B1 L2Bacterial cells

• 01.1 label 1: plasmid(1)
• 01.1 label 2: single loop of DNA(1)
• 01.1 label 3: cell membrane(1)
• 01.2 To move the bacterium(1)
• 01.3 any one from: cell membrane / cytoplasm / ribosomes(1)

01.1: 1 mark for each correct label. If more than one word from the box is written on one line, do not give that mark. allow "DNA" or "loop of DNA" for 2. do not accept "nucleus" for 2.
01.2: if more than one box is ticked, give 0 marks.
01.3: allow DNA. do not accept cell wall, plasmid, flagellum or nucleus.

Model answer01.1 1 plasmid; 2 single loop of DNA; 3 cell membrane. 01.2 To move the bacterium. 01.3 Ribosomes.

• 02.1 the bacterium, because it has no nucleus(1)
• 02.2 200 (µm)(1)
• 02.3 200 ÷ 2(1)
• 02.3 = 100(1)

02.1: both the cell and the reason are needed for the mark. The reason must be about the nucleus. do not accept size on its own ("it is smaller"): prokaryotic is about the nucleus, not the size.
02.3: allow their 02.2 answer used correctly: their 02.2 ÷ 2. Correct answer with no working = 2 marks. ignore units. do not accept 198 (subtracted).

Model answer02.1 The bacterium, because it has no nucleus. 02.2 0.2 × 1000 = 200 µm. 02.3 200 ÷ 2 = 100 times.

• plasmids are (much) smaller / small rings(1)
• a cell may have several plasmids but only one main loop(1)
• plasmids carry only a few (extra) genes / the main loop carries most of the genes(1)
• not all bacteria have plasmids, but every bacterium has the main loop(1)
• plasmids carry genes such as one that helps the bacterium survive an antibiotic(1)

any two: max 2. do not accept "plasmids are not made of DNA" or "plasmids are in a nucleus".

Model answerPlasmids are much smaller than the main loop. Plasmids carry only a few extra genes, but the main loop carries most of the genes.

• bacteria / bacterial cells do have DNA(1)
• the DNA is (the pale tangled area at) A / in the middle of the cell(1)
• the DNA is not enclosed in a nucleus / is free in the cytoplasm / is a single loop(1)

max 3. allow "bacteria may also have DNA in plasmids" for 1 mark. do not accept "A is the nucleus".

Model answerBacteria do have DNA. The pale tangled area A is the DNA. It is not enclosed in a nucleus: it is a single loop, free in the cytoplasm.

Level of response. Read your answer, choose the level that fits best, then pick your mark.

Indicative content

• Similarities: both have a cell membrane; both have cytoplasm; both have ribosomes; both have DNA; both have a cell wall.
• the plant cell wall is made of cellulose, but the bacterial cell wall is not
• a plant cell has a nucleus, but a bacterial cell does not
• the bacterial DNA is a single loop, free in the cytoplasm; the plant cell's DNA is enclosed in a nucleus
• a plant cell is eukaryotic; a bacterial cell is prokaryotic
• a bacterial cell may have plasmids (small rings of DNA); a plant cell does not
• a plant cell has mitochondria; a bacterial cell does not
• some plant cells have chloroplasts; a bacterial cell does not
• a plant cell has a permanent vacuole; a bacterial cell does not
• some bacteria have a flagellum; a plant cell does not
• a bacterial cell is much smaller (about 1 to 5 µm, against up to about 100 µm for a plant cell)

Your mark:

Model answer (Level 3)Both cells have a cell membrane, cytoplasm and ribosomes, and both have DNA. Both also have a cell wall, but the plant cell wall is made of cellulose, whereas the bacterial cell wall is not. The plant cell's DNA is enclosed in a nucleus, so it is eukaryotic, but the bacterial cell has no nucleus: its DNA is a single loop, free in the cytoplasm, so it is prokaryotic. A bacterial cell may also have plasmids, small rings of DNA, which a plant cell does not have. A plant cell has mitochondria, a permanent vacuole and, in some cells, chloroplasts, but a bacterial cell has none of these. A bacterial cell is also much smaller: about 2 µm long, compared with up to about 100 µm.