Detailed explanations in West Bengal Board Class 9 Life Science Book Solutions Chapter 2.2 Cell offer valuable context and analysis.
WBBSE Class 9 Science Chapter 2.2 Question Answer – Cell
Very Short Questions and Answers : (1 mark for each question)
What do you mean by cell organelles?
The intracellular components of a cell, which take part in different cellular functions, are called cell organelles.
Which is denoted as the structural and functional unit of life?
Cell is denoted as the structural and functional unit of life.
Which part of a cell acts as the site of different cellular reactions?
Protoplasm acts as the site of different cellular reactions
Which cell organelle is present in between cell wall and protoplasm of a plant cell?
Cell membrane is present in between cell wall and protoplasm of a plant cell.
Besides cytoplasm and nucleus, which is another basic cellular component, present in all living cells?
Besides cytoplasm and nucleus, cell membrane is another basic cellular component, present in all living cells.
Which component of cell membrane behaves like a fluid?
The lipid bi-layer of cell membrane behaves like a fluid.
Which type of proteins in the cell membrane are called intrinsic proteins?
The protein molecules, which remain submerged in the lipid bi-layer of cell membrane, are called intrinsic proteins.
Which type of proteins in the cell membrane are called extrinsic proteins?
The protein molecules, which remain attached to the surface of the lipid bi-layer of cell membrane, are called extrinsic proteins.
Name the rigid, thick and non-living protective layer present outside the plasma membrane of bacterial and plant cells.
The rigid, thick and non-living protective layer, present outside the plasma membrane of bacterial and plant cell, is known as cell wall.
Who proposed the famous ‘Unit Membrane Model’ of cell membrane?
Scientist Robertson proposed the ‘Unit Membrane Model’ of cell membrane.
What is cytoplasm?
Cytoplasm is the translucent, homogeneous and amorphous matrix of a living cell, present in between the cell membrane and the nuclear membrane.
How do different intracellular organelles remain evenly distributed within the cell?
Continuous flow of cytoplasm distributes different intracellular organelles evenly within the cell.
Which portion of protoplasm has the maximum density?
Within protoplasm, nucleus has the maximum density.
Mention a similarity between matured RBC of human blood and sieve tube of a mango tree.
Both matured RBC of human blood and sieve tube of a mango tree are devoid of nucleus.
What is the name of the densest part of a nucleus?
The densest part of a nucleus is called nucleolus.
Name the matrix, where DNA and RNA are synthesised within an eukaryotic cell.
DNA and RNA are synthesised within the nucleoplasm of an eukaryotic cell.
Which membrane separates cytoplasm and nucleoplasm?
Nuclear membrane separates cytoplasm and nucleoplasm.
Which cell organelies maintain direct contact with nuclear membrane?
Endoplasmic reticula and ribosomes maintain direct contact with nuclear membrane.
How do different larger intracellular molecules move in and out through nuclear membrane?
Different larger intracellular molecules move in and out through the pores of nuclear membrane.
What is the name of the inward projections of the inner membrane of mitochondria?
The inward projections of the inner membrane of the mitochondria are called cristae.
Which cell organelle is called the ‘power house’ of a cell?
Mitochondrion is called the ‘power house’ of a cell.
Which type of plastid is present in the cells of leaves and tender twigs of green plants?
Chloroplastid is present in the cells of leaves and tender twigs of green plants.
Which type of plastid is present in the cells of carrot root?
Chromoplastid is present in the cells of carrot root.
Which type of plastid is present in the cells of potato?
Leucoplastid is present in the cells of potato.
Which cell organelle is directly involved in photosynthesis in green plants?
Chloroplastid is directly involved in photosynthesis in green plants.
Which cell organelle is involved in cellular respiration?
Mitochondrion is involved in cellular respiration.
Which membrane-less cell organelle is involved in protein synthesis within the living cell?
Ribosome is the membrane-less cell organelle, involved in protein synthesis within a living cell.
Which structural components constitute a Golgi complex?
Flat sac-like cisternae, small spherical vesicles, large saccular vacuoles and fine connecting tubules constitute the Golgi complex.
Which component of Golgi apparatus appears like flat sac?
Cisterna of Golgi apparatus appears like flat sac.
What is the full form of GERL system?
The full form of GERL system is Golgi Endoplasmic Reticulum Lysosome system.
