Cell Division, Grade 10: DNA Is Copied in Interphase, Not Prophase, and This Topic Says Both

"When cells are about to divide, each chromosome copies itself (prophase)."

DNA is copied in interphase, before mitosis starts. By the time prophase begins, every chromosome already consists of two identical chromatids joined at a centromere. That is why they look like an X.

If the copying happened in prophase there would be nothing to see at the start of prophase.

And this topic takes two different positions on it in the same twelve pages, with the formal assessment taking a third.

This page gives both units, six corrections, the cancer section handled properly, and a free 60-mark worksheet with its memo.

Where this fits in the curriculum

Subject Life Sciences
Grade 10
Term 1
Topic Topic 3, Cell division
Units Unit 1 the cell cycle and mitosis. Unit 2 cancer: when cell division goes wrong
Formal assessment Not of its own, but the Term 1 class test covers it. There is also an end-of-topic test, 28 marks, which adds up correctly
Marks Our worksheet is 60

Finding 1: four places, three positions, on the same question

Where When does DNA get copied? Right?
The cell cycle pages Interphase. "Replication of DNA and duplication of chromosomes" is listed as one of the stages of interphase Yes
The revision summary Prophase. "When cells are about to divide, each chromosome copies itself (prophase)" No
The end-of-topic test Before mitosis. "The chromosomes make copies of themselves before mitosis so that after division..." Yes
The Term 1 class test Prophase. A matching question leaves prophase to be paired with "the cell replicates its DNA", because every other option is used No

The two that are wrong are the two that matter most: the summary a learner revises from the night before, and the formal assessment they are marked on.

What actually happens, in order

Stage What happens Roughly how long
Interphase, growth The cell grows, makes proteins and builds organelles 8 to 10 hours
Interphase, replication Each chromosome copies itself. It now consists of two identical chromatids joined at a centromere 7 hours
Interphase, final growth Last preparations, and a check that the copying was done properly 5 hours
Prophase The already-doubled chromosomes become visible as the threads shorten and thicken. Nuclear membrane breaks down, spindle forms 60 minutes
Metaphase Chromosomes line up on the equator and attach to the spindle 10 minutes
Anaphase Centromeres split, chromatids pulled to opposite poles 10 minutes
Telophase New nuclear membranes form, chromatin unwinds 10 minutes
Cytokinesis The cytoplasm divides 25 minutes

About 90 per cent of a cell's life is interphase, which the end-of-topic test asks about directly, and the whole of DNA replication sits inside it.

Finding 2: prophase barely appears in the revision summary

Here are the mitosis bullets, as printed:

  • The chromosomes move to the centre of the cells (metaphase)
  • The centromere splits
  • The chromatids start to separate from one another (anaphase)
  • The chromatids move to opposite ends of the cells
  • A new nucleus forms at each end of the cell (telophase)

Metaphase, anaphase, telophase. Three of the four phases are named. The only time prophase appears in the whole summary is in the sentence that puts DNA replication in it.

So a learner revising from it meets three phases and one misconception, and will be asked for four phases in the exam.

Learn the four with what makes each one different. Prophase: the chromosomes appear and the nuclear membrane goes. Metaphase: they line up in the middle. Anaphase: the centromeres split and they are pulled apart. Telophase: new nuclei form. Everything before prophase is interphase.

Finding 3: centrioles are not in the nucleus

"There are no centrioles in the plant cell nucleus."

Centrioles are not inside the nucleus in any cell. In an animal cell they sit in the cytoplasm, just outside the nuclear membrane, which is exactly where the topic's own interphase diagram draws them.

The sentence should say there are no centrioles in plant cells. As written it tells a learner that animal cells keep theirs inside the nucleus, which is wrong and which contradicts the interphase diagram in the same unit.

The rest of that section is good, and these really are the two differences worth knowing:

Animal cell Plant cell
Centrioles Present, in the cytoplasm, and the spindle forms between them Absent. The spindle forms from the cytoplasm anyway
Cytokinesis A constriction pinches the cell in two from the outside A cell plate forms across the middle and grows outwards into a new cell wall

Finding 4: the test question that covers two phases

The end-of-topic test shows six micrographs and asks learners to identify the micrograph and name the stage for each description. Two of the three are clean. The first one is not:

"The nuclear membrane disappears and the chromosomes line up at the centre of the cell. (2)"

Half of the description Which stage
The nuclear membrane disappears Late prophase
The chromosomes line up at the centre Metaphase

Those are two stages and two different micrographs, and the question asks for one of each, for two marks.

If you are setting it, accept either, and then use it. The prophase to metaphase boundary is exactly where learners get lost, and a question that accidentally straddles it is a good place to stop and draw the line.

