CIE iGCSE Co-ordinated Sciences-B17.2 Selection- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-B17.2 Selection – Study Notes
CIE iGCSE Co-ordinated Sciences-B17.2 Selection – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
Describe natural selection with reference to:
(a) genetic variation within populations
(b) production of many offspring
(c) struggle for survival, including competition for resources
(d) a greater chance of reproduction by individuals that are better adapted to the environment than others
(e) these individuals passing on their alleles to the next generation
Describe selective breeding with reference to:
(a) selection by humans of individuals with desirable features
(b) crossing these individuals to produce the next generation
(c) selection of offspring showing the desirable features
Supplement
Describe the development of strains of antibiotic-resistant bacteria as an example of natural selection
Outline how selective breeding by artificial selection is carried out over many generations to improve crop plants and domesticated animals and apply this to given contexts
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Natural Selection
📌 Introduction
Natural selection is the process by which individuals with traits that make them better adapted to their environment are more likely to survive and reproduce, passing on those traits to the next generation.
🔬 Key Steps
- Genetic variation
Within any population, individuals show differences in features (caused by mutations and genetic recombination).
Example: Some rabbits run faster than others. - Overproduction of offspring
Organisms usually produce more offspring than the environment can support.
Example: A fish lays hundreds of eggs, but only a few survive. - Struggle for survival
Because resources (food, space, mates) are limited, individuals must compete.
Predators, disease, and climate also act as pressures. - Differential survival & reproduction
Individuals better adapted to the environment have a higher chance of surviving.
These individuals are more likely to reproduce successfully. - Passing on alleles
Beneficial alleles (genes) are passed on to the next generation.
Over many generations, these advantageous traits become more common in the population.
📊 Summary Table
| Step | Natural Selection Process |
|---|---|
| (a) Variation | Genetic differences exist within population |
| (b) Overproduction | More offspring than can survive |
| (c) Struggle | Competition for limited resources |
| (d) Survival & reproduction | Best-adapted survive and reproduce |
| (e) Allele transfer | Beneficial traits passed to offspring |
⚡ Quick Recap
Variation exists.
Too many offspring → struggle.
Best-adapted survive and reproduce.
Pass on beneficial alleles.
Population becomes better adapted over time.
👉 Memory tip: “VOSSAP” → Variation, Offspring, Struggle, Survival, Alleles, Population.
Selective Breeding
📌 Introduction
Selective breeding (artificial selection) is when humans choose organisms with desirable traits and breed them to produce offspring with those traits. Over generations, the traits become more common in the population.
🔬 Key Steps
- Selection of individuals with desirable features
Humans pick plants or animals that show traits they want.
Examples: Cows that give more milk, Dogs that are gentle and loyal, Wheat plants with higher yield. - Crossing these individuals
The selected individuals are bred together.
Aim: Combine and strengthen the desirable characteristics in the offspring. - Selection of offspring
From the next generation, humans again choose offspring showing the best traits.
The process is repeated for many generations until the trait becomes common in the population.
📊 Examples
| Organism | Desirable Feature | Selective Breeding Result |
|---|---|---|
| Cows 🐄 | High milk yield | Herd with better milk production |
| Dogs 🐕 | Temperament, size | Breeds like Labradors or Pugs |
| Crops 🌾 | Disease resistance, yield | Wheat with high yield & strong stalks |
⚡ Quick Recap
Step 1: Humans select individuals with desired traits.
Step 2: Breed them together.
Step 3: Select offspring with best features.
Repeat → trait spreads in population.
👉 Memory trick: “Pick → Pair → Pick again.”
Selective Breeding (Artificial Selection)
📌 Introduction
Selective breeding = when humans choose organisms with desirable traits and breed them for several generations so the trait becomes common.
Used to improve crop plants and domesticated animals.
🌱 Process of Selective Breeding
- Identify desirable features
Crops → high yield, disease resistance, better taste.
Animals → more milk, fast growth, good temperament. - Select parents
Humans choose individuals showing the desired trait. - Cross-breeding
These individuals are bred together. - Select offspring
From the next generation, individuals with the best traits are chosen. - Repeat for many generations
After many cycles, the desirable feature becomes common and stable in the population
📊 Applications
| Context | Example | Desired Outcome |
|---|---|---|
| Crop plants | Wheat with disease resistance | Higher yield & less loss to infections |
| Maize | Large kernels, sweet taste | Better food quality |
| Dairy cows | High milk yield | More milk production |
| Sheep | Thick wool | Better wool quality |
| Dogs | Gentle temperament | Safe family pets |
⚡ Quick Recap
Steps: Select parents → Breed → Pick best offspring → Repeat many generations.
Goal: Spread desirable traits in population.
Applied to: Crops (yield, resistance), Animals (milk, meat, temperament).
👉 Memory trick: “Select → Breed → Select → Repeat.”
Antibiotic Resistance – Natural Selection in Bacteria
📌 Introduction
Some bacteria develop resistance to antibiotics. This happens by natural selection, and resistant strains (like MRSA) are now a serious medical problem.
🔬 Step-by-Step Development
- Variation in bacteria
Within a bacterial population, random mutations occur.
Some mutations give resistance to antibiotics. - Exposure to antibiotic
When treated with an antibiotic, most bacteria (non-resistant) are killed.
Resistant bacteria survive. - Survival and reproduction
The resistant bacteria reproduce quickly by binary fission.
They pass on their resistant alleles/genes to offspring. - Spread of resistance
Over many generations, the resistant strain becomes the majority of the population.
The antibiotic becomes less effective.
📊 Summary Table
| Step | What happens |
|---|---|
| Variation | Some bacteria mutate → resistance |
| Antibiotic use | Non-resistant die, resistant survive |
| Reproduction | Resistant bacteria multiply |
| Result | Resistant strain spreads |
🧬 Key Example
MRSA (Methicillin-resistant Staphylococcus aureus) → resistant to many antibiotics.
Shows how misuse/overuse of antibiotics speeds up natural selection.
⚡ Quick Recap
Resistance arises by mutation.
Antibiotics kill non-resistant bacteria.
Resistant survive → reproduce → spread.
Natural selection in action.
👉 Memory trick: “Mutate → Survive → Multiply → Spread.”