Which structural elements constitute an endoplasmic reticulum?
Wide flat, sac-like cisternae, long, branched and tube-like structures and tiny spherical vesicles constitute endoplasmic reticulum.
Which type of endoplasmic reticulum carries ribosomes?
Rough endoplasmic reticulum carries ribosomes.
Which single membrane-bound cell organelle takes part in intracellular digestion?
Lysosome is the single membrane-bound cell organelle which takes part in intracellular digestion.
Which cell organelle stores food particles within Amoeba?
Food vacuoles store food particles within Amoeba.
Which cell organelle maintains the turgidity of a plant cell?
Vacuoles maintain the turgidity of a plant cell.
Which macromolecule is involved in the formation of a polyribosome chain?
RNA molecule is involved in the formation of a polyribosome chain.
Which are the structural constituents of a centriole?
Protein microtubules are the structural constituents of a centriole.
What constitutes a microtubule?
Several fine, rod-shaped protein microfilaments constitute a microtubule.
Which is the only cell organelle present in a prokaryotic cell?
The only cell organelle present in a prokaryotic cell is ribosome.
Name a prokaryotic and an eukaryotic organism.
Bacteria is an example of a prokaryotic and Amoeba is the example of an eukaryotic organism.
Which cell organelle is present only in animal cell?
Centrosome is present only in animal cell.
Name a photosynthetic organism with centrosome.
Chlamydomonas is a photosynthetic organism with centrosome.
Name a unicellular organism with plastid.
Euglena is a unicellular organism which has plastid in its cytoplasm.
Which cell organelle is also known as chondriosome?
Mitochondrion is also known as chondriosome.
Which cell organelle is also known as lipochondrion?
Golgi body is also known as lipochondrion.
What is meant by the term monosomes?
Freely scattered ribosomes, present in prokaryotic cells, are known as monosomes.
Which cells of higher plants do not possess cell walls?
Germ cells (male and female gametes) of higher plants do not possess cell walls.
Which is the largest cell presert on earth?
Ostrich egg is the largest cell (170mm x 135mm ) present on earth.
Which cell organelle acts as the hub of several microtubules?
Centrosome acts as the hub of several microtubules.
Which two cell organelles are involved in intracellular digestion of food?
Vacuole and lysosome take part in intracellular digestion of food.
Which double membrane-bound cell organelles are present exclusively in plant cells?
Plastids are the double membrane-bound cell organelles, present exclusively in plant cells.
Which is the longest cell in human body?
The longest cell in human body is neuron or nerve cell.
Who discovered nucleus?
Nucleus was discovered by Robert Brown.
What is the other name of Golgi body?
Golgi body in animal cell is also known as dictyosome in plant cell.
Name the yellow coloured plastid present in plants.
Xanthoplast is the yellow coloured plastid present in plants.
Short Questions and Answers : (2 marks for each question)
What is a cell? Name an organism, which is made up of a single cell.
- A cell is the structural and functional unit of life, composed of a mass of protoplasm, bounded by a thin, elastic, lipo-protein membrane.
- Amoeba is a protozoa which is made up of a single cell.
What are cell organelles? How do cell organelles help a cell to organise its life processes?
All components, either membrane-bound or without membrane, performing specific and individual functions within a cell, are called the cell organelles.
Within a living cell, all different organelles perform their specific functions in a concerted manner. By this process, different cell organelles help a cell to organise its life processes.
What is meant by cell membrane? Which are the main structural components of a cell membrane?
- Cell memberane: Cell membrane is a thin, transparent, delicate, flexible, living and selectively permeable sheath that bounds the protoplasm.
- Structural component: Proteins and lipids are the main structural components of a cell membrane. A few carbohydrate chains often remain attached to it.
What is phagocytosis?
Phagocytosis is a process of cellular ingestion, in which cell membrane of certain animal cells in-folds to engulf tiny food particle. Example-In Amoeba food is ingested by phagocytosis.
What is phagosome?
In phagocytosis, cell membrane infolds to engulf a food particle. This folding, along with food particles detaches from the cell membrane and enters the cytoplasm as a food vacuole. This food vacuole is known as phagosome.
What are microvilli? Mention their functions.
- Microvilli: Cell membrane of some animal cells projects numerous minute finger-like projections along its periphery, these are called microvilli.
- Function: Microvilli increase cell surface area to help cellular absorption.
