paper 1 biology

• Microscopy


  The study of small objects using a microscope
• Light microscope


  • First developed in the mid 17th century
  • Uses light to form an image
  • Can be used to view live specimens
  • Relatively cheap and easy to use
  • Can magnify up to 2,000 times
• Resolution


  The ability to see two things as separate objects
• Light microscope has a resolving power of around 200 nanometers
• Electron microscope


  • Developed by scientists in the 1930s
  • Uses electrons to form an image
  • Specimens must be dead first
  • 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
• Organelles in animal cells

  • Nucleus
  • Cell membrane
  • Cytoplasm
  • Mitochondria
  • Ribosomes
• Organelles in plant cells

  • Nucleus
  • Cell membrane
  • Cytoplasm
  • Mitochondria
  • Ribosomes
  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Eukaryotic cells


  Cells that have a nucleus and membrane-bound organelles
• Prokaryotic cells


  Cells that lack a nucleus and membrane-bound organelles, such as bacteria
• Organelles in prokaryotic cells

  • Cell membrane
  • Cytoplasm
  • Ribosomes
  • Cell wall
  • Single loop of DNA
  • Plasmids
  • Slime layer
  • Flagella
• Prokaryotic cells lack chloroplasts and mitochondria
• Specialized animal cells


  • Sperm cell
  • Muscle cell
  • Nerve cell
• Sperm cell


  Has a tail to swim, mitochondria in the mid-piece to provide energy, an acrosome to break down the egg, and a large nucleus to contain DNA
• Muscle cell


  Has many mitochondria to release energy for contraction, and special proteins that cause contraction by sliding across each other
• Nerve cell


  Has a long axon to carry electrical impulses, dendrites to connect to other nerve cells, and nerve endings that release chemical messengers
• Specialized plant cells


  • Root hair cell
  • Xylem cell
  • Phloem cell
• Root hair cell


  Has a large surface area for absorption, a large permanent vacuole to speed up osmosis, and many mitochondria for active transport of mineral ions
• Xylem cell


  Forms long hollow tubes with spirals of lignin to allow easy movement of water and mineral ions up the plant
• Phloem cell

  Has sieve plates to allow easy movement of dissolved food up and down the plant, and companion cells with many mitochondria to provide the energy for this
• Diffusion

  The spreading out of particles in a solution or gas from an area of higher concentration to an area of lower concentration
• Diffusion is a passive process that does not require additional energy
• 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 a passive process that occurs down a concentration gradient
• Osmosis is important in animal cells to maintain the right internal environment
• 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's no further net movement of water, the water is balanced on both sides
• Importance of osmosis in animal cells

  • Ensures 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 determines how much osmosis occurs
• What happens when a red blood cell is put into a hypotonic solution

  Water moves into the cell, stretching it, and the cell may even burst if a lot of water moves in, killing the cell
• What happens when a red blood cell is put into an isotonic solution


  Nothing happens, as the two solutions are the same, there is no net movement of water (no osmosis)
• What happens when a red blood cell is put into a hypertonic solution

  Water moves out of the red blood cell and into the beaker, as the red blood cell solution is more dilute, the cell will shrink and not function properly
• Required practical A is on the effect of concentration of salt or sugar on the mass of plant tissue
• Active transport


  Substances move from a low concentration to a high concentration, against the concentration gradient, requiring energy from respiration
• Active transport


  • Moves substances against the concentration gradient
  • Requires energy from respiration
• Nucleus


  Contains chromosomes made up of DNA, which codes for genes
• Cell cycle


  1. Stage 1: Cell grows and DNA replicates

  2. Stage 2: Mitosis - one set of chromosomes is pulled to each end of the cell, nucleus divides

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


  • Allows for development from a single cell to a multicellular organism
  • Allows for growth during childhood and puberty
  • Allows for repair of damaged tissues
• Stem cell


  An undifferentiated cell that can differentiate into many different cell types and can regenerate new stem cells