Life Sciences: Photosynthesis

Life Sciences: Photosynthesis

In this lesson we'll cover the definition of photosynthesis, the equation for photosynthesis, as well as the reactants and products. Using diagrams of photosynthesis, we'll go over the formula and process.

What is Photosynthesis

Plants have a power we humans can only dream of - making food from sunlight. Sure, we can cook some savory dishes, but we use food already made, mostly by plants. This process of assembling carbohydrates fueled by the power of sunlight is called photosynthesis.

Keep in mind that the sun emits all sorts of different kinds of energy, such as heat and gamma rays, but photosynthesis specifically captures light energy. In addition, photosynthesis generates basic sugar molecules called glucose, which can be used to build more complex carbohydrates.

The Process of Photosynthesis

The prefix 'photo' means light, and 'synthesis' means to bring together. In other words, photosynthesis is the bringing together of molecules using light energy. Just what does the process of photosynthesis bring together to make sugar molecules? Two things: carbon dioxide and water.

The Process of Photosynthesis

How this process works can be understood from two overarching perspectives: matter and energy.

a. In terms of matter, photosynthesis takes smaller, simpler materials and assembles them into larger, more complex ones.

b. In terms of energy, photosynthesis transforms light energy from the sun into a form living things can access: the stored chemical energy in food molecules.

The Process of Photosynthesis

Technically, one round of photosynthesis requires six molecules of carbon dioxide and six molecules of water. From this, one molecule of glucose is produced along with six molecules of oxygen as a by-product.

a. carbon dioxide + water + sunlight --> oxygen and glucose

b. or more specifically: 6CO₂ + 6H₂ O + sunlight --> C₆ H₁₂ O₆ + 6O₂

Multiple Choice

Which of the following is the correct equation for photosynthesis?

• 6CO₂ + 6H₂ O -------> C₆ H₁₂ O6 + 6O₂

• 6CO₂ + H₂ O --------> C₆ H₁₂ O₆ + O₂

• 6O₂ + 6CO₂ --------> C₆ H₁₂ O₆ + 6H₂ O

Where does Photosynthesis occur?

The first part of the process of photosynthesis is the light-dependent reactions. As mentioned, sunlight is the energy source for this process. In terms of cellular structures, plants and other organisms capable of carrying out photosynthesis must have certain specialized components.

One component that photosynthetic organisms require is a pigment molecule, which is a special-colored substance that acts like an antenna capable of absorbing light energy. Pigment molecules channel the light energy into the right spot where the cell is carrying out photosynthesis. The most common pigment is chlorophyll, which is responsible for the widespread green color we all associate with plants.

Multiple Choice

What is the role of the pigment molecules in photosynthesis?

• To release oxygen

• To produce color

• To absorb light energy

• To take in carbon dioxide

Chloroplast

Plants contain their chlorophyll and pigments inside a type of organelle called a chloroplast, and it is within this structure that photosynthesis is carried out. Prokaryotic organisms that lack organelles simply carry out the food-making process in the cytoplasm but still require pigment molecules to do so.

Chlorophyll

Chloroplasts are organelles inside plant cells where photosynthesis is carried out perhaps you have seen plants with red or yellow leaves, and not just in fall? These plants have other types of pigments in them instead of or in addition to chlorophyll.

Products of Photosynthesis

One round of photosynthesis produces a single sugar molecule. The most common sugar made is glucose, which has the chemical formula C₆ H₁₂ O₆. Like all molecules, glucose contains chemical potential energy.

Living things can only access the energy needed to survive from food molecules. In other words, plants convert solar energy into a form of energy living things can be fueled by because, clearly, we cannot satisfy our hunger from taking in rays at the beach.

In addition to sugar, photosynthesis releases six molecules of oxygen gas (O₂).

Multiple Choice

What happens to the solar light energy in photosynthesis?

• It is reflected from the leaf into the surrounding environment.

• Some of it is transformed into chemical energy stored in a sugar molecule.

• All of it is used up during the process of making sugar and dissipates as heat.

• Most of it remains in the pigment molecule.

Photosynthesis in Other Organisms

There are other organisms capable of carrying out photosynthesis aside from plants, such as certain types of bacteria and protists. To be fair to the bacteria, they are likely the ones who evolved the process in the first place. Any organism, plant or otherwise, carrying out photosynthesis would have to contain one of the pigment molecules, usually chlorophyll.

Multiple Choice

What are the reactants of photosynthesis?

• carbon dioxide, water and sunlight

• carbon dioxide and oxygen and sunlight

• oxygen and sunlight

• oxygen, water and sunlight

Multiple Choice

Which statement correctly describes what photosynthesis accomplishes?

• Carbon dioxide and water are assembled into food molecules.

• Water molecules are turned into carbon dioxide and then into food.

• Carbon dioxide and oxygen combine to make food molecules.

• Sunlight is converted into carbon dioxide and then into food.