How do plants make sugars and acids in fruits?

In one line

The rule

Plants make sugars in their leaves by photosynthesis, then move these sugars to fruits, where they are stored or changed into acids and other substances.

Let's understand it simply

Imagine a mango tree in your backyard. The leaves are like tiny kitchens. They use sunlight, water, and air to cook up food — this food is called sugar (glucose). The plant sends this sugar to the growing fruit, just like your mother sends you lunch at school. Some of this sugar stays sweet, while some gets changed into acids, which make fruits taste tangy or sour, like in lemons or raw mangoes.

Think of the plant like a busy railway station. Sugars are the passengers, made in the leaves, and travel by train (the plant's tubes) to the fruits. In the fruit, some passengers stay as they are (sweet), while others change into new passengers (acids) to give the fruit its special taste.

How it works

1. Leaves take in sunlight, water, and carbon dioxide (from air).
2. Leaves use photosynthesis (making food with light) to create glucose (a simple sugar).
3. The plant moves this glucose through special tubes called phloem to the fruit.
4. In the fruit, some glucose stays as sugar, making it sweet.
5. Some glucose is changed by enzymes (tiny helpers) into acids, like citric acid or malic acid, making the fruit sour or tangy.
6. As the fruit ripens, the amount of sugar usually increases, and acids may decrease, making the fruit taste sweeter.

The story behind it

Scientists learned about photosynthesis in the 1700s. Jan Ingenhousz, a Dutch scientist, showed that plants use sunlight to make food. Later, scientists found that this food is mostly sugar, and that fruits store or change these sugars to make different tastes. The study of how fruits ripen and change their taste is still going on, helping farmers grow tastier fruits.

Where you see it in real life

• Mangoes ripening in summer: Start sour (more acid), become sweet (more sugar) as they ripen.
• Lemons and oranges: Both have sugars and acids, but lemons have more acid, so they taste sour.
• Bananas: When green, they have more starch (a kind of sugar), which turns into sweet sugar as they ripen.
• Jamun (black plum): Tastes both sweet and a little tangy because of a mix of sugars and acids.
• Tomatoes: Unripe tomatoes are sour due to acids; ripe ones are sweeter as sugars increase.
• Sugarcane: Full of sugar made by the plant, stored in the stem, not the fruit.

Why it matters

• Sweetness and sourness decide if we like a fruit or not.
• Farmers use this knowledge to pick fruits at the best time for taste and market.
• Food companies use it to make juices, jams, and candies.
• Understanding this helps in making fruits last longer (storage and transport).
• This topic links to later chapters on plant nutrition, food processing, and health.

Worked example

Let's see how a mango changes as it ripens:

Given: Unripe mango (more acid, less sugar)
Step 1: Plant makes glucose in leaves by photosynthesis.
Step 2: Glucose moves to mango fruit.
Step 3: In unripe mango, enzymes turn some glucose into citric acid (sour).
Step 4: As mango ripens, more glucose stays as sugar, less is turned into acid.
Step 5: Result: Ripe mango tastes sweeter, less sour.

Common mistakes

• Thinking fruits get sugar only from the soil — actually, plants make sugar in their leaves.
• Believing all fruits are sweet from the start — most are sour or bland when young.
• Forgetting that acids are natural and safe in fruits, not harmful.
• Mixing up starch and sugar — starch is a storage form, which turns into sugar as fruit ripens (like in bananas).

Remember it

Leaves make the sugar, fruits store or change it — that's why fruits taste sweet or sour.