Chapter 2 Levels Of Organization Of Life Cell
- The cell is the structural and functional unit of life.
- The cell body contains cytoplasm, surrounded by a cell membrane.
- The cytoplasm carries a nucleus and several other organelles.
- A plant cell has a rigid non-living wall outside the cell membrane. It protects the cell from external injury.
- Singer and Nicolson first proposed the fluid mosaic model of the cell membrane.
- According to this model, several protein molecules remain scattered in a fluid-like lipid bilayer to constitute the cell membrane.
- The cell membrane protects the cytoplasm and takes part in the transportation of different cellular materials through it.
- Cytoplasm is a viscous, granular, intracellular matrix.
- Cytoplasm and nucleus together constitute protoplasm.
- It is the site for cellular metabolism.
- The nucleus is a eukaryotic cell organelle.
- DNA present in its chromatins takes part in the control and transmission of genetic characteristics from parents to offspring.
- Mitochondria are double membrane-bound cytoplasmic organelles, which take part in cellular respiration.
- Plastids are typical plant cell organelles.
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Based On The Presence Or Absence Of Pigments In It, Plastids Are Of Three Types:
1. Green-coloured chloroplast or chloroplastid contains green chlorophyll pigment and takes part in photosynthesis,
2. Chromoplast or chromoplastids carry yellow, orange, red or other coloured carotenoid pigments which are responsible for the colour of different parts of plants other than green.
3. Leucoplasts are colourless as they carry stored food rather than pigments.
Endoplasmic reticula take part in protein and steroid synthesis.
Golgi bodies play an important role in cellular secretion.
Lysosome destroys damaged, unwanted cell organelles and also helps in intracellular digestion.
Vacuoles take part in excretion.
The ribosome is involved in protein synthesis.
Centrioles play some role in cell division and microtubules maintain the shape of a cell intact.
Prokaryotic cells do not possess well-organised, membrane-bound nuclei and other cell organelles, whereas, the cells with well-organised nuclei and membrane-bound cell organelles, are called eukaryotic cells.
The difference between plant and animal cells is very distinct.
Plant cells have cell walls and plastids but centrosomes are absent in them.
Chapter 2 Levels Of Organization Of Life Cell Long Answer Type Questions
WBBSE Life Science And Environment Class 9 Solutions
Question 1. Define cell membrane and discuss its occurrence, structure and function.
Part question: Briefly describe the fluid mosaic model of the cell membrane with a diagram.
Part question: Mention two functions of the cell membrane.
Answer:
Definition:
The cell membrane is the thin, transparent, delicate, elastic, living and selectively permeable sheath that delimits the protoplasm from the external medium or objects.
Occurrence:
Cell membrane occurs outside the cytoplasm of all living cells.
Fluid Mosaic Model Of Cell Membrane
1. The plasma membrane is a thin, delicate, flexible, living and selectively permeable membrane. It separates the cytoplasm from the external environment.
2. Singer and Nicolson (1972) proposed the most acceptable model for the structure of cell membranes. According to this model, the plasma membrane is composed of two very closely placed lipid layers, in which various globular protein molecules float in a mosaic pattern.
Phospholipid Being fluid, lipid molecules also can change their place. For this reason, this model is popularly known as ‘the fluid mosaic model.
3. The protein molecules are of two types-extrinsic proteins (remain attached to the membrane surface) and intrinsic proteins (remain submerged wholly or partially in the lipid bilayer to form transmembrane protein channels).
4. As the lipid layer Labelled diagram of the plasma membrane is fluid in nature, the protein molecules are free to move. Sometimes, extrinsic proteins are attached to antenna-like carbohydrates, proteins or lipid molecules.
Functions Of The Cell Membrane:
1. It protects the cell against any external injury and repairs damages sustained by it.
2. Transportation of all solvents and some selected solutes in and out of the cell, hence, it is called a selectively permeable membrane.
3. It helps to engulf tiny food particles and liquid droplets through the process of endocytosis. Waste matter of the cells is discharged by exocytosis.
4. 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.
5. It also helps in the formation of several cell organelles, like vesicles, cilia, flagella, microvilli, etc.
WBBSE Life Science And Environment Class 9 Solutions
Question 2. Define the cell wall and discuss its origin, occurrence and structure.
Answer:
Definition:
The rigid, thick and non-living protective layer present outside the plasma membrane of bacterial and plant cells is known as the cell wall.
Origin:
In the cytokinesis phase of cell division, vesicles from the endoplasmic reticulum and dictyosomes are gathered and arranged at the equatorial zone of a plant cell. Later vesicles get attached to each other to form cell plates.
This cell plate eventually gives rise to the cell wall by depositing pectin. Present just outside the cell membrane of bacterial and plant cells.
