Most of this occur with B and T lymphocytes.
5. Most B-lymphocytes begin to produce antibodies which bind with the antigens, causing the pathogens to clump together. This makes it easier for phagocytes to ingest it through phagocytosis where pseudopodia enclose the pathogen. Some antibodies also cause the pathogens to burst apart. Some also develop into memory cells which remain  for a long time and if the cells re-infect, the memory cells will start to reproduce and produce antibodies. Because of these, the secondary immune response is much faster than the primary.
6. T-lymphocytes destroy our own cells. These cells have become infected with a virus or are cancerous. This is done by releasing chemicals that “punch a hole” in the cell or activates a “programmed cell death” that is put into the genetic coding of every cell. Some also become memory cells like B-lymphocytes.

Antibiotics:

• Source - antibiotics such as penicillin are created by fungi. For example, penicillin is excreted by the fungus penicillium.
• Role - bacteria can be stopped by antibiotics. Antibiotics can be both bactericidal where bacteria are killed or bacteriostatic where the bacteria are stopped from multiplying. For example, penicillin and tetracycline are bactericidal while nalidixic acid is bacteriostatic.
• How - penicillin works by weakening cell walls by interfering with the manufacture of bacteria cell wall. Water, therefore, enters through osmosis and bursts the cell. Nalidixic acid interferes with DNA replication meaning bacteria cannot multiply. Tetracycline interfered with protein synthesis meaning no enzymes can be made to control the cell.

Non-pathogenic organisms and their importance:

Non-pathogenic bacteria and fungi are useful to humans because they are decomposers which break down complex organic materials into simple substances. These are then released into the environment. For example, decomposers are used to break down protein into ammonia and then nitrates which are essential for plants.

Decomposers are involved in sewage treatment. Sewage must be treated as they contain pathogenic bacteria which can cause diseases if drunk and also because aerobic bacteria in the water will deplete the amount of oxygen in the water by breaking down the organic material in the sewage. This then causes death to species not adapted to low oxygen levels. The sewage must, therefore, be treated first to remove any organic material.

There are two ways of treating sewage. The percolating (biological) filter method is one of them and works like this:

1. Sewage is screened to remove any large objects and left to stand in a large setting tank to allow other solid material to settle out.
2. The sewage is then pumped through sprinklers rotating over a filter bed. The filter bed contains bacteria, fungi, and protozoa which oxidise any organic material.
3. The treated sewage is discharged into a waterway.

The second method is called the activated sludge method:

1. Sewage is screened and stood in a large settling tank.
2. It is then passed into an aeration tank which when oxygen is pumped in, allows the bacteria to oxidise the organic material.
3. It passes to a sedimentation tank where the activated sludge settles.
4. Some are returned to the aeration tank carrying bacteria. The purified effluent is discharged.

A pit latrine is used in less developed countries and is basically a hole in the ground with a pit underneath containing microorganisms which can break down the urine and faeces.

All these different methods of sewage treatment rely on both aerobic and anaerobic microorganisms. Aerobic microorganisms are used to oxidise any organic matter in the sewage creating an effluent that contains much less organic material and fewer pathogens.

Anaerobic microorganisms are needed to treat the waste sludge that settles in the settling tanks. The microorganisms are placed with the sludge in a fermentation tank and the organic material is converted to biogas, a mixture of methane and carbon dioxide. The biogas can be used as a fuel in electricity generator or for heating. The remaining dry, solid material can be used for fertiliser or disposal of in a landfill site.

Eutrophication occurs when excess minerals such as nitrates and phosphates enter a body of water from sewage or fertilisers. Fertilisers can enter the water through leaching as nitrates and such are washed out of the soil by rain since it dissolves in water. This can also occur through surface run offs. Excess minerals stimulate the growth of algae. An algal bloom will develop and block out the light needed for photosynthesis and are also decomposed as they die. This is done by aerobic bacteria which uses up oxygen in the water. This causes oxygen depletion, causing many fish and plants to die. In severe cases, the water will become anoxic (containing very little oxygen) and become smelly from the gases such as hydrogen sulphide and methane which are released by the bacteria. Only anaerobic bacteria can survive conditions like these.

Environment:

Humans inhabit many of the Earth’s ecosystems. An ecosystem is a distinct, self-supporting system interaction with each other and with their physical environment.

Ecosystems have:

• Producers - green plants that photosynthesise.
• Consumers - animals that eat plants or other animals.
• Decomposers - Microorganisms that break down dead material and help in recycling nutrients.
• Physical environment - the non-biological components such as water, soil and air.

Plants are the source of all the food that animals, including humans, eat. They also create oxygen which aerobic organisms need for respiration. Plants can create from glucose, starch, sugars such as fructose or sucrose, cellulose and lipids.

