BIO Paper 2

glucose are used to make larger, complex structures that the plant/algae need to grow - this makes up the plants biomass (the mass of the living material). 

Carbon dioxide + water  -----> glucose + oxygen

Photosynthesis is an endothermic reaction (energy is taken in during the reaction). 

Light intensity is one of the factors that affects the rate of photosynthesis. An aquatic plant can be used to measure the effect - the faster the rate of oxygen production, the faster the rate of photosynthesis. This is how it works: Sodium hydrogencarbonate (it releases CO2 into the water) may be added to the water to make sure the plant has enough carbon dioxide. A source of white light is placed at a specific distance away from the pondweed and the pondweed is left for a certain time. As it photosynthesises, the oxygen released will collect in a gas syringe which allows you to measure the exact volume of oxygen produced. The whole experiment is repeated using different distances from the pond weed. The higher the light intensity, the more oxygen produced and so the more the plant photosynthesises. You can also use this test to measure the effect of carbon dioxide. 

Not enough light slows down the rate of reaction - light transfers the energy needed for photosynthesis. The light intensity increases the rate of photosynthesis up to a certain point. 

Light intensity is inversely proportional to 1 / distance (sqaured). 

To little carbon dioxide slows down the rate of reaction - CO2 is one of the raw materials needed for photosynthesis. Increasing the carbon dioxide increases the rate of photosynthesis only up to a certain point. If the carbon dioxide and light intensity are constant, the limiting factor must be the temperature. 

Temperature is a limiting factor - if the temperature is too low, the enzymes will work more slowly and if it is too hot, the enzymes could possibly denature; this happens at 45 degrees, 

Root hair cells - the cells on the surface of plant roots grow into 'hairs' which stick out into the soil; each branch of a root will be covered with millions of these microscopic hairs. This gives the plant a large surface area for absorbing water and mineral ions from the soil. The concentration of mineral ions is usually higher in the root hair cell than in the soil around them, so mineral ions are absorbed by active transport and water is absorbed by osmosis. 

Phloem Tubes - phloem tubes are made of columns of elongated living cells that have small pores in their end walls to let things pass through. They transport food substances (mainly sucrose) in the leaves to the rest of the plant for immediate use of storage - this process is called translocation and it requires energy from respiration. The transport goes in both direction.

Xylem Tubes - made up of dead cells joined together with no end walls between them and a hole down the middle. They're strengthened with a material called lignin. They carry water and mineral ions from the roots to the stems and leaves. The movement of water from the roots, through the xylem and out of the leaves is called transpiration stream. 

Transpiration - the loss of water from the plant. Transpiration is caused by diffusion and evaporation of water from a plant's surface, usually the leaves, and the loss of water creates a shortage of water in the leaf. As there is a shortage, water is drawn up from the roots to the xylem vessels to the leaf to replace it. This means more water is being drawn from the roots, so there is a constant transpiration stream of water through the plant - the transpiration stream also carries dissolved minerals along with it.

Stomata - tiny pores that allow carbon dioxide and oxygen to directly diffuse in or out of the leaf. However, this allows water vapour to escape during transpiration. Transpiration is a side effect of the way the plant is adapted to photosynthesis. The stomata are needed for gas to be exchanged easily, but because their is more water inside the plant than outside in the air, the water URGES to move outside to balance the water concentration (because of osmosis) - this leads to transpiration. 

Stomata are surrounded by guard cells which change shape to control the size of the pore. When the guard cell is turgid (swollen with water), the stomata opens to let water out. When the guard cell is flaccid (lacking water) the guard cell closes to keep the water inside. 

Light intensity - the brighter the light, the greater the transpiration rate - the stomata begins to close as it gets darker, photosynthesis can't happen in the dark (as the energy from the sun is needed for photosynthesis to actually happen) as they don't need to let any carbon dioxide in. When the stomata are closed, very little water can escape. 

Temperature - the warmer it is, the faster the rate of transpiration. When it's warm, water particles have more energy to evaporate and diffuse into the stomata.

Air flow - the better the air flow around a leaf, like wind, the faster the rate of transpiration. If air flow around the leaf is poor, the water vapour just surrounds the leaf and this means there is a high concentration of water particles in the surrounding area, so diffusion doesn't happen quickly (as osmosis isn't needed to balance the water concentration inside and outside the plant). However, if the water vapour is swept away by fast winds, diffusion happens very quickly.

You can use a potometer to estimate transpiration rates. It measures the water being uptaken by a plant, but it's assumed that water uptake by the plant is directly related to water loss from the leaves. You set up a apparatus with water in a beaker, a capillary tube with a scale and a plant in water. You record the starting position of the air bubble and start the stopwatch to record the distance moved by the bubble per a certain time. Calculating the speed of the air bubble movement = estimate of transpiration rate.

You can also use the polometer (capillary tube with scale) to measure the effects on the rate of transpiration with light intensity, air flow or temperature.

Leaves =broad: so there's a large surface area exposed to light, which is needed for photosynthesis. 

The palisade layer = lots of chloroplasts: which means they are near the top of the leaf where they can get the most light.

The upper epidermis = transparent: so that light can pass through them to the palisade layer. 

The xylem and phloem = form a network of vascular bundles: so provides leaf with water for photosynthesis and takes away the glucose produced - they also support the structure. 

The tissues of leaves = adapted to efficient gas exchange: the lower epidermis has lots of stomata, which let carbon dioxide diffuse into the leaf. Also, the spongy mesophyll tissue contains air spaces which increase the rate of diffusion of gases into and out of the leaf's cells. 

Small leaves or spines - have a small surface area which reduces water loss by evaporation. The spines stop the plant from getting eaten by animals trying to get water.

Thick, fleshy stem - stores water

Waxy thick cuticles- reduces water loss by evaporation.

