Following statements are regarding to gastrulation in chick embryo.

A. During gastrulation, future mesodermal and endodermal cells migrate from the epiblast through the primitive streak into the interior of the blastoderm.

B. An aggregation of cells, known as Hensen’s node, forms at the posterior end of the streak.

C. As the streak extends, cells of the epiblast move toward the primitive streak, through it, and then outward again underneath the surface to give rise internally to the mesoderm and endoderm, the latter displacing a lower layer of cells called the endoblast.

D. Cells that remain in the epiblast form the endoderm.

Which of the following statements are correct?

#Question id: 4637

#Unit 11. Evolution and Behavior

A biologist studied a population of squirrels for 15 years. During that time, the population was never fewer than 30 squirrels and never more than 45. Her data showed that over half of the squirrels born did not survive to reproduce, because of competition for food and predation. In a single generation, 90% of the squirrels that were born lived to reproduce, and the population increased to 80. Which inference(s) about this population might be true?

A) The amount of available food may have increased.

B) The number of predators may have decreased.

C) The squirrels of subsequent generations should show greater levels of genetic variation than previous generations, because squirrels that would not have survived in the past will now survive.

Choose correct combination,

#Question id: 4639

#Unit 11. Evolution and Behavior

If the HMS Beagle had completely bypassed the Galapagos Islands, Darwin would have had a much poorer understanding of the

#Question id: 4640

#Unit 11. Evolution and Behavior

During drought years on the Galapagos, small, easily eaten seeds become rare, leaving mostly large, hard-cased seeds that only birds with large beaks can eat. If a drought persists for several years, what should one expect to result from natural selection?

#Question id: 4641

#Unit 11. Evolution and Behavior

Which of the following statements is an inference of natural selection?

#Question id: 4642

#Unit 11. Evolution and Behavior

Which of Darwinʹs ideas had the strongest connection to Darwin having read Malthusʹs essay on human population growth?

#Question id: 4643

#Unit 11. Evolution and Behavior

The treeʹs horizontal axis is a timeline that extends from 100,000 years ago to the present; the vertical axis represents nothing in particular. The labeled branch points on the tree (V—Z) represent various common ancestors. Letʹs say that only since 50,000 years ago has there been enough variation between the lineages depicted here to separate them into distinct species, and only the tips of the lineages on this tree represent distinct species.

How many separate species, both extant and extinct, are depicted in this tree?