KS3 Science Study Pack: Variation and Inheritance

Key Knowledge

Variation means the differences between individuals of the same species. A species is a group of organisms that can reproduce with one another to produce offspring of the same species. Humans are one species, but no two people in a class are exactly the same. Oak trees are one type of plant, but their leaves may differ in length, shape, colour, or the amount of insect damage. A population of rabbits living in the same field may contain individuals with different sizes, fur colours, running speeds, and resistance to disease.

Variation matters because it helps explain why organisms look and behave differently. It is also important for survival. If all individuals in a population were identical, a new disease or environmental change might affect all of them in the same way. When there is variation, some individuals may have features that help them survive better in the changed conditions.

Variation can be caused by:

• inherited factors, which come from genetic information passed from parents to offspring
• environmental factors, which come from surroundings, lifestyle, diet, climate, injury, disease, or learning
• a combination of inherited and environmental factors

For example, natural eye colour is mostly inherited. A scar from an accident is environmental. Height is affected by inherited information, but also by diet, health, and exercise during growth.

What Variation Means

In a class, students may vary in height, hand span, natural hair colour, eye colour, fingerprints, reaction time, language spoken, and learned skills such as playing a musical instrument. Some of these differences are inherited, some are environmental, and some are affected by both.

In a garden, plants of the same species may vary in height, leaf length, flower colour, fruit size, and how quickly they grow. Some plant variation is inherited, such as a variety of apple tree producing a particular fruit colour. Some is environmental, such as a plant growing taller when it receives more light, water, and minerals.

In a population of animals, individuals may vary in fur thickness, body mass, speed, camouflage, beak shape, resistance to disease, and behaviour. These differences can affect how well animals survive in their habitat.

Types of Variation

Variation can be continuous or discontinuous.

Continuous variation means values can take any value across a range. It is usually measured using numbers and units. Height, body mass, hand span, leaf length, reaction time, and running speed are examples. In a class, heights might range from 1.35 m to 1.75 m, with many possible values between them.

Discontinuous variation means values fall into separate categories or groups. It is usually counted, not measured on a continuous scale. Blood group, attached or detached earlobes, eye colour categories, flower colour in some plant varieties, and sex in many species are examples. At KS3, tongue rolling is sometimes used as a simplified example, but real human characteristics are often more complex than simple classroom categories.

Feature	Continuous variation	Discontinuous variation
Meaning	Values can take a range of measurements	Values fall into clear groups
Data type	Measured data	Category counts
Examples	Height, mass, hand span, leaf length, reaction time	Blood group, eye colour category, flower colour category
Suitable display at KS3	Line graph for change over time, grouped bar chart, histogram if taught	Bar chart or tally chart
Common mistake	Treating measurements as fixed groups only	Joining category bars with a line as if there are values between groups

Inherited and Environmental Variation

Inherited variation is caused by genetic information passed from parents to offspring during reproduction. This is why offspring often resemble their parents. Humans may inherit natural eye colour, natural hair colour, blood group, and some aspects of height. Plants may inherit flower colour, fruit type, or leaf shape. Animals may inherit fur colour, body shape, and some behaviours.

Environmental variation is caused by the conditions an organism experiences during its life. Examples include scars, suntan, language, learned skills, body mass affected by diet and exercise, plant growth affected by light and water, and animal size affected by food supply or disease.

Many characteristics are affected by both inherited and environmental factors. Height is a good example. A person may inherit genetic information that affects potential height, but poor nutrition or illness during growth can affect the final height reached. A plant may inherit the ability to grow tall, but it may stay small if it receives little light or water.

Type of variation	Cause	Human example	Plant or animal example	Important note
Inherited variation	Genetic information from parents	Natural eye colour, blood group	Fur colour in some animals, flower colour in some plants	Passed on during reproduction
Environmental variation	Conditions during life	Scar, language learned, suntan	Plant height affected by light; animal body mass affected by food	Usually not passed on as inherited information
Both inherited and environmental	Genetic information plus surroundings	Height, body mass, sporting performance	Crop yield affected by variety and fertiliser	Both factors interact

DNA, Chromosomes, Genes, and Inheritance

Most body cells contain a nucleus. The nucleus controls many cell activities and contains chromosomes. Chromosomes are long structures made of DNA. DNA is a chemical that carries genetic information. A gene is a short section of DNA that contains instructions for a particular inherited characteristic.

Body cell
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Nucleus
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Chromosomes
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DNA
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Genes = sections of DNA with instructions

Chromosomes and DNA are not unrelated things. Chromosomes are made from DNA. Genes are sections of DNA. Plants, animals, fungi, and many microorganisms have genetic material, not only humans.

Inheritance is the passing of genetic information from parents to offspring during reproduction. Offspring usually resemble their parents because they receive genetic information from them. However, offspring are not usually identical to either parent because they receive a mixture of genetic information. Environmental factors also affect how some characteristics develop.

Parent 1 genetic information  \
                                >  Offspring with a mixture of inherited features
Parent 2 genetic information  /

At KS3, you do not need detailed genetic crosses or Punnett squares for this topic. The key idea is that inherited information is carried in DNA and passed from parents to offspring.

Inherited Characteristics and Learned Behaviours

Inherited characteristics are features passed through genetic information. Natural eye colour, natural hair colour, blood group, and some aspects of height are inherited.

