biology paper 1 lielle

• Plant cell


  • Cell membrane - responsible for determining which bits go to in or out of the cell
  • Cell wall - important for structure
  • Vacuole - important for structure
  • Cytoplasm - where most reactions take place
  • Ribosomes - responsible for protein synthesis
  • Chloroplasts
  • Mitochondria - where energy is produced
  • Nucleus
• Animal cell


  • Cell membrane - controlling what goes in and out
  • Mitochondria - where energy is produced
  • Ribosomes - protein synthesis
  • Cytoplasm - where most reactions take place
  • Nucleus - where DNA is held and control center of the cell
• Plant cells have features that animal cells don't share, like cell wall, vacuole, chloroplasts
• There isn't really a typical type of cell because there are a wide range of differentiated specialized cells
• Leaf cross-section


  • Different types of specialized cells
• Neuron


  • Very different to muscle cell, skin cell, gut cells
• All cells start off looking the same and then various different genes will be turned on and turned off, causing differentiation and specialization
• Microscope techniques


  From very basic lenses to sophisticated computer-controlled electron microscopes
• Magnification calculation


  Magnification = image height / object height
• Metric prefixes


  Meter (m), centimeter (cm), millimeter (mm), micrometer (μm), nanometer (nm), picometer (pm)
• Enzymes


  • Lock and key mechanism with specific active sites
  • Affected by temperature and pH
  • Limited by number of active sites
  • Can act as catalysts to increase reaction rates
• Digestive enzymes


  • Lipase - breaks down fats
  • Protease - breaks down proteins
  • Amylase - breaks down starch
• Diffusion


  Movement of particles from high to low concentration
• Osmosis


  Movement of water through a partially permeable membrane from high to low water concentration
• Active transport


  Movement of substances from low to high concentration, against the concentration gradient
• Cancer


  • Uncontrolled cell division leading to malignant tumors that can spread throughout the body
  • Risk factors include smoking, diet, sun exposure, unprotected sex
• Stem cells


  • Cells with the potential to develop into any cell type
  • Can be used to grow new cells/tissues/organs to treat injuries and diseases
  • Controversial due to use of human embryos
• Nervous system


  • Central nervous system (brain and spinal cord)
  • Receptors and effectors
  • Electrical signals in neurons
  • Slow chemical signals at synapses
  • Reflex actions vs conscious responses
• Advantages of sexual reproduction

  • Genetically diverse population
  • Better protection from diseases
• Disadvantages of asexual reproduction

  • Genetically identical population
  • Susceptible to diseases
  • Requires finding a mate
• Advantages of asexual reproduction


  • Only one parent required
  • Energy conserved by not needing to find a mate
• Mitosis


  1. DNA condenses into chromosomes

  2. Chromosomes line up in the middle

  3. Chromosomes pulled apart to opposite ends

  4. New nuclei form

  5. Cell divides into two identical daughter cells
• Meiosis


  1. Chromosomes line up and undergo crossing over

  2. Cell divides twice to produce four genetically distinct daughter cells
• Selfish gene


  The parent is putting all of its energy into conserving its own genes
• Mitosis


  1. DNA condenses into chromosomes

  2. Chromosomes line up down the middle

  3. Chromosomes pulled apart to either end of the cell

  4. New nuclei form

  5. Two identical daughter cells
• Meiosis


  1. Chromosomes line up

  2. Crossing over occurs

  3. Divide into two

  4. Line up and divide into two again

  5. Four different daughter cells
• Mitosis


  Leads to two identical daughter cells
• Meiosis


  Leads to four different daughter cells
• Gametes


  Eggs in women, sperm in men
• Plant gametes


  Eggs in the stigma, pollen on the stamen
• Extracting DNA


  1. Mash up

  2. Add salt water

  3. Add detergents

  4. Leave for 15 minutes at 60 degrees C

  5. Filter

  6. Add iced ethanol
• DNA structure


  • Made of A, T, C, G bases
  • Sugar phosphate backbone
  • Double helix
• Gene


  Stretch of DNA that codes for a characteristic
• Genome


  All the genes in a body
• Gamete


  Sex cell (sperm or egg)
• Chromosome


  Bundled up DNA
• Alleles


  Different versions of genes
• Dominant


  Need one gene to express characteristic
• Recessive


  Need two identical recessive genes to express characteristic
• Homozygous


  Genes are the same