Cell Biology

• Plant and Animal cells (eukaryotic cells)

  • Eukaryotic cells have these features:
  • Cell Membrane
  • Cytoplasm
  • Genetic material within a nucleus
• Typical size of animal cell

  10-30 μm
• Typical size of plant cell

  10-100 μm
• Bacteria (prokaryotic) cells

  • No true nucleus
  • Contain cytoplasm and a membrane surrounded by a cell wall
  • DNA not in a distinct nucleus
  • No mitochondria or chloroplasts
  • May have small rings of DNA called plasmids
• Typical size of bacterial cell

  2 μm
• A Typical Animal Cell

  • Ribosomes - protein synthesis happens here
  • Mitochondria - energy is released here during aerobic respiration
  • Cell Membrane - controls what comes in and out
  • Cytoplasm - this is where the reactions happen and these are controlled by enzymes
  • Nucleus - controls the cell's activities
• A Typical Plant Cell

  • Cell wall - made of cellulose which strengthens and supports the cell
  • Cell membrane - controls what comes in and out
  • Nucleus - controls what the cell does and stores information
  • Large vacuole - contains cell sap and maintains shape and supports the cell
  • Cytoplasm - Chemical reactions happen here
  • Chloroplasts (containing chlorophyll) - this is needed for photosynthesis
  • Mitochondria - energy is released here during aerobic respiration
• Specialised animal cells

  • Nerve cell (neurone) - branched connections (dendrites), axon has a fatty sheath to speed up nerve impulses
  • Sperm - nucleus with half the number of chromosomes, contains digestive enzymes, filled with mitochondria, long tail
  • Muscle Cell - layers of protein filament that can slide over each other, a high density of mitochondria for respiration,
  • Root hair cell - increased surface area, thinner walls allow for diffusion, permanent vacuole contains sap for a water concentration gradient, mitochondria for active transport of mineral ions
• Xylem

  • Used by the plant to transport water and soluble mineral salts from the roots to the stem and the leaves
  • no top and bottom walls in cells for flow of water
  • cells are dead
  • no cytoplasm or subcellular structures
  • cells thickened with lignin to strengthen tubes
• Phloem

  • Tubes used by the plant to transport dissolved food to the whole plant for respiration and storage, transports in all directions
  • made of living cells
  • cells joined end to end with sieve plates in between
  • also has very few subcellular structures for flow of minerals
• Cell differentiation

  1. During the development of a multi-celled organism cells differentiate to form specialised cells

  2. They do this by acquiring different sub-cellular structures

  3. Animal cells differentiate at an early stage whereas plant cells retain the ability to specialise throughout their life
• Scanning Electron Microscopes

  • Have much higher magnification powers than light microscopes
  • This has led to a much greater understanding of cell structure
• Growing Bacteria (Biology only)

  1. Bacteria can grow and multiply at very quick rates, especially inside the human body where the conditions are right

  2. They grow through an asexual process called "binary fission"
• Growing Bacteria (Biology only)

  1. Sterilise the inoculating loop

  2. Dip the loop in the bacteria and spread it across the agar

  3. Secure (but don't seal) the lid with tape and store upside down
• Mitosis

  • Occurs in all body cells; forms 2x identical daughter cells
• Meiosis

  • Occurs in sex organs only to form gametes- 4 non-identical daughter cells with half the number of chromosomes
• The nucleus of a cell contains chromosomes made of DNA molecules. Each chromosome carries a large number of genes and chromosomes are often found in pairs.
• Facts about Mitosis

  • Used for growth and repair of cells
  • Used in asexual reproduction
  • Cells with identical number of chromosomes and genetic information are produced ("clones")
• Stem cell research

  • Stem cells are cells that have not yet specialised: egg and sperm, embryo, cloned embryos
  • These stem cells have the potential to develop into any kind of cell
  • In grown adults they can be taken from bone marrow or they can come from embryos from unused IVF treatments
  • They can be used to treat conditions such as diabetes and paralysis
• Factors that might influence a decision:

  • Beliefs/religion
  • What does "the right thing" mean?
  • "Playing God"
  • Risks – acceptable or unacceptable?
  • Social and economic contexts
• I could benefit from stem cell research but

  Doctors are worried that my body will reject the treatment
• Therapeutic cloning

  May be the answer to produce an embryo with the same genes as the patient
• Stem cell research does also carry the risk of transmitting viral infections.
• Stem Cells in Plants - Meristems

  • Plant growth occurs in areas called meristems
  • Stem cells can come from meristems
  • Cells from the meristem behave like stem cells – they can develop into any kind of cell
  • Cloned plants can be produced from these cells
  • this can save rare species from extinction
  • plants with helpful characteristics can also be cloned
• Diffusion

  When liquid and gas molecules travel from an area of high concentration to an area of low concentration, until an equilibrium
• Diffusion Summary

  • Diffusion is when particles spread from an area of high concentration to an area of low concentration
  • The particles move along a "concentration gradient"
  • Diffusion can be accelerated by increasing the temperature of the particles, which makes them move faster, or by making the surface area of the membrane bigger
• Gas Exchange in Fish

  1. The fish gulps water through its mouth and then pushes it out of the gill flap

  2. The oxygen is absorbed by the fine filaments (which increase surface area) in the gills

  3. The oxygen is transported away from the gill filaments by the blood supply
• Diffusion in the lungs

  • Alveoli have four things that help them to do this job:
  • A massive moist surface area-max diffusion surface
  • A lining that is only one cell thick-decreases diffusion distance
  • A very good blood supply – maintain a steep concentration gradient
  • Well –Ventilated
• Osmosis

  A "special kind of diffusion" where water diffuses from a dilute area to a more concentrated area through a partially permeable membrane (i.e. one that allows water to move through but not anything else)
• Active Transport

  Substances move against the concentration gradient, requires energy, carrier proteins are required
• Active transport enables cells to take in substances even though there are in very small concentrations.
• Preparing a microscope slide

  • take a thin sample of tissue with tweezers
  • add a drop of water to a clean slide
  • place tissue on slide and add a drop of iodine stain (so structres can be observed)
  • place a cover slip over the specimen
• Main features of a microscope

  
• Process of Mitosis

  • Chromosomes replicate, resulting in X-shaped chromosomes with two 'arms' known as chromatids
  • The chromosomes line up along the equator of the cell
  • The chromatids are separated and pulled to opposite ends of the cell
  • A new nucleus forms around each new group of chromosomes
  • the cytoplasm and cell membrane divides in a process known as cytokinesis
  • this results in the formation of two genetically identical daughter cells