1.3Unit 1 · Living Organisms & Cells
Cell Structure — Edexcel IGCSE Biology Modular - UNIT 1 Revision Notes & Topical Questions
10 min read 7 parts Lesson 4 of 6 Unit quiz
Lesson summary
Describe the functions of the main cell structures.All cells with a nucleus contain the same genes; differentiation depends on which genes are switched on.Plant cells store starch; animal cells store glycogen.Examples of specialised animal cellsred blood cells, sperm, nerve cells…
- Examples of specialised plant cells
- Similarities and differences
- Importance of cell differentiation
- Stem cells in medicine — advantages
- Stem cells — disadvantages
- Light vs electron microscope
Part 1 of 7Key ideas
1
All cells with a nucleus contain the same genes; differentiation depends on which genes are switched on.
2
Plant cells store starch; animal cells store glycogen.
3Examples of specialised animal cells
Examples of specialised animal cells red blood cells, sperm, nerve cells, ciliated cells.
4Examples of specialised plant cells
Examples of specialised plant cells root hair cells, palisade cells, xylem, guard cells.
5
Stem cells could treat conditions such as diabetes, paralysis and some blood disorders.
6
Bone marrow transplants use adult stem cells to treat leukaemia.
Part 2 of 7Learning objectives
1
Describe the functions of the main cell structures.
2
Compare animal and plant cells.
3
Explain the importance of cell differentiation.
4
Evaluate the use of stem cells in medicine.
Part 3 of 7Essential knowledge
Essential knowledge
Cell structures
Cell structures the nucleus holds DNA and controls the cell; cytoplasm is the site of most reactions; the cell membrane controls entry and exit; mitochondria release energy by aerobic respiration; ribosomes make proteins.
- Plant cells also have a cellulose cell wall for support, chloroplasts for photosynthesis and a vacuole containing cell sap.
Similarities and differences
Similarities and differences animal and plant cells share nucleus, cytoplasm, membrane, mitochondria and ribosomes. Only plant cells have a cell wall, chloroplasts and a large permanent vacuole. Animal cells usually have irregular shapes; plant cells are more regular due to the wall.
Importance of cell differentiation
Importance of cell differentiation multicellular organisms need different cells for different jobs. During development, cells differentiate by expressing only certain genes, producing specialised cells such as nerve cells (long axons) or palisade cells (many chloroplasts). This division of labour makes the organism more efficient.
Most animal cells lose the ability to differentiate early, while many plant cells keep this ability throughout life in meristems at shoot and root tips.
Stem cells in medicine — advantages
Stem cells in medicine — advantages embryonic stem cells can form almost any cell type and could replace damaged cells, e.g. insulin-producing cells for diabetes or nerve cells after spinal injury. Adult stem cells from bone marrow are already used to treat leukaemia.
Stem cells — disadvantages
Stem cells — disadvantages using embryos raises ethical concerns because the embryo is destroyed; stem cells may divide uncontrollably and form tumours; transplanted cells may be rejected by the immune system; cultures could transfer viral infections; adult stem cells can make only a limited range of cells.
Light vs electron microscope
Nucleus, cell wall, vacuole and chloroplasts can be seen with a light microscope, but mitochondria and ribosomes are too small and are only visible using an electron microscope.
Red blood cell adaptations
Red blood cells have a biconcave disc shape giving a large surface area to volume ratio for oxygen diffusion. They have no nucleus, leaving more room for haemoglobin, the protein that carries oxygen.
Ciliated and root hair cells
Ciliated cells lining the trachea and bronchi have tiny hairs (cilia) that beat to sweep mucus and trapped particles up towards the throat. Root hair cells have a long extension that increases surface area for absorbing water and mineral ions.
Stem cells divide by mitosis
A stem cell can divide by mitosis many times. Each new cell either stays unspecialised as another stem cell or differentiates into a specialised cell. Adult stem cells (e.g. in bone marrow) mainly replace and repair cells such as blood and skin cells.