Structure:
The cell wall occurs only in plant and bacterial cells. It is a rigid, thick and non-living protective layer present outside the cell membrane. Cell wall has three layers which are as follows-
1. Middle Lamella:
It is a jelly-like intercellular matrix, present in between the primary cell wall of the two adjacent cells. It is composed of calcium and magnesium pectate.
2. Primary Cell Wall:
The primary cell wall is the outermost layer of the cell wall. It is comparatively thin, permeable and elastic. Mainly it is composed of cellulose and hemicellulose.
3. Secondary Cell Wall:
This layer is situated between the primary cell wall and cell membrane. This layer is mainly built by the deposition of lignin, suberin, hemicellulose, etc. from the cell. Therefore, its thickness increases with the age of the cell.
Question 3. Distinguish between the cell membrane and cell wall.
Answer:
Distinguishing Features Between The Cell Membrane And Cell Wall
Question 4. Define cytoplasm and discuss its occurrence, structure and function.
Answer:
Cytoplasm Its Occurrence,Structure And Function
Definition
The colourless, translucent, homogeneous, viscous, amorphous matrix of a living cell is known as cytoplasm.
Occurrence
In eukaryotic cells, cytoplasm fills the space between the nuclear membrane and the plasma membrane. In prokaryotic cells, it fills the whole space inside the cell membrane. The cytoplasm is absent in dead cells.
Structure:
Cytoplasm has two main structural components.
1. Cytoplasmic Matrix Or Cytosol Or Hyaloplasm:
The semi-transparent, homogeneous, colloidal portion of cytoplasm excluding all its organelles is called hyaloplasm or cytoplasmic matrix. It has two portions:
Ectoplasm:
The transparent, non-granular, elastic, highly viscous, outermost portion of cytoplasm, is present in the vicinity of the cell membrane.
Endoplasm:
The semi-transparent, granular, less viscous, innermost portion of the cytoplasm remains close to the nuclear membrane.
2. The portion of the hyaloplasm that encircles the vacuoles is called tonoplasm.
3. 75% of cytoplasm is composed of water and the remaining 25% comprises different organic and inorganic substances as nutrients, different enzymes, mineral salts, etc.
4. The network of proteinaceous microtubules in the cell is called the cytoskeleton.
2. Cell Organelles: Membrane-bound or non-membranous structures which remain suspended in the hyaloplasm to perform specific functions inside living cells are known as cell organelles.
Functions:
1. Helps in maintaining the normal shape of the cell.
2. Acts as the matrix for holding all cell organelles.
3. Acts as the site for cellular metabolic processes.
4. By means of cytoplasmic rotation and circulation, different hormones, food, enzymes and other intracellular substances are transferred within the cell.
WBBSE Life Science And Environment Class 9 Solutions
Question 5. Define the nucleus and discuss its occurrence, structure and function. or, Describe the structure and function of the eukaryotic nucleus. or, Discuss the structure of the eukaryotic nucleus.
Answer:
Definition:
The densest, round, double membrane-bound organelle of cellular protoplasm that carries genetic material and controls all cellular activities is called the nucleus.
Occurrence:
All eukaryotic cells contain a nucleus. The well-developed nucleus is absent in prokaryotic cells. Structure
The shape of a nucleus is generally spherical or oval. It has four components, which are-
1 Nuclear Membrane:
This is a bilayered lipoprotein membrane, structurally similar to the plasma membrane. The layer of a nuclear membrane that approaches the cytoplasm is called the outer membrane and that one, touching the nucleoplasm, is called the inner membrane.
The space in between these two layers is called perinuclear cisterna or perinuclear cisternal space. The nuclear membrane separates nucleoplasm from cytoplasm. However, it has several pores, called nuclear pores, to exchange substances with the cytoplasm.
2 Nucleoplasm Or Karyolymph:
It is a dense semi-transparent sap, almost similar to that of hyaloplasm. A thin reticulum of protein fibres remains arranged below the nuclear membrane to keep it intact. This is called nuclear lamina. Nucleoplasm acts as the site for the synthesis of DNA and RNA.
3 Nuclear reticulum: This is a very fine and almost
invisible network of fine chromatin fibres, composed of DNA and proteins. During cell division, these fibres become visible and countable as rod-shaped structures by the process of dehydration and condensation. These are called chromosomes.
4 Nucleolus: It is a dense granular structure that remains attached to chromatin fibres at a specific region, called nucleolar organiser. Nucleolus is made up of RNA (ribonucleic acid).
Functions Of The Eukaryotic Nucleus:
1. Nucleus controls the overall activity of a living cell. It is therefore called the ‘brain of a cell
2. Structural and functional unit of heredity, i.e., genes are located on chromosomes.
3. Hence, it plays an important role in cell division.
4. Chromosomes present in the nucleus are the sites for DNA synthesis.
5. Nucleolus helps in protein and RNA synthesis which in turn, gives rise to ribosomes.
WBBSE Life Science And Environment Class 9 Solutions
Question 6. Define mitochondrion and discuss its occurrence, structure and function.
