Cells

8 methods · 14 questions

★ Signature method unlocked: the technique this chapter rewards most often, with 3 worked questions.

The full chapter (8 methods · 14 worked questions) comes with Platform Access. See pricing

Almost every cell identification question in this chapter is settled by one recalled contrast, not by reasoning. A prokaryote (a bacterium) has a cell wall and a cell membrane with its DNA free in the cytoplasm, but NO nucleus and NO membrane-bound organelles at all, so no mitochondria and no chloroplasts. A eukaryote (animal, plant, fungus, alga) always has a nucleus and mitochondria.

Trigger: a checklist of features, or a question of the form 'which cell type', or 'which cells have or lack this organelle'.

Instances:
(i) bacterium: cell wall yes, nucleus no, mitochondria no, chloroplasts no;
(ii) animal cell: nucleus and mitochondria yes, cell wall no, chloroplasts no;
(iii) plant or algal cell: cell wall, nucleus, mitochondria, chloroplasts and a large vacuole all yes;
(iv) fungal cell: cell wall and nucleus yes, chloroplasts no.

One tell fixes the cell: 'a wall plus no mitochondria', or 'no nucleus', pins a prokaryote, and the rest then follows without checking each organelle.

Linked questions (3)

NSAA 2016 Section 1, Part D (Biology questions) · Q57

A student described a population of organisms as having the following features

1. single celled
2. chloroplasts present
3. cell wall present

Using this information, which type of organism could this describe?

Aalgae
Bbacteria
Cferns
Dfungi
Eflowering plants

Worked solution

Answer:A

Bacteria have a cell wall but no chloroplasts (they have no membrane-bound organelles at all). Fungi have a cell wall but never contain chloroplasts. Ferns and flowering plants have chloroplasts and cell walls but are multicellular.

Only algae can be single-celled organisms that possess both a cell wall and chloroplasts, for example Chlamydomonas.

The answer is A.

NSAA 2017 Section 1, Part D (Biology questions) · Q60

The diagram shows three features which are used to group organisms.

Fungi, bacteria and animals can each be placed in one of the regions labelled P, Q, R or S on the diagram.

Which row in the following table is correct?

(Each option gives the region for fungi, then for bacteria, then for animals.)

A Venn diagram of three overlapping circles. The upper-left circle is labelled: cell has an external wall forming a layer that gives it a defined shape. The upper-right circle is labelled: within the cell is a membrane-bound structure that contains DNA. The lower circle is labelled: cell uses enzymes to release energy for cell processes. Region P is the overlap of the two upper circles outside the lower circle; S is the central region common to all three; Q is the overlap of the upper-left and lower circles only; R is the overlap of the upper-right and lower circles only.

Afungi P; bacteria S; animals R
Bfungi P; bacteria R; animals S
Cfungi Q; bacteria R; animals P
Dfungi S; bacteria Q; animals R
Efungi S; bacteria S; animals S
Ffungi R; bacteria P; animals Q
Gfungi R; bacteria Q; animals P

Worked solution

Answer:D

Every living cell uses enzymes to release energy in respiration, so fungi, bacteria and animals all lie inside the bottom circle, which rules out region P (outside it).

Fungi have a cell wall and a nucleus, so they lie in all three circles: region S. Bacteria have a cell wall but no nucleus (their DNA lies free in the cytoplasm), so they are in the cell-wall circle and the enzyme circle only: region Q. Animal cells have a nucleus but no cell wall: region R.

The answer is D.

NSAA 2019 Section 1, Part D (Biology questions) · Q55

Which of the following statements is/are correct for both bacterial cells and sperm cells?

1. The cell can divide.
2. The cell contains DNA.
3. The cell has a cell wall.
4. The cell has a nucleus.
5. The cell can carry out respiration.

A2 only
B4 only
C1 and 2 only
D2 and 5 only
E3 and 4 only
F3 and 5 only
G1, 2 and 5 only
H1, 3 and 4 only

Worked solution

Answer:D

Bacterial cells and sperm cells both contain DNA (2) and both respire to release energy (5): a sperm cell needs energy to swim.

A sperm cell is a specialised gamete that cannot divide; it can only fuse with an egg, so statement 1 fails for sperm. Bacteria have a cell wall but sperm cells do not (3), and sperm cells have a nucleus but bacteria do not (4).

The answer is D.