Avoiding rejection
Cells grown from donor stem cells carry different antigens, so the patient must take immunosuppressant drugs to prevent rejection.
- Using the patient's own stem cells avoids this, because the new cells have the same genes and antigens.
- Bone marrow stem cells can produce red cells, white cells and platelet-forming cells.
Part 4 of 7Process & sequence
1
A zygote divides by mitosis to form a ball of identical unspecialised cells.
2
Cells receive signals that switch particular genes on or off.
3
Only certain genes are expressed, so specific proteins are made.
4
The cell changes shape and gains structures suited to its function.
5
Specialised cells group into tissues, then organs.
From stem cell to organwrite these steps in this order; each step is a marking point.
1
Unspecialised stem cell
2
Genes switched on or off
3
Specialised cell forms
4
Cells form tissue
5
Tissues form organ
Part 5 of 7Worked examples
1Explain why a root hair cell does not contain chloroplasts.
- Root hair cells are underground and receive no light, so they cannot photosynthesise.
- The genes for chloroplast development are not expressed, as the cell has differentiated to absorb water and minerals instead.
2
Give one argument for and one against using embryonic stem cells to treat paralysis.
- For: embryonic stem cells can differentiate into nerve cells, which could replace damaged cells and restore movement.
- Againstthe embryo is destroyed, which many people think is unethical, and there is a risk of tumour formation or rejection.
Part 6 of 7Summary
1
Both animal and plant cells have a nucleus, cytoplasm, membrane, mitochondria and ribosomes.
2
Only plant cells have a cell wall, chloroplasts and a permanent vacuole.
3
Differentiation produces specialised cells.
4
Stem cells offer treatments but raise ethical and safety issues.
Part 7 of 7Compare: Compare
| Structure | Animal cell | Plant cell |
|---|---|---|
| Nucleus, cytoplasm, membrane | Yes | Yes |
| Mitochondria and ribosomes | Yes | Yes |
| Cellulose cell wall | No | Yes |
| Chloroplasts | No | Yes (in green parts) |
| Large permanent vacuole | No (small temporary vacuoles only) | Yes |
| Source | Can form | Issues |
|---|---|---|
| Embryonic stem cells | Almost any cell type | Ethical objections; risk of rejection |
| Adult stem cells (e.g. bone marrow) | Limited range of cell types | Fewer ethical issues; limited use |
| Plant meristems | Any plant cell type | Used for cloning plants |
Key terms
Command 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
Keywords the mark scheme looks for in this lesson
Nucleus · Cytoplasm · Cell membrane · Mitochondrion · Ribosome · Chloroplast · Cell wall · Vacuole · Differentiation · Stem cell
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)
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.
Instant feedbackCheck yourself
Q1. Where does aerobic respiration take place?
- A. Ribosome
- B. Mitochondrion
- C. Nucleus
- D. Vacuole
Show answer
B. Mitochondria are the site of aerobic respiration.
Q2. Which structure is found in plant cells but not animal cells?
1
A. Cell membrane
2
B. Ribosomes
3
C. Chloroplasts
4
D. Cytoplasm
Show answer
C. Only plant cells (green parts) contain chloroplasts.
Q3. What is the function of ribosomes?
- A. Protein synthesis
- B. Photosynthesis
- C. Controlling the cell
- D. Support
Show answer
A. Ribosomes join amino acids to make proteins.
Q4. What is cell differentiation?
1
A. Cell death
2
B. Cell division by meiosis
3
C. Uptake of water
4
D. A cell becoming specialised
Show answer
D. Differentiation is a cell gaining features for a specific function.
Q5. A disadvantage of stem cell therapy is
1
A. the cells can form many types
2
B. risk of tumours or rejection
3
C. they can replace damaged tissue
4
D. they are used for leukaemia
Show answer
B. Uncontrolled division can cause tumours and foreign cells can be rejected.
Q6. What is the plant cell wall made of?
- A. Cellulose
- B. Glycogen
- C. Protein
- D. Chitin
Show answer
A. Plant cell walls are made of cellulose.
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