Plants are an essential part of life on Earth: even if an animal doesn’t eat plants directly, it certainly relies on them in some other way. For example, a wolf might not eat grass, but it hunts animals that do, takes shelter in the trees of the forest, and breathes the oxygen that plants have released. How did plants become such a staple of our existence? The same reason why every living thing is the way it is: they have evolved that way.
You’ve probably heard of Charles Darwin, a famous scientist. Darwin’s Theory of Natural Selection is what most scientists study to answer questions about how plants and animals have changed over time–and how we can answer your question about the very first plants. In nature, certain traits make some organisms more successful than others, allowing them be “selected” to pass on those successful traits to their offspring. For instance, a tree might mutate to grow fruits that look different from those of all of its fellow trees. Birds might find this new fruit particularly tasty-looking, so they will eat lots of them and spread that mutant tree’s seeds. Since that mutant tree had lots of offspring, it’s now more likely that its mutation will be passed on and become a common trait of the species. These changes happen gradually over many generations, but they contribute to the evolution of that species.
The very first ancestor of plants on land was, believe it or not, actually single-celled bacteria! Early in Earth’s history (more than two thousand million years ago!), this water-dwelling bacteria learned how to harness energy from the sun to move and grow–a process called photosynthesis, the trademark party trick of today’s plants. A chemical side effect of transforming this energy is releasing oxygen, so we owe the oxygen-rich atmosphere we enjoy today to these early photosynthesizers! This bacteria could photosynthesize much more efficiently if it grouped together into multiple-celled organisms, so it further evolved to form green algae. This algae eventually washed up on shore and had to evolve again to exist on land, developing cell walls, like stems, to avoid drying out and solid structures, like leaves, to collect sunlight for photosynthesis. The rest, as they say, is part of of plants’ family tree.
Why is water important?
What’s one thing that today’s highly-evolved land plants have in common with their damp ancestors? They still need water. Water plays an important part of the photosynthesis process, and therefore is an important part in how a plant gets the energy it needs. Water’s molecular structure is H2O, or two hydrogen atom bonded with an oxygen atom, and is very easy to split. During photosynthesis, a plant takes in carbon dioxide and water molecules. With some energy supplied by the sun, it rearranges the atoms in those molecules to create the complex sugars it needs for food and pure oxygen, just like its bacterial ancestors. This is represented by the chemical formula below.
The chemical process at play during photosynthesis. Via Wikipedia.
This reaction is why photosynthesis and plants are so important: not only did their great-great-gandbacteria transform early Earth’s poisonous carbon dioxide atmosphere into one that animals could breathe, but they continue to convert the carbon dioxide we emit back into breathable oxygen. This is one reason why it’s so important to protect today’s oceans and forests: oceanic algae and phytoplankton account for 50-85% of all photosynthesized oxygen, and land plants account for the rest. Altogether, they remove lots of carbon dioxide from our atmosphere. Humans need to be careful not to emit more carbon dioxide than nature can convert, however. By burning fossil fuels, humans have been gradually increasing the carbon dioxide levels in the atmosphere, which scientists believe has led to alarming global warming trends that could lead to disastrous consequences.
More Awesome Plant Adaptations!
Carrion for carryin’ pollen– The titan arum, also called the “corpse plant,” grows to an amazing size and shape, but its most astounding feature is its smell. It gives off the odor of rotting meat to attract insects, which help pollinate the flower.
A corpse flower in bloom at the Eden Project in Cornwall, UK. Via The Daily Mail.
Pyroscience – Rather than being wiped out by wildfire, some trees in dry areas have adapted to have their own fire-activated time capsules. Trees such as eucalyptus and sequoia store their seeds in cones that only open when they encounter smoke. Not only does this protect the seeds, but the burnt land is clear and nutrient-rich when they’re ready to grow!
Dancing Leaves – The telegraph plant likes to get plenty of sun, so it constantly moves its leaves to get the perfect angle. Most plants do this gradually, but the telegraph plant is so speedy that its movement can be seen! (Video via Youtube.com.)
Shrew Poo – Pitcher plants are already well-known for being carnivorous, gathering energy from the sun as well as from digesting insects, but one particular species in Borneo has evolved to eat something even stranger. The unique shape of Nepenthes lowii invites a certain tree shrew to have a seat and enjoy some nectar. If the shrew poops during its meal, the pitcher plant gets some much-needed nitrogen from its droppings!
A mountain tree shrew makes a pit stop
atop a pitcher plant. Via Live Science.
More amazing plant science at the Cambridge Science Festival!
Spring Wildlife Walk at Alewife Reservation, Sunday, April 17, 1-3pm. See the plants of spring in bloom within walking distance of the T! Led by author and naturalist David Brown, lead surveyor for the Biodiversity Study of the Alewife Reservation Area. Ages 13+, free!
Animals and Plants: Use Your Eyes at the Mass Audubon Habitat Education Center and Wildlife Sanctuary, Wednesday, April 20, 4pm-6pm. Explore the relationship between plants and animals through a variety of projects: Vernal Pool Invertebrate Count; Squirrels, Chipmunks and Voles; Cover Board and Red-Backed Salamander Monitoring; Photo Mini Bio-Blitz. Register in advance at massaudubon.org/cambridge-science-festival-habitat. Free!
E. Rosser is a science writer and mechanical engineer currently wrapping up a degree at MIT. She grew up in the mountains of Maryland, where she spent a lot of time in the woods identifying edible and useful plants. She’s thankful for plants’ adaptation of solid cell walls every time she climbs a tree.