|Introduction to Organismal Biology (BIOL221) - Dr. S.G. Saupe; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; firstname.lastname@example.org; http://www.employees.csbsju.edu/ssaupe/|
Vegetative Structure & Function
I. General Terms II. Plant Cells
(remember the hierarchy of biological
organization? cells → tissues
→ organs) A. Plant Cells: Water balloons
in a box
Consider a water balloon inside a cardboard box. This is a good model for a plant cell. Thus, there are two major components to a plant cell: (1) the box which is analogous to the cell wall, and (2) the water balloon which is analogous to the cytoplasm or protoplast. The protoplast is everything inside the cell wall. It is the "living" part of the cell and includes the cytoplasm, nucleus, vacuole, and other goodies. Like a cardboard box, the cell wall is relatively rigid, it is non-living and highly structured. Its more obvious functions are to support and protect the cell. It is produced by the protoplast.
I. General Terms
II. Plant Cells (remember the hierarchy of biological organization? cells → tissues → organs)
A. Plant Cells: Water balloons
in a box
Putting a cell in a box presents a problem - how do cells talk to one another since they are now effectively isolated in their own small compartment? Plants solved this problem by putting windows in the box! Or in other words, there are lots of specialized pores through the wall called plasmodesmata that provide a cytoplasmic connection ("cytoplasmic bridges") between adjacent plant cells. The plasmodesmata are 40-50 nm in diameter. The maximum sized object that can pass through as a molecular mass of 700-1000 daltons, which is equivalent to a molecule 1.5 - 2.0 nm. Thus, the cytoplasm of a plant is essentially contiguous throughout the entire plant. Imagine hopping on board a tiny submarine like in the films Fantastic Voyage or Innerspace. You can essentially travel from cell-to-cell throughout the plant without ever leaving the cytoplasm or crossing any cell membranes. Cool!
B. Separating the balloon from the box
(not on exam)
Just as you can remove a balloon from a box, so too can a plant physiologist liberate the protoplast from the cell wall. This is accomplished by slicing up a leaf (or other tissue) and then floating it in a solution containing wall-digesting enzymes like cellulase suspended in an inert osmotic agent in a buffered solution. The enzymes degrade the components of the cell wall releasing the protoplasts.
C. Wall Structure
wall components - All walls contain cellulose, pectins, hemicelluloses, proteins. Many walls are further strengthened by a 'hardening agent' called lignin. Some walls are waterproofed with waxy materials such as suberin
primary vs. secondary
formation - the wall is constructed by the protoplast. For most of the wall materials, they are built somewhere within the cell (i.e., proteins via ribosomes; hemicellulose and pectins in Golgi) and then packaged in vesicles that fuse with the cell membrane to release their contents into the wall (=exocytosis). Cellulose is too big to be packaged and transported so the enzymes necessary for making cellulose are moved to the cell membrane where the cellulose is made in situ. Since the wall is produced by the protoplast, this means that the wall is made from the outside in. Or in other words, the oldest region of the wall is the outmost area. And, as the wall is made, the space available for the protoplast decreases.
D. Cell Types
E. Consequences of having a cell wall
III. Plant Tissues
A. Why do plant cells stick together?
Returning to our balloon in box model, if you stack up a bunch of boxes you generally cant make a very large tower before it comes crashing down. Since a plant is essentially constructed of numerous small boxes, why dont they fall apart, too? The answer is glue! Plants glue their cells together with pectic polysaccharides (pectins). These carbohydrates, which make up the outermost layer of the plant cell wall, which is called the middle lamella, bind adjacent cells together. Cooks use pectins extracted from the middle lamella to solidify jams and jellies.
IV. Major Vegetative Organs
There is often no clear anatomical distinction between leaf and stem. The
is the junction of the root and stem. A shoot is a stem with leaves. V. Roots A. Structure
There is often no clear anatomical distinction between leaf and stem. The crown is the junction of the root and stem. A shoot is a stem with leaves.
C. Roots as food
D. Mycorrhizae - fungal interactions with plant roots
Botanically, a stem is the structure to which the leaves and roots are attached. The stem supports the plant and is characterized by having buds and leaves.
- node region to which a leaf is attached
- internode region between nodes
- bud found at base of leaf, immature shoot system
- axillary (or lateral) bud bud at base of leaf, along stem
- terminal bud bud at end of stem
- bud scales protective covering over bud, modified leaves
- bud scale scar scar left on stem where the terminal bud scales fell off
- leaf scar scar left on stem where leaf detached
- lenticel areas on stem for gas exchange
- vascular bundle scar in leaf scar, where vascular bundle went into leaf
B. Specialized Types
- rhizome (ginger)
- stolon (strawberry)
- bulb (onion)
- corm (gladiolus)
- tuber (potato)
C. Stems As Food
We typically think of stems as growing above the ground, but as we discussed earlier, some specialized types of stems (i.e., tubers, rhizome, corm, bulb) grow underground.
