Alternative mechanism of C fixation occurs in C4 and CAM plants

C4 plants:

1. occurs both in mesophyll + bundle sheath cells.

2. CO₂ fixation is catalyzed by PEP carboxilase in mesophyll cells and sugar formation by RUBISCO in bundle sheath cells via Calvin cycle.

3. First product of CO₂ fixation is a 4C compound oxaloacetate in C4 plants.

CAM plant:

1. live in hot climatic conditions

2. both C₃ and C₄ cycles occur.

4. fix CO₂ during the night + synthesise sugar during the day.

5. G3P produced = used for the synthesis of sugars, amino acids and fatty acids.

6. Sugars formed = glucose, sucrose, starch + cellulose.

7. Lipids:

·  formed from glycerol + fatty acids.

·  Glycerol = formed directly from G3P

·  fatty acids = built from acetyl coenzyme A.

8. Protein formed by: conversion of G3P --> acetyl Co A (enters Krebs cycle) --> α-glutarate --> glutamate --> transamination --> form amino acids + proteins.