Imagine sitting in the sunshine on a sandy riverbank on the Serengeti 500 million years ago. As waves gently lap

against the bank, a warm gentle breeze rolls off the plain. Although all seems well at first, an eerie feeling soon comes

over you. As you look around, something seems terribly wrong. There are no birds flying in the sky. There are no

flies nipping at your toes. In fact, there are no animals anywhere in sight. Worse yet, there aren't even any plants!

Everywhere you look, the plain appears devoid of living things. Where did they all go? The answer is that they went nowhere. This is because 500 million years ago

virtually all visible organisms still lived in water. Yet all of this was about to change. Aquatic organisms were poised

to invade the land. What aquatic organisms were about to make the

transition?

What obstacles would the first land plants have had to overcome to make this transition to land? (Identify at least 3)

Share your ideas with your neighbor

More than 280,000 species of plants inhabit Earth today.

Most plants live in terrestrial environments, including deserts, grasslands, and forests.– Some species, such as sea grasses, have returned to

aquatic habitats. Land plants (including the sea grasses) are thought

to have evolved from a certain green algae, called charophyceans.

Introduction

Think about how each of the following events profoundly shaped and affected the course of organic history and why each step was necessary for the following events to occur. (think structure and function).

The Eight Monumental Events in the History

of Plants

1. The evolution of the first form of life.

3.5 billion years- oldest prokaryotic fossil

2. The origin and development of photosynthetic cells.

2.7 billion years BP, accumulation of oxygen increases in atmosphere.

3. The appearance of cells with organelles. What type of cell is this?

4. The acquisition of multicellular construction.

Oldest multicellular organism (algae) fossil is 1.2 billion years old

5. The ecological assault of plants on land.

Fossil record shows this to have occurred about 500 million years ago.

6. The evolution of conducting tissues.

Approximately 420 million years ago

7. The evolution of seed plants.

Oldest seed plants according to the fossil record are about 360 million years old

8. The rise of flowering plants.

125 million years ago

Archaefructus sinensis

What is this called?

1. The first organisms to successfully colonize dry land some 1.5 billion years ago were probably part fungal and part green algal creatures called lichens. The fungal part afforded protection from drying while the green algal part conducted photosynthesis to supply food.

2. The first plants to invade land some 500 million years ago were probably some form of photosynthetic freshwater green alga, which during times of periodic drought evolved novel land adaptations (e.g., thick waxy coverings with small holes, vascular tissues). These first vascular plants were soon followed by a fungal invasion, which radiated into four major groups (imperfect fungi, land molds, sac fungi, and club fungi).

3.About 450 to 425 million years ago, the vascular land plants first radiated into a group of spore-producing land plants (whisk ferns, club mosses, horsetails, ferns) and later, about 380 million years ago, to seed-producing ferns that probably gave rise to the gymnosperms and angiosperms before going extinct.

4. Some 400 million years ago, freshwater green algae gave rise to another land group called bryophytes (liverworts, hornworts, and mosses). Because bryophytes did not acquire vascular tissue, they remained short, tied to moist environments, and relatively inconspicuous.

5. Present-day gymnosperms, which produce seeds encased in a seed coat and little else, include four groups: cycads, ginkos, gnetophytes, and conifers. Gymnosperm reproduction represents several evolutionary advances over that of ferns, such as protected internal fertilization, protected sperm passage, and protected embryo development.

6. Angiosperms (vascular plants with flowers and encased seeds) first appeared about 180 million years ago and became dominant about 65 million years ago. Their domination was due primarily to adaptations such as well-developed vascular tissues, waxy surface secretions, flowers that attract pollinating agents, and seeds encased in tasty fruits that attract animals that aid in seed dispersal.

7.The evolutionary trend seen in plant life cycles toward dominance of the diploid over the haploid phase can be understood as a consequence of natural selection favoring the hardier diploid phase thanks to its ability to mask the expression of harmful genes.

The timing of meiosis and fertilization does vary among species.

The life cycle of humans and other animals is typical of one major type.– Gametes, produced by meiosis,

are the only haploid cells.– Gametes undergo no divisions

themselves, but fuse to form a diploid zygote that divides by mitosis to produce a multicellular organism.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Plants and some algae have a third type of life cycle, alternation of generation.– This life cycle includes both haploid (gametophyte) and

diploid (sporophyte) multicellular stages.– Meiosis by the sporophyte produces haploid spores that

develop by mitosis into the gametophyte.

– Gametes produced via mitosis by the gametophyte fuse to form the zygote which produces the sporophyte by mitosis.

Life on Earth is solar powered. The chloroplasts of plants use a process called

photosynthesis to capture light energy from the sun and convert it to chemical energy stored in sugars and other organic molecules.

Introduction

Photosynthesis nourishes almost all of the living world directly or indirectly.– All organisms require organic compounds for energy

and for carbon skeletons.

Autotrophs produce their organic molecules from CO2 and other inorganic raw materials obtained from the environment.– Autotrophs are the ultimate source of organic

compounds for all nonautotrophic organisms.– Autotrophs are the producers of the biosphere.

1. Plants and other autotrophs are the producers of the biosphere

Any green part of a plant has chloroplasts. However, the leaves are the major site of

photosynthesis for most plants.– There are about half a million chloroplasts per square

millimeter of leaf surface. The color of a leaf comes from chlorophyll, the

green pigment in the chloroplasts.– Chlorophyll plays an important role in the absorption

of light energy during photosynthesis.

2. Chloroplasts are the sites of photosynthesis in plants

Chloroplasts are found mainly in mesophyll cells forming the tissues in the interior of the leaf.

O2 and water exit and CO2 enters the leaf through microscopic pores, stomata, in the leaf.

Veins deliver water from the roots and carry off sugar from mesophyll cells to other plant areas.

Fig. 10.2

A typical mesophyll cell has 30-40 chloroplasts, each about 2-4 microns by 4-7 microns long.

Each chloroplast has two membranes around a central aqueous space, the stroma.

In the stroma aremembranous sacs, the thylakoids.– These have an internal

aqueous space, the thylakoid lumen or thylakoid space.

– Thylakoids may be stacked into columns called grana.

Fig. 10.2

Photosynthesis

The requirements and the products for cellular respiration are exactly opposite as they are for photosynthesis.

Animals use O2 and Green Plants use CO2. Each depends on the other for the gases that

they need to survive. Photosynthesis

6H2O + 6CO2 + Light C6H12O6 + 6O2

Photosynthesis

CO2 is diffused through the stomata.

Water is taken up through the roots and transported in the xylem vessels.

Light energy is absorbed by the chlorophyll.

O2 & H2O leave the plant through the stomata.

Glucose and Starch are stored or used for growth within the plant and travel in the phloem.