GCSE Biology paper 1 revision

• Microscopy


  The study of small objects using a microscope
• Types of microscopes


  • Light microscope
  • Electron 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
  • Magnification up to 2,000 times
  • Resolution around 200 nanometers
• Electron microscope


  • Developed by scientists in the 1930s
  • Uses electrons to form an image
  • Specimens must be dead
  • Very expensive and has many conditions
  • Magnification up to 2 million times
  • Resolution of 0.2 nanometers
• The electron microscope is much better than the light microscope in terms of magnification and resolution
• Animal cell


  Contains a nucleus, cell membrane, cytoplasm, mitochondria, ribosomes
• Plant cell


  Contains a nucleus, cell membrane, cytoplasm, mitochondria, ribosomes, chloroplasts, permanent vacuole, cell wall
• Eukaryotic cells


  Have a nucleus and membrane-bound organelles
• Prokaryotic cells


  Lack a nucleus and membrane-bound organelles, have a single loop of DNA
• Specialized animal cells


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


  Has a tail for movement, an acrosome with enzymes to penetrate egg, a large nucleus for DNA
• Muscle cell


  Has many mitochondria for energy, special proteins for contraction, can store glycogen
• Nerve cell


  Has a long axon to carry electrical impulses, dendrites to connect to other cells, nerve endings to 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 vacuole for osmosis, many mitochondria for active transport
• Xylem cell


  Forms long hollow tubes with lignin spirals to transport water and minerals up the plant
• Phloem cell


  Has sieve plates to allow flow of dissolved food, companion cells with mitochondria to provide energy
• Diffusion


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

  • Temperature
  • Concentration gradient
  • Surface area
• 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 concentrations
• 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

  2. From a dilute solution to a more concentrated solution

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

  4. Water concentration will eventually be equal on both sides

  5. Water molecules will continue to move back and forth across the partially permeable membrane but there is no further net movement of water
• 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

  1. Water moves into the cell, stretching it

  2. If a lot of water moves in, the cell may burst, killing it
• What happens when a red blood cell is put into an isotonic solution

  No net movement of water, no osmosis occurs
• What happens when a red blood cell is put into a hypertonic solution

  1. Water moves out of the cell and into the beaker

  2. The cell will shrink and not function properly
• Required practical A by osmosis looks at the effect of concentration of salt or sugar on the mass of plant tissue
• Active transport


  • Moves substances from a more dilute solution to a more concentrated solution, against the concentration gradient
  • Requires energy from respiration
• Active transport


  • Moves substances against the concentration gradient
  • Requires energy from respiration
• Examples of active transport

  • Mineral ions moving from soil into plant root hair cells
  • Glucose moving from small intestine into bloodstream
• Nucleus


  Contains chromosomes made up of DNA
• Cell cycle


  1. Stage 1: Cell growth, DNA replication

  2. Stage 2: Mitosis - chromosomes move to opposite ends, nucleus divides

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


  • Development from single cell to multicellular organism
  • Growth during childhood and puberty
  • Repair of damaged tissues
• Stem cell

  • Undifferentiated cell that can differentiate into many cell types
  • Can regenerate new stem cells
• Embryonic stem cells

  • Found in early embryo
  • Can differentiate into almost any cell type
  • Can be cloned
• Adult stem cells


  • Found in some adult tissues like bone marrow
  • More limited in the cell types they can differentiate into
• Plant stem cells


  • Found in meristem tissue of shoots and roots
  • Can differentiate into all plant cell types even in adulthood
  • Used for cloning plants
• Issues with stem cells include risk of viruses, rejection, and ethical concerns