Curled leaves, or hairs on leaves - reduces the amount of air flow around the leaf as it traps water vapour near the surface and reduces the diffusion from the leaf to air. Sprines do the same. 

Fewer stomata or stomata that only opens at night - reduces water loss by evaporation.

Stomata sunken in pits - this makes the stomata lower than the leaf's surface and therefore reduces air flow near the stomata and reduces water loss the same way as curled leaves. 

Auxins - plant hormones which control the growth at the tips of the roots and shoots. They move through the plant in solution (dissolved in water).

Auxin is produced in the tips and diffuses backwards to stimulate the cell elongation which occurs in the cells just behind the tips. Auxin promotes growth in the shoot, but inhibits growth in the root. Auxins are involved in the growth responses of plants to light (phototropism) and gravity (gravitropism). 

Shoots are postively phototropic (grow towards the light) - when a shoot tip is exposed to light, it accumulates more auxin on the side that's in the shade than the side that's in the light. - this makes the cells grow (elongate) faster on the shaded side so the shoots bend towards the light.  By bending towards the light, the shoot will absorb more light for photosynthesis which enables the plant to grow. Shoots growing in complete darkness will be tall and spindly as the auxin will be make the plant's cells elongate on all sides; a taller shoot has a better chance of finding light. 

Shoots are negatively gravitropic (grow away from the gravity) - when a shoot is growing sideways, gravity produces an unequal distribution of auxin at the tip on the lower side which causes the lower side to grow faster, bending the tip upwards. 

Roots are postively gravitropic (grow towards the gravity) - a root growing will also have more auxin on its lower side, but in a root, extra auxin inhibits growth, so the cells on the top elongate faster which causes the roots to bend downwards. 

Root are negatively phototropic (grow away from the sunlight) - if a root is exposed to light, more auxin accumulates on the shaded side. The auxin inhibits cell elongation on the shaded side , so the root bends downwards, back into the ground. Roots that are underground aren't exposed to light grow downwards BECAUSE of positive gravitropism. 

Practical: you can investigate how light effects a cress seed. Put some cress seeds in a petri dish with moist filter paper. Surround the petri dish with black card. Cut a hole in one side of the card. Shine a light into the box through the hole. Leave your cress seed alone for one week - you shoud find the seedlings growing towards the light. You can measure the angle they are growing out. 

1) As selective weedkillers - most weeds growing in fields of crops or in a lawn are broad-leaved, in contrast to grasses and cereals which have very narrow leaves. Selective weedkillers have been developed from auxins, which only affect the broad-leaved plants -  they totally disrupt their normal growth patterns which soon kills thems, whilst leaving the grass and crops untouched. 

2) Growing from Cuttings with Rooting Powder. A cutting is part of a plant that has been cut off like a branch with a few leaves. If you stick cuttings in the soil, they don't grow but if you add rooting powder, which contain auxins, they will produce root rapidly and start growing as a new plants. This enables growers to produce lots of clones (exact copies) of a good plant quickly. 

3) Controlling Flower and Fruit Formation - Gibberellins are plant hormones that stimulate seed germination, stem growth and flowering. They can be used to make plant flower earlier than they usually wuld or under conditions in which they wouldn't flower (e.g. when it is warmer than usual). They can also be used to reduce flower formation, which can improve fruit quality - fruit grows from pollinated flowers. Example: apricot trees are often produce too many flowers and this causes too many fruits to form - the tree can't support them all and they grow small. Therefore, fewer flowers mean fewer but bigger fruits. 

Produces Seedless Fruit - fruit normally grows on flowering plants which have been pollinated by insects. If the flower doesn't get pollinated, the fruit and seeds don't grow. If plant hormones such as gibberellins are applied to the unpolinated flowers of some types of plant, the fruit will grow but the seeds won't.  Some seedless citrus fruit can be grown this way. Grapes are seedless. 

Controlling the Ripening Fruit - the ripening of fruits can be controlled either while they are still on the plant or during the transport to the shops. This allows the fruit to be picked while it's still unripe. (and therefore firmer and less easily damaged). A ripening hormon called ethene is then added and the fruit will ripen on the way to the supermarker and be perfect as it reaches the shelves.

Controlling Seed Germination - Lots of seeds won't germinate until they have been under certain conditions (a period of cold or dryness). Seeds can be treated with gibberellins to make them germinate at times of year that they wouldn't normally. It also helps to make sure all the seeds in a batch germinate at the same time. 

Hormones - chemicals released directly into the blood. They are carried around the blood to other parts of the body, but only affect particular cells in a target organ. Hormones are given to cells that need constant adjustment. Hormones are produced in endocrine glands. 

Pituary gland - known as the 'master gland' as it produces hormones that act on other glands - directing the glands to release hormones that bring the change.

Thyroid gland: produces thyroxine, which regulates things like rate of metabolism, heart rate and temperature.

Adrenal gland: produces adrenaline, preparing the body for a fight or fight response.

The Pancreas: produces insulin, used to regulate the blood glucose levels. 

Ovaries: (female) produce oestrogen, which is involved in the menstrual cycle. 

Testes: (male) produces testosterone, controlling puberty and sperm production in males. 

Neurones: very fast, not long-lasting, act on a very precise area. This is because information needs to be passed to effectors quickly to get you out of harm's way. 

Hormones: slower action, act for a long time and act in a more general way. If the response lasts for a long time, it is hormonal. For example: when you get a shock, the hormone adrenaline is released into the body and you would be able to tell it is hormonal because you will still feel the effect afterwards. 

- hormone released by the adrenal gland (located above the kidney) to prepare the body for a 'flight or fight response'.

