Chapter 29 Plant Diversity I

26

-The ancestors of modern lycophytes, horsetails, and ferns grew to great heights during the Devonian and Carboniferous, forming the first forests. -Increased growth and photosynthesis removed CO2 from the atmosphere and may have contributed to global cooling at the end of the Carboniferous period. -The decaying plants of these Carboniferous forests eventually became coal.

25

-Vascular plants have two types of vascular tissue: xylem and phloem. -Xylem conducts most of the water and minerals. It also provides structural support (lignin). -Phloem has cells arranged into tubes that distribute sugars, amino acids, and other organic products. -Vascular tissue allowed for increased height, which provided an evolutionary advantage.

16

A seed is an embryo and nutrients surrounded by a protective coat. Seed plants form a clade and can be divided into further clades. Gymnosperms, the naked seed plants, including the conifers. Angiosperm, the flowering plants.

13

Additional derived traits include: 1) Cuticle, a waxy covering of the epidermis. 2) Stomata are specialized cells that allow for gas exchange between the outside air and the plant. 3)Mycorrhizae, symbiotic associations between fungi and land plants that may have helped plants without true roots to obtain nutrients.

8

Alternation of generations Plants alternate between two multicellular stages, a reproductive cycle called alternation of generations. The gametophyte is haploid and produces haploid gametes by mitosis. Fusion of the gametes gives rise to the diploid sporophyte, which produces haploid spores by meiosis.

12

Apical Meristems Plants sustain continual growth in their apical meristems.

19

Bryophyte sporophytes are the smallest and simplest sporophytes of all extant plant groups Hornwort and moss sporophytes have stomata; liverworts do not

17

Bryophytes are represented today by three phyla of small herbaceous plants. -Liverworts, phylum Hepatophyta -Mosses, phylum Bryophyta -Hornworts, phylum Anthocerophyta These groups are thought to represent the earliest lineages to diverge from the common ancestor of land plants.

22

Bryophytes were prominent types of vegetation during the first 100 million years of plant evolution The earliest fossils of vascular plants date to 425 million years ago Vascular tissue allowed these plants to grow tall

5

Comparisons of both nuclear and chloroplast genes point to charophytes as the closest living relatives of land pants.

7

Five key traits appear in nearly all land plants but are absent in the charophytes. 1) Alternation of generations 2) Multicellular, dependent ambryos 3) Walled spores produced by sporangia 4) Multicellular gametangia 5) Apical meristems

1

For much of Earth's History, the terrestrial surface was lifeless. Cyanobacteria and protists likely existed on land 1.2 billion years ago. Around 500 million years ago, small plants, fungi, and animals emerged on land.

3

Green algae called charophytes are the closest relatives of land plants.

18

In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes. Sporophytes are typically present only part of the time

6

In charophytes a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out. Sporopollenin is also found in plant spore walls. The movement onto land by charophyte ancestors provided unfiltered sun, more plentiful CO2, and nutrent rich soil.

24

In contrast with bryophytes, sporophytes of seedless vascular plants are the larger generation, as in familiar ferns. The gametophytes are tiny plants that grow on or below the soil surface.

14

Land plants can be informally grouped based on the presence or absence of vascular tissue. Most plants have vascular tissue; these constitute the vascular plants. Nonvascular plants are commonly called bryophytes.

23

Living vascular plants are characterized by: -Life cycles with dominant sporophytes -Vascular tissues called xylem and phloem -Well-developed roots and leaves

4

Many characteristics of land plants also appear in some algae. Howevor, land plants share the following traits with only charophytes: 1) Rings of cellulose synthesizing proteins 2) Structure of flagellated sperm 3) Formation of a phragmoplast during cell division

11

Multicellular Gametangia Gametes are produced within organs called gametangia. Female gametangia, called archegonia, produce eggs and are the site of fertilization. Male gametangia, called antheridia, produce and release sperm.

9

Multicellular, Dependent Embryos The diploid embryo is retained within the tissue of the female gametophtye. Nutrients are transferred from parent to embryo through placental transfer cells. Land plants are called embryophytes because of the dependency of the embryo on the parent.

21

Overharvesting of Sphagnum and/or a drop in water level in peatlands could release stored CO2 to the atmosphere

15

Seedless vascular plants can be divided into clades: 1) Lycophytes (club mosses and their relatives). 2) Monilophytes (ferns and their relatives). Seedless vascular plants do not form a clade. Organisms that are grouped based on shared key biological features, rather than shared ancestry, can be referred to as a grade.

2

Since colonizing land, plants have diversified into roughly 290,000 living species. Land plants are defined as having terrestrial ancestors. Land plants do not include photosynthetic protists (algae). Plants supply oxygen and are the ultimate source of most food eaten by land animals.

20

Sphagnum, or "peat moss," forms extensive deposits of partially decayed organic material known as peat Peat can be used as a source of fuel Low temperature, pH, and oxygen level of peatlands inhibits decay of moss and other organisms

10

The sporophytes produces spores in organs called sporangia. Diploid cells called sporocytes undergo meiosis to generate haploid spores.