Life depends on an enormous number of interlocking chemical reactions. These reactions make it possible for organisms to do work - such as moving around or catching prey - as well as growing, reproducing, and maintaining the structure of their bodies. Living things must use energy and consume nutrients to carry out the chemical reactions that sustain life.
A combination of a balanced diet and regular exercise is needed to help keep the body healthy. There's an old saying, "You are what you eat." In some senses, this is literally true! When we eat food, we take in the large biological molecules found in the food, including carbohydrates, proteins, lipids (such as fats), and nucleic acids (such as DNA)
Our bodies provide an excellent environment for many microbes which can make us ill once they are inside us. Therefore, the body firstly needs to stop most microbes getting in then deal with any microbes which do happen to get in. Vaccination can be used to prevent infection although, the human body has its own natural defense systems.
Compounds in living organisms
A nutrient is a substance which is needed for growth, repair and metabolism (The sum total of the biochemical reactions occurring in an organism). Our three main nutrients are:
- lipids (fats and oils)
These nutrients are all examples of organic chemicals. This means that they all contain carbon atoms, covalently bonded to the atoms of other elements
Carbohydrate, lipid and protein consist of carbon (C), hydrogen (H) and oxygen (O). Proteins also contain nitrogen (N), and sometimes sulfur (S).
Remember that these nutrients contain hydrogen atoms and not hydrogen gas.
Carbohydrate is the group of organic compounds occurring in foods and living tissues that are made of sugars, starch and cellulose. Typically can be broken down to release energy in the animal body. It is vital for energy in humans and is stored as fats if eaten in excess. In plants, carbohydrates are important for photosynthesis.
Monosaccharides: The basic units of carbohydrates are simple sugars, such as glucose and fructose - called monosaccharides.Glucose and fructose have the same molecular formula, C6H12O6, however their structure is different. Monosaccharides are relatively small molecules.
Disaccharides: Sucrose (table sugar) is a disaccharide. It consists of two monosaccharides, glucose and fructose, joined together.
Polysaccharides: Starch and cellulose (found in plants) and glycogen (found in animals) are polysaccharides. They are long chains of monosaccharides consisting of many glucose molecules joined together which make them very large carbohydrate molecules.
Lipids are large molecules of fats and oils. Fats and oils are natural substances produced from the reaction of glycerol with fatty acids. The large molecules are made from smaller units of fatty acids and glycerol.The fatty acid tails are long chains of carbon and hydrogen.
Proteins are organic compounds made up of smaller units of amino acid molecules (the building blocks to make a protein molecule) composed of carbon, oxygen, hydrogen, nitrogen and sometimes sulfur. They carry out many important bodily functions, such as giving cells their structure. They are essential for healing wounds and repairing tissue, especially in the muscles, bones, skin and hair as well as for the removal of all kinds of waste deposits produced in connection with the metabolism.
As one of the three main food groups, proteins are needed by the body for cell growth and repair.There are only about 20 different naturally-occurring amino acids. However, each protein molecule has hundreds, or even thousands, of them joined together in a unique sequence and folded into the correct shape. This gives each protein its own individual properties.
An enzyme is a protein that functions as a biological catalyst - a substance that speeds up a chemical reaction without itself being changed by the reaction.
In the lock and key model, the shape of the active site matches the shape of its substrate (substance on which enzymes act) molecules. This makes enzymes highly specific - each type of enzyme can catalyse only one type of reaction (or just a few types of reactions).
If the shape of the enzyme changes, its active site may no longer work. We say that the enzyme has been denatured. Enzymes can be denatured by high temperatures or extremes of pH. When a substance is denatured, its structure and function is altered. This can be caused by heat, altered pH or by chemical agents.
Chemical and physical tests
Starch is detected using iodine solution. The solution is brown but turns blue-black if starch is present.
Proteins are detected using biuret reagent. In the presence of protein, this blue solution will change color to mauve or purple.
