What does the plant do with the
glucose produced by photosynthesis?
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(4) What does the plant do with the glucose produced by photosynthesis using sunlight energy?
Glucose 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
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!
presence of starch in plant leaves.
Plants need energy from sugars (from
to power their own life supporting systems just as we do.
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.
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.
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
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
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 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
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
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.
oxygen for aerobic respiration of plants and animals is a by-product
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