Plethysmograph is used to measure

Assertion $A$: In an open circulatory system, the blood volume is high, but the blood pressure is low and irregular.
Reason $R$: In a closed circulatory system, the blood volume is limited, and the blood pressure is high and regular.
Which option is correct for Assertion $A$ and Reason $R$?

Analogy type questions:
$(1)$ Fish : Single circulation :: Amphibians : ...........
$(2)$ Between right atrium and right ventricle : Tricuspid valve :: Between left atrium and left ventricle : .............

Identify the correct option:

Vessel	Renal vein	Pulmonary artery	Hepatic portal vein	Main Aortic arch
$(a)$	$PO_2 = 95 \, mm \, Hg, PCO_2 = 40 \, mm \, Hg$	Less concentration of ions in blood	More fatty acid and glycerol in the blood	$PO_2 = 95 \, mm \, Hg, PCO_2 = 40 \, mm \, Hg$
$(b)$	Blood $pH = 7.4$	Less excretory substances than other blood vessels	More nutritive substances	More oxygen than pulmonary artery
$(c)$	Less excretory wastes	$PO_2 = 40 \, mm \, Hg, PCO_2 = 45 \, mm \, Hg$	Less amount of fatty acid and glycerol compare to other blood vessels	More excretory substances than renal vein
$(d)$	More oxygen than pulmonary artery	More excretory waste than renal vein	$PO_2 = 95 \, mm \, Hg, PCO_2 = 40 \, mm \, Hg$	Less excretory waste than hepatic portal vein

Alkalaemia is defined as:

What is the function of the spleen in humans?