20 short questions with answers on Cell Biology for a graduation-level biology course
1. Question: What are the key differences between prokaryotic and eukaryotic cells?
Answer: Prokaryotic cells lack a membrane-bound nucleus and other membrane-bound organelles, while eukaryotic cells possess a nucleus and various organelles like mitochondria, Golgi apparatus, and endoplasmic reticulum. Prokaryotic DNA is typically a circular chromosome located in the nucleoid, whereas eukaryotic DNA is linear and organized into chromosomes within the nucleus.
2.Question: Briefly describe the fluid mosaic model of the plasma membrane.
Answer: The fluid mosaic model describes the plasma membrane as a fluid structure with a phospholipid bilayer in which various proteins are embedded or attached. The phospholipids can move laterally, and the proteins can also drift within the bilayer, creating a mosaic-like appearance.
3.Question: What are the main functions of the plasma membrane?
Answer: The plasma membrane acts as a selective barrier, controlling the movement of substances into and out of the cell. It also plays a role in cell signaling, cell adhesion, and maintaining the cell's shape and integrity.
4.Question: Distinguish between passive and active transport across the cell membrane, providing one example of each.
Answer: Passive transport does not require energy and moves substances down their concentration gradient. An example is facilitated diffusion of glucose via a transport protein. Active transport requires energy (usually ATP) to move substances against their concentration gradient. An example is the sodium-potassium pump.
5.Question: Describe the structure and primary function of the nucleus in a eukaryotic cell.
Answer: The nucleus is a large, membrane-bound organelle containing the cell's genetic material (DNA) organized into chromosomes. Its primary function is to control gene expression and mediate the replication of DNA during cell division.
6.Question: What is the role of the nucleolus within the nucleus? Answer: The nucleolus is a dense structure within the nucleus where ribosomal RNA (rRNA) is synthesized and ribosomal subunits are assembled.
7.Question: Explain the endosymbiotic theory and provide evidence supporting it. Answer: The endosymbiotic theory proposes that mitochondria and chloroplasts originated from free-living prokaryotes that were engulfed by an ancestral eukaryotic cell and developed a symbiotic relationship. Supporting evidence includes the double membranes of these organelles, their own circular DNA, their prokaryote-like ribosomes, and their ability to divide independently.
8.Question: Describe the structure and function of mitochondria.
Answer: Mitochondria are double-membraned organelles with an inner membrane folded into cristae. They are the primary sites of cellular respiration, generating ATP (adenosine triphosphate), the cell's main energy currency, through the oxidation of glucose and other fuel molecules.
9.Question: What are the main functions of the endoplasmic reticulum (ER)? Distinguish between smooth ER and rough ER.
Answer: The ER is a network of interconnected membranes forming sacs and tubules. Rough ER has ribosomes attached to its surface and is involved in protein synthesis and modification of proteins destined for secretion or insertion into membranes. Smooth ER lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage.
10.Question: Describe the structure and function of the Golgi apparatus.
Answer: The Golgi apparatus is a stack of flattened, membrane-bound sacs called cisternae. It modifies, sorts, and packages proteins and lipids synthesized in the ER for secretion or delivery to other organelles.
11.Question: What are lysosomes and what are their main functions in the cell? Answer: Lysosomes are membrane-bound organelles containing hydrolytic enzymes. Their main functions include intracellular digestion of macromolecules, breakdown of worn-out organelles (autophagy), and destruction of engulfed pathogens (phagocytosis).
12.Question: Briefly describe the structure and function of ribosomes.
Answer: Ribosomes are macromolecular complexes composed of ribosomal RNA (rRNA) and ribosomal proteins. They are the sites of protein synthesis (translation), where the genetic information encoded in mRNA is used to assemble amino acid chains.
13.Question: What are the components of the cytoskeleton and what are its major roles?
Answer: The cytoskeleton is a network of protein fibers including microtubules, microfilaments (actin filaments), and intermediate filaments. Its major roles include providing structural support and maintaining cell shape, facilitating cell motility, and enabling intracellular transport.
14.Question: Describe the structure and function of microtubules. Answer: Microtubules are hollow rods composed of tubulin dimers (α-tubulin and β-tubulin). They are involved in maintaining cell shape, chromosome movement during cell division, and the movement of organelles and vesicles. They are also components of cilia and flagella.
15.Question: What are cell junctions? Briefly describe three main types found in animal cells.
Answer: Cell junctions are specialized structures that connect adjacent cells. Three main types in animal cells are:
Tight junctions: Form water-tight seals between cells, preventing leakage of extracellular fluid.
Desmosomes: Anchoring junctions that provide strong mechanical attachments between cells.
Gap junctions: Communicating junctions that allow the passage of small molecules and ions between adjacent cells.
16.Question: What is the cell cycle? List its main phases.
Answer: The cell cycle is the ordered sequence of events that a eukaryotic cell undergoes from its formation until it divides into two daughter cells. Its main phases are: G1 (gap 1), S (synthesis), G2 (gap 2), and M (mitotic) phase.
17.Question: Briefly describe the process of mitosis and its significance.
Answer: Mitosis is the process of nuclear division in eukaryotic cells that results in two daughter nuclei each having the same number and kind of chromosomes as the parent nucleus. Its significance lies in ensuring the accurate segregation of chromosomes during cell division, leading to genetically identical daughter cells, which is crucial for growth, repair, and asexual reproduction.
18.Question: What is cytokinesis and how does it differ in animal and plant cells? Answer: Cytokinesis is the division of the cytoplasm following mitosis or meiosis, resulting in two separate daughter cells. In animal cells, cytokinesis involves the formation of a cleavage furrow that pinches the cell in two. In plant cells, a cell plate forms in the middle of the cell and grows outward to divide the cytoplasm.
19.Question: What is apoptosis and what is its importance in multicellular organisms?
Answer: Apoptosis is programmed cell death, a tightly regulated process characterized by cell shrinkage, chromatin condensation, and DNA fragmentation. It is crucial in multicellular organisms for development (e.g., removing webbing between fingers), tissue homeostasis (balancing cell division), and eliminating damaged or infected cells.
20.Question: Briefly explain the role of checkpoints in the cell cycle.
Answer: Cell cycle checkpoints are control mechanisms that ensure the fidelity of cell division. They monitor the progress of the cell cycle and halt its progression if errors such as DNA damage or incomplete chromosome replication are detected, allowing time for repair or triggering apoptosis if the damage is irreparable. This prevents the propagation of genetic abnormalities.