Learned behaviours are gained through experience, teaching, practice, or the environment. Speaking a language, playing the piano, riding a bicycle, and remembering a route to school are learned. A person may inherit features that affect their body or nervous system, but the skill itself is not passed on as a ready-made ability through DNA.

This distinction is important because inherited information can be passed to offspring, but most learned skills are not inherited. If a parent learns to play the guitar, their child does not inherit the ability to play the guitar automatically.

Variation in a Population

A population is a group of organisms of the same species living in the same area. Variation within a population can help survival. Suppose a disease affects a crop plant. If all plants are genetically very similar, the disease may spread through the whole crop. If there is more inherited variation, some plants may be more resistant and survive.

Variation also matters when habitats change. If a habitat becomes colder, drier, hotter, or more polluted, individuals with helpful inherited features may survive and reproduce more successfully. Over many generations, helpful features may become more common. This does not mean individual organisms change because they try hard. Adaptations usually become common in populations over many generations.

Variation can also help a population recover after environmental stress. For example, if some insects in a population are better camouflaged on darker tree bark, they may be less likely to be eaten by birds in that habitat. This is a simplified example of how variation and survival can be linked.

Adaptations for Survival

An adaptation is a feature or behaviour that helps an organism survive and reproduce in its environment. The environment includes living factors, such as predators and food, and non-living factors, such as temperature, light, water, and soil.

Habitat condition -> Useful feature -> Better survival -> More likely to reproduce

Adaptations can be structural, behavioural, or physiological.

Structural adaptations are physical features of an organism's body. Examples include thick fur, cactus spines, streamlined fish bodies, bird beak shapes, and leaf shape.

Behavioural adaptations are actions that help survival. Examples include migration, hibernation, nocturnal activity, courtship behaviour, and grouping together for protection.

Physiological adaptations are internal body processes that help survival. At KS3, these should be kept simple. Examples include camels conserving water and some plants opening and closing stomata to control water loss.

Organism	Habitat	Adaptation	Type	Survival advantage
Polar bear	Arctic ice and cold seas	Thick fur and fat layer	Structural	Reduces heat loss in cold conditions
Cactus	Desert	Spines instead of broad leaves	Structural	Reduces water loss and protects the plant
Camel	Dry desert	Conserves water and can cope with long periods without drinking	Physiological	Helps survival where water is scarce
Fish	Water	Streamlined body	Structural	Reduces water resistance when swimming
Finch	Islands with different foods	Different beak shapes	Structural	Helps feeding on different food types
Hedgehog	Seasonal UK habitat	Hibernation in winter	Behavioural	Reduces energy use when food is limited
Insect	Tree bark or leaves	Camouflage colour	Structural	Makes it harder for predators to see it

Not every feature of an organism is an adaptation. Some features may be neutral, caused by the environment, or inherited without giving a clear survival advantage. Scientists need evidence before claiming that a feature is an adaptation.

Adaptations do not appear instantly because an organism needs them. A polar bear does not grow thicker fur during its lifetime because the Arctic is cold. Instead, inherited variation exists in a population, and over many generations features that help survival and reproduction may become more common.

Worked Example: Explaining an Adaptation

Example: a cactus in a desert.

1. Name the feature: cactus spines.
2. Link it to the habitat: deserts are dry and water is limited.
3. Explain how it helps survival: spines have a smaller surface area than broad leaves, so they reduce water loss. They also protect the cactus from animals that might eat it.
4. Explain why it does not appear instantly: cactus spines are inherited features. They became common over many generations because plants with helpful features were more likely to survive and reproduce in dry habitats.

Selective Breeding

Selective breeding is when humans choose parents with useful inherited characteristics and breed them to produce offspring with those characteristics. It has been used for crops, farm animals, and pets.

Choose parents with useful feature
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Breed them
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Select offspring with strongest useful feature
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Repeat for many generations

Selective breeding only works for inherited characteristics. Training an animal is not selective breeding because training changes behaviour during the animal's life and is not automatically passed to offspring. For example, training a dog to sit does not mean its puppies are born knowing how to sit.

Examples of selective breeding include:

• wheat bred for high yield and disease resistance
• dairy cattle bred for high milk production
• sheep bred for wool quality or meat production
• apples bred for taste, storage life, or disease resistance
• tomatoes bred for fruit size or shelf life
• dog breeds selected for body shape, coat type, or behaviour

Desired characteristic	Chosen parents	Benefit	Possible risk
High milk yield in dairy cattle	Cows and bulls from high-yield families	More milk for food production	Reduced genetic variation or health problems
Disease resistance in wheat	Plants that stay healthy during disease exposure	Less crop loss and fewer chemical sprays	Other useful traits may be lost if selection is too narrow
Large tomato fruits	Plants producing large fruits	Higher food yield	Fruit may become more easily damaged or need more resources
Thick wool in sheep	Sheep with thick, good-quality fleece	More wool for clothing	Inbreeding may increase inherited health problems
Flat face in some pet dogs	Dogs with a chosen face shape	Appearance preferred by some owners	Breathing problems and ethical concerns

Worked Example: Selective Breeding Sequence

A farmer wants wheat plants with high yield and disease resistance.

