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Biology - Living Things in their Environment

Grade 7Cambridge (IGCSE)

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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An ecosystem consists of all the living organisms (biotic factors) in a particular area interacting with their non-living environment (abiotic factors) such as H2OH_2O, O2O_2, and minerals.

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Producers (autotrophs) synthesize their own food using light energy through the process of photosynthesis: 6CO2+6H2O→C6H12O6+6O26CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2.

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Energy flows through a food chain from producers to consumers. At each trophic level, approximately 90%90\% of energy is lost to the environment as heat or waste, leaving only 10%10\% for the next level.

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Food webs represent interconnected food chains and demonstrate how the survival of one species depends on others within the habitat.

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Adaptations are specific features that increase an organism's chance of survival. For example, desert plants (xerophytes) have thick waxy cuticles to prevent H2OH_2O loss via transpiration.

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The population of a species can be affected by limiting factors such as food availability, predation, and accumulation of toxic waste products like CO2CO_2 or nitrogenous compounds.

📐Formulae

6CO2+6H2O→lightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{\text{light}} C_6H_{12}O_6 + 6O_2

C6H12O6+6O2→6CO2+6H2O+Energy (ATP)C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy (ATP)}

Efficiency of Energy Transfer=Energy available to next levelEnergy from previous level×100\text{Efficiency of Energy Transfer} = \frac{\text{Energy available to next level}}{\text{Energy from previous level}} \times 100

💡Examples

Problem 1:

In a simple food chain: Grass→Rabbit→Fox\text{Grass} \rightarrow \text{Rabbit} \rightarrow \text{Fox}, if the Grass contains 5000 kJ5000\text{ kJ} of energy, calculate the energy available to the Fox assuming a 10%10\% transfer efficiency at each step.

Solution:

Step 1: Energy at Rabbit level = 5000 kJ×0.10=500 kJ5000\text{ kJ} \times 0.10 = 500\text{ kJ}. Step 2: Energy at Fox level = 500 kJ×0.10=50 kJ500\text{ kJ} \times 0.10 = 50\text{ kJ}.

Explanation:

Energy decreases at each trophic level due to metabolic processes and heat loss. Following the 10%10\% rule, the Fox receives 50 kJ50\text{ kJ}.

Problem 2:

Identify the gas consumed and the gas produced by a green plant in an environment with high light intensity.

Solution:

Gas consumed: CO2CO_2 (Carbon Dioxide). Gas produced: O2O_2 (Oxygen).

Explanation:

During the day, the rate of photosynthesis (6CO2+6H2O→C6H12O6+6O26CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2) is higher than the rate of respiration, resulting in a net intake of CO2CO_2 and a net release of O2O_2.