Plant Diversity

1. Plant Diversity Chapter 22

2. 22.1 Objectives • What is a plant? • What do plants need to survive? • How did the first plants evolve?

3. What Is a Plant? • What Is a Plant? • Plants are multicellular eukaryotes that have cell walls made of cellulose. • Plants develop from multicellular embryos and carry out photosynthesis using the green pigments chlorophyll a and b.

4. What Is a Plant? • Plants include trees, shrubs, and grasses, as well as other organisms, such as mosses and ferns. • Most plants are autotrophs, although a few are parasites or saprobes that live on decaying materials.

5. What Plants Need to Survive • What Plants Need to Survive • In order to survive, plants need: • sunlight • water and minerals • gas exchange • transport of water and nutrients throughout the plant body

6. What Plants Need to Survive • Sunlight • Plants use energy from sunlight to carry out photosynthesis. • Photosynthetic organs such as leaves are broad and flat to maximize light absorption.

7. What Plants Need to Survive • Water and Minerals • All cells require a constant supply of water. • Water is used up quickly when the sun is shining. As a result, plants have structures that limit water loss.

8. What Plants Need to Survive • As they absorb water, plants also absorb minerals. • Minerals are nutrients in the soil needed for plant growth.

9. What Plants Need to Survive • Gas Exchange • Plants require oxygen to support cellular respiration as well as carbon dioxide to carry out photosynthesis. • They must exchange these gases with the atmosphere without losing excessive amounts of water through evaporation.

10. What Plants Need to Survive • Movement of Water and Nutrients • Plants take up water and minerals through their roots, but they make food in their leaves. • Most plants have specialized tissues that carry water and nutrients from the soil and distribute products of photosynthesis throughout the plant body. • Simpler plants carry out these functions by diffusion.

11. Early Plants • How did the first plants evolve? • The First Plants • DNA sequences confirm that plants are closely related to certain groups of green algae, suggesting that the ancestors of the first plants were indeed algae.

12. Overview of the Plant Kingdom • Overview of the Plant Kingdom • Plants are divided into four groups and are Seed-Less Plants 1. Mosses and their relatives • Non vascular 2. Ferns and their relatives • Vascular Seed-Bearing Plants Vascular 3. Cone-bearing plants 4. Flowering plants

13. How are they Placed into the 4 Groups They are placed into these groups according to these features: • water-conducting tissues • seeds • flowers • Plants are also classified by other features, including reproductive structures and body plan.

14. Overview of the Plant Kingdom • Evolutionary Relationships Among Plants Flowering plants Cone-bearing plants Ferns and their relatives Flowers; Seeds enclosed in fruit Mosses and their relatives Seeds Water-conducting (vascular) tissue Green algae ancestor

15. Overview of the Plant Kingdom • Today, scientists can classify plants more precisely by comparing the DNA sequences of various species.

16. Learning Targets 22.2 • Describe the adaptations of bryophytes (mosses and their relatives) • Identify the three groups of bryophytes

17. Bryophytes(mosses and their relatives) • Mosses and their relatives are called bryophytes, or nonvascular plants. • They do not have vascular tissues, or specialized tissues that conduct water and nutrients.

18. Bryophytes(mosses and their relatives) • Describe the adaptations of bryophytes • Bryophytes have life cycles that depend on water for reproduction. • Bryophytes draw up water by osmosis only a few centimeters above the ground. • Bryophytes are low-growing plants found in moist, shaded areas.

19. Bryophytes (mosses and their relatives) • Identify the three groups of bryophytes • The three groups of bryophytes are: • mosses • liverworts • hornworts

20. Bryophyte: Mosses • Mosses • The most common bryophytes are mosses. • Mosses: • are adapted to life in wet habitats and nutrient-poor soils. • can tolerate low temperatures. • are clumps of gametophytes growing together.

21. The Structure of a Moss • Each moss plant has a shoot that looks like a stem with leaves. • These are not true stems or leaves, because they do not contain vascular tissue.

