Genetics And Evolution

Step 1: A sea anemone attached to the shell of a hermit crab gains:

Transportation to food-rich areas
Access to food particles from the crab’s meals

Step 2: The hermit crab gains:

Protection from predators due to the stinging cells (nematocysts) of the sea anemone

Step 3: Since both organisms benefit from this association, the relationship is a type of mutualism.
Step 4: Mutualism is a form of symbiosis.

Step 1: During menstruation, the endometrium (not myometrium) breaks down. Hence, option (A) is incorrect.
Step 2: During ovulation, there is a peak in LH (and a small rise in FSH), but progesterone does not fall sharply; it rises after ovulation. Hence, option (B) is incorrect.
Step 3: In the proliferative phase, there is regeneration of the endometrium (not myometrium) along with maturation of the Graafian follicle. Hence, option (C) is incorrect.
Step 4: After ovulation, the ruptured Graafian follicle develops into the corpus luteum, which marks the secretory phase. This phase is characterized by increased secretion of progesterone to prepare the uterus for implantation.

Step 1: Growth Hormone (GH) is secreted by the anterior pituitary gland.
Step 2: If GH is secreted in excess during childhood, before epiphyseal plates close, it leads to gigantism.
Step 3: If GH is secreted in excess during adulthood, after epiphyseal plates have closed, it leads to acromegaly.
Step 4: Acromegaly is characterized by enlargement of hands, feet, jaw, and facial bones.

Step 1: Recall the structure of chromatin. Chromatin is the genetic material present in the nucleus of eukaryotic cells. It appears as a thread-like structure during interphase.
Step 2: Identify the components of chromatin. Chromatin consists of:
DNA (a nucleic acid), which carries genetic information.
Proteins, mainly histones and some non-histone proteins, which help in packaging and regulation of DNA.
Step 3: Eliminate incorrect options.
Only nucleic acid — incorrect, proteins are essential for DNA packaging.
Only protein — incorrect, DNA is the genetic material.
None of these — incorrect.
Hence, the correct answer is

Step 1: Recall the structure of DNA. DNA consists of two antiparallel polynucleotide strands forming a double helix.
Step 2: Identify the bonds between the strands. The two DNA strands are held together by hydrogen bonds formed between complementary nitrogenous bases:
Adenine (A) pairs with Thymine (T) via two hydrogen bonds.
Guanine (G) pairs with Cytosine (C) via three hydrogen bonds.
Step 3: Eliminate incorrect options. Nitrogen, oxygen, and carbon atoms are part of the bases and backbone, but they do not form the bonds that hold the two strands together.
Hence, the correct answer is

Step 1: Recall the discovery of DNA structure. James Watson and Francis Crick proposed the double helical structure of DNA based on:
X-ray diffraction data (by Rosalind Franklin and Maurice Wilkins),
Chargaff’s rules on base pairing.
Step 2: Identify the year of discovery. Their landmark paper titled \emph{“A Structure for Deoxyribose Nucleic Acid”} was published in the journal \emph{Nature} in the year:
Step 3: Eliminate incorrect options.
1951 — Before sufficient experimental evidence
1952 — X-ray studies ongoing
1962 — Year Watson, Crick, and Wilkins received the Nobel Prize
Hence, the correct answer is