Lipids are detected using the emulsion test. This is what happens:
- the test substance is mixed with 2 cm3 of ethanol
- an equal volume of distilled water is added
- a milky-white emulsion forms if the test substance contains lipids
Sources and uses table
Vitamins are only needed in small amounts to maintain a healthy body. Having a lack of vitamins in the diet leads to deficiency symptoms.
Vitamin C is also known as ascorbic acid and is needed to:
- help heal wounds
- maintain healthy connective tissue - which gives support and structure for other tissues and organs
Vitamin C deficiency leads to scurvy. The symptoms of scurvy include bleeding and swelling of the gums, loss of teeth, tiredness and muscle and joint pain.
Vitamin C is found in a wide variety of fruit and vegetables:
- citrus fruits - oranges, lemon and lime
- berries - blackcurrant and strawberries
- red and green peppers
- leafy green vegetables - such as brussels sprouts and broccoli
Vitamin D has several important functions. For example, it helps to regulate the amount of calcium and phosphate in the body. These nutrients are needed to keep bones and teeth healthy. That is why a lack of vitamin D can lead to bone deformities such as rickets in children, bone pain and tenderness as a result of a condition called osteomalacia in adults.
The human body can make vitamin D when our skin is exposed to sunlight and that is where most of our Vitamin D comes from. Though good dietary sources of vitamin D include:
- margarine and breakfast cereals fortified with vitamin D
- oily fish such as salmon, mackerel and sardines
Vitamin A is also known as retinol, needed to maintain:
- good vision
- healthy skin
- immunity against infection - when a person's body is not prone to a disease because they have a resistance to it.
Good sources of vitamin A are:
- dairy products - milk, cheese, eggs and yoghurt
- mackerel and other oily fish
The body can convert beta-carotene (found in carrots, spinach and mangoes) into vitamin A. Vitamin A deficiency leads to night blindness, which is when a person finds it difficult to see well in dim light.
Like vitamins, mineral ions are only needed in small amounts to maintain a healthy body. A lack of the correct mineral ions in the diet also leads to deficiency symptoms.
Calcium is needed to help build strong bones and teeth, ensuring that blood clots normally and to regulate muscle contractions, including heartbeat. The symptoms of calcium deficiency are weak bones and teeth, poor clotting of the blood and muscle spasms. Sources:
- milk, cheese and other dairy foods
- green leafy vegetables – broccoli, cabbage and okra, but not spinach
- bread and anything made with fortified flour
- sardines and pilchards
Iron is needed to produce haemoglobin, found in red blood cells.Iron deficiency causes anaemia. People with anaemia become tired and weak because their blood does not transport enough oxygen. Good sources of iron are liver, red meat, beans and nuts and dried fruits such as dried apricots.
Water and dietary fibre
Water and dietary fibre (roughage) are also important components in the diet.
About two-thirds of the human body is water. It is found in the cytoplasm of our cells and in body fluids like blood. Sources of water are food, drinks, and metabolic processes - aerobic respiration.
Dietary fibre consists of material in food that cannot be digested, in particular cellulose from plant cell walls. Sources of fibre include:
Dietary fibre is important because it provides bulk, which helps the walls of the intestine move food and faeces along the gut. Lack of dietary fibre can lead to constipation.
Eat well plate
A balanced diet is a diet in which all the components needed to maintain health are present in appropriate sizes. Because the different food groups have diffeent uses in the body, a balanced diet should involve the right amounts of...
- carbohydrates to release energy
- fats to keep warm
- protein for growth, cell repair and cell replacement
- fibre to keep everything moving smoothly through our digestive system
- vitamins and mineral ions to keep skin, bones, blood and everything else generally healthy
Unsaturated fats are healthier fats and include vegetable, rapeseed, olive and sunflower oils. Remember all types of fat are high in energy and should be eaten sparingly.
