CELL STRUCTURE AND TRANSPORT

• light microscope

  • use a beam of light to form an image
  • can magnify objects up to 2,000 times (school microscopes usually only go up to 400)
  • can be used to view living objects
  • are relatively cheap and easy to carry around
  • have a resolving power of about 200 nm
• electron microscope

  • use a beam of light to form an image
  • can magnify objacts up to 2,000,000 times
  • cannot be used for living objects
  • are very expensive and need to be kept in special conditions
  • have a resolving power of around 0.2 nm
• units

  • 1 km = 1000 m
  • 1 m = 100 cm
  • 1 cm = 10 mm
  • 1 mm = 1,000 μm (micrometers)
  • 1 μm = 1,000 nm (nanometres)
• magnification = image size ÷ object size
• resolving power


  the ability of a microscope to distinguish between two points that are close together
• eukaryotic cells


  • all animals, plants, fugni and protista are eukaryotes.
  • they contain a cell membrane, cytoplasm and a nucleus
• prokaryotic cells


  • bacteria
  • single celled living organisms
  • contain cytoplasm, cell membrane and a cell wall
• nerve cells

  specialised to carry electrical impulses around the bodies of animals and have:

  • many dendrites to make connections to other nerve cells
  • an axon to carry the impulses from one place to the other
  • nerve endings or synapes which pass impulses to other cells by producing transmitter chemicals
  • many mitochondria in the synapses to transfer the energy needed to make the transmitter chemicals
• muscle cells

  can contract and relax, striated muscle cells are found in the muscles that enable the body to move. smooth muscle cells are found in the tissues of the digestive system and contract to move food along the gut, striated muscle cells contain:

  • special proteins that slide over each other
  • many mitochondria to transfer the energy needed for chemical reactions
  • a store of glycogen that can be broken down and used in respiration to transfer energy
• sperm cells

  carry the genetic information from the male parent, specialised to move through water or the female reproductive system to reach the egg and contain:

  • a long tail that whips from side to side to move
  • a middle section full of mitochondria to transfer the energy needed by the tail to move
  • an acrosome to store digestive enzymes to break down the outer layers of the egg
  • a large nucleus to contain the genetic information
• root hair cells


  occur near the tips of roots, increase the surface area of the root so that it can absorb water and mineral ions through the plant and contain:

  • a large permanent vacuole: speeds up the movement of water by osmosis from the soil across the root hair cell
  • many mitochondria: transfer the energy needed for the active transport of mineral ions into the root hair cells
  • and greatly increase the surface area available for water to move into the cell
• photosynthetic cells

  plants make thier own food by photosynthesis and the photosynthetic cells contain:

  • chloroplasts containing chlorophyll to trap the light needed for photsynthesis
  • a large permanent vacuole that helps keep the cell rigid
  • are found in continuous layers in the leaf and outer layers or stems
• xylem cells

  transport water and mineral ions from the roots to the stem and leaves, xylem tissue supports the plant

  • the cells are living when they're first formed
  • a chemical (lignin) builds up in spirals in the cell wall
  • the cells die leaving long hollow tubes so that water and mineral ions can move up the tube
  • the spirals and rings of lignin make the tubes of xylem very strong
• phloem

  the tissue that transports food made by photosynthesis to the rest of the plant, the cells form tubes but don't become lignified like xylem

  • the cell walls between phloem cells break down to form sieve plates
  • phloem cells lose a lot of their structures but are kept alive by companion cells
  • the companion cells contain mitochondria that transfer energy to aid the movement of dissolved food in the phloem
• Diffusion


  the spreading out of particles of a gas or solute moving from a high concerntration to a low concerntration down a concerntration gradient
• what affects the rate of diffusion?

  • difference in concerntrations
  • temperature
  • surface area
• osmosis


  movement of water from a dilute to a more concerntrated solution through a partially permeable membrane
• concerntrations of two soloutions

  if the solutions have the same concerntrations they are isotonic

  • the solution that is more concerntrated (more solute) is hypertonic
  • the solution that is less concerntrated (more water) is hypotonic
• turgor pressure

  occurs when no more water can enter a cell due to the pressure inside

  • as long as the outside solution is hypotonic water moves in and keeps the cells rigid which supports the plant
  • plant cells in a hypertonic solution lose water and become flaccid so the plant wilts
  • when plant cells are placed in hypertonic solutions in a laboratory, a lot of water leaves the cell. the vacuole and cytoplasm shrink, then the membrane pulls away from the cell wall - plasmolysis
• active transport


  moves substances from a more dilute solution to a more concerntrated solution (against the concerntration gradient)

  • allows plant root hairs to absorb mineral ions required for healthy growth from very dilute solutions in the soil against a concerntration gradient
  • enables sugar molecules used for cell respiration to be absorbed from lower concerntrations in the gut into the blood where the concerntration of sugar is higher
• single-celled organisms have a relatively large surface area to volume ratio so all necessary exchanges with the environment can take place over this surface
• exchange surfaces usually have a large surface area and thin walls which give short diffusion distances