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SAQ 1 a) Microfilaments, composed of the protein …………………… play a key role in cell movement and contraction. Answer: actin b) The cytoskeleton is essential for the proper segregation of chromosomes during …………………… . Answer: mitosis c) The cytoskeleton is crucial for the maintenance of …………………… the balance of solutes inside and outside the cell. Answer: homeostasis. Answer: homeostasis d) The dynamic nature of actin filaments involves constant …………………… and depolymerization. Answer: polymerisation e) Actin-binding proteins like …………………… regulate the branching of actin filaments. Answer: Arp2/3 complex f) In treadmilling, the addition of…………………… to the barbed end occurs while monomers are simultaneously removed from the pointed end. Answer:  G-actin SAQ 2  a) What is the cortical cytoskeleton? The cortical cytoskeleton is a specialized and dynamic part of the cell's cytoskeleton located just beneath the plasma membrane. It is primarily composed of  actin filaments  (micr...

SAQ 1  i. What is a Cell? What Are the Essential Characteristics of Cells? A cell is the basic structural, functional, and biological unit of all living organisms. It is the smallest unit of life and is often referred to as the  "building block of life."  Cells carry out essential functions such as metabolism, energy production, and reproduction. Organisms can be unicellular (made of a single cell) or multicellular (composed of many cells). Discovery of the Cell Robert Hooke discovered the cell structure in 1665 by observing a thin slice of cork, specifically from the cork cambium of the cork oak tree (Quercus suber). The cork cambium is a layer of tissue found in the bark of plants that produces cork. Under his microscope, Hooke saw small, hexagon box-like compartments, which he named "cells" because they resembled the small rooms. These compartments were the cell walls of dead plant cells, a key observation that laid the foundation for the study of cell biology. D...

SAQ 1 1. (a) Write answers to the following questions in brief. i.  What is the longest phase of the cell cycle? The longest phase of the cell cycle is  Interphase,  which occupies about 90% of the total duration of the cycle. It is a highly active stage where the cell prepares for division. Interphase has three sub-phases: G1 phase, where the cell grows and synthesizes proteins; S phase, where DNA replication takes place; and G2 phase, where the cell checks for DNA errors and prepares for mitosis. Though no visible division occurs in interphase, it is crucial for the success of mitosis or meiosis. Cells that do not divide frequently may remain in G1 or enter a resting state called G₀ phase. ii.  During which phase of interphase does DNA replication occur?  DNA replication occurs during the S phase (Synthesis phase) of Interphase. In this phase, the entire genetic material of the cell is duplicated so that each daughter cell formed after cell division will recei...

SAQ 1 Fill in the blanks   a) .......................... discovered plasma membrane. Answer:   Karl Nageli and C. Cramer b) The phospholipid contains ......................... charged phosphate group in the hydrophilic part of head. Answer:  Negatively c) ........................... proposed Sandwich (lipid-protein) model of cell membrane. Answer:  Danielli and Davson d) The protein layer present in cell membrane model proposed by Robertson is .......................... thick. Answer:  20 A° e) The proteins are aligned properly with the help of ........................... within the lipid bilayer in membrane. Answer:  Transmembrane segments SAQ 2 i) Answer in one word: a) Complex integral proteins transmit signals via plasma membrane. Answer:  Receptors b) The cellular processes such as movement, growth, division etc. are regulated by this property of membrane. Answer:  Fluidity c) No energy is required for transter of substances from high concent...

SAQ Fill in the blanks:  a) The basic unit of microtubules is ……….....…… . Answer:  α β tubulin heterodimers b) α tubulin occurs at ...................... end, and β tubulin is at ........................ of microtubules. Answer:  plus, minus c) GTP-GTP tubulin cap stabilises and promotes the ........................... . Answer:  polymerisation of microtubules d) The plus end-directed motor protein of microtubules is ……..........……. . Answer:  kinesin e) The hydrolysis of GTP from β-tubulin causes ……..........……. of microtubules. Answer:  Depolymerisation f) The cellular function of γ-tubulins is. ……........…..... . Answer:  nucleate the growth of MTs  g) Colchicine binds to ………............… . Answer:  free tubulin SAQ 2 a) Classify the microtubules involved in mitosis. Microtubules play a central role during mitosis by forming the  mitotic spindle,  which ensures the correct segregation of chromosomes into daughter cells. These mi...

