Biology Unit 3

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  • Created by: angel-234
  • Created on: 14-09-15 20:37

B3 1.1- Exchange of materials

  • Osmosis is a special case of diffusion. Osmosis is the diffusion or movement of water from a dilute to a more concentrated solution through a partially permeable membrane that allows water to pass through.
  • Differences in the concentrations of solutions inside and outside a cell cause water to move into or out of the cell by osmosis.
  • Substances are sometimes absorbed against a concentration gradient by active transport.
  • Active transport uses energy from respiration.
  • Cells can absorb ions from very dilute solutions, and actively absorb substances such as sugar and salt against a concentration gradient using active transport.
  • Most soft drinks contain water, sugar and mineral ions.
  • Sports drinks contain sugars to replace the sugar used in energy release during activity. They also contain water and ions to replace the water and mineral ions lost during sweating.
  • Evidence suggests that for normal levels of exercise water is at least as effective as a sports drink.
  • Certain features such as a large surface area, short diffusion paths and steep concentration gradients increase the effectiveness of an exchange surface. 
  • The alveoli are the air sacs in the lungs. 
  • The lungs are adapted to make gaseous exchange as efficient as possible. They have  many alveoli, which provide a large surface area with a good blood supply and short diffusion distances. The lungs are ventilated to maintain steep diffusion gradients.
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B3 1.1- Exchange of materials

  • The lungs are in your thorax protected by your rib cage and separated from your abdomen by the diaphragm.
  • The intercostal muscles contract to move your ribs up and out and flatten the diaphragm, increasing the volume of your thorax. The pressure decreases and air moves in.
  • The intercostal muscles relax and the ribs move down and in, and the diaphragm domes up, decreasing the volume of your thorax. The pressure increases and the air is forced out.
  • Different types of artificial breathing aids have been developed over the years to help people when their lungs or breathing systems don't function properly. 
  • The different methods have advantages and disadvantages.
  • The villi in the small intestine provide a large surface area with an extensive network of blood capillaries.
  • This makes villi well adapted to absorb the products of digestion by diffusion and active transport.
  • Plants have stomata that allow them to obtain carbon dioxide from the atmosphere. Carbon dioxide enters the leaf by diffusion. Leaves have a flat, thin shape and internal air spaces to increase the surface area available for diffusion.
  • Most of the water and mineral ions needed by a plant are absorbed by the root hair cells, which increase the surface area of the roots.
  • The loss of water vapour from the surface of plant leaves is transpiration. Water is lost through the stomata, which are opened and closed to let in carbon dioxide for photosynthesis. Transpiration is more rapid in hot, dry, windy or bright conditions.
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B3 2.1- Transporting Materials

  • The circulatory system consists of the blood vessels, the heart and the blood. Humans have a double circulation. The heart is an organ that pumps blood around the body. The valves make sure blood flows in the right direction through the heart.
  • The main types of blood vessels are arteries, veins and capillaries. Substances diffuse in and out of the blood in the capillaries. Stents can be used to keep narrowed or blocked arteries open. Damaged heart valves can be replaced.
  • Your blood plasma transports dissolved food and molecules, carbon dioxide and urea and has the blood cells suspended in it.Your red blood cells carry oxygen from your lungs to the organs of the body. Red blood cells are adapted to carry oxygen by being biconcave, giving them a bigger surface area, by containing haemoglobin and by having no nucleus so more haemoglobin can fit in. 
  • White blood cells are part of the defence system of the body. Platelets are cell fragments involved in the clotting of the blood.
  • Artificial blood is a solution which can be used to replace real lost blood. The advantages of artificial blood: always available, doesn't need to be in a fridge, doesn't contain cells so it can get any tissue and no blood group matching is needed.
  • Disadvantages: expensive, doesn't carry as much oxygen as whole blood, some artificial blood does not dissolve in water, so does not mix easily with the blood, broken down quickly in the body and there can be unpleasant side- effects.
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B3 2.1- Transporting Materials

  • Advantages of artificial hearts: no wait for a donor,no meed to match tissue, no need for immunosuppressant drugs. Disadvantages: size problems with blood clotting until recently always involved staying in hospital, expense
  • Flowering plants have separate transport systems. Xylem: transports water & mineral ions from roots to stems and leaves
  • Phloem: transports dissolved sugars from leaves to rest to plant, including growing regions and storage organs
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B3 3.1- Keeping internal conditions constant

