CIE iGCSE Biology-6.2 Leaf structure- Study Notes- New Syllabus
CIE iGCSE Biology-6.2 Leaf structure- Study Notes – New syllabus
CIE iGCSE Biology-6.2 Leaf structure- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- State that most leaves have a large surface area and are thin, and explain how these features are adaptations for photosynthesis
- Identify in diagrams and images the following structures in the leaf of a dicotyledonous plant: chloroplasts, cuticle, guard cells and stomata, upper and lower epidermis, palisade mesophyll, spongy mesophyll, air spaces, vascular bundles, xylem and phloem
- Explain how the structures listed in 6.2.2 adapt leaves for photosynthesis
Leaf Structure – Adaptations for Photosynthesis
📘 Why Leaf Structure Is Important:
- The main function of a leaf is to carry out photosynthesis.
- To do this effectively, the leaf has evolved several structural adaptations that:
- Maximize light absorption
- Allow efficient gas exchange
- Support water and nutrient transport
🌞 Key External Adaptations
1. Large Surface Area
- Most leaves are broad and flat, exposing a wide area to sunlight.
- More light absorbed = faster rate of photosynthesis
2. Thin Structure
- Leaves are usually only a few cells thick, allowing gases to diffuse rapidly.
- Short diffusion distance = faster gas exchange
🧬 Internal Leaf Features That Support Photosynthesis
| Leaf Structure | Function |
|---|---|
| Upper epidermis | Transparent to let light through; often covered with a waxy cuticle |
| Palisade mesophyll | Packed with chloroplasts → main site of photosynthesis |
| Spongy mesophyll | Contains air spaces for easy gas exchange (CO₂ in, O₂ out) |
| Stomata | Small pores mostly on the lower surface → control gas exchange |
| Guard cells | Open/close stomata to regulate CO₂ entry and water loss |
| Xylem and phloem | Xylem delivers water, phloem removes sugars (like glucose) |
💧 Water & Nutrient Support:
- Leaves are connected to the vascular system (xylem and phloem).
- Water is needed for photosynthesis and is transported by xylem.
- Glucose made in photosynthesis is moved away by phloem for storage or use.
📌 Summary Table: Key Leaf Adaptations
| Adaptation | How it supports photosynthesis |
|---|---|
| Large surface area | Captures more sunlight |
| Thin structure | Short path for CO₂ and O₂ to diffuse in/out |
| Chloroplast-rich palisade | Maximizes light absorption |
| Air spaces in spongy layer | Allows easy movement of gases |
| Stomata with guard cells | Controls gas exchange and limits water loss |
| Xylem and phloem | Deliver water and removes glucose efficiently |
Identifying Leaf Structures in a Dicotyledonous Plant
How Leaf Structures Are Adapted for Photosynthesis (6.2.2)
1. Cuticle:
- A waxy, waterproof layer that is transparent to allow light through. Prevents water loss while letting sunlight reach cells.
- Helps conserve water without blocking light.
2. Upper Epidermis:
- Transparent layer with no chloroplasts. Allows light to pass directly to the photosynthetic layers.
- Acts like a window for light entry.
3. Palisade Mesophyll:
- Column-shaped, tightly packed cells rich in chloroplasts. Located at the top of the leaf.
- Site of most photosynthesis due to maximum light capture.
4. Chloroplasts:
- Contain chlorophyll to absorb light energy. Found mostly in palisade and some spongy cells.
- Converts light to chemical energy (glucose).
5. Spongy Mesophyll:
- Loosely packed cells with air gaps to allow easy gas flow.
- Supports efficient internal gas exchange.
6. Air Spaces:
- Between spongy mesophyll cells. Allow CO₂ to diffuse to photosynthetic cells and O₂ to leave.
- Improves gas diffusion efficiency.
7. Vascular Bundles (Veins):
- Xylem: Brings water from roots, essential for photosynthesis.
- Phloem: Carries glucose to other parts of the plant.
- Maintains water supply and sugar transport.
8. Lower Epidermis:
- Bottom protective layer with stomata. Helps regulate water loss and gas exchange.
- Hosts stomata – key for controlled exchange.
9. Stomata:
- Small openings mainly on the lower surface. CO₂ enters, O₂ exits.
- Essential for gas exchange during photosynthesis.
10. Guard Cells:
- Surround stomata and control their opening and closing. React to light and water availability.
- Balance CO₂ intake and water conservation.
📌 Summary Table
| Structure | Adaptation for Photosynthesis |
|---|---|
| Cuticle | Prevents water loss, lets light through |
| Upper epidermis | Transparent, allows light to pass |
| Palisade mesophyll | Packed with chloroplasts, absorbs most light |
| Chloroplasts | Contain chlorophyll to trap light energy |
| Spongy mesophyll | Loose structure, allows gas diffusion |
| Air spaces | Speed up CO₂ and O₂ diffusion |
| Vascular bundle | Xylem brings water, phloem removes glucose |
| Lower epidermis | Supports stomata function |
| Stomata | Allow CO₂ in and O₂ out |
| Guard cells | Regulate stomata – balance CO₂ intake and water loss |