Not all Plants are Created Equal!

“Photosynthesis is an ancient process that originated not long after the origin of life and has evolved via a complex path to produce the distribution of types of photosynthetic organisms and metabolisms that are found today.”

http://www.plantphysiol.org/content/154/2/434.full

Plant Evolution

Examples

C3 plants

Are the most numerous on the planetThrive during conditions that are cool and moist

with normal light Get its name because the carbon dioxide is

incorporated into a 3-carbon compound.RUBISCO, the enzyme involved in photosynthesis,

is also the enzyme involved in the uptake of CO2.

It takes place throughout the leaf.

C4 Photosynthesis :

• CO2 is first incorporated into a 4-carbon compound.• Stomata are open during the day.• Uses PEP Carboxylase for the enzyme involved in

the uptake of CO2. This enzyme allows CO2 to be taken into the plant very quickly, and then it "delivers" the CO2 directly to RUBISCO for photsynthesis.

• Photosynthesis takes place in inner cells

C4 Photosynthesis :

Adaptive Value: •Photosynthesizes faster than C3 plants under high light intensity and high temperatures because the CO2 is delivered directly to RUBISCO, not allowing it to grab oxygen and undergo photorespiration. •Has better water-use-efficiency because PEP Carboxylase brings in CO2 faster, and the stomata does not need to be open as much (less water lost by transpiration) for the same amount of CO2.

CAM Photosynthesis or Crassulacean Acid Metabolism

• Named after the plant family in which it was first found (Crassulaceae) and because the CO2 is stored in the form of an acid before use in photosynthesis. • Stomata open at night (when evaporation rates are usually lower) and are usually closed during the day. • The CO2 is converted to an acid and stored during the night. During the day, the acid is broken down and the CO2 is released to RUBISCO for photosynthesis

CAM Photosynthesis or Crassulacean Acid Metabolism

•Adaptive Value: • Better water-use-efficiency than C3 plants under arid conditions due to opening stomata at night when transpiration rates are lower (no sunlight, lower temperatures, lower wind speeds, etc.). • When conditions are extremely arid, CAM plants can just leave their stomata closed night and day. Oxygen given off in photosynthesis is used for respiration and CO2 given off in respiration is used for photosynthesis.•This allows the plant to survive dry spells, and for the plant to recover very quickly when water is available again (unlike plants that drop their leaves and twigs and go dormant during dry spells).

EVOLUTION OF PHOTOSYNTHESIS & AEROBIC RESPIRATION

by C. Grier SellersDoctoral Candidate in BiologyNSF GK12 FellowTemple University

History of the Earth: Four Eons:

• Hadean Eon: 4500 - 3800 millions of years ago (mya)

• Archean Eon: 3800 - 2500 mya

• Proterozoic Eon: 2500 - 542 mya

• Phanerozoic Eon: 542 mya - Present

http://en.wikipedia.org/wiki/Geologic_time_scale

Hadean Eon:

• For its first billion years, the Earth’s surface was molten rock

• It was too hot for life to exist or to originate

Archean Eon:(Image: American Museum of Natural History)

• Prokaryotic life originated soon after Earth cooled and oceans were formed

• Earth was anoxic

• Photosynthetic bacteria, including cyanobacteria evolved (bumps are “stromatolites”, made by them)

Photosynthetic Bacteria:

• Some photosynthetic bacteria (such as green sulfur bacteria) use Hydrogen sulfide (H2S) & do not produce oxygen:H2S + CO2 + Light --> Sugars + Sulfur

• Cyanobacteria (& in eukaryotes, chloroplasts) use water instead, & produce oxygen:H2O + CO2 + Light --> Sugars + O2

Cyanobacteria: http://universe-review.ca/F11-monocell.htm

Key Dates in the Early Evolution of Life:

• Origin of Life: (the first prokaryotes) c. 3800 mya

• Origin of Photosynthesis: c. 3500 mya ??

• Origin of Oxygenic Photosynthesis: (oldest cyanobacterial fossils) c. 2900 mya

• Origin of Aerobic Respiration: c. 2400 mya??

• Origin of Eukaryotes: (the first protists) c. 2000 mya

Oxygen Terminology:

• An environment lacking oxygen is: Anoxic.

• Anaerobe: an organism that lives without oxygen (many are killed by oxygen).

• An environment containing oxygen is:Oxic.

• Aerobe: an organism that requires oxygen to live.

The Oxygen Revolution:

• The first O2 on Earth was a waste product of a new type of photosynthesis invented by cyanobacteria (oxygenic photosynthesis)

• This caused formation of oxidized compounds (banded iron formations - or “rusty rocks”)

• Oxygen first dissolved in the oceans, then accumulated in the atmosphere - it currently makes up 21% of the air.

Gradual Increase in Atmospheric O2: http://www3.ncc.edu/faculty/bio/fanellis/biosci119/marineorg.html

Banded Iron Formation: (c. 2400 mya) formed by the oxidation of iron, forming rust http://rst.gsfc.nasa.gov/Sect19/Sect19_2a.html

Consequences of Oxygen in the Environment:

• Caused a mass extinction of anaerobic prokaryotes, for whom it is toxic

• Made evolution of aerobic respiration in bacteria possible (later, some of these oxygen-respiring bacteria were eaten by eukaryotes, and became mitochondria)

• These aerobic bacteria were very successful, since aerobic respiration produces much more ATP than anaerobic bacteria can produce