CIE iGCSE Co-ordinated Sciences-B6.2 Leaf structure- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-B6.2 Leaf structure – Study Notes
CIE iGCSE Co-ordinated Sciences-B6.2 Leaf structure – Study Notes -CIE iGCSE Co-ordinated Sciences – 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
Supplement
- Explain how the structures listed in 6.2.2 adapt leaves for photosynthesis
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Leaf Adaptations for Photosynthesis
📌 Main Features
- Most leaves are broad → large surface area.
- Leaves are thin → only a few cell layers thick.
- Contain chlorophyll in chloroplasts of mesophyll cells.
- Veins (xylem and phloem) form a network for transport.
- Air spaces in spongy mesophyll allow gas diffusion.
🔹 How These Features Help
- Large surface area
Maximises light absorption by chlorophyll.
More sunlight captured → higher rate of photosynthesis. - Thin structure
Short distance for CO₂ to diffuse into cells and O₂ to diffuse out.
Speeds up gas exchange. - Veins (xylem & phloem)
Xylem supplies water for photosynthesis.
Phloem transports sugars away to other parts of the plant. - Air spaces in spongy mesophyll
Allow rapid movement of CO₂ and O₂ inside the leaf. - Chlorophyll in palisade cells
Absorbs light energy and converts it into chemical energy.
📝 Quick Recap
Large surface area + thin shape = efficient light capture + fast gas exchange.
Veins + chlorophyll + air spaces → support photosynthesis and transport of products.
Leaf structure is perfectly adapted for maximum photosynthesis.
Leaf Structure (Dicotyledonous Plant)
📌 Key Structures & Functions
| Structure | Location / Appearance | Function |
|---|---|---|
| Cuticle | Outer waxy layer on upper & lower epidermis | Reduces water loss |
| Upper epidermis | Single cell layer beneath cuticle | Protection, allows light to pass |
| Lower epidermis | Single cell layer at bottom | Contains stomata for gas exchange |
| Stomata | Pores in lower epidermis | CO₂ in, O₂ out, water vapour loss |
| Guard cells | Paired cells around stomata | Open/close stomata |
| Palisade mesophyll | Column-shaped cells beneath upper epidermis | Main site of photosynthesis (lots of chloroplasts) |
| Spongy mesophyll | Loosely packed cells with air spaces | Gas diffusion (CO₂, O₂) |
| Air spaces | Between spongy mesophyll cells | Allow circulation of gases inside leaf |
| Vascular bundles (veins) | Embedded in mesophyll | Transport of water, minerals, and sugars |
| Xylem | Upper part of vascular bundle | Transports water & minerals from roots |
| Phloem | Lower part of vascular bundle | Transports sugars and other organic compounds |
| Chloroplasts | In palisade and spongy mesophyll cells | Contain chlorophyll for photosynthesis |
🔹 Tips for Diagram Identification
- Chloroplasts → small green dots in mesophyll cells.
- Cuticle → thin shiny layer on top.
- Guard cells & stomata → bean-shaped pairs with central pore on lower epidermis.
- Upper/lower epidermis → outermost cell layers.
- Palisade mesophyll → tightly packed, column-shaped cells.
- Spongy mesophyll → loosely packed, irregular cells with air spaces.
- Vascular bundles → look like small circles or ovals; xylem on top, phloem below.
📝 Quick Recap
Upper epidermis + cuticle → protection & prevent water loss.
Palisade + spongy mesophyll → photosynthesis & gas exchange.
Stomata + guard cells → control CO₂/O₂/water loss.
Vascular bundles (xylem + phloem) → transport nutrients and water.
Leaf Adaptations for Photosynthesis
| Structure | Adaptation for Photosynthesis |
|---|---|
| Cuticle | Transparent, thin layer allows light to pass to underlying cells while reducing water loss. |
| Upper epidermis | Transparent layer; allows light to reach palisade cells efficiently. |
| Palisade mesophyll | Tightly packed, column-shaped cells with many chloroplasts → maximises light absorption for photosynthesis. |
| Spongy mesophyll | Loosely packed cells with air spaces → allow diffusion of CO₂ to photosynthesising cells and O₂ out. |
| Air spaces | Increase surface area for gas exchange → CO₂ can reach mesophyll cells quickly. |
| Stomata | Openings controlled by guard cells → allow CO₂ to enter and O₂/water vapour to exit. |
| Guard cells | Can open/close stomata → regulate gas exchange depending on environmental conditions. |
| Vascular bundles (xylem + phloem) | Xylem brings water to leaf for photosynthesis. Phloem transports sugars made by photosynthesis to other parts of the plant. |
| Chloroplasts | Contain chlorophyll → absorb sunlight and convert light energy into chemical energy for carbohydrate synthesis. |
| Lower epidermis | Protects leaf while also containing stomata for gas exchange. |
🔹 Key Points
Large surface area of leaf → captures more light.
Thin leaf → short diffusion distance for gases.
Palisade layer → main photosynthesis site.
Spongy mesophyll + air spaces → efficient CO₂ circulation.
Stomata + guard cells → controlled gas exchange.
Vascular bundles → water supply and sugar transport.