Unit 3: Cells & Subcellular Organelles — Short Questions

Ans. (a) Resolution of light microscope is 0.2 nm/ while its magnification is 1500X
(b) Resolution of electron microscope is 0.2 nm / while it can magnify objects upto 250,000 times.

Ans. 1. Cell theory All living organisms are made of cell and cell products.
Three essential points of cell theory.
2. Cell theory can be validated by
(i) visualizing cell structure under microscope.
(ii) having live cell imaging and genetic studies.
(iii) By studying DNA sequencing and metabolic pathways.
(iv) By experiments such as cell culture studies and tissue engineering.
3. Exception to cell theory are
a) viruses because they are not made of cells and cannot carry out life processes independently
b) prions and viroids, because they show properties of living organisms but are not composed of cells.
c) Muscle cells in vertebrates.
d) Multinucleated organisms like certain fungi and algae.
e) Self replication of organelles like mitochondria and chloroplast.

Ans.
Description | Simple Diffusion | Facilitated Diffusion | Active Transport
Is ATP required? | NO | NO | YES
Are carrier proteins involved? | NO | YES | YES
Is direction of transport always from higher to lower concentration? | YES | YES | NO

Ans. (i) Single membrane bound organelles include Lysosomes, Peroxisomes, Glyoxisomes, Endoplasmic reticulum, Golgi apparatus.
(ii) Double membrane bound organelles include Mitochondria, Chloroplast, nucleus
(iii) organelles lacking any membrane are Ribosomes, centrioles, cytoskeleton, Nucleolus.

Ans. (i) Transport Some protein act as channels or carriers to transport substances like glucose or amino acids across membrane.
(ii) Cell signaling: Receptor proteins in membrane receive chemical signals from outside the cell and transmit into the cell for a response.

Ans. Mitochondria have two features common with prokaryotes:
(i) Presence of circular DNA: Like prokaryotes, mitochondria contain their own circular DNA.
(ii) Self-replication: Mitochondria can self-replicate independent of the nucleus, similar to prokaryotes.

Ans. 1. In Eukaryotic cells distinct nucleus is present, while absent in prokaryotes.
2. In Eukaryotic cells ribosomes are of 80S while in prokaryotic cells it is of 70S.
3. Mitosis and Meiosis are present in eukaryotic cells while absent in prokaryotic cells.

Ans. a) Nuclear pores are permeable to small molecules.
b) Some large proteins like histones can also pass the nuclear membrane.
c) Ribosomal sub-units can also pass out through the nuclear membrane.

Ans. a) Exocytosis and Endocytosis
Exocytosis | Endocytosis
(i) In this process bulky material is exported out of cell | (i) In this process bulky material, is moved into cell across plasma membrane.
(ii) In exocytosis, the bulky material is packed inside a membrane and vesicle is formed. This vesicle fuses with plasma membrane to release content to extra cellular environments. | (ii) Here, the plasma membrane engulfs the material forming a vesicle which detaches and moves into cytoplasm.

b) Phagocytosis: In this cell takes in solid material.
Pinocytosis
Phagocytosis | Pinocytosis
(i) It is a type of endocytosis in which cell takes in solid material. | (i) It is a types of endocytosis in which cell takes in liquids in the form of droplets.
(ii) It is also called as cell eating. | (ii) It is also called as cell drinking.

c) Peroxisomes and Glyoxisomes:
Peroxisomes | Glyoxisomes
(i) They are involved in break down fatty acids and detoxification of hydrogen peroxide. | (i) They convert stored lipids into carbohydrates during seed germination they are found only in plants cells and
(ii) They are found in most eukaryotic cells. | (ii) are abundant in lipid rich seeds.
(iii) Catalases and oxidases enzymes are present in them. | (ii) They contain enzymes that convert lipids into carbohydrates.

Ans. Lysosomes are membrane bound organelles that contain digestive enzymes to breakdown macromolecules, damaged organelles and foreign particles. They play key role in intra cellular digestion and recycling of cellular components, often called as autophagy.