1. Identify the useful characteristics: high grain yield and resistance to a common disease.
2. Choose parent plants: select wheat plants that produce a high mass of grain and show little disease damage.
3. Breed the chosen plants.
4. Grow the offspring and measure their yield and disease resistance.
5. Choose the best offspring as parents for the next generation.
6. Repeat the process for many generations.

Benefit: the crop may produce more food and lose fewer plants to disease.

Risk: repeated breeding from a narrow group of related plants can reduce genetic variation. If a new disease appears, many plants may be vulnerable.

Selective breeding can improve food production, but it can also raise ethical issues. Some selectively bred animals suffer health problems because humans have selected extreme features. Responsible breeding should consider health and welfare, not only appearance or profit.

Extinction

Extinction is the permanent disappearance of a species. A species is extinct when no living members of that species remain anywhere on Earth. Extinction does not mean an animal has moved away from one area. If a species has disappeared from one region but still exists elsewhere, it is locally extinct in that region, not globally extinct.

Environmental change
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Food or habitat becomes limited
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Fewer individuals survive and reproduce
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Population falls
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Species may become extinct

Extinction can happen naturally, but human activity can increase extinction risk. Causes include rapid environmental change, habitat loss, climate change, pollution, overhunting, disease, competition, lack of food, and failure to reproduce successfully.

Cause of extinction	How it affects survival or reproduction	Example
Habitat loss	Removes food, shelter, nesting sites, or breeding areas	Orangutans affected by forest loss
Climate change	Changes temperature, rainfall, ice cover, or food webs	Polar bears affected by reduced sea ice
Pollution	Poisons organisms or damages habitats	Amphibians affected by polluted water
Overhunting or overfishing	Removes individuals faster than they can reproduce	Dodo hunted and affected by introduced species
Disease	Kills individuals or reduces breeding success	Disease affecting amphibian populations
Competition	New or existing species use the same food or space	Native species outcompeted by introduced species
Lack of food	Individuals cannot survive or raise offspring	Species affected when prey or plants decline
Failure to reproduce	Population cannot replace individuals that die	Small isolated populations with few mates

Examples of extinct species include the dodo and woolly mammoth. Dinosaurs are often used as an extinction example, but dinosaurs included many different groups, and their extinction involved major environmental changes long ago. Birds are living descendants of one dinosaur group, so it is more accurate to say that many non-bird dinosaur groups became extinct.

Modern threatened species include rhinos, orangutans, bees, and many amphibians. Human actions can increase risk through habitat destruction, pollution, climate change, overfishing, and hunting. Humans can also reduce risk through habitat protection, conservation breeding, reducing pollution, protecting food sources, and laws that prevent overhunting.

Worked Example: Extinction Reasoning

Imagine a small lizard species living in a dry grassland. Over 20 years, the habitat becomes hotter and drier. Farming also breaks the habitat into small fragments.

Food supply may fall because fewer insects survive in the drier habitat. Reproduction may decrease because lizards have fewer safe nesting places and fewer mates nearby. Competition may increase if other species move into the remaining suitable areas. If the lizard population has variation, some individuals may cope slightly better with heat or find food more successfully. However, if the change is too rapid or the population is too small, not enough individuals survive and reproduce. The population may fall until the species becomes extinct.

Working Scientifically with Variation Data

Scientists collect data to investigate variation. Data must be collected fairly, safely, and respectfully.

For human variation surveys:

• avoid sensitive or intrusive characteristics
• use simple measurements such as hand span, height, arm span, or reaction time
• anonymise results where possible
• do not judge ability, health, worth, identity, or future from inherited characteristics
• use the same measuring method for everyone
• explain that correlation does not always prove causation

For plant investigations:

• use the same plant species
• use plants with the same starting size where possible
• keep soil type, container size, temperature, and water the same unless one of them is the independent variable
• repeat measurements and calculate a mean
• look for anomalies

Repeatability means the same person or group can repeat the method and get similar results. Reliability means the evidence is trustworthy, often because there are enough repeats, a suitable sample size, and consistent methods. Accuracy means how close a measurement is to the true value. Precision means how close repeated measurements are to each other, or how small the measurement intervals are.

Investigation	Independent variable	Dependent variable	Control variables	Reliability improvements
Does light affect seedling height?	Light level	Seedling height in cm	Plant species, starting size, soil, water, container size, temperature, time grown	Use several plants per light level, repeat measurements, calculate means
Do students in a class vary in hand span?	Student tested, or group compared	Hand span in cm	Same measuring method, same hand, same ruler position	Use a larger sample, repeat each measurement, anonymise data
Does fertiliser affect plant growth?	Fertiliser amount	Plant height or mass	Plant species, soil, water, light, temperature, time	Use repeat plants, keep fertiliser amounts accurate, calculate mean growth

Data Task 1: Hand Span Variation

The table shows hand span measurements for 12 students. Hand span is measured from the tip of the thumb to the tip of the little finger when the hand is stretched out.

Student	Hand span (cm)
A	16.2
B	18.1
C	17.5
D	19.0
E	15.8
F	18.4
G	17.9
H	16.7
I	20.1
J	18.0
K	17.3
L	16.9

To calculate the range:

1. Find the largest value: 20.1 cm.
2. Find the smallest value: 15.8 cm.
3. Subtract: 20.1 cm - 15.8 cm = 4.3 cm.

The range of hand spans is 4.3 cm.

