🌱 Structure of Phloem
Just like our body has blood vessels to carry nutrients, plants also have vascular tissues to carry water and food. These tissues are like pipelines.
There are two main types:
- Xylem (carries water)
- Phloem (carries food)
🔬 What is Phloem?
Phloem is the tissue in plants responsible for transporting organic nutrients, especially the sugars (like sucrose) made during photosynthesis.
Photosynthesis is the process where plants make food using sunlight, carbon dioxide, and water in their leaves.
So, phloem carries these sugars from leaves to roots, fruits, stems, and growing buds — basically to all the parts that need energy or want to store it.
📍 Location of Phloem in Plants
In plants that grow thicker over time (like trees), the phloem is found on the outer side of the vascular tissue. In such plants:
- The inner part of the trunk is mostly xylem (wood).
- The outer layer, just beneath the bark, is the phloem.
This phloem in the outer layer is also known as the inner bark.
🧱 Components of Phloem
Phloem is made up of different types of cells, each with a special job. The main parts are:
- Sieve tube elements
- Companion cells
- Phloem fibers
- Phloem parenchyma
Let’s understand each one:
1️⃣ Sieve Tube Elements
These are long, tube-like cells that are responsible for transporting sugars and other organic materials throughout the plant.
- Each sieve tube is made of sieve tube elements arranged in a line, one on top of another, like stacked pipes.
- These cells have special perforated walls (called sieve plates) which allow materials to flow from one cell to the next.
- However, sieve tube elements don’t have a nucleus when mature, so they can’t control themselves or make their own proteins.
This is where companion cells help them.
2️⃣ Companion Cells
Each sieve tube element is closely linked to a companion cell. Think of the companion cell as a caretaker or helper.
- These cells have a nucleus and are connected to sieve tubes through tiny channels called plasmodesmata.
- Companion cells provide energy (in the form of ATP) and proteins to sieve tube elements.
So, the companion cells support the sieve tube cells and help in loading and unloading sugars.
3️⃣ Phloem Parenchyma
These are living cells in the phloem that have storage roles.
They store substances like:
- Sugars – for energy
- Resins – for protection
- Latex – for defense against animals
- Mucilage – a sticky substance that helps retain moisture and protect cells
4️⃣ Phloem Fibres
These are supporting cells — strong and fibrous, they help to give strength to the phloem tissue. Think of them like the steel rods in concrete, which give structure and support.