Question

The following cells are without nucleus (a) Erythrocytes of many mammals (b) Sieve tube cells of vascular plant (c) Bacterial cell (d) All of these

Short answer

The correct answer is (d) All of these. All the given cells - erythrocytes of many mammals, sieve tube cells of vascular plants, and bacterial cells - are without a nucleus.

Step-by-step solution

Understand the concept of nuclei in cells

First, get an understanding of what a nucleus is. In cell biology, the nucleus is a membrane-bound organelle found in most eukaryotic cells. It contains most of the cell's genetic material, organized as multiple discrete DNA molecules along with different proteins, such as histones, to form chromosomes.

Analyzing Answer Option (a) - Erythrocytes of Many Mammals

The erythrocytes, also known as red blood cells, of many mammalian species do not contain nuclei when mature. Therefore, this is a correct statement.

Analyzing Answer Option (b) - Sieve Tube Cells of Vascular Plants

Sieve tube elements, found in vascular plants, are cells that do not contain nuclei. Thus, this statement is also correct.

Analyzing Answer Option (c) - Bacterial Cell

Bacterial cells are prokaryotic and thereby do not have a membrane-bound nucleus. Hence, this statement is correct too.

Key concepts

Erythrocytes

Erythrocytes, commonly known as red blood cells, play a pivotal role in transporting oxygen from the lungs to various tissues and organs within the body, and in transferring carbon dioxide back to the lungs for exhalation. A key characteristic of mature erythrocytes in many mammals, including humans, is their lack of a nucleus.

During their development, erythrocytes initially possess a nucleus, which is later ejected to provide more space for hemoglobin, the protein responsible for oxygen transport. This structural adaptation allows erythrocytes to maximize their oxygen-carrying capacity. The absence of a nucleus means these cells cannot repair themselves or divide, which limits their lifespan to about 120 days in humans.

Sieve Tube Cells

Sieve tube cells are specialized cells that are crucial for the transport of sugars and nutrients in vascular plants. They are one of the two types of cells that make up the phloem, the other being companion cells.

Sieve tube cells are unique as they are enucleated at maturity, meaning they do not contain a nucleus. This lack of a nucleus creates a large space within the cells, which facilitates the efficient flow of sap. To function, they rely on the close association with companion cells, which are nucleated and regulate the metabolic activities necessary for the survival and functionality of the sieve tube cells.

Prokaryotic Cells

Prokaryotic cells represent a group of organisms that includes bacteria and archaea. Unlike eukaryotic cells, which have a defined nucleus containing genetic material, prokaryotic cells do not have a membrane-bound nucleus. Their DNA is located in a region called the nucleoid, which is an open area within the cytoplasm.

Prokaryotic cells are generally smaller and less complex than eukaryotic cells, lacking many of the organelles found in the latter. However, they are incredibly diverse and adaptable, capable of surviving in a wide range of environments, from extreme heat to intense cold. Their simple structure is one reason prokaryotes can replicate quickly, allowing for rapid evolution and adaptation.

Cell Biology

Cell biology is a scientific discipline that focuses on the study of cells, which are the basic building blocks of life. This field examines the structure, function, and behaviors of cells, as well as the way in which they interact with their environment.

Understanding the nucleus, an organelle found in most eukaryotic cells, is crucial as it houses the majority of genetic material in the form of chromosomes. The presence or absence of a nucleus, as in the case of erythrocytes, sieve tube cells, and prokaryotic cells, has significant implications for cell function and differentiation. Cell biology encompasses a wide array of topics, including cellular processes such as the cell cycle, signaling pathways, cell division, and energy dynamics within the cell.