cell biology

• Organisms are made up of cells
• Most organisms are multicellular and have cells that are specialised to do a particular job
• Microscopes are needed to study cells in detail
• Light microscope


  Cells range in size: animal cells are between 0.01 mm – 0.05 mm, plant cells are between 0.01 mm – 0.10 mm
• The human eye can see objects as small as around 0.05 mm
• A microscope is required to see cells in any detail
• Microscopes


  Magnify the image of a biological specimen so that it appears larger
• Compound microscope


  Uses two lenses, the objective lens and the eyepiece
• Calculating the magnification of the microscope

  Magnification of the microscope = magnification of eyepiece × magnification of objective
• Magnification


  • ×10
  • ×4
  • ×40
• Organisms are made up of cells
• Most organisms are multicellular and have cells that are specialised to do a particular job
• Microscopes are needed to study cells in detail
• Resolution


  The fineness of detail that can be seen in an image - the higher the resolution of an image, the more detail it holds
• Resolving power


  The ability to see two points as two points, rather than merged into one
• The resolution of a light microscope is around 0.2 μm, or 200 nm
• This means that it cannot distinguish two points closer than 200 nm
• Nanometre (nm)


  One billionth of a metre
• Scanning electron microscope (SEM)

  • Has a large field of view
  • Can be used to examine the surface structure of specimens
  • Often used at lower magnifications
• Transmission electron microscope (TEM)

  • Used to examine thin slices or sections of cells or tissues
  • Has a maximum magnification of around ×1 000 000
  • Images can be enlarged beyond that photographically
  • Limit of resolution is less than 1 nm
• The TEM has revealed structures in cells that are not visible with the light microscope
• Diffusion


  The movement of molecules from an area of higher concentration to an area of lower concentration
• Particles (molecules and ions) in a liquid and a gas move continuously
• Because of this movement, particles will spread themselves evenly throughout a liquid or a gas
• If there is a situation where particles of a substance are in a higher concentration, they will move from this region to where they are in a lower concentration
• The particles will move in both directions, but there will be a net movement from high to low concentration
• The particles will end up evenly spread throughout the liquid or gas, but will continue to move
• Examples of diffusion in biological systems


  • Substances moving into and out of living cells
  • In a leaf
  • In the lungs
  • Liver cells
• Peroxisomes are small sacs found in plant and animal cells that contain oxidative enzymes responsible for breaking down toxic compounds and producing energy.
• Lysosomes are membrane-bound organelles that contain digestive enzymes used to break down waste materials and foreign substances inside the cell.
• The Golgi apparatus functions in modifying, sorting, and packaging proteins for secretion.
• The Golgi apparatus is involved in the modification, sorting, packaging, and transport of proteins within cells.
• The endoplasmic reticulum is involved in protein and lipid synthesis in the cell.
• The mitochondria are known as the powerhouse of the cell, responsible for generating ATP through cellular respiration.
• Capillaries have thin walls to allow fast diffusion
• Protein synthesis occurs at ribosomes attached to rough endoplasmic reticulum (RER) or free in the cytoplasm.
• Protein synthesis occurs at ribosomes attached to rough endoplasmic reticulum (RER) or free in the cytoplasm.
• Oxygen diffuses from alveoli into blood
• Oxygen diffuses from alveoli into blood
• Oxygen diffuses from alveoli into blood