1.1.1The Nature and Variety of Living Organisms

Characteristics of Living Organisms — Edexcel International GCSE Science Double Award (Modular) - Biology Unit 1 Revision Notes & Topical Questions

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📚 Edexcel International GCSE Science Double Award (Modular) - Biology Unit 1 Hub / Topical Revision

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Part 1 of 7Key ideas

All living organisms show eight characteristics (MRS C GREN), including control of internal conditions.

2Eukaryotes

Eukaryotes plants, animals, fungi and protoctists.

3Prokaryotes

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.

All seven life processes must be shown for something to be described as living; a single process such as movement is never enough on its own.

Respiration releases energy from nutrients inside cells — it is not the same as breathing in and out.

Growth is permanent and includes dry mass, so a cell that only takes up water has not grown.

Excretion removes materials made inside the organism by metabolism, not material simply passed through the gut.

Animals and fungi both store carbohydrate as glycogen; only plants store it as starch or sucrose.

Fungal cell walls are not made of cellulose; plant cell walls are.

Viruses contain RNA or DNA inside a protein coat and take over host cells, but they do not carry out the life processes themselves, so they are not classified as living.

Part 2 of 7Learning 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 7Essential 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.

The seven life processes, individually

Movement an action that causes a change of position or place.
Respiration the breakdown of nutrients in cells to release energy.
Sensitivity detecting a stimulus and making an appropriate response.
Growth a permanent increase in size and dry mass.
Reproduction making more organisms of the same kind.
Excretion removing toxic materials, waste products of metabolism and any excess substances.
Nutrition taking in materials for energy, growth and development.
An organism is described as living only when it shows these processes — not when it shows one of them.

Cells and nutrition across the groups

Animals
- multicellular cells with a nucleus and no cell wall;
  - feed on organic substances.
Plants
- multicellular, with chloroplasts and a cellulose wall;
  - feed by photosynthesis.
Fungi
- usually multicellular, with a non-cellulose (chitin) wall;
  - feed saprophytically or parasitically.
Protoctists
- mostly single-celled with a nucleus;
  - some photosynthesise, such as Chlorella.
Prokaryotes (bacteria)
- no nucleus and no mitochondria;
  - single-celled.

Why a virus is not placed in a living group

A virus is genetic material (RNA or DNA) inside a protein coat.
It is not a cell and does not carry out respiration, nutrition, growth or excretion.
It reproduces only by taking over a host cell, which is why it sits outside the living groups.

Control of internal conditions

Living things keep their internal environment within set limits (homeostasis). Humans hold body temperature near 37 °C by sweating or widening skin blood vessels, and also regulate water content (osmoregulation); plants lose heat as water evaporates from stomata.

Excretory products

Animals excrete CO₂ and water from aerobic respiration and urea, a nitrogen-containing waste formed when spare amino acids are broken down.

Plants excrete CO₂ from respiration and O₂ from photosynthesis.
Faeces are egested, not excreted, because they never took part in cell reactions.

Sensitivity in animals and plants

Animals respond to stimuli using the nervous system (receptors, neurones, effectors carrying electrical impulses) and the endocrine system (hormones carried in the blood). Plants respond by tropisms: shoots grow towards light (phototropism) and roots grow downwards with gravity (geotropism).

Movement in plants

Moving from place to place is called locomotion and is mostly seen in animals. Plants cannot travel, but parts of them still move by changing direction or orientation, for example flowers or leaves turning to follow the Sun during the day.

Sexual and asexual reproduction

Sexual reproduction needs two parents whose gametes fuse to form a zygote, so offspring carry a mix of both parents' DNA. Asexual reproduction involves one parent and gives genetically identical offspring (clones), e.g. bacteria and Amoeba dividing, or plants producing runners.

Tobacco mosaic virus

TMV stops chloroplasts forming in infected leaf cells, giving a mottled, discoloured leaf. With less chlorophyll the plant photosynthesises less, so it grows poorly and crop yield falls. It spreads by contact between plants and is controlled by field hygiene and resistant varieties.

Viruses infect all groups

Every kind of organism, from bacteria to plants and animals, can be infected by viruses. Each virus contains only one type of nucleic acid (DNA or RNA) and has no cytoplasm, membrane or ribosomes of its own.

Part 4 of 7Process & 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.

Is it made of cells?

Nucleus present or absent?

Chloroplasts and cellulose wall?

Hyphae and chitin wall?

Assign to kingdom

Part 5 of 7Worked 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.
- Deciding whether something is living
  - A fungal thread lengthens as it grows through bread.
    - Apply the definitions: growth is a permanent increase in size and dry mass, and nutrition is taking in materials — both are shown,
    - so this is a living process.
  - A pot of water freezes and the ice increases in size.
    - Size increases, but dry mass does not and no nutrient is taken in or respired, so this is not growth.
  - The answer is built by naming the process being tested, then quoting the defining words (permanent, dry mass, energy release).
- Two-mark define question
  - "Define respiration." Award both marks for breakdown of nutrients + to release energy, and note that it happens in cells.
  - Writing "breathing in oxygen" scores zero for this command word.

Part 6 of 7Summary

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 7Compare: 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

The seven life processes: what each one must include
Process	Full definition to write	Answer that loses the mark
Movement	An action causing a change of position or place	"Moving around" only — no change of place stated
Respiration	Breakdown of nutrients in cells to release energy	"Breathing" — that is gas exchange, not respiration
Sensitivity	Detecting a stimulus and making an appropriate response	"Responding" without detecting the stimulus
Growth	A permanent increase in size and dry mass	"Getting bigger" — temporary swelling is not growth
Reproduction	Making more organisms of the same kind	"Having babies" — asexual reproduction must be included too
Excretion	Removal of toxic waste products of metabolism and excess substances	"Passing out faeces" — egestion is not excretion
Nutrition	Taking in materials for energy, growth and development	"Eating" — no function stated

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: 20 October 2026