Settler Explain how transpiration is a consequence of

Settler Explain how transpiration is a consequence of gas exchange

Module 3 Exchange and transport 9. 3 Transpiration (2 lessons)

Starter • A 3 memory game of a labelled potometer

Why does transpiration vary?

Feature that affects the rate of water How it affects water loss Number of leaves Number, size and position of stomata Presence of cuticle Light Temperature Relative humidity Air movement or wind Soil-water availability

Learning Objectives • Define the term transpiration Success Criteria • Define the term transpiration (Grade D – C) • Describe the factors that affect transpiration rates and how a potometer is used to measure these (Grade C –B) • Describe how a potometer, with the aid of diagrams, is • Explain how practical investigations are used to estimate transpiration rates (Grade B – A) • Describe the factors that effect transpiration rate

Transpiration • Transpiration is the Loss of water vapour from the upper parts of the plant by evaporation. Transpiration involves 3 processes 1) Osmosis from the xylem to mesophyll cells 2) Evaporation from the surface of the mesophyll cells to the intercellular spaces 3) Diffusion of water vapour from the intercellular spaces out through the stomata • Write a step by step journey of how and why a water molecule would travel from the soil into the xylem • Include keywords Minerals, active transport, ATP, water potential endodermis, casparian strip, cortex, water potential gradient, xylem • Define the term transpiration (Grade D – C)

Transpiration rates 8 of 26 © Boardworks Ltd 2008

Potometer experiment • A potometer is used to estimate transpiration rates. • Practical: investigate how wind affects transpiration rate. • Demo – set up, students to set up experiment and write a method, whilst recording results. • Describe the precautions that should be taken when • Include key points using a potometer to • shoot is healthy and leaves are dry ensure results are valid • cut last 2 -3 cm off cut end / cut at an angle and reliable • assemble apparatus / cut shoot, under water ; (Grade B – A) • check there are no air bubbles in apparatus • once apparatus assembled make sure its water tight / air tight / has no leaks ; ACCEPT screw clip tight • Problem is that potometer is only an estimate • Measures water uptake ; • not all water (taken up) is lost. 99% water taken up is lost • some water used is used in photosynthesis / making cells turgid

Results • Quantitative task Record your raw data in the most suitable form • Evaluative task 1) Plot a suitable graph of your results 2) Use your processed data and graph to describe the trends in the data

Why is transpiration important? • • Write down your reason on a post it. Share ideas on whiteboard Cools plant Minerals Cells turgid Growth/elongation Water is a raw material in photosynthesis Mineral ions and products of photosynthesis are transported

HD Opening and closing of stoma

Why does transpiration vary?

plenary • Complete table on factors affecting transpiration worksheet • Jan 10 Question 4 - homework • Describe the factors that affect transpiration rates and how a potometer is used to measure these (Grade C –B)

Exam Practice