Why is pinocytosis called ‘cell drinking’?
During pinocytosis, the liquid food materials enter the cell through the cell membrane, forming an invagination and then remain suspended within vesicles. That is why, pinocytosis is called cell drinking
What is pinosome?
The vacuole, containing the liquid food material, which is formed by infolding of cell membrane within the cell during pinocytosis, is called pinosome.
What is glycocalyx?
The thin layer, made up of polysaccharides and glycoproteins, present outside the cell membrane of bacterial cells and animal cells, is called glycocalyx.
How does the cell wall form beyond the cell membrane of a plant cell?
As a plant cell matures, it releases some polysaccharide materials outside the cell. These materials mainly include cellulose and hemicellulose, which slowly accumulate on the outer surface of the cell membrane and become hard to form the cell wall. Here, long cellulose chains form the structural framework and hemicellulose constitute the matrix of the cell wall.
Mention the functions of cell wall.
Functions of cell wall are as follows-
- Cell wall provides a definite shape to the cell.
- It retains the cell structure during turgid condition and protects the cell from bursting due to osmotic pressure
- It protects the cell against internal or external pressure and mechanical injury.
- Being a freely permeable layer, it allows entry and exit of various molecules.
What are plasmodesmata? Mention its function.
- Plasmodesmata: Plasmodesmata are the ultrafine cytoplasmic connection through the fine pits on the cell wall between two adjacent plant cells.
- Function: Inter-cellular transport is the main function of plasmodesmata.
What are desmosomes? Mention its function.
- Desmosomes: Desmosomes are protein plaques, developed in the cell membrane at the site of adhesion between two adjacent animal cells.
- Function: Inter-cellular transport between the cells.
What is hyaloplasm or cytosol? Mention its function.
- Hyaloplasm: The colourless, viscous matrix of a living cell without the cell organelles, is called hyaloplasm or cytosol.
- Function; Hyaloplasm holds all cellular functions within it.
What is meant by ectoplasm and endoplasm?
- Ectoplasm: The transparent, amorphous, homogeneous portion of a cytoplasm with low viscosity, present close to the cell membrane, is called ectoplasm.
- Endoplasm: The denser, granular, nonhomogeneous portion of cytoplasm with greater viscosity, present at the inner portion of a cell, is called endoplasm.
Mention the constituents of cytoplasm.
In eukaryotic cells, cytoplasm contains matrix and different cell organelles. Matrix also contains 90% water and different types of organic and inorganic matters, such as nutrient molecules, different enzymes, mineral salts etc. Cytoplasm of prokaryotic cells contain all the above materials except membrane-bound cell organelles.
What is nucleus?
The densest portion of protoplasm within the cytoplasm, bounded by a double membrane that carries chromosomes and controls all cellular activities, is called nucleus.
Name two protists with multiple nuclei.
Paramoecium and Opalina are two protists with multiple nuclei.
Name a plant cell with multiple nuclei and another without nucleus.
Coenocytic hyphae of fungi have many nuclei while matured seive tube cells do not have nucleus.
Name a human cell which has multiple nuclei and one which has no nucleus.
Voluntary muscle fibres have many nuclei, whereas, matured red blood cells do not have any nucleus in human.
What is nucleoplasm or karyolymph? Mention its functions.
- The transparent, viscous and granular matrix of nucleus that holds chromatin reticula, is called nucleoplasm or karyolymph.
- Functions: Nucleoplasm acts as a site for synthesis of DNA and RNA. It also transports essential materials those involve in vital metabolism and cell function.
What are chromatin reticula? Mention its function.
- Chromatin reticula: Chromatin reticula are the network of several fine thread-like structures, made up of DNA and histone protein, spread in the nucleoplasm of an eukaryotic cell.
- Function: DNA in chromatin material regulate protein synthesis and carry hereditary characteristics from parents to off-spring by giving rise to chromosomes before cell division.
What is chromosome? Mention its function.
- Chromosome: Chromosome is a fine threadlike, self-replicating nucleoprotein structure, created from chromatin reticulum, inside the nucleus of eukaryotic cells, just before cell division.
- Function: Chromosomes contain genetic material DNA which in turn carries hereditary characters from one generation to the next.
What is meant by euchromatin and heterochromatin?
- Euchromatin: The portions of chromatin reticula which are faintly stained with chromosomal stain, are called euchromatin.
