Chapter 29 – Plant Tissue

Types of Plant Tissue

A. Complex plant tissue can fit into three systems, depending upon function:

1. Vascular Tissue System - used to move fluids and solutes throughout the plant. The two main types are xylem (made of cells that conduct water up the plant; consists of both tracheid cells and vessel members) and phloem (made of living cells that conduct the products of photosynthesis down the plant).

2. Dermal Tissue System – protective coat on outside of plant. Many dermal cells are specialized in leaves, but almost all plant dermal tissue has a cuticle coating (waxy layer for water retention).

3. Ground Tissue System – Most of plant; photosynthetic, storage, support, etc.

B. Simple plant tissue can be classified based on cell characteristics:

1. Parenchyma – Living cells with thin cell walls; can still divide; cells associated with primary growth; PHOTOSYNTHESIS and STORAGE.

2. Schlerenchyma – Usually dead when mature, these cells have thick walls of lignin (a strong and waterproof carbohydrate). SUPPORT and TRANSPORT.

3. Collenchyma – More common in growing areas of plants, these living cells are flexible and are part of veins and ribs. FLEXIBLE SUPPORT.

II. Monocots vs. Dicots: For the rest of the plant unit, we will be drawing a

distinction between monocotyledons and dicotyledons, the two main

divisions of angiosperms. The differences between the two groups represent a

fundamental division between two large groups of vascular plants. The names

come from the fact that each monocot has one cotyledon (or seed leaf) while

each dicot has two cotyledons (think of the two parts of a been seed).

Monocots Dicots

Seed Cotoleydon(s) 1 2

Venation Parallel Net-like

Flower Parts 3(s) 4-5(s)

Vascular Bundles Evenly distributed Around outer

edge of plant

III. Regions of Growth in Plants:

A. Apical Meristem: Most shoots grow from the tip, an area known as the

apical meristem. The elongation of a plant is known as primary growth.

B. Vascular meristem/cambium: Plants also grow outward due to division of

the vascular cambium. In dicots, there is a ring of vascular meristem tissue towards the outside of a plant shoot, while monocots have tissue evenly spread out over the entire shoot diameter.

C. Relevant vocabulary: In dicots, the interior of a shoot is divided into a few regions: at the center is the pith (can be used for storage of water and nutrients), vascular bundle, the cortex, and epidermis. In monocots, the vascular bundles are evenly distributed within the stem of the plant.

IV. Structure of Leaf:

A leaf is a plant structure designed to capture sunlight and absorb carbon

dioxide. Study the picture on page 507 and understand the value of the

following leaf features:

A. Leaf Epidermis: The epidermis is usually covered by a waxy cuticle that

prevents water loss.

B. Mesophyll: Just beneath the epidermis is usually a layer of tightly packed

cells packed with chloroplasts. These cells make up the palisade

mesophyll layer (think of the vertical formations at Palisades park).

Under this layer is a layer of mesophyll cells with large spaces between

the cells, known as the spongy mesophyll layer. The "sponge" cells soak

up carbon dioxide and releases oxygen.

C. Stoma (Stomata plural): These are openings in a leaf that allow carbon

dioxide in (and, at the same time, water out) so the leaf can

photosynthesize. A stoma is surrounded by guard cells that can prevent

gas/water exchange when conditions are unfavorable.

D. Veins: The veins in a leaf are vascular bundles (bunches of xylem and phloem) supported by collenchyma cells.

V. Structure of Roots

Roots come in a few "styles." Taproot systems have a central root (think carrot) with root hairs (small extensions to expand surface area) extending off the root, while fibrous systems (think grass) consist of a large bunch of small, fine roots to absorb nutrients and water.

A. Roots of dicots: In the roots, the vascular bundles of a dicot are arranged

in the form of "X", with large xylem cells making up most of the X and

small phloem cells filling the gaps between the arms of the X.

B. Roots of monocots: In the roots, the vascular bundles occur in a ring

formation (almost the opposite of the stems, in which dicots have the

vascular ring).

VI. Wood Tissue

Wood is unique in that the previous year’s xylem remains intact. Almost all trees are dicots, so the vascular bundle (vascular cambium) grows just under the bark. As the tree grows outwards, the vascular bundles adds xylem to the inside and phloem to the outside. The annual rings left in a tree are visible because spring wood leaves large xylem cells while later summer growth is characterized by smaller xylem cells. The interior of a tree may contain old xylem that is no longer used, known as heartwood. The famous chimney tree in California remains alive because it still has its vascular bundles, it is only missing the heartwood. The sapwood is the lighter wood between the vascular bundle and the heartwood.