Download - Lecture 22
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Lecture 22: Evolution of Plants
Covers Chapter 21
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Taxonomy• Branch of biology concerned with naming and
classifying organisms• 8 major categories and ranks:– Domain– Kingdom– Phylum– Class– Order – Family – Genus– Species
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Taxonomy
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Example of taxonomy
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How do we know where to place an organism?
• Anatomy plays a key role in taxonomy (organisms that are anatomically similar are placed in the same or closely related categories)
• DNA similarities are also useful
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Domains• At first, it was thought there were only TWO
domains: plantae and animalia (bacteria were considered plants!)
• Then came the realization of the differences between procaryotes and eucaryotes (no nucleus vs nucleus)
• Bacteria and Archaea were moved to their own domains, and the domain of eukarya was created.
• (Eukarya was later split into Animalia, Protists, Fungi and Plants!)
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Plants
• The first thing you notice: plants are green!• *Due to chlorophyll: molecule (a pigment)
that carries out photosynthesis. • Pigment: a material that changes the color of
reflected or transmitted light as the result of wavelength-selective absorption (more in lecture 23)
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Chlorophyll
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Chemical Structure of Chlorophyll
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But….some protists, bacteria and archaea all have chlorophyll!
• The fact that plants do photosynthesis is not unique to them….other organisms also perform photosynthesis.
• So how are plants unique?• *Answer: THE MULTICELLULAR EMBRYO • *Multicellular Embryo: Just like humans, plant
reproduction results in an embryo that is attached to and dependent upon its parent as it grows and develops. Protists, bacteria and archaea do not!
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So, what are the ancestors of modern plants?*
• It is now believed that plants evolved from photosynthetic protists like the green algae (stoneworts) that still live in the ocean today.
• Stoneworts are the closest living relative to modern plants.
• Why? – DNA in modern plants and green algae are similar– Both use chlorophyll for photosynthesis– Both store food as starch– Both have cell walls made of cellulose
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Stonewort
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How exactly did plants evolve?*• Green algae:– Lives in water– Lacks true roots, stems, leaves– Lacks complex reproductive system (flowers, fruit)– Requires water to facilitate reproduction
• As evolution continued and plants moved on land, they needed to solve these problems:– Survive without living IN the water– 1.) Gravity (need structural support to live on land)– 2.) Prevent body from drying out– 3.) Find a way to get nutrients– 4.) Find a way to reproduce outside of the water
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1.) Gravity (structural support)*
• Roots: anchor plant in the ground• Tissues evolved that contain rigid cell walls to
allow plant to support itself (more later in anatomy lecture)
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2.) Prevent body from drying*
• Cuticle: waxy substance that covers leaves to prevent evaporation
• Stomata: pores that can open for gas exchange and close to prevent drying
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3.) Getting nutrients and water*
• Roots: have the ability to absorb nutrients and water from soil
• Xylem & Phloem: specialized plant cells that can transport water and nutrients to all parts of plant (not all plants have X & P, however)
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4.) Reproduction on land*
• Seed: protection and nourishment of embryos in dry land environments
• Pollen: grains that contain male gametes (sperm), can be dispersed by wind
• Flowers: attract pollinators…get other organisms to carry pollen to other plants
• Fruit: attracts organisms to eat fruit and poop out seeds
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Modern Plants (see handout)*
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Timeline of evolution of plants