Question

Nucleus is absent in one of the following
(a)Companion cell
(b)Sieve tube cell
(c)A vessel and tracheid
(d)Both B and C

Answer 1

Hint: The cells that don’t contain a functioning nucleus are known as anucleated cells and such types of cells are found in plants with no Nucleus and organelles like ribosomes. These cells are dependent on nearby cells for their metabolic functions.

Complete answer:
There are some cells in plants that are dead and don’t contain a nucleus. These are the sieve tube cells and are called anucleate cells.
Sieve tube cells responsible for transportation in plants but they don’t contain a functional nucleus at maturity. They also lack organelles such as ribosomes and depend on a close association with the companion cells. These cells carry out all cellular functions of the sieve tube elements as they have a large number of ribosomes and mitochondria. These are connected to the sieve tube cells by plasmodesmata. In the case of seedless vascular plants, another similar type of cells exists which are known as albuminous cells and play the same role as companion cells.

Additional Information:
Xylem is another transport tissue of the plants but only carries transportation of water sap in one direction i.e. from root to the leaves. These consist of tracheid, vessels, parenchyma, and fibers. There are mainly two types of xylem- primary and secondary in which the former is formed during primary growth from procambium and the latter is formed during secondary growth from vascular cambium.

So, the correct answer is “Sieve tube cells”.

Note:
Companion cells are the cells that are in close association with the sieve tube elements as mentioned above and carry out all its metabolic functions with the help of its abundant ribosomes and mitochondria. These are of two types- Ordinary and transfer cells. Ordinary companion cells have smooth walls and have no plasmodesmata connection with any other cells except sieve cells. Transfer cells have uneven folded walls and scavenge solutes from the cells walls that actively pump requiring energy.