WJEC Biology for A2: Student Bk

Apparatus – Wind-pollinated flower, e.g. plantain ( Plantago sp.) – Insect-pollinated flowers, e.g. lily such as Alstromeria ; herb robert ( Geranium robertianum ) – White tile – Fine forceps – Fine scalpel – Fine scissors – Lens – Microscope slides and cover slips – Iodine–potassium iodide solution – Dropping pipette Method Insect-pollinated flower Herb robert ( Geranium robertianum ) Alstromeria 1. Count the sepals and remove them from where they insert on the receptacle. If you are dissecting a monocot, such as a lily, the sepals may be coloured rather than green. They can be distinguished from petals because they insert into the receptacle further out than the petals. 2. Count the petals and remove them from where they insert on the receptacle. 3. Count the stamens and remove them from where they insert on the receptacle. Note the number of lobes on the anthers. If the anthers have dehisced, pollen grains may be exposed on the surface. 4. This leaves the carpel attached to the receptacle. Holding the carpel horizontally, slice it longitudinally, from the stigma down through the style and ovary into the receptacle and note the ovules in the ovary. 5. Microscopy (a) If the anthers have dehisced, brush a little pollen on to a slide and mount in two drops of iodine–potassium iodide solution. If the anthers have not dehisced, cut a section which is as thin as possible and crush it on the microscope slide, in two drops of iodine–potassium iodide solution. Add a cover slip. Find the pollen grains using the × 10 objective and then focus on well-separated grains with the × 40 objective. Focus up and down on an individual pollen grain to distinguish the surface markings. (b) Ovules should be visible in the ovary as small white spheres. Remove a small number of these and place them on a microscope slide in a few drops of iodine–potassium iodide solution. Macerate them so that the cover slip will be able to lie flat. Place the cover slip on the fragments and view under a × 4 and then a × 10 objective. Focus through the specimen so that you can distinguish individual cells. WJEC A2 Biology: Chapter 10 192