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| Respiration supplies the body with energy. The circulatory system takes oxygen and glucose to the cells and removes waste products. We can improve our fitness by taking exercise. Anaerobic respiration occurs when there is too little oxygen present. | What is respiration? Enzymes in cells catalyse photosynthesis, protein synthesis - joining amino acids together, and aerobic respiration. Aerobic respiration Respiration is not the same thing as breathing. That is more properly called ventilation. Instead, respiration is a chemical process in which energy is released from food substances, such as glucose - a sugar. Aerobic respiration needs oxygen to work. Most of the chemical reactions involved in the process happen in tiny objects inside the cell cytoplasm, called mitochondria. This is the equation for aerobic respiration: glucose + oxygen → carbon dioxide + water (+ energy) The energy released by respiration is used to make large molecules from smaller ones. In plants, for example, sugars, nitrates and other nutrients are converted into amino acids. Amino acids can then join together to make proteins. The energy is also used: To allow muscles to contract in animals To maintain a constant body temperature in birds and mammals |
| The circulatory system Blood carries oxygen and nutrients to the body's cells,and waste products away from them. The circulatory system consists of: The heart, which is the muscular pump that keeps the blood moving The arteries, which carry blood away from the heart The veins, which return blood to the heart The capillaries, which are tiny blood vessels that are close to the body's cells The diagram outlines the circulatory system. Oxygenated blood is shown in red, and deoxygenated blood in blue. A process called diffusion takes place in the capillaries. Diffusion is where particles of a high concentration move to an area of low concentration. Glucose and oxygen diffuse into the cells from the capillaries. Carbon dioxide diffuses out of the cells into the blood in the capillaries. | |
| Effect of exercise on breathing During exercise, the muscle cells respire more than they do at rest. This means: Oxygen and glucose must be delivered to them more quickly Waste carbon dioxide must be removed more quickly This is achieved by increasing the breathing rate and heart rate. The increase in heart rate can be detected by measuring the pulse rate. The stroke volume also increases – this is the volume of blood pumped each beat. The total cardiac output can be calculated using the equation: Cardiac output = stroke volume x heart rate During hard exercise, the oxygen supply may not be enough for the needs of the muscle cells. When this happens, anaerobic respiration takes place, as well as aerobic respiration. | Fitness versus health Fit people are able to carry out physical activities more effectively than unfit people. Their pulse rate is likely to return to normal more quickly after exercise. But being fit is not the same as being healthy. Healthy people are free from disease and infection: they may or may not be fit as well. It is possible to be fit but unhealthy, or healthy but unfit. |
| Anaerobic respiration When exercising very hard, the heart cannot get enough oxygen to the muscles. Anaerobic respiration does not need oxygen. It releases energy from glucose but the amount is much lower. It happens when there is not enough oxygen for aerobic respiration. Here is the word equation: glucose → lactic acid (+ energy) Much less energy is released by anaerobic respiration than by aerobic respiration. The lactic acid that forms causes muscle fatigue and pain. | . |
| The after effect of exercise During hard exercise when anaerobic respiration occurs with aerobic respiration, an oxygen debt builds up. This is now known as Excess Post-exercise Oxygen Debt or EPOC. This is because glucose is not broken down completely to form carbon dioxide and water. Some of it is broken down to form lactic acid. Panting after exercise provides oxygen to break down lactic acid. The increased heart rate also allows lactic acid to be carried away by the blood to the liver, where it is broken down. | Blood pressure Arteries carry blood away from the heart. The blood in the arteries is under pressure because of the contractions of the heart muscles. This allows the blood to reach all parts of the body. You can see how the heart pumps the blood to the lungs and rest of the body by studying this animation: Blood pressure is measured in millimetres of mercury, mmHg. There are two measurements: Systolic pressure - the higher measurement when the heart beats, pushing blood through the arteries. Diastolic pressure - the lower measurement when the heart rests between beats. A young, fit person may have a blood pressure of about 120 over 70, which means their systolic pressure is 120 mmHg, and their diastolic pressure 70 mmHg. Blood pressure varies with age. It also varies with lifestyle factors such as: Diet Stress Exercise Body mass Alcohol consumption |
| Leaves enable photosynthesis to occur. Photosynthesis is the process by which leaves absorb light and carbon dioxide to produce carbohydrate (food) for plants to grow. Leaves are adapted to perform their function, eg they have a large surface area to absorb sunlight. Plants have two different types of 'transport' tissue, xylem and phloem, that move substances in and around the plant. When water evaporates from the leaves, resulting in more water being drawn up from the roots, it is called transpiration. Structure of a leaf Functions of leaves The function of a leaf is photosynthesis – to absorb light and carbon dioxide to produce carbohydrates. The equation for photosynthesis is: Carbon dioxide and water → glucose and oxygen Did you know: Leaves are the source of all of food on the planet Leaves recycle all of the world's carbon dioxide in the air Leaves contain the world's most abundant enzyme | |
