AQA

Life Processes and Living Things

Humans as Organisms

10.4 Nutrition	KS3	The human diet includes carbohydrates, proteins and fats. The digestive system breaks down food and absorbs it into the bloodstream. The digestive system includes the gullet, stomach, liver, pancreas, small intestine and large intestine.
	FT and HT	Starch (a carbohydrate), proteins and fats are insoluble. They are broken down into soluble substances so that they can be absorbed into the bloodstream in the wall of the small intestine. In the large intestine much of the water is absorbed into the bloodstream. The indigestible food which remains makes up the bulk of the faeces. Faeces leave the body via the anus. The breakdown of large molecules into smaller molecules is speeded up (catalysed) by enzymes. The enzyme amylase is produced in the salivary glands, the pancreas and the small intestine. This enzyme catalyses the breakdown of starch into sugars. Protease enzymes are produced by the stomach, the pancreas and the small intestine. These enzymes catalyse the breakdown of protein into amino acids. Lipase enzymes are produced by the pancreas and small intestine. These enzymes catalyse the breakdown of lipids (fats and oils) into fatty acids and glycerol. The stomach also produces hydrochloric acid. The acid kills most of the bacteria taken in with food. The enzymes in the stomach work most effectively in these acid conditions. The liver produces bile which is stored in the gall bkdder before being released into the small intestine. Bile neutralises the acid that was added to food in the stomach. This provides alkaline conditions in which enzymes in the small intestine work most effectively. Bile also emulsifies fats (breaks large drops of fats into smaller droplets). This increases the surface area of fats for lipase enzymes to act upon.
10.5 Circulation	FT and HT	The circulation system transports substances around the body. The heart pumps blood around the body. Much of the wall of the heart is made from muscle fibres. Blood enters an atrium of the heart. The atrium contracts and forces blood into a ventricle. The ventricle contracts and forces blood out of the heart. Valves in the heart ensure that blood flows in the correct direction. Blood flows from the heart to the organs through arteries and returns through veins. There are two separate circulation systems, one to the lungs and one to all other organs of the body. Arteries have thick walls containing muscle and elastic fibres. Veins have thinner walls and often have valves to prevent the back-flow of blood. In the organs, blood flows through very narrow, thin-walled, blood vessels called capillaries. Substances needed by the cells in body tissues pass out of the blood, and substances produced by the cells pass into the blood through the walls of the capillaries. Blood consists of a fluid called plasma in which are suspended white blood cells, platelets and red blood cells. Plasma transports: carbon dioxide from the organs to the lungs; soluble products of digestion from the small intestine to other organs; urea from the liver to the kidneys. White blood cells have a nucleus. They form part of the body's defence system against microbes. Platelets are small fragments of cells. They have no nucleus. Platelets help blood to clot at the site of a wound. Red blood cells transport oxygen from the lungs to the organs.
	HT	Red blood cells have no nucleus. They are packed with a red pigment called haemoglobin. In the lungs haemoglobin combines with oxygen to form oxyhaemoglobin. In other organs oxyhaemoglobin splits up into haemoglobin and oxygen.
10.6 Breathing	KS3	The breathing system includes ribs, rib muscles, diaphragm, lungs, trachea, bronchi, bronchioles and alveoli. The windpipe (trachea) splits into two branches called bronchi, one going to each lung. The bronchi divide repeatedly into smaller branches called bronchioles which end in a very large number of alveoli.
	FT and HT	The breathing system takes air into and out of the body so that oxygen from the air can diffuse into the bloodstream and carbon dioxide can diffuse out of the bloodstream into the air. The lungs are in the upper part of the body (thorax), protected by the ribcage and separated from the lower part of the body (abdomen) by the diaphragm. To make air move into the lungs the ribcage moves out and the diaphragm becomes flatter. These changes are then reversed to make air move out of the lungs. The movement of air into and out of the lungs is called ventilation.
	HT	To inhale: muscles between the ribs contract, pulling the ribcage upwards; at the same time the diaphragm muscles contract causing the diaphragm to flatten; these two movements cause an increase in the volume of the thorax; the consequent decrease in pressure results in atmospheric air entering the lungs. The alveoli provide a very large, moist surface, richly supplied with blood capillaries so that gases can readily diffuse into and out of the blood.
10.7 Respiration	KS3	All living cells in the body respire. During aerobic respiration (respiration which uses oxygen) chemical reactions occur which: use glucose (a sugar) and oxygen; release energy; produce carbon dioxide.
		Aerobic respiration is summarised by the equation: Glucose + oxygen —> carbon dioxide + water [+ energy] During vigorous exercise, muscle cells may be short of oxygen. They can then obtain energy from glucose by anaerobic respiration (respiration which does not use oxygen). The waste product from this process is lactic acid. The body then needs oxygen to break down this lactic acid. The oxygen that is needed is called an oxygen debt. The energy that is released during respiration is used: to build up larger molecules using smaller ones; to enable muscles to contract; to maintain a steady body temperature in colder surroundings. in the active transport of materials across boundaries.
