Specialised Cells, Tissues and Organs — Answers
Answer sheet with model answers and success criteria for the Year 8 cells & classification worksheet.
Success TutoringWorksheetsAnswer sheetYear 8 · Science · Cells & ClassificationSpecialised Cells, Tissues and Organs — Answers
Part A: Specialised cells
In a multicellular organism, cells are specialised: each type has a shape and set of structures suited to one job. This is called cell specialisation or differentiation.
For example, a nerve cell is long and thin so it can carry signals over long distances, and a root hair cell has a long projection that gives it a large surface area for absorbing water and minerals from the soil.
- Red blood cell
- Nerve cell (neuron)
- Sperm cell
- Root hair cell
- Palisade cell (leaf)
- Muscle cell
- No nucleus and a disc shape, leaving more room to carry oxygen
- A tail for swimming and many mitochondria for energy
- Packed with chloroplasts to absorb light for photosynthesis
- A long, thin projection that increases surface area for absorbing water
- Long fibres that can contract, with many mitochondria
- Very long, thin extensions that carry electrical signals
Answer: Red blood cell → No nucleus and a disc shape, leaving more room to carry oxygen; Nerve cell (neuron) → Very long, thin extensions that carry electrical signals; Sperm cell → A tail for swimming and many mitochondria for energy; Root hair cell → A long, thin projection that increases surface area for absorbing water; Palisade cell (leaf) → Packed with chloroplasts to absorb light for photosynthesis; Muscle cell → Long fibres that can contract, with many mitochondria
- AThey are underground, where there is no light for photosynthesis
- BChloroplasts would make the root too heavy
- CThey use their cell wall to make food instead
- DChloroplasts are found only in animal cells
Answer: They are underground, where there is no light for photosynthesis
Chloroplasts trap light energy. Roots grow in the dark soil, so chloroplasts would have no job there.
Answer: They open and close the stomata (small pores), controlling how much carbon dioxide enters the leaf and how much water vapour leaves it.
Answer: Without a nucleus there is more space inside the cell for haemoglobin, the protein that carries oxygen, so each cell can carry more oxygen.
Part B: Levels of organisation
Specialised cells are organised into larger structures. Cells of the same type group together to form a tissue. Different tissues work together to form an organ, such as the heart or a leaf. Organs work together in an organ system, such as the digestive system, and all the systems together make up the organism.
Answer: cell → tissue → organ → organ system → organism
- AA muscle cell
- BBlood
- CThe stomach
- DThe digestive system
Answer: The stomach
The stomach is made of several tissues (muscle, lining tissue, nerves) working together. A muscle cell is a cell, blood is a tissue and the digestive system is an organ system.
- ACell
- BTissue
- COrgan
- DOrganism
Answer: Organ
A leaf is a plant organ made of different tissues.
Answer: True
For example, muscle tissue is made of many muscle cells that contract together.
Answer: An organ system (here, the circulatory system).
Answer: False
A single-celled organism carries out all life processes within one cell, so it has no tissues or organs.
Part C: How big is a cell?
Cells are measured in micrometres (µm). One micrometre is one thousandth of a millimetre: 1 mm = 1000 µm.
Image size = real size × magnification, so real size = image size ÷ magnification. Make sure both lengths are in the same unit before you divide.
Answer: 100 µm
- 1 mm = 1000 µm
- 0.1 × 1000 = 100 µm
Answer: 0.06 mm
- 60 ÷ 1000 = 0.06 mm
Answer: 10 mm
- Image size = real size × magnification
- 25 µm × 400 = 10 000 µm
- 10 000 ÷ 1000 = 10 mm
Answer: 20 µm
- Real size = image size ÷ magnification
- 8 mm = 8000 µm
- 8000 ÷ 400 = 20 µm
Answer: 100 µm
- 2 mm ÷ 20 = 0.1 mm
- 0.1 mm × 1000 = 100 µm
Part D: Explain
Model answer: A sperm cell's function is to reach and fertilise an egg cell. Its tail lets it swim towards the egg, and it has many mitochondria to release the energy needed for swimming. A root hair cell's function is to absorb water and minerals from the soil. Its long, thin projection gives it a large surface area for absorption, and it has no chloroplasts because it grows underground where there is no light.
Success criteria:
- Correct function for an animal cell
- Two features of the animal cell, each linked to its function
- Correct function for a plant cell
- Two features of the plant cell, each linked to its function
Marking tips
- Give credit for correct method even when the final answer slips — the working shows where the thinking went right.
- For open-ended tasks, use the success criteria as a checklist rather than looking for one "right" answer.
- Celebrate what went well first, then pick one thing to work on next.
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