Grouped data:

Hand span interval (cm)	Number of students
15.0-15.9	1
16.0-16.9	3
17.0-17.9	3
18.0-18.9	3
19.0-19.9	1
20.0-20.9	1

The most common intervals are 16.0-16.9 cm, 17.0-17.9 cm, and 18.0-18.9 cm, each with 3 students. A suitable pattern sentence is: most students had hand spans between 16.0 cm and 18.9 cm, while only one student had a hand span above 20 cm.

Limitations:

• The sample size is small, so it may not represent all Year 8 students.
• Measurement technique may vary between students.
• Hand span can be sensitive if used to compare individuals, so data should be anonymised and discussed respectfully.

Data Task 2: Plant Growth Investigation

A class investigated how light level affects seedling height after 14 days. They used the same species of seedling, the same soil, the same container size, and the same amount of water.

Light level	Seedling 1 (cm)	Seedling 2 (cm)	Seedling 3 (cm)	Mean height (cm)
Full light	12.0	11.5	12.4	12.0
Half light	8.2	8.5	8.0	8.2
Very low light	3.1	9.8	3.4	5.4

The independent variable is the light level. The dependent variable is seedling height in centimetres. Control variables include plant species, starting size, soil type, water amount, container size, temperature, and time grown.

The best growth condition was full light, with a mean height of 12.0 cm. Half light produced a lower mean height of 8.2 cm. Very low light produced a mean of 5.4 cm, but Seedling 2 at very low light was 9.8 cm, which is an anomalous result because it is much taller than the other two seedlings in the same condition. It might have received extra light, been measured incorrectly, or started larger than the others.

An improvement would be to use more seedlings in each light condition and calculate a mean from a larger number of repeats. This would make the conclusion more reliable.

Data Task 3: Discontinuous Variation Bar Chart

The table shows eye colour categories recorded in a class survey. The data should be shown as a bar chart because eye colour is counted in groups.

Eye colour category	Number of students
Brown	12
Blue	9
Green	4
Hazel	5

Simple text bar chart:

Brown | ############ (12)
Blue  | #########    (9)
Green | ####         (4)
Hazel | #####        (5)

Pattern: brown was the most common category with 12 students, while green was the least common with 4 students. A limitation is that eye colour categories can be difficult to judge accurately because some people have mixed colours or different lighting can affect observations.

Data Task 4: Extinction Risk Data

The table shows a simplified population of a wetland bird species over four years.

Year	Wetland habitat area (hectares)	Breeding pairs	Chicks surviving to autumn
2022	120	80	96
2023	95	65	70
2024	70	44	38
2025	52	31	21

The trend is that habitat area, breeding pairs, and surviving chicks all decrease. Habitat area falls from 120 hectares in 2022 to 52 hectares in 2025. Breeding pairs fall from 80 to 31. Chicks surviving to autumn fall from 96 to 21. This suggests extinction risk is increasing because fewer adults are breeding and fewer young birds are surviving.

A conservation action could be to protect and restore wetland habitat, reduce pollution, and prevent disturbance during the breeding season. A limitation is that the table does not show disease, predator numbers, weather, or food supply, so habitat loss may not be the only cause.

Worked Examples

Classifying Variation

Characteristic	Inherited, environmental, or both?	Reasoning
Eye colour	Mostly inherited	Natural eye colour is affected by genetic information from parents
Height	Both	Genetic information affects potential height, but diet and health also matter
Scar from an accident	Environmental	It is caused by an event during life, not inherited genetic information
Blood group	Inherited	Blood group is passed through genetic information
Ability to play the piano	Environmental	It is learned through practice and teaching
Natural hair colour	Mostly inherited	It is affected by genetic information
Body mass	Both	Inherited factors can affect body build, but diet, exercise, health, and lifestyle also affect mass
Plant leaf length	Both	Plant variety may inherit a typical leaf size, but light, water, and minerals affect growth

Identifying Continuous and Discontinuous Variation

Height is continuous variation because it is measured on a scale and can take many values, such as 142.5 cm, 142.6 cm, or 150.2 cm. A line graph is suitable if height is measured over time. A grouped bar chart or histogram can be used to show the distribution of heights in intervals.

Eye colour is discontinuous variation because it is counted in categories, such as brown, blue, green, or hazel. A bar chart is suitable because the categories are separate. A line graph would not be suitable because there is no continuous scale between brown and blue.

Interpreting a Variation Table

Use the hand span table from Data Task 1.

1. Smallest value = 15.8 cm.
2. Largest value = 20.1 cm.
3. Range = 20.1 cm - 15.8 cm = 4.3 cm.
4. Most common grouped intervals = 16.0-16.9 cm, 17.0-17.9 cm, and 18.0-18.9 cm.
5. Pattern sentence: most students had hand spans between 16.0 cm and 18.9 cm, and only two students had hand spans of 19.0 cm or more.

