What you'll learn
This revision guide covers how organisms develop features that help them survive in specific environments and how they compete for limited resources. You'll understand the different types of adaptations, why organisms must compete, and how these processes shape communities in ecosystems. These concepts are fundamental to understanding ecology and evolution at GCSE level.
Key terms and definitions
Adaptation — a feature or characteristic that helps an organism to survive and reproduce in its environment, developed through natural selection over many generations.
Competition — the struggle between organisms for limited resources such as food, water, space, light, or mates.
Extremophile — an organism adapted to live in extreme environmental conditions such as high temperature, high pressure, or high salt concentration.
Structural adaptation — a physical feature of an organism's body that helps it survive, such as the shape of a beak or the colour of fur.
Behavioural adaptation — an action or pattern of behaviour that helps an organism survive, such as migration or hibernation.
Functional (physiological) adaptation — a process or chemical reaction inside an organism's body that helps it survive, such as venom production or antifreeze proteins in blood.
Intraspecific competition — competition between members of the same species for resources.
Interspecific competition — competition between members of different species for resources.
Core concepts
Types of adaptation
Organisms possess three main categories of adaptations that enable survival in their particular habitats.
Structural adaptations are visible physical features:
- Arctic foxes have white fur for camouflage in snow (predation avoidance and hunting advantage)
- Cacti have spines instead of leaves to reduce water loss and deter herbivores
- Polar bears have thick fur and fat layers for insulation in cold climates
- Large ears on desert foxes increase surface area for heat loss
- Streamlined body shapes in fish reduce water resistance
Behavioural adaptations are actions organisms perform:
- Many birds migrate to warmer climates in winter when food is scarce
- Desert animals are nocturnal to avoid daytime heat
- Some animals hibernate during winter to conserve energy when food is unavailable
- Meerkats post sentries to watch for predators while others forage
- Leaf-cutter ants cultivate fungus gardens for food
Functional adaptations are internal processes:
- Bacteria in hot springs produce heat-resistant enzymes
- Penguins produce antifreeze proteins in their blood to prevent ice crystal formation
- Snakes produce venom to kill prey and aid digestion
- Camels can tolerate significant changes in body temperature without sweating
- Some plants produce toxins to deter herbivores
Many organisms possess multiple adaptations working together. Polar bears, for example, have white fur (structural), hibernate in dens during the harshest weather (behavioural), and maintain high metabolic rates to generate body heat (functional).
Adaptations to extreme environments
Extremophiles survive in conditions that would kill most organisms. Understanding these adaptations demonstrates the range of conditions life can tolerate.
Hot environments (deserts, thermal vents):
- Desert plants have extensive shallow root systems to absorb rainwater quickly or deep tap roots to reach underground water
- Thick, waxy cuticles on leaves minimize water loss through transpiration
- CAM photosynthesis allows stomata to open at night, reducing daytime water loss
- Bacteria in hot springs have heat-stable enzymes that function above 80°C
- Some desert animals excrete concentrated urine to conserve water
Cold environments (Arctic, Antarctic):
- Small surface area to volume ratio reduces heat loss (compact body shapes)
- Counter-current heat exchange systems in limbs prevent heat loss
- Dark coloured fur or feathers absorb more heat radiation
- Thick blubber or fat layers provide insulation
- Production of antifreeze compounds in body fluids
High salt environments (salt lakes, salt marshes):
- Specialized cells pump excess salt out of the organism
- Production of compatible solutes to balance osmotic pressure
- Thick, waterproof outer coverings prevent water loss
- Some halophilic bacteria require high salt concentrations for enzyme function
Competition between organisms
All organisms require resources to survive and reproduce. When resources are limited, competition occurs.
