The Two Most Important Energy-Producing Processes

Both photosynthesis and respiration are responsible for producing and delivering both the energy and gases that all living organisms need for life.

Photosynthesis
Nearly every living organism on earth depends on the oxygen, food, and energy that are produced by photosynthesis in plants.The only known exceptions are organisms living around deep sea vents on the ocean floor.

Photosynthesis is our ultimate source of food and energy.Photosynthesis is responsible for converting the energy in sunlight into chemical forms (ATP and glucose) that we use for food and energy.

How Photosynthesis works:
Photosynthesis converts the carbon dioxide (CO₂) that plants produce into oxygen (O₂) that animals breathe.

It takes place in two steps.

Step 1. In the light phase: Solar energy is converted into and stored as energy in the form of ATP (adenosine triphosphate).
Step 2. CO₂ and energy from ATP are used to form glucose - a sugar. The net effect of photosynthesis is:
C CO₂, and H₂O + energy from the sun O₂ + C

Source: Wikimedia By: Daniel Mayer. License: Creative Commons Attribution Sharealike 3.0 unported.
During photosynthesis plants use energy from the sun to manufacture food. Solar energy transforms carbon dioxide and water into glucose and oxygen.This is the source of the O₂ we breathe, and thus, a significant factor in the concerns about deforestation.

Where Photosynthesis takes place

Photosynthesis occurs in chloroplasts, tiny organelles found in leaves. Chloroplasts are often described as little carbohydrate factories powered by solar energy. These tiny factories produce the food that plants and practically every other living thing on earth rely on for survival.

Leaf - Source: Wikimedia. Photo courtesy of PDPhoto.org. License: Public Domain.

Plagiomnium - Source: Wikimedia. By: Kristian Peters. License: Creative Commons Attribution Sharealike 3.0.
Underside of leaf - Source: http://remf.dartmouth.edu/images/botanicalLeafSEM/source/16.html. By: Photohound. License: Creative Commons Zero (Non-US)

Cellular Respiration makes Energy Available for Use

Cellular Respiration happens in all living organisms. In plants, it follows photosynthesis. Respiration serves the same purpose in all organisms --It converts the energy in sugar (glucose) into a form every organism can use for energy (ATP).

Source: Wikimedia. By: Bogjgalindo. License: Creative Commons Attribution Sharealike 3.0 unported.
During humans respiration, we inhale (take in) oxygen and exhale (release) carbon dioxide. Cellular respiration is not entirely different.During respiration, cells use the glucose from photosynthesis and oxygen to release stored energy

Mirror Images: photosynthesis and respiration

The equations for photosynthesis and respiration are opposites

Energy is stored as ATP
the Primary Energy Source for all Organisms

Plants are the prime source of energy for all living organisms. This energy is stored in every plant cell as glucose a molecule called ATP - and used by consumers, like the insects, deer, and cows that eat plants.

Plants and some deep sea bacteria are the only organisms on earth that are capable of producing their own food and deriving energy from it.

Plants and bacteria produce energy and store it as ATP. (adenosine triphosphate. Energy (as ATP) is passed up the food chain from producer to consumer to carnivore.

A Comparison between Photosynthesis and Respiration

Photosynthesis and Cell Respiration

The Process	Photosynthesis	Respiration
Which organisms use this metabolic pathway?	Plants	Plants, Animals, & Bacteria (all living organisms)
Short explanation of the process	Carbon dioxide, energy from the sun and some minerals are used to manufacture food	Food (carbohydrates) is turned into energy that the organism can actually use: ATP
When does the process take place in plants?	Before respiration	After photosynthesis
Where does the process occur?	In chloroplasts, (tiny organelles in leaves)	In all plant, animal, and bacterial cells
What happens to the energy?	Solar energy is used for the synthesis of glucose, which is used or stored as ATP	Energy in glucose is converted to a form of energy the cell can use: ATP. (This done by breaking chemical bonds in glucose molecules.)
What is consumed during the process?	carbon dioxide, water and energy from sunlight	oxygen
What is released during the process?	Oxygen	carbon dioxide and energy
Chemical reactions	6CO₂ + 6H₂O + solar energy→ C₆H₁₂O₆ + 6O₂	C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP energy