B1

• Differences between eukaryotic and prokaryotic cells

  • Prokaryotic cells are much smaller than eukaryotic cells
  • Eukaryotic cells contain membrane bound-organelles and a nucleus containing genetic material, while prokaryotes do not
• Order of magnitude

  A power to the base 10 used to quantify and compare size
• Centimetre (cm)

  1 x 10-2 metres
• Millimetre (mm)

  1 × 10-3 metres
• Micrometre (µm)

  1 × 10-6 metres
• Nanometre (nm)

  1 x 10-9 metres
• Function of the nucleus (other than storing genetic information)

  Controls cellular activities
• Function of the mitochondria


  Site of later stages of aerobic respiration in which ATP is produced
• Function of the ribosomes


  Joins amino acids in a specific order during translation for the synthesis of proteins
• Function of the plant cell wall

  Provides strength, Prevents the cell bursting when water enters by osmosis
• Adaptations of root hair cells in plants

  • Large surface area to absorb nutrients and water from surrounding soil
  • Thin walls that do not restrict water absorption
• Importance of cell differentiation

  Allows production of different tissues and organs that perform various vital functions in the human body
• Purpose of cell division in mature animals


  Repair of tissues and replacement of cells
• Magnification


  The number of times bigger an image appears compared to the size of the real object
• Resolution

  The smallest distance between two objects that can be distinguished
• Advantages of light microscopes

  • Inexpensive
  • Easy to use
  • Portable
  • Observe both dead and living specimens
• Disadvantage of light microscopes

  Limited resolution
• Types of electron microscope

  • Transmission electron microscope (TEM)
  • Scanning electron microscope (SEM)
• Advantage of electron microscopes

  Greater magnification and resolution
• Electron microscopes have greater magnification and resolution because they use a beam of electrons which has a shorter wavelength than photons of light
• How electron microscopes have enabled scientists to develop their understanding of cells

  • Allow small sub-cellular structures (e.g. mitochondria, ribosomes) to be observed in detail
  • Enable scientists to develop more accurate explanations about how cell structure relates to function
• Disadvantages of electron microscopes

  • Expensive
  • Large so less portable
  • Require training to use
  • Only dead specimens can be observed
• Chromosomes


  DNA molecules combined with proteins that contain genes which provide the instructions for protein synthesis
• Gene


  A section of DNA which codes for a protein
• Stem cell

  An unspecialised cell which is capable of differentiating into other cell types and of self-renewal
• Function of embryonic stem cells

  • Can replicate themselves and differentiate into many other types of cells
  • May be able to treat conditions such as paralysis and diabetes by dividing to replace damaged cells
• Issues associated with the use of stem cells

  • Many embryonic stem cells are sourced from aborted embryos - some people have an ethical/religious objection
  • Development of stem cell therapies is slow, expensive and difficult
  • Adult stem cells infected with viruses could transfer infections to patients
  • If donor stem cells do not have a similar genetic makeup to the patient, an immune response could be triggered
• Factors affecting rate of diffusion

  • Concentration gradient - larger gradient, faster diffusion
  • Temperature - higher temperature, faster diffusion
  • Surface area - larger surface area, faster diffusion
• Substances transported by diffusion

  • Lungs: oxygen diffuses into the blood from the lungs and carbon dioxide diffuses into the lungs from the blood, both down their concentration gradient
  • Kidney: urea diffuses from cells into blood plasma so it can be excreted in urine
• Adaptations of single-celled organisms for diffusion

  • They have a large surface area to volume ratio - maximises the rate of diffusion of molecules to meet the organism's needs
• Factors increasing effectiveness of gas exchange surface

  • Large surface area
  • Thin membrane (short diffusion path)
  • Efficient blood supply (animals)
  • Ventilation (animals)
• Isotonic solution


  The concentrations of the external and internal (inside cell) solutions are the same
• Animal cell in very hypotonic solution


  Water moves into the cell, causing it to burst
• Animal cell in very hypertonic solution


  Water moves out of the cell, causing it to shrivel up
• Turgor pressure


  Water moves in by osmosis, causing the vacuole to swell and the cytoplasm to press against the cell wall
• Plant cell in very hypertonic solution

  Water moves out of the cell by osmosis and the vacuole and cytoplasm decrease in size. The cell membrane may pull away from the cell wall, causing the cell to become plasmolysed
• Use of active transport by plant root hair cells

  • Root hair cells use active transport to take up mineral ions from a more dilute solution in soils. Ions such as magnesium and nitrates are required for healthy growth
• Use of active transport to absorb products of digestion

  • Active transport is used to transport glucose from a lower concentration in the gut to a higher concentration in the blood. Glucose is then transported to the tissues where it can be used in respiration