- Heterochromatin: The portions of chromatin reticula which are intensely stained with chromosomal stain, are called heterochromatin.
What is gene? Where does it occur?
- Gene: A gene is the specific portion of a DNA that commands a definite protein synthesis or carries a particular hereditary character from one generation to the next.
- Occurrence of gene: Gene occurs in DNA within chromosomes of eukaryotic cells. In prokaryotic cells it occurs in its naked DNA.
Why mitochondrion is called the power house of a cell?
The main energy generating reactions of respiration, i.e. Krebs cycle and electron transport occurs in mitochondrion. Through these reactions, energy is liberated from food by oxidation and is stored in ATP. These ATP molecules are kept in mitochondrial matrix for future utilisation. Therefore, mitochondrion is called the power house of cell.
What does a nucleus do within a cell?
Role of nucleus within a cell are as follows:
- Nucleus controls the overall activity of a living cell by regulating gene expression.
- It plays the main role in cell division.
- Nucleus carries hereditary features from mother cell to daughter cell through the DNA in chromosomes.
Apart from energy generation, which other functions does mitochondrion perform in a cell?
Different functions of mitochondrion are as follows-
- Mitochondria can synthesise amino acids to make their own protein as they have their own DNA.
- They help in the metabolism of fatty acids and synthesise cytochrome and many other biomolecules.
Mention the functions of different plastids.
The functions of different plastids are as follows-
- Chloroplastids act as the site of photosynthesis in green plants.
- Chromoplastids help to develop the colour of flowers and fruits.
- Leucoplastids store food matters within plant cells in the form of starch.
What do you mean by primary lysosome? Define secondary lysosome.
- Primary lysosome: Newly produced lysosomes are called as primary lysosomes. These lysosomes do not take part in digestion as their enzymes remain in granular form.
- Secondary lysosome: Secondary lysosomes actively take part in digestion in presence of different hydrolytic enzymes like protease, lipase, nucleosidase and phosphatase.
Why are lysosomes called suicidal bags?
Any cell may show disturbances in cellular metabolism when it sustains an injury or becomes aged. Then the lysosomal vesicles within it bursts to release enzymes in the cytoplasm, which digest the cell within itself. Due to this, lysosomes are called suicidal bags.
State difference between cytoribosome and mitoribosome.
Cytoribosomes are those ribosomes which are present in cell cytoplasm. It is 70S type in prokaryotic cell and 80 S type in eukaryotic cell. Mitoribosomes are the special type of ribosomes present in mitochondrial matrix. These are 55Stype.
Why ribosomes are called as protein factory of a cell?
Within cytoplasm of all types of living cells, ribosomes directly take part in synthesis of protein with the help of mRNA and tRNA. Therefore, ribosomes are popularly called as the ‘protein factory of the cell.’
What is the main function of centrosome? Why neurons are incapable of dividing?
Main function of centrosome is to prepare spindle fibres during cell division. Centrosome within a neuron remains in inactive state and cannot form spindle fibre. Therefore, neurons are incapable of division.
What is meant by prokaryotic cell? Give example.
The primitive cells without a true and organised nucleus and any of the membranebound cytoplasmic organelles are called prokaryotic cells. In these cells, genetic activities are controlled by a naked circular DNA. Example-Bacterial cell.
What is meant by eukaryotic cell? Give example.
The cells with a true and various membranebound cell organelles, in which genetic activities are controlled by chromosome-borne DNA, are called eukaryotic cells. Example-Algal cell.
Mention three basic features of a plant cell.
Basic features of a plant cell are as follows-
- Plant cells have dead cell wall beyond the cell membrane.
- These cells possess plastids in the cytoplasm.
- The vacuoles are large and lesser in number.
Mention the three basic features of an animal cell.
Basic features of an animal cell are as follows-
- The outermost coating of an animal cell is a lipo-protein cell membrane.
- These cells possess centrosome in cytoplasm.
- Animal cells have many small vacuoles.
Why water turns red when beet root is boiled in it but remains unchanged when carrot is boiled in it?
The pigment present in beet root is betacyanin which is water soluble. So when beet root is boiled in water, the pigment comes out of it and gets dissolved in water. On the other hand, carrot has a yellow pigment called carotene which is water insoluble. So when it is boiled in water, water colour remains unchanged.
Write down the functions of microtubules.
