Explanation

Explanation

A counter-current exchange mechanism in gill respiration increases efficiency because Blood meets water with decreasing oxygen concentrations

• Water and blood flow in opposite directions.

• Blood continuously encounters water with higher O₂ concentration.

• This maintains a diffusion gradient along the entire gill surface.

• As a result, oxygen uptake is maximized.

Explanation

 The evidence for chordate ancestry in echinoderms mainly relies on Deuterostome embryonic development

• Both echinoderms and chordates are deuterostomes.

• In deuterostomes, the blastopore forms the anus first.

• They show similar patterns of early embryonic development.

• This developmental similarity indicates a common evolutionary ancestry.

Explanation

Explanation

Explanation

Explanation

• The SA (sinoatrial) node initiates the heartbeat.
• It produces rhythmic electrical impulses automatically.
• It sets the normal heart rate, so it is called the natural pacemaker.
• Located in the right atrium
• It is the dominant pacemaker because its cells generate action potentials faster than other parts of the conduction system.

Explanation

Explanation

Since none of the given options show features like cell specialization or permanent cell association

The transition to multicellularity is better supported by colonial organization and cell differentiation.

Contractile vacuole is used for osmoregulation 

Encystment is a survival mechanism to withstand unfavorable conditions

Binary fission is a type of asexual reproduction

Explanation

The corpus callosum is only found in placental mammals.

It spans part of the longitudinal fissure, connecting the left and right cerebral hemispheres,

It consists of 300 million fibres