Revision:A2 Biology - Behaviour and Populations

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Contents 1 Patterns of behaviour 1.1 Learned behaviour 2 Reproductive behaviour 2.1 The menstrual cycle 2.2 Oral Contraception 2.3 Infertility 3 Pregnancy 3.1 Conception 3.2 Acrosome reaction 3.3 The placenta 3.4 Structure adaptations of placenta for diffusion 3.5 Physiological changes in mother 4 Human growth and development 4.1 Patterns of human growth 4.2 Hormonal control 4.3 Puberty 4.3.1 Evolutionary importance of a long pre-puberty stage 4.4 Ageing 4.4.1 Nervous system 4.4.2 Decline of physiological function 4.5 Why do we age? 5 Human populations and health 5.1 Calculations 5.2 The demographic transition model, DTM 5.2.1 Stage 1 – High Stationary 5.2.2 Stage 2 – Early Expanding 5.2.3 Stage 3 – Late Expanding 5.2.4 Stage 4 – Low Stationary 5.3 Social conditions affecting DTM, birth and death rates 5.4 Infectious Diseases 5.4.1 Viruses 5.4.2 Bacteria 5.4.3 Fungi 5.4.4 Transmission of pathogens 5.4.5 Disease 5.4.5.1 Influenza – Droplet infection 5.4.5.2 Athletes foots - Contact 5.4.5.3 Salmonella – Food 5.4.5.4 Cholera – Water 5.4.6 Immunity 5.4.7 Cell mediated response (T cells) 5.4.8 Humoral response (B cells) 5.4.9 Immunisation can be 5.4.10 Artificial Immunity – vaccination 5.4.11 Why do you get some diseases once and others lots of times? 5.4.12 The herd immunity effect 5.5 Effects of lifestyle on health 5.5.1 Diet 5.5.2 Mineral Ions 5.5.3 Vitamins 5.6 Non-communicable disease 5.6.1 The biological basis of heart disease 5.6.1.1 Atheroma as a cause of aneurysm and thrombosis 5.6.1.2 Myocardial Infarction 5.6.1.3 Risk factors associated with coronary heart disease 5.6.2 Respiratory diseases 5.6.2.1 Chronic bronchitis 5.6.2.2 Emphysema 5.6.2.3 Lung cancer 5.6.3 The biological basis of Cancer 5.6.3.1 Tumours and tumour cells 5.6.4 Benign or Malignant tumours? 5.6.5 Genes and Cancer 5.6.6 Cancer cells and the immune response 5.6.7 Carcinogens 5.6.7.1 Common causes of mutation 5.6.8 Lung and skin cancers 5.6.9 Screeneing 5.6.10 Pros and cons for a genetic screening programme 5.6.10.1 Pros 5.6.10.2 Cons 6 Comments

Patterns of behaviour

• Innate behaviour – Inherited so stereotyped for species, doesn’t need to be learned, genetically controlled.
• Kinesis – change in speed of random non-directional movement, with respect to stimulus.
• Taxes – directed movement towards or away related to direction of stimulus.
• Reflex – movement of a body part in response to stimulus. Rapid and automatic.

Breast feeding in humans as reflexes linked together:

1. Rooting reflex (baby) – seek > turn head with mouth open until it finds nipple.
2. Sucking reflex (baby) – when attaches to nipple begins to suck.
3. Let-down reflex (mother) – stimulation of nipple – oxytocin hormone – triggers smooth muscle contraction – mammary glands release milk.

• Modified reflexes – conscious control of bladder emptying.

- Full bladder = stimulus, sphincter muscles around base of urethra relax, under CNS control, to modify it muscular relaxations has to be prevented ^time by brain learning.

Learned behaviour

• Habituation – learning to ignore stimuli because they are followed by neither reward nor punishment.
• Imprinting – If an animal is exposed to a moving object with reasonable size and sounds, they will follow the object for the rest of its life & imprinted object is goal of sexual drive. E.g. newly hatched geese.
• Classical conditioning – new stimuli are introduced which lead to the same response as a result of experience.
  • E.g. Pavlov on the control of salivation in dogs.
  1. He noted when presented with the sight and smell of food the dogs began to salivate in preparation of eating.
  2. Pavlov began to ring a bell each time the dog was shown their food.
  3. After a while he found dogs salivated when the bell was rung, regardless of whether food was present.
• Operant conditioning - ‘Trial and reward’ learning or associative learning.
  • E.g. The work of Skinner on pigeons/rats.
  1. Trained rats and pigeons to press a leaver in order to obtain food.
  2. Certain motor-output responses generated e.g. running around, resting, pressing leaver.
  3. After training the subject will show the conditioned response (e.g. pressing the leaver) if the response-unconditioned stimulus (a food reward) association has been memorized.

