BIOLOGY PAPER 1

• All life consists of cells
• Light microscope


  • Can see cells and nucleus, but not subcellular structures
• Electron microscope


  • Can see finer details and subcellular structures, has better resolving power and higher resolution
• Calculating cell size


  1. Measure image size

  2. Divide by magnification
• Cell types


  • Eukaryotic cells
  • Prokaryotic cells
• Eukaryotic cells


  • Have a nucleus where DNA is found
• Prokaryotic cells


  • Don't have a nucleus, DNA is in a ring called a plasmid
• Cell structures


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


  Keeps everything inside the cell, semi-permeable
• Cell wall


  Provides rigid structure (in plant cells and bacteria)
• Cytoplasm


  Liquid that makes up the cell, where most chemical reactions take place
• Mitochondria


  Where respiration takes place, releasing energy for the cell
• Ribosomes


  Where proteins are assembled or synthesized
• Chloroplasts


  Contain chlorophyll, where photosynthesis takes place (in plant cells)
• Permanent vacuole


  Stores sap (in plant cells)
• Enzymes


  Biological catalysts that break down larger molecules into smaller ones
• Enzymes


  • Specific, work on a lock and key principle
  • Rate of activity increases with temperature until active site changes shape and enzyme denatures
• Enzyme activity practical


  1. Mix enzyme with substrate

  2. Take samples at intervals

  3. Test for presence of substrate using iodine

  4. Plot time taken for substrate to be broken down against temperature or pH

  5. Optimum temperature or pH is between the two lowest points
• Food tests


  • Iodine turns black in presence of starch
  • Benedict's solution turns orange in presence of sugars
  • Biuret reagent turns purple in presence of proteins
  • Cold ethanol goes cloudy in presence of lipids
• Diffusion


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


  Diffusion of water across a semi-permeable membrane
• Osmosis practical


  1. Cut equal-sized cylinders from potato

  2. Weigh and place in sugar solutions of varying concentrations

  3. Reweigh after a day

  4. Calculate percentage change in mass

  5. Plot against sugar concentration, where line crosses x-axis is the concentration with no change in mass (same as inside the potato)
• Active transport


  Movement of substances through a membrane against a concentration gradient, using energy
• Cell division


  • Mitosis
  • Meiosis
• Mitosis


  • Genetic material is duplicated, number of organelles is doubled, one set of chromosomes goes to each new cell
• Cell specialisation


  Cells take on specific functions depending on their role
• Stem cells


  Unspecialised cells that can develop into different cell types
• Parts of the nervous system


  • Central nervous system (brain and spinal cord)
  • Peripheral nervous system (nerves)
• Nerve impulse transmission


  1. Receptor detects stimulus

  2. Electrical signal travels to spine through sensory and relay neurons

  3. Signal crosses synapse using neurotransmitter

  4. Signal goes to brain for conscious decision

  5. Signal travels back to effector (e.g. muscle) through relay and motor neurons
• Reflex arc


  Electrical signal bypasses the brain and goes straight from spine to effector
• MRI scans


  Safely show brain activity
• Sexual reproduction


  1. Meiosis to produce gametes

  2. Fusion of gametes
• Asexual reproduction


  Mitosis to produce genetically identical offspring
• 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 genetic code is expressed in an organism's characteristics
• Harmful mutations can change a gene so much that it results in a protein being synthesized that doesn't do the job it's supposed to
• Phenotype


  How the genetic code is expressed in your characteristics and physiology
• A and T always match, C and G always match in the DNA sequence