Part question: What is mitochondrion? Give an idea of the structure and function of the mitochondrion.
Answer:
Definition:
The mitochondrion is a double membrane-bound, self-replicating, semi-autonomous cell organelle, which remains scattered in the cytoplasm to play a vital role in cellular respiration and energy generation. Mitochondria are known as the ‘powerhouse’ of all living cells.
Occurrence:
Except for matured RBCs of mammals and prokaryotic cells, mitochondria occur in the cytoplasm of all living cells.
Structure:
1. The mitochondrion is a double membrane-bound cell organelle. The space between the outer and the inner membrane is called per mitochondrial space.
2. The inner membrane folds inwardly and irregularly to form several finger-like projections, called cristae.
3. The inner chamber of mitochondrion remains filled with a jelly-like mass, called the mitochondrial matrix. DNA, RNA, ribosomes and various types of enzymes are present within this matrix.
4. Inner surface of the inner membrane bears several tennis racket-shaped tiny granular structures, called oxysome of Fernandez-Moran subunits (F, particles).
5. Several spherical granules, known as ‘the subunit of Parson, remain attached to the outer surface of the outer membrane.
Function:
Labelled Diagram Of A Mitochondrion:
1. Mitochondria act as the site for the reactions of Krebs’ cycle. Energy-packed ATP molecules are produced here.
2. Energy required for different metabolic functions is released here by of sugar molecules. Hence, the mitochondrion is popularly known as the ‘powerhouse of a cell.
3. It controls the B-oxidation of lipids.
4. It helps in the oxidation of amino acids and storage of calcium in the cytoplasm.
Wbbse Class 9 Life Science Solutions
Question 7. Define plastid and write about its types and occurrence. Describe the structure of chloroplastid.
Answer:
Types Of Plastid And Its Occurrence:-
Definition:
Double membrane-bound, self-replicating, semi-autonomous cytoplasmic organelles, which take part in the synthesis and storage of food and the formation of colours in different plant parts, are known as plastids.
Plastids Are Of Three Types:
1. Chloroplast or green plastids,
2. Chromoplast or coloured plastids
3. Leucoplast or colourless plastids.
Occurrence:
Chloroplastids are present in the cells of green leaves, tender branches, petioles and calyces of flowers and immature pericarp (skin of fruit). Chromoplastids are present in the coloured petals, fruits, coloured leaves and roots of carrots, beets, etc. Leucuplastids are present in the roots.
Structure Of Chloroplastid
1. These are green-coloured plastids, usually biconvex or planoconvex in shape.
2. A double-unit, lipoprotein membrane defines its shape. The thin, fluid-filled space in between the outer and the inner membrane is known as periplastidial space.
3. 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.
4. Grana (plural of granum) remain interlinked by thin membranous strips, called stroma-lamellae. Chlorophyll molecules are stored within thylakoids, which are the sites for photosynthesis.
Wbbse Class 9 Life Science Solutions
Question 8. Based on the nature of pigments, classify plastids. Mention the function of each type.
Answer:
Classification Of Plastids:
On the basis of the presence of pigments or stored food, plastids are classified into three types:
1. Chloroplast:
This type of plastid contains green pigments, like-Chlorophyll a and Chlorophyll b, xanthophyll (yellow pigment) and carotene (orange pigment). This type of plastid has varied sizes and shapes. Each of these plastids has grana and stroma in the inner chamber.
2 Chromoplast:
These plastids carry several pigments other than green. These are-orange- coloured carotene, yellow-coloured xanthophyll, red-coloured phycoerythrin, blue-coloured phycocyanin, etc. Chromoplasts are spherical, rod-shaped or star-shaped cell organelles.
3 Leucoplast:
These plastids do not possess any pigment, hence are colourless. These are spherical, oval or rod-shaped structures.
Based on the content of food stored in it, leucoplasts are of three types:
1. Amyloplast (stores starch),
2. Proteinoplast or Aluroplast (stores protein)
3. Elaioplast (stores fats).
Functions of different plastids:
1. Chloroplast:
The green pigment chlorophyll present in it absorbs sunlight and directly helps in photosynthesis to produce simple sugar from water and carbon dioxide.
2. Chromoplast:
These types of plastids create the colour of flowers and fruits. These plastids indirectly help in pollination by creating attractive colours of flower petals.
3. Leucoplast:
Different types of leucoplasts store food materials like starch, protein granules and oil droplets.
Wbbse Class 9 Life Science Solutions
Question 9. Compare mitochondria and chloroplast. Or, Mention three similarities and four dissimilarities between mitochondria and plastids.
