Problem 26 - Objective Biology for NEET

Question

Where are ribosomes found in eukaryotic cells? (a) Cytoplasm (b) Mitochondria (c) Chloroplast (d) All of these

Step-by-Step Solution

Answer

Ribosomes are found in all these organelles: the cytoplasm, mitochondria, and chloroplasts. Answer is (d) All of these.

Step 1: Understanding Eukaryotic Cells

Eukaryotic cells contain many organelles, among them the cytoplasm, mitochondria, and chloroplasts. Understand the role of these organelles in the cell and the possible presence of ribosomes there.

Step 2: Ribosomes in the Cytoplasm

Decipher that the cytoplasm, the jelly-like substance within the cell, is the site where most cellular activities occur. Ribosomes can be found here floating freely or attached to the endoplasmic reticulum, facilitating protein synthesis.

Step 3: Ribosomes in the Mitochondria

Realize that mitochondria, known as the powerhouse of the cell, contain their own set of ribosomes. This is because they have their own DNA and can create some of their own proteins.

Step 4: Ribosomes in the Chloroplasts

Ascertain that chloroplasts, present in plant cells for photosynthesis, also contain their own ribosomes. Similar to mitochondria, they have their own DNA and can synthesize some of their own proteins.

Step 5: Conclusion

To conclude, ribosomes are found in all these organelles: the cytoplasm, mitochondria, and chloroplasts of eukaryotic cells. Therefore, the correct answer is (d) All of these.

Key Concepts

Eukaryotic Cells

Eukaryotic cells are complex structures that make up plants, animals, fungi, and protists. Unlike prokaryotic cells, they have a defined nucleus enveloped in a nuclear membrane. This nucleus houses the cell’s genetic material. But that's just the beginning. Eukaryotic cells also contain various specialized structures known as organelles. These organelles perform essential tasks for the cell's survival and function. For instance, the mitochondria generate energy, while the chloroplasts carry out photosynthesis in plant cells. Understanding these components helps to appreciate the complexity and efficiency of eukaryotic cells.

Cytoplasm

The cytoplasm is the jelly-like substance within the cell. It fills the space between the cell membrane and the nucleus. One of its main roles is hosting many of the cell's metabolic activities.

• Contains water, ions, and nutrients vital for cell function.


• Provides a medium where cell organelles can remain suspended and separated.


• Acts as a venue for cellular processes like glycolysis and protein synthesis.

In eukaryotic cells, ribosomes—essential for protein production—either float freely in the cytoplasm or are attached to the surface of the endoplasmic reticulum.

Mitochondria

Mitochondria are crucial organelles known as the cell's powerhouse. They produce ATP (adenosine triphosphate), the energy currency of the cell, by breaking down sugar through a process called cellular respiration. Mitochondria are unique because:

• They have a double membrane structure.


• Contain their own DNA, enabling them to produce some of their own proteins through ribosomes.


• Have their own set of ribosomes, making them semi-autonomous.

These features underline the mitochondria’s evolutionary history, hinting at their ancestral origins as independent organisms.

Chloroplasts

Chloroplasts are unique to plant cells and some algae, and they play a pivotal role in the process of photosynthesis—where light energy is converted into chemical energy for the plant. They contain a distinctive set of structures:

• Thylakoid membranes where the photosynthesis takes place.


• A green pigment called chlorophyll, which captures the sunlight.


• Similar to mitochondria, chloroplasts also have their own DNA and ribosomes.

These ribosomes enable chloroplasts to synthesize some of their proteins. The presence of ribosomes in chloroplasts highlights their autonomous capabilities, further suggesting their origin as independent entities before becoming part of plant cells.