CIE iGCSE Co-ordinated Sciences-B15.2 Sexual reproduction- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-B15.2 Sexual reproduction – Study Notes
CIE iGCSE Co-ordinated Sciences-B15.2 Sexual reproduction – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
Describe sexual reproduction as 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
Describe a species as a group of organisms that can reproduce to produce fertile offspring
Supplement
State that nuclei of gametes are haploid and that the nucleus of a zygote is diploid
Discuss the advantages and disadvantages of sexual reproduction to a population of a species in the wild
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Sexual Reproduction
📌 Definition
Sexual reproduction is a process that:
- Involves the fusion of the nuclei of two gametes (sex cells).
- Produces a zygote (fertilised egg).
- Results in offspring that are genetically different from each other and from the parents.
🌱 Key Points
- Gametes:
Male → sperm (in animals), pollen grain (in plants).
Female → egg/ovum (in animals), ovule (in plants). - Fusion = fertilisation → zygote formed.
- Zygote divides by mitosis → develops into an embryo.
- Variation arises due to:
Mixing of parental genes.
Random fusion of gametes.
📊 Summary Table
| Feature | Asexual Reproduction | Sexual Reproduction |
|---|---|---|
| Parents involved | 1 | 2 |
| Gametes | Not involved | Involved |
| Offspring | Genetically identical (clones) | Genetically different (variation) |
| Adaptability | Low | High |
⚡ Quick Recap
Sexual reproduction = fusion of gametes → zygote → genetic variation.
Helps species adapt & survive in changing environments.
Memory tip: “Sexual = Shuffle genes → Strong variation.”
Species – Definition
📌 Definition
A species is a group of organisms that:
- Share similar characteristics.
- Can reproduce with each other (interbreed).
- Produce fertile offspring (offspring that can also reproduce).
🌱 Key Points
- Fertile = able to produce more offspring.
- Members of the same species share a common gene pool.
- Different species usually cannot interbreed successfully.
- If they do, the offspring (hybrid) is often sterile (e.g. mule = horse × donkey).
📊 Examples
| Species | Offspring | Fertility |
|---|---|---|
| Horse × Horse | Foal | Fertile |
| Donkey × Donkey | Foal | Fertile |
| Horse × Donkey | Mule | Sterile |
⚡ Quick Recap
Species = Same group → Interbreed → Fertile offspring.
Hybrids (e.g. mule) show why fertile offspring is the key test.
Memory tip: “Species = Same set, same success in breeding.”
Haploid & Diploid Nuclei
📌 Key Statement
Gametes (sperm, egg, pollen, ovule) have haploid nuclei → contain half the normal number of chromosomes (n). When gametes fuse at fertilisation, they form a zygote. The zygote’s nucleus is diploid → contains the full set of chromosomes (2n).
🌱 Key Points
- Haploid = one set of chromosomes (n).
- Diploid = two sets of chromosomes (2n).
- In humans:
- Gamete nucleus = 23 chromosomes (haploid).
- Zygote nucleus = 46 chromosomes (diploid).
📊 Summary Table
| Cell Type | Chromosome Set | Example |
|---|---|---|
| Gametes | Haploid (n) | Sperm, Egg, Pollen, Ovule |
| Zygote | Diploid (2n) | Fertilised egg |
⚡ Quick Recap
Gametes = Haploid (n) → half set.
Zygote = Diploid (2n) → full set.
Memory tip: “Half in gametes, Double in zygote.”
Sexual Reproduction in the Wild
📌 Introduction
Sexual reproduction involves the fusion of gametes to form a zygote, producing genetically varied offspring. In wild populations, this has both benefits and risks.
✅ Advantages (to the species)
- Genetic variation → Offspring are different, increasing adaptability. Some may survive better if the environment changes.
- Natural selection → Favourable traits spread, harmful traits eliminated.
- Disease resistance → Variation means not all individuals are equally vulnerable to the same disease.
- Survival in changing conditions → Species more likely to persist under climate change, predators, or competition.
❌ Disadvantages (to the species)
- Slower process → Finding mates takes time, slower than asexual reproduction.
- Energy costly → Requires energy for producing gametes, finding mates, and sometimes courtship.
- Not guaranteed → If mates are scarce, reproduction may not happen.
- Smaller population growth → Fewer offspring in the same time compared to asexual reproduction.
📊 Summary Table
| Advantages | Disadvantages |
|---|---|
| Produces variation → adaptability | Slower than asexual |
| Allows natural selection | Energy costly |
| Increases disease resistance | Needs mates |
| Better survival in changing environments | Fewer offspring in same time |
⚡ Quick Recap
Sexual = Variation = Survival in change
Disadvantage = Slow & costly
Memory tip: “Sexual shuffles genes → strong but slow.”