Biology

• Subcellular structures of eukaryotic and prokaryotic cells and their functions


  • Animal cells - nucleus, cell membrane, mitochondria, ribosomes
  • Plant cells - nucleus, cell membrane, cell wall, chloroplasts, mitochondria, vacuole, ribosomes
  • Bacteria - chromosomal DNA, plasmid DNA, cell membrane, ribosomes, flagella
• Adaptations of specialised cells

  • Sperm cells - acrosome, haploid nucleus, mitochondria, tail
  • Egg cells - nutrients in cytoplasm, haploid nucleus, changes in cell membrane after fertilisation
  • Ciliated epithelial cells - long hair-like cilia
• Acrosome of sperm cell


  • Contains digestive enzymes which help to break down cell membrane of egg cell
• Haploid nucleus of sperm and egg cells

  • When zygote is formed it will have a full diploid nucleus
• Mitochondria in sperm cell mid piece


  • Release lots of energy via aerobic respiration for swimming
• Tail of sperm cell

  • Allows sperm cell to swim to reach egg cell
• Nutrients in egg cell cytoplasm

  • Allow the zygote to grow
• Changes in egg cell membrane after fertilisation


  • Becomes impermeable so that only 1 sperm cell can fertilise an egg cell
• Cilia of ciliated epithelial cells

  • Waft bacteria trapped by sticky mucus down to the stomach, where they are killed by stomach acid
• Development of microscope technology

  1. Robert Hooke observed cells in cork in 1665 using light microscope

  2. Electron microscopes developed in 1930s, enabling viewing of sub-cellular structures

  3. Scanning electron microscopes create 3D images, transmission electron microscopes create 2D images of organelles

  4. Electron microscopes have much higher magnification and resolving power than light microscopes

  
• Magnification


  Eyepiece lens magnification x objective lens magnification
• Size of an object

  Size of image / magnification = size of object
• Quantitative units in relation to cells

  • milli (10^-3)
  • micro (10^-6)
  • nano (10^-9)
  • pico (10^-12)
• Observing plant and animal cells under a microscope

  1. Place specimen on stage

  2. Switch on microscope light

  3. Start with x4 objective lens

  4. Bring specimen into focus using coarse focus

  5. Move to x10 and x40 objective lenses, focusing with fine focus

  
• Enzyme


  Protein that acts as a biological catalyst
• Enzymes


  • Can break up large molecules and join together small ones
  • Shape of enzyme is vital to its function
  • Each enzyme has a uniquely shaped active site where substrate binds
• Enzyme-substrate complex


  Form when shape of substrate is complementary to shape of enzyme active site
• Enzyme denaturation due to changes in active site shape

  Caused by high temperature breaking bonds holding enzyme together, or extreme pH affecting forces holding amino acid chains
• Effect of temperature on enzyme activity

  Rate increases with temperature up to optimum, then rapidly decreases as enzyme denatures
• Effect of substrate concentration on enzyme activity

  Rate increases with concentration up to saturation point, then no further increase
• Effect of pH on enzyme activity

  Optimum pH is around 7, deviations cause denaturation
• Investigating effect of pH on enzyme activity

  1. Use amylase enzyme, starch solution, iodine solution, buffer solutions of different pH

  2. Measure time taken for starch to be broken down at each pH

  3. Plot graph of pH vs time to find optimum pH
• Rate of enzyme activity

  Calculated as change in substance / time
• Enzymes and their roles

  • Carbohydrases convert carbohydrates to sugars
  • Proteases convert proteins to amino acids
  • Lipases convert lipids to fatty acids and glycerol
• Identifying food components using chemical tests

  1. Starch - iodine solution turns blue-black

  2. Reducing sugars - Benedict's solution turns reddish brown

  3. Proteins - Biuret test turns blue to violet

  4. Lipids - emulsion test forms white layer
• Calorimetry


  Measuring energy content of food by burning sample and measuring temperature increase of water
• Mechanisms of transport into and out of cells

  • Diffusion - passive movement from high to low concentration
  • Osmosis - passive movement of water from dilute to concentrated solution
  • Active transport - requires energy to move substances against concentration gradient
• Investigating osmosis in potatoes

  1. Cut potato discs, measure initial mass

  2. Place in sucrose solutions of different concentrations

  3. Measure mass change and calculate percentage gain/loss
• Stages of mitosis


  1. Interphase - cell grows, organelles increase, DNA replicates

  2. Prophase - nuclear membrane breaks down

  3. Metaphase - chromosomes line up on spindle fibres

  4. Anaphase - chromosomes pulled to opposite ends

  5. Telophase - nuclear membrane reforms

  6. Cytokinesis - cytoplasm and cell membrane divide to form two daughter cells

  
• Importance of mitosis


  • Enables growth, repair, and asexual reproduction
  • Produces two genetically identical diploid daughter cells
• Cancer is the result of uncontrolled cell division
• Animal growth


  • Occurs by cell division and differentiation
• Mitosis


  The production of two daughter cells, each with identical sets of chromosomes to the parent cell
• Mitosis is a vital part of asexual reproduction, as this type of reproduction only involves one organism, so to produce offspring it simply replicates its own cells
• Mitosis produces 2 daughter cells, each with identical sets of chromosomes to the parent cell
• Because the sets of chromosomes in the daughter cell's nucleus are the same as in the parent cell's nucleus, mitosis produces 2 genetically identical diploid daughter cells
• Division of a cell by mitosis

  1. Production of two daughter cells

  2. Identical sets of chromosomes in the nucleus to the parent cell

  3. Formation of two genetically identical diploid body cells
• Cancer


  The result of changes in cells that lead to uncontrolled cell division
• Growth in animals


  1. Cell division

  2. Cell differentiation
• In animals, growth occurs via cell division and differentiation