Biology Paper 1

• All life consists of cells
• Light microscope


  Can see cells and maybe the 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
  • Examples: plant and animal cells
• Prokaryotic cells


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


  • 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 in plant cells, stores sap
• 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 experiment


  1. Mix enzyme with substrate

  2. Measure time for reaction to complete

  3. Plot against temperature or pH
• Diffusion


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


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


  1. Cut equal-sized 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
• Active transport


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


  Process of cell division to produce two genetically identical daughter cells
• Cell types


  • Specialised cells
  • Stem cells
• 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. Signal bypasses brain and goes straight to effector
• Parts of the brain

  • Cerebral cortex
  • Cerebellum
  • Medulla oblongata
• MRI scans


  Magnetic resonance imaging, used to safely see brain activity
• Accommodation


  Eye's ability to change lens shape to focus light from different distances
• Pupil


  Hole in the iris that changes size depending on light intensity
• Retina


  Back of the eye, contains rods and cones that detect light
• Meiosis


  Cell division to produce gametes with half the normal number of chromosomes
• Reproduction methods


  • Sexual
  • Asexual
• 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
• Genotype


  The code stored in your DNA