C4 and CAM pathway

• Allows for more diversification of species, higher survival rate because can produce their own food in different climates than other plants
• Less dependence on H20
• Based off C3

• Metabolic pathway converting CO2 and
RuBP into 3 phosphoglycerate
• Occurs in all plants as first step of calvin cycle
• Plants that solely survive on this pathway tend to live where sunlight and temperatures are moderate, and H2O is abundant

• those that have to survive in high day temperatures, intense sunlight, drought like conditions
• Allow for stomata to remain closed more to retain
H2O
• Draws CO2 from malate, an organic compound
• -C4 evolved from C3 plants in order to effectively fix CO2 at low concentrations
• C4 plants have a unique leaf anatomy

• two different types of photosynthetic cells:
• -Bundle-sheath: arranged into tightly packed sheaths around the veins of the leaves
• -Mesophyll cells: between the bundle sheath and the leaf surface
– pump CO2 into the bundle sheath, keeping the concentration high enough for RUBISCO to bind to
CO2 rather than O2 , tendency to waste energy is thus minimized
– The enzyme responsible for this is PEP carboxylase.

• 1. CO
2 is fixed effeciently to phosphoenolpyruvate to produce oxaloacetate by PEP carboxylase, The oxaloacetate is then converted to another four-carbon compound called malate in a step requiring the reducing power of NADPH.

• 2. The malate then exits the mesophyll cells and enters the chloroplasts of specialized cells called bundle sheath cells. Here the four-carbon malate is decarboxylated to produce CO
2
, a three-carbon compound called pyruvate, and NADPH. The CO
2 combines with ribulose bisphosphate and goes through the Calvin cycle.

• 3. The pyruvate re-enters the mesophyll cells, reacts with ATP, and is converted back to phosphoenolpyruvate, the starting compound of the C
4 cycle.

• Crassulacean acid metabolism
• Named after plants family Crassuleae, where it was first discovered
• discovered in the 1940s by Ranson and Thomas
• Second photosynthetic adaptation to arid conditions
• Evolved in succulent (water-storing) plants
– Jade, many cacti, pineapples, other families

• Plants open their stomata during night and close them during the day
– Opposite of what other plants do
• Closing stomata during day conserves H20 and prevents CO2 from entering

• Plants open stomata during night
• Take in CO2 and incorporates it into a variety of organic acids
• Mesophyll cells store organic acids in vacuoles until morning

• Plants close stomata at morning
• Light reaction supply ATP and NADPH for calvin cycle
• CO2 is released from organic acids to become incorporated into sugars in chloroplasts

• Similar to C4 because CO2 first incorporated into organic intermediates before entering calvin cycle
• Different from C4 because the 2 initial steps of carbon fixation occur at separate times within the same cell, but in C4, the 2 steps are separated structurally
• All 3 pathways eventually use calvin cycle to make sugar from CO2

• “I lost an electron!”
• “Are you sure?”
• “I’m positive!”