Common Features: Eukaryotic Organisms (Edexcel IGCSE Biology)

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Common Features of Eukaryotic Organisms: Basics

  • All living organisms can be grouped or 'classified' using a classification system that consists of five kingdoms
  • These five kingdoms are:
    • Animals
    • Plants
    • Fungi
    • Protoctists
    • Prokaryotes
  • The first four kingdoms in this list (the animals, plants, fungi and protoctists) can actually be grouped together, as they are all eukaryotic organisms (also known as eukaryotes)

The Kingdoms of Eukarya

Animals, plants, fungi and protoctists are all eukaryotes.

  • Eukaryotic organisms can be multicellular or single-celled and are made up of cells that contain a nucleus with a distinct membrane

An animal and plant cell as seen under a light microscope

An animal cell (left) and plant cell (right) as seen under a light microscope. They are both eukaryotic cells as they both have a distinct membrane-bound nucleus.

  • Prokaryotic organisms (also known as prokaryotes) are in a separate kingdom and are different from eukaryotes as they are always single-celled and do not contain a nucleus (instead, the nuclear material of prokaryotic cells is found in the cytoplasm)
    • Bacteria are prokaryotic organisms
  • Prokaryotic cells are substantially smaller than eukaryotic cells

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

A typical animal cell

Cell structures found in both animal and plant cells table

Structure Function
Nucleus
  • Contains the genetic material (DNA) which controls the activities of the cell
Cytoplasm
  • A gel-like substance composed of water and dissolved solutes
  • Supports internal cell structures
  • Site of many chemical reactions, including anaerobic respiration
Cell membrane
  • Holds the cell together, separating the inside of the cell from the outside
  • Controls which substance can enter and leave the cell
Ribosomes
  • Found in the cytoplasm
  • Site of protein synthesis
Mitochondria
  • Site of most of the reactions involved in aerobic respiration, where energy is released to fuel cellular processes
  • Cells with high rates of metabolism (carrying out many different cell reactions) have significantly higher numbers of mitochondria than cells with fewer reactions taking place

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
    • They feed by photosynthesis
    • They store carbohydrates as starch or sucrose
    • They do not have nervous coordination

A typical plant cell

A typical plant cell

Cell structures found only in plant cells table

Structure Function
Cell wall
  • Made of cellulose (a polymer of glucose)
  • Gives the cell extra support, defining its shape
Chloroplasts
  • Contains green chlorophyll pigments (to absorb light energy) and the enzymes needed for photosynthesis
A permanent vacuole
  • Contains cell sap; a solution of sugars and salts dissolved in water
  • Used for storage of certain materials
  • Also helps support the shape of the cell

Examiner Tip

You need to be able to recognise, draw and interpret images of cells, so practice drawing and labelling animal and plant cells as part of your revision.

Fungi

  • Main features of fungi:
    • They are usually multicellular but some are single-celled (e.g. yeast)
    • Multicellular fungi are mainly made up of thread-like structures known as hyphae that contain many nuclei and are organised into a network known as a mycelium
    • Their cells contain a nucleus with a distinct membrane
    • Their cells have cell walls made of chitin (chitinous cell walls)
    • Their cells do not contain chloroplasts (so they cannot carry out photosynthesis)
    • They feed by secreting extracellular digestive enzymes (outside the mycelium) onto the food (usually decaying organic matter) and then absorbing the digested molecules. This method of feeding is known as saprotrophic nutrition
    • Some fungi are parasitic and feed on living material
    • Some fungi store carbohydrates as glycogen
    • They do not have nervous coordination
    • Examples of fungi include: moulds, mushrooms, yeasts

A typical fungal cell

A typical fungal cell

Fungi Structure

The typical structure of a multicellular fungus e.g. Mucor (bread mould)

Protoctists

  • Main features of protoctists:
    • The protoctists are a very diverse kingdom of organisms that don't really belong in any of the other eukaryotic kingdoms (animals, plants and fungi)
    • They are mainly microscopic and single-celled but some aggregate (group together) into larger forms, such as colonies or chains of cells that form filaments
    • Their cells contain a nucleus with a distinct membrane
    • Some have features making them more like animal cells e.g. Plasmodium (the protoctist that causes malaria)
    • Some have features, such as cell walls and chloroplasts, making them more like plant cells e.g. green algae, such as Chlorella
    • This means some protoctists photosynthesise and some feed on organic substances made by other living things
    • They do not have nervous coordination
    • Examples of protoctists include: amoeba, Paramecium, Plasmodium, Chlorella

Two examples of protoctist cells

Two examples of protoctist cells

Examiner Tip

You need to be able to recognise, draw and interpret images of cells, so practice drawing and labelling fungal cells and protoctist cells as part of your revision.

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Lára

Author: Lára

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.