Animal and Plant Cells
- Most animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes.
- Plant cells contain a nucleus, cytoplasm, cell membrane, mitochondria, ribosomes, a cell wall, chloroplasts and a permanent vacuole filled with sap.
- Enzymes control the chemical reactions inside cells.
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- 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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Movement of Substances
- 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 high concentration to an area where they are at a lower concentration.
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- Osmosis is a special case of diffusion.
- Osmosis is the movement of water from a high water concentration to a low water concentration through a partially permeable membrane.
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- Photosynthesis is:
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 have a large surface area to volume ratio, contain lots of chlorophyll, have air spaces and plenty of veins to allow maximum photosynthesis to take place.
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- Limiting factors of photosynthesis are:
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 photosynthesis. We can also use it to control their rate of photosynthesis.
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How Plants Use Glucose
- Plant cells use some of the glucose they make during photosynthesis for respiration.
- Some of the soluble glucose produced during respiration is converted into insoluble starch for storage.
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Uses of Minerals
- Plant roots aborb 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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Pyramids of Biomass
- 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 a 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.
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- The amount of biomass and energy gets less at each successive stage in a food chain.
- Material is always lost in:
Maintaining Body Temperature
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Energy in Food Production
- 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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- Living organisms remove materials from the environment as they grown. They return them when they die through the action of the decomposers.
- Dead materials decay because they are 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 process that remove materials are balanced by the process which return materials.
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The Carbon Cycle
- The constant cycling of carbon in nature is know 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 where the substrate of the reaction binds with the enzyme.
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Factors Affecting Enzyme Action
- Enzyme activity is affected by temperature an 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:
glucose + oxygen ---> carbon dioxide + water [+energy]
- Most of the reactions in aerobic respiration take place inside the mitochondria.
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Enzymes in Digestion
- 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 ribosomes catalyse the build up of proteins from amino acids.
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Speeding Up Digestion
- 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 produces by the liver neutralises acid and emulsifies fats.
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Making Use of Enzymes
- 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 isomerases are all used in the food industry.
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Controlling Internal Conditions
- 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.
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Controlling Body Temperature
- 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 fails.
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Controlling Blood Sugar
- 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; glucagon 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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Cell Division and Growth
- In body cells, chromosomes are found in pairs.
- Body cells divide by mitosis to produce more identical cells for growth, repair, replacement or in some cases asexual reproduction.
- Most types of animal cells differentiate at an early stage of development. Many plant cells can differentiate throughout their life.
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- Embryonic stem cells (from human embryos) and adult stem cells (found in bone marrow) can be made to differentiate into many different types of cells.
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Cell Division in Sexual Reproduction
- Cells in the reproductive organs divide to form the gametes.
- 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.
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From Mendel to DNA
- Gregor Mendel was the first person to suggest seperately inherited factors which we now call genes.
- Chromosomes are made up of large molecules 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 has unique DNA which can be used to identify them using DNA fingerprinting.
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Inheritance in Action
- In human body cells the sex cells 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.
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Inherited Conditions in Humans
- Some disorders 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 cause by a recessive allele of a gene and must be inherited from both parents.
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