How plants make food from sunlight, air, and water

Learning Objectives

Know reactants and products and what organelle the processes occur in. Understand the role of chlorophyll and stomata

Just like certain organisms need cellular respiration in order to sustain life, plants go through a process called photosynthesis. Photosynthesis is a plant’s process of converting light energy into chemical energy that it can live off of.

Plants are photoautotrophs, which means they are able to produce their own food from light. In other words, just like humans need food for energy, plants need light. Plants use solar energy (sunlight), carbon dioxide, andwater in order to make glucose, which it uses as energy to live. Oxygen is also a byproduct of this process, which plants release into the air. This is convenient for humans and other animals who need oxygen to breathe.

Plants need a certain amount of carbon dioxide and water in order to complete this process. The exact equation is shown here:

6 carbon dioxide molecules + 6 water molecules → 1 glucose molecule and 6 oxygen molecules

Photosynthesis takes place in organelles within the plant called chloroplasts. Chloroplasts give plants their green color, and contain chlorophyll, which carry out the functions of converting the sunlight absorbed by the plant into chemical, usable energy. Chlorophyll is located in the mesophyll, which is the middle layer of leaf tissue, as seen here in figure 2.

Figure one depicts photosynthesis moving from a macroscopic to microscopic level. It shows a leaf. Then it zooms in on a cross section of the leaf. Then it zooms in to depict a chloroplast within a plant cell. It then zooms in one more time to show chlorophyll in the chloroplasts. On the right, photosynthesis is shown as chlorophyll takes in sunlight and carbon dioxide to make sugar and energy.
Fig. 1 Zooming in on photosynthesis. The location of chlorophyll in relation to the leaf is depicted on the left. On the right, the input and output of photosynthesis is shown on a microscopic level.

Light is absorbed through the top layers of the leaf, known as the cuticle and upper epidermis. We already know the mesophilic layers are where photosynthesis takes place, but what about the lower epidermis? The lower epidermis of a leaf contains stomata and guard cells that allow carbon dioxide to enter the leaf, and oxygen and excess water to exit the leaf. The structure of the leaf can be seen here in figure 3.

A cross section of a leaf is depicted. From top to bottom the cuticle, upper epidermis, palisade mesophyll, spongey mesophyll, and the lower epidermis are labelled. Sun rays are hitting the top of the leaf. A stomata is depicted on the bottom of the leaf where carbon dioxide is leaving the leaf.
Fig. 2 A cross section of the leaf. Most carbon dioxide enters the leaf through the stomata which are tiny whole guarded by cells. Most stomata are found on the leaves of plants.

All of these parts work together to help the plant go through photosynthesis. Without this process, plants would not be able to produce and retain their energy.

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Authored by: Jamie Wahout. Provided by: University of Minnesota. License: CC BY 4.0


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