Functions of microtubules are as follows-
- Microtubules form the cytoskeleton of the cell to give strength to it.
- These act as structural components of spermatozoa, flagella and cilia of cells, spindle fibres etc.
- They help to produce spindle fibre during cell division
What do you mean by GERL system?
The three cell organelles, viz. Golgi complex (G), endoplasmic reticulum (ER) and lysosome (L) maintain a close functional relationship to establish sceretory system of a living cell. This secretory system is known as GERL system.
What are ergastic materials? Give an example.
The non-living particles present in the cytoplasm of animal cells are together known as ergastic materials. These are produced during metabolic activities of cell. Example-Glycogen.
Mention two differences between centrosome and ribosome.
|Centrosome is composed of two centrioles which are made up of several protein microtubules
|Ribosomes are composed of two sub-units which are made up of ribonucleoprotein particles
|It forms spindle fibres, cilia and flagella
|It takes part in protein synthesis
Distinguish between ribosome and lysosome.
|All types of cells
|Lined by single membrane
|3. Location inside cell
|Cytoplasm, surface of nuclear membrane and ER
|Scattered in cytoplasm
Distinguish between cytoplasm and protoplasm.
|In the space between cell membrane and nuclear membrane of any living eukaryotic cell, in prokaryotic cells inside the cell membrane
|Inside cell membrane of all living cells
|It is the portion of protoplasm
|It is not a portion of cytoplasm
|Acts as the site for all cellular functions except mRNA transcription and DNA replication in eukaryotic cells
|Act as the site for all possible cellular functions
Distinguish between phagocytosis and pinocytosis.
|2. Received material
|Solid organic matter or living cell
|Water or any aquatic solution
|3. Received structure
|Engulfing of pathogens by neutrophils and monocytes
|Absorption of liquid digested food matters by intestinal mucosal cells
Distinguish between true nucleus and nucleoid.
|3. State of DNA
|Compacted as chromosome by histone proteins
|Nakedly suspended in the cytoplasm
|4. Nuclear membrane
|5. Chromatin reticulum
Distinguish between smooth endoplasmic reticulum and rough endoplasmic reticulum.
|1. Structural component
|Tubule and vesicle
|Cisternae and few tubules
|2. Attachment with ribosome
|No contact with ribosome
|Ribosomes attach on outer surface
|3. Location inside cell
|In contact with cell membrane
|In contact with nucleus
|Synthesis of lipids
|Helping in protein synthesis
Long Questions and Answers : (5 marks for each question)
Briefly describe the structure of a mitochondrion along with a labelled diagram. Structure of mitochondria
Structure of mitochondria
The structure of a mitochondrion is described as follow:
- Mitochondrion is a double membrane-bound, oval or rod-shaped cell organelle, present in all animal and plant cells.
- The inner membrane forms finger-like folds, called cristae, projecting towards the mitochondrial chamber.
- On the inner side of the inner membrane, several tiny tennis racket-like particles are present. These are called elementary particles or F1 particles or F0-F1 particles or oxysomes.
- The outer membrane is smooth and contains spherical granules called Parson’s subunit, on its outer side.
- The inner chamber of mitochondria is filled with matrix (dense fluid). It contains a number of respiratory enzymes, proteins, lipids, ribosomes and circular DNA.
Briefly describe the structure of nucleus along with a labelled diagram.
Structure of nucleus
The portion of protoplasm, which is deeply stained and with maximum density, is called nucleus. It is the most important organelle of the cell, containing the genetic material. It has four components.
- Nuclear membrane: It is a double-unit membrane structure. It is structurally similar to that of the cell membrane and separates nucleoplasm from the cytoplasm.
- Nuclear reticulum: It is made up of fine chromatin fibres that are composed of DNA and proteins. During cell division, it becomes visible as rod-shaped structures called chromosomes.
- Nucleolus: It is a dense granular structure that remains attached to chromatin fibres at a specific region, called nucleolar organiser region (NOR). Nucleolus is made up of RNA (ribonucleic acid).
- Nucleoplasm: It is a viscous granular sap, almost similar to that of cytoplasm. It acts as the site for synthesis of DNA and RNA.
Briefly describe the fluid mosaic model of plasma membrane. Mention the functions of it.
Fluid mosaic model of cell membrane
The fluid mosaic model of plasma membrane is described as follows—
- [Plasma membrane is a thin, delicate, flexible, living and selectively permeable membrane. It separates the protoplasm from external environment.
