Lab 6- Green Algae and Plants

Green algae are

a group of photosynthetic organisms that are not plants. • Eukaryotic • Most are protists • Contain chlorophyll for photosynthesis • Can be unicellular or multicellular (or colonial) • Primarily aquatic

Two major groups of algae

Chlorophytes Charophytes

Plants (Kingdom: Plantae)

Photosynthetic organisms that have complex tissue structures that evolved for living on land. • Eukaryotic • Photosynthetic (contain chlorophyll and chloroplasts) • Multicellular • Primarily terrestrial (live on land)

Types of plants

non-vascular (moss), seedless vascular, and seeded

Autotrophs

like plants and green algae are primary producers: they are responsible for generating the earth’s organic matter.

Heterotrophs

use the organic molecules produced by autotrophs as fuel for their own cells.

Plant adaptations

Protective cuticle (waxy covering) [Preventing desiccation], [Support for the body] Fibrous stems provide stability, [Obtaining resources for growth] Vascular tissues (roots absorb H2O and minerals, while green shoots conduct photosynthesis), [Gas exchange] Stomata (pores in the cuticle), [Fertilization of gametes with limited water] Protective housing for gametes called gametangia (antheridia for sperm and archegonia for eggs)

alternation of generations:

Sporophyte diploid (2n) Gametophyte haploid (n)

Sporophyte (2n)

multicellular diploid stage

Sporangium (2n)

location of spore production by meiosis

Spore (n)

a haploid cell for asexual reproduction

Gametophyte (n)

multicellular haploid (n) stage

Gametangia (n)

locations of gamete production and mitosis

Antheridium (n)

location of sperm production

Archegonium (n)

location of egg production

-phyte =

plant body

-angia/angium =

vessel

charophytes

are the closest relatives of terrestrial plants:

charophyte mechanisms that resemble terrestrial plants

Similar mechanism for forming a cell plate in cell division 2. Similar nuclear and chloroplast genes 3. Cell walls with a high concentration of cellulose 4. Flagellated sperm similar to some land plants’ sperm 5. Genus Chara produce gametes within gametangia—a key feature that allowed plants to colonize dry la

charophytes include:

Spirogyra and Chara

Spirogyra

are haploid (n) under normal conditions (sufficient warmth and sunlight) and usually reproduce asexually by mitosis. • When conditions deteriorate (e.g. cold, dry), Spirogyra undergoes sexual reproduction (conjugation). Conjugation results in a diploid (2n) zygospore with a thick coat that can withstand harsh conditions.

pirogyra sexual reproduction

(conjugation) A B C D TIME A: Vegetative filament (n) B: Formation of conjugation tubes between two filaments C: Gamete (n) from one filament migrates to other filament D: Fusion of two gametes (n) forms a zygospore (2n)

Seedless plants, i.e. bryophytes (mosses) and ferns,

were the earliest land plants. • Most abundant plants on earth until ~285 MYA. • Reproduce using spores, not seeds. and many grow on rocks

Bryophytes Phylum Bryophyta (mosses, hornworts, and liverworts)

do not have have vascular tissue (e.g. roots) to transport water. • Instead rely on diffusion and osmosis for transport of water and minerals. • Anchored to rocks/soil by rhizoids—not roots!

In bryophytes, the gametophyte (n) is the dominant generation. • The sporophyte is dependent on the gametophyte for energy and nutrition

ferns

(monilophytes) have vascular tissue including roots, leaves, and stems. • Dominant generation is the sporophyte (2n) • Both generations are free-living (neither depends on the other for nutrition). Note the difference from bryophytes!

Fern sporophyte (2n) - sori

The fern sporophyte contains structures called sori under the fronds. • Sori (singular: sorus) contain the sporangia, where meiosis takes place to produce spores