B4 - The Processes of Life

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  • Created by: Hallie23
  • Created on: 29-03-13 19:15

Animal and Plant Cells

Animal Cells:

  • Nucleus - Contains DNA. DNA contains the instructions for making proteins, eg. the enzymes used in chemical reactions of respiration and photosynthesis.
  • Cytoplasm - gel-like substance where proteins like enzymes are made. Some enzymme-controlled reactions take place in the cytoplasm, eg. the reactions of anaerobic respiration.
  • Cell membrane - holds the cell together and controls what goes in and out. It lets gases and water pass through freely while acting as a barrier to other chemicals.
  • Mitochondria - these are where the enzymes needed for the reactions of aerobic respiration are found, and where the reactions take place.

Plant cells also have a few extra things that animal cells don't have:

  • Rigid cell wall - made of cellulose. It supports the cell and strengthens it.
  • Vacuole - Contains cell sap, a weak solution of sugar and salts.
  • Chloroplasts - these are where the reactions for photosynthesis take place. They contain a green substance called chlorophyll and the enzymes needed for photosynthesis. 
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Cell Structure and Function

  • Yeast are single cell microorganisms.
  • Bacterial cells are slightly different to animal, plant and yeast cells.
  • Bacterial cells don't have a nucleus, but instead have a circular molecule of DNA which floats around the cytoplasm. 
  • Bacterial cells don't have mitochondria, but they can still respire aerobically.
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  • Enzymes are proteins that speed up chemical reactions - produced by all living things.
  • Chemical reactions usually involve things either being split apart or joined together.
  • A substrate is a molecule that is changed in a reaction.
  • Every enzyme molecule has an active site.
  • For an enzyme to work, a substrate has to be the correct shape to fit into the active site.
  • The 'lock and key' model shows the substrate fits into the enzyme just like a key fits into a lock.
  • Enzymes need to be at a specific constant temperature to work at their optimum.
  • Changing the temperature changes the rate of an enzyme-controlled reaction.
  • The higher the temperature, thre increase in the rate of reaction.
  • If it gets too hot, some of the bonds holding the enzyme together break. This denatures the enzymes active site and so the substrate will no longer fit in and the enzyme will not work anymore. 
  • In humans the optimum temperature is 37 Degrees.
  • All enzymes have an optimum pH that they work their best at. If the pH is too low or too high, it interfered with the bonds holding the enzyme together. This changes the shape of the active site and denatures the enzyme. 
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  • The processes of life depend on chemical reactions. Most of these reactions are powered by the energy released in respiration.
  • Respiration is a series of chemical reactions that release energy by breaking down large food molecules. It happens in every living cell.
  • Food molecules are thing like glucose (a sugar)
  • Movement - Energy is need to make muscles move.
  • Active Transport - This process uses energy to move some substances in and out of cells.
  • Synthesis of large molecules - Lots of large molecules (polymers) are made by joining smaller molecules together. This requires energy, eg. Glucose is joined together to make things like starch and cellulose in plant cells. Also, in plant cells, animal cells and microorganisms, glucose and nitrogen are joined together to make amino acids. The amino acids are joined together to make proetins.
  • There are two types of respiration - aerobic and anaerobic.
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Aerobic Respiration

  • Aerobic means with oxygen.
  • Aerobic respiration releases more energy per glucose molecule than anaerobic.
  • We use aerobic respiration most of the time.
  • Aerobic respiration takes place in animal and plant cells, and in some microorganisms.
  • Glucose + Oxygen - Carbon dioxide + Water (+Energy)
  • C6H12O6 + 6O2 - 6CO2 _ 6H2O (+Energy)
  • Reactants are turned into products during a reaction.
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Anaerobic Respiration

  • Anaerobic means without oxygen.
  • This type of respiration takes place in cells when there is little or no oxygen.
  • Human cells - When you do really vigorous exercise your body can't supply enough oxygen to your muscle cells for aerobic respiration so they have to start respiring anaerobically.
  • Plant cells - If the soil a plant is growing in becomes waterlogged, there will be no oxygen available in the roots so the root cells will have to respire anaerobically.
  • Bacterial cells - Bacteria can get under your skin through puncture wound caused by things like nails. There is very little oxygen under your skin, so only bacteria than can respire anaerobically can survive. 
  • Glucose - Lactic Acid (+Energy)
  • Anaerobic respiration releases less energy per glucose molecule than aerobic.
  • In plant cells and some microorganisms, anaerobic respiration produces ethanol and carbon dioxide.
  • Glucose - Ethanol + Carbon Dioxide (+Energy)
  • Fermentation is when microorganisms break down sugard into other products as they respire anaerobically.
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Uses of Fermentation


  • Biogas is a fuel used for things like heating and lighting.
  • Lots of different microorganisms are used to produce biogas.
  • They ferment plant and animal waste, which contains carbohydrates.
  • The biogas they produce is mainly made of methane and carbon dioxide.


