Cell Structure (Cambridge International IGCSE Biology)

Animal & plant cells

Spec point — 2.1.1 · Describe and compare the structure of a plant cell with an animal cell, limited to: cell wall, cell membrane, nucleus, cytoplasm, chloroplasts, ribosomes, mitochondria, vacuoles

Animal cell structure

• The main features of animal cells:

  • they contain a nucleus with a distinct membrane
  • cells do not have cellulose cell walls
  • their cells do not contain chloroplasts (so they are unable to carry out photosynthesis)
  • they contain carbohydrates stored as glycogen

Animal cell diagram

A typical animal cell

Plant cell structure

• The main features of plant cells:

  • they contain a nucleus with a distinct membrane
  • cells have cell walls made out of cellulose
  • they contain chloroplasts (so they can carry out photosynthesis)
  • carbohydrates are stored as starch or sucrose

Plant cell diagram

A typical plant cell

Animal and plant cell structure and function table

Cell structure diagram

An animal and plant cell as seen under a light microscope

Additional plant cell structure and function table

Bacteria cells

Spec point — 2.1.1 · Describe the structure of a bacterial cell, limited to: cell wall, cell membrane, cytoplasm, ribosomes, circular DNA, plasmids

Bacteria cell structure

• 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)

Bacteria cell diagram

A typical bacterial cell

Identifying cell structures & function

Spec point — 2.1.1 · Identify the cell structures listed in diagrams and images of plant, animal and bacterial cells Describe the functions of the structures in plant, animal and bacterial cells

Identifying cell structures & function

• 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

Identifying cell structures under a microscope

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