Key Concepts in Biology



Organisms can be Eukaryotes or Prokaryotes. Eukaryots cells ae complex and include all animal and plant cells. Prokaryotic cells are smaller and simpler, eg. bacteria. A prokaryote is a prokaryotic cell (a single celled organism).

Plant and animal cells

Nucleus - contains genetic material that controls the activity of the cells.

Cytoplasm- gel like substance where most og the chemical reactions happen

Cell membrance- holds cell together and controls what enters and leaves the cell.

mitrochondia-Respiration happens

Ribosomes-Protein synthesis

Cell Wall- made of cellulose, supports cell.

Vacuole- contains cell sap, a weak solution of sugar and salts

chloroplasts- Photosynthesis occurs here, contains chlorophyll.

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Bacterial Cells

Bacteria cells are a lot smaller than plant or animal cells and have thes sub-cellular structures:

1) Chromosomal DNA- (one long circular chromosome) it controls the cells activities and replication. It floats free in the cytoplasm.


3)Cell membrane

4)Plasmid DNA- small loops of extra DNA that aren't part of the chromosome. Plasmids contain genes for dug resistance, and can be passed between bacteria.

5)Fragellum (plural fragella)- a long hair like structure that rotates to make the bacterium move. It can me used to move the bacterium away from harmful substances like toxins and towards benificial things like nutrients and oxygen. 

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Microscopy Practical


  • To use a light microscope to examine animal and/or plant cells.
  • To make observations and draw scale diagrams of cells.

1) Take a thin slice of your specimen

2)Take a clean slide and with a pipete add a drop of water to it- this secures the specimen in place- then will tweezers place the specimen to the slide.

3)Place a small circle of thin glass, called a coverslip over the specimen.

4)Stain the specimen.

5)Turn the coarse focus to adjust the space between the stage and objective lens

6) Place the microscope slide on the stage. Line it up so that the specimen is in the centre of the stage, where the light passes through.

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1)  Total magnification= eyepiece lens magnification x objective lens magnification

2) magnification=image size/actual size

Units                              Metre in standard form  

Millimetre (mm)            x10-3m

Micrometre (μm)          x10-6

Nanometre (nm)          x10-9m

Picometre (pm)            x10-12m

(so 1pm= 0.000000000001m)

(Going down the rows ÷1000 each time)

(Going up the table X 1000 each time)

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Enzymes are proteins that function as biological catalysts. So, they are molecules that speed up a chemical reaction without being changed by the reaction.

1.Substrate collides with active site of enzyme and becomes attached.Active site has a complementary shape to the substrate. The fit between the enzyme and substrate is like a lock and key.

2.Enzyme catalyses breakdown of substate.

3.The products are released from the active site

Temperature, pH and substate concentration affect the rate of reaction.

If enzymes are exposed to extremes of pH or high temperatures the shape of their active site may change.

If this happens then the substrate will no longer fit into the enzymes. This means the key will no longer fit the lock. We say that the enzyme has been denatured.

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Enzyme Practical

Aim-To determine the optimum pH at which an enzyme’s activity is greatest.

  1. Set up a Bunsen burner, heatproof mat, tripod and gauze.
  2. Place a beaker of water on the gauze and adjust the flame to keep the water at about 35°C.
  3. Now put two drops of iodine solution into each spot of a spotting tile.
  4. Add 3 cm3 of amylase enzyme solution to a test tube.
  5. Place 3 cm3 of starch solution into the same tube.
  6. Finally add 1 cm3 of pH solution (buffer solution) to the tube. This will keep the pH constant.
  7. Mix the solution in the test tube and place it into the beaker of water on the Bunsen burner.
  8. Use a pipette to remove a few drops of solution every 10 seconds from the test tube and put them into a different well of the spotting tile.
  9. Repeat until the iodine solution stops turning black.
  10. Record the time this takes.
  11. Repeat with different pH solutions.                     ( Rate of reaction= 1000/time)


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Enzyme Practical 2


  • Iodine solution is an irritant. If it touches skin it should be washed off.
  • Goggles should be worn at all times.


The enzyme amylase breaks down starch into glucose. If the enzyme is working effectively, this will happen quickly. At pH 7 it took the shortest time before the iodine no longer changed colour. This shows that the starch was broken down more quickly at this pH. The optimum pH for amylase is therefore pH 7.

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Proteins, Lipids and Carbohydrates.

Carbohydrates, proteins and lipids are large molecules that are needed by the body for growth, repair and metabolism. They are found in our food. These molecules are too large to pass from the intestine into the blood, so digestive enzymes break them down into smaller molecules. Once in the body, different enzymes use these raw materials to synthesise larger molecules.

Enzymes called carbohydrases convert carbohydrates into simple sugars. Amalyse is an example of a carbohydrase, it breaks down startch.

Proteases convert proteins into amino acidsLipases convert lipids into glycerol and fatty acid.

Some Enzymes join molecules together.

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Food Testing Practical

There are different tests which can be used to detect carbohydrates, proteins and lipids in foods.

1) Iodine Test- Starch is detected using iodine solution. This turns blue-black in the presence of starch.

2) Benedicts Test- Benedict's solution gradually turns from blue to cloudy orange or brick red when heated with a reducing sugar. Sucrose is a non-reducing sugar and does not react with Benedict's solution.

3) Biuret Test- Proteins are detected using Biuret reagent . This turns a mauve or purple colour when mixed with protein.

4) Emulsion Test- A milky-white emulsion forms if the test substance contains lipids.


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