Notes

• 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 to resolve images that are 0.2 µm apart
• What is the reason for the resolution limit of light microscopes?

  The resolution is limited by the wavelength of light
• What is the resolution capability of electron microscopes?

  Electron microscopes can distinguish between items 0.1 nm apart
• How can the magnification of an image seen through a microscope be calculated?

  Magnification = size of image / size of real object
• What is resolution in the context of microscopy?

  Resolution is the minimum distance apart that two objects can be distinguished as separate objects in an image
• 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?

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

  A vacuum is needed 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 produced

  
• How does a Scanning Electron Microscope (SEM) work?

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

  • Must be in a vacuum, so living specimens cannot be observed
  • Requires a complex staining process that 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?

  Cell fractionation is the process of separating different parts and organelles of a cell for study
• What is the most common method of cell fractionation?

  Differential centrifugation
• What are the steps involved in the process of homogenization during 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. Heaviest organelles (nuclei) form a pellet at the bottom
  4. Supernatant is removed and spun faster to sediment the next heaviest organelle (mitochondria)
  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, inactivate enzymes, and maintain pH
• What type of cells are humans made up of?


  Humans are made up of eukaryotic cells
• What is the ultrastructure of eukaryotic cells?

  Ultrastructure refers to the detailed structure of cells obtained using a microscope
• What are the components of the nucleus in eukaryotic cells?


  • Double membrane called the envelope
  • ~3000 nuclear pores
  • Contains chromatin and a nucleolus
  • Nucleoplasm makes up the bulk of the nucleus
• What is the function of the rough endoplasmic reticulum (RER)?

  • Series of flattened sacs with ribosomes on the surface
  • Folds and processes proteins made on the ribosomes
• What is the function of the smooth endoplasmic reticulum (SER)?

  • System of membrane-bound sacs
  • Produces and processes lipids
• What is the function of the Golgi apparatus?

  • Series of fluid-filled, flattened & curved sacs
  • Processes and packages proteins and lipids
  • Produces lysosomes
• What are the key features of mitochondria?

  • Oval-shaped, bound by a double membrane
  • Inner membrane folded into cristae
  • Contains a matrix with enzymes for respiration
• What are centrioles and their function?

  • Hollow cylinders containing microtubules
  • Involved in producing spindle fibres for cell division
• What are ribosomes and their function?

  • Composed of two subunits
  • Site of protein production
• What are lysosomes and their function?


  • Vesicles containing digestive enzymes
  • Bound by a single membrane
• What are the components of prokaryotic cells?

  • Cell wall made of peptidoglycan
  • Capsule for moisture retention and adhesion
  • Plasmid (circular DNA)
  • Flagellum for movement
  • Pili for attachment
  • Ribosomes for protein production
  • Mesosomes for respiration
• What are the characteristics of viruses?

  • Non-living structures
  • Consist of nucleic acid (DNA or RNA)
  • Enclosed in a protective protein coat (capsid)
  • Sometimes covered with a lipid layer (envelope)

  
• 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?

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

  Mitosis, interphase, and cytokinesis
• What happens during interphase of the cell cycle?

  • The cell grows and prepares to divide
  • Chromosomes and some organelles are replicated
  • Chromosomes begin to condense
• What occurs during cytokinesis?

  • Parent and replicated organelles move to opposite sides of the cell
  • Cytoplasm divides, producing two daughter cells
• Why is mitosis important for growth, repair, and reproduction?

  • Growth: produces identical cells for organism growth
  • Repair: replaces dead tissues with identical cells
  • Reproduction: single-celled organisms reproduce by dividing into two identical daughter cells

  
• What is binary fission?

  • Process by which prokaryotic cells divide
  • Circular DNA replicates and attaches to the cell membrane
  • Cell membrane grows and pinches inwards, dividing the cytoplasm
  • New cell wall forms between DNA molecules, resulting in two identical daughter cells

  
• Why do viruses not undergo cell division?

  Viruses are non-living and rely on host cells to replicate
• 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

  
• 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, but not water-soluble molecules
  • Membrane is flexible and self-sealing

  
• What are the components of the cell membrane?

  1. Proteins (intrinsic and extrinsic)
  2. Cholesterol (makes membrane rigid and prevents leakage)
  3. Glycolipids (cell surface receptors and adhesion)
  4. Glycoproteins (cell surface receptors and neurotransmitters)

  
• What are the types of movement through the cell membrane?

  • 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, especially in epithelial cells