How is water lost in leaves and how do the layers within a leaf make that happen? In this IBDP Biology Blog post, we will recap on the layers within leaves and the process of transpiration.
Layers within a Leaf
- Upper epidermis: Covered by a waxy cuticle which provides protection
- Palisade Mesophyll cells: Many chloroplasts for photosynthesis
- Spongy Mesophyll cells: Air spaces fordiffusion of gases
- Lower epidermis: Protects the underside of a leaf and has stomata (pores)
- Chloroplast: Light is absorbed for photosynthesis
- Stomata: Small pores allowing gases to diffuse in and out of the leaf
The Relationship between Gas Exchange and Transpiration
Gas Exchange in Plants:
- Exchange of CO2 and O2 between the leaf and atmosphere
- CO2 diffuses into leaf and O2 diffuses out due to photosynthesis
Transpiration in Plants:
- Loss of water vapour from the leaves and stems of plants
- Inevitable concequence of gas exchange due to photosynthesis
Why Transpiration is inevitable and important
1. Leaves must absorb CO2 and excrete O2 in photosynthesis so that Gas Exchage occurs
2. Adaptation for effcient Gas Exchange having moist cell walls and large surface area
3. Spongy Mesophyll layer has many air spaces to increase the surface area of moist cell walls exposed to air
4. Water evaporates from the moist cell walls as air spaces have a high relative humidity
5. Water vapour diffuses from air spaces to the air/atmosphere outside the leaf
6. Hence leading to Transpiration
7. Expidermis secretes wax forming a waxy cuticle (waterproof coating to leaf) this prevents excessive Transpiration but also blocks Gas Exchange
8. Stomata are needed to open and allow gas exchange of CO2 and O2
9. Inevitablely water vapour also escapes during Transpiration
Why is Transpiration Important?
- Provides Photosynthesis with a needed raw material
- Minerals are transported in the leaves to synthesise important molecules
- Provide cooling effects to the leaves
That's all!
References:
- https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.edrawsoft.com%2Ftemplate-leaf-cross-section.html&psig=AOvVaw2oO8LxpH0xtiqWZMtdm2xi&ust=1626754804219000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCMjWvISk7vECFQAAAAAdAAAAABAD
- https://www.google.com/url?sa=i&url=https%3A%2F%2Fplantlet.org%2Ftranspiration-mechanism-in-plant-body%2F&psig=AOvVaw0do02W5k2efAi13GBzXXyf&ust=1626754999286000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCJiJvuGk7vECFQAAAAAdAAAAABAD
Drafted By Venetia (Biology)