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Transcript
Respiration 3.6 Living things need energy Plants and animals need energy to stay alive. Energy is used by: all organisms to build up large molecules from smaller ones (for example, building up proteins from amino acids or making starch from glucose needs energy) animals to contract muscles during movement mammals and birds to keep their body temperature steady in colder surroundings plants to make amino acids from sugars and nitrates. Releasing energy Energy, in the form of glucose, is made available to cells by the breakdown of food molecules. The process of releasing energy from glucose is called respiration. Question The food store in a seed provides the energy to build large molecules during growth. a What sorts of foods would be broken down to give the glucose required for respiration? The energy in glucose can be released in a single reaction. When this happens heat energy is released as glucose burns. This is combustion. During respiration glucose is broken down gradually by a series of reactions, each catalysed by a different enzyme. This releases energy in small amounts so that it can be used by cells. ������������������������������������������������� ������� ������ ������ ������ ������ ������ ���������������������� ������ The gradual breakdown of glucose enables cells to use the energy released. � Energy is released as heat when glucose breaks down rapidly during combustion. 50 B2 � Energy can be used by cells when glucose is broken down gradually during respiration. Using oxygen Respiration which uses oxygen is called aerobic respiration. During aerobic respiration reactions take place which use glucose and oxygen to release energy. These reactions are summarised by the equation: glucose + oxygen → carbon dioxide + water + energy Powering cells Most of the reactions in aerobic respiration take place inside the mitochondria found in the cytoplasm of cells. Cells such as muscle cells, which need lots of energy contain large numbers of mitochondria. Because mitochondria release the energy needed by cells they are called the ‘powerhouse’ of the cell. Question glucose b Nerve tissue contains many mitochondria. Suggest why this type of tissue needs many mitochondria. R E S P I R A T I O N energy mitochondrion Question Cells using a lot of energy need a lot of mitochondria. This shows muscle tissue. oxygen Building large molecules Cells use energy to synthesise large molecules such as proteins. Proteins are made by joining amino acids together to form long chains. Amino acids produced by the digestion of proteins are absorbed into the blood. They are transported around the body by the blood for use by cells to make the proteins they need. The joining of amino acids is catalysed by enzymes found inside cells. Protein synthesis needs energy which is provided by respiration. amino acid enzyme amino acid + energy amino acids bonded together Key points amino acids attach to enzyme Animals get the amino acids they need from food. Plants make all their own amino acids. Nitrate ions in the soil are absorbed by roots. In the root cells, enzymes convert nitrates and sugars into amino acids using enzymes and energy from respiration. nitrates + sugars + c Food provides the amino acids needed to make body proteins. Describe the steps involved in: (i) getting amino acids into the body (ii) using the amino acids to make proteins. energy from respiration→ amino acids In aerobic respiration oxygen and glucose are used and energy is released. Most aerobic respiration takes place inside mitochondria. Some of the energy released in respiration is used to make larger molecules from smaller ones, to enable muscles to contract and to keep temperature steady. Some of the energy released in respiration in plants is used to make amino acids and proteins. Enzymes and homeostasis � � 51 Homeostasis 3.7 Staying the same Even though the temperature of the air around you might be freezing in winter and very hot in summer your core body temperature stays at 37 °C. Keeping conditions steady inside the body is called homeostasis. For example, your body temperature, the amount of glucose in your blood and the amount of water and ions in your body are all kept at a steady level. These conditions are being adjusted all the time by your body to prevent any big changes. Homeostasis helps your cells to work as efficiently as possible. The chemical reactions in cells are controlled by enzymes. Enzymes work best in particular conditions, so keeping the conditions at a steady level provides enzymes with the best working environment. Getting rid of waste Chemical reactions in body cells produce waste. This waste includes carbon dioxide and urea. The diagram shows the organs that remove waste products from your body. liver breaks down excess amino acids and forms urea kidneys remove urea as urine lungs remove carbon dioxide produced in respiration Although there may be very large temperature changes around you, your core body temperature stays very steady. bladder stores urine before it is removed by urinating Your lungs play a part in homeostasis by keeping the concentrations of oxygen and carbon dioxide at the best level for respiration. The rate of respiration inside muscle cells increases when you exercise. More waste carbon dioxide will be produced. When this happens you change your breathing to get rid of carbon dioxide more quickly. The graph shows the amount of air taken in and out of the lungs at rest and during exercise. 52 B2 Volume of air breathed in and out (cm3/minute) exercise starts exercise ends 2000 1500 1000 500 0 0 1 2 3 4 5 Time (minutes) 6 7 8 Questions blood flowing to the kidneys contains urea a Calculate the increase in the volume of air breathed in and out each minute after 3 minutes of exercise. b The air that is breathed out contains 4% carbon dioxide. Calculate the volume of carbon dioxide breathed out each minute (i) at rest (ii) after 3 minutes of exercise. Your body needs amino acids for building new cells. You get these amino acids by digesting the protein in food. Your body is unable to store the excess amino acids it does not use. Instead, these are broken down in the liver to make urea. The urea is taken from the liver to the kidneys where it is converted into urine. Urine is stored in the bladder before being removed from the body. Controlling water and ions Your body cells need a constant amount of water. If the amount of water is not controlled then too much water may move in or out of cells and damage them. The diagram here shows how water is lost and gained by your body each day. Your body has to balance the amount of water it takes in with the amount it loses. Sweating helps to cool your body down, so on a hot day more water is lost as sweat. When you lose water you become thirsty so you take in more water by drinking more fluids. When you sweat you lose ions as well as water. Sweat contains about 0.15 g of salt (sodium chloride) per 100 cm3 water. Sports drinks help to replace both the water and the salt. blood flowing away from the kidneys contains very little urea urea is removed from the kidneys in urine urine is stored in the bladder a ring of muscle keeps the bladder closed until you urinate The kidneys convert urea to urine. water gain water loss food 900 cm3 exhaled air 250 cm3 drink respiration 300 cm3 skin 600 cm3 urine 1400 cm3 faeces 150 cm3 Question c The body balances water losses with water gains. Use the information in the diagram to calculate: (i) the volume of water taken in by drinking (ii) the percentage of water lost via the skin. Key points When you sweat you lose both water and salt. This is why athletes drink sports drinks – to replace both salt and water. Waste products include carbon dioxide and urea. Carbon dioxide is formed in respiration; urea is formed from excess amino acids. Carbon dioxide is removed from the lungs. Urea is produced in the liver and removed as urine from the kidneys. Internal conditions, including water and ion content, are controlled at a steady level. Enzymes and homeostasis 53