Adrenaline binds to receptors in the heart, which causes the heart to contract more frequently and with more force. This causes an increase in blood flow and heart rate which increases blood flow to the muscles, so the cells receive more oxygen and glucose for respiration (transferring energy for cells to work). The adrenaline also binds to receptors in the liver, causing the liver to break down its store of glycogen to produce glucose. The blood glucose levels increase, so there is more glucose in the blood to be transported to cells. When the brain detects a stressful situation, it sends nervous impulses to the adrenal gland which in response, secretes adrenaline to get the body ready for action. 

Hormone release can be affected by negative feedback: you can control the level of hormones (and other substances) in the blood using negative feedback - when the body detects a level of a substance going above or below the normal level, it triggers a response to bring it back to normal.

- hormone released by the thyroid gland that plays a role in regulating metabolic rates (the speed at which chemical reactions in the body occur). A negative feedback system keeps the amount of thyroxine in the blood at the right level:

When the blood thyroxine levels are lower than normal, the hypothamulus (structure in the brain) releases thyrotropin releasing hormone (TRH). The TRH then stimulates the pituitary gland release tyroid stimulating hormone (TSH). This stimulates the thyroid gland to release thyroxine which makes the blood thyroxine levels rise back to normal. 

When the blood thyroxine levels become higher than normal, the release in TRH from the hypothalamus is inhibited, which reduces/ inhibits the production of TSH and so the blood thyroxine levels fall. 

An underactive thyroid gland can make you gain weight as less glucose will be broken down in respiration causing it to be stored as fat. 

- when the female body releases an egg and prepares the uterus (womb) in case the egg is fertilised monthly. Stage 1: Day 1 - when the menstrual cycle begins, the lining of the uterus is broken down and is released. Stage 2: The uterus lining is repaired, from day 4 to day 14, until it becomes a thick spongy layer full of blood vessels ready for a fertilised egg to implant there. Stage 3: An egg develops and is released from the ovary (ovulation) at day 14. Stage 4: The lining is maintained for 14 days until day 28: if no fertilised egg lands on the uterus wall by day 28, the spongy lining starts to break down again and the whole cycle starts over. 

The menstrual cycle is controlled by 4 hormones: 1) Follicle stimulating hormone (FSH) is produced by the pituitary gland and makes the follicle (the egg and surrounding cell) mature in one of the ovaries. This stimulates oestrogen. 2) Oestrogen is released from the ovaries which causes the uterus lining to thicken and grow. This stimulates a LH surge (a rapid increase). 3) Luteinising hormone (LH) is released by the pituitary gland and stimulates ovulation at day 14: the follicle ruptures and the egg is released. This stimulates the remains of the follicle to develop into a structure called a corpus luteum - this secretes progesterone.4) The progesterone is releasd by corpus luteum after ovulation and this maintains the uterus lining. It inhibits the production of FSH and LH. When the level of progesterone falls, and there's a low oestrogen level, the uterus lining breaks down and the low progesterone allows the FSH to increase, starting the cycle over...

Infertile people - people who can't reproduce naturally. 

Clomifene therapy - some women are infertile because they don't ovulate/don't ovulate regularly. These women can take drugs called clomifene and this causes more FSH and LH to be release into the body, which stimulates egg maturation and ovulation. By knowing when a woman will be ovulating, the couple can have intercourse during this period to improve their chances of becoming pregnant. 

IVF (in vitro fertilisation) - IVF involves collecting eggs (egg collection) from the woman's ovaries and fertilising them in a lab using the man's sperm. These are then grown into embryos and once the embryos are tiny balls of cells, one or two are transferred to the woman's uterus to improve the chance of pregnancy. FSH and LH are given before before egg collection to stimulate egg production. IVF is an example of ART (Assisted Reproductive Technology) - a fertility treatment involving eggs being handled outside the body.

Oestrogen can be used to prevent eggs being released. If oestrogen is taken everyday to keep the levels permanently high, it inhibits the production of FSH, and after a while egg development and production stops. 

Progesterone can be used to reduce fertility as it stimulates the production of thick cervical mucus, which prevents any sperm getting through the entrance of the uterus and reaching the egg. 

Some hormonal contraceptives contain progesterone and oestrogen. The combined pill (oral contraceptive) and the contraceptive pad (which is worn on skin).

The mini-pill and the contraceptive injection both contain progesterone only. 

Pregnancy can also be prevented by barrier methods of contraception  (barrier between sperm and egg) like condoms, diaphragms (dome-shaped devices that fit over the opening of the uterus).

Pros: hormonal methods are more effective at preventing pregnancy than barrier methods. Also, the hormonal methods mean the couple don't have to stop and think about contraception each time they have intercouse. Cons: However, hormonal methods have side effects like headaches, acne and mood changes. They also don't protect you from STIs whilst condoms do. 

Homeostatis - maintaining a constant internal environment. Conditions in the body need to be kept steady in order for your cells to function properly (like the right conditions for enzymes). 

To maintain a constant internal environment, your body needs to respond to both internal and external changes whilst balancing the inputs and outputs. 

Osmoregulation: (regulating water content) - the balance between water you gain and the water you pee, sweet and breathe out. 

Thermoregulation: (regulating body temperature) - reducing the body temperature when it is hot externally and increasing the body temperature when it is cold externally. 

Blood glucose regulation: making sure the amount of glucose in the blood isn't too high or too low. 

Negative feedback systems: helping to keep the body's internal features steady. This means if a condition changes away from the normal, a response is triggered that counteracts the change. 

Eating food containing carbhoydrates puts glucose into the blood from the small intestines. Glucose in the blood are removed by your normal metabolism. Exercising vigorously removes much more glucose from the blood. Excess glucose are stored as glycogen in the liver and the muscles. When the stores are full, the excess glucose is stored as lipids (fat) in the tissues. Changes in the blood glucose is monitored and controlled by the pancreas, using the hormones insulin and glucagon.

