What is the Role of Photosynthetic Pigments?

In Modern Biology, Inc.’s new experiment, IND-32: Plant Pigment/Peroxidase Analysis, students choose a variety of vegetables and fruits. They then extract pigments and peroxidase the fun way, with a mortar and pestle. Finally, students do electrophoresis against cytochrome C and hemoglobin-albumin to characterize the pigments they extract.

Modern Biology, Inc.‘s experiments are self-contained hands-on experiences of scientific method. Your students will state and test their own hypotheses about the molecular structures of the pigments they release from plant matter with mortar and pestle and hydrogen peroxide. But how can you make the topic even more relevant and memorable?

We suggest that you proceed this lab with a discussion of plant pigments in well-known fruits. This can answer the question “What are photosynthetic pigments?” in a way that your students will understand and remember.

Start your lecture with some show and tell. Display either a photo of an unripe fruit, or an actual unripe fruit. Then show your students either a photo of a fully ripe fruit, or an actual ripe fruit. Then ask them “What’s the difference?”

The answer, of course, is flavor, softness, and color! Even if you only have a photo of fruit to show your students, chances are that all of them will have a concept of the differences between ripe and unripe fruit.

This is the time to point out that plants get their colors from pigments. But what advantage does having pigments confer to the plant?

Fruits contain pigments. They also contain seeds. Plants depend on animals to disperse their seeds, and the green, yellow, red, purple, orange, and blue pigments in fruits, berries, and vegetables make them more attractive to the animals that the plants need to spread their seed around.

The green pigment chlorophyll is essential for photosynthesis. Without the capture of photons of sunlight by chlorophyll in the chloroplasts, plants could not transform water and carbon dioxide into carbohydrates.

Red, blue, and purple anthocyanin pigments also help plants attract animals to pollinate their flowers as well as to eat their fruit. But these antioxidant pigments also protect chlorophyll. They shade the chloroplasts from the effects of excessive sunlight. The longer the fruit stays in the sun, the more protection its chlorophyll needs from excessive UV rays, so the darker and deeper the red, blue, and purple pigments become.

Orange and yellow carotenoid pigments stabilize the chemical bonds between chlorophyll and proteins in the plant. They also act as a kind of sunblock for the plant. In the presence of sunlight, carotenoids combine with oxygen to become xanthophylls. They capture free radicals of oxygen and prevent them from damaging the DNA inside active cells.

Carotenoids and xanthophylls make it safe for the plant to produce oxygen in the process of photosynthesis. Otherwise, the oxygen released by photosynthesis would damage the organelles that produce it.

By protecting the process of photosynthesis, plant pigments power the process of ripening in fruits. They enable the fruit to continue to manufacture the sugars that make it sweet. A fruit that doesn’t look ripe is almost never sweet. It can’t be, because its chloroplasts cannot use chlorophyll to make the sugars we desire in the fruit.

Your students may also be interested in the role plant pigments can play in human health. The human body can transform carotenoids such as beta-carotene, gamma-carotene, lutein, astaxanthin, cryptoxanthin, and zeaxanthin into vitamin A. This ability makes vegan diets for humans nutritionally possible. But some of our pets, notably cats, don’t have this ability and have to get their vitamin A from animal fats.

Modern Biology, Inc. has dozens of experiments for introductory, AP, and college biology classes. Every kit provides all the test materials, reagents, and experiment-specific equipment students need for a laboratory experience of an important concept. Everything Modern Biology, Inc. supplies to schools is thoroughly tested and non-toxic, and every experiment comes with a teacher’s guide.

Have questions? Modern Biology, Inc. has answers! Call us weekdays at (765) 446-4220 or contact us anytime.