Question

Name the following
A. Thread-like structure in the nucleus
B. The only animal cell to have plastid.

Answer 1

There are numerous organelles in a living cell of a living organism. Nucleus is the most important organelle among all as it contains the whole genetic information of a cell or of a living organism. Another organelle called plastid is specifically found in plant cells and it is extremely rare in any animal cell except one.

Complete step by step answer:
-Thread - like structure in the nucleus
In the nucleus the thread-like structure is present called as chromosome
All the genetic information of a cell is present in the chromosome in the form of DNA. Also the chromosome contains some basic proteins , non-histone proteins and RNA molecules.
There is an essential constriction present in the structure of every chromosome called primary constriction or centromere which plays an important role during the division of nucleus.
Equal division of DNA between the daughter cells during cell division is due to presence of chromosomes only.

-The only animal cell having plastids
Plastids are the typical plant cell organelle , but the only animal cell having plastids in it's cell is the sea slug (Elysia chlorotica).
It is a marine mollusc (included in animal kingdom) . The major use of having plastid in these is a process called photosynthesis as chloroplasts (type of plastid) are found in them.
This chloroplast is not present in these animals from the starting of their life cycle instead they incorporate the chloroplast by phagocytosis process through an alga.

Note: There are 4 types of chromosomes on the basis of position of centromere - metacentric, sub metacentric , acrocentric and telocentric .The pictorial representation of a person's chromosome is called the karyotype . From this the chromosomes can be examined.Elysia chlorotica , uses the green colour obtained from the algae as a camouflage against predators that improves their survival