Blood Glucose Concentration ---> insulin is added: when there is too much glucose in the blood, insulin is secreted by the pancreas. Glucose move from the blood to liver and muscle cells - insulin makes liver turn glucose into glycogen which makes the blood glucose concentration decrease. 

Blood Glucose Concentration ---> glucagon is added: when there is too little glucose in the blood, glucagon is secreted by the pancreas. Glucagon makes liver turn glycogen into glucose which are then released into the blood by the liver and the blood glucose concentration increases.

Type 1 diabetes - condition where pancreas produces little or no insulin which makes blood glucose concentration increase - this could kill them. They can be treated with insulin therapy (injecting insulin into the blood at mealtimes to make sure glucose are quickly removed after digestion) - this stops blood glucose getting too high and is effective. Insulin is injected in subcutaneous tissue (fatty tissue under skin) and the amount of insulin needed depends on the person's diet and how active they are. People with diabetes need to limit the intakes of carbohydrates (which cause blood glucose to rise) and exercise regularly (to remove glucose). 

Type 2 diabetes - when a person is resistant (their body cells don't respond properly) to insulin which causes blood glucose to rise. Obese people are at increased risk of getting type 2 diabetes. Obese people are over 30 BMI and storing fat around their abdomen is associated with the increased risk of type 2 diabetes (a ratio above 1.0 for men and 0.85 for women's hip to waist ratio). Type 2 diabetes can be controlled by: a healthy diet, exercise and losing weight - people with type 2 diabetes also have medication and insulin injections. 

Enzymes in our body work best at 37 degrees. Homeostasis maintains body temperature at a steady 37 degrees. The thermoregulatory centre in the hypothalamus contains receptors that are sensitive to the blood temperature in the brain. It also receives impulses from receptors in the skin (in the epidermis and dermis) that provide information about the external temperature.

When you are too hot: erector muscles relax , so hairs lie flat. Lots of sweat (containing water and salt) is produced in the sweat glands in the dermis. The sweat is released onto the skins surface through the pores of the epidermis. When the sweat evaporates, it transfers energy from the skin into the air, which causes the body to cool down. Blood veseels close to the surface dilate (widen) and this is called vasodilation. It allows more blood to flow near the surface so it can transfer more energy into the surroundings which cools you down.

When you are too cold: erector muscles contract and hairs stand on end to trap an insulating layer of air near the surface of the skin, which keeps you warm. Very little sweat is produced and blood vessels near the surface of the skin constrict (vasocontriction). This means less blood flows near the surface so less energy is transferred to surroundings. When you're cold, you shiver (muscles contract automatically) making your rate of respiration increase, which transfers more energy to warm the body. 

If the concentration of water content in the blood is too high, the water will move into body cells by osmosis and might cause the cells to burst.If the concentration of water content in the blood is too low, the water will move out of the body cells by osmosis, causing them to shrink. 

The kidney has three roles: to remove urea (waste produced in the liver from the breakdown of amino acids), adjustment of ion levels in blood and adjustment of water in the blood. The end product is urine. 

Nephrons are the filtration units (areas) in the Kidneys: the liquid part of the blood (glucose, mineral ions, water and urea) is forced out of the glomurulus and into the Bowman's capsule at high pressure (ultrafiltration). Bigger molecules, like protein and blood cells, can't get through the membranes and are not forced out. As the liquid flows along the nephron, the useful substances are reabsorbed: all the glucose are selectively reabsorbed (they move against a concentration gradient back into the blood), sufficient ions and water is reabsorbed (according to the levels of ADH). Whatever isn't reabsorbed (urea, excess water and ions) continue out of the nephron via the collecting duct and into the ureter where it down to the bladder as urine. Urine is then released through the urethra.

The amount of water reabsorbed is controlled by the anti-diuretic hormone (ADH). The brain monitors the water content of the blood and instructs the pituitary gland to release ADH into the blood - ADH makes the collecting duct more permeable which allows more water to be reabsorbed and this stops the body becoming dehydrated. The whole process is a negative feedback system - Example, if there is too much sodium ions in the blood, the pituitary gland inhibits the secretion of ADH, which makes the collecting duct less permeable so less sodium ions are reabsorbed. 

Dialysis filter the blood mechanically - patients who have kidney failure can't filter their blood properly. Dialysis has to be done regularly to keep dissolved substances at the right concentration and remove waste products. Dialysis fluid has the same concentration of salts and glucose as blood plasma (which means those aren't removed from the blood). The barrier is permeable to things like ions and waste substances but not big molecules like proteins, just like the membrane in the kidney. So the waste substances, plus excess ions and waste from the blood, move across the membrane into the dialysis fluid. Cells and proteins stay in the blood. 

Kidney transplants are the only cure for kidney failure - healthy kidneys are transplanted from people who have died suddenly (e.g. car crash) and who carry a donor card or are on the organ donor register. The donor kidney could, however, be rejected by the patient's body by the patient's immune system seeing the kidney as a foreign object and attacking it by antibodies. To prevent this: use a donor that has the same tissue type as the patient and give them drugs that will supress the immune system, so that their immune system won't attack the donor kidney.

All organisms must take in substances that they need from the environment and get rid of waste products. For example: cells need oxygen for aerobic respiration which produces carbon dioxide as a waste product - these two gases move between cells and the environment by diffusion. 2) Water is taken up by cells by osmosis. In animals, dissolved food molecules (like glucose and amino acids) and mineral ions are also diffused along with it. Urea (waste product) diffuses from cells to the blood plasma for removal from the body by the kidneys. How easy it is for an organism to exchange substances by diffusion depends on their surface area to volume ratio. 

The larger the organism, the smaller the surface area compared to the volume. 

