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Fungi and protists: Class 11 Biology
General features and classification of protists including Amoeba, Paramecium, Euglena and Plasmodium, and the structure, nutrition, reproduction, classification, uses and harms of fungi, with lichens and mycorrhizae.
Key points
Protists are a varied group of mostly unicellular eukaryotes. Each cell has a nucleus and organelles. They are not plants, animals or fungi, and most live in water or moist places. Some are free living and some are parasites. They are grouped by how they get food and move.
Main groups of protists:
- Protozoa (animal-like): heterotrophs that take in food, such as Amoeba (pseudopodia), Paramecium (cilia) and Plasmodium (no locomotory organ in its adult stage).
- Algae (plant-like): autotrophs with chloroplasts, such as Euglena, diatoms and dinoflagellates.
- Slime moulds and water moulds (fungus-like): feed on dead matter and form spores.
Amoeba moves and feeds by pseudopodia, which are extensions of cytoplasm. It engulfs food by phagocytosis into a food vacuole, digests it and removes waste. A contractile vacuole expels extra water, because the surrounding fresh water enters by osmosis. It reproduces by binary fission. Paramecium is covered with cilia, has a gullet for food, and has two nuclei: a large macronucleus and a small micronucleus.
Euglena has features of both plants and animals. It has chloroplasts and makes food in light, and it has a flagellum and an eyespot (stigma) that senses light. In the dark it can feed by absorbing organic matter. It has no cell wall, only a flexible pellicle.
Protists cause serious diseases. Plasmodium causes malaria and is carried by female Anopheles mosquitoes. Entamoeba histolytica causes amoebic dysentery, spread by contaminated food and water. Trypanosoma causes sleeping sickness and is spread by the tsetse fly. Algae are also useful, because they form the base of food chains in water and give much of the oxygen in air.
Fungi form a separate kingdom of eukaryotes. They have cell walls of chitin and no chlorophyll. They are heterotrophs that feed by absorption: the fungus releases digestive enzymes onto food, then absorbs the small molecules. They store food as glycogen. Examples are yeast, Mucor, Penicillium, mushrooms and Aspergillus.
The body of most fungi is made of thread-like hyphae. A mass of hyphae is a mycelium. In some fungi hyphae have cross walls called septa. In others, such as Rhizopus and Mucor, they have no septa and are called coenocytic, with many nuclei in one cytoplasm. Yeast is unicellular. Fungi grow best in warm, moist, dark places.
Fungi reproduce asexually by spores made in sporangia (Rhizopus) or as conidia (Penicillium), and yeast reproduces by budding. Sexual reproduction occurs when hyphae of different mating types fuse, giving a zygospore or other spore forming structures. Spores are light and spread by wind.
Classification of fungi (main phyla):
- Zygomycota: coenocytic hyphae and zygospores, such as Rhizopus (bread mould).
- Ascomycota: sac fungi with ascospores, such as yeast, Penicillium and Aspergillus.
- Basidiomycota: club fungi with basidiospores, such as mushrooms and toadstools.
Fungi are useful. They decompose dead matter and recycle minerals. Yeast is used in baking and brewing. Penicillium produces the antibiotic penicillin, discovered by Alexander Fleming. Mushrooms are food. Some are harmful: they spoil food, cause plant diseases like rust and smut, and cause human diseases such as ringworm and athlete's foot. Lichens are a partnership of a fungus and an alga or cyanobacterium. They are pioneers on bare rock and indicate clean air. Mycorrhizae are links between fungi and plant roots that help the plant absorb water and minerals.
Study tip: Learn Amoeba, Paramecium, Euglena and Rhizopus with a labelled diagram each, and write one line on how each feeds, moves and reproduces. Keep a short table of diseases with the causative organism, the carrier and the spread. For fungi answers, always use the words hyphae, chitin and absorption.
Definitions and flashcards
Say the meaning first, then open the card to check.
Protist
A mostly unicellular eukaryote that is not a plant, animal or fungus.
Pseudopodium
A temporary extension of cytoplasm used for movement and feeding.
Contractile vacuole
An organelle that pumps excess water out of a freshwater protist.
Hypha
A thread-like filament that makes up the body of a fungus.
Mycelium
A network of hyphae.
Chitin
A tough carbohydrate in the cell wall of fungi.
Coenocytic
Having many nuclei in one continuous cytoplasm without cross walls.
Lichen
A partnership between a fungus and an alga or cyanobacterium.
Budding
Asexual reproduction in which a small outgrowth separates, as in yeast.
Short questions with model answers
These are the kind of questions asked for 2, 3 and 5 marks. Try each one before opening the answer.
Why is Euglena said to be both plant-like and animal-like? (2 marks)
It has chloroplasts and makes food by photosynthesis, like a plant. It has no cell wall, has a flagellum for moving and can feed on organic matter in the dark, like an animal.
What is the function of the contractile vacuole in Amoeba? (2 marks)
It collects excess water that enters the cell by osmosis and expels it. In this way it controls the water balance and stops the cell bursting.
Describe how fungi obtain their food. (3 marks)
Fungi are heterotrophic. Their hyphae release digestive enzymes into the dead matter or host around them, and these break down large molecules. The fungus then absorbs the soluble products through the cell wall and membrane. This is called absorptive nutrition. The extra food is stored as glycogen.
Name one disease caused by each: Plasmodium, Entamoeba histolytica, Trypanosoma. (3 marks)
Plasmodium causes malaria, spread by the Anopheles mosquito. Entamoeba histolytica causes amoebic dysentery, spread by contaminated water or food. Trypanosoma causes sleeping sickness, spread by the tsetse fly.
Describe the structure and reproduction of Rhizopus. (5 marks)
Rhizopus is a bread mould. Its body is a mycelium of branching hyphae with no cross walls. Rhizoids anchor it and absorb food, stolons spread over the surface, and upright sporangiophores carry round sporangia. Asexual reproduction is by spores that form in sporangia, are released when the sporangium bursts and are blown by the wind. Where a spore lands on moist food it grows into a new mycelium. In sexual reproduction, hyphae of opposite mating types fuse and form a thick walled zygospore, which survives bad conditions and later germinates.
What is a lichen? State its importance. (3 marks)
A lichen is a mutual partnership between a fungus and an alga or cyanobacterium. The fungus gives shelter and absorbs water, and the partner makes food by photosynthesis. Lichens are pioneer species on bare rock and help form soil. They are sensitive to sulphur dioxide, so they show air pollution.
Common mistakes
- Saying fungi are plants. They have chitin walls, no chlorophyll and absorb their food.
- Writing that fungi store starch. They store glycogen.
- Mixing up the contractile vacuole with the food vacuole.
- Saying all protists are harmful. Many are useful producers.
- Writing that malaria is caused by the mosquito. It is caused by Plasmodium and only carried by the mosquito.