All questions of Membrane-Bound Organelles (BIO) for MCAT Exam

Single membrane-bound: Some organelles are bounded by a single membrane. For example, vacuole, lysosome, Golgi Apparatus, Endoplasmic Reticulum etc. They are present only in a eukaryotic cell.

Carbohydrates are organic compounds synthesized in the chlorophyll containing cells of some bacteria,-algae and green plant cells, during photosynthesis. Certain photoautotrophic bacteria eg. Green sulphur bacteria and purple sulphur bacteria contain pigments like chlorobium chlorophyll and bacteriochlorophyll respectively that helps them in photosynthesis. During photosynthesis carbon dioxide is reduced into carbohydrates by water and oxygen is liberated. so option C ) is correct ( . __ .)

Lysosomes are spherical bodies, or vacuoles that are enclosed by a single membrane  (membrane- bound organelles). It contains different hydrolytic enzymes, such as proteases, lipases, and nucleases that are capable of breaking down all types of biological polymers (e.g., proteins, nucleic acids, carbohydrates, and lipids) that enter the cell or are no longer useful to the cell. So, the correct answer is 'Lysosome'.

It is consisted of a porphyrin head and a phytol tail. Porphyrin is a cyclic tetrapyrol structure, having a magnesium atom in the centre. Chlorophyll a methyl group (CH3) is attached to the third carbon in the porphyrin head.

Plastids have no role in mitotic division of a cell. They are only responsible for colors. Eg; Animal cells do not have plastids yet they can divide.

Oxysomes are the structure present in the inner surface of mitochondra.it is also known as f0-f1particle or Atp synthese.oxysomes play an important role in formation energy for the functioning of the cell.oxysome help in the electron transport i.e oxidation and reduction rxn in respiration.

**Mitochondria and Cristae**

The correct answer is option B: Mitochondria. Cristae are indeed associated with mitochondria.

**Explanation**

Mitochondria are double-membrane-bound organelles found in most eukaryotic cells. They are often referred to as the "powerhouses" of the cell because they generate most of the cell's supply of adenosine triphosphate (ATP), which is used as a source of chemical energy.

One important feature of mitochondria is their inner membrane, which is highly folded to form structures called cristae. Cristae are invaginations or inward folds of the inner mitochondrial membrane. These folds increase the surface area of the inner membrane, allowing for more space where ATP synthesis can occur.

**Function of Cristae**

The presence of cristae in mitochondria is crucial for their function. The inner membrane of the mitochondria contains the electron transport chain (ETC) complexes, which play a key role in generating ATP through aerobic respiration. The ETC complexes are responsible for transferring electrons from electron donors to electron acceptors, creating a proton gradient across the inner mitochondrial membrane. This proton gradient is then used to drive the synthesis of ATP.

The highly folded structure of cristae increases the surface area available for the ETC complexes and ATP synthase, which are embedded in the inner membrane. This allows for more efficient ATP production, as there is a higher concentration of these proteins in the cristae. The increased surface area also allows for more efficient electron transfer and proton pumping, further enhancing ATP synthesis.

**Summary**

Cristae are associated with mitochondria. They are invaginations or inward folds of the inner mitochondrial membrane. The presence of cristae increases the surface area of the inner membrane, allowing for more efficient ATP synthesis through the electron transport chain and ATP synthase.

Overview of the Endomembrane System
The endomembrane system is a complex network of membranes that play crucial roles in the synthesis, modification, transport, and degradation of biomolecules within eukaryotic cells.
Key Components
- Endoplasmic Reticulum (ER):
- There are two types: rough ER (with ribosomes) and smooth ER (without ribosomes).
- Rough ER is involved in protein synthesis and folding, while smooth ER is associated with lipid synthesis and detoxification.
- Golgi Apparatus:
- Acts as a processing and packaging center for proteins and lipids synthesized in the ER.
- Modifies, sorts, and sends these molecules to their destinations, which can include lysosomes, the cell membrane, or secretion outside the cell.
- Vesicles:
- Small membrane-bound sacs that transport materials between the different components of the endomembrane system.
- They carry proteins from the ER to the Golgi apparatus and from the Golgi to other destinations.
Why Other Options Are Incorrect
- Option A (Nucleus, mitochondria, and chloroplasts):
- The nucleus is part of the endomembrane system, but mitochondria and chloroplasts are not; they have their own membranes and functions.
- Option B (Ribosomes, Golgi apparatus, and lysosomes):
- Ribosomes are not membrane-bound organelles; they are involved in protein synthesis and can be free in the cytoplasm or attached to the rough ER.
- Option C (Cytoskeleton, peroxisomes, and vacuoles):
- The cytoskeleton provides structure but is not part of the endomembrane system. Peroxisomes are involved in metabolic processes and are not part of this system either.
Conclusion
Thus, the correct answer, option D, accurately reflects the essential components of the endomembrane system, highlighting their interconnected roles in cellular function.

The tonoplast is the cytoplasmic membrane surrounding a vacoule,separating the vacuolar contents from the cells cytoplasm.It is also known as vacuolar membrane.Hence,the correct answer is option 'A'.