  • The internal conditions of your body have to be controlled to maintain a constant internal environment. Includes your body temperature, water and ion balance and blood sugar levels.
  • Carbon dioxide is produced during respiration and leaves the body via the lungs when you breathe out. Urea is produced by your liver as excess amino acids are broken down and is removed by your kidneys in the urine.
  • The kidney is important for excretion and homeostasis. A healthy kidney produces urine by filtering the blood. If then reabsorbs all the sugar, plus any mineral ions and water needed by your body. Excess mineral ions, water, along with urea are removed in the urine.
  • People suffering from kidney failure may be treated by regular sessions on a kidney dialysis machine or by having a kidney transplant. In a dialysis machine, the concentration of the dissolved substance in the blood is restored to normal levels. The levels of useful substances in the blood are maintained while urea and excess mineral ions pass out from the blood into the dialysis fluid. 
  • In a kidney transplant diseased or damaged kidneys are replaced with a healthy kidney from a donor. To try and prevent rejection of the donor kidney, the tissue types of the donor and the recipient are matched as closely as possible. Immunosuppressant drugs are also used. 
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B3 3.1- Keeping internal conditions constant

  • Your body temperature is monitored and controlled by the thermoregulatory centre in your brain. Your body temperature must be kept at the level at which enzymes work best. Your body responds to cool you down or warm you up if your core body temperature changes. 
  • The blood vessels that supply the capillaries in the skin dilate and constrict to control the blood flow to the surface. Energy released through the evaporation of sweat from the surface of the skin to cool the body down. Shivering involves the contraction of muscles that produces energy from respiration to warm the body.
  • A kidney transplant allows someone to live a normal life apart from taking immunosuppressant drugs. It costs less than dialysis in the long term. Control of the body temperature in different conditions involves several different processes which cannot always cope in extreme conditions. 
  • Your blood glucose concentration is monitored and controlled by your pancreas. The pancreas produces the hormone insulin, which allows glucose to move the blood into the cells. In type 1 diabetes, the blood glucose may rise to fatally high levels because the pancreas does not secrete enough insulin. It can be treated by injections of insulin before meals.
  • Glucagon allows glycogen to be converted back into glucose and released into the blood.
  • A variety of different methods is being used/developed to treat diabetes using genetic engineering and stem cell ideas. Type 2 diabetes is treated by careful attention to diet and taking more exercise alone. If this does not work, drugs may be needed.
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B3 4.1- How humans can affect the environment

  • Human population is rapidly growing and the standard of living is increasing. More waste is being produced, if not handled properly it can pollute the water, air and the land.
  • The activities of humans reduce the amount of land available for other animals and plants. Raw materials including non-renewable resources are rapidly being used up.
  • Toxic chemicals like pesticides and herbicides can pollute the land. If sewage is not properly handled and treated it can pollute the water, Fertilisers and toxic chemicals can be washed from the land into the water and pollute it.
  • When we burn fossil fuels, carbon dioxide released into the atmosphere. Sulphur dioxide and nitrogen oxides can be released when fossil fuels are burnt. These gases dissolved in rainwater and make it more acidic. Acid rain may damage trees directly. It can make lakes and rivers too acidic so plants and animals cannot live in them. Air pollution can cause global dimming as tiny solid particles in the air reflect away the sunlight.
  • Deforestation is the destruction or removal of areas of forest or woodland. Large-scale deforestation has led to an increase in the amount of carbon dioxide released into the atmosphere (from burning and the actions of microorganisms.) It has also reduced the rate at which carbon dioxide is removed from the air by plants. More rice fields and cattle have led to increased levels of methane in the atmosphere because rice and cattle both produce methane as they grow.The destruction of peat bogs releases carbon dioxide into the atmosphere. 
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B3 4.1- How humans can affect the environment

  • Increasing levels of carbon dioxide and methane in the atmosphere give an increased greenhouse effect, leading to global warming- an increase in the temperature of the surface of the Earth. Global warming may cause a number of changes including climate change, rise in sea level, loss of biodiversity and changes in migration patterns and distribution of species.
  • Some land has been deforested that crops can be grown, from which biofuels based on ethanol can be produced. Biofuels can be made from natural productions using fermentation by yeast.
  • Biogas-mainly methane can be produced by anaerobic fermentation of a wide range of plant products and waste materials that contain carbohydrates.
  • Biogas generators can be small, to supply a single family, or large, to deal with the sewage from an entire city.
  • Sustainable food production means producing food in a way which can continue for many years. It is important to control the net size and impose flashing quotas to conserve fish stocks, so breeding continues and the decline in numbers is halted.
  • The fungus Fusarium is grown on sugar syrup in aerobic conditions to produce mycoprotein foods.
  • Methods used to produce food and water for people can have short and long-term effects on the environment. These are a lot of data on environmental change. The validity, reproducibility, and repeatability of all data must be evaluated before conclusions can be drawn.
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