Contents page . . . Get in contact Next Unit?


This unit covers some organisms which Biologists describe as "simple" because they are not particularly specialised and complicated in structure, and so can be fairly easily studied (usually using the microscope). Although not so "advanced" as some other groups, each one carries out the 7 processes of life, perhaps with certain limitations.

Most of them are fascinating to study in their own right. Despite their small size, many have great economic and social importance. They also challenge some of the apparently straightforward assumptions such as the distinction between plants and animals, and how to carry out classification.

This unit does not cover bacteria and viruses , which are even simpler and smaller organisms.


also known as protozoa (plural) - newer term Protoctists

- SINGLE CELLED MICROSCOPIC "ANIMALS" (some on borderline with plants)

- Usually in WATER or as PARASITES inside larger organisms

e.g. Amoeba, Paramecium, Euglena (?), & causative organisms of malaria, sleeping sickness, etc.

Why do protozoans only seem to have latin names, not everyday ones?


FUNGI (plural)

(fungus - singular ; their study is called mycology)

- NON-GREEN "PLANTS" - do not contain chlorophyll, so they cannot make their own food by photosynthesis like other plants. Instead, many of them ( saprophytes) break down dead things, such as plant and animal remains. Others ( parasites ) grow on living plants and animals, causing diseases. Fungi can cause spoilage by growing on stored food and most "natural" products. They are of enormous importance in recycling of nutrients in nature. Some are quite easily grown, and are used in fermentation to make alcoholic drinks, also for antibiotics and new biotechnology industries. In the way they grow and feed, fungi are rather similar to bacteria (which are single celled, much smaller than protozoa and fast growing).

The "feeding" parts of fungi are cylindrical strands called hyphae which grow into their food substances and break it down with enzymes they release, then absorb the soluble results. Sometimes this feeding part (mycelium) is widespread underground but not very easy to see, and in the "higher fungi" these simple threads are built up into special large structures (fruiting bodies). Some of these are very tasty, but some are poisonous. Their biological function is to help to spread the large numbers of tiny spores by which they reproduce.

- "Mushrooms" and "Toadstools", bracket fungi, puffballs, stinkhorns,
- moulds, e.g. Penicillium (different sorts make penicillin and blue cheese), Mucor (the "pinmould"),
- yeasts,
- plant diseases: mildews,ergot, rusts, smuts, potato blight
- animal diseases:
"ringworm", athlete's foot
- some also found in water, e.g. cotton wool disease of fish.

How is it that fungi can grow in the dark, i.e. what is the substitute for light energy?


In what ways are we similar to fungi?
Clue: what do we eat?


ALGAE (plural)

(alga - singular)

Simple plants, without specialisations such as roots or stems or leaves. A very widespread group, able to carry out photosynthesis, so they require light for energy. Can be green, brown or red (blue-green algae are similar but closer to bacteria). Mostly in sea and fresh water. Very important as food for other organisms, and able to reproduce quite fast in ideal conditions.

Great range of size, from single cells to large seaweeds. e.g.:
- (phyto)plankton, Euglena (also thought of as a protozoan), Spirogyra (filamentous), "blanket weed" in ponds, "green water", algal "blooms"
- seaweeds such as bladderwrack, oarweeds etc.(several colours)

Seaweed can be as big as a tree, but are not very specialised for support, with no wood, for example.
How do they get away with it?



(not in most textbooks)

These consist of an alga and a fungus, growing in close combination. Able to survive in hostile conditions, such as on exposed rock (including walls, roofs & gravestones), on tree trunks & beneath snow, and at high altitudes. Easily damaged by atmospheric pollution.

What do you think each partner contributes?



Use words from these lists to label the diagrams below:

cell membrane, contractile vacuole, ectoplasm, endoplasm, food particles, food vacuole, nucleus, pseudopodium


cell wall, chloroplast, cytoplasm, nucleus, vacuole.