Agriculture Sphere

How do plants use light to make their own food?

Plants can make food for themselves, and eventually animals, through a process known as photosynthesis. Photosynthesis involves using the energy from light to put carbon, oxygen, and hydrogen together in a way that produces sugars.

Photosynthesis is made up of two parts. The first part is known as the light reactions. They are called the light reactions because they utilize the light for energy. Some of the energy is used to create a particle called ATP, which plants and animals get their energy from. The rest of of the light energy is used to break apart water particles into hydrogen and oxygen. The oxygen is released into the air, which we can breathe. The hydrogen is then attached to a carrier molecule called NADP. This molecule takes the hydrogen to the second part of photosynthesis, the dark reactions.

The name of the dark reactions is somewhat misleading. Unlike the light reactions, the dark reactions do not necessarily take place in the dark. They are only called the dark reactions because they do not need light. Another name for the dark reactions is the carbon-fixation reactions. In these reactions, 6 carbon dioxide molecules (1 carbon atom and 2 oxygen atoms) are combined with the hydrogen atoms attached to the NADP to form a kind of sugar, called glucose. If you have ever had corn starch, you have had glucose. The chemical formula of glucose is C6H12O6. When two glucose molecules combine, they can form sucrose, which is the sugar that you buy in the store. On Mars, the process of photosynthesis is very important because it produces two very important components for humans, food and oxygen.

Before performing this experiment, it is important to understand the relationship between cellular respiration and photosynthesis.

Bromothymol Blue, or BTB, is an indicator for weak acids. Carbon dioxide forms a weak acid in water, carbonic acid, which is in all brands of soda. Try putting different plants in BTB to see if they released carbon dioxide. For this experiment you will need some water plants.

In one test tube, place BTB and a plant. In a second one, place another one of the water plants. Finally, have two tubes with only BTB. Place one tube with the plants in the light, along with a tube that has only BTB. Place the two remaining tubes in the dark.

Notice the color of the BTB at the beginning of the experiment. After a few days, notice any color changes. If BTB turns yellow in the presence of carbon dioxide, what can you determine about the gases released during photosynthesis? How is this related to light? Why were the tubes with only BTB used?

Send us your results!

How much of the food that you eat is derived from the sugars produced in photosynthesis?

Look around your house or supermarket (but don't make a mess!) for foods with sugar or corn starch. All of these foods are products of photosynthesis. Judging by the list of foods you find, you can see how important it is for the colony on Mars.