Biology Paper 1 Revision

• 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)
• 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)
• Vacuole


  Permanent structure in plant cells that stores sap
• Enzymes


  Biological catalysts that break down larger molecules into smaller ones
• Types of enzymes


  • Carbohydrases (break down carbohydrates)
  • Proteases (break down proteins)
  • Lipases (break down lipids)
• Enzyme specificity


  Enzymes only work on specific substrates, like a lock and key
• As temperature increases


  The rate of enzyme activity increases
• At optimum temperature


  Enzyme activity is maximised
• At too high or too low pH


  Enzyme can denature
• Practical on enzyme activity

  1. Mix enzyme and 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
• Food tests


  Iodine turns black in presence of starch

  Benedict's solution turns orange in presence of sugars

  Biuret's reagent turns purple in presence of proteins

  Ethanol goes cloudy in presence of lipids
• Diffusion


  Movement of molecules from high to low concentration, down a concentration gradient, without energy input
• Osmosis


  Diffusion of water across a semi-permeable membrane
• Factors affecting rate of diffusion and osmosis

  • Concentration gradient
  • Temperature
  • Surface area
• Practical on osmosis


  Cut equal-sized cylinders from potato

  Weigh and place in sugar solutions

  Reweigh after a day

  Calculate percentage change in mass

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


  Movement of substances against a concentration gradient, using energy
• Eukaryotic cell nucleus


  • Contains DNA in chromosomes

  Humans have 23 pairs of chromosomes (diploid)

  Gametes have 23 chromosomes (haploid)
• Cell division by mitosis


  Genetic material duplicated

  Nucleus breaks down

  Chromosomes pulled to opposite sides

  New nuclei form, creating two identical cells
• Cell specialisation


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


  Unspecialised cells that can develop into different cell types
• Types of stem cells

  • Embryonic stem cells

  Adult stem cells (e.g. in bone marrow)
• Cloning can be used to produce crops with specific characteristics or prevent species extinction
• Parts of the nervous system

  • Central nervous system (brain and spinal cord)

  Peripheral nervous system (nerves)
• Nerve impulse transmission


  Receptor detects stimulus

  Electrical signal travels to spine via sensory neuron

  Signal crosses synapse using neurotransmitter

  Signal travels to brain via relay neuron

  Brain processes signal and sends response via motor neuron

  Effector (e.g. muscle) responds
• Reflex arc


  Electrical signal bypasses brain and goes straight from spine to effector
• Glands


  Produce specific chemicals the body needs
• Investigating reaction time


  Drop ruler and measure distance fallen before caught

  Repeat multiple times and take average

  Introduce independent variable (e.g. stimulant, depressant)
• Parts of the brain

  • Cerebral cortex (higher functions)

  Cerebellum (motor skills, balance)

  Medulla oblongata (unconscious functions)