Investigating Living Cells

• Cells are the basic unit of all living things.
  
• There are two distinctive cells - An Animal cell
  - A Plant Cell
  

CELL COMPONENT: Nucleus
FUNCTION: Controls the cells activities

CELL COMPONENT: Cell membrane
FUNCTION: Controls what leaves and enters the cell

CELL COMPONENT: Cytoplasm
FUNCTION: Site of all chemical reactions

CELL COMPONENT: Cell wall
FUNCTION: Gives the plant cell a definite shape. It is made of the complex carbohydrate cellulose.

CELL COMPONENT: Chloroplast
FUNCTION: Contains the green pigment chlorophyll. Site of photosynthesis.

CELL COMPONENT: vacuole
FUNCTION: Only occurs in plant cells and contains cell sap (a solution of salt and sugar).

Investigating Diffusion

• Diffusion is the movement of a substance e.g. glucose, oxygen, carbon dioxide, amino acids etc. from an area of high concentration to an area of low concentration. This occurs across a selectively permeable cell membrane.
• Diffusion is essential for life especially in unicellular organisms. It allows oxygen to pass into the organism and carbon dioxide to leave it.
• Osmosis is the movement of water only from an area of high water concentration (HWC) to an area of low water concentration (LWC) down a concentration gradient.
• The principle behind osmosis and diffusion is to achieve equilibrium. That is all concentrations are equal both sides of a cell membrane.
  

Investigating Cell Division

• During cell division the number of cells increases. This occurs during the growth of a multicellular organism, it is also the method of reproduction in a unicellular organism.
• Chromosomes are thread-like structures found in the nucleus of every cell. Each chromosome carries all the genetic information required for the survival of an organism.
• Mitosis is the process by with the nucleus divides into two identical daughter cells. Each new cell contains an exact copy of the chromosomes present in the original nucleus.
• A chromosome is made up of two identical chromatids these are held together by a centromere.

Investigating Enzymes 

• Enzymes are biological catalysts and are made from proteins.
  
• Their function is to increase the speed of a reaction and they remain unchanged, this allows them to be used a number of different times.
  
• Enzymes work on a substrate and produce an end product.
  
• There is an active site on the enzyme and this is where the chemical reaction takes place.
  
• Enzymes are specific to their substrate. This means that they can only work on one type of substrate.
  
• Enzymes are also specific to temperature (normally around 37oC) and pH.
  e.g. Pepsin breaks down protein at pH 2.8
  Amylase breaks down Starch at pH 7
  Catalase breaks down Hydrogen Peroxide at pH 9
  
• When the conditions are not favourable for an enzyme to work in the enzyme is not active.
  
• If an enzyme is subjected to a temperature > 50oC the enzyme becomes denatured (permanently destroyed).
  
• Enzymes have the ability to build small molecules up into larger ones (synthesis reaction)
  e.g.
  
  potato phosphorylase
  glucose-1-phosphate------------------------------------------------¨¤ starch
  (substrate) (enzyme) (end product)
  
• Enzymes have the ability to break large molecules down into smaller ones (degradation reaction)
  e.g.
  amylase
  starch --------------------------¨¤ simple sugar (maltose)
  (substrate) (enzyme) (end product)
  
  
  Investigating Aerobic Respiration.
  
• All living cells require energy for the following:-
  1. cell division
  2. muscular contractions
  3. building up of large molecules
  4. cell growth
  5. uptake of chemicals
  
• The energy present in food is measured in kilojoules (kJ) or kilocalories (kcal).
  
• 4.2kJ is the quantity of energy required to raise the temperature of 1000g of water by 1oC
• The calorific value of food is the quantity of energy released when 1g of it is burned.
• A food calorimeter can be used to establish how much energy is in a given food product. To gain an accurate result the calorimeter is set up in such a way that reduces a number of errors.
  1. The food sample is enclosed therefore heat loss is reduced to a minimum.
  2. The stirrer and coiled chimney bring about the even distribution of heat.
  3. The oxygen supply ensures that the food sample burns completely.
  
• All living cells have to have an uptake of oxygen to release the energy that is contained within the food, a result of this is the production of carbon dioxide which is then exhaled. This type of reaction is known as Aerobic Respiration.
  
  e.g.
  
  FOOD + OXYGEN ¡ú CARBON DIOXIDE + WATER + ENERGY
  (e.g. glucose) (e.g. heat)
  
• Metabolism is the sum of all the chemical reactions that take place in a living cell.
• All of these reactions are controlled by enzymes.
• Metabolism is made up of many small enzyme-controlled reactions that produce small quantities of energy at a time. This allows the living organism to use this energy as it is required, rather than a huge release of energy that could possibly kill the living organism.