“Why Do Bananas Curve?”

by, Jo Carol Hebert

Here’s a Banana Joke

Question:  “What do bananas say when they answer the phone”

(Answer:  ‘Y-ellow.”)

Question:  Why do bananas curve?

(Answer):  ‘Geotropism’ – ge-o-trop-ism.

Not very funny, but true and very interesting.

Geotropism – A Force of Gravity!

‘Tropism’ means the movement or growth of an organism (a plant). In the science of Botany (the study of plants), geotropism is a term referring to the influence of gravity that determines what direction a plant grows. It is from the word, ‘geo’, meaning ground or Earth, and the word, ‘trope’, meaning ‘to turn’.  

Roots grow down (positive geotropism), due to the stimulus of the pull of gravity (the gravity that keeps us from falling off the Earth). This is also called gravi-tropism. Positive geotropism also involves hydro-tropism, (water+turn) growing down to reach water.  

But banana stems, leaves, and fruit grow up and against the natural pull of gravity (negative geotropism), due to the stimulus of light. Negative geotropism is also called photo-tropism, growing towards light – the Sun.

Smarty” Plants

Remember, ‘tropism’ is movement and movement is always in some direction.

So, plants, including banana trees, can sense gravity, light and water. No matter how you plant a seed, the parts of the seed will know which way to grow – up or down.  

How do they know this?  

There is a ‘hormone’ (growth molecule) called the auxin in the seed. This little ‘plant-brain’ tells the parts which way to grow – up or down.

Houseplants near a window will bend noticeably to the sunlight. Houseplants need to be turned and the back side of the plant will also stretch toward the light.

Growing Against Gravity

So, the banana tree takes root. The roots grow deep into the soil to get water and to hold on and provide support for the plant. The tree stem and leaves grows up toward the light of the sun. 

This ‘photo-tropism’ toward the sun also provides ‘photosynthesis’ which makes sugar for the plant to grow. Now, when the fruit blooms and the ‘bunch of bananas’ form, the pull of gravity starts it growing downward. As the banana fruit matures, it goes against the downward direction of gravitropism and reaches up toward the light.  

Gradually, the struggle to grow up while being pulled downward results in the slight curve of the banana. Our brave little banana has battled valiantly and its curve is the victory!  

Squash and cucumbers sometimes have a slight curve from the same process.

One More Banana Joke

Question:  “What did the banana say when someone tried to tie it around their neck?”

Answer:  “I’m a Banana, not a Bandana!”

(This is an original Banana joke made up by Smarty Pants staff. So blame us if this one is ‘r e.e.e.ly bad!”

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Categories: Nature, Science

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