Topic 1 - cell biology

• Mitosis recap and stages

  One parent cell divides to make two non-identical daughter cells. Produces diploid cells (any cell except sperm and egg)

  Stage 1: DNA replicates, organelles and subcellular structures are duplicated

  Stage 2: chromosomes line up in centre of the cell and are pulled apart by spindle fibres.

  Stage 3: cytokinesis - cell membrane and cytoplasm split
• Components of animal and plant cells


  • Cell membrane
  • Cytoplasm
  • Nucleus containing DNA
• Conversions - cell sizes 


  • Centi (0.01) x 10 to mm
  • Milli (0.001) x1000 to um
  • Micro (0.000,001) x 1000 to nm
  • Nano (0.000,000,001) divide 1,000,000 to mm
• 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
• Sperm cells


  • Specialised to carry male's DNA to egg cell for successful reproduction:
  • Streamlined head and long tail to aid swimming
  • Many mitochondria to supply energy
  • Top of head with digestive enzymes to break down egg cell membrane
• Nerve cells


  • Specialised to transmit electrical signals quickly from one place to another:
  • Long axon to transmit impulses
  • Many extensions for branched connections
  • Mitochondria to supply energy for neurotransmitter production
• Muscle cells


  • Specialised to contract quickly to move bones or simply to squeeze therefore causing movement:
  • Proteins (myosin and actin) that slide over each other to cause contraction
  • Many mitochondria to provide energy
  • Can store glycogen for respiration
• Root hair cells

  • Specialised to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots:
  • Large surface area for water and mineral ion uptake
  • Large vacuole affects water movement speed
  • Mitochondria provide energy for active transport of mineral ions
• Xylem cell

  • Specialised to transport water and mineral ions up from the plant from the roots to the shoots:
  • Lignin deposited to form hollow tubes for water and mineral ion transport
  • Lignin spirals help withstand pressure
• Phloem cells


  • Specialised to carry products of photosynthesis to all parts of plants:
  • Sieve plates allow movement of substances between cells
  • Companion cells provide energy through their mitochondria
• Cell differentiation


  Process where a cell changes to become specialised for its job

  In plants, many cell types retain ability to differentiate throughout life

  In animals, most cells differentiate early and lose ability to differentiate further
• Advantages of Electron microscope:

  • Higher magnification
  • Higher resolution
• 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
• Binary fission


  One bacterial cell splitting into two
• Calculating bacterial population growth


  1. To calculate number of bacteria: Bacteria at beginning x 2^(number of divisions) = bacteria at end

  2. To calculate Number of divisions = time left / mean division time
• Calculating cross-sectional areas involves using the formula πr^2
• 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
• Functions 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 to have differentr functions
• Types of stem cells


  • Embryonic stem cells
  • Adult stem cells
  • 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: Can replace damaged/diseased body parts, use unwanted embryos, research differentiation
  • Problems: Don't fully understand differentiation, destroying embryos, ethical concerns, risk of contamination, money/time better spent elsewhere
• Substances that can move by diffusion across cell membranes include oxygen, glucose, amino acids, and water, but not starch and proteins
• Examples of diffusion in the body


  • Oxygen and carbon dioxide in gas exchange
  • Urea from liver to blood to kidneys
• Diffusion


  • The movement of particles from an area of high concentration to an area of low concentration
  • Happens in solutions and gases as particles are free to move
  • Only small molecules can diffuse through cell membrane like oxygen, glucose, amino acids and water
  • Big molecules like starch and protein can’t fit through the membrane
• 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
• How is the rate of diffusion affected

  Concentration gradient: the bigger it is, the faster the rate of diffusion. Due to net movement from one side being greater.

  Temperature: the higher it is, the faster the rate. Because particles have more energy so move around faster

  Surface area: the larger it is the faster the rate of diffusion. Because more particles can pass through at once
• Calculating surface area to volume ratio

  1. Find the volume (length x width x height)

  2. Find the surface area (length x width)

  3. Write the ratio in the smallest whole numbers
• Large surface area to volume ratio

  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
• Organisms with large surface area to volume ratio

  • Single-celled organisms
• Small surface area to volume ratio


  Multicellular organisms cannot rely on diffusion alone and require adaptations to transport molecules in and out of cells
• Adaptations in multicellular organisms


  • Lungs: alveoli and capillaries
  • Small intestine: villi
  • Fish gills: lamellae
  • Plant roots: root hair cells
  • Plant leaves: stomata
• Adaptations for efficient diffusion


  • Having a large surface area
  • Having a thin membrane
  • Having an efficient blood supply/being ventilated (in animals)
• Osmosis


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


  The movement of particles from an area of low concentration to an area of high concentration, against the concentration gradient, requiring energy