Photosynthesis, Respiration, and Cell Division
Cells have to do two big jobs: capture and release energy, and make new cells. Photosynthesis and respiration handle the energy; cell division handles the copying. These three processes power and renew all life, and they show up constantly on science tests, usually as a matched set.
This lesson gives you a clear, plain-language handle on each one.
Photosynthesis is how plants use sunlight to make food (sugar) from carbon dioxide and water, releasing oxygen. Cellular respiration is how cells break down sugar to release energy, using oxygen and giving off carbon dioxide. Cell division is how one cell splits to make new cells for growth and repair.
How does photosynthesis work?
Photosynthesis takes place in plant cells, in structures called chloroplasts that contain the green pigment chlorophyll. Plants take in carbon dioxide from the air and water from the soil, and use the energy in sunlight to combine them into sugar, releasing oxygen as a byproduct. In short: sunlight plus carbon dioxide plus water makes sugar plus oxygen. This is how the energy of the sun enters the living world.
How does cellular respiration work?
Cellular respiration is nearly the reverse. Cells take the sugar made by photosynthesis and break it down to release its stored energy, using oxygen and producing carbon dioxide and water. It happens in nearly all living cells, in structures called mitochondria. Notice the neat partnership: photosynthesis stores energy in sugar and makes oxygen, while respiration releases that energy and uses oxygen. The two processes cycle carbon and oxygen between plants and animals.
| Process | Takes in | Gives off |
|---|---|---|
| Photosynthesis | Carbon dioxide, water, sunlight | Sugar, oxygen |
| Respiration | Sugar, oxygen | Energy, carbon dioxide, water |
What is cell division?
Cell division is how organisms grow, heal, and reproduce. In the most common form, called mitosis, one cell copies its DNA and splits into two identical cells. This replaces worn-out cells and lets a body grow from a single fertilized egg into trillions of cells. A different kind of division, meiosis, makes sex cells with half the usual DNA, which matters for reproduction and inheritance.
Watch: A Short Video Lesson
Point Source Science walks through this skill clearly in a few minutes. It is a helpful companion to the reading above:
A routine for these process questions
- Photosynthesis: sunlight and carbon dioxide and water make sugar and oxygen (in plants).
- Respiration: sugar and oxygen release energy, giving off carbon dioxide and water (in most cells).
- Notice they are near-opposites that cycle carbon and oxygen.
- Cell division: one cell copies its DNA and splits to make new cells.
- Mitosis makes identical body cells; meiosis makes sex cells with half the DNA.
Practice questions
- What gas does photosynthesis release?
- What does cellular respiration release from sugar?
- In which cell structure does photosynthesis occur?
- How are photosynthesis and respiration related?
- What is the purpose of cell division in the body?
- True or false: mitosis produces two identical cells.
Answers:
- Oxygen.
- Energy (along with carbon dioxide and water).
- The chloroplast.
- They are near-opposites: photosynthesis stores energy and makes oxygen; respiration releases that energy and uses oxygen.
- Growth and repair, by making new cells.
- True.
Where this fits
These processes power the cell you met in the cell: life’s basic unit, and cell division sets up the study of heredity and DNA. The energy they manage flows through whole ecosystems, a theme in energy flow and the cycles of matter. Find every topic on the ASVAB General Science Learning Hub.
Recommended Prep Books
These study guides and practice books help you keep building momentum as you prepare:
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