3️⃣ Cohesion – Water Sticking to Water

Cohesion means water molecules stick to each other because of hydrogen bonding — a type of attractive force between them.

🔍 Why it matters:

• Because of cohesion, water forms a continuous “chain” or “column” from the roots to the leaves.
• When one molecule of water is pulled up (due to transpiration), it pulls the others along with it — like links in a chain.

🌿 Example: Imagine a group of people holding hands. If you pull one person, the whole line moves. That’s how cohesion works — all water molecules in the xylem are “holding hands” and move together.

4️⃣ Tension – The Pulling Force

Tension is the negative pressure or pulling force created at the top of the plant (the leaves) due to transpiration.

🔍 How it helps:

• As water keeps evaporating from the leaves, more water is pulled up from below.
• This tension is transmitted downward through the cohesive water column all the way to the roots.
• It’s like pulling a rope — when you pull one end, the rest of the rope follows.

🌿 Example: When you suck water through a straw, you create tension that pulls water up. Similarly, transpiration creates tension in the plant that pulls the water up through xylem.

🌳 Why is the TACT Mechanism Important?

• It explains how water can move from soil to the top of tall trees — sometimes up to 100 meters!
• It works without any energy from the plant. It’s a purely physical process.
• It helps deliver not just water but dissolved minerals from the soil to all parts of the plant.
• It helps in cooling the plant and maintaining internal water balance.

🔁 Recap in Simple Words

Term	Meaning	Role in Water Transport
Transpiration	Water evaporates from leaves	Creates suction or pull
Adhesion	Water sticks to xylem walls	Helps water move upward
Cohesion	Water sticks to other water molecules	Keeps water in a continuous chain
Tension	Pull created by transpiration	Pulls water up from the roots

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✅ In Summary

Water travels in plants through a smart and natural system called the TACT mechanism. It all starts with transpiration (water loss from leaves), which creates a pull. Then, cohesion and adhesion help maintain the flow, and tension keeps pulling the water upward. This entire process happens inside xylem vessels, which are like tiny pipes running from the roots to the leaves.

It’s a beautiful example of how nature uses simple physics to solve a complex problem — transporting water up a tall, living structure without any pump or electricity!

🌿 Lesson 4: Translocation of Food in Plants

❓What Does “Translocation” Mean?

Let’s begin with the word translocation. It simply means the movement or transport of substances from one part of the plant to another.

In this case, we are talking about the movement of food, mainly sugars produced during photosynthesis, from the leaves (where food is made) to other parts of the plant (where it is used or stored).

Now let’s understand how this process works.