1.1The Nature & Variety of Living Organisms

Characteristics of Living Organisms — Edexcel International GCSE Biology 4BI1 Revision Notes & Topical Questions

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Lesson summary

Characteristics of Living Organisms Edexcel IGCSE Biology 4BI1 notes: List the characteristics shared by all living organisms.All living organisms show the seven life processes (MRS GREN).Eukaryotesplants, animals, fungi and protoctists.Prokaryotesbacteria, with circular chromoso…

Unifying characteristics of living organisms
Common features of eukaryotic organisms — plants
Common features of prokaryotic organisms
Excretion vs egestion
Respiration vs gas exchange
Bacterial cell features

Part 1 of 8Key ideas

All living organisms show the seven life processes (MRS GREN).

Eukaryotes

Eukaryotes plants, animals, fungi and protoctists.

Prokaryotes

Prokaryotes bacteria, with circular chromosomal DNA and plasmids.

Viruses are not living cells; they can only reproduce inside host cells.

Pathogens include some fungi, bacteria, protoctists and viruses.

Plasmodium (a protoctist) causes malaria; Pneumococcus causes pneumonia.

Tobacco mosaic virus causes discolouring of tobacco leaves; HIV causes AIDS.

Part 2 of 8Learning objectives

List the characteristics shared by all living organisms.

Describe the features of plants, animals, fungi and protoctists.

Describe the features of bacteria and viruses.

Give examples of pathogens.

Part 3 of 8Essential knowledge

Essential knowledge

Unifying characteristics of living organisms

Unifying characteristics of living organisms all organisms need nutrition, respire to release energy, excrete waste, respond to their surroundings (sensitivity), move, control internal conditions, reproduce and grow and develop.

Common features of eukaryotic organisms — plants

Common features of eukaryotic organisms — plants multicellular, with chloroplasts for photosynthesis, cellulose cell walls, storing carbohydrate as starch or sucrose.

Animals

Animals multicellular, no chloroplasts, no cell walls, usually have nervous co-ordination and can move; store carbohydrate as glycogen.

Fungi

Fungi cannot photosynthesise; body made of hyphae forming a mycelium; cell walls of chitin; feed saprotrophically by secreting extracellular enzymes; store glycogen. Yeast is single-celled.

Protoctists

Protoctists microscopic single-celled eukaryotes; some have chloroplasts (Chlorella), others are more like animals (Amoeba).

Common features of prokaryotic organisms

Common features of prokaryotic organisms bacteria are single-celled with a cell wall, cell membrane, cytoplasm and plasmids but no nucleus; some have a flagellum. Some photosynthesise but most feed on other organisms, living or dead. Lactobacillus bulgaricus is used to make yoghurt.

Pathogens

Pathogens disease-causing organisms, including fungi, bacteria, protoctists and viruses. Viruses are particles with a protein coat and genetic material; they take over host cells to make more virus particles.

Organisms

Organisms the word covers every living thing, from single bacteria to multicellular plants and animals; classification places organisms into these groups using shared features.

Excretion vs egestion

Excretion removes waste made by chemical reactions in cells, such as carbon dioxide, urea and excess water. Egestion removes undigested food as faeces, which never entered cells, so it is not excretion.

Growth

Growth is a permanent increase in size (or dry mass). Animals stop growing at adulthood, but plants keep adding new shoots, leaves and roots throughout their lives.

Respiration vs gas exchange

Respiration is a chemical reaction in cells that releases energy from glucose. Gas exchange is the diffusion of oxygen in and carbon dioxide out across an exchange surface such as the alveoli or a leaf.

Bacterial cell features

Bacterial cells are much smaller than eukaryotic cells and have no nucleus, mitochondria or other membrane-bound organelles. Their DNA is a single circular chromosome in the cytoplasm, plus plasmids.

Effect of tobacco mosaic virus

The virus stops chloroplasts forming in parts of the leaf, giving a mottled (mosaic) pattern. Less photosynthesis means the plant grows less, so crop yield falls.

