Section 8 biology

• Organisms take in: Oxygen, water, food and mineral ions. And they get rid of waste products such as: Carbon dioxide (a waste product of aerobic respiration) and urea (a waste product of protein breakdown in animals)
• Oxygen and carbon dioxide move between cells and the environment by diffusion.
• A surface area to volume ratio show how big a surface is compared to its volume. A way of calculating an organisms surface area to volume ratio is: Step 1: The area is found by doing length x width. Step 2: The volume can be found by doing length x width x height. Step 3: Write it as a ratio and to get it to equal to one divide both sides of the ratio by the volume.
• The larger the organism the smaller the surface area is compared to its volume. The smaller its surface is compared to volume the harder it is for an organism to exchange substances with its environment.
• The alveoli are specialised exchange surfaces found in the lungs of mammals.
• Single celled organisms have a large surface area compared to its volume. So they can exchange all the substances they need across their cell membrane. Multicellular organisms (e.g. Animals) have a smaller surface area compared to their volume. They cant normally exchange enough substance across their outside surface area. Instead they have specialised exchange surfaces.
• Multicellular organisms also have a mass transport system to move substances between exchange surfaces and the rest of the body. In animals this is the circulatory system.
• Oxygen and Carbon Dioxide are exchanged in the lungs in mammals. The alveoli fill up with air from the environment when you breathe in and this air has lots of oxygen but very little carbon dioxide. The alveoli are surrounded by capillaries witch carry blood. Blood arriving at the alveoli have lots of carbon dioxide and little oxygen. The oxygen diffuses from the air to the blood. And the carbon dioxide diffuses from the blood to the air.
• Alveoli have: A moist lining for dissolving gases. A good blood supply. Very thin walls so gases don't have far to diffuse. They also give lungs large surface area to volume ratios which maximises the rate of diffusion.
• Red blood cells carry oxygen from the lungs to all cells in the body. Their shape gives them a large surface area for absorbing oxygen. And contain a red substance called haemoglobin. This substance allows red blood cells to carry oxygen. Red blood cells don't have a nucleus so it leaves more space for oxygen.
• White blood cells are part of your immune system. Lymphocytes are white blood cells that produce antibodies against microorganisms. Phagocytes are white blood cells that can change shape to get rid of microorganisms.
• Platelets are small fragments of cells. They have no nucleus. They help your blood to clot a wound and this stops your blood pouring out of cuts. It also stops microorganisms getting in.
• Plasma is a pale liquid and carries everything in the blood including: Red and white blood cells and platelets. Glucose and Amino acids. Waste products e.g. Carbon dioxide. Hormones. And antibodies.
• Arteries have thick walls. And the hole (lumen) in the middle is small. Arteries carry blood away from the heart. Arteries have strong elastic walls because the heart pumps blood out high pressure. They have thick layers of muscle to make them strong. As well as elastic fibres to make them stretch.
• Capillaries are branches of arteries. They are tiny and can squeeze into gaps between cells and and carry blood really close to every cell in the body. They supply food and oxygen and take away waste. They have permeable walls so substances can diffuse in and out. And their walls are usually one cell thick so substances can diffuse out quickly.
• Veins are formed from joined up capillaries. Veins carry blood back to the heart. Vein walls are thinner because they carry blood at low pressure. Veins have a bigger lumen than arteries witch helps blood to flow even though there is low pressure. Veins also have valves which helps to stop blood flowing backwards.
• Mammals have a double circulatory system which means that the heart pumps blood around the body in two circuits: Circuit 1: Heart pumps deoxygenated blood to the lungs and the blood picks up oxygen from the lungs. Oxygenated blood then returns to the heart. Circuit 2: Heart pumps oxygenated blood around all other organs of the body and delivers oxygen to the body cells. Deoxygenated blood returns to the heart.
• Some organisms have a single circulatory system. E.g. fish: Heart pumps blood to the gills to pick up oxygen. And then around the rest of the body in one circuit.
• A mammals heart has 4 chambers and 4 major blood vessels. Number 1: Right Atrium: Gets deoxygenated blood from the body which comes from the vena cave. Number 2: Deoxygenated blood goes to the right ventricle which pumps it to the lungs via the pulmonary artery. Number 3: Left Atrium: Gets oxygenated blood from the lungs which comes through the pulmonary vein. Number 4 Oxygenated blood goes to the left ventricle which pumps it around the whole body via the aorta.
• The Left Ventricle has a thicker wall than the right ventricle. The left ventricle needs more muscle because it has to pump blood around the whole body.
• Cardiac output is the total volume of blood pumped by a ventricle every minute. Cardiac output= heart rate x stroke volume.
• Your body needs energy to keep going. Energy comes from food and energy is released by respiration. Respiration is an exothermic reaction which means it releases energy.
• Some energy is released as heat. And some is used in metabolic reactions. There are two types of respiration: Aerobic and Anaerobic. Aerobic means with oxygen so aerobic respiration is respiration with oxygen. Equation: Glucose + oxygen -- Carbon dioxide + water. Anaerobic respiration happens without oxygen. So it releases less energy but is still useful. E.g. during hard exercise your muscles can't get enough oxygen to just respire aerobically. So they respire anaerobically to. Equation: Glucose -- lactic acid.
• Anaerobic respiration in plants is different. They can respire without oxygen too, but they produce ethanol and carbon dioxide instead of lactic acid. Equation: Glucose -- ethanol + carbon dioxide.