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A megaspore is...?
a female spore
A microspore is...?
a male spore
Multicellular, photosynthetic eukaryotes that range in size from the duckweed to the giant coastal redwoods.
When did plants evolve? What evidence?
- believed to have evolved from freshwater green algae over 500 million years old.
- Contain chlorophylls a and b and various accessory pigments.
- Store excess carbohydrates.
Green Algae ancestry. How is this known?
- terrestrial plants arose from a green algal ancestor.
- both have the same photosynthetic pigments (chlorophyll a and b)
- some green algae have a cell wall made of cellulose
- cells divide similarly
- largest and most diverse group of algae
- Habitat: found mostly in fresh waters and on land
- Float in rivers, lakes, resevoirs, creeks
- Can also live on rocks, trees, soil
Plants evolved from algae
- algae cannot survive on land
- plants adapted characteristics
Earliest known land plant...
- nonvascular and similar to today's bryophytes
Probable alga ancestor
- both have same pigments (chlorophyll a and b, carotenes, etc.)
- both use starch to store photosynthetic products
- both have cellulose in their wall
- both have alternation of generations
- both form a cell plate during cell division
Adaptations for plants to obtain enough water
- plants evolved roots to anchor the plant
- roots to absorb water and dissolved minerals
Adaptation to preventing water loss
- plants evolved a cuticle- waxy layer
- evolution of multicellular gametangia (sex organs)- helped protect gametes from drying out.
- evolution of a resistant coat on spores that prevents drying out
Adaptations to getting enough energy
- In land, plants obtained enough sunlight for photosyntsis
- different strategies for obtaining light
- -growing taller and taller above other plants- plants began to evolve support cells
- -others had to adapt to lower light intensities
- such as mosses
- vascular (xylem and phloem)
- ferns and fern allies
- seed plants
Photosynthetic (water) dilemma
- Problems- plants need pores for gas exchange for photosynthesis, but open pores (stomata) allow water to leave (95% water taken is lost)
- solution- stomata open during the day (for photosynthesis gas exchange) and close during the night (to allow platn to recover from water loss)
Affects of having multicellular organism
- advantages: roots better, protect gametes, grow tall to obtain sunshine
- disadvantage: getting water to all cells
Algae vs Plant Life Cycle
- algae: water dependent life cycle.
- plants: water independent life cycle in land plants. plants developed dry-resistant gametophytes (spores) or zygotes (seeds).
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