Resources organisms compete for:
- Plants compete for light, water, minerals (nutrients), and space
- Animals compete for food, water, mates, and territory (space)
The intensity of competition depends on:
- Population density (more organisms = more competition)
- Availability of resources (scarcity increases competition)
- Overlap in resource requirements between species
Intraspecific competition occurs between members of the same species. This is typically more intense because individuals have identical resource requirements. Examples include:
- Oak trees in a forest competing for light
- Male deer competing for access to females during mating season
- Bacterial cells in a culture competing for glucose
- Blackbirds competing for nesting territories
Intraspecific competition is a key factor in controlling population size. As populations increase, competition intensifies, leading to reduced reproduction and increased mortality.
Interspecific competition occurs between different species that require similar resources. Examples include:
- Red and grey squirrels competing for food and nesting sites in UK woodlands
- Different species of grass competing for soil nutrients in a meadow
- Predators such as lions and hyenas competing for prey animals
- Weeds and crop plants competing for water and minerals in agricultural fields
When two species compete for identical resources, competitive exclusion may occur — one species outcompetes and eliminates the other from that habitat. More commonly, species develop slightly different niches, reducing direct competition.
Adaptations for competition
Organisms possess adaptations that improve their competitive ability.
Adaptations for competing for food:
- Sharp claws and teeth in predators for catching and consuming prey
- Keen eyesight in birds of prey for spotting prey from distance
- Speed in cheetahs for pursuing fast prey
- Venom in spiders for immobilizing prey
- Long tongues in hummingbirds for accessing nectar in deep flowers
Adaptations for competing for mates:
- Bright plumage in male birds attracts females (sexual selection)
- Elaborate courtship displays and calls
- Antlers in male deer for fighting rival males
- Larger body size in males of many species
- Production of pheromones to attract mates
Adaptations for competing for light (plants):
- Tall growth to overshadow competitors
- Broad leaves to maximize light capture
- Climbing structures (vines) to reach sunlight using other plants for support
- Phototropism — growth toward light sources
Adaptations for competing for territory:
- Territorial marking using scent or visual signals
- Aggressive behaviours toward intruders
- Vocalizations warning others to stay away (birdsong)
The relationship between adaptation and competition
Adaptations evolve through natural selection driven partly by competition. Organisms better adapted to compete for limited resources are more likely to survive and reproduce, passing advantageous alleles to offspring.
This creates an evolutionary "arms race":
- Prey evolve better defences (camouflage, speed, toxins)
- Predators evolve better hunting adaptations (sharper senses, faster speed)
- Plants evolve mechanisms to outcompete neighbours (faster growth, allelopathy)
- Competitors evolve to exploit slightly different resources (niche differentiation)
Over many generations, this process produces the diverse adaptations observed in nature. Competition acts as a selection pressure, favouring individuals with beneficial variations.
Adaptations in different habitats
Understanding how organisms adapt to specific habitats is essential for explaining biodiversity patterns.
Rainforest adaptations:
- Drip-tip leaves channel water off quickly, preventing fungal growth
- Climbing plants (lianas) reach the canopy for light
- Bright colours in tree frogs warn predators of toxicity
- Epiphytic plants grow on tree branches to access light without competing for ground space
- Camouflage in leaf insects and stick insects
Marine adaptations:
- Streamlined body shapes reduce drag
- Gills extract oxygen from water
- Salt excretion mechanisms maintain osmotic balance
- Bioluminescence in deep-sea organisms for communication or prey attraction
- Pressure-resistant proteins in deep-sea organisms
Grassland adaptations:
- Grasses grow from the base, allowing recovery after grazing
- Deep root systems access water during dry periods
- Fast growth rates in response to favourable conditions
- Herding behaviour in prey animals provides protection from predators
- Camouflage in both predators and prey
Worked examples
Example 1: Explaining adaptations (4 marks)
Question: The Arctic hare lives in cold regions. It has white fur in winter, short ears, and a compact body shape. Explain how these features help the Arctic hare survive in its environment.
Model answer:
White fur provides camouflage against snow (1 mark), making it harder for predators to spot the hare (1 mark). Short ears reduce surface area (1 mark), minimizing heat loss in cold temperatures (1 mark).
