Ecosystems and Habitats

Factors affecting organisms in an ecosystem can be classified as:

Abiotic Factors (Non-living)

Biotic Factors (Living)

Adaptations are features that help organisms survive in their habitat. They can be:

Structural Adaptations (Physical features)

• Polar bear: Thick fur and fat layer for insulation; white fur for camouflage; large paws to spread weight on ice
• Cactus: Thick stem stores water; spines instead of leaves reduce water loss; extensive root system
• Camel: Hump stores fat (not water); wide feet prevent sinking in sand; can tolerate water loss

Behavioural Adaptations (Actions)

• Migration — birds fly to warmer areas in winter for food
• Hibernation — animals enter dormancy to survive winter when food is scarce
• Nocturnal activity — desert animals are active at night to avoid daytime heat

Functional Adaptations (Physiological)

• Desert rats: Produce very concentrated urine to conserve water
• Bacteria in hot springs: Heat-resistant enzymes that don't denature
• Poison dart frogs: Produce toxins to deter predators

Extremophiles

• Organisms that live in extreme environments (very hot, very cold, high salt, high pressure)
• Many are bacteria or archaea
• Examples: bacteria in hot springs ($>70°C$), organisms near deep-sea hydrothermal vents

Food Chains

A food chain shows the transfer of energy from one organism to the next:

$\text{Producer} \rightarrow \text{Primary consumer} \rightarrow \text{Secondary consumer} \rightarrow \text{Tertiary consumer}$

Example: $\text{Grass} \rightarrow \text{Rabbit} \rightarrow \text{Fox} \rightarrow \text{Eagle}$

Food Webs

A food web is a network of interconnected food chains in an ecosystem. It shows the complex feeding relationships.

If one species is removed, it can affect many others — this demonstrates interdependence.

Energy enters an ecosystem as light energy from the Sun. Producers (plants) convert this into chemical energy (glucose) through photosynthesis.

At each trophic level, energy is lost as:

• Heat from respiration (the biggest loss)
• Movement (kinetic energy)
• Waste products (urine, faeces — not digested/absorbed)
• Dead organisms not consumed by the next level

Only about 10% of energy is transferred to the next trophic level. This is why:

• Food chains are usually short (3-5 levels)
• There are fewer organisms at higher trophic levels
• Pyramids of biomass are typically pyramid-shaped (larger at the bottom)

Organisms must compete for limited resources:

Interspecific Competition (between different species)

• Different species competing for the same resources (e.g., two plant species competing for light and water)
• Can lead to one species being outcompeted and declining in numbers

Intraspecific Competition (within the same species)

• Individuals of the same species competing for the same resources
• Often more intense because they have identical needs
• Regulates population size

What Do Organisms Compete For?

Predator and prey populations are interdependent and often show cyclical patterns:

1. If prey population increases (plenty of food), predator numbers increase (more food available)
2. If predator population increases, more prey are eaten, so prey numbers decrease
3. With fewer prey, predators have less food, so predator numbers decrease
4. With fewer predators, prey population can increase again
5. The cycle repeats

Predator-prey graphs show oscillating curves with the predator curve slightly behind (lagging) the prey curve.

Question: Using the food chain: Grass → Grasshopper → Frog → Snake → Hawk, explain what would happen if the frog population decreased due to disease. (3 marks)

Solution:

If the frog population decreased, the grasshopper population would increase because there are fewer frogs to eat them (reduced predation). The snake population would decrease because they have less food (fewer frogs to eat). With fewer snakes, the hawk population might also decrease due to reduced food supply. This shows interdependence — a change in one population affects the entire food chain.

• Abiotic = non-living; Biotic = living. Learn examples of each.
• For adaptation questions, always explain HOW the feature helps the organism survive (don't just list features).
• In food chain questions, use the terms producer, consumer, trophic level, and energy transfer.
• When describing predator-prey, mention the time lag — predator changes follow prey changes.

• An ecosystem is a community of organisms interacting with their abiotic environment.
• Organisms are affected by abiotic factors (light, temperature, water, pH) and biotic factors (competition, predation, disease).
• Adaptations (structural, behavioural, functional) help organisms survive in their habitats.
• Food chains and food webs show energy transfer between trophic levels; only ~10% of energy passes to the next level.
• Predator-prey populations show cyclical, interdependent patterns.