Section 1A: Human Biology

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A Balanced Diet

  • For good health, your diet must provide energy.
  • You need to have the right balance of foods.
  • Carbohydrates to release energy.
  • Fats to keep warm and release energy.
  • Protein for growth, cell repair and cell replacement.
  • Fibre to keep everything moving smoothly through your digestive system.
  • Tiny amounts of various vitamins and mineral ions to keep your skin, bones, blood and everything generally healthy.
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Metabolic Rate Part 1

  • You need energy to fuel to chemical reactions in the body that keep you alive.
  • There are slight variations in the resting metabolic rate of different people. For example, muscle needs more energy than fatty tissue  which means people with a higher proportion of muscle to fat will have a higher metabolic rate.
  • However, physically bigger people have a higher metabollic rate than smaller people. The bigger you are, the more energy your body needs to be supplied with as you have more cells
  • Men tend to have a slightly higher metabollic rate than women. They're slightly bigger and have a larger proportion of muscle. 
  • Genetic factors may have some effect.
  • Regular exercise can boost your resting metabolic rate because it builds muscle.
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Metabolic Rate Part 2

  • When you exercise, you need more energy so your metabolic rate goes up and stays high for some time after you finish, particularly if the exercise is strenuous.
  • People who have more active jobs need more energy on a daily basis. Builders require more energy than office workers. 
  • Your activity level should reflect the amount of energy your diet should contain.
  • If you do little exercise then you are going to need less energy so less fat and carbohydrates in your diet.

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Factors Affecting Health Part 1

  • People with a bad diet are malnourished. They can be too fat or too thin or unhealthy in other ways.
  • Eating too little can lead to: slow growth; fatigue; poor resistance to infection; irregular ovulation.
  • Deficiency diseases are caused by a lack of vitamins or minerals.
  • Excess carbohydrates in the diet can lead to obesity.
  • Obesity = 20% over maximum recommended body mass.
  • Problems caused by obesity: arthiritis (inflammation of the joints); type 2 diabetes (inabilty to control blood sugar level); high blood pressure and heart disease.
  • Too much saturated fat in your diet can increase your blood cholesterol level.
  • Eating too much salt can cause high blood pressure and heart problems.
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Factors Affecting Health Part 2

  • Exercising increases the amount of energy used by the body and decreases the amount stored as fat.
  • It also builds muscle as it helps to boost your metabolic rate.
  • Your health can depend on inherited factors.
  • An underactive thyroid gland can lower the metabolic rate and cause obesity.
  • Cholesterol is a fatty substance that is essential for good health. It is found in every cell in the body. Some inherited factors increase blood cholesterol level which increases the risk of heart disease.
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Fighting Disease

  • There are two main types of pathogen: bacteria and viruses.
  • Bacteria are very small living cells which can reproduce rapidly inside your body.
  • They make you feel ill by damaging your cells and producing toxins.
  • Viruses are much smaller than bacterium. They replicate themselves by invading your cells and using the cells' machinery to produce copies of themselves. Then they burst, releasing all of the new viruses. This cell damage is what makes you feel ill.
  • Small fragments of cells called platelets help blood to clot quickly to seal wounds.
  • White blood cells called phagocytes engluf foreign cells before digesting them. 
  • Each invading cell has antigens on its surface. When your white blood cell comes across a antigen it doesn't recognise they start to produce proteins called antibodies to lock on to and kill the invading cells. Antibodies are then produced rapidly and carried around the body to kill similar bacteria.
  • If the person is infected with the same pathogen again, the white blood cells will rapidly produce anyibodies to kill it. The will not develop the symptoms.
  • Antitoxins counteract the antibodies.
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  • Vaccinations are compromised of inactive microorganisms which carry antigens, prompting the body to produce antibodies to attack them.
  • If live microorganisms of the same type appear again, the white blood cells automatically and rapidly produce mass numbers of antibodies.
  • Epidemics can be prevented if a large percentage of the population has been vaccinated.
  • Very rare side effects include bad reactions.
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Medicine and Resistance