Ans.
(i) The Golgi body is involved in production of cell secretions.
(ii) It converts protein and lipids into glycoproteins and glycolipids.
(iii) In plant cells they produce pectin and other polysaccharides needed for plant structure and metabolism.

Ans. Histones are group of small proteins DNA strand wraps around there histone protein to form a structure called nucleosome. which is part of chromatin.

Ans. Stem cells are unique cells with remarkable ability to develop into many different cell types, such on muscle cell, red blood cell or brain cell.
Usage: Stem cells can be used in regeneration medicine, drug testing and development of personalized medicine.

Ans.
A – DNA
B – Ribosomes
C – Matrix
D – Inner membrane
E – Outer membrane
F – F₁ particle
G – Cristae

Ans. a) Label
[Labeled diagram showing cell structures including Golgi bodies, Plasma membrane, Vacuole, Cytoplasm, Mitochondria, Smooth endoplasmic reticulum, Nuclear envelope, Nucleolus, Ribosomes (attached with ER), Rough endoplasmic reticulum, Centriole, Free ribosomes]

b) (i) Mitochondria are present
(ii) Secretory vesicles are coming out of endoplasmic reticulum and forming Golgi apparatus. From Golgi apparatus Golgi vessels are formed, have various enzymes secretions.

Ans. 1. Movement
2. Nutrition
3. Respiration
4. Excretion
5. Homeostasis
6. Growth
7. Reproduction

Ans. In 1665 Robert Hooke examined thin cilia of cork of oak tree under microscope. He observed that cork was made of many little boxes. He named these as cellulae (cell).

Ans. (i) All living organisms are composed of one or more cells.
(ii) Cells are the basic units of structure and function in an organism.
(iii) Cells come only from the division of pre-existing cells.

Ans. In light microscope, light is used to make the image of object while in electron microscope beam of electrons passes through, the object. Image is formed on a screen.

Ans. This refers to a microscope's ability to enlarge the image of an object. Different lenses within a microscope offer varying levels of magnification. It is denoted by the symbol 'X', indicating how many times larger the image appears compared to the actual size. For example, a 10X lens can enlarge a 1 µm object to 10 µm. Total magnification in a microscope is determined by multiplying the magnification of all lenses.

Ans. Resolution This refers to a microscope's ability to distinguish between two points that are close together on an object. The greater the resolution, the finer the detail that can be observed. The naked human eye has a resolution of about 0.1 mm. In contrast, a light microscope can resolve details down to approximately 250 nm (nanometres).

Ans.
TEM | SEM
• Transmission electron microscope is used to view the interval structure of cell. | • Scanning electron microscope is used to study the details of surfaces of cells or other objects.
• TEM transmits a beam of electrons through a very thin specimen. | • The surfaces are coated with metal. When electron beam hits the metal, it is reflected and makes enlarged image.
• It can magnify objects upto 250,000 times. | • SEM can magnify objects upto 100,000 times.

Ans. When cell wall is removed, using cell wall degrading enzymes the remaining components of the cell are called a protoplast.

Ans. Primary wall is the actual cell wall of the cell. It is composed of polysaccharides i.e. cellulose, hemi cellulose and pectin. The cellulose microfibrils are aligned at angles and are held together by hydrogen bonds. Many proteins are also present in primary walls.

Ans. In some plant cells, after maturation a secondary wall is made between protoplast and primary wall. Secondary wall is composed of lignin, cellulose and hemicellulose. Due to presence of lignin, secondary wall is more rigid than the primary wall.

Ans. Plasmodesmata are small channels that directly connect the cytoplasm of neighbouring plant cells to each other. Plasmodesmata penetrate both the primary and secondary walls. They allow movement of materials between cells and so important in cellular communication.

Ans. Plasmodesmata have caused debate among scientists regarding cell theory. Some scientists suggest that the cells of higher plants are not really cells since they are not physically separated or independent from one another.