Photosynthesis:

Carbon Dioxide + Water —> Glucose + Oxygen

Food chains are made up of trophic levels:

Producer —> consumer—> decomposers

Energy and substances are transferred along a food chain. Every time energy is transferred, a large amount of it is lost through the lack of digestion and, therefore, passes out as faeces. Some form excretory products such as urea and some is respired to release energy. Not only this, but a large amount of energy is also lost through respiration. Because of this, only around 10% of energy is used to create new cells and, therefore, can be passed on to the next trophic level.

Transfer of energy:

1. Photosynthesis creates glucose.
2. Respiration releases energy from compounds such as glucose.
3. Almost all biology processes use the energy released in respiration.
4. If the energy is used to create new cells then it can be passed on to the next trophic level.
5. If not then once used it will eventually escape as heat.

Food preparation, storage and preservation:

Preparation: cooking food properly to kill any microorganisms present.

Storage:

• Packaging of food to prevent transmission of microorganisms.
• Display before and best before dates to tell you when the food is unsafe to eat.
• Placing cooked and raw food separately.
• Not refreezing after cooking as bacteria will multiply very quickly.
• Food should not be left open to the air on a work surface.

Preservation:

• Salting - bacteria lose water by osmosis and are killed. (e.g.fish, some meats)
• Pickling - food butler in vinegar (ethanoic acid). The low pH inactivates most microorganisms.
• Pasteurisation - 63-65°C for 30 minutes or 71.5°C for 15 seconds (milk)
• Canning - packed in cans, heated, sealed, then finally heats to 105-160°C. (e.g. soup, beans).
• Drying - blowing hot air to remove water (e.g.cereal, grains)
• Freezing - frozen to -10°C rapidly (e.g. meats, prepared meals)
• Irradiation - high energy gamma rays are passed through food (e.g.potatoes, onions)

Water purification:

1. Water is taken from a source.
2. It is then passed through a screen to filter large solid objects such as weeds and other debris.
3. It is pumped to a settling tank for particles to settle. The sludge is removed at intervals and used as fertiliser or in landfill.
4. Pumped to a filter bed where it is sprayed onto it from a revolving arm. It slowly trickles down from sand at the top to stones and gravel at the bottom. Bacteria and fungi among the particles break down any organic matter and protozoa feed on the bacteria, including pathogens.
5. Chlorine is added to kill any remaining pathogens.
6. It is then stored in covered reservoirs which prevent the growth of algae and contaminants from entering.
7. Water is finally pumped to homes.

Air pollution:

Carbon Monoxide:

This is a colourless, odourless and tasteless gas which can cause death by asphyxiation. Haemoglobin bind with this rather than oxygen and so a person may become unconscious if it’s breathed in for a certain time as a result of a lack of oxygen.

Sulphur Dioxide:

This is a major constituent of acid rain which kills plants and also ruins the landscape.

Green House Gases:

These include water vapour, carbon dioxide, nitrous oxide, methane and CFCs (chlorofluorocarbons).

The level of greenhouse gases has risen rapidly in the past 100 years. The increasing burning of fossil fuels such as coal, oil and natural gases as well as petrol and diesel in vehicle engines has led to this. The increasing deforestation also means that the greenhouse gas carbon dioxide is used less in photosynthesis.

The increasing levels of greenhouse gases have resulted in the enhanced greenhouse effect. The normal greenhouse effect is where gases absorb some long wavelength infra-red radiation from the sun and re-emit some as longer wavelength IR. This heats up the surface of the Earth. However, with too much greenhouse gases, global warming has occurred where the earth heats up quicker than it should. This has caused the melting of the ice caps and, therefore, sea level rises, changing ocean currents meaning warm water is redirected to cooler areas, more rainfall in some areas (climate changes), species to become extinct as they cannot adapt fast enough and changes to agricultural practices as some pests become more abundant.

Deforestation:

Each year tens of thousands of hectares of rainforests are cut down. This causes several problems:

• Soil erosion occurs as it is exposed due to lack of a canopy meaning the soil is down or washed away.
• Leeching occurs where minerals are washed out by rain. This occurs as there are no tree roots to hold the soil together.
• Destruction of habitats and reduced biodiversity occurs. Around 50-70% of all species live in rainforests.
• The water cycle is disturbed as trees are an important part of returning water vapour from the soil.
• The balance in atmosphere oxygen and carbon dioxide changes as photosynthesis decrease. This will cause global warming.

So that's all there is to IGCSE Human Biology. Once again now all you have to do is learn these notes, memorise them and then you're done.

Good luck in your exams!

PS. I've attached a complete copy in case you're too lazy to read it from the blog (it has a mighty 32 pages).

Click here