Reproductive behaviour

• Courtship is a pattern of behaviour used to attract a mate.
• Courtship behaviour of a species allows species recognition, sexual selection and stimulates synchronisation of breeding behaviour.
• The onset of courtship involves formation of a pair bond – relationship between male and female of same species which means they recognise each other as individuals and act in coordinated way.
• Sign stimuli - The cue (visual, olfactory) which starts an innate behaviour pattern. *E.g. male robin defends territory against other males (stimulus is the red breast).
• Innate releaser mechanism – filters out stimuli which are irrelevant from those which will produce the correct behavioural response.
• Pheromones – chemical substances which smell.
  1. Indicate sexual maturity
  2. Attract mates and mark territories, or indicate danger
  3. Volatile and disperse well
  4. Trigger courtship
  5. May be a sign of dominance

Advantages – recipient does not need to be in direct visual contact, operate in darkness, have effect for a long time and needed only in very low concentrations.

• Territorial behaviour – used by organism to defend territory (by aggression and/or pheromones) and increase breeding success. Advantages of doing so:
  1. Maintain a food resource. Larger organisms need larger territories.
  2. Defending a nesting site
  3. Attracting a mate.

The menstrual cycle

Four hormones:

• FSH (Follicle stimulating hormone)
  1. Stimulates growth and development of follicle
  2. Stimulates secretion of oestrogen

• LH (Lutenising hormone)
  1. Stimulates final development of follicle
  2. Stimulates ovulation

(LH and FSH produced by pituitary gland). Gondatrophic hormones.

• Oestrogen
  1. Stimulates repair of uterine lining/ thickening of endometrium
  2. At high concentration inhibits FSH (negative feedback)

• Progesterone
  1. Maintains uterine lining
  2. Inhibits release of FSH and LH (negative feedback)

(Oestrogen and progesterone are produced by the ovaries)

The sequence of the human menstrual cycle:

1. FSH stimulates growth of the follicle.
2. Developing follicle in ovary produces oestrogen
3. Rising oestrogen levels inhibit FSH and promote LH production
4. LH stimulates follicle development
5. Rising oestrogen levels stimulate increase in FSH
6. A surge of FSH and LH brings about ovulation
7. LH stimulates progesterone production
8. Progesterone inhibits FSH and LH. (negative feedback – Module 4 homeostasis)

Oral Contraception

• Oestrogen based
  • inhibit FSH production, grafian follicle can’t mature, no ovulation > conception not possible.

• Minipill contains only progestin
  • Inhibit LH and FSH, thickens cervical mucus preventing sperm entering.

• Other methods of birth control -
  • Abstinence – not engaging sexual activity
  • Avoid intercourse during period of maximum fertility (usually day 11-15 /28).
  • Spermicides – killing the sperm
  • Physical – condoms, diaphragms, IUDs – intra-uterine device (coil)
  • Surgery - Vasectomies (in men), Cut ovary duct, vas deferens (in women).

Infertility

Inability to conceive naturally.

• Male – low sperm count, poor sperm mobility/deformed, erectile problems.
• Female – Oviduct blocked, ova not viable, hormone imbalance, poor implantation.

Treatment of female infertility with extracted and synthetic hormones:

Clomiphene citrate and artificial FSH and LH stimulate production of oocytes – produce several ripe follicles in one cycle (called super ovulation). Ripe follicles then removed and fertilised outside womb – in vitro fertilisation – IVF.

Key stages of IVF:

• Use of fertility drugs to stimulate ovulation;
• Collection of mature egg cells and their incubation with sperms;
• Insertion of embryos into the uterus.

Pregnancy

Conception

• Fertilisation – occurs when a nucleus from a male sperm fuses with the nucleus of the ova.
• Capacitation – the removal of the sperms protective coating of proteins and glycoproteins.

Acrosome reaction

As soon as the sperm head touches the ovum surface the acrosome reaction is triggered.

