The relationship between Photosynthesis and Respiration


Remember this:


Plants make food for all other living things by photosynthesis.

Plants capture the Sun's energy and turn it into Glucose (food) - which is stored chemical energy

Without plants (photosynthesis) all animals would die.

Animals eat food to extract energy in order live and grow.

During respiration Glucose and oxygen  are used up and turned back into carbon dioxide and water.

in fact respiration is the opposite of photosynthesis!

If you look at the chemical equations of these two processes, you will notice that they are the same, but in opposite directions:


PHOTOSYNTHESIS - Requires energy











RESPIRATION - releases energy










RESPIRATION - eating food and using energy

PHOTOSYNTHESIS - the energy factory

During respiration energy is used to do work.

During photosynthesis energy is trapped and stored.

During respiration food is used.

Photosynthesis make food.

Carbon dioxide, water and energy are released during respiration.

Carbon dioxide, water and energy are used during photosynthesis to make food.


Photosynthesis and respiration


Respiration releases energy stored during photosynthesis


Plants also do respiration

We know that during daylight (or artificial light, except green) plants carry out photosynthesis and release OXYGEN.  Like animals, plants also require energy to live and grow.  This energy comes from  glucose during respiration.  Respiration uses oxygen and give up carbon dioxide.  To demonstrate this, we can do the following:


enclosed plant

Enclosed plant, with different levels of O2 and CO2




The graph shows that the level of oxygen rises in the daytime.  This is due to photosynthesis producing more oxygen than the plant's respiration using it up.  The level of oxygen falls during night due to the plant's respiration using it up and no more is being produced as there is no photosynthesis happening.  The amount of oxygen rises gradually, over the period of time.


The level of CO2 falls during day time due to photosynthesis using it up.  However, it rises at night because of respiration.  On the whole the level of CO2 falls since the plant use up more CO2 than it produces.

Fate of Glucose in side plants


Tags:Photosynthesis, Oxygen, Carbon dioxide, Respiration, Glocose, Energy, Chlorophyll



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