Cell Structure (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

Animal cells

• Animal cells have the following structural features:
  
  • A cell membrane that separates them from their surroundings
  • A gel-like liquid known as cytoplasm
  • A nucleus
  • Mitochondria (singular mitochondrion)
  • Many tiny ribosomes

Animal cells have a cell membrane, cytoplasm, nucleus, mitochondria and ribosomes

Plant cells

• Plant cells share the features of animal cells, so they contain:
  • Cell membrane
  • Cytoplasm
  • Nucleus
  • Mitochondria
  • Ribosomes
• Plant cells also have some structural features that are not present in animal cells:
  • A cell wall made of cellulose
  • Large structures called chloroplasts that contain the green pigment chlorophyll
  • A permanent vacuole

Plant cells have all of the features found in animal cells, as well as a cellulose cell wall, chloroplasts and a permanent vacuole

Comparing animal and plant cell structures

Comparing animal and plant cell structure diagram

Animal and plant cells have some features in common, while other features are found only in plant cells

• Bacteria are microscopic, single-celled organisms
• They have a cell structure that is distinct from that of animals and plants: 
• Features of bacterial cells include:
  • Bacterial cells contain a cell membrane, and have cytoplasm and ribosomes
  • Bacterial cells have cell walls made of a chemical called peptidoglycan; this is different to the cellulose cell walls of plants
  • The DNA of bacteria is circular
  • Some bacteria have small loops of DNA known as plasmids
• Bacteria lack some features that are present in animal and plant cells:
  • They do not contain internal membranes, so they lack:
    • A nucleus
    • Mitochondria
    • Chloroplasts

Bacteria have a cell wall, cell membrane, cytoplasm, ribosomes, circular DNA and, in some cases, plasmids

Identifying cellular structures

• It is possible to identify cellular features in diagrams and when looking at microscope images
• The structures that are visible depend on the magnification at which a cell is being viewed, e.g.
  • Under a light microscope structures are viewed at a relatively low magnification, so it is possible to view:
    • Nucleus
    • Chloroplasts
    • The position of the cytoplasm, cell membrane and cell walls, but no details of these structures
  • Under an electron microscope much higher magnification can be achieved, so it is possible to view:
    • Mitochondria
    • Ribosomes
    • Details of structures, e.g. cell walls and chloroplasts

The structures visible in animal and plant cells will differ depending on the type of microscope used

Functions of cellular structures