biology paper one

• 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)
  • Vacuole (in plant cells)
• Enzymes


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


  • Specific - only break down certain molecules
  • Work on a lock and key principle with substrates
• Enzyme activity rate


  Increases with temperature (until active site is denatured)
• Enzyme activity rate


  Affected by pH (optimum pH)
• Practical to find enzyme optimum temperature/pH

  1. Mix enzyme and substrate

  2. Take samples at intervals

  3. Test for presence of substrate using indicator

  4. Plot time taken for substrate to be broken down against temperature/pH
• Food tests can identify nutrients: iodine for starch, Benedict's solution for sugars, Biuret's reagent for proteins, ethanol for 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 diffusion/osmosis rate

  Concentration gradient, temperature, surface area
• Practical to investigate osmosis

  1. Cut equal-sized vegetable cylinders

  2. Weigh and place in sugar solutions

  3. Reweigh after time, calculate % change in mass

  4. Plot against sugar concentration to find no-change point
• Active transport


  Using energy to move substances against a concentration gradient
• Cell division


  • Mitosis (for growth and repair)
  • Meiosis (for sexual reproduction)
• Mitosis


  • Genetic material duplicated, cell divides into two identical cells
• Meiosis


  • Genetic material halved, four genetically different cells produced
• 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. Motor neuron carries signal to effector
• Parts of the brain

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


  Magnetic resonance imaging, used to safely view brain activity
• Eye


  • Cornea, pupil, lens, retina (rods and cones)
• Accommodation


  Changing lens shape to focus light from different distances
• Glasses/contacts/laser surgery can correct vision issues
• Meiosis


  1. Chromosomes duplicate

  2. Homologous chromosomes pair up and swap genes

  3. Cell divides twice to produce 4 haploid cells
• Asexual reproduction


  Producing genetically identical offspring by mitosis
• Sexual reproduction


  Producing genetically varied offspring by meiosis and fusion of gametes
• 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