- Singer and Nicholson (1972) proposed the most acceptable model for the structure of cell membrane. According to this model, the plasma membrane is composed of two very’ closely placed lipid layers, in which various protein molecules float in a mosaic pattern. For this reason, this model is popularly known as ‘fluid mosaic model;
- The protein molecules are of two types—extrinsic proteins (remain attached to the membrane surface) and intrinsic proteins (remain submerged in the lipid bi-layer).
- As the lipid layer is fluid in nature, the protein molecules are free to move. Some times, extrinsic proteins are attached with antenna-like carbohydrates, proteins or lipid molecules.
Functions of plasma membrane:
The functions of plasma membrane are as follows—
- It protects the cell against any external injury and repairs damages sustained by it.
- Transportation of all solvents and some selected solutes in and out of the cell, hence, it is called selectively permeable membrane.
- It helps to engulf tiny food particles and liquid droplets by the process of endocytosis. Waste matters of the cells are discharged by exocytosis.
- The plasma membrane also plays a pivotal role in protecting and maintaining the integrity of the cell by allowing specific substances to enter, while keeping the others out.
Briefly describe the structure of chloroplastid with a labelled diagram of it.
Structure of chloroplastid
The structure of chloroplastid is described as follows—
- These are green coloured plastids, usually biconvex or planoconvex in shape.
- A double-unit, lipo-protein membrane defines its shape. The thin, fluid-filled space in between the outer and the inner membrane is known as periplastidial space.
- The inner chamber is wide and full of jelly-like matrix, called stroma. The inner chamber contains membrane-bound disc-like sacs, called thylakoids which are stacked to form granum.
- Grana remain interlinked by thin membranous strips, called stroma-lamellae. Chlorophyll molecules are stored within thylakoids, which form the site for photosynthesis.
Briefly describe the structure of Golgi body. Mention its function.
Structure of Golgi body
The structure of Golgi body is described as follows—
- Golgi body is a cluster of single membrane- bound cisternae, small vesicles and large vacuoles.
- Cisternae are curved, flat tube-like sacs arranged in parallel manner. Cisternae remain associated with small vesicles by small, branched tubules. These components constitute the Golgi apparatus.
- The Golgi apparatus is basically made up of compartments consisting of two main networks, the convex face as C is Golgi Network (CGN) and the concave face as Trans Golgi Network (TGN). The convex face of Golgi apparatus maintains connection with ER by some tubules.
- Lysosomes are formed from the concave face of Golgi apparatus.
Function of Golgi body
The functions of Golgi body are as follows—
- It participates in secretion of enzymes, hormones, mucous etc.
- It helps in transportation of proteins, enzymes, hormones within and outside the cells.
- It helps in the production of complex sugar, glycoproteins and glycolipids and acts as ‘storage of food.’
- It helps in the formation of lysosomes and other cell-organelles.
- It helps in the formation of acrosome of sperm.
Briefly describe the origin and structure of cell wall.
Origin of cell wall
In the cytokinesis phase of cell division, vesicles from endoplasmic reticulum and Golgi bodies are gathered and arranged at equatorial zone of plant cell. Later vesicles get attached with each other to form cell plate. This cell plate eventually gives rise to cell wall by depositing pectin.
Structure of cell wall
The cell wall occurs only in plant and bacterial cells. It is rigid, thick and non-living protective layer present outside the cell membrane. Cell wall has three layers which are as follows—
- Middle lamella: It is a jelly-like intercellular matrix, present in be adjacent cells. It is composed of calcium and magnesium pectate.
- Primary cell wall: The primary cell wall is the outermost layer of cell wall. It is comparatively thin, permeable and elastic, it is composed mainly of cellulose and hemicellulose.
- Secondary cell wall: This layer is situated in between the primary cell wall and cell membrane. This layer is mainly built by deposition of lignin, suberin, hemicellulose etc. from the cell. Therefore, its thickness increases with the age of the cell.
Briefly describe the occurrence, structure and functions of endoplasmic reticulum.
Occurrence of endoplasmic reticulum:
ER is present in endoplasm of eukaryotic cells, extended from nuclear membrane to cell membrane.
