MCQs on Cell: The Unit of Life

Ans. a) Mesosomes

Explanation: The mesosome structure is formed by foldings of the plasma membrane. Mesosomes also help increase the surface area of the plasma membrane. The structure of mesosomes consists of tubules and vessels. This is usually seen at the site of cell division. Mesosomes serve the role of mitochondria in bacteria. This is because mesosomes are similar to eukaryotic mitochondria and mesosomes also aid in respiration in bacteria.

Ans. a) Cell membrane

Explanation: E.coli is a prokaryotic cell whose cell wall is composed of peptidoglycan while Chlamydomonas is a eukaryotic plant, whose cell wall is composed of cellulose. Prokaryotic cells contain 70S ribosomes while eukaryotes contain 80S ribosomes in their cytoplasm.

Prokaryotes do not have histone proteins associated with their DNA while eukaryotes have histone proteins for chromosome organization. The structure of the cell membrane is essentially the same in prokaryotic and eukaryotic cells and is composed of a phospholipid bilayer.

Ans. b) Differential centrifugation

Explanation: The basic principle involved in Orangelo's Septrin is the sedimentation of particles in suspension by centrifugal force. 

Centrifugation is a common procedure in microbiology and cytology used to separate many organelles from whole cells to study their characteristics and properties.

In centrifugation, particles sediment at different rates when subjected to an accelerating force. Organelles can be separated from cell homogenates by differential centrifugation.

Ans. a) Grana

Explanation: A chloroplast is an organelle that contains chlorophyll, a photosynthetic pigment that absorbs and converts sunlight into an energy source and thereby releases oxygen from the water.

• Grana are connected by stromal lamellae, extensions that extend through the stroma from one granum to neighbouring granums. A major aqueous region called the thylakoid lumen is bounded by the thylakoid membrane. A thylakoid disc stack is a granum. Chloroplasts may contain 10 to 100 granules.
• Grana, also called intergranular thylakoids or lamellae, are associated with stroma thylakoids. Grana thylakoids and stroma thylakoids can be characterized by different protein concentrations.

Ans. a) Mesosome

Explanation: A mesosome is an elongated part of the plasma membrane that is in the form of an invasion or lamella. Mesosomes are membrane-bound organelles that are formed by the plasma membrane and are located close to the cell membrane. They are also known as chondrins. They are known to play a role in respiration and are considered to be the site of respiration in bacterial cells.

Ans. d) Plasmodesmata

Explanation: Plasmodesmata are tubular extensions of the plasma membrane, which can range from 40 to 50 nm in diameter, that span the cell wall and connect the cytoplasm of adjacent cells in plants. The intracellular transport of solutes by plasmodesmata is called symplastic transport. It consists of pores and channels that help in transport.

Ans. c) Magnesium

Explanation: The two subunits of a ribosome do not stay together all the time. The two units merge during the translation process itself. Magnesium ion is crucial for the binding of ribosome subunits.

• The value is 0.5 millimoles for prokaryotes and 1 to 2 millimoles for eukaryotes. Below this concentration the subunits separate.
• Dissociation occurs at a magnesium ion value of 0.5 millimoles in eukaryotes and below 0.3 millimoles in prokaryotes. Ribosomes create dimers when the magnesium ion concentration is increased.

Ans. a) Acrocentric

Explanation: Based on the position of the centromere, chromosomes can be categorized into four classes: Acrocentric, Metacentric, Telocentric, and Submetacentric.

• A metacentric chromosome has a central centromere that forms two identical arms of the chromosome.
• A sub-metacentric chromosome contains a centromere slightly away from the centre of the chromosome resulting in a short arm and a long arm.
• A telocentric chromosome has a terminal centromere.
• In the case of an acrocentric chromosome, the centromere is located near its ends forming one very short and one very long arm.

Ans. c) Calcium pectate

Explanation: The middle lamella consists mainly of calcium pectate. The middle lamella is a layer of pectin that cements the cell walls of two adjacent cells together. To give them stability, plants need this so they can form plasmodesmata between cells. It is the first layer composed which is deposited at the point of cytokinesis.

During cell division itself, the developed cell plate grows into the middle lamella or lamella. Magnesium pectates and calcium pectates form the central (middle) lamella.

