Cell Structure (Cambridge (CIE) IGCSE Biology)

Animal & plant cells

 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

Plant and animal cell structure and function

Cell structure diagram

An animal and plant cell as seen under a light microscope

Plant cell structure and function

Bacteria cells

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

• 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