Dicot stem

Epidermis ; 

Cutinized, bears multicellular hairs.

Cortex ;

It is differentiated into hypodermis, general cortex and endodermis.

Hypodermis is Collenchymatous

Pericycle ;

Above vascular bundle it is Sclerenchymatous

Vascular bundles ;

Conjoint, Collateral, Endarch and Open

TLS Online TPP Program

#Id: 9315

#XL - T Zoology

In resting rod cells high cGMP concentration generated from GTP catalyzed by guanylyl cyclase.

TLS Online TPP Program

#Id: 9316

#XL - T Zoology

Light absorption by rhodopsin→activation of a cGMP PDE → hydrolyzes cGMP to 5′-GMP→ cGMP levels  drop →channel close →membrane hyperpolarization→reduction in NT release→transmitted to brain

TLS Online TPP Program

#Id: 9317

#XL - T Zoology

TLS Online TPP Program

#Id: 9318

#XL - T Zoology

Rapid termination mechanisms of the Rhodopsin Signalling:

1.GAP that inactivates Gαt·GTP

2.Ca2+ -sensing proteins that activate Guanylate Cyclase

3.Rhodopsin Phosphorylation and Binding of Arrestin

TLS Online TPP Program

#Id: 9319

#XL - T Zoology

Gαt contains an intrinsic GTPase activity by GAP complex, RGS9-Gβ5 triggers the rapid inactivation of the PDE

TLS Online TPP Program

#Id: 9320

#XL - T Zoology

Light-triggered closing of the cGMP-gated cation

channels causes a drop in the cytosolic Ca2+ concentration inside the rod cell.