Key Vocabulary

Term	KS3 definition	Example
Variation	Differences between individuals of the same species	Different heights in a class
Inheritance	Passing genetic information from parents to offspring	A child inheriting natural eye colour information from parents
DNA	A chemical that carries genetic information	DNA is found in chromosomes
Chromosome	A long structure made of DNA, found in the nucleus of most body cells	Human body cells contain chromosomes in the nucleus
Gene	A short section of DNA with instructions for an inherited characteristic	A gene may affect a particular inherited feature
Inherited variation	Differences caused by genetic information from parents	Blood group
Environmental variation	Differences caused by surroundings or experiences	A scar from an accident
Continuous variation	Variation with values across a range	Hand span measured in centimetres
Discontinuous variation	Variation with values in clear categories	Blood group categories
Adaptation	A feature or behaviour that helps survival and reproduction in a habitat	Thick fur in a cold habitat
Structural adaptation	A physical body feature that helps survival	Streamlined fish body
Behavioural adaptation	An action that helps survival	Migration
Physiological adaptation	An internal process that helps survival	Conserving water
Selective breeding	Humans choosing parents with useful inherited features to produce offspring with those features	Breeding wheat for disease resistance
Extinction	Permanent disappearance of a species	The dodo is extinct
Species	A group of organisms that can reproduce to produce offspring of the same species	Humans are one species
Population	Members of the same species living in the same area	A population of bees in a meadow
Habitat	The place where an organism lives	Woodland, pond, desert, Arctic ice
Biodiversity	The variety of living organisms in an area	A rainforest has high biodiversity
Independent variable	The factor deliberately changed in an investigation	Light level in a plant growth test
Dependent variable	The factor measured in an investigation	Seedling height
Control variable	A factor kept the same to make a test fair	Same soil type
Repeatability	Getting similar results when the same method is repeated	Measuring hand span three times and getting similar values
Reliability	How trustworthy evidence is	More repeats and a larger sample improve reliability
Accuracy	How close a measurement is to the true value	Reading a ruler correctly
Precision	How close repeated measurements are to each other, or how detailed the scale is	Measuring to the nearest millimetre is more precise than nearest centimetre

Common Misconceptions

All variation is inherited. This is incorrect because some variation is caused by the environment. Scars, language, and suntan are environmental. Many features, such as height and plant growth, are affected by both inherited and environmental factors.

Environmental changes directly change an individual's DNA in a helpful way during its lifetime. This is incorrect. Organisms do not choose useful inherited changes because they need them. Environmental conditions can affect how an organism grows or behaves, but helpful inherited adaptations usually become common over many generations.

Adaptations happen instantly because an organism needs them. This is incorrect. Adaptations usually develop in populations over many generations. Individuals with helpful inherited features are more likely to survive and reproduce.

Every feature is an adaptation. This is incorrect. Some features may be neutral, environmental, or inherited without a clear survival advantage.

DNA and chromosomes are unrelated. This is incorrect. Chromosomes are made of DNA, and genes are sections of DNA.

Genes, DNA, and chromosomes are only found in humans. This is incorrect. Plants, animals, fungi, and many microorganisms have genetic material.

Offspring are identical to their parents. This is incorrect. Offspring inherit genetic information from parents, but usually receive a mixture of features and are also affected by their environment.

Learned skills are inherited. This is incorrect. Speaking a language or playing an instrument is learned through experience and practice.

Selective breeding is the same as training. This is incorrect. Selective breeding uses inherited characteristics passed to offspring. Training affects an animal during its life.

Selective breeding always improves a species. This is incorrect. It may improve one useful characteristic, but it can reduce genetic variation and increase inherited health problems.

Extinction means an animal has moved away. This is incorrect. Extinction means no living members of the species remain.

Continuous variation can only be counted in fixed categories. This is incorrect. Continuous variation is measured across a range.

Discontinuous variation should always be shown with a line graph. This is incorrect. Separate categories are usually shown with bar charts.

Real-World Examples

Humans

Inherited human variation includes natural eye colour, natural hair colour, blood group, and some aspects of height. Environmental variation includes scars, language, suntan, diet, exercise, and learned skills. It is important not to make judgements about a person's ability, worth, identity, or future from inherited characteristics.

Plants

Plants vary in height, leaf size, flower colour, fruit size, and growth rate. A plant variety may inherit the ability to produce large fruits, but fruit size can also be affected by light, water, minerals, disease, and temperature.

Animals

Dog breeds show selective breeding because humans have chosen parents with particular inherited features. Bird beak shapes can be linked to food type. Fish have streamlined bodies that help them move through water. Insects may have camouflage that helps them avoid predators.

UK Agriculture and Conservation

UK examples of selective breeding include wheat bred for yield and disease resistance, dairy cattle bred for milk production, sheep bred for wool or meat, and apples bred for taste and storage. UK conservation work may protect habitats such as wetlands, woodlands, wildflower meadows, and rivers to reduce extinction risk and support biodiversity.

Global Examples

Polar bears are suited to Arctic habitats, cacti to deserts, camels to dry habitats, and fish to aquatic habitats. Rhinos, orangutans, bees, and many amphibians are examples of modern threatened groups affected by habitat loss, pollution, disease, hunting, and climate change.

Diagram Interpretation

Diagram 1: Cell to Gene

[Body cell]
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[Nucleus]
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[Chromosome]
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[DNA strand]
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[Gene: a section of DNA]

Questions:

1. Where are chromosomes found in most body cells?
2. What are chromosomes made from?
3. What is a gene?
4. Explain how the diagram links to inheritance.