Answer:
Similarities between mitochondria and plastids:
1. Both mitochondria and plastids are double membrane-bound structures.
2. Both of these cell organelles possess DNA and both are self-replicating.
3. Both the cell organelles contain a 70S (prokaryotic) type of ribosome.
Dissimilarities between mitochondria and plastids:
Wbbse Class 9 Life Science Solutions
Question 10. What is the endoplasmic reticulum? Briefly discuss the occurrence, structure and function of endoplasmic reticulum.
Answer:
Endoplasmic reticulum:
Single layered, lipo proteinaceous membrane-bound branched tubules and vesicles spread through the cytoplasm from nuclear membrane to the plasma membrane to divide the intracellular space into some compartments and play an important role in synthesis and transport of proteins, are called the endoplasmic reticulum (ER).
Occurrence:
ER is present in the endoplasm of eukaryotic cells, extended from the nuclear membrane to cell membrane.
Structure:
It is a system of networks made up of membrane-bound flat, sac-like structures called cisternae, small spherical vesicles and narrow tube-like structures known as tubules. Cisternae and vesicles remain interconnected by the tubules.
ER is Of Two Types:
1. Rough ER has ribosomes on its surface,
2. Smooth ER has no ribosomes on its surface.
Functions:
1. 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.
2. It acts as a cytoplasmic barrier between different biochemical reactions.
3. Rough ER helps in the synthesis and transportation of protein.
4. Smooth ER takes part in the synthesis of lipids.
Wbbse Class 9 Life Science Solutions
Question 11. Define the Golgi body and discuss its occurrence, structure and function of it.
Answer:
Definition Of Golgi Body:
Single membrane-bound, flat sacs or spherical vesicles which collectively take part in cellular secretion, are made up of lipoproteins and cluster near the nucleus are known as Golgi bodies. Occurrence
Golgi bodies are present in the cytoplasm, near the nucleus of all animal and plant cells. In plant cells, Golgi bodies are called dictyosomes.
Structure Of Golgi Body :
1. The Golgi body is a cluster of single membrane-bound cisternae, small vesicles and large vacuoles.
2. Cisternae are curved, flat tube-like sacs arranged in a parallel manner. Cisternae remain associated with small vesicles by small, branched tubules. These components constitute the Golgi apparatus.
3. The Golgi apparatus is basically made up of compartments consisting of two main networks, the convex face as the Cis Golgi Network (CGN) and the concave face as the Trans Golgi Network (TGN). The convex face of the Golgi apparatus maintains a connection with ER by some tubules.
4. Lysosomes are formed from the concave face of Golgi apparatus.
Function Of Golgi Body:
1. It participates in the secretion of enzymes, hormones, mucous, etc.
2. It helps in the transportation of proteins, enzymes, and hormones within and across the cells.
3. It helps in the production of complex sugar, glycoproteins and glycolipids and acts as ‘storage of food.
4. It helps in the formation of lysosomes and other cell organelles.
5. It helps in the formation of the acrosome of sperm.
Question 12. Mention three similarities and four dissimilarities between the Golgi body and the endoplasmic reticulum.
Answer:
Similarities between the Golgi body and endoplasmic reticulum:
1. Both the Golgi body and endoplasmic reticulum have single-layered membranes.
2. Both have flat sac-like cisternae and tiny vesicles. Both of these organelles are involved in intracellular transportation.
3. Both organelles are involved in the biosynthesis of different molecules like hormones and steroids.
Dissimilarities between the Golgi body and endoplasmic reticulum:
Wbbse Class 9 Life Science Solutions
Question 13. Define lysosome and discuss its occurrence, structure and function.
Answer:
Definition Of Lysosome:
Single membrane-bound, small, hydrolytic enzyme-filled vesicles, which remain scattered in the cytoplasm of animal cells and take part in intracellular digestion are known as lysosomes.
Occurrence Of Lysosome:
Lysosome occurs in all types of animal cells from protozoa to higher vertebrates. It is also seen in a few plant cells like yeast, root-tip cells of maize, pea seeds, etc.
Structure Of Lysosome:
1. Lysosomes are small spherical vesicle-shaped structures.
2. Lysosomal vesicles remain surrounded by a membrane made up of a single layer of lipoprotein.
3. Within these vesicles there remains a homogeneous fluid that contains a number of acids and hydrolytic enzymes like- protease, lipase, nuclease, glycosidase, etc.
Functions Of Lysosome:
1. Damaged cytoplasmic organelles and other cellular fragments are digested by lysosomal enzymes. Digestion of cellular components by lysosome is known as autophagy. If a cell is injured, the lysosomes burst and dissolve the whole cell. This phenomenon is known as autolysis. Due to this feature, the lysosome is called ‘suicidal bag
2. The food vacuole that is formed inside the cell after phagocytosis is called a phagosome. Lysosomal vesicles join with the phagosome to transform it into a hetero phagosome. Within these heterophagosomes the food is then digested by lysosomal enzymes.
