1.1 Cell structure

• What are the differences between eukaryotic and prokaryotic cells?

  Prokaryotic cells are much smaller than eukaryotic cells.

  Eukaryotic cells contain membrane bound-organelles and a nucleus containing genetic material, while prokaryotes do not.
• What is the prokaryotic cell wall composed of?

  Peptidoglycan
• How is genetic information stored in a prokaryotic cell?

  Found free within the 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 order of magnitude?

  A power to the base 10 used to quantify and compare size.
• What is a micrometre (um)?

  1 × 10-6 metres
• What is a nanometre (nm)?

  1 x 10-9 metres
• List the components of both plant and animal cells

  (5)

  • Nucleus

  • Cytoplasm

  Cell membrane

  • Mitochondria

  • Ribosomes
• List the additional cell components found in plant cells (3)

  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• 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.

  Transport medium.
• 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 later stages of aerobic respiration in which ATP is produced.
• What is the function of the ribosomes?

  Joins amino acids in a specific order during translation for the synthesis of proteins.
• What is the plant cell wall made of?

  Cellulose
• What is the function of the plant cell wall?

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

  Cell sap (a solution of salts, sugars and organic acids).
• What is the function of the permanent vacuole?

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

  Site of photosynthesis
• Describe how sperm cells in animals are adapted to their function

  • Haploid nucleus contains genetic information.
  • Tail enables movement.
  • Mitochondria provide energy for tail movement.
  • Acrosome contains enzymes that digest the egg cell membrane.
• Describe how nerve cells in animals are adapted to their function

  • Long axon allows electrical impulses to be transmitted all over the body from the central nervous system.
  • Dendrites from the cell body connect to and receive impulses from other nerve cells, muscles and glands.
  • Myelin sheath insulates the axon and speeds up the transmission of impulses along the nerve cell.
• Describe how muscle cells are adapted to their function

  • Arrangement of protein filaments allows them to slide over each other to produce muscle contraction.
  • Mitochondria to provide energy for muscle contraction.
  • Merged cells in skeletal muscle allow muscle fibre contraction in unison.
• Describe how root hair cells in plants are adapted to their function

  • Large surface area to absorb nutrients and water from surrounding soil.
  • Thin walls that do not restrict water absorption.
• Describe how xylem cells in plants are adapted to their function

  • No upper or lower margins between cells to provide a continuous route for water to flow.
  • Thick, woody side walls strengthen their structure and prevent collapse.
• Describe how phloem cells in plants are adapted to their function

  • Sieve plates let dissolved amino acids and sugars be transported up and down the stem.
  • Companion cells provide energy needed for active transport of substances along the phloem.
• What is cell differentiation?

  The process by which cells become specialised.
• Why is cell differentiation important?

  Allows production of different tissues and organs that perform various vital functions in the human body.
• At what point in their life cycle do most animal cells differentiate?


  Early in their life cycle
• For how long do plant cells retain the ability to differentiate?

  Throughout their entire life cycle
• What is the purpose of cell division in mature animals?

  Repair and replacement of cells
• What changes does a cell go through as it differentiates?

  Becomes specialised through acquisition of different sub-cellular structures to enable a specific function to be performed by the cell.
• Define magnification

  The number of times bigger an image appears compared to the size of the real object.
• Define 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? (4)

  • Inexpensive
  • 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.
• Name the two types of electron microscope

  Transmission electron microscope (TEM)

  Scanning electron microscope (SEM)
• What is the advantage of electron microscopes?

  Greater magnification and resolution.