b2

• Cell Cycle


  The time when the cell grows and replicates (copies) its contents
• Cell Cycle


  1. Growth

  2. DNA replication

  3. Cell division
• Gap Phases


  G1, G2, G0
• Synthesis Phase


  Cell replicates DNA
• Mitosis


  When a cell reproduces itself by splitting to form two identical offspring
• Chromosomes


  • Formed from long lengths of coiled DNA
  • Each 'arm' of a chromosome is an exact copy of the other
  • Line up at the centre of the cell
  • Cell fibres pull them apart
  • Two sets go to opposite ends of the cell
• Cell Division


  1. Membranes form around each set of chromosomes

  2. Cytoplasm divides
• Cell Differentiation


  Most cells are specialised to carry out a particular job
• Specialised Cells


  • Sperm cell
  • White blood cell
• Tissues


  Groups of cells working together to perform a particular function
• Organs


  Different tissues working together
• Organ Systems


  Different organs working together
• Stem Cells


  Undifferentiated cells that can divide by mitosis to become new cells, which then differentiate
• Embryonic Stem Cells


  • Found in early human embryos
  • Can turn into any kind of cell
• Adult Stem Cells


  • Found in certain places like bone marrow
  • Can only produce certain types of specialised cells
• Meristems


  Plant tissues containing stem cells that can divide and form any cell type in the plant
• Diffusion


  The net overall movement of particles from an area of higher concentration to an area of lower concentration
• Active Transport


  The movement of particles across a membrane from an area of lower concentration to an area of higher concentration, using energy
• Diffusion


  Particles move through the cell membrane from where there's a higher concentration to where there's a lower concentration
• Active Transport


  Moves particles against a concentration gradient, requiring energy
• Only very small molecules can diffuse through cell membranes (e.g. glucose, amino acids, water and oxygen)
• Big molecules like starch and proteins can't fit through the cell membrane
• Osmosis


  The movement of water molecules across a partially permeable membrane from an area of higher water concentration to an area of lower water concentration
• Partially permeable membrane


  • Has very small holes in it
  • Allows small molecules to pass through, but not larger molecules
• Osmosis


  1. Water molecules pass both ways through a membrane

  2. But the overall movement of water molecules is from where there are lots of them to where there are fewest of them
• Concentrated solution


  Has lots of solute molecules compared to water molecules
• Dilute solution


  Has lots of water molecules compared to solute molecules
• Water potential


  • How likely it is that water molecules will diffuse out of or into a solution
  • Higher water potential means higher concentration of water molecules
  • Lower water potential means lower concentration of water molecules
• Osmosis


  Diffusion of water molecules across a partially permeable membrane down a water potential gradient (from higher to lower water potential)
• Pure water has the highest water potential, all solutions have a lower water potential than pure water
• Organisms need to take in substances from the environment and get rid of waste
• Substances are exchanged by diffusion, osmosis and active transport
• The rate at which substances are exchanged is affected by surface area to volume ratio
• Calculating an organism's surface area to volume ratio

  1. Length x Width = surface area of a square/rectangle

  2. Length x Width x Height = volume of a block

  3. Divide surface area by volume to get the ratio
• Surface area to volume ratio

  • The larger the organism, the smaller its surface area compared to its volume
  • The smaller the surface area compared to volume, the harder it is for an organism to exchange substances with its environment
• Multicellular organisms need specialised exchange surfaces because substances have to travel further to reach all the cells
• The alveoli in the lungs are an example of a specialised exchange surface
• Alveoli


  • Have a large surface area
  • Substances only have to travel short distances
  • Good blood supply to allow rapid exchange of oxygen and carbon dioxide
• Double circulatory system


  • Two circuits joined together
  • One circuit pumps deoxygenated blood to the lungs, the other pumps oxygenated blood around the body
• How the heart pumps blood

  1. Right atrium receives deoxygenated blood from the body

  2. Right ventricle pumps it to the lungs

  3. Left atrium receives oxygenated blood from the lungs

  4. Left ventricle pumps it around the body