The amount of energy different people need varies because of who they are and what they do; factors of age, gender, pregnancy and activity levels. Energy is needed to fuel chemical reactions in the body that keep you alive. The slight variations in the resting metabolic rate of different people are caused because:
- Muscle needs more energy than fatty tissue which means (all things being equal) people with a higher proportion of muscle to fat in their bodies will have a higher metabolic rate.
- Regular exercise can boost metabolic rate because it builds muscle. Also the metabolic rate increases as we exercise and stays high for a while afterwards. People who exercise regularly are usually healthier than people who don't.
- In general, the greater a person’s mass, the more energy they need. A woman’s energy needs increase when she is pregnant.
- Similarly, physically bigger people are likely to have a higher metabolic rate than smaller people because there are more cells in a bigger body that needs to be supplied with energy. That is why men tend to have a slightly higher rate than women
- Genetic/ inherited fators
If someone’s diet consists of food with a lower energy content than the amount of energy their body uses, the person will lose body mass.
People who are active tend to need more energy than sedentary people - taking little or no physical activity as part of everyday living.
Your metabolic rate increases during exercise and stays high for some time after finished (particulary if the exercise is strenuous - requiring or using great effort or exertion),
This means activity level affects the amount of energy one's diet should contain - little exercise needs less energy so less fat and carbohydrates should be in the diet, as opposed to a person constantly on the go. For example, an adult office worker might need 10,000 kJ per day, but a manual worker might need 15,000 kJ per day.
Healthy is free from of disease but health can be affected in ways which some are linked.
Having an extremely unbalanced diet means one is malnourished (both fat or thin). Eating too much can lead to obeisity and follow on with related diseases such as arthritis, type 2 diabetes, high blood pressure and heart disease. Too much saturated fat causes cholesterol while consuming excess salt can cause high blood pressure and heart problems.
An lack of exercise means not enough energy is being used up therefore, the amount of food stored as fat will not decrease. Exercise is a way to prevent obeisity.
It's not just about what you eat and how much exercise you do because inherited factors like cholesterol level in the blood can affect health. Cholesterol is made in the liver and is needed for healthy cell membranes. However, too much cholesterol in the blood increases the risk of heart disease and diseased arteries.
Evaluating food and diet
Evaluate means to present a judgement of an issue by stressing both strengths and advantages, and weaknesses and limitations. The emphasis is on assessing the value, worth or relevance of the matter under scrutinty.
Evaluate information about:
- nutritional information
- how food affects health
- how lifestyle affects health - what you do and what you eat
- slimming claims that are not scientifically proven
Pathogen - bacteria
Pathogens are microorganisms that cause disease. Bacteria and viruses are the main types of pathogen. Bacteria release toxins, and viruses damage our cells.
White blood cells can ingest and destroy pathogens by producing antibodies that destroy the infectious microorganisms, and antitoxins to neutralise toxins created as a by-product.
Bacteria are microscopic organisms. They come in many shapes and sizes, but even the largest are only 10 micrometres long - that's 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 by bacteria:
- Food poisoning from Escherichia coli and salmonella
- Gonorrhea, the sexually transmitted disease, by neisseria gonorrhoeae
- Whooping cough because of bordetella pertussis
- Meningitis caused by neisseria meningitidis
Pathogen - viruses
Viruses are not cells, they are many times smaller than bacteria. They are among the smallest organisms known and 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. A virus can get inside a cell and, once there, take 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)
- The common cold
- Measles, mumps and rubella
- Chicken pox - Varicella-Zoster Virus
- AIDs - Human Immunodeficiency Virus
- Tuberculosis - mycobacterium tuberculosis
- Ebola - filoviridae virus
Most pathogens have to get inside someone’s body in order to spread infection. Once they are in, the body provides ideal living conditions: plenty of food, water and warmth. Standing in their way are our immune systems, which are the body’s coordinated response to invading pathogens.