Model answers:

1. Chromosomes are found in the nucleus of most body cells.
2. Chromosomes are made from DNA.
3. A gene is a short section of DNA that contains instructions for an inherited characteristic.
4. DNA carries genetic information. This information is organised in chromosomes and genes, and it can be passed from parents to offspring during reproduction.

Diagram 2: Selective Breeding

Generation 1: many wheat plants vary in yield and disease resistance
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Choose plants with high yield and low disease damage
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Breed selected plants
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Generation 2: offspring vary
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Choose the best offspring and repeat

Questions:

1. Why must the farmer start with variation in the wheat plants?
2. Why does the farmer choose the best offspring, not just any offspring?
3. Why is this process repeated over many generations?
4. Give one risk of selective breeding.

Model answers:

1. The farmer needs variation so that some plants have more useful inherited characteristics than others.
2. Choosing the best offspring increases the chance that useful inherited characteristics are passed to the next generation.
3. Repeating over many generations makes the desired inherited characteristics more common in the bred population.
4. A risk is reduced genetic variation, which may make the crop more vulnerable to a new disease.

Practice Questions

Multiple-Choice Questions

1. What does variation mean? A. Differences between individuals of the same species
   B. A species moving to a new habitat
   C. A plant growing without light
   D. A disease spreading through a population

2. Which example is mostly environmental variation? A. Blood group
   B. Natural eye colour
   C. A scar from an accident
   D. Chromosomes in the nucleus

3. Which characteristic is continuous variation? A. Blood group
   B. Hand span
   C. Eye colour category
   D. Attached or detached earlobes

4. Which graph is usually best for discontinuous categories? A. Bar chart
   B. Line graph with joined points
   C. Distance-time graph
   D. Scatter graph only

5. What is DNA? A. A chemical that carries genetic information
   B. A type of blood cell
   C. A learned behaviour
   D. A habitat

6. What are chromosomes made from? A. Soil
   B. DNA
   C. Starch only
   D. Water only

7. Why do offspring often resemble their parents? A. They learn every feature from their parents
   B. They inherit genetic information from their parents
   C. They live in exactly the same environment forever
   D. They choose their features before birth

8. Which is a behavioural adaptation? A. Thick fur
   B. Streamlined body
   C. Migration
   D. Cactus spine

9. Which statement about selective breeding is correct? A. It trains animals to pass on learned tricks
   B. It chooses parents with useful inherited characteristics
   C. It causes adaptations to appear instantly
   D. It always increases genetic variation

10. What does extinction mean? A. A species has moved away from one field
    B. A species has changed colour
    C. No living members of a species remain
    D. A species has learned a new behaviour

11. Which feature is likely to be affected by both inherited and environmental factors? A. Blood group
    B. Height
    C. A tattoo
    D. A language learned at school

12. Why can variation help a population survive environmental change? A. Some individuals may have features that help them survive
    B. All individuals become identical
    C. Every individual changes its DNA in the same helpful way
    D. Predators disappear immediately

Short-Answer Questions

1. Define inherited variation.
2. Define environmental variation.
3. Give two examples of continuous variation.
4. Give two examples of discontinuous variation.
5. Explain why height is often affected by both inherited and environmental factors.
6. Describe the relationship between DNA, chromosomes, and genes.
7. Explain the difference between an inherited characteristic and a learned behaviour.
8. Name one structural adaptation and explain how it helps survival.
9. Name one behavioural adaptation and explain how it helps survival.
10. Explain why adaptations usually do not appear during one individual's lifetime.
11. Give one benefit and one risk of selective breeding.
12. Give two causes of extinction.

Fill-in-the-Blank Questions

Use the words: DNA, chromosomes, genes, inherited, environmental, continuous, discontinuous, adaptation, extinction, selective breeding.

1. Variation caused by genetic information from parents is called __________ variation.
2. Variation caused by surroundings or experiences is called __________ variation.
3. Height is an example of __________ variation because it can be measured across a range.
4. Blood group is an example of __________ variation because it falls into categories.
5. __________ is a chemical that carries genetic information.
6. Long structures made of DNA are called __________.
7. Short sections of DNA with instructions are called __________.
8. A feature or behaviour that helps survival and reproduction is an __________.
9. The permanent disappearance of a species is called __________.
10. Humans choosing parents with useful inherited features is called __________.

Sorting and Classification Questions

Classify each feature as inherited, environmental, or both:

1. Natural hair colour
2. Scar from a cut
3. Body mass
4. Blood group
5. Ability to speak French
6. Plant height after growing in shade
7. Natural eye colour
8. Sporting performance

Classify each adaptation as structural, behavioural, or physiological:

1. A bird migrates to a warmer area in winter.
2. A fish has a streamlined body.
3. A camel conserves water.
4. A cactus has spines.
5. A hedgehog hibernates.
6. A polar bear has thick fur.

Data Interpretation Questions

Use the seedling table from Data Task 2.

1. What is the independent variable?
2. What is the dependent variable?
3. Name two control variables.
4. Which light level produced the greatest mean height?
5. Quote values to support your answer.
6. Identify the anomalous result.
7. Suggest one possible reason for the anomaly.
8. Suggest one improvement to make the investigation more reliable.

Use the wetland bird table from Data Task 4.

