BIOLOGY · Stage 7 · Chapter 3: Microorganisms and Decomposers
Biology 3.1 Microorganisms — Bacteria, Fungi and Protoctists
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Lesson summary
3.1 Microorganisms — Bacteria, Fungi and Protoctists — Alhussan International Academy — Biology (Stages 7–9) notes: Describe the structure and features of bacteria, fungi and protoctists and distinguish between them.Microorganisms (microbes) = living things too small to be seen w…
- Main groups
- Microscopes
- Growth conditions
- Single cells
- Life processes
- Features of all bacteria
Section 1 of 8What are microorganisms
- Microorganisms (microbes) = living things too small to be seen without a microscope.
- They are typically single-celled and include bacteria, some fungi and viruses.
- Habitat
- they are found nearly everywhere, in soil, water, air and on and inside the body.
- Number
- a person has about 30 to 40 trillion human cells and around 60 to 300 trillion microorganisms living in or on the body.
- Effects
- most are harmless or useful and only a small number cause disease.
- Main groups
- bacteria, fungi and protoctists, and viruses are often studied with them even though they are not cells.
Section 2 of 8Observing microorganisms
- Microscopes
- light and electron microscopes show the structure of microorganisms.
- Culturing
- microorganisms are given the conditions they need to grow and reproduce.
- Once there are enough, the colonies can be seen without a microscope.
- Culturing is very important when studying bacteria and fungi.
- Growth conditions
- microorganisms need warmth, water and food to grow.
- Food spoils faster in warm, moist places, and drying, cooling and salting preserve it.
Section 3 of 8Bacteria
- Size
- bacteria are some of the smallest living organisms, between 0.2 and 2.0 µm in diameter.
- Single cells
- they come in many shapes but are all single cells.
- The three shapes are spheres (cocci), rods (bacilli) and spirals.
- Life processes
- they feed, respire, excrete carbon dioxide and other wastes, grow and reproduce by splitting in two.
- Features of all bacteria
- A loop of genetic material lies loose in the cytoplasm, with no nucleus.
- A cell wall has a very different structure from a plant cell wall.
- A cell membrane and cytoplasm are present.
- Features of many bacteria
- Plasmids are small extra rings of genetic information.
- A slime capsule protects against drying out and attack by other cells.
- Flagella beat to move the bacterium along.
- Binary fission
- the splitting of a cell into two, which can happen every 20 minutes in warm conditions with plenty of food.
- This is how a few bacteria can become millions in a day.
Section 4 of 8Fungi
- Variety
- some fungi are microorganisms but others grow very big, such as toadstools.
- Cells
- fungal cells have a nucleus, cytoplasm, a cell membrane and a cell wall made of chitin, not cellulose.
- Nutrition
- fungi have no chloroplasts, so they cannot photosynthesise.
- They release enzymes onto food and absorb the digested nutrients.
- Yeast
- a single-celled fungus about 4 µm across and round in shape.
- It reproduces by budding, in which the cell splits into two.
- Moulds and mushrooms
- they are made of a tangle of microscopic threads called hyphae that absorb food from the surroundings.
- They reproduce by making spores.
Section 5 of 8Protoctists and viruses
1Protoctists4 points
- a varied group, mostly single-celled, with a nucleus.
- Amoeba behaves like an animal by taking in food.
- Chlorella has chloroplasts and photosynthesises like a plant.
- Plasmodium causes the disease malaria.
2Viruses3 points
- much smaller than bacteria, about 0.01 to 0.1 µm.
- They are made of genetic material inside a protein coat.
- They invade living organisms and turn them into virus-making factories.
Section 6 of 8Comparing microorganisms
| Feature | Bacteria | Fungi | Protoctists |
|---|---|---|---|
| Nucleus | No | Yes | Yes |
| Cell wall | Yes, not cellulose | Yes, chitin | Some |
| Chloroplasts | No | No | Some |
| Typical size | 0.2 to 2 µm | Larger | Larger |
| Example | Lactobacillus | Yeast | Amoeba |
Section 7 of 8Bacterial, animal and plant cells
| Feature | Bacterial cell | Animal cell | Plant cell |
|---|---|---|---|
| Nucleus | No, DNA loose | Yes | Yes |
| Cell wall | Yes, not cellulose | No | Yes, cellulose |
| Cell membrane | Yes | Yes | Yes |
| Cytoplasm | Yes | Yes | Yes |
| Mitochondria | No | Yes | Yes |
| Chloroplasts | No | No | Yes, in green parts |
| Size | 0.2 to 2 µm | 10 to 30 µm | 10 to 100 µm |
Section 8 of 8Culturing microorganisms safely
- Use agar jelly in a Petri dish, which provides nutrients and moisture.
- Sterilise the dish and the loop used to transfer the culture (aseptic technique).
- Tape the lid closed but do not seal it fully, so oxygen can enter and harmful anaerobic microbes do not grow.
- Incubate the dish at no more than 25 °C.
- Count the colonies, each of which grows from a single cell, and measure their sizes to compare conditions or disinfectants.
- Safety
- wash hands, clean the bench afterwards and never open a dish that has been incubated.
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