- Aerial stems - asparagus, bamboo, kohlrabi
- Tubers � white potato, yams
VII. Stem Anatomy
A. Herbaceous Stems - pith, vascular bundles, xylem, phloem, vascular cambium
B. Woody Stems
C. Hardwood vs. softwood
These terms refer to the species of tree from which the wood is obtained. Hardwoods are angiosperm (flowering) trees like the oaks, birches, maples, and basswood. Softwoods refer to conifers (gymnosperms) like pines, firs, and spruces. These terms are also roughly equivalent to the degree of "hardness" of the wood. In general, the hardwoods have harder wood than softwoods. However, there are hardwoods with "soft" wood such as basswood and the poplars, and similarly there are softwoods with relatively "hard" wood like southern yellow pine. The following table compares the two:
|Comparison of hardwood and softwood|
|species||Conifers (gymnosperms)||Flowering trees (angiosperms)|
|cell types||Tracheids only||Vessels & tracheids|
|hardness||"soft" easily split||"hard"|
|uses||Building, paper||Furniture, fuels|
D. Wood Appearance (not on exam)
1. Cuts � the "Jelly Roll" or Onion Model
- Transverse (Cross) Section � across the stem, perpendicular to the long axis; annual growth rings appear as concentric circles
- Radial Section � parallel to the long axis, through the center; grain pattern a series of parallel lines
- Tangential Section � parallel to the long axis, anywhere but through the center; grain pattern wavy and variable, not all parallel
- Quarter-sawn � radial cuts � note grain pattern (linear with perpendicular rays)
- Plain-sawn � tangential cuts � not grain pattern ("wavy")
- due to annual rings and cell structure
- runs in the direction of the tree
- coarse grained wood usually with conspicuous annual rings, large pores
E. Lessons from Wood (not on exam)
Wood structure has helped to solve several crimes including the conviction of Bruno Hauptmann for the abduction and murder of Charles Lindbergh�s infant son. By carefully studying the anatomical structure of the wood in the ladder left at the scene of the crime, technologist Arthur Koehler, was able to determine that:
- The ladder was constructed from scraps of ponderosa pine, Douglas fir and birch
- Part of the ladder had been constructed from wood removed from a joist in Hauptmann�s attic
- The edge of one of the rails had been smoothed by a plane found in Hauptmann�s toolbox.
2. Past History � Dendrochronology
Trees rings provide a window on the past. Tree rings can be used to:
- Date archaeological artifacts by comparing tree rings in wood samples taken from the site with rings of known age.
- Monitor climate trends can be monitored since the ring width in many species is sensitive to growth conditions (i.e., temperature, moisture, carbon dioxide concentration).
- Determine past geological events like volcanic activity, sunspots, fire
- Determine past forest types (i.e., alder wood wheels on ancient carts were much larger than those of trees today, canoe from bog 50 foot log � none that big today)
A . Parts
- blade main photosynthetic part
- petiole fancy term for the leaf stalk
- stipules appendage are base of petiole in some leaves. Stipules can be glandular, leafy, spiny, or scale-like. In many cases, the stipules fall off shortly after the leaf expands. Many plants completely lack stipules.
B. Leaf structure: The leaf blade may be all one section or broken up into smaller sections (called leaflets)
C. Function: Photosynthesis (= food production). Leaves are well-adapted for photosynthesis:
- broad - light & carbon dioxide absorption
- flat (thin) - light penetration, carbon dioxide diffusion
- pores (stomata) - carbon dioxide uptake, minimize water loss
- cuticle - prevent water loss
- veins (xylem/phloem) - water/nutrient transport, help support thin leaves
D. Specialized Leaves leaves may be modified in a variety of different ways. For example, the leaves of carnivorous plants are modified into traps. Tendrils are common in vines and used for support. Tendrils can actually be derived from modified leaves or stems
E. Leaves as food - Crops can be derived from the leaf blade ("greens") or petiole
Greens (leaf blade) - spinach, lettuce, parsley, endive, kale, beet greens, swiss chard, dandelion, amaranth, etc.
Leaf Stalk (petiole) - celery, rhubarb
Onion group - onion, garlic, leek. The tubular leaves of chives and other onions are often eaten. Also, a bulb, which we classified as a stem, is actually made up of the fleshy bases of the onion leaves attached to a small stem. Thus, even though onions are described as modified stems, the leaf base is the major part that is eaten.
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Last updated: January 28, 2009 � Copyright by SG Saupe