• Head of sperm contains acrosome with an enzyme to digest the zona pellucida.
• One sperm will not release sufficient enzyme for complete digestion – one reason for huge numbers produced per ejaculation.
• One sperm will penetrate the surface membrane of the oocyte.
• The two haploid nuclei fuse to form diploid nucleus.
• Electrical properties of cell surface membrane changes from positive to negative so no other sperm can penetrate the fertilisation membrane. This ensures only a diploid nucleus.

The final result of fertilisation is a zygote.

• Roles of human chorionic gonadotrophin (HCG) and progesterone in controlling events of pregnancy
• GGC produced by the embryo
• It travels in the blood stream to the ovaries
• Stimulates the corpus luteum to continue to produced progesterone and oestrogen
• This maintains the uterus lining for the first 3 months of pregnancy
• After three months the placenta produces these hormones
• Also stimulates a male foetus to produce testosterone
• Progesterone will inhibit FSH production – so no further ova are produced.

Levels of HCG increase after conception and can be detected in the mother’s urine – can be used as a test for pregnancy. Test wand contains antibodies to HCG. If sufficient levels of HCG are present it will bind with a second antibody and cause a colour reaction to occur (i.e. a +ve result).

The placenta

• The mother supplies oxygen, water, amino acids, vitamins and minerals to foetus.
• The foetus releases carbon dioxide, urea and other waste products into mother’s blood stream.
• The placenta allows passage of maternal antibodies to give the foetus some immunity against disease.
• Prevents some pathogens and toxins passing to foetus.
• Acts as barrier to maternal hormones and other chemicals in mothers blood.
• Blood systems can act at different blood pressures.
• Produces hormones – progesterone and HCG.

Structure adaptations of placenta for diffusion

1. Large S.A – chorionic villi and micro villi
2. Short diffusion pathway between capillaries and maternal blood sinuses
3. Concentration gradient maintained by blood circulating
4. Counter-current system = foetal blood flows in opposite direction to maternal blood – maintains concentration gradient.
5. Foetal blood has higher affinity for oxygen than maternal blood.
6. Foetal blood has larger red blood cells and more haemoglobin – more O2 uptake.

Physiological changes in mother

• Body mass – average weight gain is 12kg. (1kg protein, foetus & placenta, breast tissue, blood…). Body fat to supply mother with extra energy e.g. breast feeding.
• Plasma volume – rises by about 50% for extra blood flow through organs.
• Red blood cell mass – increases to allow constant ratio to the increasing plasma volume.
• Cardiac output – (blood pumped by left ventricle) – per minute rises by about 30%-40% during pregnancy. Heart size increases by around 12%.
• Kidney function – Blood flow through kidneys rises from 25% - 50%. Urine tends to be more concentrated removing excess urea produced by foetus.

Human growth and development

Patterns of human growth

• Four distinct phases in life characterised by a change in growth rate:
• Infancy (0-4 yrs), childhood (4-11), adolescence (11-18), adulthood (18+).
• Uneven – many parts of body grow at different times.

1. The lymphoid tissue - One of the lymph tissues major functions is to produce antibodies, so it grows most quickly in childhood for developing resistance to disease.
2. Head and brain growth - Is most rapid in early life, at birth it is a ¼ of adult size, 90% after 6 years. Rapid increase is important as foetus head needs to be small for mother to give birth, the number of cells, fibres and myelin sheeths around axons rapidly increases for learning and development of complex behaviour.
3. Reproductive organs - Show little change until puberty, when rapid growth takes place and continues throughout adolescence.
4. Humans have an extended childhood to allow for learning.

• Candidates should be able to represent and interpret graphical data relating to growth and growth rate.

Hormonal control

• Thyroxine – produced by the thyroid gland, controls growth and the rate of metabolism (rate of break down – all reactions in cells).

The pituitary gland is in control of growth.

• Childhood growth is stimulated by Pituitary Growth Hormone, PGH.
• This stimulates growth of body tissues and elongation of the long bones to increase height.
• PGH also stimulates the thyroid to produce thyroxine.
• Sex Hormones – are released in large amounts during puberty.

FSH and LH are released from the pituitary gland and affect the gonads.

Females – the ovaries release oestrogen which stimulates adolescent growth and development of female secondary sexual characteristics (wider hips, breasts develop, excess hair). It also initiates the menstrual cycle.

Males – the testes release testosterone which stimulates adolescent growth and the development of male secondary sexual characteristics (deeper voice, beards, wider-more triangular body shape). It also initiates the production of sperm.