In single celled organisms, gases and dissolved substances can diffuse directly into (or out) of the cell across the cell membrane because they have a large surface area compared to their volume, so enough substances can be exchanged across the membrane to supply the volume.  Multicellular organisms have a small surface area compared to their volume which means it is difficult to exchange enough substances to supply the entire volume, so a type of exchange surface is needed for efficient diffusion and a mass transport system is needed to move substances arounf the whole cell body. The exchange surfaces has to allow enough of the necessary substances through - they are adapted to maximise effectiveness. 

Gases are exchanged in the lungs by diffusion. The rate of diffusion is affected by: the distance (if the distance is small, diffusion happens quicker), concentration difference/gradient (diffusion is quicker when their is a large difference between concentration) and surface area (the more surface area available for molecules to move across, the faster the molecules can get from one side to another). 

The job of the lungs is to trasfer oxygen to the blood and remove waste carbon dioxide from it. Lungs contain millions of little air sacs called alveoli where gas exchange takes place between it and blood capillaries (they both have partially permeable membrames). Blood arriving at the alveoli has just returned to the lungs from the rest of the body, so contains lots of carbon dioxide and little oxygen. The maximises the concentration gradient for the diffusion of most gases - oxygen diffuses out of the air in the alveoli (where the concentration of oxygen is high) and into the blood (where the concentration is low). Carbon dioxide then diffuses in the opposite direction to be breathed out. The alveoli are specialised to maximise diffusion because they have: a moist lining for dissolving gases, a good blood supply to maintain the concentration gradients of oxygen and carbon dioxide, very thin walls to minimise the distance of diffusion and an enormous surface area (about 75m2 in humans). 

Rate of diffusion is proportional to surface area x (concentration difference / thickness of membrane)

The job of red blood cells (or erythocytres) = to carry oxygen from the lungs to all the cells in the body. They have a biconcave disc shape to give a large surface area for absorbing oxygen, they don't have a nucleus which allows more room for oxygen and contain haemoglobin (red pigment) which contains iron. In the lungs, haemoglobin binds to oxygen to become oxyhaemoglobin - body tissue, the reverse happens - oxyhaemoglobin splits to form oxygen and haemogloblin, to release oxygen to cells. 

Phagocytes are white blood cells that change shape to engulf unwelcome microorganisms - this is called phagocytosis. Lymphocytes are white blood cells that produce antibodies against microorganisms - some also produce antitoxins to neutralise any toxins produced by the microorganisms. When you have an infection, your white blood cells multiply to fight it off - so a blood test will show a high white blood cell count.

Platelets help blood clot - these are small fragments of cells that have no nucleus and help the blood to clot at a wound (to stop all your blood from pouring out). Lack of platelets can cause excessive bleeding and bruising. 

This is a pale yellow liquid which carries everything: red and white blood cells, platelets, nutrients like glucose and amino acids (they are the soluble products of digestion which are absorbed by the gut and taken to the cells), carbon dioxide from the organs to the lungs, hormones, urea from the liver to the kidneys, proteins and antibodies and antitoxins produced by white blood cells. 

Blood Vessels designed for their function: arteries carry blood away from the heart. Capillaries are involved in the exchange of materials at the tissues. Veins carry blood to the heart. 

Arteries - the heart pumps out blood at high pressure so the artery walls are strong and elastic. The walls are thick compared to the size of the hole in the middle (lumen). They contain thick layers of muscle to make them strong. Elastic fibres allow them to stretch and spring back.

Capillaries - arteries branch into capillaries; they are tiny and very narrow, so they can squeeze into gaps between cells. This means they can carry the blood really close to every cell in the body to exchange substances. They have permeable ways so substances can diffuse in and out and their walls are usually one cell thick - this increasses the rate of diffusion as the substances have a smaller distance to cross. 

Mammals have a double circulatory system - this means that the heart pumps blood around the body in two circuits. In the first circuit, the heart pumps deoxygenated blood to the lungs to take in oxygen. Oxygenated blood then returned to the heart. In the second circuit, the heart pumps oxygenated blood around all the other organs of the body to deliver oxygen to the body cells. deoxygenated blood then returns to the heart. 

Fish have a single circulatory system - deoxygenated blood from the fish's body travels to the heart, which then pumps it right round the body again in a single circuit (via the gills it picks up oxygen).

Mammalian hearts have four chambers and four major blood vessels. Arteries and deoxygenated blood is on the RIGHT HAND SIDE. Veins and oxygenated blood is on the LEFT HAND SIDE.  The right atrium of the heart receives deoxygenated blood from the body (through the vena cava). The deoxygenated blood moves through to the right ventricle, which pumps it to the lungs (via the pulmonary artery). The oxygenated blood then moves through the left ventricle which pumps it out around the whole body (via aorta). The left ventricle has a much thicker wall than than the right ventricle because it has to pump blood around the whole body at high pressure, whereas the right ventricle only has to pump it to the lungs. Valves prevent the back flow of blood in the heart. 

Cardiac output is the total volume of blood pumped by a ventricle every minute. 

Cardiac output = heart rate x stroke volume.

The heart rate is the number of beats per minute. The stroke volume is the volume of blood pumped by one ventricle each time it contracts. 

Respiration - goes on in every cell, it is the process of transferring energy from the breakdown of organic compounds (usually glucose) - the energy is needed for things like metabolic processes such as making molecules smaller, contracting muscles and maintaining a steady body temperature. Because energy is transferred to the environment, it is an exothermic reaction. Some of this energy is transferred by heat. There are two types of respiration: aerobic and anaerobic. 

Aerobic respiration - happens when there is a lot of oxygen, it is the most efficient way to transfer energy from glucose. Glucose + oxygen = carbon dioxide + water.

