(1) Introduction to natural cycles in the Earth's biosphere

The biosphere is made up of the parts of the Earth where life in some exists within complex interconnected and interdependent ecosystems.

You can consider he biosphere ranges from the deepest root systems of trees, to the deep and dark environments of ocean trenches, to lush rain forests, fields of crops, deserts, high mountaintops, woodlands and urban environments.

Within all this varied range of life-supporting systems and resources, materials are used by organisms to live, reproduce and die and in doing so, through decay, the materials of life are recycled.

An ecosystem is all the living organisms in a particular area including non-living conditions (abiotic factors) such as temperature, soil quality, water sources.

Within an ecosystem materials are continually recycled in many complex ways involving biotic (living) and abiotic (non-living) components in ecosystems.

For more on biotic/abiotic factors see Ecosystems and interactions between organisms   gcse biology notes

 

All living organisms are composed of the chemical elements they obtain from the environment in some way.

Plants will take in compounds of carbon (e.g. carbon dioxide from air), hydrogen (e.g. water through roots) and nitrogen (e.g. nitrates from soil) and the element oxygen from air.

Some plants can metabolise nitrogen from the air directly (e.g. legumes).

These elements and simple compounds are converted into all the complex biological molecules you find in plants such as carbohydrates, fats and proteins.

These are then consumed by plant eating animals, creating biomass that gets passed on up the food chain.

 

All of these elements and compounds must be recycled by some means back into the environment.

All the nutrients in our environment are being constantly recycled with many inputs balancing the many outputs.

The material might be recycled back into the soil or into the air.

This recycled material may come from animal waste products e.g. faeces or emitted gases!

 

When plants or animas die, their remains will slowly decay

Decomposer organisms like bacteria and fungi play are a very important part of ecosystems.

To decompose any dead plant or animal material, they secrete enzymes that break the dead organic material down into smaller soluble food molecules which can diffuse into the microorganisms i.e. absorption of nutrients.

Therefore decayed material in the soil is recycled by microorganisms and new plant growth and so re-enters the many complex food chains in an ecosystem.

All dead organisms decay because they are broken down by decomposers (often microorganisms) which digest the once living material replace lost nutrients like mineral ions back into the soil.

The decomposition by microorganisms is favoured by warm, moist and aerobic conditions.

 

A stable community - stable ecosystem

If the materials that plants take out of the soil and air to create biomass is balanced by recycled decayed material the community is described as stable - the natural cycle repeats itself continuously.

Poor land management and overuse of agrichemicals leads to an imbalance with a negative impact on the habitats of many plants and animals.

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Key points - Summary of ideas about the Earth's Cycles

Based on the syllabus-specifications for students taking the AQA, Edexcel and OCR GCSE level biology examinations (~US grades 9-10).

Introduction to Earth's Natural Cycles in the Biosphere

Earth's biosphere is a dynamic system where air, water, and land interact through continuous cycles that sustain life. These natural cycles regulate the movement of essential elements, ensuring the balance of ecosystems and the survival of organisms.

1. The Air Cycle – The Carbon and Oxygen Cycle:

   • The atmosphere is a crucial component of the biosphere, where gases like oxygen and carbon dioxide circulate.

   • Through photosynthesis, plants absorb carbon dioxide and release oxygen, supporting animal respiration. In turn, animals exhale carbon dioxide, completing a cycle vital for life.

2. The Water Cycle – Circulating Water Globally:

   • Water moves between the atmosphere, land, and oceans through evaporation, condensation, precipitation, and runoff.

   • This cycle supports ecosystems by distributing freshwater, influencing climate, and sustaining organisms in diverse habitats.

3. The Land Cycle – The Nutrient Cycle:

   1. Soil and rocks play a fundamental role in cycling nutrients like nitrogen and phosphorus. Decomposers break down organic matter, returning nutrients to the soil, where plants absorb them.

   2. These nutrients then move through the food chain, ensuring the continuity of life

Together, these cycles create a balanced environment where energy and matter flow seamlessly, maintaining Earth's ecosystems.

Understanding them helps us appreciate how human activities impact natural processes and why conservation is vital.

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Summary of learning objectives and key words or phrases

Understand and be able to explain the importance of natural cycles in Earth's and the role of natural decay and by decomposer organisms in ecosystems

• All living things are made of elements like carbon, nitrogen, hydrogen and oxygen which are all obtained from the environment they live in e.g. from the air, soil or water.

• By one means or other these elements are returned to the environment as e.g. carbon dioxide in air, water or nitrogen in air or nitrogen compounds in soil.

• If this did not happen, new life could not be formed from the living feeding on pre-existing food (alive or dead).

• Food chains and decomposers play important roles in this recycling as exemplified by the carbon cycle and nitrogen cycle, both of which are illustrated and described below.

• The function of bacteria, decomposers, food chains etc. is all explained.

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