Puberty

Evolutionary importance of a long pre-puberty stage

• Allows time for full physical development
• Makes birth easier = e.g. head smaller at birth
• Allow a person to reach full mental maturity

Puberty results in an individual being physically and mentally stable for child birth and child rearing.

Ageing

Nervous system

• Decreased speed of conduction of nerve impulses – slows reaction times
• Loss of neurones
• Decrease in brain size – up to 40%
• Loss of memory
• Senility
• Decreased coordination

Decline of physiological function

• Basal metabolic rate decreases – need less food, may lead to fatness and obesity.
• Filtration rate - of the kidneys decreases – may lead to kidney failure.
• Cardiac output decreases – Heart muscle weakens
• Vital capacity decreases – loss of lung volume – get out of breath more
• Muscle weakens - with age as fibres are replaced with connective tissue
• Sleep patterns – are disturbed
• Smell and taste – 60%-70% loss
• Cartilage on joints wears – arthritis and reduced ease of movement
• Ovulation and oestrogen production – declines with age (menopause).

Why do we age?

Main group of factors are – Genetic and Environmental.

1. Genetic – changes occur to DNA, changes called SOMATIC MUTATIONS. Passed on to daughter cells during mitosis. Errors may lead to cell malfunction. Accumulation of genetic errors may lead to more tissue malfunctioning and resulting in aging features. May occur due to exposure to mutagens e.g. benzene, UV light.
2. Degeneration of tissue – wear and tear and incorrect repair of damaged tissues e.g. tissue elasticity is lost – wrinkles. Changes in structure of internal organs leads to reduced efficiency. Exposure to certain substances may increase this degeneration.
3. Immune system – destroys foreign bodies. It also destroys our own tissue when it has malfunctioned – e.g. cancerous cells. Ageing causes immune system to become less efficient and less able to destroy invading pathogens or cancerous cells. May also destroy its own healthy tissues – autoimmunity.

Human populations and health

MEDNs/MEDCs (more economically developed nation) – slower population growth. LEDNs - faster growth.

Developed countries (MEDC’s) have –

1. High living standards
2. Plenty of food
3. Good medical services.

These factors affect the patterns of birth and death rates in each age group.

• 'Population pyramids – show the % of males & females in each age group in a population.
• Developing countries have a high birth rate (broad base) and a high infant mortality rate (narrow upper sections). Over 35% of population is under 15.
• Average life expectancy – The age at which 50% of the people in the sample are still alive.

An LEDC pyramid

Rapid Growth

An MEDC pyramid

Slow Growth

• Survival curves – a graph plotted from records of how long each individual in a group of 10 000 lives against the number of survivors.

The size of a population at any one time is determined by four major factors.

• Number of births
• Number of deaths
• Number of immigrations (coming into the population)
• Number of emigrations

Calculations

1.

2.

3.

4.

The demographic transition model, DTM

This shows general trends in birth and death rate and total population growth. Result of a complex interaction between social and economic factors. The DTM has four main stages.

Stage 1 – High Stationary

High birth & death rates – limited food supply & disease. Low life expectancy.

Stage 2 – Early Expanding

Reduced death rate – more reliable food sources. High birth rates – better nutrition and fewer infectious diseases.

Stage 3 – Late Expanding

Fall in birth rate – birth control, larger families not needed to contribute to the household. Industrialisation and urbanisation. Population still expanding.

Stage 4 – Low Stationary

Low birth rate and birth rate fluctuations. Low death rate. More older people in population.

Social conditions affecting DTM, birth and death rates

• Food supply – needed for growth and health. Lack of food increases child mortality and decreases birth rate.
• Disease – Overcrowded conditions spread disease – high death rate.
• Drinking water and sewage disposal –have reduced incidence of water borne diseases. Sewage has pathogens removed before it is discharged into rivers as does drinking water. Reduce incidence of diseases such as cholera – which is potentially fatal so reduces the death rate.

Infectious Diseases

Pathogens are micro organisms which cause disease. There are 3 types of pathogen: Bacteria, Fungi, and Viruses.

