Question

A common characteristic feature of plant sieve tube cells and most of mammalian erythrocytes is
A) Absence of mitochondria
B) Presence of cell wall
C) Presence of haemoglobin
D) Absence of nucleus

Answer 1

Most part of the RBC is covered with hemoglobin and sieve tube elements are associated with companion cells.

Complete answer:
Sieve element is a major conductive component of the phloem. They are highly organized tissue that transports organic compounds during photosynthesis. A sieve tube is made up of sieve-tube elements joined end-to-end. There are sieve areas, a group of pores on sieve elements, through which photosynthetic material and organic compounds for tissue function move.
In angiosperms, the sieve tube (element) and the cell associated with it is called companion cell. In gymnosperms and other primitive vascular plants, the sieve cell (element) has an associated cell with it, called an albuminous cell.
Sieve cells are long conducting cells in the phloem that do not form sieve tubes. Sieve cells are lined with albuminous cells which helps it in transporting organic materials. In most seedless vascular plants and gymnosperms, sieve cells are the only way to transport molecules.
Erythrocytes, also known as red blood cells, are specialized cells for transporting oxygen from lungs to all of the body tissue. They are flattened biconcave disks that provide a large surface-to-volume ratio. They originate in red bone marrow and a mature erythrocyte has a lifespan of 120 days. Males have about 5.4 million erythrocytes per microliter of blood and females have 4.8 million per microliter. They have a mean diameter of about 7-8 micrometers.
The cytoplasm of red blood cells (RBCs) have plenty of hemoglobin that binds to oxygen and gives red color to the cells. Hemoglobin is an iron containing molecule and can transport up to 4 molecules of oxygen or carbon dioxide. Erythrocytes make up about 25 percent of the total cells in the body.
They do not contain any organelles including nucleus. They lose their nuclei at maturity. The same goes with sieve cells, they lose their nuclei at maturity.

Thus, the correct option is option D, ‘absence of nucleus ’.

Note: Sieve cells are different from sieve tube members. Sieve tubes have companion cells which cover the function of the nucleus. Whereas, sieve cells have albuminous cells. Sieve cells are present in gymnosperms and sieve tube members in angiosperms.