Plant Life, Form, and Protection

For the past few weeks in class, we’ve been taking a highly scientific look at plant life, adaptations, and problems that all living things around the world face.

Universal Life Requirements

There are a number of problems that must be solved by all living organisms:

  • nutrition
  • gas exchange (the ability to breathe)
  • uptake and transport (how materials move through the body)
  • waste management (what do I do with those materials?)
  • growth and development
  • reproduction
  • protection

All organisms in the world, including us, have created innovative solutions to these problems over the years. Plants are no exception. But I’m going to skip a number of these problems, because I think at base we all mostly understand photosynthesis, of which I will sum up here:

Sun comes down on a leaf. Leaf takes in light energy, carbon dioxide, water from soil, and produces oxygen and sugar for export (aka, nectar). Like so:

The plant loses water during a process called transpiration, which is where water evaporates from the plant. That water is what makes our clouds.

So nutrition, gas exchange, uptake and transport, etc, are all happening during photosynthesis. I’m finding that two of the other problems on our list, reproduction and protection, are particularly dominant in our discussions of the natural world.

Today, I want to talk about protection.

The Stoma

On the underside of a leaf, there are tiny pores called stomata. These are important for gas exchange for the plant–it’s where it breathes in carbon dioxide and lets out oxygen, and it’s where the plant loses water vapor during transpiration. The stomata help with photosynthesis and hydration, and so they’re a crucial part of the plant’s structure.

This is why leaves curl–they’re protecting the stoma.

Photo drawn by author

It’s also why the stoma is on the underside of the leaf; it’s protected from wind here.

And in areas that are very hot or desert-like, you may have noticed that plant leaves are smaller in general, like those of a cactus, or a Joshua tree. This is an adaptation these plants have evolved to have to reduce how much heat they get from the sun, and therefore conserve water. Some desert-dwellers even have microscopic hairs to trap water vapor, which reduces evaporation.

Check out these Redwood Sorrel we saw recently in class at Lower Purisima Creek:

Photo by author

What’s noticeable about the leaves?

They’re folding downward. This happens because this is a plant that likes moisture, and so when it’s in sunlight for an extended period of time, it folds it’s leaves to prevent the stomata from losing water.

When it’s too hot, some plants close their leaves entirely:

Photo by author

Or they turn, so that they’re not facing the sun.

Photo by author

You can try this yourself. Put your hand in the air with your palm facing the sun. Feel how much heat is on your palm. Now rotate your hand so that only the side is getting sunlight. Do you feel the difference in heat?

Remember that we do these things as humans, too. We wear hats, or have umbrellas, or put on sunscreen, or sit in the shade.

Or when feeling threatened, we intuitively go to protect our most vital organs, like boxers with their hands up protecting their heads. Except plants can’t move, so they bend or turn or fold or create some other functional adaptation right where they are.

So these are a few ways that plants protect themselves and their stomata from heat. But how about protection from other things, like animals, or deadly chemicals, or competition?

Forms of Plant Protection

There are an incredible array of adaptions that plants have to protect themselves from various elements. Here are some that we learned.

Protection from animals

  • Bitter smell/taste (this is why my cat never ate my eucalyptus, which is deadly to cats)
  • Tall growth (to protect themselves from “browsers”; things close to the ground that could eat them)
  • Underground growth
  • Sharp edges, uncomfortable for animals with soft mouths

Protection from fire

  • Underwater growth (aquatic plants)
  • Fire-retardant bark (like that of a redwood’s)
  • Expulsion of it’s seeds (some plants dispel their seeds in old age, or when feeling threatened)

Protection against competition:

  • Growing taller than others, so as to shade them out
  • Poisoning the seeds of others

Protection against freezing:

Protection against over-saturation of water:

  • Curling downward in shape, so as to let excess water run off
  • Waxy surface

We learned to ask questions like, what is this flowers relationship with their neighbors? How are they surviving here without six months of rainfall? Why might the edges of this leaf be sharp, or hairy?

These questions help us observe different ways the plants have adapted to their environment. Whether they’re in the rainforest, or the desert, or snowy alpine slopes, the plants that are here on Earth at this moment in time have evolved to be here, and their form can tell us how and why. We just have to learn how to look.

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