This topic accounts for approximately 8% of your exam marks.
stable
Low
Stable8%
MRS GRENC (8 characteristics) listed in almost every series, usually 1 to 2 marks.
All known living organisms can be sorted into five kingdoms:
Plants, Animals, Fungi, Protoctists and Prokaryotes
The first four (plants, animals, fungi and protoctists) all have cells with a true nucleus, so they are called eukaryotes. Only prokaryotes have cells without a true nucleus.
Eukaryotes vs prokaryotes: the headline difference
Eukaryotes
Prokaryotes
Cell size
Larger (typically 10–100 μm)
Much smaller (typically 1–10 μm)
Nucleus
Yes, a true nucleus surrounded by a membrane
No; the DNA floats free in the cytoplasm
Genetic material
Long linear chromosomes inside the nucleus
A single circular chromosome in the cytoplasm, often with small extra rings of DNA called plasmids
Other membrane-bound organelles
Yes: mitochondria, chloroplasts, ER, Golgi etc.
None at all
Cell wall?
Some have one (plants, fungi); animals do not
Always; all bacteria have a cell wall made of peptidoglycan (not cellulose or chitin)
Single-celled / multicellular?
Can be either
Always single-celled
Side-by-side eukaryotic and prokaryotic cell comparison
Animals
Multicellular, built from many cells working together
Cells have a nucleus and no cell wall
Cells have no chloroplasts, so animals cannot photosynthesise
Feed by eating other organisms (heterotrophic). They digest food in a gut and absorb the products
Often store carbohydrate as glycogen in the liver and muscles
Have nervous coordination to respond quickly to stimuli
Can usually move from place to place (locomotion)
Examples: humans, dogs, fish, insects, worms
Plants
Multicellular
Cells have a nucleus
Cells have cell walls made of cellulose (a rigid carbohydrate)
Cells contain chloroplasts, so plants are autotrophic and feed by photosynthesis
Store carbohydrate as starch in roots and tubers, or as sucrose in fruit and storage tissue
No nervous coordination; responses to stimuli are slower and chemical
Are rooted and unable to relocate, although they can reorient themselves (for example, shoots bending towards light)
Examples: rose bushes, oak trees, grasses, ferns, cabbages
Fungi
Usually multicellular, but some (e.g. yeast) are single-celled
Multicellular fungi are built from long thread-like cells called hyphae, which form a tangled network called the mycelium. Each hypha contains many nuclei stretched along its length
Cells have a nucleus
Cells have cell walls made of chitin (the same material as insect exoskeletons), not cellulose
Cells contain no chloroplasts, so fungi cannot photosynthesise
Feed by saprotrophic nutrition: they release digestive enzymes out onto the surrounding food (dead organic matter), the enzymes break the food down to small molecules outside the fungus, and the fungus then absorbs the digested molecules
Some fungi are parasitic and feed on living organisms (e.g. athlete's foot fungus feeding on human skin)
Often store carbohydrate as glycogen
No nervous coordination
Examples: mushrooms, mould (e.g. Mucor), yeast (used in baking and brewing)
Protoctists
A very mixed bag. The protoctists are the "kingdom of leftovers", containing every eukaryote that is not clearly a plant, animal or fungus
Mostly single-celled and microscopic, but some form colonies or chains of cells
Cells have a nucleus
Some protoctists are plant-like: they have cellulose cell walls and chloroplasts, and they photosynthesise. Example: Chlorella (a green alga)
Some protoctists are animal-like: no cell walls, no chloroplasts, and they feed on other organisms. Example: Plasmodium (the malaria parasite)
No nervous coordination
Examples: Amoeba (single-celled animal-like), Paramecium (a swimming cilia-covered animal-like protoctist), Plasmodium (parasite that causes malaria), Chlorella (single-celled plant-like alga)
Prokaryotes
Always single-celled and microscopic
Cells have no nucleus. The DNA is a single circular chromosome sitting free in the cytoplasm, sometimes with smaller circular pieces called plasmids
No membrane-bound organelles at all (no mitochondria, no chloroplasts, no nucleus)
Have a cell wall (made of peptidoglycan, not cellulose or chitin), a cell membrane inside the wall, and cytoplasm
Feed in many different ways:
Some photosynthesise even though they have no chloroplasts. They use chlorophyll-like pigments dissolved in the cytoplasm instead
Most are heterotrophs, taking nutrients from the bodies of other organisms (alive or dead)
Those that break down dead organic matter are called saprobionts (or decomposers); they recycle the building blocks of life back into the soil
The only kingdom in which all members are prokaryotes is Bacteria
Examples of bacteria:
Lactobacillus bulgaricus: rod-shaped; used to make yoghurt from milk