1. Seedless plants
Section 22.2

2. What is algae? Seaweed is the most common form of algae
Algae are not a single group of organisms
Applied to any photosynthetic eukaryote that isn’t a land plant
Some are protists, some are plants
Those grouped with plants are called green algae

3. The first plants Green algae were the first plants on earth
Large algal mats from the Cambrian – 550 million years ago
Mostly aquatic
Found in fresh and salt water, and some moist areas on land
Photosynthetic pigment and cell wall composition shared with larger more complex plants
Absorb moisture and nutrients directly from their surroundings
Do not contain the specialized tissues found in other plants

4. Algae life cycle Life cycle switched between haploid and diploid
Some do not alternate with every generation
Chlamydomonas stays in the same haploid stage for multiple generations
Haploid cell can reproduce asexually by mitosis
Chlamydomonas can switch to asexual reproduction if conditions become unfavorable
Gametes produced that fuse into a diploid zygote – a sporophyte
Zygotes thick skin allows them to survive harsh conditions

5. Multicellularity Many green algae from colonies
In some cases, (eg. Volvox) algae are connected through strands of cytoplasm and can communicate
Allows movement of the colony
Up to 50,000 cells can form a hollow sphere
Straddles the fence between colonial and multicellular life

6. Mosses and Bryophytes Mosses are like natures carpet
Thin waxy coating allows resistance to dry conditions
Rhizoids anchor them to the soil and absorb water and minerals from surrounding soil
Mosses are a bryophyte
Bryophytes have specialized reproductive organs enclosed by other non reproductive cells
Higher degree of cell specialization than algae
Other examples are hornwarts and liverworts (Phylums)

7. Features of bryophytes
Found in damp places where lots of water
Because they do not contain vascular tissues to carry water
Also means that they can’t grow above 1 meter in height
They don’t produce lignin, meaning they can’t support large structures

8. Life cycle of bryophytes
Like all land plants display alternation of generations
Gametophyte is the dominant, recognizable stage of life cycle
Also carries out most of plants photosynthesis
Sporophyte is dependent on Gametophyte for water and nutrients
Bryophytes produce sperm cells that swim using flagella
Must be released in area with enough water for them to swim to an egg cell
Need standing water for some of the year

9. Moss life cycle explained

10. What does vascular tissue do? Why is it important to plants?
420 million years ago plants suddenly got taller!
They were the first plants to have a transport system
Contain true vascular tissue
Efficient at carrying water and nutrients

11. How did the transport system evolve?
Vascular plants are also called tracheophytes, because they contain a specialized water conducting cell
A tracheid – hollow tubelike cell with thick cell walls strengthened by lignin
Massive evolutionary step in plant kingdom
Tracheids are found in the xylem - a tissue that carries water upwards from roots to all parts of the plant
Connected end to end
Openings (pits) allow water to move more efficiently than simply by diffusion
Phloem – transports both nutrients and carbohydrates produced by photosynthesis
Fluids are moved throughout the plant against gravity

12. Seedless plants All seed bearing plants have a vascular system
So do some seedless plants
Common examples – Club mosses, horsetails and ferns
Ferns are the most common- 11,000 species
Can thrive in areas with little light and are abundant in seasonally wet habitats

13. Life cycle of ferns Ferns are actually diploid sporophytes
This is the dominant stage for all vascular plants

14. Key summary questions What are the characteristics of green algae?
What factors limit the size of bryophytes?
How is vascular tissue important? What tissues to most plants contain? What function do they perform?