- Define and explain Humans and the Environment in your own words
- Use key terms such as ecosystem accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Humans and the Environment: evaluate deforestation, pollution and global warming, and how we can respond.
Evaluate deforestation, pollution and global warming, and how we can respond.
Key ideas
Food webs and interdependence
A food web links many food chains, showing that most organisms eat, and are eaten by, several species. Removing one species ripples through the web: if rabbits decline, foxes may starve while grass flourishes. Decomposers complete the picture by breaking down dead organisms and waste, recycling nutrients back to producers.
Pyramids of biomass and energy loss
A pyramid of biomass shows the dry mass at each trophic level, and it is almost always pyramid-shaped because biomass is lost between levels. Only about 10% of energy is transferred: the rest is lost through respiration and movement, in uneaten parts, and in waste such as faeces and urine. This is why food chains rarely have more than five trophic levels — there is too little energy left.
Key term — ecosystem: A community of organisms together with their physical environment, interacting as a system.
Give two human activities that increase atmospheric carbon dioxide and one way to reduce them.
Burning fossil fuels for energy and transport, and deforestation (which also removes photosynthesis). Reduction: any one of using renewable energy, improving energy efficiency, or reforestation.
Answer: Burning fossil fuels for energy and transport, and deforestation (which also removes photosynthesis). Reduction: any one of using renewable energy, improving energy efficiency, or reforestation.
- Drawing a pyramid of biomass with the widest bar at the top Biomass decreases up the chain because energy is lost at each transfer, so the producer bar at the bottom is always the widest.
- Saying decomposers are not needed Without decomposers, nutrients would stay locked in dead bodies and waste. Decomposers recycle them into the soil for producers to reuse.
Practice
Producer: grass. Primary consumer: rabbit. Secondary consumer: fox (the flea is a tertiary consumer).
Most organisms eat several different species and are eaten by several predators, so a web shows the true feeding relationships and how species depend on one another.
Any three of: respiration (released as heat); movement; uneaten parts such as roots or bones; waste products such as faeces and urine.
Only about 10% of energy transfers at each level, so after several transfers too little energy remains to support another trophic level.
Quick check
Which of these best defines "ecosystem"?
Describe two processes that return carbon dioxide to the atmosphere.
- Humans and the Environment: evaluate deforestation, pollution and global warming, and how we can respond.
- Food webs and interdependence: A food web links many food chains, showing that most organisms eat, and are eaten by, several species.
- trophic level: A feeding level in a food chain or web, such as producer, primary consumer or secondary consumer.
- Watch out for: drawing a pyramid of biomass with the widest bar at the top