Lecture 12: Plants and the conquest of land

Charophycean

complex streptophyte alage (filament of cells with side branches)

share several derived traits with land plants: cellulose, plasmodesmata, zygotic life cycle

Cellulose

plant cell wall material for support

Plasmodesmata

channel through cell wall that allows substances to move between cells

• can allow communication between and specialization of different tissues

Apical meristem

localized regions of cell division (where plants grow)

Embryo

a multicellular diploid eukaryote in its earliest stage of development, from the first cell division until birth, hatching, or germination

Matrotrophy

zygote remains sheltered and fed within gametophyte tissue (embryophytes)

Spores

dry, air-resistant reproductive cell

Sporopollenin walled spores

tough material that comprises most of the cell wall of spores

helps prevent cellular damage during transport through the air

Alternation of generations (sporic life cycle)

1. multicellular diploid (2n) sporophyte makes haploid spores through meiosis

2. haploid spores dispersed and undergo mitosis to make multicellular haploid gametophyte

3. gametophyte makes gametes through mitosis

4. fertilization → single-celled diploid zygote → sporophyte

Zygotic life cycle

• asexual reproduction by mitosis when conditions are favorable

  • a switch to sexual when conditions are unfavorable: can be switch from summer to winter

• diploid zygote goes through meiosis to make 4 haploid spores

Embyrophytes

land plants characterized by the nurturing of young, multicellular embryonic sporophytes within the tissues of the parent gametophyte

Placental tissue transfer

• in gametophyte tissue closest to the embryos and in embryos

• calls specialized to promote movement of solutes from gametophyte to embryo

• finger-like ingrowths to increase surface area (more efficiency for transport proteins)

Cretaceous-Paleogene mass extinction

• 66 million years ago

• 6-mile wide asteroid struck earth, 75% of plant and animal life dead

• consequences: global cooling, darkness, acid rain

What evidence supports the idea that land plants evolved from Charophycean algae?

Charophycean algae shares derived traits with land plants like cellulose and plasmodesmata

Describe the characteristics found in all land plants

Alternation of generations, sporepollenin, cellulose, and photosynthesis ares some characteristics

Identify the advantages of a sporic life cycle over a zygotic life cycle

An advantage of the sporic life cycle over the zygotic is that it can produce more than 4 zygotes