BISC 102 Lecture Notes - Lecture 6: Chlorophyll, Stoma, Synapomorphy

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Plants/Fungi: Three approaches to determine relationships and possible organs
Fossil record (only direct evidence of past morphology and age) (Ordovician Period)
Comparative morphology: Anatomy, Biochemistry, and life cycle of living forms
DNA: Homology and Phylogeny
Green Plants (700 million years ago): Multicellular eukaryotes that are photosynthetic: a
monophyletic group that includes green algae, non vascular plants, vascular plants and seed
plants
Obtain energy from light and carbon from CO2
● Synapomorphies (shared traits) with green algae: Characteristics of
chloroplasts (photosynthetic organelles)
Photosynthetic pigments include chlorophyll a/b and carotene
Thylakoids (stacked membrane) in chloroplasts are similar
Synthesize starch as a storage product
Two Types of Green Plants
Green Algae: Constraint: Mostly able to live only in aquatic (marine or fresh water) or
wet environments
Land Plants: Adapted to life on land, special traits needed
● Evidence:
First fossils appear in Ordovician period (mostly spores)
Shallow. fluctuating, water table likely allowed amphibious algae to adapt to
periodic exposure to dry conditions
Silurian Period: Improved adaptations to land
Desiccation (drying out): Environmental fluctuations
■ Support (grow tall)
Gas exchange/Transport
■ Reproduction: Easy in water, reproductive cells can swim freely
Natural Selection:
Land plants are closely related to a group of freshwater algae called
charophytes
Adaptations were gradual and through natural selection
(Example: new mutations for waxy surfaces would reduce drying)
Same characteristic increased the chances of surviving out of water
Synapomorphies: Waxy cuticle/stomata (pores)
A waxy cuticle minimizes water loss through surface cells
Stomata can open and close to allow gas of (O2/CO2)
exchange while minimizing water loss
Liverworts have pores not stomata
Synapomorphies: Alternation of generation: A multicellular haploid
generation alternates with multicellular diploid sporophyte generation
Different from Algal groups
Synapomorphies: Embryophytes: The sporophyte embryo is
retained and nourished by the mother plant
Major Groups Of Land Plants:
Nonvascular plants (Liverworts, mosses, hornworts)
Constraint: Moist environment: The flagellated sperm must swim to the egg
through water
Constraint: Height: Water and nutrients are transported by diffusion/simple
conducting tissue
No true roots/leaves
Vascular plants (400 million years ago)
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