Lecture Outline - Chapter 9

9.1. The Flowering Plant (p. 146)

1. Over 80% of living plants are flowering plants (angiosperms).
2. The vegetative organs of a flowering plant include the root, stem, and leaf. (Fig. 9.1)
   • a. Root systems:
     • i. The root system is generally equal in size and area to the aboveground stems and branches.
     • ii. Roots anchor the plant in soil, absorb water and minerals (which are transported in the stem to the leaves), and store sugar as starch.
     • iii. In perennial plants that die back and regrow each year, roots store products of photosynthesis; for example, carrots and sweet potatoes.
   • b. Stems:
     • i. Stems are the main axis of a plant and its lateral branches.
     • ii. Stems display leaves to the best advantage to collect maximum sunlight.
     • iii. Stems transport water and minerals to the leaves and sugar from the leaves down to the roots;
     • iv. Some stems store water (cactus); tubers are horizontal stems that store nutrients.
   • c. Leaves:
     • i. Generally, leaves carry on photosynthesis, requiring water, carbon dioxide, and sunlight. (Fig. 9.1)
     • ii. Leaves receive water from roots via the stem.
     • iii. The wide portion of a leaf is the blade; the petiole is the stalk that attaches blade to stem.
3. Monocots and Dicots (Fig. 9.2)
   • a. Flowering plants are divided into two groups depending on the number of cotyledons or seed leaves in the embryonic plant; seed leaves provide food for growing embryo plants before true leaves begin functioning. A wide range of other features distinguish these two groups.
   • b. Monocots:
     • i. Have vascular bundles scattered in the stem;
     • ii. Have parallel leaf veins;
     • iii. Have flower parts arranged in groups of three or multiples of three; for example, corn, grasses;
     • iv. Have pollen grains with one aperture (thin area in the wall).
   • c. Dicots:
     • i. Have vascular bundles forming a ring in stem;
     • ii. Have veins in leaf that form a netlike pattern;
     • iii. Have flower parts arranged in fours or fives (or multiples); for example, beans, peas;
     • iv. Have pollen grains with three apertures.
   • d. Dicots are a larger group and include many familiar flowering plants, from dandelions to oak trees.
   • e. Monocots include our most significant food sources of rice, wheat, and corn.

1. Meristem tissue in the shoot and root apexes allows the plant to grow throughout its entire life.
2. Dermal Tissue System (Fig. 9.4)
   • a. The outer protective covering consists of epidermal cells that cover and protect inner body parts.
   • b. Waxy cuticle prevents drying out.
   • c. Root hairs on roots increase surface area for absorption of water and minerals.
   • d. In older woody plants, epidermis is replaced by dead cork tissue that was encrusted with waterproof suberin before it died.
3. Ground Tissue System (Fig. 9.5)
   • a. Parenchyma are typical plant cells with primary but no secondary wall. (Fig. 9.5a)
   • b. Collenchyma cells resemble parenchyma except they have thicker primary walls; strands in celery stalks are mostly this cell.
   • c. Sclerenchyma cells are hollow, dead cells with strong walls for support; sclereids are in seed coats and nut shells, and make pears gritty; fibers include hemp for rope and flax for linen.
4. Vascular Tissue System
   • a. Conducts water and nutrients in a plant.
   • b. Xylem transports water and minerals from roots to leaves. (Fig. 9.6a)
     • i. Tracheids are hollow and nonliving at maturity, have pits to transport water.
     • ii. Vessel elements are hollow, nonliving at maturity, and lack end walls
   • c. Phloem transports organic nutrients usually from leaves to roots.
     • i. Sieve-tube cells have cytoplasm but no nuclei, perforated end walls called seive plates; strands of cytoplasm (plasmodesmata) extend from one cell to the other through the seive plate.
     • ii. Companion cells are smaller, each has all cell components including a nucleus, and probably helps seive tube cells transport nutrients.
   • d. Vascular tissue (both xylem and phloem)
     • i. Extends from the root to the leaves and vice versa.
     • ii. In roots, it is located in the vascular cylinder.
     • iii. In the stem, it forms vascular bundles.
     • iv. In leaves, it is found in leaf veins.

1. Functions of Roots (Fig. 9.7)
   • a. Burrow through soil and anchor a plant in soil.
   • b. Absorb water and minerals from soil.
   • c. Store products of photosynthesis received from the leaves.
2. Zones of a Root
   • a. As primary growth occurs, cells differentiate and form three zones:
   • b. Zone of cell division contains apical meristem to add cells for replacement to root cap for protection, and to the zone of elongation above.
   • c. Zone of elongation cells increase in length as they become specialized.
   • d. Zone of maturation cells are mature and differentiated; has root hairs to increase absorptive surface area.
3. Tissues of a Dicot Root (Fig. 9.7b)
   • a. Epidermis
     • i. Single, outermost layer of cells.
     • ii. Many have root hairs.
   • b. Cortex
     • i. Under the epidermis.
     • ii. Large thin-walled parenchyma cells, loosely packed to allow water movement between cells.
     • iii. Cells contain starch granules and function in food storage.
   • c. Endodermis
     • i. Single layer of rectangular cells.
     • ii. Forms boundary between cortex and inner vascular cylinder.
     • iii. Has lignin and suberin barrier (Casparian strip) that only allows water and minerals to pass through the cells (Fig. 9.7c)
   • d. Vascular Cylinder
     • i. Pericycle is first layer in vascular cylinder, able to undergo mitosis to produce branch or secondary roots.
     • ii. Vascular tissue contains xylem, star-shaped in dicots (Fig. 9.7b) and phloem between arms of the xylem.
4. Tissues of a Monocot Root
   • a. Same growth zones as a dicot root, but organized differently.
   • b. Pith (Fig. 9.9) is centrally located ground tissue surrounded by a ring of alternating xylem and phloem bundles.