3. The acrosomal cap of spermatozoon contains lysosomal enzymes, which help in dissolving the outer membrane of the ovum during fertilisation.
WBBSE Class 9 Life Science Question And Answer
Question 14. What is a vacuole? Briefly describe the occurrence, structure and function of vacuoles.
Answer:
Vacuole:
Small to large variously shaped fluid-filled cavities, surrounded by thin cytoplasmic lining, which take part in maintaining hydrostatic pressure, intracellular digestion, storage of ergastic substances and removal of cellular wastes, are called vacuoles.
Occurrence Of Vacuole:
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:
1. Vacuoles are small to large, variously shaped sac-like structures, surrounded by a thin cytoplasmic lining, called tonoplast.
2. The cavity of a vacuole remains filled with a liquid, called cell sap.
3. 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 the primordial utricle.
Functions Of Vacuole:
1. Vacuoles maintain an equilibrium of pressure inside the cytoplasm.
2. Hydrostatic pressure (turgor pressure) inside the vacuole keeps the herbaceous plants erect and helps them to grow in size.
3. Contractile vacuoles remove unwanted materials from the cell.
4. Phagocytic vacuole helps in feeding and digestion in some holozoic protists like Amoeba.
5. Vacuoles store certain pigments, viz anthocyanin, anthoxanthin, etc. which are responsible for the colour of flower petals.
WBBSE Class 9 Life Science Question And Answer
Question 15. Define ribosome and discuss its occurrence, structure and function.
Answer:
Definition Of Ribosome :
The membranes, spherical granules which are made up of ribonucleoprotein, remain scattered in the cytoplasm, attached to the surface of the nuclear membrane and rough endoplasmic reticula, and play a vital role in protein synthesis, and are called ribosomes.
Occurrence Of Ribosome :
Ribosomes are present in the cytoplasm of prokaryotic cells. In eukaryotic cells, these remain attached to the surface of the nuclear membrane and rough ER. Ribosomes are also seen in chloroplastids and mitochondria.
Structure Of Ribosome :
1. Each ribosome is built with a large spherical and a small oval subunit, held together by magnesium ions.
2. In eukaryotic cells, the two subunits respectively measure 60s and 40s, whereas in prokaryotic cells these are of 50S and 30S. Here, ‘S’ indicates the sedimentation coefficient of Svedverg’s unit.
3. Ribosome contains 50% RNA and 50% histone protein.
4. During protein synthesis many ribosome units are tied in a row by an mRNA chain, like a beaded string. This structure is known as a polyribosome or polysome.
Functions Of Ribosome :
1. Ribosomes synthesise proteins with the help of mRNA and tRNA. So, it is known as the ‘protein factory of cells.
2. It also helps in the metabolism of lipids.
3. It also helps in the transportation of synthesised proteins.
Question 16. Define centrosome and discuss its occurrence, structure and function.
Answer:
Definition Of Centrosome:
The non-membranous, star-shaped cell organelle containing a pair of centrioles, mostly found near the nucleus of animal cells that takes part in spindle formation during cell division is called a centrosome.
Occurrence Of Centrosome:
The centrosome is present near the nucleus in animal cells [exception – neurone]. It is absent in plant cells, however, some photosynthetic, flagellated protists, like Chlamydomonas, primitive fungi have centrosomes.
Structure Of Centrosome:
Centrosome consists of two main parts, i.e., centriole and centrosphere, which are described as follows:
1. Centriole: Two closely placed small cylindrical structures called centrioles, are arranged at right angles to each other, and form a centrosome or diplosome. Each centriole is composed of nine very fine, protein triplet tubules, called microtubules, held by a central hub.
2. 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 astral rays.
Functions Of Centrosome:
1. It forms spindle fibres during cell division and helps in chromosomal movement.
2. It helps in the formation of structural components of flagella and cilia of cells.
3. It also helps in the formation of the tail of sperm.
WBBSE Class 9 Life Science Question And Answer
Question 17. What is a microtubule? Describe the structure and function of microtubules.
Answer:
Microtubule:
The proteinaceous cytoskeletal structure, composed of several fine tubular components, which provide shape and strength to a cell and also help in cell division, is called a microtubule.
Structure Of Microtubule
1. Microtubules are the largest of the cytoskeletal components, made up of fine tubules.
2. 13 protofilaments arrange in a cycle along its periphery to form each microtubule.
