Gravitropism: Definition & Examples

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Oxygenic and Anoxygenic Phototrophs: Definition and Examples

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:02 What Are Troposms?
  • 1:07 Positive & Negative…
  • 1:56 How a Plant Sense Gravity
  • 3:28 Shoots Grow Away from Gravity
  • 4:27 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Speed Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Catherine Konopka

Catherine has taught various college biology courses for 5 years at both 2-year and 4-year institutions. She has a Ph.D. in cell and molecular biology.

Have you ever wondered why a plant's shoots grow up, while its roots grow down? In this lesson, you'll learn about the mechanisms that control this peculiar plant behavior.

What are Tropisms?

One of the first scientific observations you probably made was how plants grow. Unlike us, plants can't get up and walk towards something they need or run away from something that threatens them. Instead, a plant responds to a stimulus , or something that causes a change, by changing how it grows. It may look like movement to us, but really the plant is just growing in one direction or another. The movements that plants make in response to stimuli are called tropisms.

Plants respond to a lot of different stimuli, including light (phototropism), touch (thigmotropism), and water in the soil (hydrotropism). In most cases, the different parts of the plant grow toward the source of the stimulus. Think about a plant sitting on a windowsill -- its shoot bends toward the light coming in from the window. However, there is one stimulus to which different parts of a plant respond differently. It's one of the most fundamental forces on earth: gravity.

Positive and Negative Gravitropism

Gravitropism is the movement or growth of plants in response to gravity. You see the effects of gravitropism on a daily basis, even if you don't realize it. If you've ever grown plants hydroponically, you probably noticed that the roots always grow down even though there's no soil for them to grow in. That's positive gravitropism, since the root is growing toward gravity.

However, even if you've never grown a plant in your life and haven't observed closely how roots grow, you've still observed gravitropism. The shoots or aerial parts of a plant grow away from gravity -- that is, they grow up. This is negative gravitropism, since the shoot of the plant is growing in the opposite direction of gravity.

How a Plant Senses Gravity

We know which way is down because we have specific organs in our body that can feel the force of gravity pulling us toward the earth. Even if we close our eyes we still know which way is down, since there are small cells in our ears that 'feel' gravity.

Plants are not much different than us -- they also have special cells at the very tips of their roots called statocytes (stato meaning 'balance' and cyte meaning 'cell') which can sense gravity. Within the statocytes are granules called statoliths (lith meaning 'stone') that are filled with starch. The starch makes the granules denser than the liquids inside the cell. This makes the granules sink toward the lowest side of the cell. When this happens, the statocytes release a hormone called auxin only on that side of the cell.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account