biology paper 1

• 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 several features that animal cells don't share, e.g. cell wall, vacuole, chloroplasts
• There isn't really a typical type of cell because there are a wide range of differentiated specialized cells
• Differentiation


  When various different genes will be turned on and turned off, and that's when cells will start to specialize
• Magnification


  Magnification = image height / object height
• Units of measurement


  • Meter (m)
  • Centimeter (cm) - 1 x 10^-2 m
  • Millimeter (mm) - 1 x 10^-3 m
  • Micrometer (μm) - 1 x 10^-6 m
  • Nanometer (nm) - 1 x 10^-9 m
  • Picometer (pm) - 1 x 10^-12 m
• Enzymes


  • Lock and key mechanism - enzyme has a specifically shaped active site that only certain substrates can fit into
  • Form enzyme-substrate complex
  • Break apart or join together substrates
  • Release products
  • Unchanged and can be used again
• Temperature affects enzyme activity


  Optimal temperature, below is not enough energy, above enzymes get denatured
• pH affects enzyme activity

  Optimal pH, too high or too low causes denaturation
• Enzyme activity increases with substrate concentration up to a point, then levels off as active sites become saturated
• Enzymes can catalyse reactions, making them happen faster but not changing the final equilibrium
• 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 lumps (tumours)
  • Benign tumours are slow-growing and generally harmless
  • Malignant tumours are fast-growing, aggressive and can spread to other parts of the body
• Cancer risk factors


  • Smoking
  • Diet
  • Sun exposure
  • Unprotected sex
• Stem cells


  • Have the potential to turn into any other type of cell
  • Can be used to grow new cells/tissues/organs to treat injuries and diseases
• Nervous system


  • Central nervous system (brain and spinal cord)
  • Neurons, receptors and effectors
  • Reflex actions - fast electrical signals
  • Voluntary actions - slower chemical signals across synapses
• Advantages of sexual reproduction

  • Genetically diverse population - better protection from diseases
  • Disadvantages of asexual reproduction
• Advantages of asexual reproduction

  • Only one parent required
  • Energy conserved as parent passes on all its genes
• 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 into two

  3. Cell divides again into four genetically distinct cells
• Mitosis


  Process where one parent cell divides into two identical daughter cells
• Mitosis


  1. DNA condenses into chromosomes

  2. Chromosomes line up down the middle

  3. Chromosomes pulled apart to opposite ends

  4. New nuclei form

  5. Two identical daughter cells
• Meiosis


  Process where one parent cell divides into four genetically different daughter cells
• Meiosis

  1. Chromosomes line up and undergo crossing over

  2. Divide into two cells

  3. Divide into four cells

  4. Each cell has half the original number of chromosomes
• Mitosis


  Leads to diploid daughter cells
• Meiosis


  Leads to haploid daughter cells
• Gametes


  Sex cells (sperm and eggs)
• DNA


  Long strand of deoxyribonucleic acid made up of A, T, C, G bases
• DNA


  • Has a sugar-phosphate backbone
  • Forms a double helix structure
• Gene

  Stretch of DNA that codes for a characteristic
• Genome


  All the genes in a body
• Chromosome


  Bundled up DNA located in the nucleus
• Alleles


  Different versions of a gene
• Dominant


  Only need one copy of the gene to express the characteristic
• Recessive


  Need two identical copies of the gene to express the characteristic
• Homozygous


  Genes are the same