Ans. The group of algae called diatoms synthesize their cell walls from silicic acid. The acid is polymerized inside cells, then the wall is extruded to protect the cell. The synthesis of Silica cell walls requires less energy. That is why there are higher growth rates in diatoms.

Ans. The cell wall of algae contains cellulose and a variety of glycoproteins.
The cell wall of fungi is composed of chitin, the same carbohydrate that gives strength to the exoskeletons of insects.
The cell walls of prokaryotes (bacteria and cyanobacteria) is composed of peptidoglycan, that is a single large polymer of amino acids and sugar.
The cell wall of archaeebacteria is composed of different polysaccharides and proteins, with no peptidoglycan.

Ans. Fluid mosaic model is widely accepted concept that describes the dynamics of plasma membrane. According to this model, the basic foundation of plasma membrane is a lipid bilayer. This bilayer is made of phospholipids. A collection of proteins floats within the lipid bilayer. In lipid bilayer the hydrophobic lipid tails are oriented inwards and the hydrophilic phosphate groups are aligned outwards, either towards the cytoplasm of cell or the extracellular environment.

Ans. The interior of lipid bilayer sheet is hydrophobic. It repels water-soluble molecules e.g., sugars, polar amino acids etc. That is why, in addition to phospholipids molecules the membranes also contain proteins that provide passageways across the membrane.

Ans. Following are few types of proteins in plasma membrane.
1. Transporters: These proteins play role in selective transport of certain substances across the lipid bilayer.
2. Anchors: These proteins help in attachment of plasma membrane to cytoskeleton and external fibers.
3. Receptors: These proteins attached with sugar and make identification marks. Some bind with messenger molecules and transmit signals to interior.
4. Enzymes: These proteins exhibit enzymatic activity.

Ans. The ability to distinguish among different cells is crucial to life. It allows cells in an embryo to sort themselves into tissues and organs. It also helps cells of the immune system to recognize and reject foreign cells, e.g., infectious bacteria.

Ans.
i. Transmission electron microscopy can reveal detailed structures of the lipid bilayer and associated proteins.
ii. Scanning electron microscopy is useful for examining the surface topology of cells and membranes.

Ans.
i. Confocal microscopy uses laser scanning and fluorescence to create sharp, detailed images of the cell membrane.
ii. Total internal reflection fluorescence microscopy is used for high resolution images of the membrane and its interactions with the cytoskeleton and other cellular components.

Ans.
i. Atomic force microscopy provides topographical images of cell membrane at high resolution.
ii. X-ray crystallography is used to determine the atomic structure of membrane proteins.

Ans.
i. Lipidiomics involves the comprehensive analysis of lipids in the cell membrane using techniques like mass spectrometry.
ii. Fluorescence recovery after photobleaching is used to study the dynamics of membrane proteins and lipids. It involves bleaching a fluorescently labelled region of membrane with a laser and observing the recovery of fluorescence as unbleached molecules move into the area.

Ans. The glycolipids and glycoprotein on outside surface of plasma membrane is called glycocalyx. It functions as cell identification marks that are recognized by other cell.

Ans.
i. Cytosol is aqueous ground substance of cytoplasm, which contain various organelles and other inclusions.
ii. Cytosol contains water in which many organic (proteins, carbohydrates, lipids) and inorganic salts are completely or partially dissolved.

Ans. Following are the major components of cell.
1. Plasma membrane 2. Cytoplasm
3. Nucleus

Ans. On the inner side of nucleus envelope, there is a protein lining called nuclear lamina. It binds to chromatin to give it structural support.

Ans. Nuclear pores are tiny holes in the nuclear envelope. A nuclear pore is made of nuclear pore complex. It has several subunits i.e., annular subunit, Column subunit, ring subunit, luminal subunit.

Ans. There are two types of chromatin.
Euchromatin is the genetically active chromatin involved in transcribing RNA to produce proteins. The other kind of chromatin is termed heterochromatin. Its DNA is genetically inactive.

Ans. These are certain sites of chromosomes that form Nucleoli. DNA found as NORs encodes the ribosomal RNA.

