Wednesday 9 May 2012

Why Are Apples Crunchy?

I'm not sure I have really managed to answer this question, although I have satisfied Garden Girl with an answer of sorts. The actual question Garden Girl asked was 'Why are apples crunchy and bananas soft?' and I couldn't really find out why the two fruits have different textures. This is what I told Garden Girl...

Apples and bananas are fruits. A fruit is part of a plant or tree and is there for two reasons.

1. Whilst the seeds of a plant, or tree, are developing, a fruit protects them from animals, birds and the weather.

2.When the seed is ready to grow into a plant of its own, the fruit helps the seed disperse. That is, the fruit helps the seed find somewhere suitable to grow.

While they are growing, seeds are in danger of being eaten by animals and birds, or of being damaged by the weather. However animals (and humans) do not want to eat fruit until they are ripe. Thus a fruit does not become fully ripe, until the seed is ready. The fleshy part of the fruit, the bit we eat, grows around the seeds to stop birds and animals getting at them and to stop the seeds getting damaged. If an apple gets hit, the skin and flesh is bruised but the seeds stay safe. The soft part of a banana, similarly protects the seeds inside.

There are lots of different kinds of fruit. Some, like apples and bananas, have juicy flesh to protect the seeds. Some, like peas, have pods to protect the seeds inside. Some, like nuts have hard, dry shells to protect the seeds inside. Conkers and sweet chestnuts have a prickly fruit to protect them. 

When the seed is ready to grow into a new plant or tree, the fruit ripens. The fruit no longer needs to protect the seed. It must now find a way to spread the seed. Instead of trying to protect the seed from animals, the fruits now want to be eaten. Apples and bananas change colour to attract birds and animals.Now that they are ripe, the fruits have the flavour and texture which will make people and animals enjoy eating them.

Birds and animals cannot digest the seeds, so when they have eaten the fruit, the seeds pass through the body and come out with the poo. Animals poo in the soil where the seed can grow into a new plant. And even better than that, the animal poo acts as a fertilizer to help the seed grow, in the same way that we use manure and compost in the garden to help our vegetables grow. So apples are crunchy and bananas are soft because this is the way animals and people like to eat them.

Other seeds are scattered by the wind. Dandelions have little parachutes so they can float away and sycamore seeds have wings so they can fly away from the parent tree to a suitable growing place. When pea pods split open the seeds burst onto the ground ready to grow into a new plant. Spiky fruits will stick to the fur of animals as they pass by, dropping off sometime later, hopefully somewhere where the seed has room to grow.

So, back to the original question and I guess the answer is that apples have a crunchy, juicy flesh because this is the best protection for seeds, against the particular animals and weather to which an apple tree will be exposed. A crunchy texture is also the most appealing to people and animals who want to eat the fruit and thus help spread the seeds.  

Bananas are soft for the same reason. Banana bushes grow in different weather conditions to apple trees and are exposed to different animals, thus a soft fruit offers the best protection for seeds against these animals and conditions. When the fruit is ripe, a soft banana offers a more appealing texture to the animals and people that want to eat them.

Garden Girl seemed happy with this explantion but I am a little bit curious about what it is that makes an apple crunchy. Is it the amount of water that apples contains? Is a banana softer because it contains more starch? I really don't know and I failed to find anything useful in library books or on the internet, so if anyone knows the physical reason for why an apple is crunchy and a banana is soft, please let us know.

If you want to learn more about fruit we found these books really useful:

Flowers, Fruits and Seeds (Plants) by Angela Royston

Flowers and Seeds (World of Plants) by Carrie Branigan and Richard Dunne

However, there seemed to be quite a few books about fruit and seeds in our local library so if you can't get hold of these ones there is bound to be something useful.


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