| Features of leaves Adaption Purpose Large surface area To absorb more light Thin Short distance for carbon dioxide to diffuse into leaf cells Chlorophyll Absorbs sunlight to transfer energy into chemicals Network of veins To support the leaf and transport water and carbohydrates Stomata Allow carbon dioxide to diffuse into the leaf | |
| Factors affecting photosynthesis Three factors can limit the speed of photosynthesis: light intensity, carbon dioxide concentration and temperature.Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis. |
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| Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide. |
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| Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide. |
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| If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot. If you plot the rate of photosynthesis against the levels of these three limiting factors, you get graphs like the ones above. In practice, any one of these factors could limit the rate of photosynthesis. |
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| Maximising growth Farmers can use their knowledge of these limiting factors to increase crop growth in greenhouses. They may use artificial light so that photosynthesis can continue beyond daylight hours, or in a higher-than-normal light intensity. The use of paraffin lamps inside a greenhouse increases the rate of photosynthesis because the burning paraffin produces carbon dioxide, and heat too. | . |
| Transpiration Transpiration explains how water moves up the plant against gravity in tubes made of dead xylem cells without the use of a pump. Water on the surface of spongy and palisade cells (inside the leaf) evaporates and then diffuses out of the leaf. This is called transpiration. More water is drawn out of the xylem cells inside the leaf to replace what's lost. As the xylem cells make a continuous tube from the leaf, down the stem to the roots, this acts like a drinking straw, producing a flow of water and dissolved minerals from roots to leaves. | Factors that speed up transpiration will also increase the rate of water uptake from the soil. When water is scarce, or the roots are damaged, it increases a plant's chance of survival if the transpiration rate can be slowed down. Plants can do this themselves by wilting, or it can be done artificially, like removing some of the leaves from cuttings before they have chance to grow new roots. |
| Transpiration Transpiration explains how water moves up the plant against gravity in tubes made of dead xylem cells without the use of a pump. Water on the surface of spongy and palisade cells (inside the leaf) evaporates and then diffuses out of the leaf. This is called transpiration. More water is drawn out of the xylem cells inside the leaf to replace what's lost. As the xylem cells make a continuous tube from the leaf, down the stem to the roots, this acts like a drinking straw, producing a flow of water and dissolved minerals from roots to leaves. | Factors that speed up transpiration will also increase the rate of water uptake from the soil. When water is scarce, or the roots are damaged, it increases a plant's chance of survival if the transpiration rate can be slowed down. Plants can do this themselves by wilting, or it can be done artificially, like removing some of the leaves from cuttings before they have chance to grow new roots. |
| Plant transport No heart, no blood and no circulation, but plants do need a transport system to move food, water and minerals around. They use two different systems – xylem moves water and solutes from the roots to the leaves – phloem moves food substances from leaves to the rest of the plant. Both of these systems are rows of cells that make continuous tubes running the full length of the plant. | Xylem Xylem cells have extra reinforcement in their cell walls, and this helps to support the weight of the plant. For this reason, the transport systems are arranged differently in root and stem – in the root it has to resist forces that could pull the plant out of the ground. In the stem it has to resist compression and bending forces caused by the weight of the plant and the wind. |
| Stem – the xylem and phloem are arranged in bundles near the edge of the stem to resist compression and bending forces. | |
| Root - xylem and phloem in the centre of the root to withstand stretching forces. | |
| Root hair cells and osmosis Roots Plants absorb water from the soil by osmosis. Root hair cells are adapted for this by having a large surface area to speed up osmosis. The absorbed water is transported through the roots to the rest of the plant where it is used for different purposes: It is a reactant used in photosynthesis It supports leaves and shoots by keeping the cells rigid It cools the leaves by evaporation It transports dissolved minerals around the plan | |
| Leaves Leaves are adapted for photosynthesis by having a large surface area, and contain openings, called stomata to allow carbon dioxide into the leaf. Although these design features are good for photosynthesis, they can result in the leaf losing a lot of water. The cells inside the leaf have water on their surface. Some of this water evaporates, and the water vapour can then escape from inside the leaf by diffusion. To reduce loss the leaf is coated in a wax cuticle to stop the water vapour escaping through the epidermis. Leaves usually have fewer stomata on their top surface to reduce this water loss. |
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