GCSE Biology

• Eukaryotic cell


  cell with a nucleus e.g. animal/plant cells
• Prokaryotic cell


  cell without a nucleus e.g. bacterial cell
• Animal cell


  contains nucleus, cell membrane, cytoplasm, mitochondria and ribosomes
• Plant cell


  contains nucleus, cell membrane, cytoplasm, mitochondria, ribosomes, cell wall, chloroplast and vacuole
• Bacterial cell


  contains cell membrane, cell wall, plasmid, chromosomal DNA, slime coat and flagella
• Nucleus


  Contains genetic info and controls all cell activities
• Cell membrane


  controls what enters and leaves the cell
• Cytoplasm


  where chemical reactions take place
• Mitochondria 


  where energy is released via aerobic respiration
• Ribosomes 


  site of protein synthesis
• Cell wall


  made of cellulose to support and protect the cell
• Chloroplast 


  contains chlorophyll that traps sunlight energy for photosynthesis
• Vacuole


  stores cell sap to keep cell firm and rigid
• Chromosomal DNA 


  contains the instructions for most of cell’s activities
• Plasmid

  contains a small proportion of bacterium’s DNA
• Flagella


  for movement
• Slime coat


  for protection (not all bacteria have this)
• Cell differentiation


  when cell becomes specialised to perform specific function
• Sperm cell


  has nucleus, cell membrane, mitochondria, acrosome, streamlined shape and tail
• Egg cell


  has nucleus, cell membrane, cytoplasm and jelly coat
• Ciliated epithelial cell


  Has nucleus, mitochondria, cytoplasm and cilia
• Specialised cell for digestion 


  small intestine has many mitochondria (gives energy to muscle to squeeze food along)

  outer membrane is folded to make microvilli (increases sa for absorption)

  cells in pancreas has lots of ribosomes (to make protein enzymes)
• Light microscope


  lower magnification, lower resolution and uses beams of light to see larger structures and living samples in colour (cheaper)
• Electron microscope 


  higher magnification, higher resolution and uses beams of electrons to see subcellular structures in dead samples in black and white (more expensive and harder to maintain temperature and pressure)
• Stain


  to see specimen clearly
• TOE


  total magnification = eye piece lens magnification x objective lens magnification
• IAM


  image size = actual size x magnification
• Field of view at new magnification (mm)


  current magnification / new magnification x distance shown by ruler (mm)
• Preparation of slide


  • place specimen onto slide
  • add a drop of stain (iodine/methylene blue)
  • place coverslip carefully
  • remove excess liquid using paper towel
• Preparation of microscope 


  • place slide onto stage
  • switch on light source
  • set objective lens at lowest magnification
  • look through eyepiece lens
  • adjust coarse focusing wheel to move stage up/down for clear image
  • adjust fine focusing wheel to produce sharp and clearer image
  • move onto next higher objective lens magnification and refocus
• Cilia


  contracts and causes wavy movements to move along substances
• Ciliated epithelial cell


  found in oviduct and trachea
• Acrosome 


  contains enzymes to break down jelly coat of egg cell to burrow inside
• Cell membrane for egg cell


  Hardens after fertilisation to ensure only one sperm enters
• Cytoplasm for egg cell


  packed with nutrients to supply fertilised egg with energy and food for growth and development of embryo
• Metre, centi, milli, micro, nano, pico


  x100, x10, x1000, x1000, x1000
• Enzymes


  biological catalysts that speed up the rate of reaction without being used up
• How an enzyme catalyses the breakdown of a substrate molecule


  • a solution of the enzyme is mixed with a solution containing substrate molecules
  • one substrate molecule fits neatly into the active site of the enzyme, like a key into a lock
  • some bonds in the substrate molecule break, causing the formation of two product molecules
  • the product molecules are a different shape to the substrate, so they no longer fit into the active site and are released from the site
  • the active site of the enzyme molecule is free to accept another substrate molecule
• When enzyme denatures 


  • shape of active site changes
  • shape of the protein fold is affected
  • substrate molecule can no longer lock onto the active site
  • enzyme can no longer catalyse the reaction
• Breakdown of starch


  The digestive enzyme called amylase breaks the chemical bonds between the individual sugar molecules in each carbohydrate chain. It is found in saliva and small intestine.