Anaerobic Respiration - doesn't use oxygen at all: happens when you do vigorous exercise, your body can't supply enough oxygen to your muscles for aerobic respiration - even though your heart rate and breathing rate increases as much as they can. Your muscles have to start respiring anaerobically as well. Anaerobic transfers much less energy than aerobic respiration so it's less efficient. In anerobic respiration, the glucose is only partially broken down, and lactic acid is also produced. The lactic acid builds up in the mmuscles - it gets painfall and leads to cramps:
Glucose = lactic acid. 

Anerobic Respiration in Plants 

Plants can respire without oxygen too, but they produce ethanol and carbon dioxide instead of lactic acid. Glucose --> ethanol + carbon dioxide. 

You can investigate what effect temperature would have on the rate of respiration.

1) Use corrosive soda lime granules in a test tube. These absorb carbon dioxide and using cotton wool, place the wood lice on top - they will respire. Connect to the respirometer and connect a control tube with glass beads (the same mass as the woodlice) and sodalime in another test tube.  The syringe is used to set the fluid of the manometer to a known level and the aparatus is left at a set time in a water bath of 15 degrees. During this time, there'll be a decrease in the volume of the air in the test tube containing the woodlice because they will be using the oxygen for respiration. The decrease in volume reduces the pressure in the tube, causing the coloured liquid in the manometer to move towards the test tube containing the woodlice. The distance moved by the liquid in a given time is measured and this can be used to calculate the volume of oxyge take in by the woodlice per minute. This gives you the rate of respiration. Repeat the experiment with different temperatures to see how respiration is affected by the temperature. 

Organised into different levels: Individual, Population (all of organisms of one species in a habitat), Community (all the organisms of different species living in a habitat), Ecosystem (a community of organisms along with abiotic conditions).

Organisms depend on each other for things like food and shelter in order to survive and reproduce. This is known as interdependence. It means that a change in the population of one sppecies will have an effect on other species in the same way. Mutualism - relationship between two organisms which both organisms benefit: like a bee and a plant, the bee get food and the plants get help reproducing (as bees spread the pollen to other plants). Parasites live very closely with host species - the parasite takes what it need to survive but the host doesn't benefits. Like flees getting food from biting dogs and dogs not getting anything. 

The environment in which organisms live changes all the time. These changes are caused by abiotic and biotic factors that affect the size or distribution of a population.

Abiotic factors: temperature: example: the distribution of bird species in Germany is changing because of a rise in temperature. For example, a mediterranean bird species is now present in parts of Germany. Amount of water - diasies grow best in soils that are slightly damp. If the soil becomes waterlogged or too dry, the population of diasies will decrease. Light intensity - as trees grow and provide more shade, grasses may be replaced by fungi which are better able to cope with lower light intensity. Levels of Pollutants - lichen are unable to survive if the concentration of sulfur dioxide (pollution) is too high. 

Biotic Factors: Competition - organisms compete with other species for the same resources. E.g. red and grey squirrels live in the same habitat and eat the same food. Competition with grey squirrels for these resources in some areas mean there isn't enough food for reds - the population of red squirrels is decreasing as a result. 

Predation - if the number of lions decreases then the number of gazelles might increase because fewer of them are being eaten by the lions. 

To investigate an abundance of something in two sample areas, place a quadrat on a random place of the sample area and count all the organisms you are interested in, in that quadrat. Repeat and work out the mean of the organisms and do the same for the second sample area - then compare the two means.

Abiotic factors change across a habitat = gradient. You can use a quadrat to help find out about how organisms are distributed along a gradient. The quadrats are laid out along a line, forming a belt transect. Here's what you do: Make out a line in the area you want to study and then collect data along this line using quadrats placed next to each other. Collect data by counting all the organisms of the species  or estimating a percentage cover. This means estimating the percentage area of a quadrat covered by a particular type of organism. You can record other data, such as mean number of organisms or mena percentage cover. 

The sun is the source of energy for nearly all life on Earth. The plants convert a small percentage of light energy that falls on them into glucose. They use some of the glucose immediately in respiration and store some of the rest as biomass. The rabbit then eats the plant and uses some of the energy it gets from the plant and some to store as biomass. The fox then eats the rabit and gets some of the energy stored in the rabbits mass. This is a food chain.

Energy is used by organisms at each stage to stay alive and this energy isn't stored as biomass so isn't transferred to the next organism in the next trophic level. Energy that does get stored as biomass doesn't all get transferred to the next trophic level because not all of the organism gets devoured (like bones) and because not all of the bits that get eaten can be digested - undigested material is lost from the food chain in faeces. This explains why you hardly ever get food chains with five trophic levels because so much energy is lost to each stage that there is not enough left to support another organism after four or five stages. 

A pyramid of biomass shows how much the creatues at each level of a food chain would weigh if you put them together. Since the biomass is a store of energy, it shows how much energy there is at each stage in the food chain.  Each time you go down a trophic level, the mass of the organism goes down because most energy is lost. 

Efficiency of Energy Transfer = 

efficiency = energy transferred to next level / energy available to previous level x 100

Biodiversity - variety of living organisms in an ecosystem. 

Fertilisers cause Eutrophication. Nitrates put onto field as fertilisers - if too much fertiliser is applied and it rains afterwards, nitrates easily find their way into rivers and lakes and as a result makes the algae grow which blocks out the sunlight so plants can't grow and decompose which means there is no more food - so microorganisms feed on the decomposing plant, increase in population and use up most of the oxygen in the water. Most of the organisms need oxygen for aerobic respiration and so die. 

