When Darwin studied the finches on the Galapagos Islands, he was able to observe the varying sizes of the finch beaks. Which of the following explains the beak size and shape in relation to the environment? a
The beak changed in size and depth only during the lifetime of the fittest birds able to survive the drought.

b
The beaks of individual birds in the population changed size and shape between the time of fledging the nest and adulthood, due to the environmental stress induced by drought.

c
The beak size and shape had corresponding genetic codes in the DNA that were modified or mutated by individuals when attempting to survive the stressful environment of the drought.

d
The beak size and shape varied across the population and sometimes conferred benefits in feeding, survivorship, and reproduction that were passed down to surviving offspring.

D. The beak size and shape varied across the population and sometimes conferred benefits in feeding, survivorship, and reproduction that were passed down to surviving offspring.

Explanation:

Natural selection, adaption, etc. This beak size and shape was most beneficial during this period (the drought), so the population made it a point to reproduce with those who had this mutation. Thus, letting their offspring survive.

you're crazy : )

the answer is: the „power stroke“ step.

muscle contraction can be divided into a few steps:

1. the release of ach (acetylcholine) in the synaptic cleft, binding of ach for its receptor and consequently opening of the ca channels.

2. the release of ca, binding of ca for the troponin

3. troponin shifting the tropomyosin, which was blocking the active site on the actin

4. myosin heads attaching to actin by breaking down atp to adp+ pi

5.   formation of the ‘cross-bridge’ on the active site of the actin filament by myosin head

6. “power stroke” -the cross bridge pulls actin, which slides over the myosin

9.     7. the release of adp completes the cross-bridge movement and atp attaches to myosin, breaking the actin-myosin cross bridge.