biology ocr gateway

• There are two types of cells eukaryotic and prokaryotic.
• examples of eukaryotic cells :

  plant cell

  animal cell
• animal cell structure:

  nucleus- contains DNA

  cytoplasm- where chemical reactions take place

  mitochondria- site of cellular respiration

  ribosomes- where proteins are made

  cell membrane- controls what enters and exits the cell
• plant cell structure:

  nucleus

  cytoplasm

  mitochondria

  ribosomes

  cell membrane

  cell wall- gives structure

  chloroplasts- site of photosynthesis

  vacuole- contains sap
• A bacterial cell is an example of a prokaryotic cell
• bacteria cell structure:

  plasmids- small loops of extra DNA

  chromosomal DNA- floats free in the cytoplasm

  cell membrane-controls what enters and exists the cell
• light microscope:

  eyepiece - where you look through

  objective lens - magnifies the image

  stage - supports the slide

  clips - holds slide in place

  handle - to carry the microscope

  lamp - to see sample more easily

  focusing wheel - moves stage up and down
• magnification

  magnification= image size / real size
• DNA


  DNA has a double helix structure made up of nucleotides which makes DNA a polymer.

  The bases are A and T which always pair together and C and G which also always pair together.

  Nucleotides contain a sugar, a phosphate group and a base
• enzymes

  enzymes are a biological catalyst which means they speed up a reaction without being used up in the process. an enzyme fuses with a substrate creating a enzyme-substrate complex, the substrate then splits into the products but the enzyme remains unchanged.

  the lock and key hypothesis shows that the enzyme can only fuse with a specific substrate due to the shape of the active site.
• enzymes have to have optimum conditions to work:

  temperature- if it is too cold there will not be enough energy for collisions to take place, if it is too hot then the enzyme will denature

  pH- if it is too high or too low then the enzyme may denature
• respiration


  glucose + oxygen = carbon dioxide + water

  c6h1206 + 6o2 = 6CO2 + 6H2O
• anaerobic respiration


  takes place when there is no or not enough oxygen

  in animals:

  glucose --> lactic acid

  in plants:

  glucose --> ethanol + carbon dioxide
• biological molecules


  carbohydrates are made up on simple sugars

  proteins are made up of amino acids

  lipids are made up of fatty acids and glycerol
• food tests


  sugars - Benedict's solution (brick red)

  starch - iodine (brown to blue-black)

  lipids - emulsion test (turn to milky emulsion)

  proteins - Biuret test (purple)
• photosynthesis


  carbon dioxide + water = glucose + oxygen

  6CO2 + 6H2O = C6H12O6 + 6O2
• mitosis


  the process where a cell reproduces by splitting to form two identical daughter cells for growth and repair.
• protein synthesis


  proteins are synthesised on ribosomes.

  1 DNA contains the gene coding for the protein

  2 the DNA strands unzip, the DNA is used as a template to make mRNA. base pairings ensure its complementary, this is transcription

  3 mRNA molecules then moves out of the nucleus into the cytoplasm and joins the ribosomes

  4 amino acids that match on the mRNA join together, this makes protein coded by the gene, the amino acids are bought to the ribosomes by RNA. this is called translation
• iris muscles

  radial muscles contract- pupil gets bigger

  circular muscles contract- pupil gets smaller