	HT	Aerobic respiration inside cells occurs in mitochondria. If muscles are subjected to long periods of vigorous activity, they become fatigued, i.e. they stop contracting efficiently. If insufficient oxygen is reaching the muscles, they use anaerobic respiration to obtain energy. This is the incomplete breakdown of glucose and produces lactic acid. Because the breakdown of glucose is incomplete, much less energy is released than during aerobic respiration. Anaerobic respiration results in an oxygen debt that has to be repaid in order to oxidise lactic acid to carbon dioxide and water.
10.8 Nervous System	FT and HT	The nervous system enables humans to react to their surroundings and coordinate their behaviour. Cells called receptors detect stimuli (changes in the environment). These include: receptors in the eyes which are sensitive to light; receptors in the ears which are sensitive to sound; receptors in the ears which are sensitive to changes in position and enable us to keep our balance; receptors on the tongue and in the nose which are sensitive to chemicals and enable us to taste and to smell; receptors in the skin that are sensitive to touch and pressure and to temperature changes. Information from receptors passes along cells (neurones) in nerves to the brain. The brain coordinates the response. Some responses to stimuli are automatic and rapid and these are called reflex actions. In a simple reflex action electrical impulses pass from a receptor along a sensory neurone to the spinal cord or brain, then along a motor neurone to a muscle or a gland. The muscle or gland brings about the response. The eye includes: sclera, cornea, iris, pupil, lens, ciliary muscle, suspensory ligament, retina and optic nerve. In the eye: the tough outer sclera has a transparent region at the front called the cornea; the muscular iris controls the size of the pupil and hence the amount of light reaching the retina; the lens is held in position by suspensory ligaments and ciliary muscles; the retina contains the receptor cells which are sensitive to light. Light from an object enters the eye through the cornea. The curved cornea and the lens produce an image on the retina. The receptor cells in the retina send impulses to the brain along sensory neurones in the optic nerve.
	HT	The shape of the lens can be altered, by contraction or relaxation of the ciliary muscles, to focus near or distant objects respectively. Electrical impulses transmit information from receptor cells along sensory neurones to the central nervous system that includes the brain and the spinal cord. Reflex actions often involve three neurones called sensory, relay and motor neurones. In such a reflex action: impulses from a receptor pass along a sensory neurone to the central nervous system; at a junction (synapse) between a sensory neurone and a relay neurone in the central nervous system, a chemical is released which causes an impulse to be sent along a relay neurone; a chemical is then released at the synapse between a relay neurone and motor neurone in the central nervous system, causing impulses to be sent along a motor neurone to the organ (the effector) which brings about the response; the effector is either a muscle or a gland; a muscle responds by contracting, a gland by releasing (secreting) chemical substances. Candidates should be able, when provided with appropriate information, to analyse a reflex action in terms of: stimulus —> receptor —> coordinator —> effector —> response.
10.9 Hormones	FT and HT	Many processes within the body are co-ordinated by chemical substances called hormones. Hormones are secreted by glands and are transported to their target organs by the bloodstream. The blood glucose concentration is controlled by the hormones insulin and glucagon which are released (secreted) by the pancreas. Diabetes is a disease in which a person's blood glucose may rise to a fatally high concentration because the pancreas does not secrete enough of the hormone insulin. Diabetes may be treated by careful attention to diet and by injecting insulin into the blood. The monthly release of an egg from a woman's ovaries and the changes in the thickness of the lining of her womb are controlled by hormones secreted by the pituitary gland and by the ovaries. Fertility in women can be controlled by giving: hormones that stimulate the release of eggs from the ovaries (fertility drugs); hormones that prevent the release of eggs from the ovaries (oral contraception).
		Candidates should be able to evaluate the benefits of, and problems that may arise from, the use of hormones to control fertility.
	HT	The blood glucose concentration of the body is monitored and controlled by the pancreas. If the blood glucose concentration is too high, the pancreas secretes insulin into the blood. This causes the liver to convert glucose into insoluble glycogen and store it. If the blood glucose concentration is too low, the pancreas secretes glucagon which causes the liver to convert glycogen into glucose and release it into the blood. Several hormones are involved in the menstrual cycle of a woman. Those hormones involved in promoting the release of an egg include: FSH which is secreted by the pituitary gland and causes an egg to mature in one of the ovaries, and also stimulates the ovaries to produce hormones including oestrogen; oestrogen which is secreted by the ovaries and inhibits the further production of FSH as well as stimulating the pituitary gland to produce a hormone called LH; LH which is secreted by the pituitary gknd and stimulates the release of the egg about the middle of the menstrual cycle. The uses of hormones in controlling fertility include: giving FSH as a 'fertility drug', to a woman whose own level of FSH is too low, to stimulate eggs to mature; giving oral contraceptives which contain oestrogen, to inhibit FSH production so that no eggs mature.
