Human Biology & Living Organisms Key Notes

Human Biology & Living Organisms Key Notes

Our energy is derived from food - whereas plants can produce their own energy from sunlight, we must consume food

This food is our raw material - needed to make new substances for: -

·  Energy (movement etc…)

·  Growth and repair

·  Health

A balanced diet contains the different nutrients in the correct amounts, keeping us healthy

Certain foods are not necessarily 'bad' for us, but eating too much of them could be

Foods contain nutrients: these are substances which provide raw materials for the body (we need nutrients, along with fibre and water for a healthy diet)

There are seven different nutrients, and some foods are particular rich in certain nutrients: -

Different foods contain different substances - there is no one food that contains all the substances the body needs. Instead you must eat a wide variety of foods - balancing your diet

Different people need different amounts of food. You need more food if you are particularly active, are pregnant etc… (the amount of energy food contains is measured in kilojules (kJ) - if you are more active, your kJ intake needs to be greater )

If we eat too little food, we will use up our store of fat and become too thin. If we eat too much food, especially foods rich in sugar and fat, we will increase our store of fat and become too fat

If you have too little of a particular nutrient, we say that you have a deficiency in that nutrient, e.g. fibre deficiency can lead to constipation

Mineral deficiencies - e.g. iron deficiency can lead to anaemia (too few red blood cells); iodine deficiency can lead to a swelling in the neck called a goitre

Vitamin deficiencies - e.g. vitamin A deficiency can cause blindness; vitamin C deficiency can cause scurvy (makes the gums bleed); and vitamin D deficiency can cause rickets (legs bow outwards in growing children)

A healthy diet contains all the different nutrients in the correct amounts, and provides the right amount of energy for each individual

An unbalanced diet can lead to a person becoming malnourished – they may be too thin or too fat as a result, and they may suffer from deficiency diseases

Respiration is the chemical reaction that allows cells to release energy from food – the metabolic rate is the speed at which such chemical reactions take place in the body

Metabolic rate is the rate at which your body burns calories

Basal metabolic rate (BMR) is the rate when resting (you can inherit a high BMR)

You can also increase your BMR with more exercise (increasing your muscle to fat ratio)

Malnourishment is a person with an unbalanced diet – these diseases are due to malnourishment: -

·  Anaemia – lack of iron

·  Obesity – too much fat

·  Kwashiorkor – too much carbohydrate and no protein

·  Anorexia – too little food

RDA is the amount of a specific nutrient which is recommended for consumption per day – food packaging must clearly show this for each nutrient

A balanced diet should contain fats, proteins and carbohydrates in roughly these amounts: carbohydrates, fat and protein

Food labels on products show the RDA of different nutrients within the food, usually per 100g and per serving of food…

Overweight people may suffer from health problems, including: -

  Diabetes(type 2) - an illness in which the body is unable to control the amount of sugar in the blood

  Arthritis- an illness in which the joints become worn, inflamed and painful

  High blood pressure

  Heart disease

BMI (body mass index) is a scale to determine your ideal weight – the calculation is your weight (kg) ÷ height2 (m)

Blood pressure is the force exerted on the blood vessel walls from circulating the blood

High blood pressure can lead to heart disease by straining the heart and damaging the blood vessels

Normal blood pressure is 120/80 – overweight people and those who eat too much salt often have high blood pressure

The heart is an organ that needs its own supply of blood to keep it working – if the blood supply is reduced, the heart muscle will not work properly and will become weaker

A heart attack happens when part of the heart does not get any blood because of a blocked artery

Table salt is sodium chloride – too much salt in the diet can lead tohigh blood pressure, which in turn leads to an increased risk of heart disease and strokes

Salt isfound naturally in many kinds of food, but more is added by food manufacturers - and many people add even more when they are eating

Processed foods often have a high proportion of salt and fat

Salt added to food during processing accounts for about two-thirds of the average salt intake

Cholesterol (C27H46O) is a substance found in the blood – it is made in the liver and is needed for healthy cell membranes

Too much cholesterol in the blood increases the risk of heart disease, and of diseased arteries

Cholesterol is important for a variety of body functions, including: -

  Cell membranes

  Hormones

  Bile acids

  Insulating nerve fibres

The bloodstream transports cholesterol around the body attached to proteins

The combination of cholesterol and protein is called lipoprotein, and there are two type: -

  Low-density lipoproteins (LDLs) - carry cholesterol from the liver to the cells

  High-density lipoproteins (HDLs) - carry excess cholesterol back to the liver

LDLs are often called 'bad' cholesterol because they lead to fat building up on artery walls, which causes heart disease – 70% of cholesterol consisting mostly of fat

HDLs are often called ‘good’ cholesterol because they help to stop fat building up in the arteries – 20% of cholesterol consisting mostly of protein

Monounsaturated and polyunsaturated oils (found in vegetable oils) help to reduce cholesterol levels in the blood, and also increase the proportion of HDLs compared with LDLs

Molecules of vegetable oils consist of glycerol and fatty acids

Glycerol has 3 carbon atoms and fatty acids have long chains of carbon atoms

The fatty acids in some vegetable oils are saturated, and only have single bonds between their carbon atoms

Saturated oils tend to be solid at room temperature, and are sometimes called vegetable fats instead of oil – lard is an example of a saturated oil

The fatty acids in some vegetable oils are unsaturated, and have double bonds between some of their carbon atoms

Unsaturated oils tend to be liquid at room temperature, and are useful for frying food – they can be divided into two categories: -

  Monounsaturated fats have one double bond in each fatty acid

  Polyunsaturated fats have many double bonds

The carbon-carbon double bonds in unsaturated oils can be detected using the elements bromine or iodine

