Great question! Fruit is the way a plant “pays” an animal to carry its seeds to a new place.

It takes a while for a seed to mature so that it is ready to grow. If an animal eats a fruit or seed before the seed is ready, the seed is wasted. Fruit takes a while to make too, so the plant can’t wait until the seed is ready to start making the fruit. Instead, it makes the fruit, but keeps it unripe, so animals won’t like it.

Think about what an unripe fruit is like. It’s usually hard, green (hiding in the leaves) and doesn’t taste good. It is usually sour instead of sweet. It stays this way, even when it is big. When the seed is ready, the plant makes a chemical that is a message to ripen. (This chemical is called ethylene and is pronounce ETH-ill-een.) When the cells in the fruit get the message, they start making chemicals that make the fruit stop being sour and get sweet and soft. They also change the color and smell. These chemicals are made right inside the fruit, so it doesn’t matter whether the fruit is attached to the tree, as long as it is ready to ripen.

Of course, the fruit isn’t going to get any bigger after it falls off the tree. The tree brings up water and nutrients from the roots that supply the fruit when it’s growing. The leaves take in carbon dioxide (the gas we breathe out) through their leaves, combine it with water, and use the power of the sun to turn it into sugar that it sends to the fruit. All of this stuff travels through the tree in tubes that act like our blood vessels.

Now here’s the more complicated part of the story. All that the fruit needs to ripen is already inside the full-sized fruit, so how does it change so much? The answer is enzymes (EN zimes). Enzymes are a sort of toolbox of chemicals that living things use to speed up chemical reactions. The ethylene signal tells the fruit cells to start making a bunch of these enzyme tools. Starch is a long chain of sugars that doesn’t taste sweet. Unripe fruit has a lot of starch in it. One ripening enzyme cuts the starch into sugar. You have this kind of enzyme in your saliva (spit). Try chewing a plain cracker or bread. It isn’t sweet at first because it’s mostly starch. Then the enzymes in your mouth break the starch into sugar and it starts to taste sweet.

Some enzymes break down the tough cell walls to make the fruit soft and juicy. Some break down the acids that made it sour. Others break down the chlorophyll (KLOR-o-fill) that makes fruit green or make pigments that are colorful. Still others break down big molecules into small ones that float off the fruit to give it a nice smell.

If you want to see the results of ethylene, take a ripe banana or apple and put it in a bag with an unripe fruit (apple, avocado, unripe banana). Leave another unripe fruit far away. Then see which fruit ripens faster. The ethylene in a ripe fruit ripens the fruit nearby.

Of course, trees don’t know any of this. Trees that get their seeds spread around leave more offspring than trees that don’t. But that’s a whole new answer.

If a green fruit gets damaged, it may start to ripen. Why do you think that is? What do you think will happen if you put a bruised apple in a bag with an unripe fruit?

You can read more at: this article.

When you pick a fruit or flower from a plant the fruit/flower doesn't die right away. It has enough vital components to continue biological processes for several days after being picked depending on the environmental conditions they're placed in (e.g. has the flower been put in water? how hot is the room where the flower/fruit has been stored?).

"Ripeness" in a fruit refers to several qualities that tend to change together over time. The fruit becomes softer because tough molecules in the skin of the fruit begin to break down. Likewise, fruit tends to become sweeter as bitter molecules are broken down, and long, non-sweet tasting sugars are cleaved into shorter, sweeter sugars. These processes are regulated by several enzymes in the fruit. Enzymes are proteins that can carry out specific tasks in an organism, like converting one molecule into a different type of molecule, and breaking down sugars. These enzymes tend to be activated by ethylene gas - as fruits ripen, they release small amounts of ethylene initially. The fruit can sense the presence of ethylene, which causes it to release more and more ethylene, until the fruit is in full "ripening mode"!

This is why if you have a bowl filled with fresh, undamaged peaches and you introduce an overripe peach, it will cause the non-ripe peaches to ripen faster. The fresh peaches in the bowl sense the ethylene gas released by the overripe peach and start the ripening process.