3. Protofilaments are composed of tubulin protein.
4. A few motor proteins remain associated with microtubules.
Functions Of Microtubule:
1. Microtubules provide mechanical strength and specific shape to a cell.
2. It forms the cellular locomotory organs like flagella and cilia.
3. It helps in spindle fibre formation during cell division.
4. It helps in intracellular transport.
Question 18. Describe the structure of prokaryotic cells.
Answer:
Structure Of A Prokaryotic Cell:
1. Most of the prokaryotic cells are very tiny, microscopic and range from 0.1 to 2.5μ.
2. An ideal prokaryotic cell has a distinct lipoprotein plasma membrane surrounding its protoplasm.
3. The nucleus is not well developed. Chromosomes and nuclear membranes are absent. Thus, a nucleus-like structure is called a nucleoid. A naked, circular DNA carries all hereditary and genetic information and controls all the metabolic activities in the cell.
4. The cytoplasm is devoid of any membrane-bound cell organelle. Food and ergastic materials remain suspended in it.
5. The cell membrane infolds to form a mesosome, which carries respiratory enzymes.
6. Few structures carry photosynthetic pigments in the cells of autotrophic form.
7. Smaller, 70S type (made up of 50S and 30S subunits) of ribosomes remain scattered in the cytoplasm.
8. A prokaryotic cell may have flagella or cilia as locomotory organs.
Question 19. Mention the salient features of eukaryotic cells.
Answer:
Salient Features Of Eukaryotic Cells:
1. Eukaryotic cells are comparatively larger in size than prokaryotic ones. Generally, these are 10-100 μm in diameter.
2. In eukaryotic cells, a well-organised nucleus is seen. It has a nuclear membrane, nucleoplasm, chromatin reticular and nucleolus.
3. Here the genetic material, that is DNA, remains associated with the basic protein to constitute chromosomes.
4. Membrane-bound cell organelles, like the Golgi body, mitochondria, plastids, and endoplasmic reticulum are found in the cytoplasm.
5. Mitotic apparatus that is spindle fibres are formed during cell division.
6. Ribosomes’ are of 80S type, composed of 60S and 40S subunits, which remain scattered in the cytoplasm, as well as attached on the surface of endoplasmic reticula and nuclear membrane.
WBBSE Class 9 Life Science Question And Answer
Question 20. Mention the differences between prokaryotic and eukaryotic cells.
Answer:
Differences Between Prokaryotic And Eukaryotic Cells:
Question 21. Describe the structure of a plant cell and mention the functions of its different parts.
Answer:
Different Parts Of A Plant Cell:
The plant cells have two main parts-cell envelope and protoplasm.
Cell Envelope: In plant cells, there are two types of cell envelopes-cell wall and cell membrane.
1. Cell wall:
It is the outermost, non-living coating of a plant cell. It is thick, hard and permeable in nature. It is composed of three layers-middle lamella, primary cell wall and secondary cell wall.
Function: The cell wall provides strong mechanical protection and provides a shape to the cell.
2. Cell Membrane:
The cell membrane is a thin, transparent, elastic, living, selectively permeable lipoprotein membrane, situated just beyond the cytoplasm.
Function: It provides a specific shape to the cell. It protects protoplasm and helps in the transportation of various organic and inorganic molecules.
Protoplasm:
Protoplasm is composed of a nucleus and cytoplasm.
1. Nucleus:
Double membrane-bound, the densest portion of protoplasm is the nucleus. It remains surrounded by a double-layered, lipoprotein membrane and contains jelly-like nucleoplasm, reticular chromatin fibres and a single granular nucleolus.
Function: It controls all metabolic and hereditary activities of a cell.
2. Cytoplasm:
It is a semi-transparent, granular, viscous matrix that fills the space between the nuclear membrane and to plasma membrane within a cell. Cytoplasm carries several cytoplasmic organelles, organic and inorganic molecules.
Function: Cytoplasm acts as the site of all physiological reactions inside the living cell. The main cytoplasmic organelles are-
1. Mitochondrion:
It is a double membrane-bound cell organelle which remains scattered all over the cytoplasm.
Function: Mitochondria play the main role in the production and release of energy inside a cell.
2. Plastid:
Plastids are present in plant cells. Based on the type of pigments they carry, plastids are of three types-chloroplast, chromoplast and leucoplast.
Function: Chloroplasts are responsible for photosynthesis. Chromoplasts give colours in flowers, fruits, etc. Leucoplasts store different types of food materials.
3. Endoplasmic reticulum:
Single membrane-bound, branched tubular cell organelles remain spread from nuclear membrane to cell membrane.
Function: Intracellular compartmentalisation, formation of new organelles and cellular transport are the different functions of endoplasmic reticulum.
4. Golgi bodies:
These are single membrane-bound, thin sac-like or fine vesicular structures that occur in the cytoplasm.
Function: These organelles take part in cellular secretion.