These elements react with the double bonds in the oils, and the more double bonds there are, the more bromine or iodine is used up

Bromine water is a dilute solution of bromine, which is normally orange-brown in colour – it becomes colourless when shaken with an alkene, or with unsaturated fats (when shaken with alkanes or saturated fats, its colour remains the same)

A disease is any condition where the body isn’t working as it should – this could be caused by a malfunction in the body (as with diabetes) or it could be caused by a pathogen (a microbe that causes disease)

Pathogens are micro-organisms that cause infectious disease: bacteria and viruses are the main pathogens

Microbes are micro-organisms that can cause diseases, entering the body in a number of ways: -

One easy way to defend the body against illness is by keeping it clean and hygienic as microbes can spread very quickly in unhygienic conditions – the spreading of microbes is known as transmission

As soon as a virus or bacterium enters the body, we are termed infected (not the same as being ill – illness results from the effects these microbes have on our body

Bacteria and viruses have the ability to produce poisons known as toxins

There are two types of outbreaks: -

  An epidemic – a local outbreak of disease

  A pandemic – a global outbreak of disease

Bacteria are microscopic organisms – they come in many shapes and sizes, but even the largest are only 10 micrometres long (10 millionths of a metre)

Bacteria are living cells and, in favourable conditions, can multiply rapidly – once inside the body, they release poisons or toxins that make us feel ill

Diseases caused by bacteria include: -

  Food poisoning

  Cholera

  Typhoid

  Whooping cough

  Gonorrhoea (STI)

Viruses are significantly smaller than the smallest bacterium (among the smallest organisms known)

Viruses consist of a fragment of genetic material inside a protective protein coat

Viruses can only reproduce inside host cells, and they damage the cell when they do this – if a virus can get inside a cell it can take it over and make hundreds of thousands of copies of itself

Eventually the virus copies fill the whole host cell and burst it open – the viruses are then passed out in the bloodstream, the airways, or by other routes

Diseases caused by viruses include: -

  Influenza (flu)

  Colds

  Measles

  Mumps

  Rubella

  Chicken pox

  AIDS

In the late 1840’s Dr. Ignaz Semmelweis noticed that the death rate in a delivery room was high

He thought that the doctors were carrying infections between patients and ordered doctors wash their hands with a chlorinated solution before examining women in labour

The mortality rate in his maternity wards eventually dropped from twelve percent to less than one percent

Diseases can be transmitted via: -

  Droplet transmission (sneezes & coughs)

  Water transmission (polluted water)

  Vector transmission (animals)

  Contact transmission (person to person)

The body has different ways of protecting itself against pathogens – the first defence is passive immunity – aimed at stopping the pathogen getting into the body in the first place

The body’s passive immunity system includes: -

  Skin

  Mucus and cilia (tiny hairs) in the respiratory system

  Acid in the stomach

  Enzymes in tears

If a pathogen still manages to get into the body, the second defence takes over – this is called active immunity, and the white blood cells have key functions in this…

White blood cells can: -

  Ingest pathogens and destroy them

  Produce antibodies to destroy pathogens

  Produce antitoxins that neutralise the toxins released by pathogens

Pathogens are not the disease – they cause the disease!

White blood cells ingest pathogens (they do not eat them!)

There are several different types of white blood cells, each with different functions, but they can be put into two main groups: -

  Phagocytes or macrophages

  Lymphocytes

Phagocytes can easily pass through blood vessel walls into the surrounding tissue and move towards pathogens or toxins

They then either ingest and absorb the pathogens or toxin; or release an enzyme to destroy them

Having absorbed a pathogen, the phagocytes may also send out chemical messages that help nearby lymphocytes to identify the type of antibody needed to neutralise them

Pathogens contain certain chemicals that are foreign to the body and are called antigens

Each lymphocyte carries a specific type of antibody - a protein that has a chemical 'fit' to a certain antigen

When a lymphocyte with the appropriate antibody meets the antigen, the lymphocyte reproduces quickly, and makes many copies of the antibody that neutralises the pathogen

Antibodies neutralise pathogens in a number of ways: -

  They bind to pathogens and damage or destroy them

  They coat pathogens, clumping them together so that they are easily ingested by phagocytes

  They bind to the pathogens and release chemical signals to attract more phagocytes

Lymphocytes may also release antitoxins that stick to the appropriate toxin stopping it damaging the body

Natural immunity – antibodies are produced by a person when needed or they are passed on by the mother during pregnancy

Artificial immunity – a vaccine with dead microbes is injected tricking the body into producing antibodies ready for the real thing

People can be immunised against a pathogen through vaccination – this involces putting a small amount of an inactive form of a pathogen, or dead pathogen, into the body

Vaccines can contain: -

  Live pathogens (treated to make them harmless)

  Harmless fragments of the pathogen

  Toxins produced by pathogens

  Dead pathogens

These all act as antigens – when injected into the body, they stimulate white blood cells to produce antibodies against the pathogen

Because the vaccine contains only a weakened or harmless version of a pathogen, the vaccinated person is not in danger of developing disease - although some people may suffer a mild reaction – if the person does get infected by the pathogen later, the required lymphocytes are able to reproduce rapidly and destroy it

Antibiotics are substances that kill bacteria or stop their growth (often targeting the bacteria’s cell capsule)

They do not work against viruses – it is difficult to develop drugs that kill viruses without also damaging the body’s tissues

The first antibiotic (penicillin) was discovered in 1928 by Alexander Fleming – he noticed that some bacteria he had left in a petri dish had been killed by naturally occurring penicillium mould

Bacterial strains can develop resistance to antibiotics, due to natural selection

In a large population of bacteria, there may be some cells that are not affected by the antibiotic – these cells survive and reproduce, producing even more bacteria that are not affected by the antibiotic