Build the hierarchy from cells to an organism
Distinguish tissues, organs and organ systems using syllabus examples.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Recall the distinction between plant, animal and bacterial cells. Read the supplied evidence before drawing a conclusion.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which example is an organ system?
What you will learn
- Define five levels of organisation.
- Use a consistent example rather than identifying levels by size alone.
Related parts form larger organisations
A cell is a basic living unit, such as a palisade mesophyll cell. A tissue is a group of cells working together for a particular function, such as palisade mesophyll tissue. A tissue is not simply any collection of adjacent objects.
An organ contains different tissues working together to perform functions. A leaf is an organ with palisade, spongy mesophyll, epidermal and vascular tissues. An organ system contains organs working together, such as the digestive system with stomach and intestine. An organism is the complete living individual.
Use both plant and animal examples
In a plant sequence, palisade cell → palisade tissue → leaf → shoot system → whole plant illustrates the hierarchy. In an animal sequence, muscle cell → muscle tissue → stomach → digestive system → human illustrates the same levels. The stomach includes several tissue types, not only muscle.
Size alone does not identify the level: a long neurone is still one cell, and a small leaf is still an organ. Name the organisation and its function, and do not classify a mitochondrion as a whole cell or a tissue as an organ system.
Sources for this lesson
Pause and explain
A very long neurone is still which level?
Worked example
Place muscle cell, stomach, human, muscle tissue and digestive system in increasing organisation.
Show the worked solution
- Cell then tissue.
- Stomach is an organ; digestive system combines organs.
- Human is the whole organism.
Answer Muscle cell → muscle tissue → stomach → digestive system → human.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Classify palisade cell, palisade tissue and leaf.
Give me a hint
Move from one cell to a group to multiple tissues.
Compare my reasoning
- Palisade cell is a cell.
- Palisade tissue is tissue.
- Leaf is an organ.
Cell, tissue and organ, respectively.
Look for these in your work
- Correct three levels.
- Explain why leaf is an organ.
Explain why the stomach is not just muscle tissue.
Give me a hint
Consider its combined tissue types.
Compare my reasoning
- It includes muscle, lining and other tissues.
- These work together as an organ.
The stomach is an organ made of different cooperating tissues.
Look for these in your work
- Multiple tissue types.
- Correct organ level.
A tiny leaf is smaller than a long neurone. Which has the higher organisational level and why?
Give me a hint
Organisation is different from measured length.
Compare my reasoning
- Leaf combines multiple tissues.
- Neurone is a single cell.
The leaf is an organ and has the higher organisational level, despite the length comparison.
Look for these in your work
- Use organisation, not size.
- Correct both levels.
Common mistakes
- An organ contains different tissues.
- Long or large does not automatically mean a higher level.
What can you explain now?
Why is a leaf an organ?
Compare with the explanation
It contains different tissues working together.
Its organisation, rather than its outline size, determines the level.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Define all five levels and give a consistent plant or animal sequence.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.