Biology 11

Transition onto Land Advantages of living in the water included… 1.Prevents drying out. 2.Gives structural support (less affected by gravity) 3.Provides nutrients and gas exchange by diffusion. 4.Helps to disperse spores and the meeting of gametes. Question to think about: Why bother move onto land?

Plant Kingdom Distribution Flowering Plants 235,000 species Cone-bearing Plants 760 species Ferns & relatives 11,000 species Mosses & relatives 15,600 species

Green algae ancestor Mosses & relatives (“Bryophytes) Ferns & relatives (Seedless vascular plants) Cone-bearing plants (Gymnosperms) Flowering plants (Angiosperms) Flowers: seeds enclosed in fruit Seeds Water-conducting (vascular) tissue Plant Phylogeny

General Plant Life Cycle Sporophyte is the dominant generation in higher plants (diploid stage: 2n) Gametophyte is the dominant generation in lower plants (haploid stage: n)

2 Major Groups of Plants Nonvascular Vascular - Lack vascular tissue which transport H 2 O and nutrients - include mosses, liverworts, and hornworts - possess water/nutrient transporting system (xylem-water and phloem-nutrients from photosynthesis) - include ferns, conifers, and flowering plants

Non Vascular Plants Primitive land plants Are photosynthetic Cell wall made of cellulose Lack vascular tissue( i.e. missing “xylem” and “phloem” ) Do NOT have true leaves, stems and roots

Require water for fertilization (adapted for wet habitats) Asexual and sexual reproduction Alternation of generations Gametophyte generation is dominant (mainly exist as a haploid individual)

Mosses: Phylum Bryophyta

Mosses Live only in wet habitats – Don’t have vascular tissue to transport water. Water moves by osmosis from one cell to the next. Remain small. – Water can only diffuse short distances to cells. Don’t have true roots to transport water.

Structure Sporophyte (diploid) generation grows out of the gametophyte, and is a skinny stalk with a capsule full of spores at the top. Gametophyte (haploid) generation is the common green fuzzy moss. – Carries out photosynthesis Rhizoids are root-like structures that anchor the moss to the ground.

Gametophyte Structures Structures protect gametes (egg and sperm) from drying out Antheridium- produces flagellated sperm cells Archegonium- produces eggs Sperm require water to swim to egg in archegonium… involves dew or rain droplets

When water is present, fertilization can occur if sperm swims to egg Diploid zygote forms and eventually germinates and grows into diploid sporophyte

Sporophyte cannot live independently… Grows out of the gametophyte Gametophyte is photosynthetic and supplies water and nutrients to the sporophyte that grows out of it

Sporophyte Structure Contains seta or stalk raises spores for dispersal (by wind or water) Capsule contains haploid spores that will be released under ideal conditions Calyptra covers and protects the capsule

If spores disperse and land in ideal area, spores germinate and a protonema grows Protonema are thread like filaments that will develop into gametophyte

Life Cycle Overview Starting with the gametophyte, draw the life cycle of a typical moss 1)Haploid Gametophyte contains archegonium and antheridium (produces haploid eggs and sperm cells through mitosis) 2)When water present, sperm cell swims to fertilize egg cell in archegonium.

3) Diploid zygote forms and develops into sporophyte… grows out of the archegonium of the gametophyte 4) Mature sporophyte produces haploid spores through meiosis 5) Spores disperse, form protonema, and develop into mature gametophyte

Why do bryophytes require an environment that is moist? – For fertilization – To transport water from cell to cell (have no vascular tissue)