Ans. In cells that produce large amounts of protein, and thus require significant numbers of ribosomes, the size of the nucleolus is considerable. At the onset of mitosis, the single nucleolus present in cell disappears. and after division new nucleus is formed from the NORs.

Ans. Nucleolus consists of granular and fibrillar components and DNA. The granular part consists of ribosomal subunits. Fibrillar part is composed of raw materials of ribosome subunits.

Ans. Inside the nucleus of every human cell, there is a 6 feet long DNA. It is subdivided into 46 individual molecules (each 1.5 inches long), one for each chromosome.

Ans. A prominent nucleus is present in all eukaryotic cells (at centre in animal cells while pushed to side in plant cells). It performs two major functions:
• It stores the cells hereditary material (DNA).
• Coordinates the cell's activities e.g., growth, protein synthesis and cell division.

Ans. Building blocks of DNA and RNA and ATPs are allowed to enter into the nucleus. Ribosomal subunits which are build in nucleoli are the examples of materials that are allowed to leave the nucleus and enter the cytoplasm.

Ans. Nucleoplasm is the semifluid matrix found inside the nucleus. Within the nucleoplasm most of the nuclear material consists of chromatin that organizes to form chromosomes during cell division.

Ans. Due to their physical membranous connection, the lumen of the endoplasmic reticulum and the space between the layers of the nuclear envelope comprise a single compartment. This close association enables the endoplasmic reticulum and the nucleus to share information in a very efficient manner.

Ans.
1. Rough endoplasmic reticulum
Its function is production and processing of protein.
★ 2. Smooth endoplasmic reticulum
It has following functions
i. Production of lipids
ii. Detoxification of drugs
iii. Store calcium and do calcium and carbohydrate metabolism

Ans. Definition Ribosomes are granular structures not bound by membrane.
Occurrence: These are found in all organisms. In eukaryotes they may be bound attached with rough endoplasmic reticulum or scattered free in cytoplasm.

Ans. In addition to the most familiar cellular locations of ribosomes, they can also be found inside mitochondria and chloroplasts of plants. These ribosomes notably differ in size and makeup than the ribosomes found in cytoplasm, and are more like those present in prokaryotes.

Ans. The proteins that are synthesized by free ribosomes are for the cell's own internal use. While the proteins produced by the ribosomes bound to RER are transported outside of the cell.

Ans. The Svedberg values are not additive i.e. the values of the two subunits of a ribosome do not add up to the Svedberg value of the complete ribosome. This is because the rate of sedimentation of a molecule depends upon its size and shape, rather than simply its molecular weight.

Ans. The sub unit of a ribosome are described by their Svedberg values, which are based upon their rate of sedimentation in a centrifuge. The complete ribosome in a eukaryotic cell has a Svedberg value of 80S. Prokaryotic cells on the other hand contains 70S ribosomes.

Ans. Scientists hypothesize about the origin of mitochondria. According to them, millions of years ago small, free-living prokaryotes were engulfed, but not consumed, by larger prokaryotes. The two organisms developed a symbiotic relationship over time, the larger organism providing the smaller with ample nutrients and the smaller organism providing ATP molecules to the larger one.

Ans. The number of mitochondria present in a cell depends upon the metabolic requirements of that cell, and may range from one to thousands. Mitochondria are found in nearly all eukaryotes, including plants, animals, fungi, and protists, and are large enough to be observed with a light microscope.

Ans. Mitochondria are the sites of cellular respiration. They generate adenosine triphosphate (ATP) from oxygen and nutrients. ATP is chemical energy "currency" of the cell that powers the metabolic activities.

Ans. In mitochondria the inner surface of cristae has knob like extensions into matrix, known as F1-particles. These particles are actually the enzymes called ATP-synthase. Here ATPs are synthesized.

Ans. Cells of plants and many protists have three types of plastids i.e., chloroplasts, chromoplasts and leucoplasts. The colourless leucoplasts are involved in the storage and yellow-to-red coloured chromoplasts give colours to plant parts while chloroplasts are green and involved in photosynthesis.