  • Bread is made using yeast.
  • The yeast ferment the carbohydrates in the flour and release carbon dioxide. 
  • Carbon dioxide causes the bread to rise.


  • Yeast ferment sugar to form alcahol (ethanol).
  • The sugar used in alcahol production comes from things like grapes and barley.
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  • Photosynthesis is a series of chemical reactions that uses energy from sunlight to produce a sugar called glucose.
  • Photosynthesis happens in the cells in green parts of plants (leaf cells) and in some microorganisms (photoplankton).
  • Chlorophyll is needed for photosynthesis to happen. It's a green substance that absorbs the sunlight and allows the energy to be used to convert carbon dioxide and water into glucose.
  • Carbon dioxide + Water - Light energy - glucose + oxygen
  • 6CO2 + 6H2O - C6H12O6 + 6O2
  • Plants use some of the glucose for respiration. This process releases energy from the glucose.
  • Glucose is converted into cellulose for making cell walls. Glucose is combined with nitrogen to make amino acids, which are then made into proteins. Glucose is also used to make chlorophyll.
  • Glucose is turned into a starch and stored in the roots, stem and leaves. It's used at times when the rate of photosynthesis is slower, like winter.
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Rate of Photosynthesis

  • The amount of light, the amount of CO2 and the temperature affect the rate of photosynthesis.
  • Light provides the energy needed for photosynthesis. As the light is raised, the rate of photosynthesis increases steadilly, but only to a certain point. Beyond that, it won't make any difference because it will be either the temperaure or the CO2 level which is the limiting factor.
  • CO2 is one of the raw materials needed for photosynthesis. As with light intensity, the amount of CO2 will only increase the rate of photosynthesis up to a certain point. After this the graoh flattens out, showing that CO2 is no longer the limiting factor. As long as light and CO2 are in plentiful supply then the factor limiting photosyntheiss must be temperature.
  • If the temperature is the limiting factor in photosynthesis, it's because it is too low. The enzymes needed for photosynthesis work more slowly at low temperatures. If the plant gets too hot, the enzymes needed for photosynthesis and its other reactions will denature. This happens at about 45 degrees.
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Investigating Photosynthesis

  • Transects are a way of investigating how something changes across and area.
  • To set up a transect, you need to measure inbetween two fixed points.
  • Start at one end of the transect and work your way down collecting the data you want to know. 
  • Light meter - You'd need to measure the level of light, eg. if you were comparing plants in areas with different levels of light. You could use a light meter to do this. It's a sensor that accurately measures light level.
  • Quadrat - To make data collection quicker and easier, you could use a quadrat (a square frame divided into a grid of 100 smaller squares). You can estimate the percentage cover of a plant species on the ground by counting how much of the quadrat is covered by the species. You can count a square if it's more than half covered.
  • Identification key - To identify the different plant species you are looking at you could use an identification key. It's a series of questions that you can use to figure out what the plant is. 
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  • Diffusion is the passive overall movement of particles from a region of their higher concentration to a region of their lower concentration. 
  • It's the gradual movement of particles from places where there are lots of them to places where there are fewer of them. 
  • Passive means that it takes place without needing any energy.
  • When plants photosynthesise, they use up carbon dioxide from the atmosphere and produce O2. these gases pass in and out of plant leaves by diffusion.
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  • Osmosis it the overall movement of waer from a dilute to a more concentrated solution through a partially permeable membrane.
  • Osmosis is a type of diffusion.
  • It's the passive movement of water molecules from an area of higher concentration to an area of lower concentration.
  • A dilute solution has a higher concentration of water molecules than a concentrated solution.
  • A partially permeable membrane only allows certain substances to diffuse through it. 
  • Plants take in water by osmosis.
  • There is usually a higher concentration of water in the soil than there is inside the plant, so the water is drawn into the root by osmosis.
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Active Transport

  • Active transport is the overall movement of chemicals across a cell membrane from a region of lower concentration to a region of higher concentration using energy released by respiration.
  • Plants take in minerals like nitrates through their roots by active transport. The concentration of minerals in root cells is normally higher than in the soil around them. 
  • Active transort uses energy from respiration to move minerals from the soil into the root cells. 
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