Photoperiodism is the physiological reaction of organisms to the length of the night or a dark period. It occurs in plants and animals. Photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light and dark periods.

Hence, the correct option is (A).

Cytokinins were originally defined as chemicals that induce cell proliferation and trigger callus differentiation to shoot when applied with auxins, but now it is known that cytokinins play a key role in many aspects of plant growth and development, including embryogenesis, maintenance of root and shoot meristems.
Hence, the correct option is (C).

Sieve elements are specialized cells that are important for the function of phloem, which is a highly organized tissue that transports organic compounds made during photosynthesis. Sieve elements are the major conducting cells in the phloem. Conducting cells aid in the transport of molecules especially for long-distance signaling. In-plant anatomy, there are two main types of sieve elements. Companion cells and sieve cells originate from meristems, which are tissues that actively divide throughout a plant's lifetime.

Hence, the correct option is (D).

VNTRs are an important source of RFLP genetic markers used in linkage analysis (mapping) of genomes. They have become essential in forensic crime investigations. The technique may use PCR, size determined by gel electrophoresis, and Southern blotting to produce a pattern of bands unique to each individual.
Hence, the correct option is (A).

Phylum Porifera are the lowest multicellular animals belonging to the kingdom Animalia. Some of the important characteristics of the phylum Porifera are mentioned below.

(1) The cells of Poriferans are loosely organized. They are mostly found in marine water.

(2) Their body is usually cylindrical.

(3) They depict the cellular grade of organization.

(4) The body comprises numerous pores known as Ostia and osculum.

(5) They reproduce asexually by budding, and fragmentation.

Hence, the correct option is (A).

The three-dimensional geometry of a protein molecule is so important to its function that four levels of structure are used to describe a protein. The first level, or primary structure, is the linear sequence of amino acids that creates the peptide chain. The enzyme amylase is a good example of a globular protein.

Hence, the correct option is (C).

The ethmoid bone is one of the 8 bones of the cranium. It is situated at the roof of the nasal cavity and between the two orbital cavities. It contributes to the medial wall of the orbit and forms part of the anterior cranial fossa, where it separates the nasal cavity (inferiorly) from the cranial cavity.

Hence, the correct option is (B).

Hydra uses regenerative cells for reproduction in the process of budding. In hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and, when fully mature, detach from the parent body and become new independent individuals.

Hence, the correct option is (B).

Many of the so-called red tides are caused by excessive blooms of dinoflagellates. When persons eat shellfish that have consumed the poisonous dinoflagellates Gonyaulax oatenella or Gonyaulax tamarensis, a disease known as shellfish poisoning results in which are often fatal. NSP is caused by the ingestion of shellfish exposed to blooms of the dinoflagellate.

Hence, the correct option is (B).

When a solute is dissolved in water, water molecules are less likely to diffuse away via osmosis than when there is no solute. A solution will have a lower and hence more negative water potential than that of pure water.

Hence, the correct option is (B).