Figure 27.9

Figure 27.29

The Algae

• haploid and diploid cells –undergo mitosis and alternation of generations. –diploid sporophyte generation forms spores by

meiosis in sporangium–The haploid gametophyte generation forms

gametes by mitosis–Gametes fuse to yield zygotes

–Form the next generation of sporophytes.

Sexual reproduction

– if gametes are identical it is isogamous: isogamy– if gametes are different it is heterogamous:• Anisogamy: gametes differ in size or form only• Oogamy: large non-motile egg and motile

male gametes– sex organs are gametangia– sporangia form from gametangia•male (sperm) within antheridia • female egg is called oogonia formed within the

archogonium

Figure 27.22

probable ancestors of the green plants(charophytes)lines of evidence:chloroplasts morphologically and biochemically

similar to plantscellulose rich cell wallsPhotosynthetic pigments include:

chlorophyll a and b Carotenoids

starch as primary storage productformation of an interior cell plate growing from the

center outward during cytokinesis (cell division)

Origin of Plant Kingdom

very little tissue differentiation algae body- thallus (Thallophyta)

division of the plant kingdommostly aquatic, some semi-terristrial moist places- soil, tree trunks

exhibit alternation of generationsContain chlorophyll a and baccessory pigments of carotene and xanthophyllcontain pyrenoids storage for starch synthesiscell walls contain cellulose and pectin

Chlorophyta

ChlorophytaChlamydomonas- microscopic single cells with flagella (anterior), eyespot within chloroplast containing rhodopsinhaploid through most of life cycle- reproduce both sexually (zygotic meiosis) and asexually (common)asexual form zoosporesmay divide and not separate to form colony

Sexual:zygote develops thick wall to become a zygospore

(resting phase- looses its flagella) isogamy (most primitive condition)only diploid stage is the zygote

Chlorophyta•Ulva- sea lettuce• large multicellular • eaten in soups and salads• used as a substitute for nori

•Chlorella• Single celled, no flagella• food source for animals and humans• pilot farms in US, Germany, Israel and Japan

•Ulothrix• reproduce by fragmentation or asexual spores • sexual reproduction• isogamous to form zygote which divides by

meiosis

Chlamydomonas Volvox

Volvocine Series: Explanation of multicellularity and differentiation

Figure 27.26

Reproduction in Filamentous Green Algae