Cell Biology

• Eukaryotes


  Complex cells with a cell membrane, cytoplasm, and genetic material enclosed in a nucleus
• Prokaryotes


  Smaller cells without a nucleus, with cytoplasm and a cell membrane surrounded by a cell wall, and genetic material as a single DNA loop
• Eukaryotes


  • Plant cells
  • Animal cells
• Prokaryotes


  • Bacterial cells
• Subcellular structures


  • Nucleus
  • Cell membrane
  • Ribosomes
  • Mitochondria
  • Cytoplasm
  • Cell wall
  • Vacuole
  • Chloroplasts
• Nucleus


  Contains the genetic material of the cell and controls the cell's activities
• Cell membrane


  Controls the movement of substances in and out of the cell, and holds the cell together
• Ribosomes


  Site of protein synthesis
• Mitochondria


  Site of aerobic respiration which releases energy needed by the cell
• Cytoplasm


  Liquid gel where most chemical reactions occur, controlled by enzymes
• Cell wall


  Rigid structure that supports and strengthens plant cells, made of cellulose
• Vacuole


  Contains cell sap to keep the cell rigid
• Chloroplasts


  Site of photosynthesis, containing chlorophyll
• Light microscope


  Uses light and lenses to magnify, can see individual cells and larger subcellular structures
• Electron microscope


  Uses electrons rather than light, has higher magnification and resolution, can see cells and subcellular structures in finer detail
• Using a microscope (practical)

  1. Add drop of water to slide

  2. Place specimen on slide

  3. Add stain

  4. Lower coverslip

  5. Focus on specimen
• Differentiation


  Process by which cells change to become specialised for a specific function
• In mature animals, undifferentiated cells are mainly used for repairing and replacing cells
• Stem cells are undifferentiated cells that can differentiate into different cell types
• Sperm cells


  • Long tail to swim
  • Streamlined head
  • Many mitochondria in head
  • Enzymes in head to digest egg cell membrane
• Nerve cells


  • Long to cover more distance
  • Branched dendrites to connect to other nerve cells
• Muscle cells


  • Very long to contract and relax
  • Many mitochondria to release energy
  • Store glycogen
• Root hair cells


  • Large surface area
  • Long and thin to get through soil
  • Thin cell membrane
  • Many mitochondria
• Xylem/phloem cells


  • Long with cells joined end-to-end
  • Xylem cells have spiral lignin
  • Phloem cells have sieve plates and companion cells
• Chromosomes


  Coiled up lengths of DNA molecules that carry genes
• Human body cells have 46 chromosomes, or 23 pairs
• The cell cycle


  1. Cell growth and division

  2. DNA replication

  3. Mitosis to produce two identical daughter cells
• Mitosis


  1. Chromosomes line up at cell centre

  2. Chromosomes pulled to opposite ends

  3. New nuclei form

  4. Cytoplasm and cell membrane divide
• Stem cells


  Undifferentiated cells that can differentiate into different cell types
• Embryonic stem cells can differentiate into any cell type, while adult stem cells can only differentiate into certain cell types
• Stem cells can be grown in labs to produce clones or be differentiated into specialised cells for medical use
• There are ethical concerns around the use of embryonic stem cells as they are derived from human embryos
• Stem cells have potential to treat diseases by replacing faulty cells, but also carry risks of rejection and transmission of viruses
• Binary fission


  1. DNA and plasmids replicate

  2. Cell grows in size

  3. DNA strands move to opposite poles

  4. Cytoplasm divides

  5. Two daughter cells formed
• Under favourable conditions, bacteria can divide very quickly, as little as every 20 minutes
• Culturing microorganisms (practical)


  1. Inoculate agar plate with bacteria

  2. Place antibiotic disc on plate

  3. Incubate plate

  4. Observe bacterial growth
• Cloning plants with meristems


  • Can be used to produce clones of whole plants quickly and cheaply, e.g. to save rare species
  • Can also grow plants with desired features like disease resistance on a large scale
• Binary fission


  1. Circular DNA and plasmids replicate

  2. Cell grows in size

  3. DNA strands move to opposite poles

  4. Cytoplasm divides, producing two daughter cells with one copy of DNA and variable plasmid copies
• Under favourable conditions, bacteria can divide very quickly, as little as 20 minutes
• When conditions become unfavourable, bacterial cells stop dividing and will eventually die