Science: Phototropism and Gravitropism

Today, I am going to be discussing phototropism and gravitropism in plants. First, let’s talk about phototropism.

Phototropism

First of all, phototropism is the scientific name for when a plant’s leaves turn towards the light of the Sun.

Now, let’s explain how and why a plant’s leaves angle toward light, much like solar panels.

So, how does a plant archive the feat of angling its leaves toward light? Well, in a plant, there are these hormones that are called auxin. These elongate cells when there are in contact with them.

So, as the day goes by, of course, the Sun seems to change its position in the sky as the Earth spins on its axis. To get as much sunlight as the plant can (sunlight is vital for photosynthesis), the plant sends auxin cells to the side with the least amount of light. In that area, the cells now elongate. And now the plant leans toward the sun.

The plant will do this periodically throughout the day as the Sun’s position in the sky shifts.

So that is the answer to ‘how.’ Now for the answer to ‘why.’

Well, plant’s leaves, as I have said before, act much like solar panels. Because 1), they angle toward the Sun, and 2), they gather the Sun’s light. I have also said previously that sunlight is vital for photosynthesis. Why?

A plant needs carbon dioxide, sunlight, and water for the completion of photosynthesis. This adds up to sugar (the plant’s food), water, and oxygen.

To gather sunlight--an essential step in photosynthesis, as you have learned--a plant uses its leaves. But the plant must collect as much sunlight as possible before the sun goes down. To do this the plant uses auxin cells.

And that is how and why phototropism works! Now let’s move on to gravitropism.

Gravitropism

Okay so what is gravitropism? Gravitropism in a plant teaches about a plant’s response to gravity.

Why doesn’t a plant grow every which way, with its roots in the air and its stem and leaves in the dirt? How can a seed tell the difference?

A seed tells the difference with the aid of gravity. Scientists found this out when the did experiments on plants in space. Out there, more or less, depending on where you are, there is little or no gravity.

In space, plants do grow every which way. But on Earth, they did not. How did they use gravity to tell which way was up, and which way was down?

The seeds could tell using the Earth’s core, which strongly emanates gravity, pulling us toward the ground. The seed then points the right way and starts to grow.

But why?

This answer is pretty much the same as the answer to ‘why’ is phototropism. The plant needs its leaves to gather sunlight and carbon dioxide (in the air), and needs its roots to gather water (in the soil). So a plant would die if it was growing upside down. Without any further adieu, that is how gravitropism and phototropism work.

-KittyLover8
© 2012