Hi Lola, this is a great question! First, I'd like to talk about why fruits ripen. As you probably know, unripe fruits are often green, hard, mealy (there is starch present), and odorless. Nobody likes that including wild animals like birds that can potentially carry the fruits and spread the seeds of the original plants to faraway places that the plants could not travel to. So evolutionarily, plants want their fruits to be sweet and tasty. So how do fruits do the ripening after they are no longer attached to the mother trees? Fruits take their cue from a ripening signal, which is a burst of gas called ethylene, also known as the "fruit-ripening hormone." This hydrocarbon gas flips a switch to trigger the enzymes that cause ripening. These enzymes cause the fruits' cell walls to break down, making the fruits softer, and the starch to also break down to sugar, making the fruits sweeter.

It is true, that some fruit can ripen on its own without its parent plant! But that isn't the case for all fruit (for example: blueberries, oranges). Fruits ripen by breaking down stored starch into sugar. Some can only do that when they are on the parent plant (like the blueberries or oranges), while others can do that while off the plant. This is because these plants respond heavily to a chemical they produce called ethylene. Once the fruit is picked, ethylene is released into the air around that fruit (and others nearby) and chemicals inside the fruit are triggered to begin to break down that stored starch into sugars. Thus, ripening! And that's why the longer you let a banana sit, the sweeter it gets.

If you want to try something out, you can stick a green banana into a bag with brown bananas, and a green banana away from this bag/brown bananas. See if you can notice which green banana ripens first!

The term "fruit" in everyday life usually refers to the fleshy edible part on a plant. However, in botany, "fruit" specifically refers to the structure developed from the Ovary of a flowering plant. In this sense, apples and strawberries are not true fruits yet wheat grains, corn kernels, and bean pods are.

The fleshy edible part of a fruit is a way the plants award animals to disperse their seed. As such, they store quite a lot energies in the form of starch. During ripening, the starch breaks down to simpler sugar, giving the fruit a sweet taste.

It should be kept in mind that the fruit is pretty much alive even after it is picked from the tree. The ripening process is trigger by ethylene gas. The ethylene gas makes the cell in the fruit to make enzymes to break down the starch. Since it is a process happens entirely within the fruit, ripening does not need to rely on the rest of the plant. In fact, if you keep unripe banana and a ripe apple in a sealed plastic bag, the banana will ripe!

Good question, Lola! The ability of a fruit to ripen off of a tree or plant actually varies a lot depending on what kind of fruit it is.

For example, tomatoes can be picked while they're still green, and they'll turn red over a few days in a bowl on your kitchen table. Bananas and apples are other examples of fruit that can ripen off the tree - have you ever heard the expression "one bad apple spoils the bunch?" How can they do this?!

Fruits like apples and tomatoes make an invisible gas called "ethylene," which is also called the ripening hormone because it tells the fruit to ripen more. Picking fruits like these signals to the fruit to start making more and more ethylene, which makes the fruit ripen faster and faster. So if you have one apple that's almost rotten, it's producing a TON of ethylene and makes the other apples in the bunch ripen and rot really quickly!

But what about other fruits, like lemons or strawberries, which won't ripen any more once they're picked? When these fruits are picked, they don't start making more ethylene, so they don't ripen anymore. However, if ethylene happens to be around (say from a bad apple), these fruits do ripen more quickly! That's why putting an apple or banana into a bag with unripe, green lemons can actually help turn the lemons yellow!

The cells in a fruit are still alive as long as they have enough water to stay alive, and fruits have evolved to be able to hold in water when they fall off of a tree.

Most of the ripening of fruit comes when the fruit turns its cellulose cell walls into sugar, making the fruit soft and sweet. Because a fruit can still do this as long as its cells are alive, it will keep ripening even while off of the tree. Eat it soon, though, because the riper a fruit gets, the sooner fungi will get into it and rot the fruit before you can eat it!

Those fruits have chemicals inside them that help them ripen, whether they're on the tree or not.

Thank you for your question! This says my blueberries and cherries don't get riper when they sit in my house:

"Fruits that can ripen after picking — including melons, peaches, apples, avocados, mangoes, pears and tomatoes — are called climacteric fruits. In these fruits, ripening is hastened by chemicals, primarily ethylene gas, that are produced inside the fruit and convert stored starch into sugar even after picking.

Non-climacteric fruit produce little or no ethylene gas and therefore do not ripen once picked; these stubborn fruits include raspberries, blueberries, strawberries, watermelons, cherries, grapes, grapefruit, lemons and limes."