The structure of alpha helix is stabilized by hydrogen bonds between the hydrogen atom attached to the electronegative nitrogen atom of a peptide linkage and the electronegative carbonyl oxygen atom of the fourth amino acid on the amino-terminal side of that peptide bonds. Within the helix, every peptide bond (except those close to each end of the helix) participates in such hydrogen bonding. Each successive turn of the helix is held to adjacent turns by three to four hydrogen bonds, conferring significant stability on the overall structure. Which of the following are correct statements regarding these findings?

A. At the ends of a helical segment, there are always three or four amide carbonyl or amino groups that participate in this stabilised helical pattern of hydrogen bonding.

B. Helix ends are exposed to the surrounding solvent, where they hydrogen-bond with water, or other parts of the protein may cap the helix to provide the needed hydrogen-bonding partners.

C. Helix can form in polypeptides consisting of either L- or D-amino acids but a D-amino acid will disrupt a regular structure consisting of L-amino acids, and vice versa.

D. The most stable form of a helix consisting of L-amino acids is left-handed.

E. 310 helix occupies similar place as turns in Ramachandran plot due to its confirmation

#Question id: 10651

#Unit 10. Ecological Principles

Which of the following value of A, B and C in above logistic growth of hypothetical population respectively?

#Question id: 10652

#Unit 10. Ecological Principles

Which factors (limited space or overcrowding; limited food; Predators; parasite and diseased) tend to act in a density-dependent manner; Tony Sinclair (1989) many studies of density dependence in 51 populations of insects, 82 populations of large mammals, and 36 populations of small mammals and birds. Which of the following observation is most likely true?

a) Insects showed a wide variety of causes of density dependence and no one density-dependent factor was of overriding importance

b) The lesser the amount of available food, the greater the mortality of large mammals

c) Space and social interactions were more important for smaller mammals and birds, because they are more territorial

#Question id: 10653

#Unit 10. Ecological Principles

All offspring are produced in a single reproductive event, we term this pattern semelparity. Which of the following is characteristics feature for semelparity individuals?

a) Semelparity is common in insects and other invertebrates

b) Semelparous organisms may live for many years before reproducing

c) semelparity occur only in plant

d) In semelparity, exploitation competition is more common than interference competition

#Question id: 10654

#Unit 10. Ecological Principles

Complete the following hypothetical life table for a bird

What will be population size in next generation?

#Question id: 10655

#Unit 10. Ecological Principles

Which of the following statements about the evolution of life histories is correct?

A) Unstable environments with unlimited resources favor r-selected populations.

B) K-selected populations are most often found in environments where density-independent factors are important regulators of population size.

C) Most populations have both r- and K-selected characteristics that vary under different environmental conditions.

D) The reproductive efforts of r-selected populations are directed at producing just a few offspring with good competitive abilities.

#Question id: 10656

#Unit 10. Ecological Principles

Which of the following is an incorrect statement about the regulation of populations?

A) The logistic equation reflects the effect of density independent factors, which can ultimately stabilize populations around the carrying capacity.

B) Density-independent factors have an increasingly greater effect as a population’s density increases.

C) High densities in a population may cause physiological changes that inhibit reproduction.

D) Because of the overlapping nature of population-regulating factors, it is often difficult to precisely determine their cause-and-effect relationships.