1bThe Nature and Variety of Living Organisms

Variety of living organisms — Edexcel Linear - OL Revision Notes & Topical Questions

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Variety of living organisms Edexcel O Level Linear Biology revision notes.A pathogen is a microorganism that causes disease.Bacteria contain plasmids and a circular chromosome.OrganismNucleus?Prokaryote or eukaryoteKingdom featuresPathogensFungi – athlete’s footBacteria – Pneumoc…

Variety of living organisms Edexcel O Level Linear Biology: what to do next
Protoctists
Give / State / Name
Evaluate / Assess
Keywords the mark scheme looks for in this lesson
How to get full marks (examiner guidance)

Section 1 of 17Process & sequence

Organism
Nucleus?
Prokaryote or eukaryote
Kingdom features

Pathogens

Fungi – athlete’s foot

Bacteria – Pneumococcus

Protoctist – Plasmodium (malaria)

Virus – HIV, influenza

Section 2 of 17Keep going

Variety of living organisms Edexcel O Level Linear Biology: what to do next

These Variety of living organisms Edexcel O Level Linear Biology notes covered the key ideas, worked examples and exam technique for this topic. Check your Variety of living organisms Edexcel O Level Linear Biology understanding with the practice questions below, then reread any Variety of living organisms Edexcel O Level Linear Biology point you were unsure about before moving on.

Practice: Variety of living organisms Edexcel O Level Linear Biology practice questions

Previous lesson: 1a Characteristics of living organisms — Notes

Next lesson: 2a Level of organisation — Notes

Course: Edexcel Linear - OL — all units

Official syllabus: Pearson Edexcel International GCSEs

Section 3 of 17From life processes to the groups of organisms

Every organism carries out the life processes, but the way it does so differs between groups.

Energy is released from glucose by respiration, either with oxygen (aerobic) or without oxygen (anaerobic).

Plants excrete oxygen (from photosynthesis) and carbon dioxide (from respiration), with a different balance by day and by night.

3Phototropism

Plants respond to light by phototropism (shoots grow towards light) and to gravity by geotropism,

and plants control their temperature by transpiration.

Animals use a nervous system of receptors, neurones and effectors, sending electrical impulses, and chemical hormones.

5Osmoregulation

Another homeostatic mechanism in humans is osmoregulation (control of water levels).

Reproduction can be asexual (cells or whole organisms) or sexual: two gametes fuse to form a zygote that contains DNA from both parents.

Section 4 of 17Eukaryote groups at a glance

Animals and plants have membrane-bound nuclei and multicellular bodies; animals lack cell walls and chloroplasts while plants have cellulose cell walls and chloroplasts.

Eukaryote groups at a glance

Fungi lack chloroplasts and, as with animals, do not have nervous coordination (animals usually do; fungi do not).

Examples of fungi include moulds, mushrooms and yeasts.

Multicellular fungi are made of thread-like hyphae containing many nuclei, organised into a network known as a mycelium.

Section 5 of 17Prokaryotes and pathogens

Prokaryotes are single-celled and have no nucleus; features include a cell wall, cell membrane, cytoplasm, plasmids and a circular chromosome. A pathogen is an infectious agent that causes disease in a host. Pathogens include certain bacteria, fungi and protoctists, as well as viruses. Most members of these groups are not disease-causing; the term applies only to those that cause disease.

Pathogen	Group	Disease or effect
Pneumococcus	Bacterium	Pneumonia
Plasmodium	Protoctist	Malaria (spread by mosquitoes)
Some fungi	Fungus	Plant diseases

Match each named disease to its pathogen group rather than assuming all infections are bacterial.

Section 6 of 17The life processes in detail and how groups differ

The unifying characteristics (movement, respiration, sensitivity, control, growth, reproduction, excretion, nutrition) apply to every group, but they are carried out differently.

1Nutrition

In nutrition, plants are producers that photosynthesise,

whereas animals and fungi must take in food; fungi digest outside the body and absorb the products.

2Movement

In movement, animals show locomotion while plants only change orientation.

3Sensitivity

In sensitivity, animals use nerves and hormones but plants use slower chemical responses such as phototropism and geotropism.

4Reproduction

In reproduction, bacteria divide into identical copies, fungi may release spores, plants and animals use gametes.

5Excretion

In excretion, animals remove carbon dioxide, water and urea; plants remove oxygen and carbon dioxide through their stomata.

Section 7 of 17Revision checklist for the variety of organisms

Name the five groups and say which four are eukaryotes.

State two features of each eukaryotic group, including the cell wall material.

Describe the structure of a bacterial cell and say where its DNA is.

Define a pathogen and give a pathogen, a group and a disease for at least three groups.