22. Bryophyte: Mosses • The “leaves” of mosses are one cell thick, so they lose water quickly if the surrounding air is dry. • Mosses have rhizoids, which are long cells that anchor them in the ground and absorb water and minerals from the soil. • Water moves through rhizoids and into the rest of the plant.

23. Bryophyte: Mosses • Human Use of Mosses • Sphagnum mosses thrive in the acidic water of bogs. • Dried sphagnum acts as a natural sponge. It can accumulate to form peat deposits. • Peat can be cut from the ground and used as fuel. • Peat can be used to improve the soil’s ability to retain water and to increase soil acidity.

24. Sphagnum Moss • Peat Moss

25. Bryophyte: Liverworts • Liverworts • Liverworts’ have broad, thin structures that draw up moisture from the soil surface. • Mature liverworts have structures that look like tiny green umbrellas. • These carry the structures that produce eggs and sperm.

27. Bryophyte: Hornworts • Hornworts • Hornworts are found only in soil that is damp nearly year-round. • They have structures that look like those of liverworts. • The hornwort has what looks like a tiny green horn.

29. Learning Targets 22.3 • How is vascular tissue important to ferns and their relatives? • What are the characteristics of the three phyla of seedless vascular plants?

30. Evolution of Vascular Tissue • The first vascular plants were the first to have vascular tissue. • That is they had a new type of cell that was specialized to conduct water. • The first vascular plants contained tracheids which are cells specialized to conduct water. • Tracheids make up xylem, a transport subsystem that carries water from the roots to every part of a plant.

31. Evolution of Vascular Tissue • Tracheids are hollow with thick cell walls that resist pressure. • They connect end to end to allow water to move efficiently.

32. Evolution of Vascular Tissue • Vascular plants have a second transport subsystem composed of vascular tissue called phloem. • Phloem transports solutions of nutrients and carbohydrates produced by photosynthesis.

33. Evolution of Vascular Tissue • How is vascular tissue important to ferns and their relatives?

34. Evolution of Vascular Tissue • Both xylem and phloem can move fluids through the plant body, even against the force of gravity.

35. Evolution of Vascular Tissue • Together xylem and phloem move water, nutrients, and other materials throughout the plant. • In many plants, xylem and lignin (a substance that makes cell walls rigid) enable them to grow upright and tall.

36. Ferns and Their Relatives • What are the characteristics of the three phyla of seedless vascular plants?

37. Ferns and Their Relatives • Seedless vascular plants include: • club mosses • horsetails • ferns

38. Ferns and Their Relatives • Ferns and Their Relatives • The most numerous phylum is the ferns. • Ferns and their relatives have true roots, leaves, and stems. • Do we need to review these?

39. Ferns and Their Relatives • Club Mosses • Ancient club mosses grew into trees and produced forests. • Fossilized remains of these exist today as huge beds of coal. • Today, club mosses are small plants that live in moist woodlands.

41. Ferns and Their Relatives • Horsetails • The only living genus of Arthrophyta is Equisetum. • Equisetum has true leaves, stems, and roots. • Equisetum is called horsetail, or scouring rush.

43. Ferns and Their Relatives • Ferns • Ferns probably evolved 350 million years ago, when club moss forests covered Earth. • Ferns thrive in wet areas with little light.

45. Life Cycle of Ferns Ferns have vascular tissues, strong roots, underground stems called rhizomes, and leaves called fronds.

46. Life Cycle of Ferns • The Underside of a Fern Frond Sporangia Sorus

47. Learning Targets 22.4 • What adaptations allow seed plants to reproduce without standing water? • What are the four groups of gymnosperms?

48. Seed-Bearing Plants • Seed plants are divided into two groups: • Gymnosperms bear seeds directly on the surfaces of cones. • Angiosperms, or flowering plants, bear seeds within a layer of tissue that protects the seed.

49. Seed-Bearing Plants • Gymnosperms include conifers, cycads, ginkgoes, and gnetophytes. • Angiosperms include grasses, flowering trees and shrubs, and all species of flowers.

50. Seed-Bearing PlantsReproduction • Reproduction Free From Water • They do not need water for fertilization of gametes. • Seed plants can live just about anywhere.