Ask A Scientist

How does sunlight help algae grow? 

Asked by: Kristen Fisher
School: Seton Catholic Middle School, Binghamton
Grade: 7
Teacher: Mr. Martinkovic
Hobbies/Interests: Soccer, drawing, hanging out with friends
Career Interest: Doctor or nurse for children with cancer

Answer from Douglas W. Green, EdD

Adjunct Lecturer, Binghamton University

Other: Former principal at Woodrow Wilson Elementary in Binghamton, NY
Research area: Leadership, Learning Theory and Social Media
Interests/hobbies: Playing my banjo, biking, golf and reading
Family: Daughter Lena, age 29, who works for the Teen Nickelodeon channel in Times Square, New York City  

Algae comes from the Latin word for seaweed. It's a general term for a large and diverse group of simple plants that vary in size from a single cell to seaweed plants 50 meters long. While scientists don't agree on how many different algae species there are, even low estimates exceed 100,000.

Due to their simplicity, scientists believe that algae were among the first plants to evolve on Earth, perhaps almost two billion years ago. Although some algae grow on snow and ice, most live in just about any body of water on Earth. 

Like other plants, algae make their own food from simple chemicals like carbon dioxide and water. We call them autotrophs. Animals that don't make their own food are called heterotrophs. Food production in plants takes place in structures inside their cells called chloroplasts. The chemical inside the chloroplasts that does the work is called chlorophyll. This is a large molecule that comes in several varieties that contain 60 to over 130 atoms. 

Chlorophyll needs energy to do its job. This is where light comes in. You can use artificial light, but in nature, algae uses sunlight. Light is composed of very small energy packets called photons. Chlorophyll molecules capture photons of light using their energy to rearrange smaller molecules into many substances that build more algae. The process is called photosynthesis.

The different kinds of chlorophyll use light photons in the red and blue range of the sun's rainbow of colors, so they reflect green photons. This is why most algae and other plants are green. If plants are not properly nourished, they don't produce enough chlorophyll and turn yellow. This makes chlorophyll a good green food coloring. Algae also finds its way into many foods and fuels, most notably the green wrappers for sushi rolls.

Chlorophyll also produces oxygen as a byproduct. This is good news for animals like us who need oxygen. In return, we produce carbon dioxide, which plants need to live and grow.

While algae are needed for the circle of life on earth, there are situations where it grows too fast. Overgrowths of algae called algal blooms are caused when excess fertilizer runs off from farms. When the algae dies and decays it depletes oxygen, causing animals in the water to die. Here is a link if you want to grow some algae at home:


Last Updated: 3/1/17