settler

Name 3 processes that help to move water up the stem

Module 2Exchange and transport

1.2.17 Transpiration(2 lessons)

Learning Objectives Success Criteria

• Define the term transpiration

• Describe the factors that effect transpiration rate

• Describe how a potometer, with the aid of diagrams, is used to estimate transpiration rates

• 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 the precautions that should be taken when using a potometer to ensure results are valid and reliable

(Grade B – A)

Transpiration• Transpiration is theLoss of water vapour from the upper parts of the plant by evaporation.Transpiration involves 3 processes1) Osmosis from the xylem to mesophyll cells2) Evaporation from the surface of the mesophyll cells to

the intercellular spaces3) Diffusion of water vapour from the intercellular spaces

out through the stomataTask - Describe how water enters and leaves the leaf. Use

keywords osmosis, water vapour potential gradient, diffuse, stomata, •Define the term transpiration

(Grade D – C)

6 of 26 © Boardworks Ltd 2008

Transpiration rates

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.

• Include key points• shoot is healthy and leaves are dry• cut last 2-3 cm off cut end / cut at an angle• assemble apparatus / cut shoot, under water ;• 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

•Describe the precautions that should be taken when using a potometer to ensure results are valid and reliable (Grade B – A)

Why is transpiration important?

• Cools plant• Minerals• Cells turgid• Growth/elongation• Photosynthesis in leaf

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)