- Most animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribisomes.
- Plant cells contain all the structures seen in animal cells as well as as a cell wall and, in many cases, chloroplasts and a permanent vacuole filled with sap.
- Enzymes control the chemical reactions inside cells.
- Cells may be specialised to carry out a particular function.
- Examples of specialised cells are fat cells, cone cells, root hair cells and sperm cells.
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- Dissolved substances move in and out of cells by diffusion, osmosis and active transport.
- Diffusion is the net movement of particles from an area where they are at a high concentration to an area where they are at a lower concentration.
- Osmosis is a special case of diffusion.
- Osmosis is the diffusion/movement of water from a high water concentration (dilute solution) to a low water concentration (concentrated solution) through a partially permeable membrane.
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How plants produce food 1
- Photosynthesis can be summed up by the equation:
Carbon dioxide + water [+light energy] = glucose + oxygen.
- During photosynthesis light energy is absorbed by the chlorophyll in the chloroplasts. It is used to convert carbon dioxide and water into sugar (glucose). Oxygen is released as a by-product.
- Leaves are well adapted to allow the maximum photosynthesis to take place.
- There are three main factors that limit the rate of photosynthesis- light, temperature and carbon dioxide levels.
- We can artificially change the environment in which we grow plants. We can use this to observe the effect of different factors on the rate of photosynthesis. We can also use it to control their rate of photosynthesis.
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How plants produce food 2
- Plants use some of the glucose they make during photosynthesis for respiration.
- Some of the soluble glucose produced during photosynthesis is converted into insoluble starch for storage.
- Plant roots absorb mineral salts including nitrate needed for healthy growth.
- Nitrates and magnesium are two important mineral ions needed for healthy plant growth.
- If mineral ions are deficient, a plant develops symptoms because it cannot grow properly.
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Energy flows 1
- Radiation from the Sun is the main source of energy for all living things. The Sun's energy is captured and used by plants during photosynthesis.
- The mass of living material at each stage of a food chain is less than at the previous stage. The biomass at each stage can be drawn to scale and shown as a pyramid of biomass.
- The amount of biomass and energy gets less at each successive stage in a food chain.
- This is because some material is always lost in waste, and some is used for respiration to supply energy for movement and for maintaining the body temperature.
- Biomass and energy are lost at each stage of a food chain. The efficiency of food production can be improved by reducing the number of stages in our food chains. It would be most efficient if we all just ate plants.
- If you stop animals moving about and keep them warm, they lose a lot less energy. This makes food production much more efficient.
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Energy flows 2
- Living organisms remove materials from the environment as they grow. They return them when they die through the action of the decomposers.
- Dead materials decay because they are broken down (digested) by microorganisms.
- Decomposers work more quickly in warm, moist conditions. Many of them also need a good supply of oxygen.
- The decay process releases substances which plants need to grow.
- In a stable community the processes that remove materials (particularly plant growth) are balanced by the processes which return materials.
- The constant cycling of carbon in nature is known as the carbon cycle.
- Carbon dioxide is removed from the atmosphere by photosynthesis. It is returned to the atmosphere through respiration and combustion.
- The energy originally captured by green plants is eventually transferred back into plants, into decomposers or as heat into the environment.
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- Catalysts increase the rate of chemical reactions. Enzymes are biological catalysts.
- Enzymes are protein molecules made up of long chains of amino acids. The chains are folded to form the active site. This is where the substrate of the reaction binds with the enzyme.
- Enzyme activity is affected by temperature and pH.
- High temperatures and the wrong pH can affect the shape of the active site of an enzyme and stop it working.
- Enzymes catalyse processes such as respiration, photosynthesis and protein synthesis in living cells.
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- Aerobic respiration involves chemical reactions which use oxygen and sugar and release energy. The reaction is summed up as:
Glucose + oxygen= carbon dioxide + water [+ energy]
- Most of the reactions in aerobic respiration take place inside the mitochondria.
- Enzymes catalyse the breakdown of large food molecules into smaller molecules during digestion.
- Digestive enzymes are produced inside cells but they work outside of cells in the gut.
- Enzymes in the ribisomes catalyse the build up of proteins from amino acids.
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- The enzymes of the stomach work best in acid conditions.
- The enzymes made in the pancreas and the small intestine work best in alkaline conditions.
- Bile produced by the liver neutralises acid and emulsifies fats.
- Some microorganisms produce enzymes which pass out of the cells and can be used in different ways.
- Biological detergents may contain proteases and lipases.
- Proteases, carbohydrases and isomerase are all used in the food industry.
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- The internal conditions of your body have to be controlled to maintain a constant internal environment.
- Poisonous waste products are made all the time and need to be removed.
- 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 it is removed by your kidneys in the urine.
- Your body temperature must be maintained at the level at which enzymes work best.
- Your body temperature is monitored and controlled by the thermoregulatory centre in your brain.
- Your body responds to cool you down if you are overheating and to warm you up if your core body temperature falls.
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- Your blood glucose concentration is monitored and controlled by your pancreas.
- Insulin and glucagon are the hormones involved in controlling blood sugar concentration. Insulin converts glucose to glycogen: glycagon converts glycogen to glucose.
- In 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.
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- Embryonic stem cells (from human embryos) and adult stem cells (from adult bone marrow) can be made to differentiate into many different types of cells.
- Cells in the reproductive organs divide to form the gametes (sex cells).
- Body cells have two sets of chromosomes; gametes have only one set.
- Gametes are formed from body cells by meiosis.
- Sexual reproduction gives rise to variety because genetic information from two parents is combined.
- Gregor Mendel was the first person to suggest separately inherited factors which we now call genes.
- Chromosomes are made up of large molcules of DNA.
- A gene is a small section of DNA which codes for a particular combination of amino acids which make a specific protein.
- Everyone (except identical twins) has unique DNA which can be used to identify them using DNA fingerprinting.
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- In human body cells the sex chromosomes determine whether you are female (XX) or male (XY).
- Some features are controlled by a single gene.
- Genes can have different forms called alleles.
- Some alleles are dominant and some are recessive.
- We can construct genetic diagrams to predict features.
- Some disorder's are inherited.
- Huntington's disease is caused by a dominant allele of a gene and can be inherited from only one parent.
- Cystic fibrosis is caused by a recessive allele of a gene and so must be inherited from both parents.
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