Explain why a virus is non-living and why it needs a host cell to reproduce.

Recall that respiration releases energy as ATP, whereas gas exchange only moves gases.

If you can answer all six quickly, you have covered the variety of living organisms for this topic.

Remember that every group is judged against the same eight life processes. A useful exam habit is to state the process, name the group, and give the specific feature, for example: “plants respond to light (sensitivity) by phototropism, growing their shoots towards the light so that more light reaches the leaves for photosynthesis.”

Section 8 of 17Compare

Groups of living organisms
Group	Cells	Cell wall	Nutrition	Storage	Example
Plants	Multicellular	Cellulose	Photosynthesis	Starch, sucrose	Maize, pea
Animals	Multicellular	None	Feed on organisms	Glycogen	Human, housefly
Fungi	Mostly multicellular (yeast single)	Chitin	Saprotrophic	Glycogen	Mucor, yeast
Bacteria	Single (prokaryote)	Yes (not cellulose)	Some photosynthesise	—	Lactobacillus, Pneumococcus
Protoctists	Mostly single	Some	Varies	—	Amoeba, Chlorella
Viruses	Not cells	Protein coat	Parasitic	—	Influenza, HIV, TMV

Section 9 of 17Worked examples

Name the pathogen group that includes Plasmodium and the disease it causes. [2]2 marks
State two homeostatic mechanisms in humans. [2]2 marks
Define phototropism and geotropism. [2]2 marks
Describe how sexual reproduction differs from asexual reproduction. [2]2 marks
Explain why not all bacteria and fungi are called pathogens. [2]2 marks

Section 10 of 17Pathogens and disease

A pathogen is an infectious agent that causes disease in a host. Pathogens include certain bacteria, fungi and protoctists, as well as viruses. Most members of these groups are not necessarily disease-causing; the term pathogen applies to those that cause disease.

Examples:

Examples Pneumococcus is a bacterium associated with pneumonia; some fungi cause plant diseases; the protoctist Plasmodium causes malaria and is transmitted by mosquitoes. Match each named disease to its pathogen group rather than assuming all infections are bacterial.

Section 11 of 17Why viruses are different

Why viruses are different

Viruses are much smaller than bacteria and are not cells. A virus contains genetic material (DNA or RNA) enclosed in a protein coat. It cannot carry out the full set of life processes independently and can reproduce only after entering a living host cell.

Antibiotics target bacterial structures or processes. They do not kill viruses, so identifying the type of pathogen matters when discussing treatment and control.

Section 12 of 17Tobacco mosaic virus

Tobacco mosaic virus

Tobacco mosaic virus (TMV) infects plants, including some crop species. Infected leaves develop a patchy mosaic pattern because chloroplast function is disrupted. With less effective photosynthesis, growth and crop yield can fall.

TMV spreads through contact with infected plants or contaminated material and can persist in the growing environment. Good field hygiene and resistant crop varieties help limit spread; there is no simple cure for an infected plant.

Section 13 of 17HIV and influenza

HIV and influenza

HIV infects cells of the immune system.

An early flu-like illness may be followed by a long period with few obvious symptoms.
If the immune system becomes severely damaged, the late stage is called AIDS and the person becomes vulnerable to other infections.
HIV can pass through sexual contact, contaminated blood or shared needles, and from mother to child.
Antiretroviral treatment can control viral replication and greatly slow progression.

Influenza virus infects cells lining the airways and causes a contagious respiratory illness. Typical symptoms include fever, body aches and fatigue. In an exam answer, describe both the affected tissue and the resulting symptoms, rather than simply naming the virus.

Section 14 of 17Check your understanding

Question:

Question Why can TMV lower a crop's yield? Answer: Damaged chloroplast function reduces photosynthesis, so the plant makes less glucose for growth and produces a smaller yield.

Question:

Question Why would an antibiotic not cure influenza? Answer: Influenza is caused by a virus, while antibiotics act on bacterial targets.

Section 15 of 17Key terms

Term	Meaning
Pathogen	An infectious agent that causes disease in a host.
Phototropism	Growth of plant shoots towards light.
Geotropism	Growth of plant roots in response to gravity.
Osmoregulation	Control of the water levels of the body.
Zygote	The cell formed when two gametes fuse.
Mycelium	A network of fungal hyphae.

Section 16 of 17Command 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.

Section 17 of 17Exam technique

Assuming every infection is caused by bacteria — match the disease to bacteria, fungi, protoctists or viruses.

Thinking plants do not respire — they respire all the time and photosynthesise in the light.

Confusing phototropism (response to light) with geotropism (response to gravity).

Calling all microorganisms pathogens.

Last updated: 11 October 2026