Photosynthesis and Cellular Respiration

All living things on earth are made up of small microscopic structures called cells. Photosynthesis and cellular respiration are two most important energy producing processes that occur in these microscopic structures, to sustain life.

Photosynthesis Process
Photosynthesis is a chemical process that takes place in the presence of sunlight, wherein plants make their food and build stores of energy. This phenomenon occurs in chlorophyll containing plant cells. Chlorophyll is a pigment found in plant leaves that gives plants their green color. Chlorophyll absorbs the light energy and utilizes it to produce carbohydrates (sugars) from carbon dioxide (CO₂) and water (H₂O). This chemical reaction produces oxygen which is released into the atmosphere.

The reaction can be described as follows:
Carbon Dioxide + Water + Sunlight = Glucose + Oxygen
6CO₂ + 6H₂O + Sunlight --> C₆H₁₂O₆ + 6O₂

The carbohydrates produced by photosynthesis are used by the plants as a source of immediate energy for growth, reproduction, absorption of nutrients, etc. They also act as energy reserves and are stored in the form of starch which enable the plants to survive in drastic conditions, like, extreme winters or droughts. Carbohydrates are also used in the formation of plant tissues to grow leaves, wood, flowers, fruits, roots, etc. Read more on:

• Steps of Photosynthesis
• Importance of Photosynthesis

Factors Affecting Photosynthesis
The process of photosynthesis is influenced by various factors which are as follows:

• Temperature: The optimum temperature for the process is somewhere between 20 and 35°C. The process ceases at temperatures below 0°C due to the slowing of the plant's physiology.
• Carbon Dioxide: High carbon dioxide concentration in the atmosphere promotes the process of photosynthesis.
• Sunlight: As the intensity of the light increases, chlorophyll becomes more effective, thereby enhancing the process of photosynthesis.
• Water Availability: Plants have to transpire to absorb carbon dioxide, therefore, if the water becomes scarce, it reduces transpiration and slows down photosynthesis.

Now let's look at the concept of cellular respiration to understand the relation between photosynthesis and cellular respiration.

Cellular Respiration
Cellular respiration is the process of oxidizing food molecules or breaking down chemical bonds of glucose into carbon dioxide and water. The energy released during the process is trapped in the form of ATP (Adenosine Tri-Phosphate) and used by different energy consuming activities of the cell. In other words, it's a set of the metabolic reactions that occur in the mitochondria of the cells of organisms to convert biochemical energy from nutrients into ATP, and release byproducts. The complete breakdown of glucose into carbon dioxide and water involves two major steps: glycolysis and aerobic respiration.

Glycolysis: It's an anaerobic catabolism of glucose that occurs in all the cells and produces two molecules of pyruvate and two molecules of ATP.
Aerobic Respiration: It's a process wherein the pyruvate molecules produced in glycolysis, undergoes further breakdown in the presence of oxygen and generates thirty four molecules of ATP. Read more on aerobic cellular respiration.

The reaction can be described as follows:
Glucose + Oxygen = Carbon Dioxide + Water + Energy
C₆H₁₂O₆ + 6O₂ --> 6CO₂ + 6H₂O + Energy (36 ATP)

Difference Between Photosynthesis and Cellular Respiration

Sr. No.	Photosynthesis	Cellular Respiration
1	Photosynthesis is a process wherein plants utilize sunlight to make food.	Cellular respiration is a process that converts this food into energy which is used by plants and other living organisms.
2	It takes place inside the chloroplasts, organelles inside the plant cells that contain chlorophyll.	It takes place inside the mitochondria, organelles capable of breaking down glucose.
3	Photosynthesis requires energy to produce glucose.	Cellular respiration uses this glucose to create energy (ATP).
4	It takes carbon dioxide, water and sunlight from the atmosphere to create sugar and releases oxygen back into the air.	It combines sugars with oxygen, releases the energy as ATP and carbon dioxide and water as by products.
5	Photosynthesis occurs in plants and some bacteria.	Cellular respiration occurs in all living organisms.

Photosynthesis and cellular respiration are two processes that involve electron transport chains and affect concentrations of carbon dioxide and oxygen in the atmosphere. They are the main source of energy in all living things and hence provide power for different cellular activities.