WJEC Biology for A2: Student Bk

Wind-pollinated flower The inflorescence of plantain is a spike. This means that the flower head has many individual flowers arranged along the stem, with each flower attached directly to the stem, and not on the receptacle. Flowers ripen from the bottom to the top, with stamens then anthers being mature. 1. Remove a flower with an exposed stigma. 2. Using a lens and dissecting equipment, identify and separate the stigma, style and ovary. 3. Remove a flower with a mature stamen. 4. Using a lens and dissecting equipment, identify and separate the filaments and anthers. Scientific drawing of anther and calculations of size and magnification To examine a TS anther, look at it on the slide with the naked eye to gauge its size and shape. Place the slide on the microscope stage, with the vascular strand at the top of the image. Focus using a × 4 objective and then a × 10 objective. Use a × 40 objective to examine the individual cells. You should be able to distinguish the epidermis, the vascular strand, the parenchyma surrounding it, the pollen sac containing pollen cells undergoing meiosis, tetrads or mature pollen, the tapetum, sometimes called the inner wall, and the fibrous layer surrounding it, which is sometimes called the outer wall. In some sections, you may see the filament. 1. Draw a plan of an entire TS anther or, if it is too large to fit into one field of view, a representative portion. If only part of the anther is drawn, make a small sketch of the whole anther and indicate which part is shown in your tissue plan. 2. Align the eyepiece graticule with a clearly identifiable part of the specimen, e.g. the maximum diameter of a pollen sac, and count the number of eyepiece units that distance represents. Let us say that it measures 4 eyepiece units. 3. Having calibrated the microscope, the following calculation of the diameter may be made: With × 10 objective, maximum diameter of pollen sac = 4 eyepiece units From the calibration with a × 10 eyepiece, 1 eyepiece unit = 10 µm maximum diameter of pollen sac = (10 × 4) = 40 µm 4. The distance measured should be marked on the diagram with a straight line, with a small bar at each end, placed very precisely on the pollen sac. 5. The length marked on the diagram is measured in mm. Let us say it measures 168 mm. 6. Calculate the magnification of the diagram: Distance on drawing = 168 mm = (168 × 1000) µm = 168000 µm Actual distance = 40 µm Magnification = actual size image size = 40 168000 = 4200 SpIke of the ribwort plantain, ( Plantago lanceolata ) flowers with exposed stigmas flowers with mature stamens pollinated flowers Sexual reproduction in plants 193