Ans. Mitochondria are similar and different to chloroplasts in following ways.
• Both organelles convert energy for the cell.
• Mitochondria perform aerobic respiration. They generate chemical energy in the form of ATP by metabolizing sugars, fats and other chemical fuels with the assistance of oxygen.
• Chloroplasts perform photosynthesis. They convert energy from the sun into the biosynthesis of organic nutrients using carbon dioxide and water. Like mitochondria, chloroplasts also contain their own DNA and are able to grow and reproduce independently of the cell.

Ans. Chloroplasts are specialized organelles to perform function of photosynthesis, in which light energy is converted into chemical energy. All of the green structures in plants including stems and unripened fruit contain chloroplast, but majority of the photosynthesis occurs in leaves.

Ans. Thylakoids The inner membranes of chloroplast lie in close association with one another and fuse along with their periphery. In this way, two adjacent membranes form a disc shape compartment called thylakoid.
Grana: Many thylakoids form stacks called grana (singular granum). Thylakoids are green due to the pigment chlorophyll.
Lamellae: These are non-green compartments that connect two grana.

Ans. Stroma is a semi-fluid present inside the inner membrane of chloroplast. It contains dissolved enzymes and comprises most of the chloroplast volume.
Process: ATPs produced during light reaction are used in stroma to transform low energy carbon dioxide into high energy compound like glucose.

Ans. Golgi apparatus consists of five to eight cup-shaped membrane covered sacs called cisternae that are stacked over each other. It is found in cells of plants, animal and unicellular eukaryotes.

Ans. Golgi apparatus may consist of 60 cisternae. Animal cells generally contains between ten and twenty Golgi stacks. This complex is usually located close to the nucleus.

Ans. Each Golgi stack has two distinct faces. The cis face is found near the endoplasmic reticulum and the trans face is positioned near the plasma membrane.

Ans. Golgi apparatus was discovered by Camillo Golgi in 1898. He discovered this organelle during his research on nervous system by using a new staining technique known a 'Golgi staining'.

Ans. Golgi apparatus is the distribution and shipping department for the cell's chemical products. It modifies proteins and lipids that have been built in the endoplasmic reticulum and prepare for export outside the cell or for transport to other locations in the cell.

Ans. Small vesicles that contain proteins, polysaccharides, phospholipids and other carbohydrates bud off from ER. These molecules reach to cis face of Golgi apparatus, and fuse with it, releasing molecules into it. Here the compounds are further processed. Enzymes present in the Golgi lumen convert them into glycoproteins and glycolipids.

Ans. The processed products are released from 'trans' face of Golgi apparatus in a vesicle and directed to its final destination inside or outside the cell. The exported products are known as secretions while other products are returned to the endoplasmic reticulum or may become lysosomes.

Ans. In plant cells, the Golgi apparatus also produce pectin and other polysaccharides that are essential for plant structure and metabolism.

Ans. Lysosomes are spherical organelles bounded by single membrane. They serve as digestive compartments of the cell. They breakdown cellular waste products, fats, carbohydrates, proteins and other macromolecules into simple compounds for re-use by cell.

Ans. In animals, lysosomes are most numerous in disease fighting cells e.g., white blood cells. This is because white blood cells must digest materials like bacteria, viruses and other foreign invaders.

Ans. Lysosomes are involved in breaking the cellular material that have exceeded their life time of are no longer needed by the cell.

Ans. As the lysosomal matrix is acidic and cytosol is neutral environment, so even if a lysosome is ruptured, its digestive enzymes become inactive and the cell remains uninjured.

Ans. Lysosomes have 40 different hydrolytic enzymes. All of these enzymes are manufactured in endoplasmic reticulum and modified in Golgi apparatus. The membrane covering of lysosomes protect the rest of cell from there possible damage.

