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Lecture 7

BIOL 215 Lecture Notes - Lecture 7: Lophotrochozoa, Blastula, Hydrostatic Skeleton

Course Code
BIOL 215
Neil Price

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Modern Diversity 2
Plantae & Unikonts
-Choanoflagellates more related to animals than plants
-Up to 390 species or more of different land plants
-Certain plant features reflect transition of aqueous environment to land
Algal Ancestry
-Land plants evolved from green algae 480 m.y.a
-Share similarities such as:
- Store carbs reserves as starch
- Have rigid, cellulose enforced cell wall
- Similar types of pigments: chlorophyll a & b and yellow orange carotenoids
alpha & beta.
-Evolved into organisms which most cells are somatic (formed body cells) and only
few were reproductive.
-Land plants also referred to as “Embryophytes” (zygote develops within
-Land plants have alternation of generation: gametophyte (haploid) and sporophyte
(diploid). The alternation can shift between either where one is more dominant.
4 major evolutionary inventions in plants
1. Origin of plants: alternation of haploid/diploid, stomata, cuticle.
2. Vascular lineage: Vascular system, lignin, true leaves and roots
3. Seed lineage: Seeds and pollen
4. Flower lineage
-Simplest land plants
-Limited to moist environments
-Paraphyletic group: liverworts, mosses, club mosses, and hornworts
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-3 major divisions: hornwort, liverwort, moss
Major Features:
-Lack vascular tissue & true roots to transport water and nutrients
-Thrive in damp places, but can withstand drought
-Lack lignin to strengthen cell walls and supportive structure
-Reproduce by spores
-Have stomata (except liverworts), cuticle and multicellular reproductive structures.
Cuticle and Stomata
-Allow gas exchange in plants
-Prevents desiccation and so allows plants to move away from water
Byrophytes were important in 2 major transitions:
1. water to land
2. Haploid gametophyte-dominated life cycle to a diploid sporophyte-dominated life.
-Sporophytes are parasitic
Early Vascular Plants
-Vascular means theres a present of conductive tissue:
- xylem that enables water to reach erect parts
- phloem that enables nutrients to be distributed from leaves and stems
-Earliest fossil vascular plants: cooksonia
-Ferns: origin in early carboniferous 350 m.y.a. Are most abundant in lineage and
posses specialized underground stem.
-Includes ferns, horsetail, club moss
Moving onto land
3 evolutionary changes:
1. Reduction in size of gametophyte
2. Evolution of easily dispersible pollen
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