Notes of Lessons: Biology, Class III

[We have thought that it might be of use to our readers (in their own families) to publish from month to month during the current year, Notes of Lessons prepared by students of the House of Education for the pupils of the Practising School. We should like to say, however, that such a Lesson is never given as a tour de force, but is always an illustration or an expansion of some part of the children’s regular studies (in the Parents’ Review School), some passage in one or other of their school books.—Ed.]

Subject: Botany • Group: Science • Class III • Time: 30 minutes

By Patricia Jameson
The Parents’ Review, 1915, pp. 557-558

Objects

I. To increase the girls’ interest in Botany and to direct their observations.

II. To give them a general idea of the internal structure of plants.

III. To teach them about the chief kinds of tissue (the contents of Chapter XVII. of the “Study of Plant Life”).—Stopes.

Course Of The Lesson

Introduction. Ask what the girls were learning about last. (The parts of the flower.) Connect with last lesson by saying that they have studied all the visible parts of the plant except fruit and seeds and are now going to study the internal structure.

Step I. Tell the girls that they will presently see under the microscope that the different parts of the plant are made up of numbers of roundish chambers, so small that it takes seven or eight layers of them to make up the thickness of a beech-leaf. Tell them that these chambers are called cells because they often resemble the cells of a honeycomb in shape. Let them look at picture in their books.

Step II. Let one girl read a paragraph on p. 93 of ‘Stopes’ describing a typical cell. Tell the girls that the living substance mentioned is called protoplasm and that it is essential to the life of the plant.

Step III. Describe, with the help of diagrams, the appearance of the cell at three different ages. When mentioning the cell-sap in the spaces, tell them that if they bruise a leaf, they break down the cell-walls and let out the cell-sap, and that is why the leaf becomes moist.

Step IV. They have just read (Step II.) that the protoplasm often contains granules of various substances. Tell them that if the cells of any green part of the plant are examined under the microscope, numbers of tiny green bodies will be seen in the protoplasm. Tell them the name (chlorophyll-grains) and meaning of word (green leaf). Explain that the grains are made of protoplasm and can only develop green colouring matter if grown in the light. Recall the result of growing plants in the dark.

Step V. Tell children that cells may be tightly packed or may, in some cases, have air-spaces between them. Illustrate latter by picture of water-lily stem and section of bog-bean.

Step VI. Let them look through microscope in turn to see sections of a few cells from stem and leaf. While one looks let the others draw cells at three stages, also leaf-cells with chlorophyll-grains (if time).

Show Slides.—Foxglove: Growing point of stem; older stem. Leaf of Sorrel: Showing chlorophyll-grains.

Step VII. Narration of what they have seen and heard of the structure of plants. [Headings and new words on board.]

Step VIII. Explain that cells are modified and arranged according to their purpose, and that different arrangements are called tissues. There are three chief kinds: (1) Ground Tissue, such as they saw on slides. This forms fleshy parts of stems, leaves, etc.

Step IX. Let them cut pieces of sunflower stem, to see if they can find anything except the ground tissue. Explain that the strings they see are bundles of very long cells with thickened walls. Give names: Vessels, vascular bundles, vascular tissue (adj. from “vessel”). Let them also find bundles in leaf-stalk of Hog-weed. Recall a well-known leaf-stalk in which bundles are clearly seen (Rhubarb).

Step X. Show the girls stems that have been in red ink and let them find out that the ink has run up the stem through the vascular bundles, which are now stained red. Water, of course, does the same, but we cannot see it, because it is colourless.

Step XI. Ask girls if they would expect to see vascular bundles in any other parts of the plant besides the stem. In leaves. Let them see that the red ink has run through the veins, so these are the vascular bundles. In roots: Ask if they have seen the ring of white spots in a radish that has been cut; they look denser than the ground tissue round them.

Step XII. Tell them that the vascular tissue plays an important part in stems that become woody. Let one girl read a paragraph from ‘Stopes,’ p. 94-95, which describes the vascular tissue of woody stems. Show sycamore twigs and let them examine them.

Step XIII. The third kind of tissue. The girls have now heard of the fleshy ground tissue and the stringy vascular; what is it that covers them both? Skin: Get from them the scientific name, which is the same as that used in human physiology, Epidermis: So the tissue forming the skin is called Epidermal Tissue. Let them pull off pieces of the skin ofblue-bell leaves and say what it is like (thin, transparent). Tell them that epidermal tissue nearly always consists of a single layer of cells. Get from them the fact that these cells contain no chlorophyll.

Step XIV. Let one girl read a paragraph from ‘Stopes,’ p.95-96, describing the corky covering of woody stems and older parts of roots. Explain that the thick skin of a twig is the beginning of this cork layer.

Step XV. Let another girl read next paragraph (on lenticels) and let the girls find the lenticels on elder and sycamore twigs. Ask if they know any other twigs which show the lenticels clearly (cherry, birch, etc.). Tell them that the thin epidermis of leaves is also provided with breathing-holes, which are invisible. They are called stomata (mouths). Diagram on board. The epidermis of a parallel-veined leaf, like the bue-bell,consists of long parallel cells, but those of the epidermis of a net-veined leaf, like sorrel are irregular in shape.

Step XVI. Show microscope slides of epidermis of blue-bell and sorrel. Let girls draw sections of stem showing vascular bundles from memory, also epidermal tissue (if time).

Step XVII. Narration on the three kinds of tissue [from headings on board]

Conclusion. Tell the girls that there is still a great deal to learn about tissues. Ask them if they do not think it wonderful that there are some things in Nature, such as these cells, which are so small that one can hardly believe they exist, while there are other things so great, as the size and distance of stars, that we can form no idea of them.