Which vertebrate class is characterized by a three-chambered heart (except crocodiles)?
A. Birds
B. Amphibians
C. Reptiles
D. Mammals
Answer: Option C
Solution (By JKSSB Mock Tests)
Reptiles generally have a three-chambered heart with two atria and one partially divided ventricle; crocodiles are an exception with a four-chambered heart. Amphibians have a three-chambered heart with two atria and one undivided ventricle. Mammals and birds have four-chambered hearts. This adaptation reflects their metabolic demands and evolutionary advancement.
Explanation:
The sinoatrial (SA) node, located in the right atrium, generates electrical impulses spontaneously and initiates each heartbeat, setting the rhythm. It is called the natural pacemaker. The atrioventricular (AV) node delays the impulse before it travels to the ventricles. The bundle of His and Purkinje fibers conduct the impulse through the ventricles.
Explanation:
Cuscuta (dodder) is a holoparasite, lacking chlorophyll, and derives nutrients from the host plant via haustoria. Therefore, A is true but R is false.
Explanation:
Semi-conservative replication means that when a new DNA double helix is formed, it consists of one original (parental) strand and one newly synthesized strand. This was proven by the Meselson-Stahl experiment in 1958 using isotopes of nitrogen (15N and 14N) in E. coli. This mechanism ensures genetic continuity.
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