biology paper 1

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


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


  Provides rigid structure (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 (plant cells)
• Vacuole


  Permanent structure that stores sap (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 denaturation
• Enzyme activity practical


  1. Mix enzyme with substrate

  2. Measure time for reaction to complete at different temperatures or pH

  3. Plot graph to find optimum temperature or pH
• Food tests


  • Iodine test for starch
  • Benedict's solution for sugars
  • Biuret reagent for proteins
  • Ethanol for lipids
• Diffusion


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


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


  1. Cut equal cylinders from potato

  2. Weigh and place in sugar solutions

  3. Reweigh after a day

  4. Calculate percentage change in mass

  5. Plot graph to find concentration with no change
• Active transport


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


  • Mitosis
  • Meiosis
• Mitosis


  • Produces two genetically identical daughter cells
• Meiosis


  • Produces four genetically different haploid cells (gametes)
• 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)
• Reflex arc


  1. Receptor detects stimulus

  2. Sensory neuron carries signal to spinal cord

  3. Relay neuron carries signal to effector
• Reaction time


  Time taken to respond to a stimulus, can be measured by dropping a ruler
• 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
• DNA structure


  • Double helix
  • Nucleotides with A-T and C-G base pairing
• Mutation


  Change in a gene that can result in a non-functional protein
• A and T always match, C and G always match in the DNA sequence
• Harmful mutation


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


  Different types of the same gene
• Dominant allele


  Results in a characteristic being expressed even if another allele is present
• Recessive allele


  Only expressed when there is no dominant allele present