Year 7 Science · Unit 1 · Lesson 5

Microorganisms

Foundation Worksheet

Name

Date

Class

Learning Goals

Name the four groups of microorganisms and place a named microbe in its group.
Give useful and harmful examples of microbes.
Use data to explain why decomposers are essential.

Warm Up

Fill the gap

Choose the correct word from the word bank. Each word is used once. Two words are not needed: cross them out.

host vaccines nucleus protein alive DNA antibiotics RNA cells

A virus is a tiny package of genetic material wrapped in a coat. It is not made of , and on its own it cannot move, grow, eat or respire, so most biologists say it is not . The genetic material inside the influenza virus is . To make copies of itself, a virus must get inside a living cell and take over its machinery. Medicines called do not work on viruses, so are our best defence against them.

1. State two features that make bacteria different from viruses.

Recall 2 marks

Odd one out

In each row, three microbes belong to the same group (bacteria, viruses, fungi or protists). Circle the one that does not. In the last column, write its group and one reason it does not fit.

Row	Microbes	Odd one out: its group and why
1	E. coli · Streptococcus · SARS-CoV-2 · Mycobacterium tuberculosis
2	bread yeast · Penicillium mould · mushroom · Salmonella
3	Amoeba · Paramecium · Lactobacillus · Plasmodium

Your Turn

Sort it

Is each microbe useful or harmful to people? Write it in the correct box. The boxes do not hold the same number of items.

Salmonella on undercooked chicken bread yeast Plasmodium gut bacteria the fungus that causes tinea soil bacteria that rot dead leaves influenza virus Lactobacillus in yoghurt Penicillium mould that Fleming used to discover penicillin

Useful

Harmful

2. Name one useful fungus and explain how humans use it.

Apply 2 marks

3. E. coli was left out of the sort because it could go in either box. Explain how the same kind of bacterium can be both useful and harmful.

Analyse 2 marks

Go Deeper

Read the data

Scenario: the leaf-bag test

A class filled mesh bags with 20 g of dry gum leaves each. Half the bags were buried in ordinary garden soil. The other half were buried in soil that had been heated to kill the microbes in it. Every two weeks the class dug up one bag of each kind and weighed the leaves left inside.

Table 1. Mass of leaves left in each bag (g)

Week	Ordinary soil	Heated soil (microbes killed)
0	20	20
2	16	20
4	12	20
6	9	19
8	6	19

Source: sample class results.

4. Use Table 1 to work out the mass of leaves that was broken down in the ordinary soil by week 8. Show your working.

Apply 2 marks

Answer g

5. Explain why the leaves in the heated soil hardly changed. Then explain why this matters for a forest. Use the word decomposer.

Analyse 3 marks

Show What You Know

6. Jess says: “All microbes are dangerous. We should kill every one we can.” Explain whether Jess is right. Use examples from at least two different microbe groups.

Analyse 5 marks

Answer Key (for teachers)

Fill the gap

protein; cells; alive; RNA; host; antibiotics; vaccines. Not used: nucleus, DNA.

Question 1

Any two (1 each): a bacterium is a cell, a virus is not; a virus copies itself only inside a host cell; antibiotics work on bacteria, not viruses. [2 marks]

Odd one out

1: SARS-CoV-2, a virus, not a cell (others bacteria). 2: Salmonella, a bacterium (others fungi). 3: Lactobacillus, a bacterium, no nucleus (others protists). [1 mark per row]

Sort it

Useful: bread yeast; gut bacteria; soil bacteria that rot dead leaves; Lactobacillus in yoghurt; Penicillium mould that Fleming used to discover penicillin. Harmful: Salmonella; Plasmodium; the tinea fungus; influenza virus.

Question 2

Bread yeast (1): its CO₂ makes dough rise (1). Or Penicillium: gave penicillin. [2 marks]

Question 3

Gut E. coli is useful (1); another strain on undercooked mince causes food poisoning (1). [2 marks]

Question 4

20 − 6 (1) = 14 g (1). [2 marks]

Question 5

Heating killed the decomposers (bacteria, fungi) (1), so nothing broke the leaves down (1). In a forest, decomposers return nutrients to the soil for new plants (1). [3 marks]

Question 6

Marking guide: 1 position (Jess is wrong); 1 each for two useful microbes from different groups, with their job; 1 for a pathogen and its disease; 1 for a consequence of killing all microbes (nothing would rot). [5 marks]

Model answer: Jess is wrong: only a few microbes are pathogens, such as Salmonella, which causes food poisoning. Gut bacteria aid digestion, yeast makes bread rise and decomposers rot dead matter. If every microbe were killed, dead leaves and animals would never rot and nutrients would never return to the soil for new plants.

Common error: writing that antibiotics cure the flu.