Botany and Plant Science

(A)An apical bud is the one that is at the end of the shoot.

Stems are characterized by the presence of nodes and internodes, whereas roots lack these structures.

Callus is unorganized actively dividing mass of cells maintained in culture. It has meristematic cell which has ample amount of cytoplasm to trigger cell division. It is an undifferentiated mass of cell which differentiates when treated with the growth hormones to promote cell division, differentiation and morphogenesis. It heals the injury in the cell as callus has meristematic cell which replaces the worn out and damaged cell by rapid cell division and it can also replace damage tissue developed in the region of wound.

Stigma, style, and ovary are parts of the female reproductive organ (pistil/carpel) of a flower. Pollen is the male gametophyte.

Out of the given fungi, Rhizopus, Mucor, and Saccharomyces are saprophytes. Puccinia is an obligate parasite causing rust disease in plants, and Albugo is a parasitic fungus causing white rust on crucifers. Thus, exactly three of them are saprophytic in nutrition.

Mucor and Rhizopus are fungi belonging to the family Mucoraceae. Mucor is called as pin mould. Rhizopus is known as black mould. They are saprophytic fungi that grow on dead and decaying organic material. The fungal mycelium of Mucor and Rhizopus look like fine cottony threads on the surface of the bread. Thus the correct answer is option C.

The black color of bread mold (Rhizopus) is primarily due to the mass of black-colored sporangia containing spores.

In mucor during sexual reproduction, compatible strains form short, specialized hyphae called gametangia. At the point where two complementary gametangia fuse, a thick-walled, spherical zygosporangium develops. The zygosporangium typically contains a single zygospore.

Sexual reproduction takes place during the unfavourable condition by means of gametangial copulation. The gametangia look alike and by conjugation, they give rise to zygospore.

• Citrus canker is a disease that affects citrus species caused by the bacterium Xanthomonas axonopodis.
  
• The bacteria causing diseases in humans are- Tuberculosis and cholera.
• Cholera is caused by the bacterium Vibrio cholera.
• Tuberculosis is caused by Mycobacterium tuberculosis. 

Roots do not show the distinction of nodes and internodes because the meristematic part of the roots is at the tip, but not in the middle showing differentiation. Roots have endogenous primary secondary and tertiary roots and rootlets.

A root cap is a protective covering over the tip of the root. Pandanus is known to have multiple roots because it has multiple prop roots covered with root caps.

Hygroscopic roots occur means water absorbing roots from the atmosphere. Hygroscopic roots occur in Vanda because it is an epiphyte which absorbs moisture from the atmosphere as its source of water.