Part 4 of 8Process & sequence

- Check whether it is made of cells.
- If cells, check for a nucleus (eukaryote) or none (prokaryote).
- For eukaryotes, check for chloroplasts and cellulose walls (plant).
- Check for hyphae and chitin walls (fungus).
- Otherwise single-celled eukaryote (protoctist) or multicellular animal.
Classifying an organismwrite these steps in this order; each step is a marking point.
1. Is it made of cells?
2. Nucleus present or absent?
3. Chloroplasts and cellulose wall?
4. Hyphae and chitin wall?
5. Assign to kingdom

Part 5 of 8Worked examples

Explain why viruses are not usually classed as living organisms.
- Viruses are not made of cells and cannot carry out life processes such as respiration, nutrition or growth on their own.
  - They can only reproduce inside a living host cell.

Part 6 of 8Summary

- Living things share seven life processes.
- Eukaryotes have a nucleus; prokaryotes do not.
- Fungi feed by saprotrophic nutrition.
- Pathogens can be bacteria, viruses, fungi or protoctists.

Part 7 of 8Keep going

Characteristics of Living Organisms Edexcel IGCSE Biology 4BI₁: what to do next
These Characteristics of Living Organisms Edexcel IGCSE Biology 4BI₁ notes covered the key ideas, worked examples and exam technique for this topic. Check your Characteristics of Living Organisms Edexcel IGCSE Biology 4BI₁ understanding with the practice questions below, then reread any Characteristics of Living Organisms Edexcel IGCSE Biology 4BI₁ point you were unsure about before moving on.
Characteristics of Living Organisms Edexcel IGCSE Biology 4BI₁: revision checklist
- Revise the main Characteristics of Living Organisms Edexcel IGCSE Biology 4BI₁ definitions until you can write them from memory.
- Practice: Characteristics of Living Organisms Edexcel IGCSE Biology 4BI1 practice questions
- Next lesson: 2.1 Levels of Organisation — Notes
- Course: Edexcel International Gcse Biology 4BI1 — all units
- Official syllabus: Pearson Edexcel International GCSEs

Part 8 of 8Compare: Compare

Groups of organisms
Group	Key features	Examples
Plants	Multicellular; chloroplasts; cellulose walls; store starch / sucrose	Maize, peas, beans
Animals	Multicellular; no chloroplasts or walls; nervous co-ordination; store glycogen	Humans, mosquitoes
Fungi	Hyphae forming mycelium; chitin walls; saprotrophic; store glycogen	Mucor, yeast (single-celled)
Protoctists	Mostly microscopic single cells; some plant-like, some animal-like	Chlorella, Amoeba, Plasmodium
Bacteria (prokaryotes)	Single-celled; no nucleus; cell wall; plasmids; some have flagella	Lactobacillus bulgaricus, Pneumococcus
Viruses	Not cells; protein coat; DNA or RNA; parasitic	Influenza, HIV, tobacco mosaic virus

Key terms

Command terms

Give / State / Name

Recall a fact; one idea per mark.

Define

Give the exact meaning using the specification keywords.

Describe

Give an account of what happens / the pattern in data, quoting values; no reasons needed.

Explain

Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.

Suggest

Use knowledge in a new context; more than one answer may be accepted.

Compare

Similarities and differences; each point must refer to both items.

Calculate

Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.

Discuss

Explore the issue from different angles and link the points.

Evaluate / Assess

Weigh strengths and weaknesses and reach a supported judgement.

Deduce

Draw a conclusion from the information given.

Justify

Support a statement/choice with evidence.

Exam technique

Keywords the mark scheme looks for in this lesson

Eukaryote · Prokaryote · Plasmid · Pathogen · Hyphae · Saprotrophic nutrition · Protoctist · Virus · MRS GREN

Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

Use specification keywords exactly (e.g. eukaryotic/prokaryotic, enzyme–substrate complex, active site, complementary).

Link ideas

Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.

Use the information in the question

“discuss/evaluate” answers must use the data provided and match the number of marks.

Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.

Avoid vague words

“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.

Do not extrapolate a graph line beyond the data or to zero unless asked.

Six-mark extended responses are marked on content AND a logical, linked line of reasoning.

Last updated: 18 October 2026