CIE iGCSE Biology-8.2 Water uptake- Study Notes- New Syllabus
CIE iGCSE Biology-8.2 Water uptake- Study Notes – New syllabus
CIE iGCSE Biology-8.2 Water uptake- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- Identify in diagrams and images root hair cells and state their functions
- State that the large surface area of root hairs increases the uptake of water and mineral ions
- Outline the pathway taken by water through the root, stem and leaf as:
root hair cells, root cortex cells, xylem, mesophyll cells - Investigate, using a suitable stain, the pathway of water through the above-ground parts of a plant
Root Hair Cells – Identification and Function
📌 What Are Root Hair Cells?
Root hair cells are specialized cells found in the epidermis (outer layer) of plant roots. They are essential for absorbing water and mineral ions from the soil.
How to Identify Root Hair Cells in Diagrams
| Feature | Description |
|---|---|
| Position | Located near the root tip (just behind the growing region) |
| Shape | Long and thin hair-like extension from the surface of a root cell |
| Single, Slender Projection | Each cell has one fine projection to increase contact with soil particles |
| Nucleus and Cytoplasm | Visible under microscope; shows that it’s a living, single cell |
⚙️ Functions of Root Hair Cells
| Function | Explanation |
|---|---|
| Absorption of Water | Water enters root hair cells by osmosis due to a lower water potential inside the cell |
| Absorption of Mineral Ions | Mineral ions (like nitrates, phosphates) enter by active transport |
| Increased Surface Area | The long hair-like projection increases surface area for efficient absorption |
| Anchoring the Plant | Helps roots grip the soil firmly as they grow |
🌿 Summary Box:
Root Hair Cells and Absorption of Water & Mineral Ions
🌱What Are Root Hair Cells?
Root hair cells are specialized cells found just behind the growing tip of a plant’s root. Each root hair is a long, thin extension from a root epidermal cell. These cells are not covered by a cuticle, allowing easy exchange with the soil environment. They grow between soil particles, making close contact with water and nutrients.
Structure of Root Hair Cells:
| Feature | Description |
|---|---|
| Long extension (hair) | Increases surface area for absorption. |
| Thin cell wall | Allows easy movement of water and minerals. |
| No cuticle | Maximizes water uptake from soil. |
| Large vacuole | Stores water and mineral ions. |
| Close to xylem | Enables quick transport of absorbed materials to the rest of the plant. |
Why is Large Surface Area Important?
1. Water Absorption (by Osmosis):
The soil usually has a higher water potential than the cell sap in the root hair cell. Water moves into the root hair cell by osmosis. The large surface area means more water molecules can enter at once, helping the plant remain hydrated.
2. Mineral Ion Absorption (by Active Transport):
The concentration of mineral ions in soil is often lower than in root cells. So, ions like nitrates, phosphates, potassium, magnesium are taken up against the concentration gradient. This process requires energy (ATP) and is called active transport. The large surface area allows many transport proteins to work at once, increasing efficiency.
🌟 Summary
| Role of Root Hair Cell | How Large Surface Area Helps |
|---|---|
| Absorb water by osmosis | More surface in contact with soil = faster water uptake |
| Absorb minerals by active transport | More room for transporter proteins = more ion uptake |
| Support rapid growth | Ensures roots get enough nutrients for cell division |
📌 Final Point to Remember:
Pathway of Water Through a Plant (From Root to Leaf)
Water taken up by plants follows a specific route through the plant body to reach the leaves, where it’s used in photosynthesis or lost by transpiration.
Step-by-Step Pathway:
1. 🌱 Root Hair Cells (Absorption)
- Water from the soil enters root hair cells by osmosis.
- Osmosis happens because the cell sap inside the root hair has a lower water potential than the surrounding soil water.
- Root hairs increase surface area for absorption.
2. 🟣 Root Cortex Cells (Transport Across Root)
Water moves across the cortex of the root through two main pathways:
- Apoplast pathway (through cell walls)
- Symplast pathway (through cytoplasm via plasmodesmata)
Water continues moving towards the central vascular tissue (stele) where xylem is located.
3. 🔷 Xylem Vessels (Upward Transport in Stem)
Water enters the xylem vessels in the root and is then transported upwards through the stem.
Movement of water is driven by:
- Transpiration pull from leaves
- Capillary action
- Root pressure
Xylem vessels are long, hollow, and lignified – ideal for water transport.
4. 🍃 Mesophyll Cells in the Leaf (Distribution and Use)
Water moves from the xylem in the leaf veins into mesophyll cells.
Some water is:
- Used in photosynthesis
- Helps maintain turgidity of cells
The rest evaporates from mesophyll surfaces into the air spaces and exits through stomata (this is transpiration).
🌿 Summary Table: Water Pathway
| Step | Location | Process |
|---|---|---|
| 1. Absorption | Root hair cells | Osmosis from soil |
| 2. Movement inward | Root cortex cells | Osmosis or diffusion |
| 3. Upward flow | Xylem (root → stem → leaf) | Transpiration pull |
| 4. Use and loss | Mesophyll cells in leaf | Photosynthesis, transpiration |
📌 Final Tip:
Investigating the Pathway of Water in a Plant Using a Stain
🎯 Aim of the Experiment:
To observe how water moves through the stem and leaves of a plant by using a colored stain.
🧪 What You Need:
- A leafy celery stalk or a white-petaled flower (like a carnation)
- A beaker or glass of water
- Colored dye (blue or red food coloring works best)
- Knife or scissors
⚙️ Method:
- Fill a beaker with water and add a few drops of food coloring.
- Cut the bottom of the plant stem (e.g., celery) at an angle for better water absorption.
- Place the stem into the colored water.
- Leave the setup for a few hours or overnight.
- Observe the changes in color on the leaves or petals.
- Cut thin cross-sections of the stem and look for the colored lines inside.
👀 What You Will See:
- The colored dye travels upwards through the xylem vessels.
- The leaves or flower petals show streaks or patches of color.
- The stem cross-section shows colored circles or lines where the dye moved.
✅ Conclusion:
Water moves through the xylem in the stem.
The dye helps us trace the water’s pathway.
This shows how plants transport water from the roots to the leaves.
🧠 Scientific Explanation:
It then moves through the xylem by capillary action and transpiration pull.
The colored dye travels with the water and stains the xylem tissue, making it visible.