Biology Paper 1

• All life consists of cells
• Light microscope


  • Can see cells and nucleus, but not subcellular structures
  • Electron microscope has better resolving power and resolution, can see organelles
• Magnification


  Image size / Object size
• Cell types


  • Eukaryotic cells (have nucleus, e.g. plant and animal cells)
  • Prokaryotic cells (no nucleus, DNA in plasmid)
• Subcellular structures


  • Cell membrane
  • Cell wall (in plant cells and bacteria)
  • Cytoplasm
  • Mitochondria
  • Ribosomes
  • Chloroplasts (in plant cells)
  • Vacuole (in plant cells)
• Enzymes


  • Biological catalysts that break down larger molecules into smaller ones
  • Specific to certain substrates, work on a lock and key principle
• Enzyme activity increases with temperature


  Until active site changes shape and substrate no longer binds (enzyme denatured)
• Enzyme activity affected by pH

  Optimum pH, too high or too low can denature enzyme
• Practical to find enzyme optimum temperature/pH

  1. Mix enzyme and substrate, take samples over time, test for presence of substrate

  2. Plot time taken for substrate to be broken down vs temperature/pH

  3. Optimum is lowest point on graph
• Food tests


  • Iodine turns black with starch
  • Benedict's solution turns orange with sugars
  • Biuret reagent turns purple with proteins
  • Ethanol goes cloudy with lipids
• Diffusion

  Movement of molecules/particles from high to low concentration, down concentration gradient, passive
• Osmosis


  Diffusion of water across a semi-permeable membrane
• Factors affecting rate of diffusion/osmosis

  • Concentration gradient
  • Temperature
  • Surface area
• Practical to investigate osmosis


  1. Cut equal sized vegetable cylinders, weigh, place in sugar solutions, reweigh after time

  2. Plot % change in mass vs sugar concentration, point of no change is osmotic equilibrium
• Active transport


  Using energy to move substances against a concentration gradient
• Diploid cells


  Have 23 pairs of chromosomes
• Haploid cells


  Have 23 single chromosomes
• Mitosis


  1. Genetic material duplicated

  2. Nucleus breaks down

  3. Chromosomes pulled to opposite sides

  4. New nuclei form, resulting in two identical cells
• Cell specialisation


  • Cells specialise to perform specific functions
  • Stem cells are unspecialised
• Parts of the nervous system

  • Central nervous system (brain and spinal cord)
  • Peripheral nervous system (nerves)
• Reflex arc


  1. Stimulus detected by receptor

  2. Electrical signal to spinal cord

  3. Signal bypasses brain, goes straight to effector
• Reaction time


  Time taken to respond to a stimulus
• Main parts of the brain

  • Cerebral cortex (higher functions)
  • Cerebellum (motor skills, balance)
  • Medulla oblongata (unconscious functions)
• MRI scans


  Magnetic resonance imaging, can see brain activity safely
• Eye


  • Accommodation - lens changes shape to focus light
  • Pupil changes size to control light intensity
  • Cornea, lens, retina (rods and cones)
• Meiosis

  1. Chromosomes duplicated

  2. Homologous chromosomes pair up and swap genes

  3. Cell divides twice to form 4 haploid cells
• Advantages of sexual/asexual reproduction

  • Sexual - variation, better suited to environment
  • Asexual - only one parent needed, faster
• Genome


  All the genetic material in an organism
• Gene


  Section of DNA that codes for a specific protein
• Genotype

  Genetic code stored in DNA
• Phenotype


  How the genotype is expressed in an organism's characteristics
• Harmful mutations can change a gene so the resulting protein doesn't function properly
• Genotype


  The code stored in your DNA
• Phenotype


  How the genetic code is expressed in your characteristics and physiology
• Monomers between DNA strands

  • Nucleotides
  • Made from sugar and phosphate group
  • 4 types: A, T, C, G
• A and T always match, C and G always match in the DNA sequence
• Codon


  A sequence of 3 bases that codes for an amino acid
• Protein synthesis


  1. DNA copied to mRNA

  2. mRNA taken to ribosome

  3. Amino acids connected in order to make protein
• Harmful mutation


  Changes a gene so much that it results in a protein being synthesized that doesn't do its job
• Epigenetics


  DNA that doesn't directly code for proteins but influences how other genes are expressed