Biology Unit 3

The cards give a brief but detailed overview of key facts that you need to know for the exam.

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Gas and Solute Exchange

- Dissolved substances move by DIFFUSION, which is the movement of substances from a region of high to low concentration. Substances are sometimes absorbed against a concentration gradient, known as ACTIVE TRANSPORT.

- OSMOSIS is the diffusion of water molecules from a region of high to low concentrated water through a partially permeable membrane.

- The breathing system takes air into and out of the body. This means that oxygen from the air can diffuse into the blood stream, and carbon dioxide can diffuse out of the blood stream into the air.

- Alveoli have the following properties which makes them idea for gas exchange; large surface area, good blood supply, moist and thin lining.

- The surface area of the roots is increased by root hairs, the surface area of leaves are increased by the flattened shape and many internal air spaces, and the plants have stomata to obtain carbon dioxide from the atmosphere.

- Most transpiration is through the stomata, which is controlled by the surrounding guard cells. The stomata is able to close to prevent the plant from wilting.

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- Substances are transported around the body by the circulatory system (the heart, the blood vessels and the blood).

- Main organs: HEART, LUNGS & KIDNEYS.

- Substances needed by the cells in the body tissues pass out of the blood, and substances produced by the cells pass into the blood through the walls of the capillaries.

- Blood 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.

- Red blood cells transport oxygen from the lungs to the organs.

- Red blood cells are packed with a red pigment named haemoglobin, meaning these cells therefore have no room for a nucleus.

- In the lungs, haemoglobin combines with oxygen to form OXYHAEMOGLOBIN.

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- The human body needs to react to the increased demand for energy during exercise. The energy that is released during respiration is used to enable the muscles to contract.

- During exercise; heart rate increases, rate and depth of breathing increases, arteries supplying the muscles dilate (vasodilation).

- These changes increase the blood flow to the muscles, which increases the supply of sugar and oxygen.

- GLYCOGEN stores in the muscles are used during exercise. If insufficient oxygen is reaching the muscles, the body uses ANAEROBIC RESPIRATION.

- Anaerobic respiration is known as the incomplete break down of glucose, producing lactic acid.

- Anaerobic respiration results in OXYGEN DEBT.

- This has to be repaid in order to oxidise lactic acid to carbon dioxide and water.

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The Kidneys

- People whose kidneys do not function properly die due to toxic substances accumulating in their blood. Their lives can be saved by dialysis or transplant.

- A healthy kidney produces urine by; first filtering the blood, reabsorbing all the sugar, reabsorbing the dissolved ions needed by the body, reabsorbing as much water as the body needs, releasing urea and excess ions and water as urine.

- Sugar and dissolved ions may be actively absorbed against a concentration gradient (active transport).

- In a dialysis machine, a person's blood flows between semi-permeable membranes; dialysis fluid contains the same concentrations as the blood, this ensures that glucose and useful mineral ions are not lost. Urea passes out of the blood into the dialysis fluid. Treatment by dialysis restores the concentrations of dissolved substances in the vlood to normal levels and has to be carried out at regular intervals.

- A kidney transplant enables a diseased kidney to be replaced with a healthy one from a donor. However, the kidney may be rejected by the body's immune system. To prevent this the donor must find the correct 'tissue type' to match theirs. Also, immunosuppressant drugs can be prescribed.

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- People used to believe that life could spontaneously generate from non-living material. Evidence disproved this. Evidence instead supported the theory of BIOGENESIS- that living things are created from other living organisms.

- Many experiments were carried out by scientists in an attempt to prove and/or disprove theories. In 1859, Louis Pasteur carried out an experiment which showed that it was microbes, and not the air that caused food and drink to go off.

- Yeast is a single-celled organism. It can respire anaerobically producing carbon dioxide and ethanol (alcohol). This is called FERMENTATION.

- In brewing beer and winemaking, carbohydrates are used. This is because they are needed as an energy source for yeast to respire.

- For making beer; starch and barley grains is broken down into a sugary solution by enzymes (malting). Sugary solution us extracted and fermented, and hops are added to give beer flavour. In winemaking, grapes are the energy source.

- Production of yoghurt; a starter of bacteria is added to warm milk, bacteria ferment the milk sugar (lactose) producing lactic acid, lactic acid causes the milk to clot and solidify into yoghurt.

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Industrial Microbe Production

- Microorganisms are used on a large scale to make many useful substances; antibiotics such as penicillin, foods such as mycoprotein, and fuels such as biogas.

- Microorganisms are grown in large vessels called FERMENTERS. These usually have air supply to provide oxygen, stirrer to keep microorganisms in suspsension and maintain an even temperature, water-cooled jacket to remove heat by respiration and instruments to monitor factors such as PH and temperature.

- Penicillin is made by growing the mould Penicillium, in a fermenter. The medium contains sugar and other nutrients, e.g a source of nitrogen. Penicillin is produced after most of the nutrients are used for growth.

- The fungus Fusarium is used to make mycoprotein. This is a protein-rich food for vegetarians. The fungus is grown on starch in aerobic conditions. Its biomass is harvested and purified.

- Biogas (mainly methane) can be produced by anaerobic fermentation of a wide range of plant products or waste material containing carbohydrates. On a small scale, biogas generators can be used to supply the energy needs of individual families or farms.

- Using biofuels has environmental advantages. Biofuels are a greener alternative to fossil fuels. Carbon dioxide is taken in by plants so this is CARBON NEUTRAL. Raw material is cheap and readily available.

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Using Microbiology Safely

- If the microorganisms that we want to use are contaminated, the other microorganisms that are present may produce harmful substances. Therefore, it is only safe to use microorganisms if we have a pure culture.

- Microorganisms can be grown in a culture medium containing carbohydrates as an energy source, mineral ions, and in some cases supplementary proteins and vitamins. These nutrients are often contained in an agar medium which can be poured into a petri dish.

- In order to prepare useful products, uncontaminated cultures of microorgansims are required;

  • Petri dishes and culture media must be steralised. 
  • Inoculating loops used to transfer media must be steralised by passing through a flame.
  • The lid of the petri dish should be taped down to prevent microorganisms in the air contaminating the culture.

- In school labs, cultures should be incubated at a maximum temperature of 25 degrees. This greatly reduces the likelihood of harmful pathogens growing.

- In industrial conditions, higher temperatures are used to produce more rapid growth.

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