Ans. In lysosomal storage diseases the patient lacks one of the hydrolytic enzymes of lysosomes. Due to this the abnormal lysosomes gets filled with the indigestible substances, which interfere with cellular functions e.g., Pompe's disease and Tay sacks disease.

Ans. This is type of lysosomal storage disease. In this lysosome lack glycogen – digesting enzyme. So, harmful amounts of glycogen accumulate in liver cells.

Ans. In this essential lipid digesting enzyme is missing. So accumulation of lipids in nerve cells of brain damages the nervous system causing mental retardation and death in early childhood.

Ans. Selective cell death is done by lysosomes during development e.g., when tadpole develops into a frog the cells of tail are destroyed by the enzymes of lysosomes.

Ans. The cell is safe from the enzymes of lysosomes. These enzymes require acidic environment (of pH of about 4.8). The lysosomal matrix is acidic but cytosol is a neutral environment. So, even if a lysosome is ruptured, its digestive enzymes become inactive and the cell remains uninjured.

Ans. In the mid-18th century, Belgian scientist Christian Rene de Duve was investigating carbohydrate metabolism in liver cells. He observed that when cells are damaged in the centrifuge, they released acid phosphatase. He suggested that this digestive enzyme was encased in some membrane bounded organelle within the cell, which he named as lysosome.

Ans. Many cells in your brain die during development. This directed suicide is accomplished by the rupture of the lysosomes within the cells that are being eliminated.

Ans. Peroxisomes are single membrane bound organelles found in all eukaryotic cells. They contain variety of enzymes whose function is to get rid the cell of toxic substances. E.g., Hydrogen peroxide, a common toxic by product of cellular metabolism is broken down to water and oxygen.

Ans. The catalase enzymes break down hydrogen peroxide, a common by-product of cellular metabolism into water and oxygen.
H₂O₂ --Catalase--> 2 H₂O + O₂
(Hydrogen peroxide) | (Water) (Oxygen)

Ans. Zellweger syndrome is one of the metabolic disorder caused due to defect in peroxisome. In this syndrome number of peroxisomes in a cell is less or absent. This is a congenital disorder (present at birth) and has no cure or effective treatment hence causing early death.

Ans. Glyoxisomes are similar to peroxisomes but found only in plant cells. These contain enzymes that convert lipids into carbohydrates in the cells of lipid-rich seeds e.g caster bean this provides energy to germinating seeds.

Ans. Vacuoles are membrane – bound sacs in cytoplasm, their functions are
1. In mature plant cells, they provide structural support.
2. It serves as storage, waste disposal etc.

Ans. Many plant cells have a large, single central vacuole. This large vacuole slowly develops by fusion of smaller vacuoles. It takes up 80% or more space in the cell.

Ans. The central vacuole in plant cells plays an important structural role for the plant. This role of vacuole is relate to its ability to control turgor pressure. Turgor pressure makes the rigidity of the cell. This also helps maintain the structural integrity of the plant along with the support from the cell wall.

Ans. Vacuoles are fluid filled single-membrane bounded organelles. Cells have many small vacuoles in their cytoplasm. However, when a plant cell matures its small vacuoles fuse to form a single large vacuole.

Ans. Several materials commonly stored in plant vacuoles have been found to be useful for humans, such as opium, rubber, and garlic flavouring.

Ans. 1. Vacuoles also often store the pigments that give certain flowers their colors, which aid them in attraction of bees and other pollinators.
2. Vacuoles also release molecules that are poisonous to various insects and animal thus discouraging them from consuming the plant.

Ans. Centrioles are hollow and cylindrical organelles associated with assembly and organization of fibres of cytoskeleton i.e microtubules. A centriole is made of nine triplets of microtubules.
Location: In eukaryotic cells centrioles occur in pairs located at right angle to one another near the nuclear envelope.

Ans. Each cilium and flagellum is anchored by a modified centriole known as basal body.

Ans. The cells of plants and fungi lack centrioles and basal bodies. Their microtubules and spindle fibres are organized from the structures of cytoplasm like MTOCs, microtubule organizing centres.

