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Newcastle University – Teacher’s toolkit Identification of stomatal physiology Student work book Introduction All plants are unique! Each person on this earth is individual and different. Did you know that plants are too? Each plant species is unique and each individual plant within that species is unique too, just like you and me! There are many characteristics that are very important, and are found in all plants. All plant leaves contain a pore called stomata. These act like a ‘mouth’ and regulate a plants gas exchange and water movement. The size, shape, abundance and location of the stomata will vary depending on the plant species. Many plants have stomata on the upper surface and others have stomata on the underside. Stomata structure Stomata are made of specialised cells called guard cells and subsidiary cells. There are two guard cells for each stomata, again think of this as a ‘mouth’ and the guard cells as the ‘lips’. These cells help control whether the stomata is open or closed. For example, as a plant loses water it will close the stomata to prevent losing more water, or if a plant needs more carbon dioxide, for photosynthesis, it will open the stomata. Why are stomata important? Stomata play an important role in plant homeostasis, which means to maintain a constant internal environment. Gaseous molecules are exchanged from the plant. Without this pore, no oxygen would be released from the plant and that means animals would not be able to survive! Water molecules can also be lost from the stomata by evaporation. Plant species are adapted to the environment that they live in. Cacti are adapted to hot dry deserts, whereas water lilies are adapted to living in water. Why is studying plants important? Plants are important food sources. By studying plants that can live in certain environments scientists are able to introduce a gene into another species that is not adapted to that area. The inserted gene causes a change in the second species and the adaptive characteristic is shown. This process is called genetic engineering. Subsidiary cell Stomatal pore Guard cell 1 Photography courtesy of Dr Gordon Beakes Newcastle University – Teacher’s toolkit Activity breakdown Health and safety Students should: Be provided with appropriate PPE Be responsible with the scissors and nail varnish Report any breakages or accidents to the teacher Teachers should ensure that the students are supervised throughout the duration of the activity and should make sure that there are no students that have allergies to any of the materials being used. Equipment checklist Within your group you should have: One light microscope Two pre –set up slides Two empty slides Two plant leaves for any plant species Clear nail varnish Sticky tape Scissors A4 paper Colourful pens(optional) Activity 1 Aim: Introduction into microscope use and practice examining slides. Duration of activity: 20 minutes Procedure for students Students should use the provided document ‘Introduction to Microscopy’ to understand how to use a microscope properly and should examine the pre-prepared slides. 1. Read through the document before starting to examine the slides 2. Set up the microscope and place the slides onto the mechanical stage 3. Practice using the microscope to examine different slides by altering the lighting and magnification 2 Photography courtesy of Dr Gordon Beakes Newcastle University – Teacher’s toolkit Activity 2 Aim: Preparing a slide and examining stomata Duration of activity: 30 minutes Procedure 1. Take a leaf and paint a square patch of clear nail varnish, on the underside of the leaf, approximately 2cm by 2cm. 2. Allow the patch to dry 3. Carefully use sticky tape to peel off the square and place onto a clean microscope slide 4. The specimen should not need to be stained to allow identification of the stomata 5. Examine this slide and answer the following questions: Drawing: In the space provided draw a diagram of a stomatal pore including labels and a scale bar. 1. Did you find that the leaves had stomata that varied in shape, size and distribution? 2. Would you expect the stomata on the majority of plants to be open during the night or day? 3. The stomata of a plant will close in response to: high temperature or low temperature? 4. If stomata are open, would you expect more or less photosynthesis to occur? 3 Newcastle University – Teacher’s toolkit Activity 3 Aim: Allow students to apply their knowledge to plant examples and encourage discussion. Duration of activity: 10 minutes Procedure: Within your group divide an A4 sheet of paper down the middle and compare the structure of a cactus plant and a water lily e.g. leaf size, shape, or photosynthesis rate. 4