CIE iGCSE Biology-16.2 Sexual reproduction- Study Notes- New Syllabus
CIE iGCSE Biology-16.2 Sexual reproduction- Study Notes – New syllabus
CIE iGCSE Biology-16.2 Sexual reproduction- Study Notes -CIE iGCSE Biology – 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 fertilisation as the fusion of the nuclei of gametes
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:
(a) to a population of a species in the wild
(b) to crop production
Sexual Reproduction
Definition:
Sexual reproduction is a process that involves the fusion of the nuclei of two gametes (male and female), resulting in the formation of a zygote and genetically different offspring.
🧬 Key Features:
| Feature | Description |
|---|---|
| Two Parents | Male and female organisms are involved. |
| Gametes | Sex cells: sperm and egg (animals), pollen and ovule (plants). |
| Fertilization | Fusion of gamete nuclei forms a zygote. |
| Zygote | First cell of a new organism; divides to form an embryo. |
| Genetic Variation | Offspring are genetically different due to gene mixing. |
🌱 Examples of Sexual Reproduction:
- Animals: Humans, dogs, birds
- Plants: Flowering plants using pollen and ovules
✅ Advantages:
- Genetic variation increases survival chances in changing environments.
- Allows for natural selection and evolution.
❌ Disadvantages:
- Slower process
- Requires finding a mate
- Fewer offspring in a given time compared to asexual reproduction
🗒️Note:
Sexual reproduction = Gamete fusion → Zygote
Increases genetic diversity
Involves two parents and leads to variation
Sexual reproduction = Gamete fusion → Zygote
Increases genetic diversity
Involves two parents and leads to variation
Fertilisation
Definition:
Fertilisation is the fusion of the nuclei of male and female gametes to form a zygote.
🔍 Key Details:
| Aspect | Description |
|---|---|
| Gametes | Sperm (male) and egg/ovum (female) in animals; pollen and ovule in plants. |
| What fuses? | Only the nuclei of the two gametes fuse (not the whole cells). |
| Result | A zygote is formed – the first cell of a new organism. |
| Zygote | Diploid cell – contains full set of chromosomes (half from each parent). |
| Where it happens | In animals: oviduct; in plants: inside ovary after pollination. |
🧠 Importance of Fertilisation:
- Restores diploid number of chromosomes.
- Combines genetic material from two parents.
- Leads to genetic variation in offspring.
🗒️Note:
Fertilisation = fusion of gamete nuclei
Forms zygote → develops into embryo
Enables genetic variation
Fertilisation = fusion of gamete nuclei
Forms zygote → develops into embryo
Enables genetic variation
Chromosome Number in Gametes and Zygotes
Key Statements:
- The nuclei of gametes are haploid.
- The nucleus of a zygote is diploid.
📘 What Does That Mean?
| Term | Meaning | Example in Humans |
|---|---|---|
| Haploid (n) | Contains half the normal number of chromosomes (one set) | Gametes have 23 chromosomes |
| Diploid (2n) | Contains the full number (two sets – one from each parent) | Zygote has 46 chromosomes |
🔁 Gametes → Zygote:
Sperm (haploid, n) + Egg (haploid, n) → Zygote (diploid, 2n)
🧠 Why It’s Important:
- Maintains the chromosome number across generations.
- Diploid zygote divides by mitosis to grow into a full organism.
🗒️ Note:
Gametes = Haploid (n) → 1 set of chromosomes
Zygote = Diploid (2n) → 2 sets (1 from each parent)
Maintains chromosome stability across generations
Gametes = Haploid (n) → 1 set of chromosomes
Zygote = Diploid (2n) → 2 sets (1 from each parent)
Maintains chromosome stability across generations
Sexual Reproduction – Advantages & Disadvantages
Definition:
Sexual reproduction involves the fusion of gametes from two parents, producing genetically varied offspring.
(a) In the Wild (Natural Populations)
✅ Advantages:
| Benefit | Explanation |
|---|---|
| Genetic variation | Offspring have different genetic combinations, increasing survival chances in changing environments. |
| Natural selection | Favourable traits can spread, aiding evolution. |
| Disease resistance | More likely some individuals survive disease outbreaks. |
❌ Disadvantages:
| Limitation | Explanation |
|---|---|
| Slower process | Finding a mate takes time and energy. |
| Fewer offspring | Compared to fast asexual reproduction. |
| Not always successful | Fertilisation may not occur or may fail. |
(b) In Crop Production (Agriculture)
✅ Advantages:
| Benefit | Explanation |
|---|---|
| Genetic diversity | Crops are more adaptable to environmental stress or pest attacks. |
| Potential for selective breeding | Desired traits like disease resistance, drought tolerance, or better yield can be introduced. |
❌ Disadvantages:
| Limitation | Explanation |
|---|---|
| Slower propagation | Producing crops from seeds takes more time than cloning via cuttings or grafting. |
| Unpredictability | Offspring may not inherit the exact traits desired. |
| Costlier and labour-intensive | Controlled pollination and breeding require effort and resources. |
🗒️Note:
Sexual reproduction = variation + adaptability
Good for long-term survival, but slower
In farming: allows trait mixing, but takes time and control
Sexual reproduction = variation + adaptability
Good for long-term survival, but slower
In farming: allows trait mixing, but takes time and control