The first line of defence, though, is the body’s natural barriers include:
- chemicals in tears
- chemicals in sweat
- stomach acid
White blood cells
The body’s first line of defence is called passive immunity, which means preventing the pathogen from entering in the first place. If a pathogen manages to get into the body, the second line of defence takes over. This is called active immunity. The white blood cells have key functions in this. White blood cells can:
- engulf pathogens digest / destroy them
- produce antibodies to destroy particular pathogens
- produce antitoxins that counteract the toxins released by invading pathogens.
In a written examination, it is easy to get carried away with metaphors about invaders and battles. Stick to the point. Note that:
- The pathogens are not the disease - they cause the disease
- White blood cells do not eat the pathogens - they ingest them
- Antibodies and antitoxins are not living things - they are specialised proteins.
Pathogens contain certain chemicals that are foreign to the body. These chemicals are called antigens. Certain white blood cells, called lymphocytes, can produce specific antibodies to kill a particular pathogen. Antibodies are proteins. They can neutralise pathogens in a number of ways. For example, they can:
- bind to pathogens and damage or destroy them
- coat pathogens, clumping them together so that they are easily ingested by white blood cells called phagocytes.
Each lymphocyte produces 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 to kill the pathogen.
Vaccination involves putting a small amount of an inactive form of a pathogen, or dead pathogen, into the body.
Vaccination promote the body to produce enough white blood cells to protect itself against a pathogen. Antibiotics are effective against bacteria, but not against viruses. Some strains of bacteria are resistant to antibiotics. So people can be immunised against a pathogen through vaccination. Different vaccines are needed for different pathogens. For example, the MMR vaccine is used to protect children against measles, mumps and rubella (German measles).
Vaccines can contain live pathogens treated to make them harmless which acts as an antigen. When injected into the body, they stimulate white blood cells to produce antibodies against the pathogen. Vaccination protects from future infection. If the person does get infected by the pathogen later, their body can respond in the same way as if they had had the disease before. If a large proportion of the population is immune to a particular pathogen, the spread of that pathogen is greatly reduced.
Fighting disease - drugs
Some medicines help to relieve the symptoms of a disease while others kill the infectious pathogens.
Painkillers helps to relieve the symptoms of an infectious disease, but they do not kill the pathogens involved. For example, paracetamol, aspirin and morphine block nerve impulses from the painful part of the body, or block nerve impulses travelling to the part of the brain responsible for perceiving pain.
Antibiotics are substances that kill bacteria or stop their growth. They do not work against viruses because they live and reproduce inside cells. It is difficult to develop drugs that kill viruses without also damaging the body’s tissues.
Penicillin, the first antibiotic, 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. Since the discovery of penicillin, many other antibiotics have been discovered and developed. Most antibiotics used in medicine have been altered chemically to make them more effective and safer for humans.
Different bacteria cause different diseases. One antibiotic may only work against one type of bacteria, or a few types. This means that a range of different antibiotics is needed for the treatment of the whole range of bacterial diseases. Different antibiotics work in different ways. It is important that specific bacteria should be treated using specific antibiotics.
- penicillin - breaks down cell walls
- erythromycin - stops protein synthesis
- ciprofloxacin - stops DNA replication
Bacterial strains can develop resistance to antibiotics. This happens because of 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. The main steps in the development of resistance are:
- antibiotics kill individual pathogens of the non-resistant strain
- resistant individual pathogens survive and reproduce
- the population of the resistant pathogens increases.
MRSA is the acronym for 'methicillin-resistant staphylococcus aureus'. It's very dangerous because it's a strain of bacterium that is resistant to most antibiotics.
The rate of development of resistant strains of bacteria can be slowed down by completing the full course and avoiding the unnecessary use of antibiotics, such as mild throat infections. The appearance of resistant strains of bacteria means that vaccinations and antibiotics may no longer work. As people are not immune to it, and there is no effective treatment, a resistant strain will spread rapidly. New antibiotics must be developed as a result.