BIOL 112 Lecture 19

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Protists

Animals probably descended from a protist ancestor under supergroup Unikonta. Our closest protist relatives are colonial choanoflagellates (based on DNA).

Very similar to choanocytes from porifera (sponge collar cells)

Land plants also come from a protist ancestor under supergroup Archaeplastida. Closest protist relative is charophycean green algae

came about as result of first-degree endosymbiosis

Chapter 29: Plant Diversity 1: How Plants Colonized Land

(See BIOL 112 Lab 4→)

Colonization occurred 500 million years ago during cambrian explosion

Movement from aquatic protists (algae and charophyceans) to land-based

• non-vascular,
• vascular, and
• seed plants

Process required

1. Reduced dependency on water for reproduction → spores covered by sporopollen, oogamous pollen and seeds
2. prevention of dessication (drying out) → waxy cuticle & cell walls, vascular tissues

Note: Animals had to go through same evolutionary trends.

Coevolution of Plants and Other Organisms

selective pressure from:

• herbivores (protection against) — production of toxins such as tannins and phenalics (also protects against UV rays)
• plant/fungal symbiosis — decomposition of complex compounds into usable forms for plants
• flowering plants and animals — animals pollinate plants and disperse seeds, plants provide food source (fruit)

Land Plants v. Charophyceans

Both have

• DNA sequence similarity
• similar cell biology

Plant growth regions (called apical meristems) are at the shoot (top of stem) and the roots