All Free Biology MCQs with Answers

• A. Lamellar model
• B. Unit membrane model
• C. Fluid mosaic model
• D. Molecular lipid model

Explanation: The fluid mosaic model is the most widely accepted and current model for the plasma membrane. In 1972, S.J. Singer and G.L. Nicolson proposed this model. According to this model, the plasma membrane consists of a phospholipid bilayer with embedded proteins. The lipid bilayer is fluid, meaning the individual lipid molecules can move laterally within the membrane. The proteins are not static but form a dynamic mosaic pattern floating within the lipid bilayer. The fluidity and mosaic arrangement of lipids and proteins in the membrane allow various functions, such as cell signaling, transport, and maintaining cell structure.

• A. Numerical aperture
• B. Focal length of objective
• C. Focal length of eye piece
• D. Tube length

Explanation: Numerical aperture (NA) is a measure of the ability of the lens in the microscope to gather light and resolve fine details of the specimen. It is related to the angle of light acceptance and the refractive index of the medium between the specimen and the lens. Higher numerical aperture generally results in better resolution and higher quality images, but it does not determine the magnification of the microscope. Other terms given in the options either directly or indirectly determine the magnification of the compound microscope.

• A. Nucleoplasm
• B. Nuclear envelope
• C. Nucleolus
• D. Cytoplasm

Explanation: The cytoplasm is the region where metabolic processes like PROTEIN SYNTHESIS occur. Nucleoproteins, which are complexes of proteins and nucleic acids, including histones, transcription factors, and RNA-binding proteins, are primarily synthesized in the cytoplasm. These proteins play essential roles in gene regulation, DNA replication, RNA processing, and other cellular processes involving nucleic acids.

• A. Ribosomes and rRNA
• B. Only rRNA
• C. Peroxisomes
• D. Several ribosomes held together by string of mRNA

Explanation: Polyribosomes, also known as polysomes, are clusters of several ribosomes bound to a single mRNA molecule. These ribosomes work simultaneously to translate the mRNA sequence into a polypeptide chain during protein synthesis. Polyribosomes play a critical role in increasing the efficiency of protein production in the cell.

• A. Proteins and carbohydrates
• B. Proteins and lipids
• C. Proteins, lipids and carbohydrates
• D. Proteins, some nucleic acids and lipids

Explanation: The plasma membrane is a dynamic and selectively permeable barrier that surrounds the cell, and it is made up of three main types of biomolecules: proteins, lipids, and carbohydrates. The lipids, mainly phospholipids, form a bilayer, while the proteins are embedded in the lipid bilayer or extend through it. The carbohydrates are often found on the outer surface of the membrane as part of glycoproteins or glycolipids.

• A. Chromatography
• B. X­-rays diffraction
• C. Differential centrifugation
• D. Auto­-radiography

Explanation: Differential centrifugation is a widely used method for separating organelles from a cell homogenate. It takes advantage of the differences in size, shape, and density of the cellular components. During the process, the cell homogenate is subjected to a series of centrifugation steps at different speeds, allowing the larger and denser organelles to pellet at lower speeds while smaller components and debris remain in the supernatant.

• A. Unicellular fungus
• B. Multicellular fungus
• C. Unicellular, uninucleate green algae
• D. Unicellular multinucleate green algae

Explanation: Acetabularia is a unicellular green alga belonging to the family Polyphysaceae. It is well-known for its large size and distinct morphological features. Acetabularia has a single cell that is uninucleate, meaning it contains a single nucleus. It is an excellent model organism for nucleocytoplasmic studies and was extensively used in Hammerling's experiments to investigate the role of the nucleus in determining cell development and characteristics.

• A. Phospholipids and oligosaccharides
• B. Phospholipids and hemicellulose
• C. Phospholipids and integral proteins
• D. Phospholipids, extrinsic proteins and intrinsic proteins.

Explanation: According to the fluid mosaic model, the plasma membrane is a dynamic structure composed of phospholipids forming a lipid bilayer. It also contains integral proteins that are embedded within the lipid bilayer and extrinsic proteins that are loosely attached to the membrane's surface. Together, the phospholipids and proteins form the fluid mosaic pattern, where the proteins float in the lipid bilayer like pieces of a mosaic. Hence, option D is the most appropriate answer.

• A. Simple microscope
• B. Compound microscope
• C. Light microscope
• D. Electron microscope

Explanation: An electron microscope uses a beam of electrons instead of visible light to image the specimen, providing much higher magnification and resolution than light microscopes. It is capable of resolving the ultrastructure and internal organelles of cells with precise details. Electron microscopes come in two main types: transmission electron microscope (TEM) and scanning electron microscope (SEM). Hence, option D is the best choice.

• A. Endoplasmic reticulum
• B. Chloroplast
• C. Golgi apparatus
• D. Mitochondria

Explanation: Mitochondria are semi-autonomous organelles found in both animal and plant cells. They are often referred to as the "powerhouses" of the cell because they are responsible for generating most of the cell's supply of adenosine triphosphate (ATP), which is used as a source of chemical energy. Mitochondria have their own circular DNA and ribosomes, allowing them to produce some of their proteins independently. This characteristic of having their own genetic material and the ability to self-replicate makes mitochondria semi-autonomous organelles.