Definitions [4]
A food chain is the sequential sequence of living organisms in an ecosystem where one organism consumes another to transfer food energy.
A network of interconnected food chains showing how various organisms are related through feeding relationships is called a food web.
Define the following term:
Photolysis of water
Releasing electrons and dividing the water molecule (H2O) into its two components (Hydrogen and Oxygen). Photolysis is the term used to describe this reaction, which is characterised by the fracturing of molecules by light (photo = light, lysis = breaking).
Photosynthesis is the process by which living plant cells, containing chlorophyll, produce food substances (glucose and starch) from carbon dioxide and water by using light energy. Plants release oxygen as a byproduct during photosynthesis.
Key Points
- A food chain is a linear sequence of living organisms in an ecosystem where food energy is transferred as one organism consumes another.
- The structural flow typically moves from primary producers to successive levels of consumers, such as from grass to insects, then to a thrush, and finally to a sparrow hawk.
- According to the principle of continuity, a complete food chain requires a continuous external energy supply, always beginning with photosynthesis and ending with decomposition.
- The principle of efficiency dictates that shorter food chains are more stable and energy-efficient because less energy is wasted across fewer transfers.
- Under the 10% law, only about 10% of the available energy is passed to the next trophic level, while the remainder is lost as heat through respiration.
- A food web is a complex network of interconnected food chains that illustrates the broader pattern of energy and nutrient flow within an ecosystem.
- The complexity of a food web increases with the length of its food chains and the availability of alternative dietary choices for consumers.
- Energy flow in an ecosystem is strictly unidirectional, meaning energy captured by autotrophs never reverts back to the solar input or to previous trophic levels.
- As energy transfers progressively through successive trophic levels, the total amount of available energy consistently diminishes due to energy loss at each stage.
- Biological magnification occurs when non-degradable, harmful chemicals enter the food chain and accumulate progressively at each consecutive trophic level.
- Because human beings occupy the apex or top level in food chains, the maximum concentration of these toxic chemicals ultimately accumulates within our bodies.
- Photosynthesis converts sunlight into chemical energy using CO₂ and water, producing glucose and releasing oxygen as a byproduct.
- Green plants are autotrophs (make their own food); all other organisms are heterotrophs. All life depends on sunlight for energy.
- Three essentials for photosynthesis: chlorophyll, light, and CO₂.
- Experiment 1 - Variegated leaf tested for starch showed that photosynthesis occurs only in green parts in the presence of light.
- Experiment 2 - Leaf part enclosed with KOH-soaked cotton (absorbs CO₂) tested negative for starch → proved CO₂ is necessary for photosynthesis.
