A. Combination
B. Single replacement
C. Decomposition
D. Double replacement
a clam basically extends with the fragile outer system frame, therefore it retracts after a while, one of the main reasons we retrieve pearls from shells and clams.
Answer:
Refractory period
Explanation:
When two stimuli are applied one after another intermediately, muscles contract in response to the first stimuli. Once a muscle fiber receives stimulation to contract, it loses its excitability temporarily and cannot respond for a time. This period when the muscle loses its excitability is called refractory period.
Different types of muscle fibers have different duration of refractory period. The refractory period of skeletal muscle is shorter than that of cardiac muscle. During an absolute refractory period, the activation gates of voltage-gated Na+ channels are open and the channels are inactivating while the voltage-gated K+ channels are open.
The passing of traits depend upon traits, if the trait is advantageous and will help the organism to survive better than it will pass down in the next generation.
Natural selection is a process by which only those organisms or traits pass down to the next generation which are best for survival conditions.
Due to natural selection, genetic variation happens.
Different traits go into next generation according to conditions.
Thus, in case of lizards, if long legs are better for lizard to survive then this trait will pass down and if short legs are better than the trait of short leg will pass down to next generation.
Here, mechanism of natural section apply.
Learn more bout natural selection, here:
b. washing
c. irrigation
d. industry
B.
Cortex
C. Renal pelvis
D.
Renal vein