Biology p1

• 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 (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


  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 taken for all substrate to be broken down

  3. Plot time against temperature or pH

  4. Optimum is lowest point on curve
• Food tests


  • Iodine (starch)
  • Benedict's solution (sugars)
  • Biuret reagent (proteins)
  • Ethanol (lipids)
• Diffusion


  Movement of molecules/particles from high to low concentration, passive
• 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 against sugar concentration, x-axis crossing is no change
• 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, number of organelles doubled, chromosomes pulled to opposite sides, new nuclei form
• Cell specialisation


  Cells take on specific functions e.g. nerve, muscle, root hair
• Stem cells


  Unspecialised cells that can develop into different cell types
• 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 neuron

  3. Signal crosses synapse using neurotransmitter

  4. Signal goes to brain

  5. Brain sends signal back through motor neuron to effector
• Reflex arc


  Signal bypasses brain and goes straight from spine to effector
• Brain regions


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


  Safely show brain activity
• Eye accommodation


  Ciliary muscles relax/contract, suspensory ligaments tighten/slacken, lens becomes thinner/thicker
• Pupil


  Changes size depending on light intensity
• Meiosis


  Chromosomes duplicate, pair up and swap genes, cell divides twice to form 4 haploid cells
• Asexual reproduction


  Daughter cells are genetically identical clones of parent
• 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