Decay And The Carbon Cycle
Overview
Nothing on this planet gets thrown away. A fallen oak leaf, a dead beetle, the shell of an egg, the carbon in your last breath: every one of them is on loan. Give it long enough and the same atoms turn up again inside a root, a seed, a fish or a person. Ecosystems do not run on fresh supplies of matter, because there are none. They run on the same finite stock of elements, used and returned and used again.
This lesson follows one element, carbon, all the way round that loop. You will see how a leaf traps it, how a feeding relationship passes it on, and how three separate routes send it back to the air: the respiration of plants and animals, the feeding of the microorganisms that rot dead material, and the burning of wood and fossil fuels. You will also learn the conditions that make decay fast or slow, why gardeners turn a compost heap, and why energy alone refuses to go round with the matter. Then you will meet the single question this topic is built around, because both biology papers, at both tiers, spend their only six-mark extended answer on it.
Objectives
- Living organisms remove materials from the environment for growth and other processes. These materials are returned to the environment either in waste materials or when living things die and decay.
- Materials decay because they are broken down (digested) by microorganisms. Microorganisms are more active and digest materials faster in warm, moist, aerobic conditions.
- The decay process releases substances that plants need to grow.
- In a stable community, the processes that remove materials are balanced by processes that return materials. The materials are part of a constant cycle.
- The constant cycling of carbon is called the carbon cycle. In the carbon cycle: carbon dioxide is removed from the environment by green plants and algae during photosynthesis; the carbon from the carbon dioxide is used to make carbohydrates, fats and proteins, which make up the body of plants and algae; when green plants and algae respire, some of this carbon becomes carbon dioxide and is released into the atmosphere; when green plants and algae are eaten by animals and these animals are eaten by other animals, some of the carbon becomes part of the fats and proteins that make up the bodies of the consumers; when animals respire, some of this carbon becomes carbon dioxide and is released into the atmosphere; when plants, algae and animals die, some animals and microorganisms feed on their bodies; carbon is released into the atmosphere as carbon dioxide when microorganisms respire; by the time the microorganisms and detritus feeders have broken down the waste products and dead bodies of organisms in ecosystems and cycled the materials as plant nutrients, all the energy originally absorbed by green plants and algae has been transferred; combustion of wood and fossil fuels releases carbon dioxide into the atmosphere. Students should be able to apply the principles of the carbon cycle.
Mind map
This topic is mapped out so you can see how the ideas connect.
Open the mind map in the app
Lesson Note
Complete Note Available on the Green Bridge App
Get the Green Bridge CBT app on your phone or computer for the complete IGCSE library: past papers, mark schemes, mind maps, flashcards and audio lessons.
Lesson Evaluation
Congratulations on completing the lesson on Decay And The Carbon Cycle. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- Which group of organisms is mainly responsible for the decay of dead material? A. Green plants B. Herbivores C. Microorganisms such as bacteria and fungi D. Carnivores Answer: C
- Which combination of conditions gives the fastest rate of decay? A. Cold, dry and aerobic B. Warm, moist and aerobic C. Warm, dry and anaerobic D. Cold, moist and anaerobic Answer: B
- In the carbon cycle, which process takes carbon dioxide out of the atmosphere? A. Respiration B. Combustion C. Decay D. Photosynthesis Answer: D
- Why does decay happen faster in aerobic conditions? A. Oxygen dissolves the dead material B. Aerobic respiration is more efficient C. Oxygen raises the temperature of the dead material D. Microorganisms only make enzymes when oxygen is present Answer: B
- A pile of dead leaves has a mass of 250 g. After 40 days its mass is 90 g. What percentage of the original mass has been lost? A. 36% B. 44% C. 64% D. 160% Answer: C
Work through these questions in the app
Work through these questions in the app
Recommended Books
Practice Mock Questions
Want to practice mock questions on Decay And The Carbon Cycle? Download the Green Bridge CBT app to access mock questions and full practice assessments for this topic.
Download The App On Google Playstore
Everything you need to excel in your exams