SAQ 1 i) The resting membrane potential is created due to: a) Buildup of the negative ions in the cytosol along the inside of the membrane. b) The separation of positive and negative electrical charges along both sides of the plasma membrane. c) Difference in charge across the membrane of the cell. d) All of the above. Answer:  d) All of the above ii) Which of the following factor/s contribute to the resting membrane potential of the cell? a) Unequal distribution of ions in the ECF and cytosol b) Activity of Na⁺/K⁺ ATPases c) Most anions cannot leave the cell d) all of the above Answer:  d) All of the above iii) The extracellular fluid (ECF) has high concentration of positively charged sodium ions and negatively charge chloride ions. a) True b) False Answer:  a) True iv) Intracellular fluid (ECF) in contact with the cell membrane is positively charged with high concentration of potassium ions, phosphate ions and anionic proteins. a) True b) False Answer:   a) True v)...

SAQ 1 a) Write the name of two glands are the main secretary gland of brain. The brain is not only the central organ of the nervous system but also contains two major secretory glands that are directly involved in endocrine functions. These are: Pituitary gland (Hypophysis) Pineal gland (Epiphysis cerebri) These glands are part of the neuroendocrine system, which links the brain and hormonal regulation. They help in maintaining homeostasis, regulating growth, metabolism, stress response, sleep cycle, reproduction and many other vital processes. 1. Pituitary Gland: The Master Gland The pituitary gland is called the  "master gland"  because it controls the activity of almost all other endocrine glands in the body. It is located at the base of the brain, in a bony cavity called the sella turcica of the sphenoid bone. It is connected to the  hypothalamus  by a stalk called the  infundibulum,  which carries signals from the brain to control hormone secretion. Th...

SAQ 1  Fill in the blanks:  a) The fibrous and rope-like structures refer to ....................... . Answers:  Intermediate filaments b) A protein that provides the mechanical strength and integrity to skin and hair is called ........................ . Answers:   Keratin  c) How many types of polypeptides are present in intermediate filaments? Intermediate filaments (IFs) are a key component of the cytoskeleton in eukaryotic cells, providing essential structural support and maintaining the shape and stability of cells. These filaments are composed of  polypeptides,  which are long chains of amino acids that fold into a functional structure. The polypeptides in intermediate filaments polymerize to form filamentous structures that help to anchor organelles, support cell shape and provide mechanical strength. Each type of intermediate filament is made from a specific group of polypeptides that are tissue-specific and vary in their amino acid composition...

SAQ 1 a) The mitotic apparatus, also known as the ................... apparatus, plays an important role in chromosome segregation during cell division. Answer:  spindle b) During interphase, the cell undergoes growth and performs its regular functions in the .................... phase. Answer:  G1 (Gap 1) c) The cell cycle is highly regulated by a group of proteins called ................... . Answer:  cyclins d) The ...................... checkpoint in the cell cycle ensures that DNA is undamaged before progressing to mitosis. Answer:  G1/S e) What are the key components of the mitotic apparatus? The mitotic apparatus is a temporary but essential structure formed during mitosis, especially during the  metaphase and anaphase stages.  It plays a critical role in the proper alignment and separation of chromosomes into daughter cells. The key components of the mitotic apparatus are mainly three and each part performs a specific function to ensure accurate chr...

In the early 1950s, scientists were exploring how life might have originated on Earth from non-living matter. At that time, it was widely believed that the early Earth's atmosphere was reducing in nature, meaning it had very low oxygen and was rich in gases like methane (CH₄), ammonia (NH₃), hydrogen (H₂) and water vapor (H₂O). This idea was strongly supported by the Russian scientist A.I. Oparin and the British biologist J.B.S. Haldane in the 1920s and 1930s, who proposed that organic molecules essential for life could form spontaneously under such conditions. In 1952, Stanley L. Miller, a graduate student, conducted an experiment under the guidance of Harold C. Urey at the University of Chicago. The experiment aimed to test whether simple inorganic molecules could give rise to organic compounds under the conditions assumed to exist on primitive Earth. This experiment became famously known as the Miller-Urey Experiment  and its findings were published in 1953. Experimental Se...