7.1 Uptake and Transport of Water and Ions

2026 📋 Syllabus Objectives

By the end of these notes, you should be able to:

  1. Relate the structure of root hair cells to their function of water and ion uptake
  2. Outline the pathway taken by water through the root, stem, and leaf — limited to: root hair cells → root cortex cells → xylem → mesophyll cells
  3. Investigate, using a suitable stain, the pathway of water in a cut stem

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Objective 1: Root Hair Cells — Structure and Function

What Are Root Hair Cells?

Root hair cells are found just behind the tip of plant roots. They are specialised cells, meaning they have a specific shape and structure that makes them very good at one particular job: absorbing water and ions (minerals) from the soil.

Think of a root hair cell like a finger poking into the soil. That "finger" shape gives the cell a huge advantage when it comes to absorbing things.

The Structure of a Root Hair Cell

Root hair cells have several key features. Each feature links directly to how the cell does its job.

1. A Long, Thin Extension Called a Root Hair

  • The cell has a long, finger-like projection that sticks out into the spaces between soil particles.
  • This extension is called the root hair.
  • The root hair massively increases the surface area of the cell — surface area means the total area of the outside of the cell that is in contact with the soil.
  • A larger surface area means more contact with the soil water, so more water and ions can be absorbed at once.

2. A Large Permanent Vacuole

  • The vacuole is a fluid-filled bag inside the cell.
  • In root hair cells, it is large and filled with cell sap (a watery solution containing dissolved substances like sugars and salts).
  • This helps maintain a low water potential inside the cell (explained below).

3. Thin Cell Wall

  • The cell wall is made of cellulose (a tough but flexible plant material).
  • Even though it is present, the wall is thin enough to allow water to pass through it easily.

4. A Large Surface Area-to-Volume Ratio

  • Because the root hair extension is long and thin, the cell has a very high surface area compared to its volume.
  • This is a major adaptation (a feature that helps the organism survive and work well) for rapid absorption.

5. Many Mitochondria

  • Mitochondria are the parts of the cell that release energy from food (by a process called respiration).
  • Root hair cells contain many mitochondria because absorbing ions (minerals) from the soil requires energy.
  • This energy-requiring process is called active transport (see Key Terms).

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