Answer:
d.The wing-assisted incline running theory postulates that wings were initially used to maintain balance while climbing up slopes.
Explanation:
Two theories were given to explain the origin of avian flight. The top-down theory suggested that the birds' ancestors were tree dwelling species. They took help of wings to glide from tree to tree in order to avoid predator or catch prey. The bottom up theory suggested that the birds' ancestors were ground dwelling species. They took help of wings to maintain a balance and provide a lift for efficient running.
Wing-assisted incline running was a mixture of both the above theories and gave a balanced view point. According to it, birds' ancestors used wings to maintain a balance while running up inclined slopes. The wings helped them to save energy while scaling slopes and eventually a flight mechanism was also developed.
Carbon dioxide and oxygen cannot pass through but move in and out
Answer:
The correct answer is ''METAPHASE I.''
Explanation:
Metaphase I is the stage in which chromosomal studies are generally performed, because its morphology is very clear. The chromosomes, moved by the mitotic spindle, are placed in the center, between the two asters and form the so-called metaphase plate, in which the chromosomes are positioned in such a way that the kinetochore of each sister chromatid are oriented towards the opposite poles. Keeping chromosomes on the cell equator implies a balance between the forces of the microtubules that tend to move the kinetochores toward opposite poles, so positioning them in the center involves a great deal of energy.In each kinetochore, between 20-30 microtubules can be anchored, which exert traction force towards the pole from which they come, so the metaphase plate is maintained by the balance between the opposite forces of the poles on the chromosomes, which hold their sister chromatids by centromeric cohesin.
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