State that new cells are produced by division of existing cells.

Cell Structure – IGCSE Biology (0610) – Organisation of the Organism

Learning Objective (AO1)

State that new cells are produced by division of existing cells.

Key Concepts (AO1)

• All living organisms are composed of cells.
• Cell continuity – cells arise only from pre‑existing cells.
• Cell division is the process by which a parent cell gives rise to two daughter cells.

1. Core Cell Structures (AO2)

Students must be able to name, locate on a labelled diagram and give a one‑sentence function for each structure listed in the syllabus.

2. Six Specialised Cells (AO2)

Identify the cell, the tissue/organ where it is found, and one key function.

3. Why Cells Divide (AO1)

1. Growth – increase the size of a multicellular organism.
2. Repair – replace cells that are damaged, lost or worn out.
3. Reproduction – produce new individuals (binary fission in unicellular organisms; mitosis in multicellular organisms).

4. Types of Cell Division (AO1)

5. Steps of Mitosis (Simplified) (AO2)

1. Prophase: Chromosomes condense; nuclear membrane disappears; spindle fibres form from centrosomes.
2. Metaphase: Chromosomes line up at the equatorial (metaphase) plate.
3. Anaphase: Sister chromatids separate and are pulled to opposite poles by spindle fibres.
4. Telophase: Nuclear membranes re‑form around each chromosome set; chromosomes begin to de‑condense.
5. Cytokinesis: Cytoplasm divides (cleavage furrow in animal cells; cell plate in plant cells) producing two distinct daughter cells.

6. Magnification, Size of Specimens & Unit Conversions (AO3)

• Magnification formula: Magnification = Image size ÷ Actual size
• Worked example:
  1. Actual length of an onion cell = 0.5 mm.
  2. Image length under the microscope = 5 mm.
  3. Magnification = 5 mm ÷ 0.5 mm = 10×.
• Unit conversions:
  • 1 mm = 1 000 µm
  • 1 µm = 0.001 mm
• Practice question: A cell appears 2 mm long when viewed with a 200× objective. What is its actual length?
  Solution: Actual length = 2 mm ÷ 200 = 0.01 mm = 10 µm.

7. Diagramming Conventions (AO2)

• Draw a clear, labelled diagram; each structure must be numbered and listed in a key.
• Include a scale bar (e.g., 10 µm) with the appropriate magnification.
• Colour‑code where possible (green = chloroplasts, red = nucleus, blue = vacuole, etc.).
• For mitosis, label each phase, the spindle fibres and the position of chromosomes.
• In plant cells, show the cell plate during cytokinesis; in animal cells, show the cleavage furrow.

8. Key Vocabulary (AO1)

• Cell division – process by which a cell splits into two new cells.
• Parent cell – the original cell that undergoes division.
• Daughter cells – the two cells produced.
• Cytokinesis – division of the cytoplasm.
• Mitosis – nuclear division in eukaryotes.
• Binary fission – cell division in prokaryotes.
• Spindle fibres – protein structures that pull chromosomes apart.
• Plasmid – small, circular DNA molecule in bacteria.
• Chromosome – DNA‑protein complex visible during mitosis.

9. Common Misconceptions (AO1)

• “New cells can arise spontaneously.” – Incorrect. All cells arise from pre‑existing cells (cell continuity).
• “All cell division produces genetically different cells.” – Incorrect. Mitosis yields genetically identical cells; meiosis (outside this topic) creates variation.
• “Plant cells do not undergo cytokinesis because they have a cell wall.” – Incorrect. Plant cells form a cell plate that develops into a new cell wall.
• “Binary fission uses a mitotic spindle.” – Incorrect. Prokaryotes lack a spindle; the DNA simply segregates as the cell elongates.

10. Assessment Checklist (Linking to AO1‑AO3)

1. State the principle that new cells are produced by division of existing cells. (AO1)
2. Identify and label the core structures of plant, animal and bacterial cells, giving a brief function for each. (AO2)
3. List the six specialised cells required by the syllabus and describe one key function for each. (AO2)
4. Explain why cell division is essential for growth, repair and reproduction. (AO1)
5. Distinguish between binary fission and mitosis, stating the types of organisms in which each occurs. (AO1)
6. Recall the correct order of the mitosis phases and describe the main event in each phase. (AO2)
7. Calculate magnification using the formula and convert between mm and µm. (AO3)
8. Draw a labelled diagram of a typical plant cell and a series of diagrams showing the stages of mitosis, using correct conventions (scale bar, key, colour‑coding). (AO2)