Cells and Microscopy

• State the two types of cells.

  Eukaryotic (animals and plants) and prokaryotic.
• What is the difference between a eukaryotic and a prokaryotic cell?

  A eukaryotic cell contains a nucleus and membrane-bound organelles. A prokaryotic cell does not.
• List the components of both plant and animal cells. (5)

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• How is genetic information stored in a eukaryotic cell?

  Within the nucleus, arranged in chromosomes.
• Other than storing genetic information, what is the function of the nucleus?

  Controls cellular activities
• Describe the structure of the cytoplasm.

  • Fluid component of the cell
  • Contains organelles, enzymes and dissolved ions and nutrients
• What is the function of the cytoplasm?

  Site of cellular reactions e.g. first stage of respiration.
• What is the function of the cell membrane?

  Controls the entry and exit of materials into and out of the cell.
• What is the function of the mitochondria?

  Site of aerobic respiration and releases energy from respiration.
• What is the function of the ribosomes?

  Joins amino acids in a specific order during translation (protein synthesis)
• Which organelles are found in plant cells only? (3)

  • Large, permanent vacuole
  • Cell wall
  • Chloroplasts
• What is the cell wall made of?

  Cellulose
• What is the function of the cell wall?

  • Provides strength
  • Prevents the cell bursting when water enters by osmosis
• What does the permanent vacuole contain?

  Cell sap.
• What is the function of the permanent vacuole?

  Supports the cells, maintaining its turgidity
• What is the function of the chloroplasts?

  Site of photosynthesis
• When looking at a cell using a light microscope, why do chloroplasts appear green?

  Contains chlorophyll, a green pigment
• List the organelles found in prokaryotic cells (6)

  • Chromosomal DNA
  • Plasmid DNA
  • Cell wall
  • Cell membrane
  • Ribosomes
  • Flagella
• How is genetic information stored in a prokaryotic cell?

  Found free within cytoplasm as:

  • Chromosomal DNA (single large loop of circular DNA)
  • Plasmid DNA
• What are plasmids?

  • Small circular loops of DNA found free in the cytoplasm and separate from the main DNA
  • Carry genes that provide genetic advantages e.g. antibiotic resistance
• What is a flagellum?

  • Long, rotating, 'whip-like' tail
  • Enables bacteria to move
• What is a haploid cell?

  A haploid cell is a cell that contains only one set of chromosomes e.g. 23 chromosomes in humans
• What is a diploid cell?

  A diploid cell is a cell that contains two sets of chromosomes e.g. 46 chromosomes in humans
• What are gametes?

  • Reproductive cells (e.g. egg and sperm cells)
  • Haploid
• Describe sexual reproduction in terms of chromosome number.

  • Two haploid gametes fuse
  • Resulting embryo has two chromosomes for each gene and two copies of each allele and is therefore diploid.
• Describe how egg cells are adapted to their function.

  • Haploid nucleus contains genetic material
  • Mitochondria in the cytoplasm produce energy for the developing embryo
  • Cytoplasm contains nutrients for the developing embryo
  • Cell membrane harden after fertilisation, preventing entry of other sperm and ensuring the zygote is diploid
• Describe how sperm cells are adapted to their function.

  • Haploid nucleus contains genetic information
  • Tail enables movement
  • Lots of mitochondria to provide energy for movement
  • Acrosome contains enzymes that digest the egg cell membrane
• Where are ciliated epithelial cells found?

  Found lining the surface of structures such as the respiratory tract and uterus.
• Describe the function of ciliated epithelial cells lining the airways.

  Move in synchronised waves to beat mucus (containing dirt and pathogens) up to the back of the throat where it can be swallowed.
• What is magnification?


  The number of times bigger an image appears compared to the actual size of the specimen.
• How can total magnification of an image be calculated from lens powers?

  Total magnification = eyepiece lens magnification x objective lens magnification
• How can the magnification of an image be calculated?

  Magnification = image size / actual size
• What is resolution?

  The smallest distance between two objects that can be distinguished.
• How does a light microscope work?

  Passes a beam of light through a specimen, which travels through the eyepiece lens, allowing the specimen to be observed
• What are the advantages of light microscopes?

  • Cheap
  • Easy to use
  • Portable
  • Observe both dead and living specimens
• What is the disadvantage of light microscopes?

  Limited resolution
• How does an electron microscope work?

  It uses a beam of electrons which are focused using magnets. The electrons hit a fluorescent screen which emits visible light, producing an image.
• What is the advantage of electron microscopes?

  Greater magnification and resolution.
• Why do electron microscopes have a greater magnification and resolution?

  They use a beam of electrons which has a shorter wavelength than photons of light
• How have electron microscopes enabled scientists to develop their understanding of cells?

  • Allows small sub-cellular structures (e.g. mitochondria, ribosomes) to be observed in detail
  • Enable scientists to develop more accurate explanations about how cell structure relates to function