What are plants?

Plants are living organisms. They come in many different shapes, sizes, and colours, but they all need air, water, nutrients, and sunlight to live. Plants cover much of our planet. Every blade of grass, tree, flower, bush, fern, or moss you see is a plant. Large or small, on the land, or in the sea, from forests to deserts, plants are almost everywhere! Plants are so important to live on earth that without them, we could not survive. Plants create food from the sun’s energy and form the foundation of nearly every food chain on the planet. Plants produce the oxygen in the air we breathe, helping animals to stay alive. Plants also create important habitats where animals can live, and provide humans with many natural resources.

So what makes something a plant?

Plants are special on the cellular level. They are always made of more than one cell – meaning there are no single-celled plants – and their cells have special parts. One special part of a plant cell is the cell wall. Cell walls are rigid and unbending. Since plants do not have skeletons, these cell walls give them their structure. Without cell walls, tall trees, cactus and even little flowers would not be able to stand up! Many plants are easy to recognize by their green leaves – in fact, most plants are green, or have green parts. This green colour is caused by another special part of their cells called chloroplasts. Chloroplasts contain chlorophyll, which is green. Chlorophyll is what allows plants to carry out photosynthesis and make food from the sun’s energy. During photosynthesis, plants use the sun’s energy to change water and carbon dioxide into a kind of sugar. They use this sugar to grow and develop and store the extra in their leaves, roots, or fruits.

In addition to sugar, plants produce oxygen during photosynthesis. Since plants do not need the oxygen, they release it into the atmosphere, where animals and people can breathe it in! Plants cannot move the same way that people or other animals do, so they have to have special strategies to solve their problems. For example, some plants cannot get enough nutrients from the soil they are growing in. The plants of eastern North American bogs have adapted to their nutrient-poor soils by getting extra nutrition from an unusual source – insects. One of these carnivorous plants, the sundew, has sticky fluid coating special hairs. This fluid has a sweet smell that attracts insects. When an insect lands on the hair, however, it becomes stuck – trapped by the plant – and the fluid digests the prey, breaking it down into nutrients. Another kind of carnivorous plant is the pitcher plant. The ‘pitcher’ of the plant is a modified leaf that is watertight. The plant fills it with a combination of nectar and digestive juices. The smell of the nectar and colours at the edge of the pitcher attracts insects and other small visitors, but once inside the prey find it too slippery to get out again and will fall into the pool at the bottom of the pitcher, where they are digested.

The most famous carnivorous plant is the Venus Flytrap. It has specialized leaves that act as the mouth of the plant. Like the other carnivorous plants, its bait is sweetened nectar. Once prey climbs onto the leaf, they activate the trigger hairs which signal the plant to close its trap. Long guard hairs interlock across the top of the leaves, preventing escape, and the prey is slowly digested. Unlike carnivorous plants, which are predators, most plants are prey for herbivores. They have developed strategies to help protect them from being eaten. One popular strategy plants like to use is to grow thorns, spines, or prickles. The cactus is famous for its sharp spines. Most cacti live in the desert, where water is a scarce and precious resource. Cacti store water in their thick, waxy stems. To prevent animals from consuming their carefully collected resources, they grow sharp spines which deter all but the hungriest – or most cautious – of animals. A plant with another interesting defence is the sensitive plant. When its leaves are touched, they close up. This makes the leaves look dead, or wilted, and may send a hungry herbivore searching for a more tasty-looking lunch.

Finally, a popular plant defence strategy is to use chemicals to protect themselves. Some plants just use chemicals to give their leaves a bitter taste. Other plants have chemicals on them that can make us itchy! Still, other plants are poisonous, making animals that eat them get sick or even die. Animals learn not to eat these poisonous plants and the plants can then grow undisturbed. One more problem that plants have to solve is the problem of how to get their seeds away from them. Plants do not want their seeds to grow right next to them, because then they would be competing for the same resources. Some plants use the wind to spread their seeds. Some plants that live near water have seeds that can float, and let the water carry their seeds away.

Popular method plants use to spread their seeds is to have animals carry them away. Some seeds, called burs, grow with hooks on their outsides. These hooks get caught on the fur of passing animals and are carried away to new areas. Other plants grow their seeds inside fruits or berries. Animals eat the fruit and it is digested, but the seeds pass through unharmed and are dropped far away from the parent plant. Still, other seeds, like acorns, are collected by animals that bury them. Not all of these buried seeds get eaten, leaving some to grow into new trees. Some plants, however, take matters into their own hands – or seed pods, that is. When touched or tapped, the fruit of the exploding cucumber splits open forcefully, spreading its seeds in one burst. On the land or in the sea, plants play a critical role in in the continuation of life on earth. They make their own food from sunlight, converting it to food that animals can use. Plants produce oxygen for us to breathe and habitats for animals to live in. No matter where they grow, or what challenges they face, plants have learned how to get enough nutrients, protect themselves from hungry animals, and spread their seeds around. Plants are incredible!