Viruses

Characteristic features

• Small (ultra-microscopic) 100-300nm
• Acellular
• Reproduce only within host cell
• Reproduction exploits metabolism and materials of host cell

Pathogens and disease

• Influenza virus – influenza
• Mumps virus – mumps
• HIV – immune deficiency syndrome (AIDS)
• Rubella virus – german measles

Bacteria

Characteristic features

• Small (0.5-10um)
• Prokaryotic (lack nuclei, nucleic acid)
• Heterotrophic nutrition
• Asexual reproduction by binary fission
• Sexual reproduction by transfer of genetic material from one cell to another

Pathogens and disease

• Salmonella enteritidis – Salmonella food poisoning
• Mycobacterium tuberculosis – tuberculosis (TB)
• Corynebacterium diphtheria – diphtheria
• Clostridium tetani – tetanus

Fungi

Below a typical eukaryotic cell

Characteristic features

• Thread like growth (hyphae) in filamentous forms of fungi
• Cell walls made of chitin
• Eukaryotic with nucleus and membrane bound organelles
• Heterotrophic nutrition
• Reproduction by spores

Pathogens and disease

• Candida – thrush
• Epidermophyton - athletes foot
• Epidermophyton –ringworm

Transmission of pathogens

Pathogens can be transmitted in several ways. The most important are:

• Droplet infection (airborne)
• Contact (STD, touch, athletes foot)
• Food and water (salmonella, cholera)

Disease

Influenza – Droplet infection

This is also known as the flu, a contagious disease that is caused by the influenza virus. It attacks the respiratory tract in humans, the virus attaching to specific epithelial cells in the nose, throat and bronchi. It can lead to bronchitis or pneumonia. Treated by an incubation period 2-3 days, high temperature - aching limbs & fatigue (from body’s defence mechanism).

Athletes foots - Contact

Caused by fungus, attacks damp areas of body, such as skin in between toes. Fungus grows hyphae, feeds on dead epithelial cells. Area becomes red, wet, itchy, and sore.

Salmonella – Food

Bacterial food poisoning. Stomach pain, nausea, vomiting and diarrhoea, chills, headaches, fatigue, fever. Sexual intercourse also spreads infection.

Cholera – Water

1992 – Began in Bangladesh. An acute infection of the intestinal lining caused by ingestion of contaminated water or food. Water can be tested for presence of bacteria, including E Coli.

Immunity

The body has several methods of preventing pathogens entering the body:

• Skin – forms a barrier
• Tears, mucus, saliva, blood clotting
• Cilia in trachea
• Acid in the stomach

Immune response Key words:

• Antigen – specific protein on the outside of a foreign body. Allows the body to recognise a cell as foreign.
• T lymphocyte (T cells) – white blood cells made in the lymph glands. Start life in bone marrow. Has receptors on its surface which can recognise certain antigens.
• Leucocytes – white blood cells.
• B lymphocytes (B cells) – lymphocyte which multiplies rapidly to produce antibodies when antigens are detected.
• Antibodies – proteins specific to an antigen
• Immune system – provides a series of defensive responses to an invading pathogen.

When a pathogen enters the body the immune response is triggered. (Details of mechanisms of immune response not required – AQA B)

Cell mediated response (T cells)

1. Pathogen enters the body
2. recognised as foreign due to its antigens
3. antigens are recognised by T cells
4. T cells attach to antigens and destroy it
5. T cell divides rapidly to produce clones called Killer T cells (leucocytes)
6. Killer T cells destroy the antigens

• Helper T cells activate killer T cells which have been cloned
• Activate B lymphocytes
• Attract phagocytes (engulfing white blood cells).

Humoral response (B cells)

1. Receptor sites on the B cells attach to the foreign antigen
2. B cells multiply and clone
3. B cells release antibodies which are specific to the antigen
4. Antibodies bind to the antigen and destroy it
5. Antibody/antigen complex can now be engulfed by a phagocyte
6. Some B cells provide the body with long term immunological memory. The B cell produces memory cells
7. When the same antigen is encountered the body produces antibodies so pathogens are destroyed before the symptoms of the disease materialise.

Immunisation can be

• Active = body learns, or
• Passive = injected with antibodies

Artificial Immunity – vaccination

Vaccine – contains the antigens from a pathogen. After administration the body will develop antibodies against the antigen. It allows the bodies natural immune system to develop without being exposed to the disease.

There are different types of vaccine:

• Killed virulent organism – consists of dead pathogens (body makes antibodies). May need boosters.
• Live non-virulent strain – attenuated (weakened) virus. One dose gives long lasting immunity e.g. rubella, polio, mumps, TB, measles.
• Antigens – vaccine consists of a modified version of the toxin produced by the pathogen.
• Genetically engineered antigens – bacteria are modified to produce the antigens.

