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Biology · Grades 7–10

Microorganisms and classification

Avoid treating all microbes as harmful or all microbes as bacteria.

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Learn the idea

Diversity

Microorganisms include bacteria, many fungi and protists; viruses are studied alongside them but are not cells.

Bacteria

Bacteria are prokaryotic cells without a membrane-bound nucleus.

Roles

Microbes can act in decomposition, food webs and beneficial associations as well as disease.

Safety

Use descriptions and supplied data; do not culture or handle unknown microbes for this worksheet.

Worked examples

Are all microorganisms bacteria?

The category includes several biological groups.

No.

Which feature fits bacteria?

Bacteria are prokaryotic cells.

They lack a membrane-bound nucleus.

Check your understanding

  1. Are viruses cells in the standard school model?

    1. Only plant viruses are cells.
    2. Yes, all have ribosomes and cytoplasm.
    3. No.

  2. Give one beneficial ecological role of microorganisms.

  3. A supplied model count doubles from 50 to 100 and then doubles once more. What is the final count?

Answers and marking notes

Answers and marking notes
  1. No.

    Viruses are acellular and depend on host systems for replication.

  2. Decomposition recycles nutrients.

    Accept relevant roles such as nitrogen cycling or symbiotic associations.

  3. 200

    100 × 2 = 200; this is abstract arithmetic, not a culturing instruction.

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.

Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.