TRANSPIRATION

Learning Objectives • Explain the mechanism of water uptake and movement in terms of transpiration producing a tension (‘pull’) from above, creating a water potential gradient in the xylem, drawing cohesive water molecules up the plant. Define transpiration as evaporation of water at the surfaces of the mesophyll cells followed by loss of water vapour from plant leaves, through the stomata • Describe how water vapour loss is related to cell surfaces, air spaces and stomata • Describe the effects of variation of temperature, humidity and light intensity on transpiration rate • Discuss the adaptations of the leaf, stem and root to three contrasting environments, to include pond, garden and desert, with emphasis on local examples (where appropriate) and the factors described in the core

Need for transport systems Plants need sugars and water to stay alive Water needs to travel from the roots to the leaves Sugars need to travel from the leaves to the rest of the plant Importance of water

Water Movement Through a Plant

Transport System in Plants Functions? Vascular bundle Xylem Phloem Sieve tubes Companion cell Label the terms

How is transpiration regulated? Transpiration is the release of water vapour from a plant through the leaves, causing water to move through the plant. Regulation is done by guard cell Number of stomata Video: http://www.biologymad.com/resources/transpiration.swf

Tiny pores found on the surfaces of a leaf http://www.phschool.com/science/biology_place/labbench/lab9/stomamov.html Tiny pores found on the surfaces of a leaf Stomata take in carbon dioxide from the air through stomata Water vapour passes out from the leaf to the atmosphere through stomata

Which factors affect the transpiration? Atmospheric conditions Leaf Structure

Atmospheric Structure Leaf Structure Atmospheric Structure Wind High temperature Low hımidity High light intensity Thick and waxy cuticle Stomata sunk Humid air Leaves shape (needle) Transpiration Rate http://twig-it.com/search#transpiration