Cells

• What are the two main types of microscopes used for studying cells?

  Light microscopes and electron microscopes
• How do light microscopes resolve images?

  They use a pair of convex glass lenses
• What is the resolution limit of light microscopes?

  0.2 µm
• Why is the resolution of light microscopes limited to 0.2 µm?

  Because it is the wavelength of light
• What is the resolution limit of electron microscopes?

  0.1 nm
• What is the formula for calculating magnification in microscopy?

  Magnification = size of image / size of actual object
• What does resolution define in microscopy?

  The minimum distance apart that two objects can be distinguished as separate
• What are the two main types of electron microscopes?

  Transmission electron microscopes (TEM) and scanning electron microscopes (SEM)
• How do electron microscopes differ from light microscopes in terms of their operation?

  They use a beam of electrons focused by electromagnets
• Why is a vacuum environment necessary for electron microscopes?

  To prevent air particles from deflecting the electrons
• How does a Transmission Electron Microscope (TEM) work?

  • A beam of electrons passes through a thin section of a specimen.
  • Areas that absorb electrons appear darker on the electron micrograph.
• How does a Scanning Electron Microscope (SEM) work?

  • A beam of electrons passes across the surface of the specimen.
  • The pattern of scattering builds up a 3D image based on the contours.
• What are the limitations of using electron microscopes?

  • Must be in a vacuum, so living specimens cannot be observed.
  • Requires complex staining, which may introduce artefacts.
  • Specimens must be very thin, especially for TEM.
  • SEM has lower resolving power than TEM, but both exceed light microscopes.
• What is cell fractionation?

  The process of separating different parts and organelles of a cell

  
• What is the most common method of cell fractionation?

  Differential centrifugation

  
• What are the steps of homogenization in cell fractionation?

  1. Cells are blended in a homogeniser to form homogenate.
  2. The homogenate is spun at a slow speed in a centrifuge.
  3. The heaviest organelles, the nuclei, form a pellet at the bottom.
  4. The supernatant is removed and spun faster to sediment the next heaviest organelle.
  5. This process continues to separate organelles by increasing speed.
• Why is the homogenate placed in a cold, buffered solution?

  To prevent organelles from bursting and to inactivate enzymes
• What type of cells are humans made up of?

  Eukaryotic cells
• What are the common features of eukaryotic cells?

  • Contain a nucleus
  • Have membrane-bound organelles
• What structures do prokaryotic cells contain?

  • Cell wall: rigid outer covering made of peptidoglycan.
  • Capsule: protective layer for moisture retention.
  • Plasmid: circular DNA.
  • Flagellum: tail-like structure for movement.
  • Pili: hair-like structures for attachment.
  • Ribosomes: site of protein production.
  • Mesosomes: infoldings for respiration enzymes.
• What are viruses composed of?

  Nucleic acid enclosed in a protective protein coat called the capsid
• How are cells organized in multicellular organisms?

  • Cells form tissues
  • Tissues form organs
  • Organs form systems
• What is the role of mitosis in cell division?

  To produce identical daughter cells for growth and asexual reproduction
• What are the three stages of the cell cycle?

  Mitosis, interphase, and cytokinesis

  
• What are the four stages of mitosis?

  1. Prophase
  2. Metaphase
  3. Anaphase
  4. Telophase

  
• Why is mitosis important for organisms?

  • Growth: produces identical cells for organism growth.
  • Repair: replaces dead tissues with identical cells.
  • Reproduction: single-celled organisms reproduce by mitosis.
• What is binary fission in prokaryotic cells?

  1. Circular DNA replicates and attaches to the cell membrane.
  2. Cell membrane grows between DNA molecules and pinches inwards.
  3. A new cell wall forms, dividing the original cell into two identical daughter cells.
• How do viruses replicate?

  By injecting their nucleic acids into a host cell, which then replicates the virus particles
• What is the structure of biological membranes?

  • Composed of a sea of phospholipids with protein molecules.
  • Partially permeable membrane controlling substance movement.
  • Contains receptors for hormones and enables cell adhesion.
  • Known as the fluid mosaic model due to its structure.

  
• What is the arrangement of phospholipids in the cell membrane?

  • Hydrophilic heads point outwards.
  • Hydrophobic tails point inwards.
  • Allows lipid-soluble molecules to pass through.
• What are the components of the cell membrane?

  1. Proteins: intrinsic and extrinsic, aiding movement and support.
  2. Cholesterol: makes the membrane rigid and prevents leakage.
  3. Glycolipids: act as cell surface receptors and aid cell adhesion.
  4. Glycoproteins: act as receptors and allow cell recognition.
• What are the types of movement through cell membranes?

  • Diffusion: passive movement of small, non-polar molecules.
  • Facilitated diffusion: requires channel proteins for polar molecules.
  • Osmosis: diffusion of water through a partially permeable membrane.
  • Active transport: requires energy to move molecules against concentration gradient.
  • Exocytosis and endocytosis: transport large particles in vesicles.
  • Co-Transport: uses ions to move substances into and out of cells.
• What factors increase the rate of gas exchange by diffusion?

  Increased surface area and decreased diffusion distance
• What process requires energy in the form of ATP?

  Active transport
• What are the main functions of exocytosis and endocytosis?

  • Exocytosis transports large particles out of the cell.
  • Endocytosis transports large particles into the cell using vesicles.
• What is co-transport primarily used for in epithelial cells of the ileum?

  To move substances into and out of cells using ions
• How do sodium and potassium ions affect glucose and amino acid transport in epithelial cells?

  Sodium and potassium ions create a gradient that facilitates the transport of glucose and amino acids into the cell.
• What factors increase the rate of gas exchange by diffusion?

  • Increased surface area
  • Decreased diffusion distance
  • Steeper diffusion gradient
  • Increased temperature
• What are the main disease-causing pathogens in humans?

  Bacteria and viruses
• How do bacteria and viruses differ in terms of genetic material?

  Bacteria have circular DNA, while viruses have nucleic acid that can be DNA or RNA.