The shape of the lesson
By the end of the lesson, learners can
- Gametes and fertilisation: In the gametes tab the sperm and egg cell are drawn at the same scale.
- Haploid and diploid: Extended.
- Sexual versus asexual: Extended.
- Sexual reproduction: fusion of the nuclei of two gametes to form a zygote; offspring genetically different.
- Fertilisation: fusion of the nuclei of gametes.
- Extended: gamete nuclei haploid (one set), zygote nucleus diploid (two sets).
- Discuss questions: give advantages and disadvantages, for the wild and for crops.
One picture every idea returns to
Sexual reproduction is a process involving the fusion of the nuclei of two gametes to form a zygote and the production of offspring that are genetically different from each other. Fertilisation is the fusion of the nuclei of gametes. Extended: the nuclei of gametes are haploid (one set of chromosomes) and the nucleus of a zygote is diploid (two sets).
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Two gametes, one zygote.. Most animals and flowering plants reproduce sexually. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Gametes and fertilisation | In the gametes tab the sperm and egg cell are drawn at the same scale. Project tab 2 of the lab (Gametes and fertilisation) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Haploid and diploid | Extended. | Pairs |
| 21 to 30 min | Teach and check: Sexual versus asexual | Extended. | Mix-Pair-Share |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 15 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Sexual versus asexual, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Mix-Pair-Share
Students mix around the room until you call pair; they pair with the nearest classmate, discuss the prompt, then mix again. Three prompts of rising difficulty, three different partners.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Fertilisation is the fusion of the nuclei, not just the sperm touching or entering the egg. | Write "the nucleus of the sperm fuses with the nucleus of the egg". |
| Variation is an advantage for the population, not a guarantee for each individual. | Write that some individuals are likely to survive a change, so the species is less likely to die out. |
Sexual reproduction: worksheet
6 questions, 15 marks. Written in the style of the papers; no past paper question is reproduced.
Describe sexual reproduction.
Define fertilisation.
Extended. A fruit fly has 8 chromosomes in each body cell. State the number of chromosomes in (a) a sperm cell and (b) a zygote. Use the terms haploid and diploid.
Extended. Explain why gametes must be haploid.
Extended. Discuss the advantages and disadvantages of sexual reproduction to a species of wild plant.
Extended. A plant breeder wants a new wheat variety that resists a fungal disease, then wants to grow large fields of it. Suggest why the breeder uses sexual reproduction for the first stage, and why the uniformity of the final crop is both useful and risky.
Answer key and marking notes
- The nuclei of two gametes (sex cells) fuse.
- This forms a zygote.
- The offspring produced are genetically different from each other (and from the parents).
The fusion of the nuclei of two gametes (a male and a female gamete).
- (a) 4: the sperm nucleus is haploid, with one set of chromosomes.
- (b) 8: the zygote nucleus is diploid, with two sets (one from each parent).
- At fertilisation two gamete nuclei fuse, so their chromosome numbers add together.
- If gametes are haploid the zygote is diploid, so the chromosome number stays the same in every generation (it does not double).
- Advantage: offspring show variation, so some may survive a new disease or a change in the environment.
- Advantage: the species can adapt by natural selection; seeds spread offspring away from the parent, reducing competition.
- Disadvantage: it needs two parents and often pollinators, so an isolated plant may not reproduce.
- Disadvantage: it is slower and uses more energy (flowers, nectar, many pollen grains).
- Sexual reproduction (crossing two parent plants) produces variation, so new combinations such as disease resistance can be found and selected.
- A uniform crop gives predictable yield and ripens at the same time.
- But if a new form of the fungus appears, all plants may be equally affected, so the whole crop could be lost.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
What is fertilisation?
- AThe fusion of the nuclei of two gametes
- BThe release of an egg from the ovary
- CThe transfer of pollen to a stigma
- DThe division of a zygote into two cells
Which word describes the cell formed when the nuclei of two gametes fuse?
- Azygote
- Bembryo
- Cgamete
- Dclone
Two black rabbits have six young. The young have different coat colours and patterns. Which feature of sexual reproduction explains this?
- AOffspring are genetically different from each other
- BOffspring are clones of one of the parents
- CGametes are made without any genes
- DOnly one parent passes on genes
Which is the correct pair of male and female gametes in humans?
- Asperm and egg cell
- Btestis and ovary
- Csemen and egg cell
- Dsperm and zygote
Which row correctly compares sexual and asexual reproduction?
- ASexual: two parents, varied offspring. Asexual: one parent, identical offspring
- BSexual: one parent, identical offspring. Asexual: two parents, varied offspring
- CSexual: two parents, identical offspring. Asexual: one parent, varied offspring
- DSexual: one parent, varied offspring. Asexual: two parents, identical offspring
Extended: a dog has 78 chromosomes in each body cell. How many chromosomes are in a dog sperm nucleus, and is it haploid or diploid?
- A39, haploid
- B78, diploid
- C39, diploid
- D156, haploid
Extended: which statement about chromosome sets is correct?
- AGamete nuclei are haploid and zygote nuclei are diploid
- BGamete nuclei are diploid and zygote nuclei are haploid
- CBoth gamete and zygote nuclei are haploid
- DBoth gamete and zygote nuclei are diploid
Extended: a rare orchid grows only in one valley and relies on one species of moth for pollination. Which is the greatest disadvantage of sexual reproduction for this orchid?
- AIf the moth dies out, the orchid cannot make seeds
- BThe offspring will all be identical to the parents
- CSexual reproduction produces too much variation
- DThe seeds will be diploid instead of haploid
Quiz key
Fertilisation is the fusion of gamete nuclei, forming a zygote. Release of an egg is ovulation, pollen transfer is pollination, and division of the zygote happens after fertilisation.
The single cell formed at fertilisation is a zygote. An embryo is the ball of cells that forms later; a gamete is a sex cell before fusion; a clone is an offspring of asexual reproduction.
Each young receives a different mix of genes from the two parents, so the offspring vary. Clones come from asexual reproduction; gametes do carry genes; and both parents pass on genes.
The human gametes are the sperm and the egg cell. Testes and ovaries are the organs that make gametes; semen is sperm plus fluid; a zygote forms after fertilisation.
Sexual reproduction (usually two parents) gives genetically varied offspring; asexual reproduction (one parent) gives identical clones. The other rows mix up the number of parents or the type of offspring.
Gametes are haploid, with one set: 78 ÷ 2 = 39. 78 is the diploid number of body cells; 39 is not diploid; 156 would be double the body cell number.
Each gamete nucleus has one set (haploid); fusion gives two sets in the zygote (diploid). If gametes were diploid the number would double each generation; a zygote with only one set or gametes with two sets would also break this pattern.
Sexual reproduction needs pollen carried between plants; relying on one pollinator is a serious risk. Sexual offspring are varied, not identical; variation is an advantage, not a disadvantage; seeds contain diploid cells, which is normal.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.