Algae To Land Plants
About 470 million years ago, a green pond scum ancestor did something no living thing had ever done before: it survived out of the water. That single change eventually led to every tree, fern, and blade of grass you see today.
What You'll Learn
- What green algae are and why scientists think plants came from them - The biggest problems algae faced when moving onto dry land - Three key adaptations that let plants survive without being surrounded by water - How to observe one of those adaptations for yourself
Life in the Water: What Green Algae Could Do
A group of green algae called charophytes lived in shallow ponds and used sunlight, water, and carbon dioxide to make food, just like plants do today. Living underwater, they had it easy in some ways: water surrounded every cell, so it could soak in moisture and nutrients directly through its outer surface without needing any special parts.
The Big Problem: Drying Out
Land was a much harder place to live. There was no water to float in, sunlight could dry out exposed cells within hours, and gravity pulled down on anything trying to grow upward instead of floating. Any algae that crept onto land without a way to hold onto water would simply shrivel up and die.
Three Adaptations That Made Land Living Possible
Over millions of years, early land plants evolved a waxy waterproof coating called a cuticle that covers leaves and stems, sealing moisture inside. They also developed tiny pores called stomata, each guarded by a pair of cells that open to let in carbon dioxide and close to stop water from escaping. Finally, plants evolved tough spore walls made of a material called sporopollenin, one of the most damage-resistant substances in nature, which let spores survive drying out, sunlight, and travel through air.
Sporopollenin is so tough that scientists have found fossilized plant spores over 400 million years old with their walls still intact. It resists acids, high heat, and even some forms of radiation, which is exactly why early plant spores could survive a harsh, dry, unprotected land surface.
Which adaptation directly stops a land plant from losing water through its leaf surface?
Why were charophyte algae able to absorb water and nutrients without special body parts?
Find the Waxy Coating
Find a thick, waxy-looking leaf outside or in your kitchen (a rubber plant, an apple, or even a pepper works). Drip a few drops of water onto its surface with a spoon and observe closely for two minutes. Record in writing whether the water beads up and rolls off or soaks in flat, and explain in two sentences what that tells you about whether the surface has a cuticle.
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