Structure of endoplasmic reticulum:
It is a system of network made up of membrane-bound flat, sac-like structure cisternae, small spherical vehicles and narrow tube-like tubules. Cisternae and vesicles remain interconnected by the tubules. ER is of two types-
- Rough ER having ribosomes on its surface.
- Smooth ER having no ribosomes on its surface.
Functions of endoplasmic reticulum:
The functions of endoplasmic reticulum are as follows-
- It divides the cell into a number of compartments and helps in the formation of different other cell-organelles directly or indirectly like Golgi body, lysosome, etc.
- It acts as a cytoplasmic barrier between different bio-chemical reactions.
- Rough ER helps in synthesis and transportation of protein.
- Smooth ER takes part in synthesis of lipid.
Briefly describe the occurrence, structure and function of centrosome.
Occurrence of centrosome
Centrosome occurs in the cytoplasm near the nucleus of eukaryotic animal cells as a non-membranous, star-shaped organelle.
Structure of centrosome
Centrosome consists of two main parts, i.e. centriole and centrosphere, which are described as follows—
- Centriole: Two closely placed small cylindrical structures called centrioles, arranged at right angles to each other, forms a centrosome or diplosome. Each centriole is composed of nine very fine protein tubules, called microtubules, held by a central hub.
- Centrosphere: Centrioles are surrounded by a transparent non-granular cytoplasmic layer, called centrosphere. Before cell division, microtubules radiate from the centrosphere like sunrays, these are called rays.
Functions of centrosome
The functions of centrosome are mentioned below.
- It forms spindle fibres during cell division and helps in chromosomal movement.
- It helps in the formation of structural component of flagella and cilia of cells and tail of spermatozoa.
Briefly describe the occurence, structure and function of vacuoles.
Occurrence of vacuoles
Vacuoles of animal cells are small, numerous and are spread all over the cytoplasm. In plant cells, one or two big vacuoles occupy a large space inside the cell.
Structure of vacuole
The structure of vacuole is described below.
- Vacuoles are small to large, variously shaped sac-like structures, surrounded by a thin cytoplasmic lining, called tonoplast.
- The cavity of a vacuole remains filled with a liquid, called cell-sap.
- In older plants one or two very large vacuoles occupy most of the space inside a cell, leaving the protoplasm as a thin layer along the inner side of the cell membrane. This thin layer of protoplasm is called primordial utricle.
Functions of vacuole:
The functions of vacuole are mentioned below.
- Vacuoles maintain an equilibrium of pressure inside cytoplasm.
- Hydrostatic pressure (turgor pressure) inside vacuole keeps the herbaceous plants erect and helps them to grow in size.
- Contractile vacuoles remove unwanted materials from the cell.
- Phagocytic vacuole helps in feeding and digestion in some holozoic protists like Amoeba.
What is primordial utricle? How many types of vacuoles can be seen in living cell?
In older plant cells, one or two very large vacuoles occupy most of the space inside a cell, pushing the protoplasm towards boundary. In this condition the protoplasm remains as a thin layer along the inner side of the cell membrane. This thin layer of protoplasm is called Primordial utricle.
Types of vacuoles
Living cells have following types of vacuoles-
- Food vacuole: Food remains stored in this type of vacuole.
- Water vacuole: Specially unicellular organisms store water in this type of vacuole.
- Gas vacuole: Sometimes unicellular organisms store gas in the vacuoles instead of water.
- Contractile vacuole: Protozoa like Amoeba store excretory substances in some vacuoles which can contract and expand and with this mechanism excretory materials are expelled from the cell.
Briefly deseribe the occurrence, structure and function of ribosome.
Occurrence of ribosome
Ribosomes are present in cytoplasm of prokaryotic cells. These remain attached to surface of nuclear membrane and rough ER. Ribosomes are seen in chloroplastids and mitochondria.
Structure of ribosome
The structure of ribosome is decribed as follows:
- Each ribosome is built with a large spherical and a small oval sub-unit, held together by magnesium ion.
- In eukaryotic cell, the two sub-units respectively measure 60 S and 40 S, whereas in prokaryotic cells these are of 50 S and 30 S. here, ‘S’ indicates sedimentation coefficient or Svedverg’s unit.
- Ribosome contains 50% RNA and 50% histone protein.
- During proteinsynthesis many ribosome units are tied in a row by an mRNA chain, like a beaded string. This structure is known as polyribosome or polysome.
