Option -D.
Mature sieve tube cells lack nucleus. the functions of sieve tubes are controlled by the nucleus of companion cells.
erythrocytes lack nucleus which enables more haemoglobin within cell to carry more oxygen.

A common characteristic feature of plant sieve tube cells and most mammalian erythrocytes is the absence of nucleus.

Explanation:

Plant sieve tube cells and mammalian erythrocytes, also known as red blood cells, both possess certain similarities in their structural and functional characteristics. One of the common features shared by these two cell types is the absence of a nucleus.

Plant sieve tube cells:

- Plant sieve tube cells are specialized cells found in the phloem tissue of plants. They play a crucial role in transporting sugars, nutrients, and other organic molecules throughout the plant.
- Sieve tube cells are elongated and arranged end-to-end to form sieve tubes, which function as conduits for the transport of organic substances.
- These cells lack a nucleus, allowing for more efficient transport of materials through the sieve tubes.
- The absence of a nucleus also enables more space for the movement of sap and other substances.

Mammalian erythrocytes:

- Erythrocytes, or red blood cells, are the most abundant type of blood cells in the human body. Their primary function is to transport oxygen from the lungs to various tissues and organs.
- These cells are biconcave in shape, enabling them to have a larger surface area for gas exchange.
- Erythrocytes lack a nucleus, which allows for more space to accommodate hemoglobin, the protein responsible for carrying oxygen.
- The absence of a nucleus also enhances their flexibility, enabling them to squeeze through narrow capillaries and deliver oxygen efficiently.

Significance of the absence of nucleus:

- The absence of a nucleus in both plant sieve tube cells and mammalian erythrocytes provides more space for specialized functions.
- In sieve tube cells, it allows for efficient movement of sap and nutrients through the sieve tubes.
- In erythrocytes, it allows for the storage of a larger amount of hemoglobin, enabling efficient oxygen transport.

In conclusion, the common characteristic feature of plant sieve tube cells and most mammalian erythrocytes is the absence of a nucleus. This absence serves specific purposes in each cell type, contributing to their specialized functions in the respective organisms.