Plants growing in tropical regions are exposed to an optimum temperature of 30°C to 45°C.
Anatomically these plants have Kranz anatomy and dimorphic chloroplasts. The vascular bundles are surrounded by a layer at bundle sheath. Bundle sheath is surrounded by a ring of Mesophyll cells.
Dimorphic Chloroplast :Bundle sheath chloroplast are larger and thylakoids are not arranged in granum.
Mesophyll Chloroplast are small and thylakoids are arranged in granum.
Plants with this kind of anatomy have the C₄ cycle or Hatch and slack pathway which takes place in two phases.
First phase in stroma of mesophyll cells and phase II in Bundle sheath cells.
Advantage of this cycle is that fixation of carbon di oxide by such plants can occur ever when the atmospheric carbon di oxide concentration is less than 10ppm.
But the cycle consumes 30 ATPs to produce one glucose molecule.

The carotenoid pigments protect chlorophyll from photo oxidative damage. Hence they are called shield pigments.

1. Glycine and Serine synthesised during this process are precursors of many biomolecules like chlorophyll, proteins, nucleotides.
2. It consumes excess NADH + H⁺ generated.
3. Glycolate protects cells from Photo oxidation.

They are proteinaceous pigments, soluble inwater, and do not contain Mg and Phytol tail. They exist in two forms such as
1. Phycocyanin found in cyanobacteria
2. Phycoerythrin found in rhodophycean algae (Red algae).

In some bacteria, oxygen is not evolved during photosynthesis and is called as non-oxygenic and anaerobic photosynthesis. Ex: Green sulphur, Purple sulphur and green filamentous bacteria.