Fish farms in areas can reduce biodiversity. Food is added to the nets to feed the fish, which produces huge amounts of waste. Both the food and waste can leak into open water and cause eutrophication ad death of wild species. Fish farms in open water act as breeding grounds for large numbers of parasites - these parasites can get out of the farm and infect wild animals, sometimes killing them. Predators, like sea lions, are attracted to the nets and become trapped and die. Farmed fish can escape into the wild which can cause problems for wild population of indigenous species. Sometimes fish are farmed in large tanks rather than in open water nets. These farms are low in biodiversity because often only one species is farmed, the tanks are often kept free of plant and predators, and any parasite and microorganism is killed. 

A non-indigenous species is one that doesn't naturally occur in an area. They can be introduced intentionally or unintentionally. The introduction of a non-indigenous species may cause problems problems for indigenous species. 

Non-indigenous species compete with indigenous species for resources like food and shelter. Sometimes, they are better at getting these resources and out-compete the indigenous species which will make them decrease in number and eventually die out. For example, signal crayfish were introduced to the UK for food, but they prey on and out-compete many indigenous river species, reducing biodiversity. Non-indigenous species sometimes also bring new diseases to a habitat. These often infect and kill lots of indigenous species, reducing the habitat's biodiversity. 

Reforestation(where a forest previously stood and is being replanted to a new forest  can increase biodiversity: Forests generally have high biodiversity because they contain a wide variety of trees and plants which provide shelter and food for other organisms. Reforestation programmes need to be planned carefully to maximise postive effects and minimise the negatives. For example, replanting a forest with a variety of tree species will result in a higher biodiversity than replanting using only a single type of tree.

Conservation: scheme that help to protect biodiversity by preventing species from dying out by: Protecting a species' natural habitat, protecting species in safe areas outside their natural habitat and introducing captive breeding programmes to increase number or the use of seed banks and distribute the seeds of rare and endangered plants. 

Pros: protecting the human food supply - over-fishing have reduced fish stock in the world's ocean and conservation programmes can ensure that the future will have enough fish to eat. Ensuring minimal damage to food chains - if one species becomes extinct it will affect all the organisms that feed on and are eaten by that species, affecting the whole food chain. This means conversing a species will help others survive. Providng future medicines - many medicine is from plants and undiscovered plant species may contain new medicinal chemicals. Cultural aspects - individual species may be important in a nation or area's cultural heritage e.g. bald eagle is being conserved in the US because thats their national symbol. Ecotourism - people are drawn to visit beautiful, unspoilt landscapes with a variety of animal and plant species. Ecotourism helps bring money into biodiverse areas where conservation work is taking place. Providing new jobs - things such as ecotourism conservation schemes and reforestation provides employment opportunities for local people. 

The world's population is rising very quickly and it's not slowing down - this means that global food production must increase too, so that we all have access to enough food that is safe for us to eat and has the right balance of nutrition.

Biological Factors Affect the Level of Food Security - increasing consumption of meat and dish, and increasing animal farming. As people become wealthier, their diets are going to change to include a variety of foofs, including more meat and fish.  There is less energ yand less biomass everytime you move up the food chai, so for a given area of land, you can produce a lot more food for humans by growing crops than by grazing animals. Animals and fish are being eaten are fed crops that would have otherwise been eaten by humans. There is also a risk of over-fishing. 

Sustainability - meeting needs of the population without affecting the ability of future generations to meet their needs. Like, diesel and petrol are made from crude oil - there is currently an increase in the growth of crops to make biofuel  - these take up the land being used for crops so we need to balance our need for this and still maintain food production. Also, the high input costs of farming9 (e.g. the price of fertilisers) may make it too expensive to farmers in some areas to continue farming and maintain food production in the future.

Pests, like insects, and pathogens, like fungi, can cause damage to livestock and crops. When new pests and pathogens emerge, they can have a negative impact on yields. e.g. if a new disease spreads to a crop, lots of the population may not be resistant to the disease. This means a large number of the crop plants will be damaged, reducing the yield and the amount that can be sold as food. 

Living things are made of elements they take from the environment,  plants take in carbon and oxygen form the air and nitrogen from the soil. They turn these elements into the complex compounds (cabohydrates, proteins and fats) and elements are passed along food chains when animals eat up the plants and each other. The elements are recycled - waste products and dead organisms are broken down by decomposers and elements in them are returned to the soil or air, ready to be taken in by new plants and put back into the food chain. 

The Carbon Cycle: There is one arrow going down from carbon dioxide in the air - this is powered by photosynthesis. Green plants use the carbon from carbon dioxide to make carbohydrates, fats and proteins. Eating passes the carbon compounds in the plant along to animals in a food chain. Both animal and plant respiration while the organisms are alive release carbon dioxide into the air. Plants and animals then die and decompose - the decomposers release carbon dioxide back into the air by respiration, as they break down the material. Some useful plant and animal product, like wood and fossil fuels, are burned are they also release carbon dioxide back into the air. Decomposition of materials means that habitats can be maintained for the organisms that live there. E.g. nutrients are returned to the soil by waste materials like dead leaves.

Energy from the Sun makes water evaporate from the land and sea, turning it into water vapour. Water also evaporates from plants - this is known as transpiration. The warm water vapour is carried upwards (as warm air rises). When it gets higher up it cools and condenses to form clouds. Water falls from the clouds as precipitation onto land, where it provides fresh water for plants and  animals. It then drains into the sea and the whole process starts again. 

Droughts are caused by a lack of precipitation and we rely on precipitation to get fresh water for drinking. In times of drought, there are methods we can use to produce potable water (water that's suitable for drinking). One of these methods is called desalination. Desalination removes salts (mineral ions) from salt water - there are few different methods of desalination = one is thermal desalination where salt water is boiled so that the water evaporates in an enclosed vessel. The steam rises to the top of the vessel and travels down a pipe from the top of the vessel and condenses back into pure water. Reverse osmosis - the higher the salt concentration in a solution, the lower the water concentration, so you could also say that osmosis is the net movement of water from an area of lower salt concentraion to an area of high salt concentration. Reverse osmosis is the process of getting rid of impurities in the water. Solids are removed from salt water, then is fed at high pressures into a vessel containing a semi-permeable membrane. This pressure causes the water molecules to move in the opposite direction to osmosis and as water is forced through the membrane, the salts are left behind, removing them from the water. 

