B1 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
• 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
• Electron microscope


  Uses electrons instead of light, two types (scanning and transmission), max magnification x2,000,000, resolving power 10nm (SEM) and 0.2nm (TEM)
• Calculating size of object

  Size of image / magnification = size of object
• Chromosomes


  Contain coils of DNA, with each chromosome carrying many genes
• Number of chromosomes


  23 pairs in body cells, 23 in gamete cells
• Cell cycle and mitosis

  1. Interphase: cell growth, organelle increase, DNA replication

  2. Mitosis: chromosomes line up and separate

  3. Cytokinesis: two daughter cells form
• 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 won't be rejected
• Benefits and problems of stem cell research

  • Benefits: Replace damaged/diseased parts, use unwanted embryos, research differentiation
  • Problems: Don't fully understand differentiation, ethical issues, risk of contamination, money/time better spent elsewhere
• Diffusion


  The spreading out of particles in a solution or gas, resulting in net movement from higher to lower concentration
• Substances that can move by diffusion across cell membranes
• Examples of diffusion in the body

  • Oxygen and carbon dioxide in gas exchange, urea from liver to kidney
• 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
• Oxygen and water can move through cell membranes by diffusion, but starch and proteins cannot
• Where diffusion takes place in the body

  • Oxygen moves from alveoli into red blood cells, and carbon dioxide moves from red blood cells into the lungs
  • Urea moves from liver cells into 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
• Surface area to volume ratio

  The size of the surface area of the organism compared to its volume
• 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
• Multicellular organisms cannot rely on diffusion alone due to their small surface area to volume ratio, so they have adaptations to allow molecules to be transported in and out of cells
• Adaptations to increase surface area for diffusion

  • Lungs: alveoli
  • Small intestine: villi
  • Fish gills: lamellae
  • Leaves: flattened shape and air spaces
• Adaptations to provide a short diffusion pathway

  • Lungs: thin alveoli and capillary walls
  • Small intestine: villi with a single layer of surface cells
• Adaptations to maintain a steep concentration gradient

  • Lungs: constant supply of oxygen to blood
  • Fish: water and blood flow in opposite directions
• Osmosis


  The movement of water from a less concentrated solution to a more concentrated one through a partially permeable membrane