An Overview of the Plant Kingdom

1. An Overview of the Plant Kingdom The relationship of plant groups is shown below Gymnosperms Mosses Ferns Angiosperms Green Algae

2. The Diversity of Plants Cone-bearing plants760 species Floweringplants235,000 species Ferns andtheir relatives11,000 species Mosses andtheir relatives15,600 species Go to Section:

3. Trends in Plant Evolution An important trend in plant evolution is the reduction in size of the gametophyte and the increasing size of the sporophyte.

4. Compare/Contrast Table Comparing Features of Seed Plants Feature Seeds Reproduction Examples Gymnosperms Angiosperms Bear their seeds on cones Can reproduce without water; male gametophytes are contained in pollen grains; fertilization occurs by pollination Conifers, cycads, ginkgoes, gnetophytes Bear their seeds within flowers Can reproduce without water; male gametophytes are contained in pollen grains; fertilization occurs by pollination Grasses, flowering trees and shrubs, wildflowers, cultivated flowers Go to Section:

5. Root, Stem, and Leaf Tissues Leaf Stem Root Dermal tissue Vascular tissue Ground tissue

6. The Structure of a Root Endodermis Root hairs Ground tissue (cortex) Phloem Epidermis Xylem Endodermis Vascular cylinder Zone of maturation Zone of elongation Apical meristem Root cap Epidermis Ground tissue(cortex) VascularCylinder Cross Section of Plant Root(magnification: 40x)

7. Water Transport in a Root Epidermis Endodermis Cortex Casparian strip Cell wall Root hairs Cortex Cell membrane Active transportof minerals Phloem Xylem Movement of water by osmosis VascularCylinder

8. The Internal Structure of a Leaf Cuticle Veins Epidermis Palisademesophyll Xylem Vein Phloem Spongymesophyll Epidermis Stoma Guardcells

9. Gas Exchange Leaves take in carbon dioxide and give off oxygen during photosynthesis. When plant cells use the food they make, the cells respire, taking in oxygen and giving off carbon dioxide. Plant leaves allow gas exchange between air spaces in the spongy mesophyll and the exterior by opening their stomata.

10. Homeostasis If stomata were kept open all the time, water loss due to transpiration would be so great that few plants would be able to take in enough water to survive. Plants maintain homeostasis by keeping their stomata open just enough to allow photosynthesis to take place but not so much that they lose an excessive amount of water.

11. Homeostasis Guard cells,shown in the figure, are highly specialized cells that surround the stomata and control their opening and closing. Guard cells regulate the movement of gases into and out of leaf tissues.

12. Homeostasis Carbon dioxide can enter through the open stomata, and water is lost by transpiration.

13. Homeostasis When water is abundant, it flows into the leaf, raising water pressure in the guard cells, which opens the stomata. The thin outer walls of the guard cells are forced into a curved shape, which pulls the thick inner walls away from one another, opening the stoma.

14. Homeostasis When water is scarce, water pressure within the guard cells decreases, the inner walls pull together, and the stoma closes. This reduces further water loss by limiting transpiration.

15. How Cell Walls Pull Water Upward Water molecules are attracted to one another by a force called cohesion. Water cohesion is especially strong because of the tendency of water molecules to form hydrogen bonds with each other. Water molecules can also form hydrogen bonds with other substances. This results from a force called adhesion, which is attraction between unlike molecules.

16. Transpiration Transpiration is the loss of water through leaves. This lost water may be replaced by water drawn into the leaf through xylem vessels in the vascular tissue. Transpiration helps to cool leaves on hot days, but it may also threaten the leaf’s survival if water is scarce, as seen in this wilting plant.

17. An Analogy for Transpirational Pull Imagine a chain of clowns who are tied together and climbing a tall ladder. When the first clown reaches the top, he falls off, pulling the clowns behind him up and over the top. Similarly, as water molecules exit leaves through transpiration, they pull up the water molecules behind them.

18. Transpiration A B Evaporation of water molecules out of leaves. Pull of water molecules upward from the roots.

19. Transpiration A B Evaporation of water molecules out of leaves. Pull of water molecules upward from the roots.

20. How Cell Walls Pull Water Upward The tendency of water to rise in a thin tube is called capillary action. Water is attracted to the walls of the tube, and water molecules are attracted to one another. The thinner the tube, the higher the water will rise inside it, as shown in the figure.

21. Root Pressure Demonstration In this setup, a glass tube takes the place of the carrot plant’s stem and leaves. As the root absorbs water, root pressure forces water upward into the tube.This is also known as osmotic pressure.