Ans. In animal and protist cells centrioles are organelles associated.

Ans. It is a network of protein fibres present in cytoplasm. It has following types
• Microfilaments
• Microtubules
• Intermediate filaments

Ans. Microfilaments are solid rods made of globular protein called actin. Function: They help dividing cell to pinch off into two cells. In association with myosin, microfilaments help in cellular contraction.

Ans. These are straight, hollow cylinders composed of subunits made of tubulin proteins.
Function:-
1. Microtubules are major components of cilia and flagella.
2. They participate in the formation of spindle fibres during cell division.

Ans. These are made of different proteins made of vimentin subunit.
Functions
1. They maintain cell shape and rigidity.
2. They also anchor (fix) several organelles in the cell.

Ans. Cilium and flagellum are thin, tail like projections extending from cell body.
Function: Their function is locomotive organs.
Difference: Cilia are short in length and usually many in number, while flagella are longer but less in number.

Ans. Axoneme is the core of eukaryotic cilia and flagella.
Structure: It contains two central microtubules that are surrounded by an outer ring of nine doublet microtubules. Dynein molecules bridge the gap between adjacent microtubule doublets. This organization is also called as "9+2" structure.

Ans. In humans cilia are found in the lining of the trachea where they sweep mucus and dirt out of the breathing tube.

Ans. A prokaryotic cell lacks a nucleus. The DNA of prokaryotic cell is present in the more 'less central region known as Nucleoid (Nucleus like).

Ans. Surrounding the plasma membrane of most prokaryotic cells is a cell wall but it does not contain cellulose. It is composed of peptidoglycan, which is a single large polymer of amino acids and sugar.

Ans. Cell size It is 10 – 100µm in eukaryotic cells and 1 – 10 µm in prokaryotic cells.
Cell division: In eukaryotes mitosis and meiosis occurs while in prokaryotic cells mitosis and meiosis are missing. Here cell divides by direct division called as binary fission.

Ans. Prokaryotic and Eukaryotic cells
1. Bacteria and archaea are made of prokaryotic cells whereas all other forms are composed of eukaryotic cells.
2. Both prokaryotic and eukaryotic cells have DNA as their genetic material.
3. Both have plasma membranes as their coverings; and both have ribosomes for protein synthesis.

Ans. Cell signalling is the ability of cells to respond to stimuli from their environment producing cellular responses. It involves the transmission of signals between cells through a series of molecular events leading to a cellular response.

Ans. In cell signalling, signal molecule bind to a receptor on the membrane of a target cell while in signal transduction, the intracellular signalling pathway is activated as result of this binding.

Ans. The signal transduction pathway leads to changes in gene expression i.e. turning specific genes on or off. This results in various cellular responses like cell growth, division, differentiation or apoptosis.

Ans. Protein/peptide signalling molecules are water soluble. They can't pass through plasma membrane they bind to its specific receptor on plasma membrane. Hence intracellular signal pathway is activated. In steroid signalling, the steroid hormone can diffuse through plasma membrane e.g. steroid hormone can diffuse through

Ans. Diffusion It is the net movement of a substance from an area of high concentration to area of low concentration, without using energy.
Facilitated diffusion: In this molecules are taken in or out of cells with the help of transport proteins present in plasma membranes. In this no energy is used.

Ans. 1. Channel proteins These proteins from hydrophilia channels across the membrane that allow specific molecules to pass through e.g., ion channels.
2. Carrier proteins: These proteins bind to the specific molecule they transport undergo a conformational change and move molecule across the membrane e.g. glucose transporters.

Ans. It is a process in which external pressure is applied to push water through a semi permeable membrane from high solute concentration to low solute concentration.

Ans. 1. Na⁺ - K⁺ pump is composed of carrier proteins for active transport.
2. This pump actively moves Na⁺ to the outside of cell and K⁺ to inside of cell.
3. It is located in the membranes of nerve cells.

Ans. Phagocytosis It is intake of solid material during endocytosis.
Pinocytosis: It is intake of liquids during endocytosis.

