Objective: Evaluate the benefits of PGD and CVS, and reach a justified conclusion.
Before we start · Load the words & the structure
Two things to fix first
If these aren’t solid, the rest of the lesson collapses. Spend real time here.
1. Six words you’ll need
Say each word, get a guess, then reveal.
Evaluate
Weigh up the good and bad points, then reach a judgement — decide which is better.
Embryo
A ball of cells in the earliest stage of development, before it becomes a foetus.
Implant
To place an embryo into the woman’s uterus (womb) so a pregnancy can begin.
Terminate
To end a pregnancy.
Miscarriage
When a pregnancy is lost.
Ethical
To do with what people think is right or wrong.
2. What “evaluate” looks like — on something easy
Same three moves you’ll use on the science. Learn the shape here, where it’s obvious.
compare a benefitweigh the other sidejudge + justify + for whom
Q: Takeaway pizza or making your own — which is better?
A benefit of takeaway is that it’s much faster and you don’t have to clean up, so it’s better on a busy night.However, making your own is far cheaper and you control what goes in it, so it’s healthier.Overall, making your own is better if you have time and want to save money, because it costs a fraction of the price — but takeaway wins when you’re in a rush.
Point at it: notice the conclusion doesn’t say “both are good.” It picks one, says why, and says when. That exact move earns the marks later.
Do Now · Retrieval
What do we already know?
Whiteboards up. Answer all four, then we reveal.
1. What is a gene?
A section of DNA that codes for a particular characteristic (a protein).
2. How many pairs of chromosomes are in a human body cell?
23 pairs (46 chromosomes in total).
3. What causes an inherited genetic disorder?
A faulty allele (a faulty version of a gene) passed from parent to child.
4. Two carriers of a recessive disorder have a child (Cc × Cc). What is the chance the child is affected?
1 in 4 (25%) — only the cc combination is affected.
Step 1 · Decode the question
Read the information together
Tap any highlighted word — its meaning appears in the blue box below.
Embryo screening can be used to screen embryos for certain inherited disorders. Two ways of doing this are through PGD (pre-implantation genetic diagnosis) and CVS (chorionic villus sampling).
PGD involves IVF (in vitro fertilisation) of a few eggs, then taking a cell from each embryo when it is 3 days old. The DNA in the cell can then be tested. An unaffected embryo can be implanted in the woman’s uterus. The possibility of a false positive result is around 1 in 6. The procedure costs about £6000. Affected embryos would be discarded. Extra unaffected embryos might be frozen and kept for later implantation. Alternatively, the extra embryos might be used in scientific research.
CVS involves taking a sample of blood from the placenta a few weeks into pregnancy. DNA from white blood cells can then be tested. If an affected embryo is detected, the parents then have to decide whether to terminate the pregnancy or allow it to continue. CVS has a 1 percent chance of giving an incorrect result and a 0.9 percent chance of causing a miscarriage. CVS costs about £600.
Step 2 · Did they actually read it?
Quick literal check
Before any evaluating. If they can’t answer these, they misread the passage — go back.
Which method happens before pregnancy begins?
PGD — the embryo is tested in the lab, then only an unaffected one is implanted.
Which method is cheaper?
CVS — about £600, versus £6000 for PGD.
Which method carries a risk of causing a miscarriage?
CVS — a 0.9% chance.
Step 3 · Build the comparison
Pull the facts out of the passage
Ask the class for each fact first — then click the box to check. Don’t reveal early.
Criterion
PGD
CVS
Talk: on each row, which method “wins” — and for whom? A method can be better for one family and worse for another.
Step 4 · Spot the good writing
What does a good answer actually look like?
A, B or C on whiteboards. These test the writing, not the facts.
Step 5 · I do
A Level 3 answer — and how it’s built
compare a benefitweigh the other sidejustified conclusion
A benefit of CVS is that it is far cheaper — about £600 compared with £6000 — so it is available to more families, and it is more accurate, with only a 1% chance of an incorrect result against a 1 in 6 false positive rate for PGD.However, a major benefit of PGD is that screening happens before pregnancy, so only an unaffected embryo is implanted and parents avoid the difficult decision about ending a pregnancy. PGD also avoids the 0.9% miscarriage risk that CVS carries. On the other hand, PGD requires IVF and means affected embryos are discarded, which some people object to.Overall, PGD is the better method for parents who can afford it and who want to avoid the miscarriage risk and a termination decision, because it screens before pregnancy begins — but for families who cannot afford £6000, CVS is the more realistic and more accurate choice.
Step 6 · We do · The conclusion is where marks are lost
Fix these conclusions together
The question literally says “include a conclusion.” A real conclusion needs all three:
1 a clear choice
2 a reason (because…)
3 who it’s best for
“Overall, both methods have good and bad points.” Why does this score nothing?
No choice and no reason — it just says it’s complicated. Missing all three ingredients.
“Overall, PGD is the best.” Better — but what’s still missing?
It makes a choice (ingredient 1) but gives no reason and no “for whom.” Still Level 1–2.
Your turn: rewrite “PGD is the best” on whiteboards so it has all three ingredients.
“Overall, PGD is better for parents who can afford it and want to avoid a termination decision, because it screens before pregnancy begins.” — choice + reason + for whom = Level 3.
Step 7 · You do
Now write the full answer
On paper, in full sentences. These are sentence starters — finish each one in your own words. You don’t have to use them all, and you can write more.
One benefit of PGD is…
One benefit of CVS is…
This is better than the other method because…
However, a benefit of the other method is…
Overall, the better method is…
Step 8 · Self / peer assessment
Which level is your answer?
Swap books. Tick the highest level that is fully true. (Teacher: still read a sample yourself — KS3 self-marking runs generous.)
Level 3 (5–6 marks) Compares both methods using facts from the passage, and a conclusion that makes a choice and says why.
Level 2 (3–4 marks) Gives some benefits, but mostly of one method, or the conclusion doesn’t really justify the choice.
Level 1 (1–2 marks) Describes the methods but doesn’t really compare them or conclude.
Stretch (top group): now write the opposite conclusion — argue CVS is better — and make it just as convincing.