22. The Structure of a Flower Stamen Carpel Stigma Anther Style Filament Ovary Petal Ovule Sepal

23. Seed coat Seed Embryo Wing Storedfood supply The Structure of a Seed B A Go to Section:

24. Secondary Growth in Stems Primaryphloem Bark Secondaryphloem Cork Epidermis Corkcambium Secondary xylem Cortex Wood Primaryxylem Primaryphloem Secondaryphloem Vascularcambium Secondary xylem Primaryxylem Pith A. Vascular cambium appears B. Secondary growth continues C. Mature stemdevelops

25. Layers of a Tree Trunk Contains old, nonfunctioning phloem that protects the tree Produces protective layer of cork Contains old, nonfunctioningxylem that helpssupport the tree Transports sugars produced by photosynthesis Produces new xylem and phloem, which increase the width of the stem Contains active xylem that transports water and minerals Wood Bark Cork Xylem:Heartwood Cork Cambium Phloem Vascular Cambium Xylem: Sapwood

26. Tree Rings When growth begins in the spring, the vascular cambium begins to grow rapidly, producing large, light-colored xylem cells, resulting in a light-colored layer of early wood. As the growing season continues, the cells grow less and have thicker cell walls, forming a layer of darker late wood. This alternation of dark and light wood produces what we commonly call tree rings.

27. Auxins and Phototropism Highconcentrationof auxin Lowconcentrationof auxin Control Tipremoved Opaquecap Clearcap Opaque shiedover base

28. Apical Dominance Apical meristem Lateral buds Auxins produced in the apical meristeminhibit the growth of lateral buds. Apical meristem removed Without the inhibiting effect of auxinsfrom the apicial meristem, lateral budsproduce many branches.

29. Ethylene In response to auxins, fruit tissues release small amounts of the hormone ethylene, which stimulates fruits to ripen.

30. Ethylene Ethylene also causes plants to seal off and drop organs that are no longer needed, for example, petals after flowers have been pollinated, leaves in autumn, and ripened fruits. Ethylene signals cells at the base of the structure to seal off from the rest of the plant by depositing waterproof materials in their walls.

31. Winter Dormancy Phytochrome also regulates the changes in activity that prepare many plants for dormancy as winter approaches. As cold weather approaches, deciduous plants turn off photosynthetic pathways, transport materials from leaves to roots, and seal off leaves from the rest of the plant.

32. Leaf Loss Many flowering plants lose their leaves during the colder months. The phytochrome in leaves absorbs less light as days shorten and nights become longer. Auxin production drops, but the production of ethylene increases.

33. Leaf Loss As chlorophyll breaks down, other pigments—including yellow and orange carotenoids—become visible for the first time. The brilliant reds come from anthocyanin pigments that are freshly made.

34. Plant Propagation To propagate plants with desirable characteristics, horticulturists use cuttings or grafting (shown) to make many identical copies of a plant or to produce offspring from seedless plants.

35. Plant Propagation One of the simplest ways to reproduce plants vegetatively is by cuttings. A grower cuts from the plant a length of stem that includes a number of buds containing meristem tissue. That stem is then partially buried in soil or in a special mixture of nutrients that encourages root formation.

36. Plant Propagation Grafting is a method of propagation used to reproduce seedless plants and varieties of woody plants that cannot be propagated from cuttings. To graft, a piece of stem or a lateral bud is cut from the parent plant and attached to another plant, as shown.

37. Plant Propagation Grafting works only when the two plants are closely related, such as when a bud from a lemon tree is grafted onto an orange tree. Grafting usually works best when plants are dormant, which allows the wounds created by the cut to heal before new growth starts.

38. Tropisms Plants respond to environmental stimuli such as light, gravity, and touch. Plants have sensors that detect the direction of stimuli and signal elongating organs to orient their growth toward or away from these stimuli. These growth responses are called tropisms.

39. Light The tendency of a plant to grow toward a light source is called phototropism. Changes in the concentration of auxins are responsible for phototropism. Experiments have shown that auxins migrate toward shaded tissue, possibly due to changes in membrane permeability in response to light.

40. Gravity Auxins also affect gravitropism, the response of a plant to gravity. Auxins migrate to the lower sides of horizontal roots and stems. In horizontal stems, the migration causes the stem to bend upright. In horizontal roots, however, the migration causes roots to bend downward.

41. Touch Some plants respond to touch, a process called thigmotropism. Vines and climbing plants exhibit thigmotropism when they encounter an object and wrap around it. Other plants, such as grape vines, have extra growths called tendrils that emerge near the base of the leaf and wrap tightly around any object they encounter.

42. Changes in Agriculture Improvements in farming techniques have contributed to dramatic improvements in crop yields, as shown in the graph.

43. Changes in Agriculture Some of the most important techniques have involved the use of fertilizers and pesticides. Fertilizers are labeled with three numbers that reflect the percentage by weight of three elements: nitrogen (N), phosphorus (P), and potassium (K).

44. Changes in Agriculture Fertilizers and pesticides must be used with great care. Overfertilizing can kill crop plants by putting too high a concentration of salts into the soil. The intensive use of fertilizers can also affect the ground water. When large amounts of nitrogen- and phosphate-containing fertilizer are used near wetlands and streams, runoff from the fields may contaminate the water. Chemical pesticides are poisons, and they have the potential to harm wildlife and leave dangerous chemical residues in food.

45. Uptake of Plant Nutrients The functions of these essential nutrients within a plant are described below.

46. Annuals, Biennials, and Perennials: Characteristics and Examples