The atmosphere contains 78% nitrogen. This is very unreactive and so it can't be used directly by plant or animals. Nitrogen is needed to for making proteins for growth. Nitrogen in the air has to be turned into mineral ions such as nitrates before plants can use it. Plants absorb these ions from the soil and use nitrogen in them to make proteins. Nitrogen is then passed along food chains as animals eat plants. Decomposers break down the proteins in rotting plants + animals and urea in animal waste. This returns nitrogen to the soil - so nitrogen in these organisms are recycled. Nitrogen fixation - process of turning nitrogen from the air into nitrogen-containing ions in the soil which plants can use. This could happen by lightning as there is so much energy it could make nitrogen react with oxygen in the air to give nitrates. Or nitrogen-fixing bacteria in the root and soil. Decomposers - decompose proteins and urea and turn the into ammonia. Ammonia forms ammonium ions in solution that plants can use. Nitrifying bacteria - turn ammonia in decaying matter into nitrites and then nitrates. Nitrogen-fixing bacteria - turn atmospheric nitrogen into anmmonia which forms ammonium ions. Denitrifying bacteria - turn nitrates back into nitrogen gas. There is no benefit to living organisms - often found in waterlogged soil. Some nitrogen-fixing bacteria live in soil, others in nodules on the roots of legume plants (beans). When these plants decompose, the nitrogen stored in them and in their nodules is returned to the soil. Nitrogen ions can also leak out of the nodule during plant growth. The plants have a mutualistic relationship with bacteria get food from the plant, and the plants gets nitrogen ions from the bacteria to make into proteins. 

Like all plants, crops take up nitrates from the soil as they grow. But crops are harvested, rather than being left to die and decompose, so the nitrogen they contain isn't returned to the soil. Overtime, the nitrogen content of the soil decreases, leading to poor crop growth and deficiency diseases. So farmers have ways of increasing the amount of nitrates in the soil to help their crops grow better. Crop rotation - instead of growing the same crop in a field for years, different crops are grown each year in a cycle. The cycle usually includes a nitrogen-fixing crop which helps to put nitrates back into the soil for another crop to use the following year. Fertilisers - spreading animal manure or compost on fields recycles the nutrients left in plant and animal waste and returns them to the soil through decomposition. Artificial fertilisers containing nitrates (and other mineral ions neded by plants) can also be used, but these can be expensive. 

Some organisms are very sensitive to changes in their environment and so can be studied to see the effect of human activities - these organisms are known as indicator species.

1) Water Pollution - if raw sewage or fertilisers containing nitrates are released into a river, the microorganisms will increases and use up the oxygen. Some invertebrate animals, like stonefly larvae and freshwater shrimps are good indicators for water pollution because they're very sensitive to the concentration of dissolved oxygen in the water. If you find stonefly larvae in a river, it indicates that the water is clean. Other invertebrate species have adapted to live in polluted conditions - so if you see a lot of them you know it is not clean like,  blood worms and sludgeworms indicate a very high level of water pollution. 

2) Air Pollution - this can be monitored by looking at lichen - they are sensitive to sulfur dioxide in the atmosphere. The air is cleaner if there are lots of lichen (especially bushy lichen which needs cleaner air then crusty lichen). Blackspot fungus is found on rose leaves. It is also sensitvie to the level of sulfur dioxide in the air, so its presence will indicate clean air. Outside a city centre, there is less pollution and the air contains less sulfur dioxide and other polluntants. 

You can use indicator species to measure pollution:you could do a survey to see if a species is present or absent from an area. This is a quick way of telling whether an area is polluted or not, but it's no good for telling how polluted an area is.

Counting the number of times an indicator species occurs in an are will give you a numerical value, allowing you to see roughly how polluted one area is in comparison to another.

Using indicator species is a simple and cost-effective way of saying wehter or not an area is polluted. But indicator species can't give accurate figures for exactly how much pollution is present. You can use non-living indicators like: 

Dissolved oxygen meters and chemical tests are used to accurately measure the concentration of dissolved oxygen in water, to show how the level of water pollution is changing.

Electronic meters and various laboratory tests are also used to accurately measure the concentraion of sulfur dioxide in the air, to show how air pollution is changing. 

Decomposition return elements that an organism had taken in back into the soil or air. The rate of decay depends on three things: TEMPERATURE - a warm temperature increases the rate of enzyme-controlled reactions in microbes, so decay happens faster. WATER CONTENT - Decay takes place faster in moist environments because of the organisms involved in decay need water to survive and carry out biological processes. OXYGEN AVAILABILITY - the rate of decomposition is faster where there is plenty of oxygen available. Many microorganisms need oxygen for aerobic respiration. 

Food Preservation - Storing food in a fridge lowers the temperature of the food and this slos down decomposers' rate of reproduction or stops it altogether if freezing. Storing food in airtight cans stops microorganisms from getting in - once the food is in, the cans are sealed and sterilised (by exposing them to a high pressure and temperature) to kill any microrganisms present. Drying food removes the water that microorganisms need to survive and reproduce, as does adding sugar or salt which cause microganisms to lose water by osmosis. 

Ideal Conditions to make compost: compost is decomposed organic matter that is used as fertiliser. They  create the ideal conditions for decomposers: mesh side to increase oxygen availbility, decomposing material is kept mosit and heat is generated from the decomposers themselves. Some compost bins are insulated to increase the temperature further.