Functions of ribosome
The functions of ribosome are as follows-
- Ribosomes synthesise proteins with the help of mRNA and tRNA.
- It helps in metabolism of lipids.
- It also helps in transportation of synthesised proteins.
Mention three similarities and four dissimilarities between mitochondria and plastids.
Similarities between mitochondria and plastids
Three similarities between mitochondria and plastids are as follows-
- Both mitochondria and plastids are double membrane-bound structures.
- Both of these cell organelles possess DNA and both are self-replicating.
- Both the cell organelles contain 70S (prokaryotic) type of ribosome.
Dissimilarities between mitochondria and plastids
|Present in all living eukaryotic cells
|Present in cells of mesophyll tissue of green plants
|Inner membrane is folded inwardly to form finger-like cristae
|Inner membrane is smooth
|Carry respiratory enzymes
|Carry photosynthetic enzymes
|Acts as the reaction site for Krebs cycle of aerobic respiration
|Acts as the reaction site for both light-dependent and light-independent phases of photosynthesis
Describe the structure of a prokaryotic cell.
Structure of a prokaryotic cell
The structure of a prokaryotic cell is described as follows—
- Most of the prokaryotic cells are very tiny and range from 0.1p to 2.5p.
- An ideal prokaryotic cell has a distinct lipoprotein plasma membrane surrounding its protoplasm.
- A circular DNA constitutes a nucleoid, which carries out all hereditary’ and genetic functions. Chromosome and nuclear membrane are absent.
- The cytoplasm is devoid of any membrane-bound cell organelle.
Food and ergastic materials remain suspended in it.
- The cell membrane infolds to form mesosome, which carries respiratory enzymes.
- Few lamellar structures carry photosynthetic pigments in the cells of Prokaryotic ceil autotrophic form.
- Smaller 70S ribosomes remain scattered in the cytoplasm.
- A prokaryotic cell may have flagella or cilia as locomotary organs.
Mention three similarities and four dissimilarities between Golgi body and endoplasmic reticulum.
Similarities between Golgi body and endoplasmic reticulum:
Three similarities between Golgi body and endoplasmic reticulum are as follows—
- Both Golgi body and endoplasmic reticulum have single-layered membrane.
- Both have flat sac-like cisternae and tiny vesicles. Both of these organelles are involved in intra-cellular transportation.
- Both the organelles are involved in biosynthesis of different molecules like hormones and steroids.
Dissimilarities between Golgi body and endoplasmic reticulum
|Present in eukaryotic animal cell. In plant cell, they are named as dictyosome. They remain scattered throughout the cytoplasm
|Present in all eukaryotic cell, it is continued from nuclear membrane and cell membrane
|Cisternae have no connection in between, rather they are parallel to each other
|Cisternae are interconnected by tubules to form a network
|Ribosomes have nothing to do with golgi body
|Rough endoplasmic reticulum has several ribosomes attached to its surface
|Main functions are secretion of hormones, enzymes etc. and formation of lysosome
|Main functions are formation of intracellular compartments and transportation of proteins and other cellular materials
Distinguish between cell membrane and cell wall.
Differences between cell membrane and cell wall
Mention the differences between prokaryotic and eukaryotic cells.
Differences between prokaryotic and eukaryotic cell!
Distinguish between a plant cell and an animal cell.
Differences between a plant cell and an animal cell
|Smaller (generally 0.1-10 y)
|Larger (generally 10-100 ji)
|2. Cell wall
|Made up of peptidoglycan or muramic acid
|Absent in animal cell and made up of mainly cellulose, hemicellulose, pectin and suberin
|Without nuclear membrane and nucleolus
|True membrane-bound nucleus present
|True chromosome absent; Genetic material is a single, circular DNA molecule called the nucleoid
|DNA and protein form true paired chromosome
|5. Cell organelles
|Membrane-bound cell organelles absent
|Membrane-bound cell organelles (mitochondria, Golgi body, plastids, ER etc.) are present
|Smaller in size, 70S type, remain scattered in the cytoplasm
|Larger in size, SOS type, some remain attached to nuclear membrane and rough ER, others remain scattered in the cytoplasm
Draw a labelled diagram of an eukaryotic plant cell.
Labelled diagram of an eukaryotic plant cell
Draw a neat diagram of an eukaryotic animal cell and label different parts of it.
Labelled diagram of an eukaryotic animal cell