Biology: Semester II

Lab: Plant Structure: the Plant Body :

Intro | Part 1 | Part 2 | Part 3

Lab: Plant Structure: The Plant Body: Part One Examine the bean plant photograph below.  Identify the parts of a leaf, including the flattened blade, the stalk-like petiole that attaches the blade to the stem, and the midrib and veins that help to support the blade and transport water and food to and from the leaf. The region of the stem to which a leaf is attached is the node and the region between two adjacent nodes is called the internode. The angle, which the leaf makes with the stem, is called the axil and in the axil of each leaf you will find a small structure called the axillary bud. Although growth from the axillary bud is usually inhibited, these buds do have the potential to elongate to form a lateral branch. Perform this drag and drop activity to identify the various parts indicated. The axillary bud is useful in identifying a leaf. Some leaves are composed of multiple small leaflets (compound leaves), while others are composed of a single blade (simple leaves). While each leaflet may appear to be an individual leaf, you will not find an axillary bud at its base, only in the axil of the entire compound leaf. So look for an axillary bud and whatever is attached to that node, no matter how complex, should be considered a single leaf. Examine the various leaf samples shown below. Identify simple and compound leaves.  Make a quick sketch of an example of each leaf type, and label the petiole, axillary bud, leaf blade, and leaf veins on each, sketch on a separate sheet of paper. Coffee, simple leaf, entire margin, net veined   Sugar maple, palmately veined, net veined Horse chestnut, palmately compound, net veined. Oak, simple, lobed-edged leaf, net veined. Carya, pinnately compound, net veined. What is the characteristic venation pattern of monocots? What is the characteristic venation pattern of dicots? Sort the leaves shown above into monocots and dicots on the basis of the leaf venation. The arrangement of leaves on the stem can be also be classified either as opposite (leaves are arranged in pairs directly opposite one another on the stem) or as alternate (leaves are not paired and are arranged on alternating sides of the stem). Examine the prepared slide of a Privet leaf shown below. This is a cross section of the leaf with the midrib in the middle and the blade extending out to each side. Notice that the blade is very thin and only a few cell layers thick. All the major tissues of an angiosperm are represented in the leaf: the epidermis, parenchyma (palisade and spongy layers), and the vascular tissue (xylem and phloem). Cross section of a Privet leaf and diagram of parenchyma cells. A generalized plant cell type, parenchyma cells are alive at maturity. They function in storage, photosynthesis, and form the bulk of ground and vascular tissues of a plant. There are many types of parenchyma cells, all specialized to a small degree for their function. Palisade parenchyma cells are elongated cells located in many leaves just below the epidermal tissue. Spongy mesophyll cells are another type of leaf parenchyma cell that occur below the one or two layers of palisade cells. Ray parenchyma cells occur in wood rays, the structures that transport materials laterally within a woody stem. Parenchyma cells also occur within the xylem and phloem of vascular bundles. The largest parenchyma cells occur in the pith region of the stem , often, as in corn (Zea ) stems, being larger than the vascular bundles. In many prepared slides they stain green. What cell organelle would you expect to be abundant in the parenchyma of the leaf? Notice that the palisade layer is close to the upper surface of the leaf while the spongy parenchyma is in close proximity to the lower epidermis. The numerous air spaces in the spongy layer assure that all cells of the leaf are in close proximity to atmosphere gases. What gas is necessary for photosynthesis to occur? What gas is a product of photosynthesis? Examine the image of the epidermis of lilac leaf. This slide was prepared by peeling the epidermal layer from a leaf. Paradermal section of lilac leaf, lower leaf epidermis. You should be able to find guard cells and stomata. Are the stomata open or closed? Make a sketch of the guard cells as you see them in the photograph above and as you see them on the privet leaf  cross-sectional image. Procedures: Obtain one or two stalks of celery.  Use a sharp knife and slice cleanly across the bottom of the celery stalk. Repeat the process at least once on another stalk. Place the cut stalks into a glass. Add water and red food coloring solution to the glass, at least one inch deep of solution. Place the glass and stalks in a sunny spot, and check back periodically. Once the red color has risen at least half-way up the stalk, place one of these stalks on a plat or cuttingboard and slice as thin a slice as you can across the stalk base.  Place this small slice on a clean plate and observe the slide with a magnifying glass. Do you see any cells? Make a sketch below of what you see. Back Next

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