Questions

Papayas are yellow due to the presence of carotene and xanthophyll pigments i.e, Caricaxanthin present in the chromoplasts of the fruit pulp.

The coloration of the different tissues in plants is due to the plastids which are present in the cells. Leucoplasts are white in colour, chloroplasts are green in colour and chromoplasts are of various colours. These plastids can take any colour at different time. Therefore, green fruits ( chloroplasts) turn colurful (chromoplasts) at maturity.

Nostoc is a prokaryote. Prokaryotic cells lack membrane bound organelles and well organized nucleus, that is nuclear envelope is absent in these cells.

The nuclear envelope, also known as the nuclear membrane, a bilayer membranes which surrounds the nucleus, and in eukaryotic cells it encases the genetic material.