  • Some drugs just relieve the symptoms, but others actually cure the problem.
  • Antibiotics kill or prevent the growth of the bacteria without damaging the bodies own cells.
  • They don't destroy viruses because they reproduce using the body's own cells, which make them difficult to kill without damaging the body cells.
  • Bacteria can randomly genetically mutate to become resistant to an antibiotic.
  • When you take antibiotics only the non-resistant bacteria will be killed. 
  • This means a new strain could spread quickly within a population of people.
  • To slow down the rate of development of resistant strains, doctors avoid over-prescribing antibiotics.
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The Nervous System

  • Sense organs detect stimuli.
  • Sense organs contain receptors, a group of cells sensitive to a stimulus.
  • The CNS contains the brain and spinal cord. This coordinates a response.
  • Neurones  transmit the information as electrical impulses.
  • Instructions are sent to the effectors (muscles and glands).
  • The five sense organs are: the eyes; the ears; the nose; tongue; skin.
  • They all contain different receptors which are sensitive to a stimulus.
  • They can simulus energy into electrical impulses.
  • A stimulus can be light, sound, touch, pressure, pain, chemical or a change in position or temperature.
  • Muscles and glands are known as effectors. They respond in different ways. Muscles contract in response to a nervous impulse, whereas glands secrete hormones.d
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  • Neurones transmit information very quickly to and from the brain.
  • Sensory: the nerve cells that carry signals as electrical impulses from the receptors in the sense organs to the CNS.
  • Relay: the nerve cells that carry signals from sensory neurones to motore neurones.
  • Motor: the nerve cells that carry signals from the CNS to the effector muscles or glands.
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  • The connection between two neurones is called a synapse.
  • The nerve signal is transferred by chemicals which diffuse across the gap.
  • These chemicals then set off a new electrical signal in the next neurone.
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  • Reflexes are an automatic response to certain stimuli.
  • They can reduce the chance of being injured.
  • If you get a shock, the body releases the hormone adrenaline automatically. The passage of information in a reflex is called a reflex arc.
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The Reflex Arc

  • The neurones in reflex arcs go through the spinal cord or through an uncounscious part of the brain.
  • When a stimulus is detected by receptors, impulses are sent along a sensory neurone to the CNS.
  • When the impulses reach a synapse between the sensory neurone and a relay neurone, they trigger chemicals to be released. These chemicals cause impulses to be sent along the relay neurones. The same thing happens when they reach a synapse between the realay and motor neurones.
  • The impulses then travel along the motor neuurone to the effector.
  • The muscle contracts or the gland secretes.
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  • Hormones are chemical messengers which travel in the blood to activate targe cells.
  • Chemicals released directly into the blood.
  • They are carried in blood plasma to other parts of the body but only affect target cells in a particular plalce. Hormones control things in organs that need constant adjustment.
  • Hormones are produced and secreted by various glands. 
  • The pituitary gland this produces many important hormones including FSH and LH.
  • The ovaries: produce oestrogen which is involved in the menstrual cycle.
  • If a response is really quick then it is probably a nervous response. But if it lasts a long time then it is probably hormonal.
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The Menstrual Cycle

  • Day 1: The uterus lining breaks down for about four days.
  • Day 4-14: The uterus lining builds into a thick, spongey layer of blood vessels, ready to recieve a fertilised egg.
  • Day 14: An egg is released from the ovary.
  • Day 15-28: The wall is maintained. If no fertilised egg has landed on the uterus wall by day 28 then the lining starts to break down and the cycle starts again.
  • Follicle-Stimulating Hormone: produced by the pituitary gland; causes an egg to mature in one of the ovaries; stimulates the ovaries to produce oestrogen.
  • Oestrogen: produced in the ovaries; cause pituitary to produce LH; inhibits the further release of FSH.
  • Luteinising Hormone: produced by the pituitary gland; stimulates the release of an egg around the middle of the menstrual cycle.
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Reducing Fertility

