Translocation (botany) facts for kids

Translocation is how vascular plants (plants with special tubes inside them, like trees and flowers) move important things around. It's like their internal delivery system! This process moves organic molecules, which are mostly sugars made by the plant, and some mineral ions.

Water moves from the soil up to the leaves through tubes called xylem. This happens because of something called transpiration. Transpiration is when water evaporates from the leaves, pulling the water column upwards. Think of it like sipping water through a straw! The water molecules stick together tightly, helping them move up.

But what about the food? The plant's food, mainly sugars, is made in the leaves through photosynthesis. This food then travels all over the plant in different tubes called phloem. This movement of food is what we call translocation.

How Plants Move Food Around

Plants need to move water and food to all their parts to grow and stay healthy. They have two main types of "pipes" or tubes for this: xylem and phloem.

Xylem: The Water Highway

The xylem tubes are like the plant's water pipes. They are made of dead cells, which form hollow tubes. Their job is to carry water and dissolved minerals from the roots all the way up to the leaves. This upward movement is mostly driven by the pull created by transpiration.

Phloem: The Food Delivery System

Unlike xylem, the phloem tubes are made of living cells. These cells transport a special liquid called sap. Sap is mostly water, but it's packed with sugars that the plant makes during photosynthesis.

What is Sap?

Sap is the sugary liquid that moves through the phloem. It's like the plant's energy drink! These sugars are sent to parts of the plant that can't make their own food, like the roots. They also go to storage areas, such as tubers (like potatoes) or bulbs (like onions).

How Food Moves: The Pressure Flow Idea

Scientists have a good idea of how food moves through the phloem. It's called the 'pressure flow' hypothesis, first suggested by Ernst Münch in 1930.

Here's how it works:

• Leaves make lots of sugars during photosynthesis.
• These sugars move into the phloem tubes (specifically, into cells called sieve-tube cells).
• When sugar enters these cells, water from the xylem moves into the phloem by a process called osmosis. Osmosis is when water moves from an area of high water concentration to an area of lower water concentration.
• This extra water creates pressure inside the phloem tubes.
• This pressure pushes the sugary sap along the phloem tubes, just like squeezing a tube of toothpaste.
• When the sap reaches parts of the plant that need the sugar (like growing tips or roots), those cells actively pull the sugars out of the phloem.

Sources and Sinks: Where Food Comes From and Goes

In plants, the places where sugar is made are called sources. Usually, the leaves are the main sources because that's where photosynthesis happens.

The places where sugar is used or stored are called sinks. Examples of sinks include:

• Growing parts of the plant, like new leaves or flowers.
• Roots, which need energy to grow and absorb water and minerals.
• Storage organs, like tubers or bulbs, where the plant keeps extra food for later.

The cool thing about phloem is that the food can move in many directions, depending on where it's needed. For example, in the spring, when a plant is just starting to grow, the stored sugars in the roots might become a source, sending food up to the new shoots. This is different from xylem, where water only moves upwards.

Besides sugars, other important molecules also travel in the phloem. These include amino acids (the building blocks of proteins), hormones (which control plant growth), and even special genetic messages called messenger RNAs.