Cell structure and organisation

1. A complete description of a cell lists a cellulose wall, chloroplasts, a large permanent vacuole, a nucleus and mitochondria. Which type of cell is it?

Answer A: Plant cell

A typical plant cell has a cellulose wall, chloroplasts and a large permanent vacuole as well as a nucleus and mitochondria. Animal cells lack the first three, while bacteria lack a nucleus and mitochondria.

2. Which structure is present in plant, animal and bacterial cells and controls movement of substances into and out of the cell?

Answer C: Cell membrane

The cell membrane occurs in plant, animal and bacterial cells and controls movement of substances into and out of the cell. A nucleus and chloroplast are absent from bacteria, and an animal cell has no cellulose wall.

3. Which structure contains genetic material and controls the activities of a typical plant or animal cell?

Answer B: Nucleus

The nucleus contains genetic material and controls the cell's activities. Ribosomes make proteins, the plant vacuole contains cell sap, and the cell wall supports and maintains shape.

4. Where does aerobic respiration occur in a plant or animal cell?

Answer D: Mitochondrion

Mitochondria are the sites of aerobic respiration. Ribosomes synthesise proteins, the nucleus contains genetic material, and a vacuole does not carry out aerobic respiration.

5. Which structure contains chlorophyll and is the site of photosynthesis?

Answer A: Chloroplast

Chloroplasts contain chlorophyll that absorbs light and are the sites of photosynthesis. Mitochondria carry out aerobic respiration, ribosomes make proteins, and the nucleus controls cell activities.

6. What is a correct function of the large permanent vacuole in a typical plant cell?

Answer C: It contains cell sap and helps support the cell when filled with water.

The large permanent vacuole contains cell sap and can contribute to support when it is filled with water. Protein synthesis occurs at ribosomes, while aerobic respiration occurs in mitochondria.

7. Which statement correctly distinguishes a plant cell wall from its cell membrane?

Answer B: The wall supports the cell, while the membrane controls movement of substances.

The cellulose cell wall supports the plant cell and helps maintain its shape. The cell membrane controls movement of substances into and out of the cell. The other listed functions belong to different structures.

8. Which structure is absent from a typical animal cell?

Answer D: Cellulose cell wall

A typical animal cell has a membrane, cytoplasm and mitochondria but no cellulose cell wall. Cellulose walls are characteristic of plant cells among the plant-animal comparison in this topic.

9. A complete cell description includes circular DNA free in cytoplasm, plasmids, ribosomes, a membrane and a wall, but no nucleus. What is the cell?

Answer A: Bacterial cell

Circular DNA free in the cytoplasm, possible plasmids and no nucleus identify a bacterial cell. Plant and animal cells contain their main genetic material within a nucleus.

10. What are plasmids in a bacterial cell?

Answer C: Small circular DNA molecules

Plasmids are small circular DNA molecules that may carry additional genetic information. They are not mitochondria, vacuoles or chloroplasts, and those membrane-bound organelles are not bacterial structures.

11. Which feature separates a bacterial cell from both a typical plant cell and a typical animal cell?

Answer B: It has no nucleus.

Bacteria have no nucleus; their main circular DNA lies free in the cytoplasm. Plant, animal and bacterial cells all have ribosomes, a cell membrane and cytoplasm, so those features do not separate bacteria.

12. A component joins amino acids to make proteins. Which component is it?

Answer D: Ribosome

Ribosomes are the sites of protein synthesis and join amino acids into proteins. Mitochondria carry out aerobic respiration, while walls and vacuoles have support or storage roles.

13. Which statement describes the source of new cells?

Answer A: New cells are produced by division of existing cells.

New cells are produced when existing cells divide. They do not form spontaneously from nutrients, the principle is not limited to animals, and mitochondria do not independently produce whole new cells.

14. A culture starts with 3 cells. In each of two rounds, every cell divides once into two surviving cells and no cell dies. How many cells are present after round 2?

Answer C: 12

The first round doubles 3 cells to 6, and the second doubles 6 to 12. The conditions explicitly say every cell divides once per round, two cells survive from each division, and no cells die, so 3 × 2² = 12.

15. Which specialised cell moves mucus in the trachea and bronchi?

Answer B: Ciliated cell

Ciliated cells line parts of the trachea and bronchi, and their beating cilia move mucus. Root hair cells absorb from soil, red blood cells carry oxygen, and palisade cells photosynthesise.

16. Which specialised cell absorbs water and mineral ions from soil?

Answer D: Root hair cell

Root hair cells are specialised for absorption from the soil. Their long projection provides a large surface area. The other options conduct impulses, take part in reproduction or move mucus.

17. Which specialised cell carries out photosynthesis in a leaf?

Answer A: Palisade mesophyll cell

Palisade mesophyll cells contain many chloroplasts and are specialised for photosynthesis. Red blood cells transport oxygen, neurones conduct impulses, and ciliated cells move mucus.

18. What is the main specialised function of a red blood cell?

Answer C: Transport of oxygen

Red blood cells are specialised to transport oxygen, which binds to haemoglobin. Absorption from soil, photosynthesis and movement of mucus belong to root hair, palisade and ciliated cells respectively.

19. Which specialised cell conducts electrical impulses?

Answer B: Neurone

Neurones are specialised to conduct electrical impulses. Egg cells are gametes, root hair cells absorb water and mineral ions, and red blood cells transport oxygen.

20. What is the shared specialised function of sperm and egg cells?

Answer D: Reproduction

Sperm and egg cells are gametes specialised for reproduction. Their structures differ, but both carry parental genetic material and take part in producing a new organism.

21. What is a tissue?

Answer A: A group of similar cells working together for a shared function

A tissue is a group of cells with similar structures working together to perform a shared function. Organs contain different tissues, organ systems contain organs, and an organism contains organ systems.

22. Which description defines an organ?

Answer C: Different tissues working together for particular functions

An organ is made from different tissues that work together for particular functions. Several organs working together form an organ system, so that final option describes the next organisational level.

23. Which sequence gives biological organisation from smallest level to largest level?

Answer B: Cell → tissue → organ → organ system → organism

The correct order is cell, tissue, organ, organ system, organism. Similar cells form tissues, different tissues form organs, organs cooperate in systems, and systems make up an organism.

24. A complete description lists a membrane, cytoplasm, ribosomes and circular DNA free in the cytoplasm. It states that no nucleus, mitochondria or chloroplasts are present. Which conclusion is best?

Answer D: It is a bacterial cell because it has free circular DNA and no nucleus.

A bacterial cell has circular DNA free in its cytoplasm and no nucleus. A membrane and cytoplasm are shared by several cell types, while absence of mitochondria is expected in bacteria and does not mean the structure is not a cell.