  • If oestrogen is taken every day, it inhibits the production of FSH. After a whiile egg development and production stop and stay stopped.
  • Progesterone reduces fertility by stimulating the production of a thick cervical mucus which prevents any sperm getting through and reaching the egg.
  • The pill is an oral contraceptive. It contains lower doses of oestrogen than it used to to reduce side effects.
  • Advantages: 99% effective; reduces the risk of getting some types of cancer.
  • Disadvantages: there is still a slight chance of getting pregnant; it can cause side effects like headaches, blood clotting, nausea, irregular menstrual bleeding and fluid retention; it does not protect against STD's..
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Increasing Fertility

  • Some women have levels of FSH that are too low to cause their eggs to mature. This means that no eggs are released and they cannot get pregnant.
  • FSH and LH can be injected into them to stimulate egg release in their ovaries.
  • Advantages: it can help a lot of women to get pregnant.
  • Disadvantages: it doesn't always work; some women may have to do it multiple times which can be very expensive; too many eggs could be stimulated resulting in unwanted multiple pregnancies.
  • In Vitro Fertilisation involves collecting eggs from the women's ovaries and fertilising them in a lab using the man's sperm. They are then grown into embryos. 
  • Once the embryos are tiny balls of cells, one or two are transferred into the woman's uterus. FSH and LH are given before egg collection to stimulate egg production.
  • Advantages: can help an infertile couple have a child.
  • Disadvantages: some women may have a strong reaction to the hormones (abdominal pain, vomiting, dehydration); there have been reports of an increased risk of cancer due to the hormonal treatments; multiple births can happen which means that there is a higher risk of miscarriage and stillbirths.
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Plant Hormones Part 1

  • Auxin is a plant hormone that controls growth near the tips of shoots and roots.
  • It controls the growth of a plant in response to light (phototropism), gravity (gravitropism or geotropism) or moisture.
  • Auxin is produced in the tips and moves backwards to stimulate cell elongation which occurs in the cells just behind the tips.
  • If the tip of a shoot is removed, no auxin is available and the shoot may stop growing.
  • Extra auxin promotes growth in the shoot but inhibits growth in the root.
  • Most weeds in crop fields are broad-leaved, unlike grasses and cereals which have very narrow leaves. Selective weedkillers are made of plant growth hormones. They only affect the broad-leaved plants. They disrupt their normal growth patterns which kills them but leave the crops untouched.
  • Plant cuttings won't always grow in soil. If you add rooting powder which contrains the plant hormone auxin, they'll produce roots rapidly and start growing as new plants. This helps growers to produce lots of clones of a really good plant very quickly.
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Plant Hormones Part 2

  • Shoots grow towards light. When a shoot is exposed to light, more auxin accumulates in the side that's in the shade than the side that's in the light. This makes the cells elongate faster on the shaded side so the shoot bends towards the light.
  • Shoots grow away from gravity. When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip with more auxin on the lower side. This causes the lower side to grow faster bending the shoot upwards.
  • Roots grow towards gravity. A root growing sideways will also have extra auxin on its lower side. But in a root the extra auxin inhibits growth. This means the cells on top elongate faster and the root bends downwards.
  • Roots grow toward moisture. An uneven amount of moisture either side of the root produces more auxin on the side with more moisture. Theis inhibits growth on that side causing the root to bend in that direction, towards the moisture.
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  • Homeostatis means all the functions in your body which try to maintain a constant internet environment. 
  • To keep all of our cells working properly certain things must be kept at the right level.
  • Bodily levels that need to be controlled include: ion content; water content; sugar content; temperature.
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Controlling Ion Content

  • Ions are taken into the body in food then absorbed into the blood. 
  • If the food contains too much of any kind of ion then the excess ions need to be removed. Salty meat may contain too much sodium. 
  • Some ions are lost in sweat, which tastes salty.
  • The kidneys will remove the excess from the blood, which is gotten rid of in urine.
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Controlling Water Content

