Biology • Year 12 • Module 5 • Lesson 9
DNA in Prokaryotes and Eukaryotes
Lock in the core vocabulary that separates prokaryotic DNA (circular, nucleoid, plasmids) from eukaryotic DNA (linear chromosomes, chromatin, nucleus), and the misconceptions that wreck exam answers.
1. Term–definition match
The ten definitions below are shuffled. In the right-hand column write the matching term from this list: prokaryote, eukaryote, nucleoid, nucleus, plasmid, chromosome, chromatin, circular DNA, linear chromosome, vector. 10 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 1.1 | An organism whose cells lack a membrane-bound nucleus, such as a bacterium. | |
| 1.2 | An organism whose cells contain a membrane-bound nucleus and other organelles. | |
| 1.3 | The region in a prokaryotic cell where the main DNA molecule is located, not enclosed by a membrane. | |
| 1.4 | A membrane-bound organelle in eukaryotic cells that contains the main DNA. | |
| 1.5 | A small circular DNA molecule found in many prokaryotes, separate from the main chromosome. | |
| 1.6 | A packaged DNA-protein structure that carries genes. | |
| 1.7 | Eukaryotic DNA associated with proteins in a less condensed form before full chromosome condensation. | |
| 1.8 | The typical form of the main bacterial chromosome — a closed loop of double-stranded DNA. | |
| 1.9 | A DNA molecule with two ends, characteristic of eukaryotic chromosomes. | |
| 1.10 | A DNA molecule (often a plasmid) used in biotechnology to carry an inserted gene into a host cell. |
2. True or false — with correction
For each statement, circle T or F. If the statement is false, write the corrected version on the line below. 12 marks (1 for T/F, 1 for the correction where needed)
2.1 Bacteria store their main DNA inside a membrane-bound nucleus, just like human cells. T / F
2.2 A plasmid is the same thing as the main bacterial chromosome. T / F
2.3 Both prokaryotes and eukaryotes use DNA as their hereditary material. T / F
2.4 Eukaryotic DNA is "floating freely" in the cytoplasm with no associated proteins. T / F
2.5 Chromatin and chromosomes describe the same eukaryotic DNA in different states of condensation. T / F
2.6 Prokaryotic DNA cannot replicate because it is not in a nucleus. T / F
3. Function recall
Answer each in 1–2 sentences using precise terms from the lesson. 10 marks (2 each)
3.1 What is the function of the nucleoid in a prokaryotic cell?
3.2 What is the function of plasmids in bacterial biology and in biotechnology?
3.3 What is the function of the nucleus in a eukaryotic cell?
3.4 What is the function of organising eukaryotic DNA as chromatin?
3.5 What is the function of organising eukaryotic DNA into multiple linear chromosomes rather than one large molecule?
4. Cloze paragraph — comparing DNA organisation
Use words from the word bank below to fill each blank in the paragraph. Each word is used once. 10 marks (1 per blank)
Word bank: circular · linear · nucleoid · nucleus · plasmids · chromatin · chromosomes · proteins · vectors · DNA
All cells store their hereditary information as 4.1 _______________. In most prokaryotes, the main chromosome is a 4.2 _______________ DNA molecule located in a region of the cell called the 4.3 _______________, which is not surrounded by a membrane. Many prokaryotes also contain small, separate circular DNA molecules called 4.4 _______________, which often carry extra genes such as those for antibiotic resistance. In biotechnology, these molecules are commonly used as 4.5 _______________ because they can carry an inserted gene into a host bacterial cell. By contrast, eukaryotic cells store their DNA inside a membrane-bound 4.6 _______________ as multiple 4.7 _______________ DNA molecules. This DNA is associated with 4.8 _______________, and the resulting DNA-protein complex is called 4.9 _______________. During cell division this material condenses into the visible 4.10 _______________ that you would see under a microscope.
Q1 — Term–definition matches (10 marks)
1.1 prokaryote • 1.2 eukaryote • 1.3 nucleoid • 1.4 nucleus • 1.5 plasmid • 1.6 chromosome • 1.7 chromatin • 1.8 circular DNA • 1.9 linear chromosome • 1.10 vector.
Marking notes. 1 mark per correct term match; no half-marks; misspelt but unambiguous terms award the mark.
Q2 — True / false with correction (12 marks)
2.1 False. Correction: bacteria do not have a membrane-bound nucleus; their main DNA is located in the nucleoid region of the cell. [1 + 1]
2.2 False. Correction: a plasmid is an additional small circular DNA molecule that is separate from the main bacterial chromosome. [1 + 1]
2.3 True. Both cell types use DNA — the difference is in how that DNA is organised, not in what it is made of. [1]
2.4 False. Correction: eukaryotic DNA is inside the nucleus and is associated with proteins as chromatin — it is not floating freely in the cytoplasm. [1 + 1]
2.5 True. Chromatin is the less condensed DNA-protein form; chromosomes are the same material in a much more condensed form during cell division. [1]
2.6 False. Correction: prokaryotic DNA replicates inside the cell despite there being no nucleus — replication does not require a nuclear envelope. [1 + 1]
Marking notes. For false statements, award the second mark only if the correction is biologically accurate and uses lesson terminology (nucleoid, plasmid, chromatin, etc.).
Q3 — Function recall (10 marks)
3.1 Nucleoid (2 marks). The nucleoid is the region of the prokaryotic cell that houses the main circular DNA molecule. It keeps the DNA spatially organised and supercoiled by proteins so it fits inside the cell, without enclosing it in a membrane.
3.2 Plasmids (2 marks). Naturally, plasmids carry extra genes (e.g. antibiotic-resistance genes) separate from the main chromosome and can transfer between bacteria. In biotechnology they act as vectors that carry inserted DNA into a host cell, where they replicate along with the bacterium.
3.3 Nucleus (2 marks). The nucleus is a membrane-bound organelle that contains the eukaryotic cell's linear chromosomes. It physically separates DNA storage and gene transcription from cytoplasmic processes such as translation.
3.4 Chromatin (2 marks). Chromatin (DNA associated with proteins) packages large amounts of DNA so it fits inside the nucleus. It also allows DNA to be in a less condensed form when genes need to be accessed and read.
3.5 Multiple linear chromosomes (2 marks). Organising DNA into multiple linear chromosomes allows the cell to manage very large genomes, supports independent inheritance of different chromosomes, and lets genes occupy specific locations that can be regulated separately.
Marking notes. 1 mark for naming the structure/process correctly, 1 mark for explaining what it does for the cell (not just a description). No mark for vague answers such as "it holds DNA".
Q4 — Cloze paragraph (10 marks)
4.1 DNA • 4.2 circular • 4.3 nucleoid • 4.4 plasmids • 4.5 vectors • 4.6 nucleus • 4.7 linear • 4.8 proteins • 4.9 chromatin • 4.10 chromosomes.
Marking notes. 1 mark per correct blank. Accept "histone proteins" for 4.8.