Food and Energy

The science background provides teachers with more in-depth information on the phenomena students explore. Here is an excerpt from the science background section on food and energy in cells.

Energy and Nutrients in Food

In addition to water, cells also need nutrients and energy to survive. All animals, including humans, get nutrients when we eat and drink. Because food is matter, the bonds that hold food molecules together store chemical energy (energy stored in the bonds of atoms and molecules). Our bodies break down and rearrange those food molecules through chemical reactions to produce new molecules that help to maintain cells and allow the organism to grow. Some of those new molecules become part of the organism, helping it grow and develop. At the same time, some energy is released as a result of the chemical reactions. Because of this, food is important because it provides both energy and building materials for organisms.

During the chemical reactions, energy is also released, and that energy powers all of the functions that are necessary for life. The process of producing energy the cell can use is called cellular respiration, and in eukaryotes, it takes place in the cell’s mitochondria. This is why mitochondria are called the power centers of the cell.

The Flow of Energy and Matter

Energy is always flowing and matter cycling between organisms and their environment. In order to understand how this happens, it is important to start with the energy source. For deep-sea organisms, that energy source comes from deep within Earth’s interior. For most other organisms, that energy begins with the sun.

As the sun shines, it produces light energy. When the chloroplasts in plant cells absorb the sunlight, they begin the process of photosynthesis. Photosynthesis uses the sun’s energy to convert carbon dioxide and water into oxygen and a kind of sugar called glucose, which holds stored chemical energy. During photosynthesis, chemical reactions happen that transform matter that is not food, including carbon dioxide and water, into matter that is food, specifically glucose. Plants use glucose as a building material for their structures, and store some of it.

That glucose gets passed from plants to animals that eat plants. When we eat food, we get some of that stored glucose, and our cells use the glucose in cellular respiration. Like animals, plants use glucose for cellular respiration as well. As a result, matter and energy are constantly interacting to power all life functions through photosynthesis and cellular respiration.