biology revision

Additional science topics

  • Created by: Courtney
  • Created on: 03-01-11 23:23


-molecules move randomly because of the energy they have.

-diffusion is the RANDOM movement of molecules from an area of high concentration to that of a lower concentration.

-it requires NO ENERGY from the cell.

-the larger the concentration difference, the higher the rate of diffusion

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-osmosis is the diffusion of water across a partially permeable membrane.

-it occurs from a dilute solution to a more concentrated solution.

-like diffusion, it too does NOT REQUIRE ENERGY from the cell and the movement of molecules is RANDOM.

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-the formula for photosynthesis is ...

carbon dioxide + water (+light energy) -> glucose + oxygen.

...You could also remember it as COW -> GO.

-carbon dioxide is taken in by the leaves and water is taken in by the roots.

-CHLOROPHYLL traps energy, from the sun, needed for photosynthesis.

-glucose is a product of photosynthesis and oxygen us given off as a waste gas.

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Limiting factors of photosynthesis

-a lack of LIGHT would slow down the rate of photosynthesis -> because light is the source of energy for the process.

-a cold TEMPERATURE would slow down the rate of photosynthesis -> because enzymes would not work effectively.

-a lack of CARBON DIOXIDE would slow down the rate of photosynthesis -> carbon dioxide may be limited in an enclosed space, e.g. A greenhouse or rapidly photosynthesising rainforest.

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Why plants need minerals

-plant roots take up mineral salts for healthy growth.

-NITRATES are taken from the soil in order to produce amino acids. These are used to make proteins for growth. A plant deficient in nitrate would have stunted growth.

-plants take up MAGNESIUM that is essential to make chlorophyll. Chlorophyll are essential for photosynthesis. A plant deficient in magnesium would have yellow leaves.

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Animal and plant cells

-animal and plant cells have some structures in common : 1) a NUCLEUS (control the cell activities) 2) CYTOPLASM (where chemical reactions take place) 3) cell CELL MEMBRANE (controls the movement of materials) 4) MITOCHONDRIA(where energy is released during aerobic respiration) 5) RIBOSOMES (where proteins are made).

-plant cells also have 1) CELL WALL (for support) 2) CHLOROPLASTS (contain chlorophyll for photosynthesis) 3) PERMANENT VAUOLE (contains cell sap).

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Specialised cells

-as organisms develop, some of their cells become specialised to carry out particular jobs. This is called 'DIFFERENTIATION'.

-differentiation happens much earlier in the development of animals then Plants

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Pyramids of biomass

-biomass is the mass of living materials in plants and animals.

-a pyramid of biomass represents the mass of the organisms at each stage in a food chain.

-a pyramid of biomass is more accurate than that of numbers. For example, one bush may have many insects feeding on it but the mass of the bush is far more than the mass of the insects.

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Energy loss

-not all of the food eaten can be digested, so energy is lost in faeces.

-some of this energy is used for RESPIRATION, which releases energy for living processes, including MOVEMENT.

-animals need to keep a constant TEMPERATURE. Energy from the previous stage of the food chains is used simply to keep the animal at the correct temperature.

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-DETRITUS FEEDERS(e.g. Worms) start the process of decay.

-they do this by eating dead animals and plants and producing waste materials.

-DECAY ORGANISMS then break down the waste and dead plants and animal.

-(decay organisms are microorganisms).

-decay is faster if it is WARM and WET. -all of the materials from the waste and dead organisms are recycled.

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Aerobic respiration

-AEROBIC RESPIRATION is the release of energy from food when oxygen is available.

-the equation for respiration is...

 glucose + oxygen -> carbon dioxide + water (+energy).

...You can also remember it as GO -> COW.

-the process happens mainly in MITOCHONDRIA.

-the energy released is used to 1) build larger molecules from smaller ones 2) enable muscle contraction 3) maintain a constant body temperature 4) build sugars, nitrates and other nutrients.

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Enzymes in digestion

-digestion involves the breakdown of large, insoluble molecules into smaller soluble molecules.

-AMYLASE; is produced by the salivary glans, pancreas and small intestine, it catalyses the breakdown of starch into glucose and other simple sugars.

-PROTEASE; is produced by the stomach, pancreas and small intestine, it catalyses the breakdown of proteins into amino acids.

-LIPASE; is produced by the pancreas and small intestine, catalyses the process of fats into fatty acids and glycerol.

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Uses of enzymes

-biological washing powders contain ENZYMES that digest some food stains. They work at lower temperatures than ordinary washing powders so they save money.

-protease enzymes are in baby foods to pre-digest proteins.

-isomerases convert glucose into fructose. Fructose is much sweeter and so less of it is needed in food, making it less fattening.

-carbohydrates convert starch into sugar syrup for use in foods.

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Controlling blood sugar

-the pancreas monitors and controls the level of sugar in our blood.

-if there is too much sugar in our blood the pancreas produces the hormone INSULIN.

-this means that excess sugars are stored as glycogen in the liver.

-if insulin is not produced than sugar levels can become fatally high.

-if the pancreas is not producing enough insulin then this is known as DIABETES.

-it can sometimes be controlled by watching the diet and insulin injections

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Cell division in asexual reproduction

-body cells need to DIVIDE in order to produce new cells for growth or repair.

-MITOSIS is a type of cell division that produces identical new cells.

-in mitosis a copy of each chromosome is made first.

-then chromosomes align at the metaphase plate.

-next the daughter chromosomes seperate and daughter cells are formed.

-the daughter nuclei are genetically identical to the parent.

-mitosis is ASEXUAL because it involves only ONE parent.

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Stem cells

-stem cells are NOT SPECIALISED.

-they can develop (differentiate) into many different types of specialised cells.

-stem cells are found in BONE MARROW and in the EMBRYO.

-there are ethical issues surrounding the use if stem cells.

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Cell division in sexual reproduction

-cells in the reproductive system (testes and ovaries) divide to make sex cells or GAMETES.

-the process for this cell division is called MEIOSIS.

-before division, a copy of each chromosome us made.

-then synapses and crossing over occur.

-then chromosomes align independently and seperate to form daughter cells.

-then the daughter chromosomes seperate to form, altogether, four cells.

-the daughter nuclei are not identical to that of the parent.

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