5. Vacuole:
Large or small, thin limiting membrane-bound, fluid-filled vesicular structures. In plant cells, one or two vacuoles become very large, which push the cytoplasm back to cell membrane.
Function: The function of vacuoles are to store gases, waste materials and secretory materials.
6. Ribosome:
Tiny, non-membranous, solid, granular cell organelles, remain scattered in the cytoplasm and attached to the surface on rough endoplasmic reticula(RER) and nuclear membrane.
Function: Protein synthesis is the main function of the ribosome.
WBBSE Class 9 Life Science Question And Answer
Question 22. Describe the structure of an animal cell and mention the functions of its different parts.
Answer:
Different parts of an animal cell:
The plant cells have two main parts-cell envelope and protoplasm.
Cell envelope:
Animal cells have only one cell envelope, i.e., cell membrane. It is a thin, transparent, elastic, living, selectively permeable lipoprotein membrane, situated just on the periphery of the cytoplasm.
Function: It provides a specific shape to the cell. It protects protoplasm and helps in the transportation of various organic and inorganic molecules.
Protoplasm:
In animal cells, protoplasm is composed of a nucleus and cytoplasm.
1. Nucleus:
The double membrane-bound, densest portion of protoplasm is the nucleus. It remains surrounded by a double-layered lipoprotein membrane and consists of jelly-like nucleoplasm, reticular chromatin fibres and a single granular nucleolus.
Function: It controls all the metabolic activity of a cell and the inheritance of characters.
2. Cytoplasm:
It is a semi-transparent, granular, viscous matrix that fills the space between the nuclear membrane and plasma membrane within a cell. Cytoplasm carries several cytoplasmic organelles, organic and inorganic molecules.
Function: Cytoplasm acts as the site of all physiological reactions inside the living cell.
Class 9 Life Science Question Answer WBBSE
1. Mitochondrion:
It is a double membrane-bound cell organelle which remains scattered throughout the cytoplasm.
Function: Mitochondria play the main role in the synthesis and release of energy inside a cell.
2. Endoplasmic reticulum:
Single membrane-bound, branched, tubular cell organelles remain spread from the nuclear membrane to cell membrane.
Function: ER helps in intracellular compartmentalisation, formation of new organelles and cellular transport.
3. Golgi bodies:
These are single membrane-bound, thin sac-like or fine vesicular structures that occur in the cytoplasm.
Function: These organelles take part in cellular secretion.
4. Lysosome:
Single membrane-bound, hydrolytic enzyme-filled vesicles.
Function: Lysosome helps in intracellular digestion and dissolving of cellular fragments.
5. Vacuole:
A number of smaller vacuoles are found in animal cells, which remain scattered in the cytoplasm.
Function: Storing food and helping in excretion are the role played by vacuoles.
6. Ribosome:
Tiny, non-membranous, solid, granular cell organelles, remain scattered in the cytoplasm and attached to the surface on rough endoplasmic reticula and nuclear membrane.
Function: Ribosome helps in protein synthesis.
7. Centrosome:
It is a star-shaped, non-membranous organelle located near the nucleus. It is composed of a pair of centrioles with radiating microtubules and a thin layer of cytoplasm surrounding it, called a centrosphere.
Function: It helps in the formation of mitotic apparatus during cell division.
8. Ergastic substances:
A number of non-living matters remain in the cytoplasm as clusters, these are collectively called ergastic substances.
Function: Storage of food in the form of glycogen.
Class 9 Life Science Question Answer WBBSE
Question 23. Distinguish between a plant cell and an animal cell.
Answer:
Distinguishing features between a plant cell and an animal cell:
Question 24. Show differences between plant cell and animal cell with simple diagram. Or, Draw a diagram of an ideal plant cell and label cell wall, plastid, vacuole. Or, Draw a neat diagram of an animal cell and label
1. Nucleus
2. Golgi body
3. Mitochondria
4. Centrosome in it.
Answer:
Diagrammatic representation of differences between plant and animal cells:
Question 25. Show differences between prokaryotic and eukaryotic cells with simple diagram.
Answer:
Diagrammatic representation of differences between prokaryotic and eukaryotic cells:
Class 9 Life Science Question Answer WBBSE
Question 26. Give an outline of structural organisation of a cell by a flow chart.
Answer:
Outline representation of structural organisation of a cell:
Question 27. Draw a labelled diagram of nucleus of a eukaryotic cell. Or, Draw a neat diagram of an ideal nucleus and label its various parts.
Answer:
Labelled diagram of an ideal nucleus
Question 28. Draw a labelled diagram of mitochondria. Or, Draw a neat and labelled diagram of mitochondria.
Answer:
Labelled diagram of mitochondria
Question 29. Draw a labelled diagram of the plastid.
