Brian McCauley 12/13/07 Page 1 of 1 PLANTS II: VASCULAR PLANT STRUCTURE & FUNCTION Bio 6A/Sanhita Datta Winter 2008 The first plant lab presented you with the main groups of plants: nonvascular plants, vascular non-seed plants, and the two groups of vascular seed plants (gymnosperms and angiosperms). Today’s lab is designed to demonstrate some of the detailed structures of vascular seed plants and to show how some of these structures work.  Reading: Campbell, Ch. 35. BASIC FEATURES OF VASCULAR PLANTS Each cell of a vascular plant is no more complex than an algal (protist) cell, and yet plant bodies are much more complex than protists. This complexity is at the level of tissues and organs. Vascular plants are more complex in their body organization than non-vascular plants, and are much more complex than photosynthetic protists such as seaweeds. Tis su es A tissue is a group of cells with similar appearance and function. Plants have three tissue systems: • Dermal tissues cover the entire outside of the plant – roots, stems, and leaves. Dermal tissues include the epidermis of leaves and green stems and the outer layer of bark in woody plants. • Vascular tissues transport water and other molecules throughout the plant body. Vascular tissues include xylem and phloem, which you’ll study in detail later. • Ground tissues make up the rest of the plant, including the cells responsible for photosynthesis inside the leaves. Org a ns An organ is a structure that carries out a particular function and contains several kinds of tissues. For example, a leaf is an organ; leaves have several kinds of tissues. Vascular plants have three basic kinds of vegetative (non-reproductive) organs: leaves, stems, and roots. In this lab, you’ll look at some of the wide variety that exists within each of these categories in terms of structure and function. Ho w p la nt s g r ow You may remember from the last lab that the large, long-lived part of a vascular plant life cycle is the diploid sporophyte. A sporophyte begins as a zygote (a fertilized egg). The development of the adult plant body from the zygote requires two processes: cell proliferation to make new cells and differentiation to give those cells their proper identity. (Later, you’ll see that both these processes also occur in animal development, but in a very different way.) Plant growth is generally confined to meristems, which are regions of the plant body specialized for growth. There are meristems in the roots and in the shoot (the part above ground). ApicalBrian McCauley 12/13/07 Page 2 of 2 meristems at the tips of roots and stems make the plant grow longer and produce leaves. This is called primary growth; it produces all the tissue types in a plant. Woody plants get thicker by adding rings of secondary growth at lateral meristems. You’ll see how this works later in this lab. Plants have indeterminate growth. This means that they can continue growing throughout their lives, can change their growth pattern in response to their environment, and can replace parts that get damaged. Animal growth is normally determinate; growth only occurs up to a specific size. Individual plant organs such as leaves also show determinate growth. LEAVES Leaves are what plants are all about; they are the sites of photosynthesis and gas exchange. The leaves of seed plants contain several different specialized types of cells, which interact to make a functioning leaf. You should become familiar with each type of cell and what it does.  Observe the whole leaves of various land plants. While these leaves show a variety of shapes, they all do more or less the same job. Some of the differences in shape can be understood in terms of the conflicting requirements that leaves face: absorbing light, exchanging gases, avoiding dehydration, avoiding predation. Break off a small piece of a leaf and look at it under the microscope; you should be able to identify dermal, ground, and vascular tissue. Which leaves are simple, and which are compound? Within the flowering plants (angiosperms), there are two large groups with different styles of leaves. Dicots (roses, for example) have leaves with a netlike, branching system of veins. Monocots (grasses, for example) have parallel veins. Later in this lab you’ll see more differences between dicots and monocots. See Campbell, p. 603 for a summary of monocots and dicots.  Observe the prepared slides of Syringa (Lilac) leaf cross section. Study fig. 35.17 in Campbell along with this slide. You should be able to recognize and describe the function of these parts of a leaf cross-section: • epidermis (dermal tissue)Brian McCauley 12/13/07 Page 3 of 3 • cuticle (this is a layer outside the cells; it’s not a tissue) • stoma (plural: stomata) • guard cells (dermal tissue) • mesophyll (ground tissue) • vascular bundles, containing: • xylem (vascular tissue) • phloem (vascular tissue) Note that all these cells share some features that mark them as typical plant cells: they are very large compared to animal cells, they are contained in a boxlike cell wall, and most of the volume of the cell is filled with a membrane-bound storage organelle, the central vacuole. The vascular bundles contain two types of vascular tissue. Phloem transports photosynthetic products from the leaves to the rest of the plant, and xylem carries water and inorganic nutrients up from the roots to the rest of the plant.  Observe the prepared slides of Zea (corn) leaf cross-section and longitudinal section. Corn is a monocot, and a member of the grass family. It contains all the features listed above for Syringa leaves, but with two notable differences. First, corn leaves have parallel veins. This means that in a leaf cross-section, you’ll see all the veins cut straight across. (In a leaf with reticulate venation, some of the veins will be cut straight across, and some will be cut at an angle.) The parallel venation of Zea leaves should also be obvious in longitudinal sections. The other notable way that Zea leaves differ from those of Syringa is that the vascular bundles in Zea are surrounded by bundle