1. Can be compared to the growth of a root.
2. Primary Growth of Stems (Fig. 9.10)
   • a. Shoot apical meristem produces new cells that elongate.
   • b. Shoot apical meristem is protected within a terminal bud where immature leaves envelope it.
   • c. Terminal bud stops growing in winter in temperate zone and is protected by bud scales, which fall off in the spring.
   • d. Axillary buds may develop into branch shoots.
3. Stems have nodes.
   • a. Nodes are site where leaves or buds are attached.
   • b. Internodes are the length between nodes.
   • c. As stem grows, internodes increase in length.
   • d. Axillary buds are dormant at the axes of leaf primordia; may develop into branch shoots or flowers.
4. Shoot Apical Meristem
   • a. Outermost primary meristem is protoderm, gives rise to epidermis.
   • b. Ground meristem produces two tissues composed of parenchyma cells.
   • c. Pith occurs in center of stem and cortex is located inside epidermis.
5. Procambium produces the first xylem and phloem cells. (Fig. 9.10b)
6. Vascular cambium, a meristem tissue, occurs between xylem and phloem of vascular bundle.
7. Herbaceous Stems
   • a. Are mature nonwoody stems.
   • b. Exhibit only primary growth.
   • c. Outermost tissue is covered with a waxy cuticle to prevent water loss.
   • d. Dicot herbaceous stems have vascular bundles with xylem found to the inside and phloem to outside, arranged in a distinct ring separating cortex from central pith. (Fig. 9.11)
   • e. Monocot herbaceous stems have vascular bundles scattered throughout the stem with no well-defined cortex or pith. (Fig. 9.12)
8. Woody Stems
   • a. Primary growth continues only a short distance behind apical meristem.
   • b. Secondary growth increases the woody plant's girth.
   • c. A woody stem is divided into three distinct areas: the bark, the wood, and the pith. (Fig. 9.13)
   • d. Vascular cambium is meristematic tissue found between xylem and phloem of each vascular bundle; produces secondary xylem and secondary phloem. (Fig. 9.14)
   • e. Both phloem rays and vascular rays store materials and conduct them radially for a short distance.
   • f. Secondary xylem forms annual growth rings.
     • i. Spring wood forms in the spring and has larger xylem cells due to abundance of water.
     • ii. Summer wood has smaller xylem cells due to less moisture.
     • iii. Therefore you can tel the age of a tree by counting annual rings.
     • iv. Sapwood represents the most recently formed xylem layer that functions to transport water.
   • g. Heartwood represents the older inner xylem layers that may become plugged with resin and rot away.
   • h. Cork cambium is located beneath the epidermis; it produces cork cells that are composed of a waterproofing material (suberin).
   • i. Gas exchange occurs locally in lenticels, dead cork cells not impregnated with suberin.
   • j. Bark is composed of cork, cork cambium, cortex, and phloem; secondary phloem does not build up; because phloem is in the bark, removal of bark can seriously damage a tree.
9. Evolution of herbaceous plants may have followed woody plants; perhaps it is advantageous to place energy into reproducing rather than defending itself over longer periods from herbivores and parasites by being woody.

1. Leaves are organs of photosynthesis in vascular plants.
2. Leaves usually consist of a flat blade and a petiole that connects blade to the stem.
3. Blades may be single or composed of several leaflets.
4. Structure of a dicot, temperate zone plant leaf: (Fig. 9.15)
   • a. Leaf veins contain vascular tissue; dicot leaves show a net pattern, a parallel pattern is in monocot leaves.
   • b. Epidermis is covered by a waxy cuticle to prevent leaf from drying out.
   • c. Lower epidermis has openings called stomata which allow for gas exchange.
   • d. Each stoma has two guard cells that regulate its opening and closing.
   • e. Leaf body has inner mesophyll tissues that are site for most leaf photosynthesis.
     • i. Palisade layer cells are elongated.
     • ii. Spongy layer is made of irregular cells bounded by air spaces, loosely packed for greater surface area for gas exchange.
5. Pathways:
   • a. Carbon dioxide enters through stomata into epidermal spaces; diffuses into mesophyll cells and into chloroplasts.
   • b. Oxygen exits the leaf by following the opposite pathway.
   • c. Water enters vascular tissue at roots and is pulled upward to leaves where it exits leaf veins and enters mesophyll, some is evaporated out stomates.
   • d. Carbohydrate is produced in mesophyll and can be stored and used in the cells there; unneeded carbohydrate is transported through vascular tissue to roots and stored in plasmids.

1. Functions of Different Types of Roots:
   • a. Fibrous roots anchor plants such as grass in the soil.
   • b. Taproots or primary roots, as in carrots, often store food.
2. Stem Modifications: (Fig. 9.16)
   • a. Stolons or runners are horizontal stems that produce new plants where they touch the ground; examples include strawberries.
   • b. Vertical stems may be modified for water storage, as in cactus.
   • c. Rhizomes are underground stems that deeply anchor sod, or form thick structures at the surface, as in iris.
   • d. Tubers are enlarged for food storage, as potatoes.
   • e. Corms are bulbous underground stems that supply energy for next year's growth; often called "bulbs" by laypeople, bulbs are technically modified leaves.
3. Leaf Modifications: (Fig. 9.17)
   • a. An onion bulb is leaves surrounding a short stem.
   • b. Tendrils of grape stems, peas and cucumbers wrap around structures to support the vine.
   • c. Insect-catching leaves utilize sticky epidermal hairs (sundew) or hinges that snap shut when sensitive hairs are touched (Venus's fly-trap).
   • d. A wide range of shapes, surface areas, stomate patterns, and physiological variations have adapted leaves to various environmental conditions through evolution.