READ: Energy from the Sun

1. Photosynthesis

Every split second that sunlight hits that leaf, photosynthesis is initiated, bringing energy into the ecosystem. It could be said that this is one of the most important - if not the absolutely most important - biochemical reaction. And it all starts with the leaf.

What can a tiny plant do that you can't do?

This tiny plant can use the energy of the sun to make its own food. You can't make food by just sitting in the sun. Plants are not the only organisms that can get energy from the sun, however. Some protists, such as algae, and some bacteria can also use the energy of the sun to make their own food.

What is Photosynthesis?

If a plant gets hungry, it cannot walk to a local restaurant and buy a slice of pizza. So, how does a plant get the food it needs to survive? Plants are producers, which means they are able to make, or produce, their own food. They also produce the "food" for other organisms. Plants are also autotrophs. Autotrophs are the organisms that collect the energy from the sun and turn it into organic compounds. So once again, how does a plant get the food it needs to survive?

Through photosynthesis. Photosynthesis is the process plants use to make their own “food” from the sun's energy, carbon dioxide, and water. During photosynthesis, carbon dioxide and water combine with solar energy to create glucose, a carbohydrate (C₆H₁₂O₆), and oxygen.

The process can be summarized as: in the presence of sunlight, carbon dioxide + water → glucose + oxygen.

 The overall chemical equation for photosynthesis is:

6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂

Glucose is a sugar that acts as the "food" source for plants.  The oxygen formed during photosynthesis, which is necessary for animal life, is essentially a waste product of the photosynthesis process.

 Photosynthesis changes light energy to chemical energy. The chemical energy is stored in the bonds of glucose molecules. Glucose, in turn, is used for energy by the cells of almost all living things. Photosynthetic organisms such as plants make their own glucose. Other organisms get glucose by consuming plants (or organisms that consume plants).

Actually, almost all organisms obtain their energy from photosynthetic organisms. For example, if a bird eats a caterpillar, then the bird gets the energy that the caterpillar gets from the plants it eats. So the bird indirectly gets energy that began with the glucose formed through photosynthesis. Therefore, the process of photosynthesis is central to sustaining life on Earth. In eukaryotic organisms, photosynthesis occurs in chloroplasts. Only cells with chloroplasts—plant cells and algal (protist) cells—can perform photosynthesis. Animal cells and fungal cells do not have chloroplasts and, therefore, cannot photosynthesize. That is why these organisms rely on other organisms to obtain their energy. These organisms are heterotrophs.

Interactive Simulation

This interactive simulation of photosynthesis has animations along with text descriptions.

Open the Simulation

CK-12 Foundation, Physical Science. http://creativecommons.org/licenses/by-nc-sa/3.0/

2. Photosynthesis and Food

3. Summary and Vocabulary

Summary

• All the energy used by living things on earth came from the process of photosynthesis.
• During photosynthesis, carbon dioxide and water combine with solar energy to create glucose and oxygen.

Vocabulary

• autotroph: Organism that produces complex organic compounds from simple inorganic molecules using a source of energy such as sunlight.
• chloroplast: Organelle that carries out photosynthesis in plants.
• glucose: Simple sugar with the chemical formula C₆H₁₂O₆; a product of photosynthesis.
• heterotroph: Organism which obtains carbon from outside sources.
• photosynthesis: Process by which specific organisms (including all plants) use the sun's energy to make their own food from carbon dioxide and water; process that converts the energy of the sun, or solar energy, into carbohydrates, a type of chemical energy.
• producer: Organism that produces food (glucose) for itself and other organisms.

CK-12 Foundation, Physical Science. http://creativecommons.org/licenses/by-nc-sa/3.0/