b2

• diffusion


  net movement of particles from a high concentration to a low concentration
• factors of diffusion


  - down a concentration gradient

  - passive (no energy required)
• increase rate of diffusion

  - making distance shorter

  - increase concentration gradient

  - increase surface area
• osmosis


  diffusion of water only
• factors of osmosis


  - high water potential to a low water potential

  - across a partially permeable membrane

  - passive (requires no energy)
• water potential


  concentration of water
• active transport


  movement of particles from a low to high concentration
• factors of active transport

  - against a concentration gradient

  - requires energy (ATP)

  - uses a carrier protein
• DNA replication (cell cycle 1)

  - DNA copied

  - each new cell has full set of chromosomes

  - DNA unzips (expose bases)

  - nucleotides line up with base

  - 2 identical molecule of DNA exposed
• mitosis (cell cycle 2)


  - cells divide by mitosis, used for; growth, repair and asexual reproduction

  - 2 genetically identical cells produced
• process of mitosis


  1. chromosomes line along centre of cell

  2. 2 identical copies of each chromosome separate and move to opposite ends of cell

  3. two new nuclei with full number of chromosomes
• cytokinesis


  split cytoplasm
• cell differentiation


  - cells differentiate, giving different features, making them specialised for particular job and makes organisms more efficient
• cell differentiation in plant cells

  palisade cell - lots of chloroplast for photosynthesis

  root hair cell - larger SA to absorb more water and minerals
• cell differentiation in animal cells

  sperm - tail to swim to ova

  red blood cell - no nucleus to carry more oxygen and biconcave to increase SA

  fat cell - less cytoplasm to store fat

  ciliated cell - more mucus containing bacteria
• stem cells


  - unspecialised cells

  - can differentiate into specialised cells

  - can be used to treat disease

  meristems - unspecialised cells in plants
• embryonic stem cell


  - found in embryos

  - can differentiate into all cell types

  - ethical issues as embryo is destroyed to get cells

  - tissues can be rejected
• adult stem cell


  - found in eg. bone marrow

  - differentiate into some cell types

  - no ethical issues

  - no rejections
• SA:V


  - larger organisms have a smaller SA:V, compared to smaller organisms which have larger SA:V

  - larger SA:V has a shorter diffusion distance so it is faster

  - lungs have alveoli and small intestine have villi to increase SA:V
• circulatory system


  - made up of heart and blood vessels

  - transports substances around body
• double circulatory system


  - blood flows through the heart twice

  - increases pressure which means transport is faster (needed for larger organisms)
• artery (blood vessel)


  carries blood away from the heart at high pressure. has thick cells to withstand pressure of blood
• vein (blood vessel)


  carries blood back to the heart at low pressure. has valves to stop back flow of blood
• capillary (blood vessel)


  forms a network through cells. has very thin partially permeable walls so substances can diffuse through easily
• the heart


  - made of cardiac muscle (contracts w/o impulse from brain)

  - consists of 4 chambers (left and right atrium, left and right ventricle)

  - have valves to stop back flow of blood
• transport of blood through heart

  deoxygenated blood from the head and body enters into the heart through the vena cava. this is them pumped into the right atrium and into the right ventricle where it is then pumped through the pulmonary artery and the deoxygenated blood is taken to the lungs where it will become oxygenated. the pulmonary vein then brings the oxygenated blood (oxygen-rich blood) from the lungs and into the left atrium, through the left ventricle and then through the aorta which carries the oxygenated blood around the body.
• red blood cell


  - transports oxygen

  - biconcave and no nucleus to carry more oxygen

  - haemoglobin blinds oxygens and gives pigment
• xylem (plant transport)


  - xylem tissue transports water and mineral ions

  - taken up the plant from roots

  - transpiration

  - made from dead cells

  - hollow tube to transport more water
• phloem (plant transport)


  - poem tissue transports sugars

  - from leaves to the rest of the plant (move up and down)

  - translocation

  - made from living cells

  - sieve plates for sugars to pass through
• transpiration


  loss of water from plants leaves by evaporation

  - lost water replaces by uptake of osmosis in roots
• transpiration stream


  constant flow of water
• stomata


  the holes at the bottom of the leaves
• guard cells


  cause stomata to open and close
• use of stomata


  - allows co2 to diffuse in for photosynthesis

  - water vapour diffuses out
• factors affecting rate of transpiration


  1. humidity (amount of water in air)

  - humidity increases, rate increases

  - decreases concentration gradient

  2. light intensity

  - photosynthesis rate increases

  - stomata is open

  - transpiration rate increases

  3. temperature

  - temp increases, rate increases

  - particles have more kinetic energy

  4. air movement (wind)

  - increase concentration gradient

  - transpiration rate increases

  - wind increases, water molecules more away from leaf