key concepts in biology

• Eukaryotes


  • Organisms made up of cells with a nucleus
  • Include plant and animal cells
• Prokaryotes


  • Single-celled organisms without a nucleus
  • Include bacteria
• Subcellular structures

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Nucleus


  Contains genetic material that controls the activities of the cell
• Cytoplasm


  Gel-like substance where most chemical reactions occur, contains enzymes
• Cell membrane


  Holds the cell together and controls what goes in and out
• Mitochondria


  Where most reactions for respiration take place, transfer energy the cell needs
• Ribosomes


  Involved in translation of genetic material
• Additional structures in plant cells

  • Rigid cell wall
  • Large vacuole
  • Chloroplasts
• Cell wall


  Made of cellulose, supports and strengthens the cell
• Vacuole


  Contains a weak solution of sugar and salts, maintains internal pressure to support the cell
• Chloroplasts


  Where photosynthesis occurs, contain chlorophyll
• Structures in bacterial cells

  • Chromosomal DNA
  • Ribosomes
  • Cell membrane
  • Plasmid DNA
  • Flagella
• Chromosomal DNA


  One long circular chromosome that controls the cell's activities and replication
• Plasmid DNA


  Small loops of extra DNA that aren't part of the chromosome
• Flagella


  Long, hair-like structures that rotate to make the bacterium move
• Cells have different structures depending on their function
• Egg cells and sperm cells are specialised for reproduction
• Ciliated epithelial cells are specialised for moving materials
• Using a light microscope

  1. Prepare specimen

  2. Place on stage

  3. Focus image

  4. Measure magnification
• Magnification


  How many times bigger the image is compared to the real object
• Magnification = eyepiece lens magnification x objective lens magnification
• To estimate magnification, round numbers and do quick mental calculation
• As temperature increases


  The rate of enzyme-catalysed reactions increases at first, but then decreases if it gets too hot and the enzyme denatures
• As pH changes


  The rate of enzyme-catalysed reactions is affected, with an optimum pH where the enzyme works best
• As substrate concentration increases

  The rate of enzyme-catalysed reactions increases
• Enzymes are catalysts produced by living things that speed up chemical reactions without being consumed
• Active site


  The part of the enzyme where the substrate binds and the reaction is catalysed
• Substrate specificity


  Enzymes usually only work with certain substrates whose shape fits the active site
• Lock and key mechanism

  The substrate fits into the active site of the enzyme like a key fits into a lock
• Enzyme specificity


  each enzyme has a specific substrate
• Enzyme catalysis

  1. Substrate has to fit into the active site

  2. If substrate's shape doesn't match active site, reaction won't be catalysed

  3. This is called the lock and key mechanism
• Factors affecting rate of enzyme-catalysed reactions

  • Temperature
  • pH
  • Substrate concentration
• Optimum temperature


  Temperature where enzyme works best
• Enzyme denaturation


  If temperature gets too high, bonds holding enzyme together break, changing the shape of the active site so substrate won't fit
• If pH is too high or too low, it interferes with the bonds holding the enzyme together, changing the shape of the active site and denaturing the enzyme
• All enzymes have an optimum pH they work best at, often neutral pH 7, but not always
• Substrate concentration

  The higher the substrate concentration, the faster the reaction
• There is a limit to how much substrate concentration can increase the rate of reaction, as enzymes can only cope with so many substrate molecules
• If the lock and key mechanism fails, the enzyme can try to get the substrate into the active site through other means