Question

These are the denselystained reticular structures present near the nucleus, consisting of many flat, disc shaped cisternae of \(0.5-1.0 \mu \mathrm{m}\) diameter. These are (a) chloroplasts (b) endoplasmic reticulum (c) mitochondria (d) Golgi apparatus.

Short answer

The correct answer is (d) Golgi apparatus.

Step-by-step solution

Identify the Organelle

To solve this exercise, recall the structure and function of each cellular organelle mentioned in the options. We are looking for an organelle that is characterized by densely stained reticular (network-like) structures present near the nucleus and consists of many flat, disc-shaped cisternae with a diameter of 0.5-1.0 micrometers.

Eliminate Incorrect Options

Chloroplasts are involved in photosynthesis and have a double membrane with thylakoids, not reticular structures near the nucleus. Endoplasmic reticulum is extensive, but not typically described as densely stained. Mitochondria have a double membrane and folds called cristae, not flat disc-shaped cisternae. The Golgi apparatus fits the description of having flat, disc-shaped cisternae and is located near the nucleus.

Choose the Correct Answer

Based on the provided information, only the Golgi apparatus matches the description of having densely stained, flat disc-shaped cisternae located near the nucleus. Therefore, the correct answer is (d) Golgi apparatus.

Key concepts

Cellular Organelles

Cellular organelles are specialized structures within cells that perform dedicated functions, often compared to the organs of a body. Each organelle has a unique role that contributes to the cell's overall operation. For example, mitochondria are known as the powerhouses of the cell, generating energy through respiration, while chloroplasts are crucial for photosynthesis in plant cells.

Organelles like the endoplasmic reticulum (ER) and the Golgi apparatus are part of what is known as the 'endomembrane system,' which synthesizes, folds, modifies, and transports proteins and lipids within the cell. It is crucial to recognize these organelles by their structure and staining patterns under a microscope; for instance, the densely stained areas near the nucleus, which the exercise describes, lead us directly to identify the Golgi apparatus.

Endoplasmic Reticulum

The endoplasmic reticulum (ER) is a network of membranous tubules and sacs called cisternae, pivotal for multiple cell functions. The ER comes in two forms: rough ER, studded with ribosomes, and smooth ER, without ribosomes.

The rough ER is primarily involved in protein synthesis and folding, as ribosomes on its surface translate mRNA into polypeptide chains that enter the ER lumen. The smooth ER is chiefly concerned with lipid metabolism and detoxification processes. The ER's extensive network contributes to its function but does not typically exhibit the densely stained reticular structures near the nucleus mentioned in the exercise, which helps in distinguishing it from the Golgi apparatus.

Cell Structure and Function

Understanding cell structure and function is essential for identifying organelles like the Golgi apparatus. This organelle is central to modifying, sorting, and packaging proteins and lipids for delivery to their destinations. It looks like a stack of pancakes, with each 'pancake' being a cisterna.

The Golgi apparatus' proximity to the nucleus and its distinctive composition of flat discs are key indicators of its identity. When observing cell structure, scientists must consider the physical characteristics of organelles and their staining patterns. This knowledge not only helps in identifying structures under the microscope but also provides insight into each organelle's specific role within the intricate tapestry of cellular functions.