1. Describe the trend in habitat area from 2022 to 2025.
2. Describe the trend in chicks surviving to autumn.
3. Use values to explain why extinction risk may be increasing.
4. Give one conservation action that could reduce the risk.
5. Give one limitation of the data.

Graph Interpretation Questions

A class records flower colour in one plant species:

Flower colour	Number of plants
Red	14
Pink	9
White	7

1. Is flower colour in this table continuous or discontinuous variation?
2. Which type of graph should be used?
3. Which flower colour is most common?
4. How many more red plants are there than white plants?
5. Why should the bars not be joined with a line?

A class measures leaf length:

Leaf length interval (cm)	Number of leaves
2.0-2.9	3
3.0-3.9	8
4.0-4.9	12
5.0-5.9	6
6.0-6.9	1

1. Is leaf length continuous or discontinuous variation?
2. Which interval has the most leaves?
3. Describe the pattern using values.
4. Give one reason why measuring more leaves would improve the evidence.

Method and Evaluation Questions

1. A student wants to investigate whether water amount affects plant height. Write a fair method using the same plant species.
2. Identify the independent variable, dependent variable, and three control variables for the water investigation.
3. Explain why repeat plants are needed.
4. Explain why calculating a mean can improve the usefulness of results.
5. Explain why correlation between two characteristics does not always prove one caused the other.

Extended Response Questions

1. Explain how inherited variation and environmental variation can both affect characteristics in a population. Use examples.
2. A farmer wants to selectively breed wheat plants for high yield and disease resistance. Describe the method, explain why it takes many generations, and evaluate one benefit and one risk.
3. Use the wetland bird population data to explain why a species may become extinct after its habitat changes. Include the role of variation and adaptation in your answer.
4. Compare continuous and discontinuous variation. Use examples and explain how each type should be displayed in a graph.

Model Answers

Multiple-Choice Answers

1. A
2. C
3. B
4. A
5. A
6. B
7. B
8. C
9. B
10. C
11. B
12. A

Short-Answer Model Answers

1. Inherited variation is variation caused by genetic information passed from parents to offspring.
2. Environmental variation is variation caused by surroundings, experiences, lifestyle, injury, disease, or learning.
3. Examples include height, body mass, hand span, leaf length, reaction time, and running speed.
4. Examples include blood group, eye colour category, attached or detached earlobes, and flower colour category in some plants.
5. Height is affected by inherited genetic information from parents, but diet, health, exercise, and living conditions during growth can also affect final height.
6. DNA is the chemical that carries genetic information. Chromosomes are long structures made of DNA and found in the nucleus of most body cells. Genes are short sections of DNA with instructions for inherited characteristics.
7. An inherited characteristic is passed through genetic information, such as blood group. A learned behaviour is gained through experience or practice, such as speaking a language.
8. A polar bear's thick fur is a structural adaptation because it reduces heat loss in a cold Arctic habitat.
9. Migration is a behavioural adaptation because animals move to places where food or suitable temperatures are available.
10. Adaptations usually become common over many generations because individuals with helpful inherited features are more likely to survive and reproduce.
11. A benefit of selective breeding is increased food production, such as higher milk yield. A risk is reduced genetic variation or inherited health problems.
12. Causes include habitat loss, climate change, pollution, overhunting, disease, competition, lack of food, and failure to reproduce.

Fill-in-the-Blank Answers

1. inherited
2. environmental
3. continuous
4. discontinuous
5. DNA
6. chromosomes
7. genes
8. adaptation
9. extinction
10. selective breeding

Sorting Model Answers

Inherited, environmental, or both:

Feature	Classification	Explanation
Natural hair colour	Inherited	Mainly caused by genetic information
Scar from a cut	Environmental	Caused by injury during life
Body mass	Both	Affected by inherited body build and environment such as diet and exercise
Blood group	Inherited	Passed through genetic information
Ability to speak French	Environmental	Learned through experience
Plant height after growing in shade	Both	Plant variety matters, but shade affects growth
Natural eye colour	Inherited	Mainly affected by genetic information
Sporting performance	Both	Body features may be inherited, but training and diet are environmental

Adaptation types:

Adaptation	Type	Explanation
Bird migrates	Behavioural	It is an action
Fish has a streamlined body	Structural	It is a physical body feature
Camel conserves water	Physiological	It is an internal process
Cactus has spines	Structural	It is a physical feature
Hedgehog hibernates	Behavioural	It is an action
Polar bear has thick fur	Structural	It is a physical feature

Data Interpretation Model Answers

Seedling investigation:

1. The independent variable is light level.
2. The dependent variable is seedling height in centimetres.
3. Control variables include plant species, starting size, soil, water, container size, temperature, and time grown.
4. Full light produced the greatest mean height.
5. Full light had a mean height of 12.0 cm, compared with 8.2 cm in half light and 5.4 cm in very low light.
6. The anomalous result is 9.8 cm for Seedling 2 in very low light.
7. It may have received extra light, been measured incorrectly, or started larger than the others.
8. Use more seedlings in each condition, repeat the investigation, and calculate means.

Wetland bird data:

1. Habitat area decreased from 120 hectares in 2022 to 52 hectares in 2025.
2. Chicks surviving to autumn decreased from 96 to 21.
3. Extinction risk may be increasing because breeding pairs fell from 80 to 31 and chick survival fell from 96 to 21, so fewer young birds are replacing adults that die.
4. Protecting and restoring wetland habitat could reduce risk.
5. The data does not show disease, food supply, predator numbers, weather, or pollution.