10.10 Homeostasis	FT and HT	Humans need to remove waste products from their bodies and to keep their internal environment relatively constant. Waste products which have to be removed from the body include: carbon dioxide produced by respiration — most of this leaves the body via the lungs when we breathe out; urea produced in the liver by the breakdown of excess amino acids - this is removed by the kidneys in the urine, which is temporarily stored in the bladder. Internal conditions which are controlled include: the water content of the body — water leaves the body via the lungs when we breathe out, and via the skin when we sweat, and excess is lost via the kidneys in the urine; the ion content of the body — ions are lost via the skin when we sweat and excess are lost via the kidneys in the urine; temperature — to maintain the temperature at which enzymes work best. Sweating helps to cool the body. More water is lost when it is hot, and more water has to be taken as drink or in food to balance this loss.
	HT	The kidneys help to maintain the internal environment by: first filtering the blood; re-absorbing all the sugar; re-absorbing the dissolved ions needed by the body; re-absorbing as much water as the body needs; releasing urea, excess ions and excess water as urine. The kidneys produce dilute urine if there is too much water in the blood or concentrated urine if there is too little water in the blood. If the water content of the blood is too low, the pituitary gland releases a hormone called ADH into the blood. This causes the kidneys to re-absorb more water and results in a more concentrated urine. If the water content of the blood is too high, less ADH is released into the blood. Less water is re-absorbed in the kidneys resulting in a more dilute urine. Body temperature is monitored and controlled by the thermoregulatory centre in the brain. This centre has receptors sensitive to the temperature of blood flowing through the brain. Also temperature receptors in the skin send impulses to the centre giving information about skin temperature. If the core body temperature is too high: blood vessels supplying the skin capillaries dilate so that more blood flows through the capillaries and more heat is lost; sweat glands release more sweat which cools the body as it evaporates. If the core body temperature is too low: blood vessels supplying the skin capillaries constrict to reduce the flow of blood through the capillaries; muscles may 'shiver' - their contraction needs respiration which releases some energy as heat.
10.11 Disease	KS3	Bacteria and viruses may reproduce rapidly inside the body and may produce poisons (toxins) which make us feel ill. Viruses damage the cells in which they reproduce. Vaccination is used to protect us against bacteria and viruses.
	FT and HT	Diseases can be caused when microorganisms such as certain bacteria and viruses enter the body: a bacterial cell consists of cytoplasm and a membrane surrounded by a cell wall; the genes are not in a distinct nucleus; viruses are smaller than bacteria; they consist of only a protein coat surrounding a few genes; they can only reproduce inside living cells. Diseases are more likely to occur if large numbers of microbes enter the body as a result of unhygienic conditions or contact with infected people. The body has several methods of defending itself against the entry of microorganisms: the skin acts as a barrier; the breathing organs produce a sticky liquid mucus which covers the lining of these organs and traps microorganisms; the blood produces clots that seal cuts. White blood cells help to defend against infective microorganisms: by ingesting microorganisms; by producing antibodies which destroy particular bacteria or viruses; by producing antitoxins which counteract the toxins (poisons) released by microorganisms. When people are vaccinated they are immunised against disease by introducing a mild, or dead, form of the infecting organism into their bodies. The white blood cells respond by producing antibodies. If the infective organism enters the body antibodies are rapidly produced to destroy it. Once they have produced antibodies against a particular bacterium or virus, white blood cells can quickly produce them again so that the person is immune to that disease.
		Candidates should be able, when provided with appropriate information, to evaluate evidence relating living conditions and lifestyle to the spread of disease.
10.12 Drugs	KS3	Solvents, alcohol, tobacco and other drugs may harm the body.
	FT and HT	Solvents: affect behaviour; may cause damage to the lungs, liver and brain. Alcohol: affects the nervous system by slowing down reactions and may lead to lack of self-control, unconsciousness or even coma; may cause damage to the liver and brain. Drugs change the chemical processes in people's bodies so that they may become dependent or addicted to them and suffer withdrawal symptoms without them. Nicotine is the addictive substance in tobacco. Tobacco smoke contains substances which can help to cause: lung cancer; other lung diseases such as bronchitis and emphysema; disease of the heart and blood vessels. Tobacco smoke also contains carbon monoxide which reduces the oxygen-carrying capacity of the blood. In pregnant women this can deprive a fetus of oxygen and lead to a low birth mass.
		Candidates should be able, when provided with appropriate information, to explain how the link between smoking tobacco and lung cancer gradually became accepted.
	HT	Carbon monoxide combines irreversibly with the haemoglobin in red blood cells