B1 - Cell structure and transport

• Features of an animal cell

  • Cell membrane
  • Nucleus
  • Mitochondria
  • Ribosomes
  • Cytoplasm
• Features of a plant cell

  • Permament vacuole
  • Chloroplasts
  • Cell wall
• Cell membrane


  Controls the movement of substances in and out of the cell
• Nucleus


  Contains DNA
• Mitochondria


  Where energy is released through respiration
• Ribosomes


  Site of protein synthesis
• Cytoplasm


  Where chemical reactions happen
• Permanent vacuole


  Contains cell sap
• Chloroplasts


  Contain chlorophyll to absorb light energy for photosynthesis
• Cell wall


  Made of cellulose, strengthens the cell
• Eurkaryotic cells


  Have a nucleus that contains genetic material
• Prokaryotic cells

  • Single celled
  • No nucleus - single loops of DNA called plasmids
  • Smaller than eukaryotic cells
• Magnification


  Image size/actual size
• Features of light microscopes

  • Uses light to form images
  • Living samples can be viewed
  • Relatively cheap
  • Low magnification
  • Low resolution
• Electron microscopes

  • Uses a beam of electrons to form images
  • Samples cannot be living
  • Expensive
  • High magnification
  • High resolution
• Function of a sperm cell


  To fertilise an egg
• Adaptations of a sperm cell


  Tail - swim to the egg and fertilise it

  Lots of mitochondria to release energy from respiration - the sperm can swim to the egg
• Function of a red blood cell


  To transport oxygen around the body
• Adaptations of a red blood cell

  • Contains haemoglobin - binds to oxygen molecules
  • No nucleus - more room to carry oxygen
  • Flat bi-concave shape - increases surface to area volume ratio - increased diffusion
• Function of a muscle cell

  Contract and relax to allow movement
• Adaptations of a muscle cell

  • Contains protein fibres - can contract to make cells shorter
  • Lots of mitochondria - release energy from respiration - allows muscles to contract
• Function of a nerve cell


  Carries electrical impulses around the body
• Adaptations of a nerve cell

  • Branched endings called dendrites - make connections with other neurones and effectors
  • Myelin sheath - insulates axon to increase transmission speed of electrical impulses
• Function of a root hair cell


  Absorb mineral ions and water from the soil
• Adaptations of a root hair cell

  • Long projection - increases surface area of the cell - speeds up the absorbtion of water and mineral ions
  • Lots of mitochondria - releases more energy from respiration - more energy for active transport to absorb mineral ions from the soil
• Function of palisade cells


  Enable photosynthesis in the leaf
• Functions of palisade cells

  • Lots of chloroplasts - contain chlorophyll to absorb light energy
  • Located at the top of the leaf - more sunlight to absorb more light energy
• Resolution


  How clear the image is
• Diffusion


  The spreading out of particles, resulting in a net movement from an area of higher concentration to an area of lower concentration
• Movement of particles in diffusion


  Particles move down the concentration gradient from an area of high concentration to an area of low concentration
• Is energy required for diffusion?


  No - it is a passive process
• Examples of diffusion

  • Substances in the small intestine ddiffuse into capilliaries through the villi
  • Carbon dioxide used for photosynthesis diffuses into leaves through the stomata
• Osmosis


  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Movement of particles in osmosis


  Water moves from an area of lower solute concentration to higher solute concentrations
• Is energy required for osmosis?


  No - passive process
• Water moves by osmosis from a dilute solution in soil to a concentrated solution in root hair cells
• Active transport


  The movment of particles from a more dilute solution to a more concentrated solution using energy from respiration
• Is energy required for active transport?


  Yes - energy from respiration required
• Example of active transport


  Allows sugar molecules to be absorbed from the small intenstine when the sugar concentration is higher in the blood than the intestine
• Factors that affect the rate of diffusion

  • Difference in concentration - the steeper the concentration gradient, the higher the rate of diffusion
  • Temperature - the higher the temperature, the higher the rate of diffusion
  • Surface area of the membrane - the larger the membrane, the higher the rate of diffusion