Graph Interpretation Model Answers

Flower colour:

1. It is discontinuous variation because flower colour is counted in separate categories.
2. A bar chart should be used.
3. Red is most common.
4. There are 7 more red plants than white plants because 14 - 7 = 7.
5. The bars should not be joined because there are no continuous values between the colour categories.

Leaf length:

1. Leaf length is continuous variation because it is measured across a range.
2. The 4.0-4.9 cm interval has the most leaves, with 12.
3. Most leaves are between 3.0 cm and 5.9 cm, with the highest number in the 4.0-4.9 cm interval. Only 1 leaf is in the 6.0-6.9 cm interval.
4. Measuring more leaves would improve reliability because the sample would be more representative.

Method and Evaluation Model Answers

1. Put the same species of seedlings into identical containers with the same soil. Give each group a different measured amount of water, such as 10 ml, 20 ml, and 30 ml per day. Keep light, temperature, soil type, container size, starting plant size, and time grown the same. Measure plant height after 14 days using a ruler. Use at least three plants for each water amount and calculate a mean height.
2. Independent variable: water amount. Dependent variable: plant height. Control variables: plant species, soil type, container size, light level, temperature, starting size, and time grown.
3. Repeat plants are needed because individual plants vary. Repeats make the evidence more reliable and help identify anomalies.
4. A mean uses all repeated measurements and gives a more representative value than one plant alone.
5. Correlation does not always prove causation because two factors may be linked by another variable, or the pattern may be due to chance or an uncontrolled factor.

Extended Response Model Answer 1

Inherited variation is caused by genetic information passed from parents to offspring. Examples include blood group, natural eye colour, and some aspects of height. Environmental variation is caused by surroundings or experiences during life. Examples include scars, suntan, language, diet, and exercise. Some characteristics are affected by both. Height is affected by inherited information, but nutrition and health during growth also affect final height. Plant height can be affected by inherited variety and by light, water, minerals, and temperature. Variation in a population matters because some individuals may have features that help them survive disease or environmental change.

Extended Response Model Answer 2

The farmer should first identify wheat plants with high yield and strong disease resistance. The farmer should choose these plants as parents and breed them. The offspring should be grown and tested for yield and disease resistance. The best offspring should be selected as parents for the next generation. This process must be repeated over many generations because selective breeding increases the chance that useful inherited characteristics become common. A benefit is increased food production and less crop loss from disease. A risk is reduced genetic variation if closely related plants are bred repeatedly, which could make the crop vulnerable to a new disease.

Extended Response Model Answer 3

The wetland bird data shows that habitat area decreased from 120 hectares in 2022 to 52 hectares in 2025. Breeding pairs decreased from 80 to 31, and chicks surviving to autumn decreased from 96 to 21. This suggests the population is at greater risk of extinction because fewer adults are breeding and fewer young birds survive to replace adults that die. Habitat change may reduce food supply and nesting sites. If there is variation in the population, some birds may be better able to find food or cope with changes, but if the habitat change is too rapid or severe, not enough birds will survive and reproduce. Adaptations usually become common over many generations, so a small population may not adapt quickly enough. Conservation actions such as wetland restoration could reduce the risk.

Extended Response Model Answer 4

Continuous variation has values across a range and is measured using numbers and units. Examples include height, mass, hand span, leaf length, reaction time, and running speed. Continuous data can be displayed using a line graph if measurements are taken over time, or using grouped intervals in a chart. Discontinuous variation has values in separate categories. Examples include blood group, eye colour category, attached or detached earlobes, and flower colour category in some plants. Discontinuous data is usually shown using a bar chart because the categories are separate. A line graph is not suitable for eye colour because there are no values between categories such as blue and brown.

Revision Checklist

Use this checklist to test your understanding.

• I can define variation as differences between individuals of the same species.
• I can give examples of variation in humans, plants, animals, and microorganisms.
• I can explain continuous variation and give measured examples.
• I can explain discontinuous variation and give category examples.
• I can choose suitable graph types for continuous and discontinuous data.
• I can explain inherited variation using genetic information from parents.
• I can explain environmental variation using surroundings and experiences.
• I can identify characteristics affected by both inherited and environmental factors.
• I can describe DNA as a chemical that carries genetic information.
• I can describe chromosomes as long structures made of DNA in the nucleus.
• I can describe genes as short sections of DNA with instructions.
• I can explain why offspring resemble parents but are not identical to them.
• I can separate inherited characteristics from learned behaviours.
• I can explain why variation in a population can help survival.
• I can define adaptation and describe structural, behavioural, and physiological examples.
• I can explain why adaptations usually develop over many generations.
• I can describe the steps in selective breeding.
• I can give benefits and risks of selective breeding.
• I can define extinction as the permanent disappearance of a species.
• I can explain causes of extinction, including human impacts.
• I can interpret variation data using values as evidence.
• I can identify independent, dependent, and control variables.
• I can explain why repeats, larger samples, and means improve reliability.
• I can identify anomalies and suggest improvements to investigations.
• I can explain why correlation does not always prove causation.
• I can discuss biological variation respectfully without judging people's worth, ability, identity, or future.