Examiner note: The compact body shape also reduces surface area to volume ratio, reducing heat loss — accept this for the same marks. Ensure you link each structural feature to its specific survival advantage.
Example 2: Competition in plants (3 marks)
Question: A gardener plants vegetables close together. Explain why the plants grow poorly compared to plants with more space between them.
Model answer:
Plants compete for resources such as light, water, and minerals/nutrients (1 mark). When planted close together, competition is more intense (1 mark), so each plant receives less of these resources and cannot grow as well (1 mark).
Examiner note: You must name specific resources plants compete for — don't just say "resources." Accept any two appropriate resources for the first mark.
Example 3: Analysing extremophile adaptations (5 marks)
Question: Bacteria living in hot springs at 80°C have enzymes that remain functional at these high temperatures. Explain why these bacteria can survive where most organisms cannot, and why this is an adaptation.
Model answer:
Most organisms have enzymes that denature (change shape) at high temperatures (1 mark), so the enzymes can no longer catalyse reactions and the organism dies (1 mark). The bacteria have enzymes with different structures (1 mark) that remain stable at 80°C and continue to function (1 mark). This is an adaptation because it allows the bacteria to survive and reproduce in an environment where there is less competition (1 mark).
Examiner note: This requires understanding of both enzyme structure/function and the concept of adaptation through natural selection.
Common mistakes and how to avoid them
Confusing individual adaptation with evolutionary adaptation. Adaptations develop over many generations through natural selection, not during an individual organism's lifetime. Don't write "the polar bear adapted by growing thicker fur" — polar bears inherit genes for thick fur; they don't develop it in response to cold.
Failing to link adaptations to survival or reproduction. Always explain how an adaptation helps the organism survive or reproduce. "Desert plants have thick waxy cuticles" is incomplete; add "which reduces water loss through evaporation, helping the plant survive in dry conditions."
Listing resources without being specific to the organism type. Plants don't compete for food — they compete for light, water, and minerals. Animals don't compete for light — they compete for food, water, and mates. Match resources to organism type.
Using vague terms instead of precise biological vocabulary. Don't write "special features" — use "structural adaptations." Don't say "chemicals inside" — say "functional/physiological adaptations" or name specific processes like enzyme production.
Confusing intraspecific and interspecific competition. Intra = within the same species; inter = between different species. Remember: intra-mural sports are within one school, inter-national sports are between countries.
Not explaining the survival advantage clearly. Stating "the cactus has spines" earns no marks. Explaining "spines reduce water loss compared to broad leaves, helping the cactus survive in dry desert conditions" earns full marks.
Exam technique for "Adaptation and Competition"
Command word "Explain" requires you to state the adaptation AND link it clearly to survival/reproductive advantage. Use connectives like "which means," "therefore," or "this helps the organism to..." to show the relationship.
Extended response questions worth 4-6 marks need multiple points fully developed. Use the mark scheme as a guide — typically 1 mark for identifying the adaptation, 1 mark for explaining how it helps. Plan to make 3-4 distinct points.
"Suggest" questions about unfamiliar organisms test whether you can apply principles. Use your knowledge of similar adaptations — an unfamiliar desert animal likely has water conservation adaptations similar to those you've learned about.
In competition questions, always specify which resources are being competed for and link competition intensity to resource availability or population density. Don't just say "they compete" — explain what for and why it matters.
Quick revision summary
Adaptations are inherited features that help organisms survive and reproduce, categorized as structural, behavioural, or functional. Extremophiles possess specialized adaptations for extreme environments. Competition occurs when organisms require the same limited resources — intraspecific competition is within a species; interspecific is between species. Plants compete for light, water, minerals, and space; animals compete for food, water, mates, and territory. Adaptations evolve through natural selection driven partly by competition as selection pressure. Always link adaptations explicitly to survival or reproductive advantage when answering exam questions.