Respiration is a process that is used to produce energy in the cells of organisms, this can be plants as well as animals. Organic compounds are oxidized during respiration and this releases energy that is used for various cellular processes. Primarily, respiration involves the conversion of carbohydrates to water and carbon dioxide.
C6H12O6 + 6O2 -> 6CO2 + 6H2O
The reaction also gives off -2880 kJ per mole of the carbohydrate that is oxidized.
Photosynthesis on the other hand takes place only in organisms that have chloroplasts containing chlorophyll. In photosynthesis, carbon dioxide from the atmosphere and water from the soil is converted to oxygen and organic compounds. This is an endothermic reaction that requires an external source of energy that is the Sun.
In the case of plants respiration and photosynthesis can be considered as reciprocal reactions. One leads to the production of organic compounds using energy from the Sun and in the other the same compounds are oxidized to release energy for the cells of the plants.