Finding 5: "benign" is never defined

The key words for the cancer unit give tumour, malignant and carcinogenic.

Benign is not among them, and it does not appear anywhere else in the topic.

Then:

  • The end-of-topic test asks whether "not all tumours are harmful" is true or false
  • The Term 1 class test offers benign as one of four options for "a tumour that is cancerous is said to be"

A learner who has never met the word cannot rule it out. It is one line:

Benign Malignant
Stays put. Does not spread to other parts of the body. Usually not dangerous, though it can press on things Spreads. Cells break away, travel in the blood, and start new growths elsewhere. This is what cancer means

Finding 6: the risks are listed in the wrong order of size

Among the causes of cancer, between ultraviolet radiation and X-rays, sits one unqualified bullet: "radiation from nuclear power stations can cause cancer."

For a learner in South Africa that is close to the smallest radiation risk there is. Normal operation of a power station gives the public a dose far below natural background radiation.

The radiation risk that matters here is the Sun. South Africa has one of the highest skin cancer rates in the world, and the test's own true or false question about sunscreen is exactly the right lesson.

And "high in protein" is not the risk either

"People with a diet that lacks fibre but is high in protein and fat have a greater chance of getting cancer of the colon."

The evidence is about red meat and processed meat, and about low fibre. It is not about protein as a category. Beans, fish, eggs and chicken are all protein.

Say red and processed meat, and say low fibre. A learner should not come away from a Life Sciences course believing that protein causes cancer.

The cancer bush, which deserves care rather than avoidance

Three consecutive bullets in the revision summary:

  • Cancer can be treated by surgery, radiation or chemotherapy
  • Traditional treatments for cancer include the cancer bush
  • There are a number of incorrect beliefs about cancer
  • Education is needed to help people understand more about cancer

Those sit against each other, and they are next to each other on the page.

Sutherlandia frutescens, the cancer bush or kankerbos, is a real South African plant with a long and genuine place in traditional medicine, and it has been the subject of proper research. There is no evidence that it shrinks a tumour or treats cancer.

Listing it immediately after surgery, radiation and chemotherapy puts it in a category it does not belong to, in a bulleted list where everything reads as equivalent.

The honest version respects both things. The cancer bush is a valuable piece of indigenous knowledge and worth studying as such, and the plant's common name reflects a hope rather than a result. The treatments that act on a tumour are surgery, radiation and chemotherapy. Those are two separate statements and the summary runs them into one.

This is not a small point in South Africa, and it is exactly what the summary's own next bullet is about.

What the material gets right

  • The cell cycle diagram has real timings, which almost no treatment bothers with: eight to ten hours of growth, seven of replication, five of final growth, then mitosis in under two. It makes the ninety per cent figure obvious rather than abstract
  • "The chromatids are now called chromosomes" at late telophase is precisely the point learners miss, and it is stated plainly
  • Mitosis in plant cells gets its own section, with the cell plate and the absent centrioles
  • The wool and Prestik model is a genuinely good free activity, and the kind of thing a class remembers
  • The end-of-topic test adds to its stated 28, and its cancer questions are well chosen: most cancers are not inherited, cancer is not contagious, sunscreen helps. Those three are the myths that matter

What this topic costs

Almost nothing, and the one thing worth buying is nearly out.

What the topic needs From us?
Wool and Prestik, for the mitosis model No. A stationery shop, and it is the best activity in the topic
Prepared slide, mitosis in onion root tip Yes, at R29,00. We have FOUR. Not four boxes. Four
A microscope to look at it with R1 990,00, 13 on hand. Everything in this topic is visible at 400x

Ask before you plan a lesson around the onion root tip slide. Four units is not a class set and it is not even a demonstration set. It is the slide every Grade 10 and Grade 12 class in the country wants, and we are nearly out of it.

Everything else in this topic is paper. The mitosis micrographs in the end-of-topic test are good enough to teach the sequence from, and sequencing six micrographs is worth six marks, so it is time well spent even without a slide.

What you should be able to do by the end

  • Define the cell cycle and name the three stages of interphase
  • Say when DNA is copied, and say it is interphase without hesitating
  • Name the four phases of mitosis in order and describe each one
  • Tell a chromosome from a chromatid, and say when a chromatid becomes a chromosome
  • Explain what cytokinesis is and that it is not part of mitosis
  • Give the two differences between mitosis in a plant cell and in an animal cell
  • Put six micrographs in order and name the stage in each
  • Define cancer, benign, malignant and carcinogen
  • Name the real causes of cancer in order of how much they matter, and recognise the common myths

Free worksheet and marking memo

Both free, no sign up, straight to the PDF.

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