Why do you get some diseases once and others lots of times?

Some pathogens are constantly mutating, so this alters the antigen very subtly – so it is a different antigen. The immune system will not recognise the antigen so you will ‘get the disease again’. You will not get the same strain more than once.

The herd immunity effect

• A vaccination is effective only if a large proportion of the population has been inoculated.
• If this does not happen a large pool of infection remains in the community.
• A drop in vaccination can lead to an epidemic.
• This is called the herd effect – if enough of the herd is protected a disease will only affect isolated individuals – even then it is not likely.
• 100% of the population does not need to be vaccinated – 95% to eradicate measles.

Effects of lifestyle on health

Diet

A balanced diet contains the right balance of all nutrients we need for a healthy functioning body. There are six food groups:

• Carbohydrate
• Lipid
• Protein
• Minerals
• Vitamins
• Water

Nutritional requirements vary according to age, gender, lifestyle etc. However, the suggested mix for the UK is:

• 50% carbohydrate
• 35% fats – actual UK intake is approx. 41% of the diet
• 15% protein

Salt intake - needs to be regulated.

• Salt changes the osmotic balance of the blood cells – may cause dehydration
• May cause high blood pressure
• This in turn increase the load on the heart and may contribute to heart attacks
• Some salt cured foods may be carcinogenic

Problems caused by excess fat intake:

• Obesity
• Arteriosclerosis – plaques of fat in the arterioles

Both can lead to coronary heart disease. High blood pressure is caused by arteriosclerosis and the chances of atheroma are increased.

Mineral Ions

Mineral	Source	Function	Deficiency disease
calcium	Milk, cheese, green vegetables	Component of teeth & bone, essential for nerve + muscle function, needed in blood clotting.	Rickets (bones become soft & bend under body weight)
Iron	Liver, meat, egg yolk, nuts, legumes (roots)	Component of haemoglobin + myoglobin, component of respiratory enzymes.	Anaemia (low red blood cell count & poor O2 transport causing lethargy).
Iodine	Seafood, iodised salt	Component of thyroxine	Goitre (enlarged thyroid)

Vitamins

Vitamin	Source	Function	Deficiency disease
A (retinol)	Fish, liver, oil, dairy produce, liver, carrot, spinich	Maintenance of healthy membranes, formation of rhodopsin (visual purple)	Dry skin, xerophthalming (dry cornea), night blindness (cannot see in low light conditions)
C (calciferol)	Milk, butter, fish liver oil, sunlight on skin	Absorption of calcium and phosphorus from gut, calcification of bone	Rickets (leg bones soften and bend under body weight)
D (ascorbic acid)	Citrus fruit, blackcurrents, tomatoes	Collagen formation	Scurvey (weak, painful joints & blood vessels rupture)

Non-communicable disease

These are diseases which cannot be passed on or ‘caught’. They include heart disease and cancer.

The biological basis of heart disease

Key words:

• Atheroma – build up of fatty material on the arterial wall
• Aneurysm – balloon shaped swelling of the artery
• Myocardial infarction – heart attack caused by obstruction of the coronary arteries
• Thrombosis – blood clot formed at the site of a tear in the artery wall
• Atherosclerosis – narrowing of the arteries caused by atheroma

Atheroma as a cause of aneurysm and thrombosis

1. Fat accumulates in the endothelium of the artery and causes an atheroma
2. Muscles cells grow into the region of the atheroma and produce a plaque
3. Atherosclerosis is caused as the lumen of the artery gets narrower

This can have two effects:

1. Aneurysm – because the lumen of the artery has got narrower there is an increase of pressure. This can cause the artery wall to balloon out and weaken. These can burst leading to loss of blood. If an artery in the brain bursts this may cause a stroke.
2. Thrombosis – the plaque may tear the artery wall. A blood clot will form at the site of thee wound. The blood clot is called the thrombis. If it comes loose in the blood vessel it is called thrombosis. Thrombosis may block an artery. This is dangerous if it blocks the coronary artery. Cutting off the blood supply to the heart will cause a myocardial infraction – a heart attack.

Myocardial Infarction

The coronary muscle dies due to lack of O2. This occurs when the coronary artery becomes blocked due to atheroma and/or thrombosis. This will cause the cells to die. If the area affected by the blockage is large the myocardial infarction can be fatal.

