B1-Cells and Organisations

• Nucleus


  Contains genetic material, which controls the activities of the cell
• Cytoplasm


  Most chemical processes take place here, controlled by enzymes
• Cell membrane


  Controls the movement of substances into and out of the cell
• Mitochondria


  Most energy is released by respiration here
• Ribosomes


  Protein synthesis happens here
• Cell wall


  Strengthens the cell-made of cellulose (not bacteria)
• Chloroplasts


  Contain chlorophyll, absorbs light energy for photosynthesis
• Permanent vacuole


  Filled with cell sap to help keep the cell turgid
• Bacterial DNA


  Loop of DNA NOT found in a nucleus
• Plasmid (DNA)


  Small ring of DNA often used as a vector in genetic modification
• Animal cell


  • Streamlined with a long tail to swim to the egg
  • Acrosome in the head containing enzymes to digest the egg cell membrane
  • Large number of mitochondria in the mid section to release energy for movement
• Nerve cell


  • Long to carry signals long distances
  • Branched connections to connect to other nerve cells and form a network around the body
  • Insulating sheath to enhance transmission of electrical signals
• Muscle cell


  • Contain a large number of mitochondria to release energy from respiration for movement
  • Long so that there is enough space to contract
• Root hair cell


  • Hair like projections to increase the surface area
  • No chloroplasts as they are in the soil
• Xylem


  • Form hollow xylem tubes made of dead tissue
  • Long cells with walls toughened by lignin
  • Water and minerals flow from the roots towards the leaves only in one direction in a process called TRANSPIRATION
• Phloem


  • Form phloem tubes made of living tissue
  • Cells have end plates with holes in them
  • Glucose in solution moves from the leaves to growth and storage tissues in a process called TRANSLOCATION
• Most types of ANIMAL cells differentiate in the early stage of development
• Most types of PLANT cells can differentiate throughout their life cycle
• Light microscope


  • First ones used in 1590's
  • Magnification up to 1500 times
  • Resolution of 200nm
  • Small and portable
  • Cost around £100 for a school one
• Electron microscope


  • First ones used in 1960's
  • Magnification up to 2,000,000 times
  • Resolution of 0.2nm
  • Very large and not portable
  • Several £100,000 to £1 million plus
• Resolution


  The shortest distance between two objects that can be seen clearly
• Electron microscopes have a higher magnification and resolution than light microscopes, allowing scientists to see more sub-cellular structures
• Calculating magnification


  Magnification = Size of image / Real size of object
• The actual diameter of a magnified animal cell structure is 0.15mm, and the magnified diameter is 6mm. The structure has been magnified 40 times.
• Calculating length of magnified cell structure


  Length of magnified structure = Actual length x Magnification
• Making a wet mount slide

  • Place a thin section of the specimen onto slide
  • Place a drop of water in the middle of the slide or stain the specimen
  • Gently lower cover slip onto the specimen without trapping air bubbles
  • Switch on the light source and place your slide on the stage
  • Use the lowest objective lens and turn the focusing wheel to move the lens close to the slide
  • Slowly adjust the focusing wheel until you can see a clear image
  • Increase the magnification by changing the objective lens and re-focus
• Drawing what you see

  • Clear line drawing-no shading
  • Label main cell structures
  • Add a title and the magnification
• Diffusion


  The spreading of the particles of a gas or substances in solution, resulting in a net movement of particles from a region where they are of a higher concentration to an area of lower concentration
• Substances transported in and out of cells in humans

  • Digested food (e.g. glucose, amino acids)
  • Oxygen
  • Urea
• Factors affecting rate of diffusion

  • Concentration gradient
  • Temperature
  • Surface area of the membrane
• Surface area to volume ratio

  • Calculated by dividing an object's surface area by its volume
  • Smaller objects have a larger surface area to volume ratio
• Adaptations of the small intestines

  • Internal surface is covered in millions of folds called villi
  • Villi increase the surface area
  • Villi have a very good blood supply to maintain the concentration gradient
  • Membranes of the villi are very thin to allow for a short diffusion distance
• Adaptations of the lungs

  • Contain millions of tiny air sacs called alveoli
  • Alveoli increase the surface area
  • Alveoli have a very good blood supply to maintain the concentration gradient
  • Membranes of the alveoli are very thin to allow for a short diffusion distance
• Adaptations of gills in fish

  • Each gill is made of lots of thin plates called gill filaments
  • Gill filaments increase the surface area
  • Gill filaments are covered with lamella that increase the surface area more
  • Lamella have a very good blood supply to maintain the concentration gradient as water flows in the opposite direction
  • Membranes of the lamellae are very thin to allow for a short diffusion distance
• Adaptations of the roots

  • The root surface is covered in millions of root hair cells
  • Root hair cells increase the surface area
  • Present on the mature parts of the roots
  • Absorb water and minerals from the soil
• Adaptations of the leaves

  • Large surface area to absorb more light
  • Thin so short distance for carbon dioxide to diffuse into leaf cells
  • Chlorophyll absorbs sunlight for photosynthesis
  • Xylem and phloem to support the leaf and transport water and glucose
  • Stomata on the lower side of the leaf to allow gases to diffuse into and out of the leaf
• Osmosis


  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Hypertonic


  More concentrated solution than in the cells
• Isotonic


  Same concentration as the solution in the cell
• Hypotonic


  More dilute than the solution in the cells