All Free Biology MCQs with Answers

• A. Mitochondria
• B. Lysosome
• C. Plastids
• D. Ribosome

Explanation: The correct answer is mitochondria. Mitochondria are known as the powerhouses of the cell because they generate most of the cell's supply of ATP, which is used as a source of chemical energy. They do this through aerobic respiration, a process that involves oxygen to convert glucose into ATP. In contrast, lysosomes are involved in breaking down waste materials, plastids are involved in photosynthesis, and ribosomes synthesize proteins, none of which are directly involved in the process of aerobic respiration.

• A. Polyploid
• B. Polysome
• C. Polynucleotide
• D. Polysaccharide

Explanation: A polyribosome (or polysome or ergosome) is a group of ribosomes bound to an mRNA molecule like "beads" on a "thread". While other options, i.e. Polyploidy is the heritable condition of possessing more than two complete sets of chromosomes. Polynucleotides are linear biopolymers that are composed of several nucleotide monomers with covalent bonds in a chain. Polysaccharides are a major class of biomolecules. They are long chains of carbohydrate molecules, composed of several smaller monosaccharides.

• A. 70S
• B. 80S
• C. 60S
• D. 40S

Explanation: Smaller ribosomes (70S) are present in prokaryotic cells, but larger ribosomes (80S) are present in eukaryotic cells.

• A. Phagocytosis
• B. Pinocytosis
• C. Exocytosis
• D. Endocytosis

Explanation: Phagocytosis is the process by which a cell uses its plasma membrane to engulf a large solid particle, giving rise to an internal compartment called the phagosome. It is one type of endocytosis, while pinocytosis, otherwise known as fluid endocytosis, is a mode of endocytosis in which small particles suspended in extracellular fluid are brought into the cell through an invagination of the cell membrane, resulting in a suspension of the particles within a small vesicle inside the cell.

• A. Ribosome
• B. Endoplasmic reticulum
• C. Nucleolus
• D. Smooth endoplasmic reticulum

Explanation: The correct answer is Ribosome. Ribosomes are the cellular organelles where proteins are synthesized by translating messenger RNA (mRNA) into polypeptide chains. While the rough endoplasmic reticulum works closely with ribosomes in protein synthesis, it is not the primary site. The nucleolus, on the other hand, is responsible for making ribosomes, and the smooth endoplasmic reticulum is involved in lipid synthesis, not protein synthesis.

• A. Golgi complex
• B. Nucleus
• C. Endoplasmic reticulum
• D. Vacuoles

Explanation: Vacuole is single membrane bounded organelle. This single membrane bounding vacuole is known as tonoplast.

• A. Leucoplasts
• B. Lysosomes
• C. Glyoxysomes
• D. Peroxisomes

Explanation: Lysosomes are membrane-bound organelles containing hydrolytic enzymes that digest cellular waste, including old or damaged organelles, through a process known as autophagy. They play a crucial role in cellular maintenance and recycling. In contrast, leucoplasts are involved in storage, glyoxysomes in fatty acid conversion in plants, and peroxisomes in oxidative reactions, none of which involve the breakdown of organelles.

• A. Ribosomes
• B. Lysosomes
• C. Golgi body
• D. Cisternae

Explanation: Ribosomes are the site of protein synthesis in the cell, where they translate genetic information from mRNA to synthesize polypeptide chains. Lysosomes are involved in digestion within the cell, the Golgi body processes and packages proteins and lipids, and cisternae are structural components of the Golgi apparatus and endoplasmic reticulum, not directly responsible for protein synthesis.

• A. Mitochondria
• B. Chloroplast
• C. Ribosomes
• D. Golgi body

Explanation: Golgi complex is considered as secretory organelle of the cell. Secretory proteins are synthesized on RER, then transferred to Golgi apparatus through SER for final processing and packaging and finally released as secretory vesicles.

• A. Nucleus
• B. DNA
• C. Ribosomes
• D. Cell surface membrane

Explanation: The correct answer is the nucleus. It is a hallmark of eukaryotic cells, encapsulating the cell's genetic material within a distinct, membrane-bound structure. Prokaryotic cells lack this feature; their genetic material is dispersed within the cell without a surrounding nuclear membrane. The other options are common to both cell types: DNA is present in all cells as the genetic blueprint, ribosomes are universal sites of protein synthesis, and the cell surface membrane is fundamental to maintaining cellular integrity and homeostasis.