Risk factors associated with coronary heart disease

Coronary heart disease affects the coronary arteries. There are certain factors which may increase the chance of a heart attack. Some you cannot help:

• Increasing age
• Gender
• Inheritance
• Diabetes mellitus

There are some factors you can avoid:

• Tobacco smoke
• Blood cholesterol
• Blood pressure
• Obesity
• Inactivity

Respiratory diseases

The most common are:

• Chronic bronchitis (chronic – comes on gradually, lasts a long time)
• Emphysema
• Lung cancer

The most common causes are:

• Air pollution
• Tar in cigarette smoke

Chronic bronchitis

Too much mucus in the airways, causing a persistent cough and phlegm. The airways are permanently irritated and are thus vulnerable to infection. Due to mucus, irritation and infections the bronchioles become narrow, leading to a chronic shortage of breath.

Emphysema

The structure of the alveoli starts to breakdown, leading to large airspaces which are not effective in gaseous exchange. Bronchitis leads to emphysema and is reversible, emphysema is not.

Lung cancer

Cancerous cells usually develop on the epithelial lining of the bronchioles and is known as carcinoma. The most common cause is tar in cigarette smoke. It is associated with bronchitis and emphysema.

The biological basis of Cancer

Cancer is caused by cells which have begun to divide uncontrollably. There are about 200 different cancers.

Tumours and tumour cells

Cells divide normally for growth and repair. They divide by mitosis. Cancer cells carry on dividing even though the cells do not need to be replaced. These calls are tumour or cancer cells.

If the cells carry on dividing they form a mass of cells called a tumour.

Benign or Malignant tumours?

Benign tumours – these are tumours which do not spread to other organs of the body. The cells stay together as a tumour – lump.

Malignant tumours – these cells break off the primary tumour and spread to other organs. This causes the growth of secondary tumours. This process is called metastasis.

Genes and Cancer

1. Normal cells growth is controlled by genes
2. Some genes code for the production of growth factors which stimulate cell division
3. Other genes code for the receptors for the growth factors. The receptors are on the cells surface membrane.
4. A mutation in one of these genes can lead to division being uncontrolled – cancer
5. A mutated gene is called an oncogene. An oncogene promotes cancer.

We have some genes which help us stop getting cancer – tumour suppressor genes.

They produce proteins which stop the growth factors causing cell division.

Cancer cells and the immune response

Cancer cells often have abnormal proteins on their cell surface membranes which usually cause an immune response – the cells are destroyed by the lymphocytes.

A mutated cell which does not cause an immune response is one which will cause cancer.

Carcinogens

These are things which may increase the likelihood of cancer; they mutate the DNA causing mutations in the genes for tumour suppressor genes.

Common causes of mutation

• High energy radiation – x-rays, UV light (in sunlight)
• Chemicals – alcohol, tar in tobacco smoke
• Viruses

Lung and skin cancers

Lung cancer is associated with smoking. The tar contains carcinogens and the evidence suggests that there is a cause and affect. Smoking is not always the cause but it will increase the risk.

Skin cancer or melanoma, is associated with exposure to UV light. Two factors which will further increase the risk:

1. Greater expose to sunlight (or sunbed UV)
2. Lighter coloured skin

Screeneing

Technique	Principals	Uses
X-rays	Dense objects appear white, soft tissue looks black. It ionises cells by radiation.	Can detect abnormalities in bone and soft tissue.
Endoscopy	It is an instrument that is inserted into an opening like a natural or incision. Can be used for diagnosis and treatment.	Used for diagnosis and treatment by examination of internal body.
Ultrasound	Sends high frequency radiowaves into the area being investigated & converts reflected sound into images.	Looking at foetus during pregnancy.
Genetic techniques	Can show whether a foetus has inherited a condition.	Also assesses risk of prospective parents to discuss the risk of passing genetic disorders to offspring.

Pros and cons for a genetic screening programme

Pros

• Allows screening of possible inherited genetic disorders
• Allows parents to assess their chances of passing on genetic conditions to their offspring.

Cons

• Could carry chance of miscarriage
• Ethical considerations
• Religion
• Decisions
• Information

Comments

These notes are aimed at people studying Edexcel Biology A Level, but will be suitable for other exam boards too.

Originally written by stratomaster on TSR Forums.