Topic 1 - Cell Biology

• Eukaryotes


  Cells that have a nucleus and membrane-bound organelles
• Prokaryotes


  Cells that lack a nucleus and membrane-bound organelles
• Components of animal and plant cells

  • Cell membrane
  • Cytoplasm
  • Nucleus containing DNA
• Components of bacterial cells

  • Cell wall
  • Cell membrane
  • Cytoplasm
  • Single circular strand of DNA and plasmids
• Orders of magnitude


  A way to understand how much bigger or smaller one object is compared to another
• Prefixes to show multiples of units

  • Centi (0.01)
  • Milli (0.001)
  • Micro (0.000,001)
  • Nano (0.000,000,001)
• Structures in animal and plant cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional structures in plant cells

  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Structures in bacterial cells


  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Single circular strand of DNA
  • Plasmids
• Cell specialisation


  The process where cells gain new sub-cellular structures to be suited to their role
• Specialised animal cells


  • Sperm cells
  • Nerve cells
  • Muscle cells
• Specialised plant cells


  • Root hair cells
  • Xylem cells
  • Phloem cells
• Cell differentiation


  The process where stem cells switch on/off genes to produce different proteins and acquire new sub-cellular structures
• In animals, most cells differentiate early and lose ability to differentiate, but some like red blood cells are replaced by adult stem cells
• In plants, many cell types retain ability to differentiate throughout life
• Light microscope


  Has two lenses (objective and eyepiece), illuminated from underneath, max magnification x2000, resolving power 200nm
• Growing microorganisms on agar gel plate


  1. Pour hot sterilised agar jelly into sterilised Petri dish

  2. Allow to cool and set

  3. Inoculate with microorganism using sterilised loop

  4. Seal plate and incubate
• Chromosomes


  Contain coils of DNA and carry genes
• There are 23 pairs of chromosomes in each body cell, and 23 chromosomes in each sex cell
• Cell cycle and mitosis

  1. Interphase: cell grows, organelles increase, DNA replicates

  2. Mitosis: chromosomes line up and are pulled to opposite sides

  3. Cytokinesis: cytoplasm and cell membrane divide to form two daughter cells
• Importance of mitosis


  • Growth and development
  • Replacing damaged cells
  • Asexual reproduction
• Stem cells


  Undifferentiated cells that can divide to produce more similar cells, some of which can differentiate
• Types of stem cells

  • Embryonic
  • Adult (e.g. in bone marrow)
  • Meristems in plants
• Therapeutic cloning


  Producing an embryo with the same genes as the patient, to obtain stem cells that can be grown into needed cells/tissues
• Benefits and problems of stem cell research

  • Benefits: Replace damaged/diseased body parts, use unwanted embryos, research differentiation
  • Problems: Don't fully understand differentiation, destroying embryos, ethical concerns, risk of contamination, money could be better spent
• Diffusion


  The spreading out of particles in a solution or gas, resulting in net movement from higher to lower concentration
• Diffusion is passive and does not require energy
• Substances that can move by diffusion

  • Oxygen
  • Glucose
  • Amino acids
  • Water
• Examples of diffusion in the body

  • Oxygen and carbon dioxide in the lungs
  • Urea from liver to kidneys
• Factors affecting rate of diffusion

  • Concentration gradient
  • Temperature
  • Surface area
  • Thickness of membrane
• Diffusion


  The movement of particles from an area of high concentration to an area of low concentration
• Where diffusion takes place in the body

  • Oxygen moves through the membranes of alveoli into red blood cells, and is carried to cells across the body for respiration
  • Carbon dioxide (the waste product of respiration) moves from the red blood cells into the lungs to be exhaled
• Gas exchange


  The movement of gases like oxygen and carbon dioxide
• Where diffusion takes place in the body

  • Urea (a waste product) moves from the liver cells into the blood plasma to be transported to the kidney for excretion
• Factors affecting the rate of diffusion

  • Concentration gradient (difference in concentrations)
  • Temperature
  • Surface area of the membrane
• Concentration gradient


  The greater the difference in concentration, the faster the rate of diffusion
• Temperature

  The greater the temperature, the greater the movement of particles, resulting in more collisions and therefore a faster rate of diffusion
• Surface area of the membrane

  The greater the surface area, the more space for particles to move through, resulting in a faster rate of diffusion
• If the surface area to volume ratio is large, the organism is less likely to require specialised exchange surfaces and a transport system because the rate of diffusion is sufficient in supplying and removing the necessary gases
• Single-celled organisms


  Can use diffusion to transport molecules into their body from the air because they have a relatively large surface area to volume ratio