Paper 1 Biology

• Light microscope


  Developed in the mid 17th century, uses light to form an image, can view live specimens, relatively cheap and easy to use, can magnify up to 2,000 times, has a resolution of around 200 nanometers
• Electron microscope


  Developed in the 1930s, uses electrons to form an image, can only view dead specimens, very expensive and has many conditions, can magnify up to 2 million times, has a resolution of 0.2 nanometers
• The electron microscope is much better than the light microscope in terms of magnification and resolution
• Animal cell organelles


  • Nucleus (controls cell activities and contains DNA)
  • Cell membrane (controls passage of substances in and out)
  • Cytoplasm (liquid gel where chemical reactions occur)
  • Mitochondria (where aerobic respiration occurs)
  • Ribosomes (protein synthesis)
• Plant cell organelles


  • Nucleus
  • Ribosomes
  • Mitochondria
  • Cytoplasm
  • Cell membrane
  • Chloroplasts (contain chlorophyll for photosynthesis)
  • Permanent vacuole (filled with cell sap for support)
  • Cell wall (made of cellulose, provides strength and support)
• Animal and plant cells are both eukaryotic cells, while bacterial cells are prokaryotic
• Prokaryotic cells


  • Have a cell membrane, cytoplasm, and ribosomes
  • Genetic material is a single loop of DNA in the cytoplasm, may also have plasmids
  • May have a cell wall, slime layer, or flagella
  • Do not have a nucleus, chloroplasts, or mitochondria
• Cell differentiation


  Cells change by developing different subcellular structures as an organism develops, allowing them to carry out specialized functions
• Sperm cell


  Has a tail for movement, mid-piece with many mitochondria for energy, acrosome with enzymes to penetrate egg, large nucleus to contain DNA
• Muscle cell


  Has many mitochondria to release energy for contraction, special proteins that cause contraction, can store glycogen for respiration
• Nerve cell


  Has a long axon to carry electrical impulses, dendrites to connect to other nerve cells, nerve endings that release chemical messengers
• Root hair cell


  Has a large surface area projection for absorbing water and minerals, large permanent vacuole to speed up osmosis, many mitochondria for active transport
• Xylem cell


  Forms long hollow tubes with spiral lignin to allow easy movement of water and minerals, supports the plant
• Phloem cell


  Has sieve plates with holes to allow easy movement of dissolved food, companion cells with mitochondria to provide energy for transport
• Diffusion


  The spreading out of particles in a solution or gas from an area of higher concentration to an area of lower concentration
• Factors affecting rate of diffusion


  • Temperature (higher temperature increases rate)
  • Concentration gradient (steeper gradient increases rate)
  • Surface area (larger surface area increases rate)
• Osmosis


  The diffusion of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane
• Osmosis is important in animal cells to maintain the right internal solute concentration
• Left side of the membrane


  Has more water molecules
• Right side of the membrane


  Has less water molecules and more sucrose or solute molecules, therefore it is the concentrated side
• Osmosis


  1. Occurs down a concentration gradient or from a dilute solution to a more concentrated solution

  2. Net movement of water is from the left side to the right side

  3. Water concentration will eventually be equal on both sides

  4. Water molecules will continue to move back and forth across the partially permeable membrane but there is no further net movement of water, i.e. the water is balanced on both sides
• Importance of osmosis in animal cells

  • Ensures that the solutes like glucose and salts are at the right concentration inside the cell
  • The internal environment needs to be kept just right for the cell to work
  • The difference in concentration between the cell's internal environment and the external solution will determine how much osmosis occurs
• Effect of different solutions on a red blood cell

  1. Hypotonic solution: Water moves into the cell, causing it to stretch and potentially burst

  2. Isotonic solution: No net movement of water, i.e. no osmosis occurs

  3. Hypertonic solution: Water moves out of the cell, causing it to shrink and not function properly
• Required practical A: Investigating the effect of concentration of salt or sugar on the mass of plant tissue
• Active transport


  1. Moves substances from a more dilute solution to a more concentrated solution, i.e. against a concentration gradient

  2. Requires energy from respiration
• Mineral ions in the soil

  Dilute solution
• Mineral ions in the root hair cells

  Concentrated solution
• Active transport in the small intestines

  Moves dissolved food molecules, e.g. glucose, from a dilute solution in the intestines to a more concentrated solution in the blood vessels
• Mitosis and the cell cycle

  1. Stage 1: Cell growth, increase in subcellular structures, DNA replication

  2. Stage 2: Chromosomes pulled to opposite ends of the cell, nucleus divides

  3. Stage 3: Cytoplasm and cell membrane divide to form two identical cells
• Importance of mitosis


  • Development, growth, and repair
• Stem cell

  Undifferentiated cell capable of differentiating into various cell types and regenerating new stem cells
• Uses of animal stem cells

  • Embryonic stem cells: Can be cloned and differentiated into various cell types for treatment of conditions
  • Adult stem cells: More limited in their uses, but can differentiate into a small number of cell types
• Uses of plant stem cells


  • Cloning plants for commercial sale, saving rare plants from extinction, cloning genetically identical plants for research
• Issues surrounding stem cells
• Binary fission in bacteria

  1. Genetic material replicates

  2. Two copies move to opposite ends of the cell

  3. New cell walls form

  4. Cytoplasm divides, splitting the cell into two
• Calculating bacterial population growth

  Given the mean division time, calculate the number of divisions in a given time period, then use 2 to the power of the number of divisions to get the final population size
• Salla


  New cell
• Cell division


  Cell divides to give two new cells
• Number of divisions


  2 to the power of the number of divisions
• 2 to the power of 7 is 128