Read More: Cytokinins: Structure, Functions & Uses 

Ans. c) Rough endoplasmic reticulum

Explanation: The nuclear envelope is the double membrane envelope that surrounds the nucleus. It consists of a lipid bilayer. This membrane is porous in nature. Due to its porous nature, it allows the movement of certain molecules such as nucleic acids and proteins between the nucleus and the cytoplasm. 

• Two layers make up the nuclear membrane: The outer layer and the Inner layer.
• The outer layer shares a common border with the rough endoplasmic reticulum. Proteins synthesized by the ribosomes of the RER are transported to the nucleus through the endoplasmic reticulum.
• The inner layer surrounds the nucleoplasm. It is attached to the outer membrane through nuclear pores.

Ans. a) Ribosomes

Explanation: Protein synthesis is carried out by ribosomes on an mRNA template. mRNA carries the genetically coded information for protein synthesis which is translated by ribosomes. Ribosomes are universally responsible for synthesizing proteins by translating the genetic code written in mRNA into amino acid sequences.

Ribosomes use cellular accessory proteins, soluble transfer RNA, and metabolic energy to complete the initiation, elongation, and termination of peptide synthesis.

Ans. d) Proline

Explanation: Biological membranes are composed of lipids and proteins. The different lipids present in the membrane are cerebrosides, gangliosides, phospholipids, glycolipids, cholesterol, etc.

Proline is an amino acid commonly known as a chain breaker due to its structure. Proline is usually absent in membrane proteins. Proline usually occurs in regions where the protein chain makes sharp turns. So, the correct answer is 'Proline'.

Ans. a) Glyoxysomes

Explanation: Glyoxysomes are specialized peroxisomes found only in plant cells and filamentous fungi.

• Glyoxysomes are found only in adipose plant cells, where they participate in the β-oxidation of fats and the glyoxylate cycle. In plant seeds, specialized peroxisomes, known as glyoxysomes, contain enzymes that convert stored fats into sugars.
• It catalyzes the formation of acetyl CoA from fatty acids and stores it inside the germinating seed.

Ans. b) Vacuoles

Explanation: A membrane-bound space located in the cytoplasm is a vacuole. They are non-cytoplasmic regions within the cytoplasm, which are later separated by tonoplasts. They are believed to be formed from the ER by elongation and pinching off. In plant cells, there is a large central vacuole and many smaller vacuoles. They play a major role in cellular osmotic expansion.

Ans. d) Peroxisome

Explanation: Many cell organelles coordinate their functions, and therefore, they are considered together as the endomembrane system. The endomembrane system consists of endoplasmic reticulum, Golgi complex, lysosomes, and vacuoles. Peroxisomes, mitochondria, and chloroplasts do not coordinate their functions; therefore, they are not part of the endomembrane system.

Ans. d) Cristae

Explanation: Each mitochondrion is a double membrane-bound structure with an outer membrane and an inner membrane that divides its lumen into two aqueous compartments, namely, the outer compartment and the inner compartment.

The outer membrane comprises a constant limiting boundary of the organelle. The inner compartment is loaded with a dense homogeneous substance known as the matrix. The inner membrane forms several infoldings known as cristae towards the matrix. The cristae raise the surface area for mitochondrial function.

Ans. a) Nerve cell

Explanation: The largest or longest cell is the nerve cell in the human body. Nerve cells also known as neurons are discovered in the nervous system. They can be a maximum of 3 feet long.

Nerve cells exist only in animals. A nerve cell is an excitable and specialized cell of nervous tissue that helps in the proper functioning of the brain and the coordination of other parts of the body.

Ans. b) Lysosome

Explanation: Lysosomes are cell organelles known as suicide bags. This is because lysosomes have hydrolytic enzymes that digest cells and undesirable substances that enter the cell. They are implicated in the breakdown of extracellular and intercellular substances.

When the lysosome bursts, the enzymes spread throughout the cell, causing the cell membrane and wall to rupture. This eventually leads to cell death.

Ans. b) Schwann and Schleiden

Explanation: Schleiden is a German botanist, and Schwann is a British zoologist. Schleiden examined a large number of plant tissues and concluded that cells are the ultimate unit of all plant tissues. Similarly, Schwann also studied a variety of animal tissues, including developing embryos. He later concluded that animal cells lack cell walls but are covered by membranes and this is the difference between plant and animal cells, otherwise, they are similar. They compared their findings and issued the cell theory in 1839.