  • Water is taken into the body through food and drink and is lost from the body in: the skin as sweat; the lungs as breath; the kidneys as urine. 
  • One a cold day or when you are not exercising you will produce more urine which will be pale since the waster carried in the urine is more diluted. 
  • On a hot day, or when you are exercising you sweat a lot so you will produce less urine but this will be more concentrated hence a deeper colour. You will also lose more water through your breath because you breath faster.
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Controlling Sugar Content

  • Eating foods containing carbohydrates puts glucose into the blood from the gut.
  • The normal metabolism rate of cells removes glucose from the blood. But if you do a lot of vigorous exercise then much more glucose it removed.
  • A hormone called insulin helps to maintain the right level of glucose in your blood, so your cells get a constant supply of energy.
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Controlling Body Temperature

  • All enzymes work best at a certain temperature. The enzymes within the human body work best at about 37 °C. This is the temperature that your body tries to maintain.
  • A part of the brain (the hypothalamus) acts as your own personal thermostat. It is sensitive to the blood temperature in the brain and it recieves messages from the skin the provide information about skin temperature.
  • By doing this, the brain helps to keep out body at the right temperature.
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  • Some of the chemical changes caused by drugs can lead to the body becoming addicted to the drug. If the drug is not taken then it can lead the addict to suffer physical withdrawal symptoms.
  • Medicinal drugs can be medically useful, like antibiotics. For some of these drugs, you don't need a prescription (paracetamol) but for others you do (morphine).
  • Performance-enchancing drugs can improve a person's performance in sport.
  • Recreational drugs are used for fun. These can be legal or illegal.
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Performance Enhancing Drugs

  • Some athletes take performance-enhancing drugs to make them better at sport.
  • There are several different types. Anabolic steroids increase muscle size and stimulants increase heart rate.
  • These drugs can have negative health effect, for example steroids can cause high blood pressure.
  • Some of these drugs are banned by law and some are prescription only. But all are banned by sporting bodies such as the IOC.
  • For: athletes have the right to make their own decision about whether taking drugs is worth the risk or not; drug-free sport isn't really fair anywat, as different athletes have access to different training facilities, coaches and equipment et cetera.
  • Against: it is unfair if people gain an advantage by taking drugs not just through training; athletes may not be fully informed of the serious health risks of the drug they take
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Recreational Drugs

  • Illegal drugs are often described as being soft or hard. Hard drugs are often more addictive and generally more harmful. However soft drugs, such as cannabis, can also cause the same heart and circulatory problems as hard drugs heroin and ecstasy.
  • A lot of people take drugs for enjoyment, relaxation, stress relief or peer pressure.
  • Almost all users of hard drugs have tried cannabis. The link between cannabis and hard drugs isn't clear but three opinions are common.
  • Cannabis is a 'stepping stone': the effects of cannabis creat a desire to try harder drugs.
  • It is a 'gateway drug': cannabis use brings people into contact with drug dealers.
  • It is all down to genetics: certain people are more likely to take drugs generally, so cannabis users will also try other drugs.
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The Impact of Legal Drugs

  • Smoking: causes disease of the heart, blood vessels and lungs; tobacco smoke also causes cancer; nicotine, the drug found is cigarettes, is addictive.
  • Alcohol: affects the nervous system and slows down the body's reactions; too much alcohol leads to impaired judgement, poor coordination and unconsciousness; excessive drinking can cause liver disease and brain damage; alcohol is also addictive.
  • Tobacco and alcohol have a bigger impact in the UK than illegal drugs as so many people take them. 
  • The NHS spends lots of money treating people with lung diseases cause by smoking.
  • The same goes for alcohol. The costs to the NHS are huge, as are the costs related to crime (police time, damage to people and property) and the economy (lost working days et cetera)
  • In addition to the financial costs, alcohol and tobacco cause sorrow and anguish to people affected by them, directly or indirectly.
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