Being Green: How Plants Work

There are more than 250,000 recognized plant species on Earth, and their contributions to our planetary ecosystems make life possible. One way or another, all the foods we consume come to us through the actions of these wonderful organisms.

Is It a Plant or an Animal?

Well over 2,000 years ago, a burgeoning curiosity among scientists about the nature of green growing things led to a basic but important distinction. It was famously expressed by Aristotle around 350 B.C. when he observed that the difference between plants and animals was profound but relatively simple: plants are stationery, while animals are mobile.

This distinction is still somewhat useful today. Plants have adapted to survive and flourish while remaining, well, grounded. That’s a tall order. Plants don’t hunt or forage for food like animals do. Most don’t wait for food to pass by so they can trap it, like, say, a Venus flytrap does. Plants are actually solar batteries harnessing the power of the sun and converting it into a form they can use. Plants represent nature’s simple and elegant solution to the problem of finding food without being mobile—they make their own.

Plant Parts: The Naming Game

Beyond devising a way to convert sunlight into food, plants have developed modifications to help them adjust to an ever-changing landscape. Although they’ve adapted to fit specific niches within different ecosystems, many plants share common characteristics. Most plants require sunlight, moisture, nutrients and a relatively narrow temperature range to survive.

The specifics of a plant’s requirements will vary based on the challenges of a particular location, and that’s actually one of the most spectacular aspects of this evolutionary success story. Because plants are severely limited in their ability to wander, they’ve come up with interesting, dynamic, sometimes unique, breathtaking and downright delicious ways to survive and spread.

Desert plants look very different from tropical plants, but they are both typically “plant-like” in aspect and predominantly green in coloration. That’s not an accident. In the next few paragraphs, let’s explore the anatomy of a plant and discuss what makes green such a popular color in the garden.

There are two broad categories of plants—non-vascular and vascular. Non-vascular plants are mostly mosses, while vascular plants include flowering species and are of the most interest to gardeners and farmers. Vascular plants are able to conduct moisture and minerals through their internal tissues, and they possess organs that perform specific functions.

Through specialization, these organs can look and act somewhat differently from one plant species to another, but their goals are the same. Think of them as the plant kingdom’s approach to a division of labor inside the energy factory that is a healthy plant. Here are some common plant parts you’ll recognize, along with the functions they perform:

• Roots - mineral and water absorption, anchoring, food storage
• Stems - support, transportation of fluids, food storage, photosynthesis (if green)
• Leaves - carbon dioxide absorption, photosynthesis
• Flowers and Fruit - reproduction

Photo What?

In the plant world, photosynthesis is the big “P” word. You probably learned about it in school and promptly forgot the details beyond the fact that photosynthesis is the reason plants are green and need sunshine to grow. Actually, it’s almost impossible to understand plants without knowing a little about photosynthesis. Much of a plant’s existence revolves around this complex process.

Photosynthesis allows plants to convert sunlight into usable energy in the form of glucose, a simple sugar. They do this using three basic ingredients: the carbon dioxide (CO2) they take in through their leaves, water and sunlight. On a basic level, here’s how photosynthesis works: deep inside plant leaves and stems, the green pigment compound chlorophyll works in conjunction with special enzymes and other chemicals to absorb light. Chlorophyll is arranged in structures called chloroplasts. One green plant cell can contain many chloroplasts, and one chloroplast can house millions of light-trapping, green chlorophyll molecules. When light hits a chloroplast, it initiates a chemical reaction.

You probably already know a water molecule is made up of hydrogen and oxygen (in science speak, that’s H2O). During photosynthesis, chemical responses in the chloroplasts break the bonds within water molecules. The hydrogen goes on to bind with carbon dioxide and produce glucose, while the oxygen is released into the air.

Plants then use the glucose to grow leaves, form flowers for reproduction, produce seeds, develop roots and perform other important functions. What glucose they can’t use right away, they store in their roots and stems. Have you ever had a sugar rush? The same energy that has you tapping your foot energizes plants and sustains them. In fact, all life on our planet is ultimately sustained by this conversion of sunlight to organically available energy.

Plants & The Oxygen Connection

That’s not all. The oxygen released as a by-product of photosynthesis is essential for most organisms to survive. The Earth is rich in oxygen because of the action of plants over many millennia. According to Environment Canada, an average mature tree produces 260 lbs. of oxygen every year, or about enough to sustain two people for a year. The fossil record shows land plants evolving more than 700 million years ago. Now imagine oxygen accumulating across all the forests, grasslands and other vegetative expanses on our planet for eons. That’s a lot of oxygen.

What About Carbon Dioxide?

Because plants use carbon dioxide as raw material during photosynthesis and convert it into glucose, they also act as air purifiers, scrubbing dangerous CO2 from the atmosphere. Based on data released by NASA’s Earth Observatory, 55% of the additional carbon dioxide released by human activity has been absorbed by the Earth’s plants and the oceans.

Other Things Aristotle Didn’t Know

Today we know much more about plants than Aristotle and his contemporaries would have dreamed possible. There are still some mysteries, though. The exact mechanism that makes photosynthesis work is not completely understood. Many experts believe a more comprehensive knowledge of the specifics of this chemical reaction could lead to breakthroughs in plant husbandry as well as more effective ways for humans to produce clean energy.

Plants are also more aware—and physically active—than ancient scientists believed. In fact, they move quite a bit. Their motions are slow, though, and usually undetectable with the naked eye. Plants also show signs of distress, may display preferences for certain sounds, can sometimes detect the best locations for root development and may even signal other plants nearby of impending threats.

The plant world is complex, diverse and still a bit of a mystery. Plant populations, and other creatures like bees that help sustain them, are often bellwethers for the health of entire geographical regions. Plants provide food, oxygen and no small measure of beauty, too. When you think about it, every seedling is a superstar, and even a small packet of seeds can hold some pretty potent secrets—and great potential.