Page 162 - PG 101-Course notes مذكرة النظري 24-25 with spec

Medicinal plants (PG 101) Level 1 Clinical Pharmacy-PharmD

Notes :

• In hot & dry environment, plants keep their stomata closed to prevent water loss

• → ↑ O2 (waste product of photosynthesis) + ↓ CO 2 (no more from atmosphere) in

the leaf

• Altered photosynthetic pathways known as C4 & CAM photosynthesis.

• Both mechanisms act as CO2 pumps that ↑ conc. of O2 at the site of Rubisco i e

having two CO 2 acceptors then separating the initial fixation of CO 2 from the final

fixation of CO 2 in the Calvin cycle. As a result, photorespiration does not occur in

these plants.

(C4 and CAM -Plants)

II. The C4 Photosynthetic Carbon Assimilation Cycle

(C4-PCA or Hatch-Slack pathway)

▪ A mechanism to ↑ O2 conc. in chloroplasts to ↓ oxygenase activity of RuBISCO.

▪ Suitable for Hot, dry environments.
▪ 15% of plants (grasses, corn, sugarcane).

st
▪ Oxaloacetate (4C acid) & not PGA is the 1 product of photosynthesis. It is formed
by adding one molecule of CO 2 to one molecule of phosphoenolpyruvate (PEP).

▪ C4 plants have special leaf anatomy which includes two types of photosynthetic

cells. The bundle-sheath cells & the mesophyll cells.

▪ Calvin cycle occurs only in the bundle-sheath cells.

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