Ans. Endocytosis In this bulky materials are moved into the cell by invagination of plasma membrane forming a vesicle.
Exocytosis: In this process bulky material is exported out of the cell, here the vesicle fuses with the plasma membrane from inside and release the contents into the extracellular environment.

Ans. While exchanging matter with cells' environment, plasma membranes maintain equilibrium inside the cell as well as outside.

Ans. Movement of substances in and out of cells is crucial for cellular functions. These movements are done for nutrient uptake, waste elimination, gas exchange, and signal transduction. Cells rely on the plasma membrane for regulating the movement of substances in and out of the cell. Membrane transport mechanisms are essential processes that enable the cell to maintain homeostasis, acquire nutrients, remove waste products. and communicate with its environment. There are two types of transport mechanisms i.e., passive transport (which requires no energy input) and active transport (which utilizes energy).

Ans. The term tonicity refers to the relative concentration of solutes in the solutions.
Hypertonic solutions are those in which more solute is present.
Hypotonic solutions are those with less solute.
Isotonic solutions have equal concentrations of solutes

Ans. Specific receptor proteins of plasma membrane pick up material from outside and pinch inside to form a vesicle. For example, the cells of liver have receptor proteins for cholesterol. Cholesterol circulate in our blood in the form of low-density-lipoproteins (LDLs). The receptor proteins of plasma membrane of liver cells, recognize and take up LDLs from the blood by receptor-mediated endocytosis.

Ans. Stem cells are unique cells with remarkable ability to divide develop into many different cell types in the body.

Ans. Totipotent Cell They can differentiate into all possible cell types e.g., zygote.
Plurpotent cell: These cells can turn into almost any cell him into almost any cell e.g., cells of early embryo.

Ans. Multipotent cells These cells can differentiate into close relate of family of cell e.g., hematopoietic stem cell can become RBCs, WBCs or platelets.
Oligopotent Cells: There can differentiate into few different cell types e.g., adult lymphoid or myeloid stem cells.

Ans. These can produce cells of one kind, which is their own type e.g., adult muscle stem cells.

Ans. Stem cells can be used in
1. Regenerative medicine
2. Drug Testing and development
3. Personalized medicine

Ans. There are derived from the inner cell mass of blastocysts (early-stage embryo). These cells are pluripotent.

Ans. These stem cells are found in various throughout the body such as bone marrow, fat and blood.

Ans. They are generated in lab by reprogramming adult somatic cells to a pluripotent state. They are similar to embryonic stem cells.

Ans. Advantage Advantage of using these cells is that they do not have any ethical issues linked to the embryonic stem cells.
Disadvantage: Disadvantage of these cells is that reprogramming process can introduce genetic changes in them forming tumours.

Ans. Plasmodesmata These are small channels that directly connect the cytoplasm of neighbouring plant cells to each other. Plasmodesmata penetrate both the primary

Ans. Use of Stem Cells
1. Regenerative Medicine: Stem cells have the potential to repair or replace damaged tissues and organs. Therefore, they are used for treating conditions such as spinal cord injuries, type 1 diabetes, Parkinson's disease, and heart disease.
2. Drug Testing and Development: By differentiating stem cells into specific cell types, researchers can create models of human diseases, allowing for more accurate testing of drug effects and reducing the reliance on animal models.
3. Personalized Medicine: Stem cells can be derived from a patient's own cells, reducing the risk of immune rejection when used in treatments. This personalized approach can lead to more effective and safer therapies.

Ans. The ability to distinguish among different cells is crucial to life. It allows cells in an embryo to sort themselves into tissues and organs. It also helps cells of the immune system to recognize and reject foreign cells, e.g., infectious bacteria.

Ans.
Percent by weight
Membrane | Protein | Lipid | Carbohydrate
Human red blood cell | 49 | 43 | 8
Mitochondria (outer membrane) | 52 | 48 | 0
Mitochondria (inner membrane) | 76 | 24 | 0
Bacteria | 75 | 25 | 0