Without photosynthesis, life would not exist.

Prof. Penny Chisholm says it is the most profound concept on the planet. Since she joined the MIT faculty 33 years ago, she has been working to spread the word. Most recently, she co-wrote a children’s book to help kids grasp that photosynthesis is responsible for life on Earth.

“Everyone should understand photosynthesis. It helps us respect our dependency on nature in a big way,” Chisholm says. “It’s only when we realize how much we’re an integral part of nature, that we begin to realize how much we need to protect its functions and abilities to sustain the Earth. It’s fundamental to our very existence.”

The 30-page book, narrated by a friendly sun, explains the process of photosynthesis in colorful pictures and words easy for everyone to understand. Living Sunlight: How plants bring the earth to life was co-written by Chisholm and her longtime friend, Molly Bang, who has written and illustrated more than 30 children’s books, and who three times won the Caldecott Medal, which is among the most prestigious children’s book awards in the country.

Chisholm, the Lee and Geraldine Martin Professor of Environmental Studies, is a professor in both MIT’s Department of Civil and Environmental Engineering and Department of Biology. She is the founding director of the Institute’s Earth System Initiative. She is best known for her research on prochlorococcus, a small microbe that is responsible for a significant fraction of the photosynthesis in the ocean.

“Photosynthesis,” she says, “which actually means ‘making life from light,’ is something that I feel is underappreciated. As humans, we forget where all our food comes from. We forget the larger tapestry of life. If it weren’t for plants, we wouldn’t be here.”

Photosynthesis, she continues, is not hard to understand.

Plants absorb sunlight with their chlorophyll and use that energy to break apart water and release oxygen; they draw in carbon dioxide from the air; and convert it into sugar. The Sun’s energy is then in the chemical bonds of the sugar. Next, plants use the chemical energy to build stems, leaves, seeds, and fruit. People then eat the plants and get the Sun’s energy from those chemical bonds. “So actually, all living creatures are sunlight. Living sunlight,” she says. “It is profound.

“All living things are dependent on each other. We all share the same atoms. As the plants photosynthesize, they take up carbon dioxide and release oxygen. All animals eat plants, breathe oxygen, and give off carbon dioxide. It is a cycle. If you look at the annual cycle of carbon dioxide and oxygen in the atmosphere, you can actually see the collective breathing of all beings on Earth.”

At the back of the book, Chisholm wrote a study guide for parents and teachers that explains the concept in a bit more depth. She writes: “We hope this understanding will help guide us toward a deeper sense of the unity of all life.”


Chisholm grew up in Marquette, Michigan, on the shores of Lake Superior. In high school, she loved biology. Twenty years later, she met writer and illustrator Molly Bang at a party on Cape Cod. Soon, they discovered a shared connection. Chisholm’s mother, like Bang, was an artist, and Bang’s mother, like Chisholm, was a scientist.

“There was a synergy there,” Chisholm says. “Ever since, we have been talking about writing a children’s book together. Finally, we decided to do it.”

Living Sunlight, which took a year to write, (“It was harder to write than a scientific paper. Every word counts,”) is the second book in a series about the Sun’s energy. Bang wrote My Light on her own in 2004, which details how most electricity comes from the Sun. The co-authors are now planning two other children’s books — one on the Earth’s carbon cycle and another on photosynthesis in the oceans.


Chisholm, who teaches ecology at MIT, is concerned about the future of the planet. Yet, she says, she has no idea what that future will be. “It depends on the decisions made by citizens and lawmakers. Every decision should be guided by a deep understanding of the Earth as a complex ecological system. We now understand which human practices are sustainable and which are not. We just have to keep pointing the compass in the right direction.”

Ecology, she says, should be a required course for all high school and college students. “Everybody on Earth should understand the dependency of different components of this Earth system on other components. We’re an integral part of nature, and it’s not sustainable to pretend that we’re not. We’re subject to nature’s laws and dependent on nature’s processes. Everything cannot be overcome by technology.”

Chisholm, who is much aware of her own relationship with nature, says: “My hope is that by understanding photosynthesis, people will look at plants differently; they’ll immediately feel connected in a profound way. What better way to get that message across than to start with children.”