(4) What does the plant do with the glucose produced by photosynthesis using sunlight energy?

• Glucose from photosynthesis, provides energy and can be converted into, and help to synthesise, a wide range of molecules in plant cell chemistry (plant biochemistry).

  • This means plants make their own food!

• The glucose produced in photosynthesis may be converted into insoluble starch for storage in leaves, roots and stems.

  • The insoluble nature of starch makes it a very useful concentrated chemical store of energy - if it was soluble, it would dissolve and diffuse all over the place.

    • Starch is a natural polymer made from linking many glucose molecules together and is the main chemical energy store in a plant.

    • A plant can't photosynthesise at night, so it needs energy from somewhere to stay alive at night!

    • When needed, starch is hydrolysed (broken down) into the useful sugar glucose for respiration, so the process of starch formation is reversed.

    • Glucose sugar is soluble and easily transported around a plant and fuels respiration in the mitochondria of plant cells - which in turn provides the energy for all the cellular processes needed by a plant.

    • If a plant tried to store the soluble glucose, the cells would absorb water by osmosis, swell up and burst!

    • See demonstrating presence of starch in plant leaves.

• Plants need energy from sugars (from photosynthesis) to power their own life supporting systems just as we do.

  • Plant cells use some of the glucose produced during photosynthesis for immediate respiration - release of energy to power the cell functions and particularly at night when no light can shine on the leaves.

    • Plant respiration in principle is the reverse of photosynthesis.

    • glucose + oxygen ==> products + chemical energy (to power the plant cell chemistry)

  • The energy released enables the plant to convert glucose plus other elements/ions like nitrogen/nitrate into other essential useful chemical substances - some are listed below.

  • At night there be a net loss of glucose/starch in respiration, but in daylight the rate of photosynthesis will exceed that of respiration in a growing plant so excess glucose can be converted into starch for storage.

  • ... noting that starch and glucose are chemical energy stores.

  • Glucose is consumed in plant respiration, e.g. in aerobic respiration, plants use oxygen to oxidise glucose to carbon dioxide and water.

    • The released chemical energy to power all the cell chemistry including the conversion of glucose into starch and making protein.

    • Don't forget that plants respire all the time, just like us!

  • Glucose can be converted into starch that can be stored in roots (e.g. potato), stems and leaves, this provides energy at night and in winter.

    • Starch has the advantage of being insoluble in water, so won't dissolve away unnecessarily from vital energy reserve storage areas.

    • It can be used when sunlight is low e.g. winter, and of course at night when photosynthesis stops completely.

    • Also, by being insoluble, it won't affect the water concentration in cells by osmosis.

    • A cell with a high concentration of glucose would swell up by water absorption interfering with its function.

• The chemical energy from glucose is needed to build larger more complex molecules.

  • Through growth and accumulation of these larger molecules biomass is built up in plants and algae.

  • Biomass means the mass of living material.

  • The energy built up in a plant's or algal organism's biomass enters the food chain so animals can now feed on it (herbivores) and themselves be fed on by other animals (carnivores).

  • This is why at the start of this page it was emphasised that photosynthesising organisms are the main producers of food for most of life on Earth.

• Examples of the larger molecules in the biomass of plants and algae

  • Glucose and nitrate ions are used to synthesise amino acids which in turn, via DNA coding, are converted into proteins e.g. tissue cells or enzymes.

  • Glucose is used to produce fats or oils (lipids) for storage - provides sources of energy via aerobic respiration, seeds contain food stores based on oils and fats (think of cooking oil from olives or sunflower oil for margarine) and waxes.

  • Glucose is used to make cellulose, which makes up and strengthens the cell walls eg of the xylem and phloem and is particularly needed in larger quantities in rapidly growing plants.

  • Amino acids are first synthesised from glucose and nitrate ions (absorbed from soil through the roots) and other minerals before conversion to proteins for tissue cell growth and repair.

• Ultimately, some of the carbohydrates like starch and cellulose, vegetable oils and plant protein end up being consumed in the food chains from microorganisms to large animals of  biomass and energy transfer systems.

• AND note oxygen for aerobic respiration of plants and animals is a by-product of photosynthesis!

• Note that to produce proteins, plants also use nitrate ions that are absorbed from the soil, the source of nitrogen for amino acid synthesis, prior to protein synthesis.

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Key points - what happens to the glucose produced in photosynthesis?

Source of information is based on textbooks and syllabus-specifications for students taking the AQA GCSE, Edexcel GCSE and OCR GCSE level biology examinations (~US grades 9-10)

Biology revision notes on what happens to the glucose made during photosynthesis - a key concept that links plant metabolism, growth, and survival.

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What Does the Plant Do with the Glucose from Photosynthesis?

Glucose produced during photosynthesis is incredibly important - it’s the starting point for making many essential substances in a plant.

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1. Used for Respiration (glucose provides energy)

• Glucose is broken down in aerobic respiration to release ATP (energy).

• This energy supports:

  • Active transport of minerals

  • Cell division and growth

  • Protein synthesis

  • Repair of damaged cells

Remember: Plants respire just like animals—day and night!

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2. Stored as Starch

• Glucose is converted into starch (an insoluble carbohydrate).

• Stored in leaves, stems, roots, or tubers (like potatoes).

• Starch:

  • Doesn't affect osmosis (unlike soluble glucose).

  • Can be broken down back into glucose when needed (e.g. at night).

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3. Converted into Cellulose

• Glucose molecules are joined to make cellulose, the main component of plant cell walls.

• Provides strength and structure.

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4. Used to Make Amino Acids and Proteins

• Glucose combines with nitrates (absorbed from soil) to make amino acids.

• Amino acids build up into proteins for:

  • Growth

  • Enzymes

  • Cell structures

This is why plants need nitrates from the soil - glucose alone isn’t enough!

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5. Converted into Fats and Oils (Lipids)

• Glucose is used to make lipids, which are stored in seeds.

• Lipids are an energy-rich store used during seed germination.

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6. Used to Make Other Organic Compounds

• Glucose is also used to form:

  • Sucrose – transported through the phloem to other parts of the plant.

  • Nucleic acids – needed for DNA and RNA.

  • Pigments and plant hormones.

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Why Is This Important for Understanding Human Biology?

• Shows how plants create the foundation of food chains—without glucose, no plant tissue would exist.

• Explains why plants are vital for oxygen, fuel, food, and raw materials.

• Highlights the role of minerals (e.g. nitrates) in enabling healthy growth.

• Connects photosynthesis to plant nutrition, metabolism, and reproduction.

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Exam Tips

• Be able to list and explain the uses of glucose.

• Understand how glucose is converted into other substances.

• Use terms like stored, converted, transported, synthesised.

• Link glucose use to survival and growth in plants.

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Keywords, phrases and learning objectives for this part on photosynthesis

Be able to describe what a plant can do with the glucose made from photosynthesis.

Be able describe that plants can make carbohydrates like starch and cellulose, and using glucose and energy from it to synthesise many useful compounds.

e.g. vegetable oils and proteins, which eventually get consumed in the food chains from microorganisms to large animals of biomass and energy transfer systems.

AND, a reminder the waste gas oxygen is used by many organisms for energy transfer in aerobic respiration.

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