Adaptations, interdependence and competitionOxford AQA IGCSE Biology: Revision notes

Adaptations are characteristics that help organisms survive and reproduce in their environment. There are three main types:

Structural adaptations are physical features of an organism's body.

• Example: A polar bear's thick fur, a cactus's waxy cuticle, a fish's streamlined body shape

Behavioural adaptations are actions or patterns of behaviour that increase survival.

• Example: Migration, hibernation, territorial defence, pack hunting

Physiological adaptations are internal processes or chemical mechanisms that help survival.

• Example: The ability to digest cellulose, producing antifreeze proteins, sweating to cool down

All three types work together to help an organism survive in its specific environment and increase its chances of reproduction.

Desert animals face extreme heat, low water availability, and intense UV radiation. Their adaptations include:

Structural adaptations:

• Large ears (like a fennec fox) to increase surface area for heat loss
• Light-coloured fur to reflect heat rather than absorb it
• Camouflage colouring to avoid predators in sandy environments
• Thick skin to reduce water loss through evaporation

Behavioural adaptations:

• Nocturnal behaviour (active at night, inactive during the day) to avoid extreme daytime heat
• Burrowing to shelter in cooler underground spaces
• Reduced activity levels to conserve energy and water

Physiological adaptations:

• Concentrated urine to conserve water
• The ability to tolerate high body temperatures
• Sweat glands that produce minimal sweat to conserve water
• Metabolism that produces water as a byproduct (e.g. in camels burning fat reserves)

These adaptations work together: a camel's fat hump stores energy, its broad feet prevent sinking in sand (structural), it is most active in cool dawn and dusk (behavioural), and its kidneys concentrate urine (physiological).

Arctic animals face extreme cold, ice coverage, and limited food. Their key adaptations include:

Structural adaptations:

• Thick fur and dense blubber (fat layer) for insulation against extreme cold
• White fur for camouflage against snow and ice
• Small ears and limbs relative to body size to reduce heat loss
• Streamlined body shape in aquatic species (e.g. seals) for efficient movement through water

Behavioural adaptations:

• Hibernation to survive winter months with minimal energy expenditure
• Migration to warmer regions during winter
• Huddling together for warmth and protection
• Storing food or building fat reserves before winter

Physiological adaptations:

• Antifreeze proteins in blood to prevent freezing
• High metabolic rate to generate body heat (though this requires more food)
• Thick skin to provide additional insulation
• Specialised haemoglobin that binds oxygen more efficiently in cold temperatures

These adaptations increase survival by maintaining body temperature in freezing conditions and allowing the animal to find or store enough food to survive when food is scarce.

Deep-sea organisms face extreme pressure, near-freezing temperatures, and complete darkness. Their adaptations include:

Deep-sea animal adaptations:

Structural:

• Large eyes or lack of eyes depending on species—some have enormous eyes to capture minimal light; others live in total darkness and have no eyes
• Bioluminescence (light-producing organs) for communication and hunting
• Small mouth and expandable stomach to handle any prey encountered
• Streamlined body for efficient movement in dense water

Behavioural:

• Vertical migration: moving upwards at night to feed in shallower waters and returning to depth during the day
• Ambush predation to conserve energy (waiting for prey rather than actively hunting)

Physiological:

• High pressure tolerance: cells are adapted to withstand crushing pressures
• Reduced metabolic rate to conserve energy when food is scarce
• Antifreeze proteins similar to Arctic species

Deep-sea plant adaptations:

• Chemosynthetic bacteria instead of photosynthesis (since no light reaches the deep sea)
• Sponges and corals depend on nutrient rain from above
• Structures adapted to withstand extreme pressure

These adaptations allow organisms to exploit a food source where there is very little competition, increasing their survival and reproductive success.

Plants in extreme environments face challenges like water scarcity, extreme temperatures, or poor soil. Their key adaptations include:

Desert plants (e.g. cacti):

• Thick, waxy cuticle to reduce water loss through evaporation
• Reduced leaf surface area or no leaves (spines instead) to minimise water loss
• Succulent tissues (fleshy stems) to store water
• Deep or extensive root systems to access scarce water
• CAM photosynthesis: stomata open at night instead of day to reduce water loss

Arctic/Alpine plants:

• Small, hairy leaves to reduce heat loss and water loss
• Compact, low-growing form to reduce exposure to harsh winds
• Dark colouration to absorb maximum solar radiation
• Thick cuticle for protection
• Short growing season adaptation: rapid reproduction when conditions are favourable

Rainforest plants:

• Waxy cuticle (though for shedding excess water, not conserving it)
• Large, thin leaves to maximise photosynthesis in dim light under the canopy
• Climbing adaptations (e.g. tendrils) to reach sunlight
• Aerial roots in epiphytes to absorb moisture from humid air

Wetland plants:

• Aerial roots or roots that penetrate waterlogged soil to access oxygen
• Large air spaces in stems and roots for oxygen transport
• Waxy cuticle to protect against water damage

Each adaptation increases the plant's ability to survive in its specific environment and successfully reproduce.

Surface area to volume ratio (SA:V) is a measure of how much surface an organism has relative to its volume. It is calculated as:

SA:V ratio = Surface area ÷ Volume

How SA:V ratio affects heat exchange:

• Small animals have a high SA:V ratio (relatively large surface area compared to volume)

  • Heat is lost more rapidly because more surface is exposed to the environment
  • They lose heat quickly and need a high metabolic rate to maintain body temperature
  • Example: mice, shrews, newborns have high metabolic rates

• Large animals have a low SA:V ratio (relatively small surface area compared to volume)

  • Heat is retained more effectively because less surface is exposed relative to volume
  • They lose heat more slowly and need lower metabolic rates
  • Example: elephants, whales, bears have lower metabolic rates per unit mass

Mathematical relationship:

For geometric shapes, as size increases:

• Surface area increases with the square of linear dimension (length²)
• Volume increases with the cube of linear dimension (length³)
• Therefore, SA:V ratio decreases as organisms grow larger

Practical examples:

Evolutionary consequences:

Small animals in cold environments often have adaptations to reduce heat loss:

• Higher basal metabolic rate to generate more heat
• Thicker insulation (fur, blubber) to compensate for high SA:V ratio
• Smaller body size is actually a disadvantage in extreme cold, which is why Arctic mammals tend to be larger than their temperate relatives

Large animals can survive in cold environments more easily because their low SA:V ratio means less heat loss, so they don't need to generate as much metabolic heat.