Cell Biology

• Cells can either be eukaryotes or prokaryotes.

  Eukaryotes are bigger and more complex.

  Prokaryotes are smaller and simpler.
• An example of prokaryote is a bacteria cell.

  An example of eukaryote is a plant or animal cell.
• Eukaryotes are made up of eukaryotic cells.

  Prokaryotes are single-celled organisms.
• Label the bacteria cell

  A) singular stand of DNA

  B) plasmids

  C) cytoplasm

  D) cell membrane

  E) cell wall

  F) flagellum

  
• Prefixes:

  Centi: x10^-2 (one-hundreth)

  Mili: x10^-3 (one-thousandth)

  Micro: x10^-6 (one-millionth)

  Nano: x10^-9 (one-billionth)
• Order of Magnitude can be calculated by the number of zeros.

  E.g. 100x means a order of magnitude of 2.
• You can calculate the size/area of an organelle by treating it as a regular shape.
• Sub-Cellular Structures and their Functions:(Animal & Plant Cells)

  • Cytoplasm: Jelly-like material that contains dissolved nutrients, salts and other organelles. This is where most chemical reactions occur.
  • Nucleus: Contains genetic material (including DNA), which controls the cell's activities.
  • Cell Membrane: Semi-permeable structure which controls the movement of substances in and out of the cell.
  • Mitochondria: Contains enzymes for respiration and releases energy from respiration.
  • Ribosomes: Site of protein synthesis.
• Sub-Cellular Structures and their Functions (Plant Cells Only)

  • Chloroplasts: Where photosynthesis occurs. Contains a green pigment (chlorophyll), which adsorbs light.
  • Vacuole: Filled with cell sap (a weak solution of sugar and salts), which keeps the cell turgid.
  • Cell Wall: Made of cellulose, which strengthens the cell.
• Most animal and plant cells are around 0.01 – 0.10 mm in size.

  The smallest thing seen with the naked eye is about 0.05 mm.
• Specialised Cells in Animals

  • Sperm cells: Transfers genetic information to the egg for fertilisation
  • Nerve cells: Carries electric signals in the body
  • Muscle cells: Contracts for movement
• How a Sperm Cell is adapted to its function

  • The head contains a haploid nucleus (which contains 23 chromosomes) so it can fuse with the egg to restore the normal 46 chromosomes.
  • The head is streamlined, which helps the cell swim.
  • The acrosome in the head contains genetic enzymes that can break down the egg's cell membrane, allowing the sperm to penetrate the egg.
  • The mid-piece contains mitochondria which provide the cell with energy to swim towards the egg.
  • The tail rotates which propels the cell forwards, allowing it to swim faster.
• How a Nerve Cell is adapted to its function

  • It is long and extended which covers more distance in the body.
  • Has branches which allows it to connect to other nerve cells and form a network throughout the body.
  • Has extensions called dendrites which allows nerve cells to communicate with other nerve cells, muscles and glands.
  • The axon is covered with a fatty sheath, which insulates the cell and speeds up the nerve impulse.
• How a Muscle Cell is adapted to its function

  • Are long to provide space for contraction.
  • Have many mitochondria which release energy for contraction.
  • Contain protein filaments which slide over each other to allow contraction.
  • The arrangement of these filaments is responsible for the bonded appearance of the heart and skeletal muscle.
  • In the skeletal muscle, the cells merge so the muscle fibers contract in unison.
• Label the Sperm Cell

  A) Acrosome

  B) Nucleus

  C) Mid-piece

  D) Tail/Flagellum

  
• Label the Nerve Cell

  A) Dendrites

  B) Nucleus

  C) Fatty sheath

  D) Axon

  E) Nerve ending

  
• Label the Muscle Cell

  A) Protein Filament

  B) Mitochondria

  C) Ribosomes

  
• Specialised Cells in Plants

  • Root Hair Cell: Adsorbs water and minerals from soil.
  • Xylem Cells: Transports water and dissolved ions.
  • Phloem Cells: Transports dissolved sugars and amino acids.
• How a Root Hair Cell is adapted to its function


  • Increased surface area so that the rate of water intake by osmosis is higher.
  • Thinner walls so water can move through easily through a shorter diffusion path.
  • Mitochondria release energy for active transport of mineral ions.
• How a Xylem Cell is adapted to its function


  • No separating walls. Continuous hollow tubes where water is drawn upwards towards the leaves.
  • Don't contain any cytoplasm or organelles, allowing water to pass freely.
  • The outer walls are thickened with lignin which strengthens the tubes, providing support for the plant.
• How a Phloem Cell is adapted to its function

  • Cells join end-to-end to create phloem tubes.
  • The walls contain holes (sieve plates) which allow substances to flow easily.
  • Have very few sub-cellular structures to allow substances to flow freely.
  • Companion cells provide energy which helps transport substances in the phloem.
• Label the Root Hair Cell

  A) Root hair

  B) Mitocondria

  C) Thinner walls

  
• Label the Xylem Cell

  A) Walls thickened with lignin

  B) No other cell contents

  
• Label the Phloem Cell

  A) Companion cell

  B) Sieve plate

  C) Joined cells

  
• Microscopy Required Practical (1)

  1. Prepare a slide by placing the sample onto the slide and covering it with a cover slip.
  2. Put the slide onto the stage, using the clips to keep it in place.
  3. Ensure the lowest powered objective lens is being used.
  4. Use the coarse focusing dial to adjust the objective lens until it is nearly touching the slide (do this by looking from the side of the microscope to avoid breaking the slide).
  5. Look through the eyepiece lens and carefully turn the coarse adjustment knob until the cells come into focus.
• Microscopy Required Practical (2)

  6. Use the fine focusing dial to bring the cells into a clear focus.

  7. Use a pencil to sketch a labelled drawing of the cells. Include the total magnification (eyepiece lens magnification x objective lens magnification) and a magnification scale (by using a clear plastic ruler on the stage to measure the diameter of the field of view)

  8. Repeat using higher powered objective lenses.