(2) The crucial role of photosynthesis in the formation of biomass

Green plants and algae are the initial producers of food, after that its all consumers, including us!

Radiation from the Sun is the initial source of energy for most communities of living organisms.

Green plants and algae absorb a small amount of the light that reaches them.

The transfer from light energy to chemical energy occurs during photosynthesis.

 carbon dioxide + water == light + chlorophyll  ==> glucose + oxygen

 6H₂O_(l) + 6CO_2(g) == sunlight ==> C₆H₁₂O_6(aq) + 6O_2(g)

Photosynthesis uses sunlight energy to convert water and carbon dioxide into sugars like glucose, the 'waste product' being oxygen - though plants need oxygen for their respiration at night!

Apparently only ~1% of sunlight energy is transferred via photosynthesis to create biomass.

the simple equation to illustrate photosynthesis is

water + carbon dioxide (+ sunlight) == chlorophyll ==> glucose + oxygen

 

Some of the glucose is used directly by the plant to power cell chemistry - making all the molecules necessary for life, but some energy is stored in the substances that partly make up the cells of the plants e.g. starch or cellulose - chemical potential energy store. This adds to the biomass of the plant.

 

Most food chains, and therefore most life-forms, are dependent on the initial input of sunlight energy.

Food chains always start with a producer, which produce their own food.

This is usually a green plant on land, or algae and phytoplankton in water.

Producers (mainly plants) take in the elements they need from their environment.

Molecular compounds like water (roots), carbon dioxide (leaves) and mineral ions e.g. nitrate for nitrogen, phosphate for phosphorus and small quantities of metals like magnesium, iron, potassium and zinc (absorbed by roots).

In producers the energy from sunlight powering photosynthesis produces sugars and other carbohydrates, which in turn provide a source of energy to make fats, glycerol and amino acids for proteins.

From small molecules, plants make long chain carbohydrates, lipids and proteins which form part of their cell structure and tissues e.g. cell membranes/walls and organelles like mitochondria, chloroplasts and ribosomes.

All of these metabolic chemical reactions are catalysed by enzymes.

These biological molecules comprise the organisms biomass - the mass of living material which is passed on up a food chain from one trophic level to another.

A trophic level is the position of an organism in a food chain, food web, pyramid of numbers or pyramid of biomass.

Plants are consumed by animals which in turn use the energy in respiration to power physical movement and build their fat and protein body structures.

Similarly, energy is also transferred through organisms in a food chain when consumers eat plant producers and animals eat other animals.

At each stage there are considerable losses of biomass and energy for various reasons (discussed later).

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Key points - Summary of ideas

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

Photosynthesis and biomass are fundamental concepts in biology, as they underpin the energy flow in ecosystems and the survival of life on Earth.

Photosynthesis: The Foundation of Life

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy.

It takes place in the chloroplasts of plant cells, using chlorophyll to absorb sunlight.

The simplified equation for photosynthesis is:

•  carbon dioxide + water == light + chlorophyll  ==> glucose + oxygen

•  6H₂O_(l) + 6CO_2(g) == sunlight ==> C₆H₁₂O_6(aq) + 6O_2(g)

Why Photosynthesis Matters

• Oxygen Production: It generates oxygen, crucial for respiration in most living organisms.

• Energy Source: It provides glucose, which plants use for respiration and growth.

• Carbon Fixation: It removes carbon dioxide from the atmosphere, helping regulate global climate.

Biomass: The Energy Currency of Ecosystems

Biomass refers to the mass of living material in organisms. Plants convert light energy into biomass through photosynthesis. This stored energy is then transferred through food chains.

Role of Biomass in Ecosystems

• Primary Producers: Plants create biomass, which supports herbivores, then carnivores.

• Energy Flow: Biomass provides energy at different trophic levels in a food chain.

• Carbon Cycling: Biomass plays a key role in the carbon cycle, influencing climate stability.

Conclusion

Without photosynthesis, life on Earth would not exist as we know it.

It drives food chains, balances atmospheric gases, and sustains ecosystems.

Biomass, meanwhile, acts as the fuel for food chains and energy transfers.

Understanding these concepts helps students appreciate the interdependence of life and the importance of environmental conservation.

See also Photosynthesis, importance explained, limiting factors, leaf adaptations

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Summary of learning objectives and key words or phrases

Understand the crucial role of photosynthesis in the accumulation of biomass in plant and animal food chains

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