Cell Structure (CIE IGCSE Biology)

Animals

• The main features of animals:
  • They are multicellular
  • Their cells contain a nucleus with a distinct membrane
  • Their cells do not have cellulose cell walls
  • Their cells do not contain chloroplasts (so they are unable to carry out photosynthesis)
  • They feed on organic substances made by other living things
  • They often store carbohydrates as glycogen
  • They usually have nervous coordination
  • They are able to move from place to place

A typical animal cell

Plants

• The main features of plants:
  • They are multicellular
  • Their cells contain a nucleus with a distinct membrane
  • Their cells have cell walls made out of cellulose
  • Their cells contain chloroplasts (so they can carry out photosynthesis)
  • They feed by photosynthesis
  • They store carbohydrates as starch or sucrose
  • They do not have nervous coordination

A typical plant cell

Cell Structures Found in Both Animal and Plant Cells Table

An animal and plant cell as seen under a light microscope

Cell Structures Found Only in Plant Cells Table

• Bacteria, which have a wide variety of shapes and sizes, all share the following biological characteristics:
  • They are microscopic single-celled organisms
  • Possess a cell wall (made of peptidoglycan, not cellulose), cell membrane, cytoplasm and ribosomes
  • Lack a nucleus but contain a circular chromosome of DNA that floats in the cytoplasm
  • Plasmids are sometimes present - these are small rings of DNA (also floating in the cytoplasm) that contain extra genes to those found in the chromosomal DNA
  • They lack mitochondria, chloroplasts and other membrane-bound organelles found in animal and plant cells
•  Some bacteria also have a flagellum (singular) or several flagella (plural). These are long, thin, whip-like tails attached to bacteria that allow them to move
• Examples of bacteria include:
  • Lactobacillus (a rod-shaped bacterium used in the production of yoghurt from milk)
  • Pneumococcus (a spherical bacterium that acts as the pathogen causing pneumonia)

A typical bacterial cell

• Within the cytoplasm, the following organelles are visible in almost all cells except prokaryotes when looking at higher magnification (ie using an electron microscope):
  • Mitochondria (singular: mitochondrion) are organelles found throughout the cytoplasm
  • Ribosomes are tiny structures that can be free within the cytoplasm or attached to a system of membranes within the cell known as Endoplasmic Reticulum
  • Endoplasmic reticulum studded with ribosomes looks rough under the microscope; this gives rise to its name of Rough Endoplasmic Reticulum (often shortened to R.E.R.)
  • Vesicles can also be seen using a higher magnification - these are small circular structures found moving throughout the cytoplasm

Structures in an animal cell visible under a light microscope and an electron microscope

Structures in a plant cell visible under a light microscope and an electron microscope