Mostly exist as solitary amoeboid cells • When food is short, amoeboid cells form a slug-likemobileaggregate • Some cells dry up and form a stalk supporting an asexual reproductive structure in which other cells develop into spores • Decompose rotting organic matter
Unicellular Algae • Algae • Are photosynthetic protists . • Chloroplasts support aquatic food chains • Arefound in plankton . • Drift or can swim weakly • Dinoflagellates • Unicellular algae reinforced by cellulose plates • Characteristic spinning movement caused by two flagella in grooves • Cause red tides
Unicellular Algae • Diatoms • Photosynthetic, unicellular algae • Have a unique, glassy cell wall • Contain silica • Two halves fit together likea box and lid • Key sourceof food in all aquatic environments • Diatomaceous earth made of thick sediments of fossilized diatoms • Green algae • Named for pigment in chloroplasts • May be unicellular, colonial, or multicellular • Some are large and complex enough to qualify as seaweeds
Chapter 16 Plants, Fungi and the Move onto Land
PLANT EVOLUTION AND DIVERSITY • Plants evolved from green algae • Plants and present-day green algaecalled charophyceans probably evolved from a common ancestor • Morphological, biochemical, and genetic similarities • Adaptations enabling permanent life on land appeared in ancestral green algae about 475 million years ago • Early environment suitablefor plant life
Terrestrial Adaptations of Plants • Plants haveadaptations for life on land • Plants and algae areboth multicellular photosynthetic eukaryotes • A set of derived characteristics distinguishes plants as a clade • Plants and algae interact differently with their environments • Key adaptations of plants to four challenges of terrestrial life
Structural Adaptations • Supporting theplant body • Lignin thickens and strengthens cell walls • Maintaining moisture • Waxy cuticle covering aerial parts prevents direct gas exchange • Stomata control gas exchangeand prevent water loss • Obtaining resources from both soil and air • Roots provide anchorageand absorb water and minerals fromsoil • Leaves absorb CO 2 fromtheair • Elongation of apical meristems maximizes exposureto resources • Vascular tissue(xylemand phloem) connects subterranean and aerial parts
ReproductiveAdaptations • Reproducing on land • Male and female gametangia (protective jackets) surround gamete- producing cells • Plants are embryophytes • Fertilized egg develops into an embryo whileattached to and nourished by theparent plant • All plant lifecycles have alternation of generations • Haploid spores areproduced in protectivesporangia
Highlights of Plant Evolution •
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