P1 - 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
• Organelles


  Structures in a cell that have different functions
• Orders of magnitude


  Used to understand how much bigger or smaller one object is from another
• Structures in animal and plant cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Structures only 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
• In animals, most cells differentiate early and lose the ability, but some like red blood cells are replaced by adult stem cells
• In plants, many cell types retain the ability to differentiate throughout life
• Light microscope


  Has two lenses (objective and eyepiece), illuminated from underneath, maximum magnification of x2000 and resolving power of 200nm
• Electron microscope


  Uses electrons instead of light, can achieve magnification up to x2,000,000 and resolving power of 10nm (SEM) and 0.2nm (TEM)
• Calculating magnification of light microscope

  Magnification of eyepiece lens x Magnification of objective lens
• Calculating size of object

  Size of image / Magnification = Size of object
• Chromosomes


  Contain coils of DNA and carry genes
• Number of chromosomes


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

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

  2. Mitosis: chromosomes line up at equator, cell fibres pull them 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 stem cells
  • Adult stem cells
  • Meristems in plants
• Benefits and problems of stem cell research

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


  Spreading out of particles in a solution or gas, resulting in net movement from higher to lower concentration
• Substances that can move by diffusion

  • Small molecules like oxygen, glucose, amino acids, water, but not large molecules like starch and proteins
• Examples of diffusion in the body

  • Oxygen and carbon dioxide in gas exchange
  • Urea from liver to kidneys for excretion
• 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
• 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 in multicellular organisms

  • Lungs: alveoli and capillaries for gas exchange
  • Small intestine: villi for absorption of digested food
  • Fish gills: gill filaments and lamellae for gas exchange
  • Plant roots: root hair cells for water and mineral absorption
  • Plant leaves: stomata for gas exchange