Answer:
Labelled Diagram Of Plastid
Chapter 2 Levels Of Organization Of Life Cell Short Answer Type Questions
Question 1. What is a cell? Name an organism, whose body is made up of a single cell.
Answer:
Cell: A cell is the self-replicating structural and functional unit of life, composed of a mass of protoplasm, bounded by a thin, elastic, lipoprotein membrane.
Unicellular organism: Amoeba is a protozoon whose body is made up of a single cell.
Class 9 Life Science Question Answer WBBSE
Question 2. What are cell organelles? How do cell organelles help a cell to organise its life processes?
Answer:
Cell Organelles:-
All components, either membrane-bound or non-membranous, performing specific and individual functions within a cell, are called cell organelles.
Within a living cell, all different organelles perform their specific functions in a concerted manner. These specific functions of different cell organelles help a cell to organise its life processes.
Question 3. What is meant by unit membrane?
Answer:
Unit Membrane:-
Scientist Robertson, in 1959 proposed a model to describe the structure of cell membrane. According to him, the cell membrane is made up of protein and lipid in which a protein layer remains sandwiched in between two lipid layers. This trilayered model of plasma membrane is popularly known as unit membrane.
Class 9 Life Science Question Answer WBBSE
Question 4. What is phagocytosis? What is phagosome?
Answer:
Phagocytosis And Phagosome:-
Phagocytosis: Phagocytosis is a process of cellular ingestion, in which cell membrane of certain animal cells infolds to produce a cavity to engulf tiny, solid food particle, example In Amoeba food is ingested by phagocytosis.
Phagosome: The solid, food bearing cavities or vesicles, which are formed by phagocytosis, are called phagosomes.
Question 5. Write the process of phagocytosis in brief.
Answer:
Process Of Phagocytosis:-
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. Digestive enzymes then are secreted within the vacuole and help in digestion of food particles.
Question 6. Why is pinocytosis called ‘cell drinking’? What is pinosome? Or what is known as pinocytosis?
Answer:
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’
Pinosome: The vacuole, containing the liquid food material, which is formed by infolding of cell membrane within the cell during pinocytosis, is called pinosome.
Class 9 Life Science Question Answer WBBSE
Question 7. Distinguish between phagocytosis and pinocytosis.
Answer:
Distinguishing features between phagocytosis and pinocytosis are:
WBBSE Class Nine Life Science
Question 8. What is glycocalyx?
Answer:
Glycocalyx:-
The thin layer, made up of polysaccharides and glycoproteins, present outside the cell membrane of bacterial cells and animal cells, is called glycocalyx.
Question 9. What are microvilli? Mention their functions.
Answer:
Microvilli And Its Functions:-
Microvilli: The 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 increase efficient cellular absorption.
Question 10 What are desmosomes? Mention its function.
Answer:
Desmosomes:
Desmosomes are protein plaques, developed in the cell membrane at the site of adhesion between two adjacent animal cells.
Function: Desmosomes are responsible for intercellular transport between the cells.
WBBSE Class Nine Life Science
Question 11 Mention the components of the cell wall and cell membrane.
Answer:
Components Of The Cell Wall And Cell Membrane:-
Components of the cell wall are-Cellulose, hemicellulose, lignin, suberin, etc. Components of the cell membrane are-Lipid, phospholipid, glycolipid, glycoprotein, etc.
Question 12 Explain briefly the formation of cell wall beyond the cell membrane of a plant cell.
Answer:
Formation Of Cell Wall 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.
Question 13 Mention the functions of cell wall.
Answer:
Functions Of Cell Wall:-
The functions of the cell wall are as follows-[1] Cell wall provides a definite shape to the cell. [2] It retains the cell structure during turgid conditions and protects the cell from bursting due to osmotic pressure. [3] It protects the cell against internal or external pressure and mechanical injury. [4] Being a freely permeable layer, it allows the entry and exit of various molecules.
Question 14 What are plasmodesmata? Mention its function.
Answer:
Plasmodesmata:
Plasmodesmata are the ultrafine cytoplasmic connection through the fine pits on the cell wall between two adjacent plant cells.
Function: Intercellular transport is the main function of plasmodesmata.
WBBSE Class Nine Life Science
Question 15. What do you mean by the ornamentation of the cell wall?
Answer:
Ornamentation Of The Cell Wall:-
Due to uneven deposition of secondary cell wall components, various patterns [annular, ladder-like, reticular, etc.] appear on the cell wall surface. This is known as the ornamentation of the cell wall.
Question 16 If an animal cell is placed in distilled water it swells and bursts due to endosmosis. However, a plant cell swells but does not burst. Explain why?
Answer:
The plant cell has a rigid, hard, elastic and permeable wall outside its plasma membrane. It resists the water pressure of a turgid cell from inside and restricts more water from coming into the cell as well as prevents the cell from bursting. The animal cell has only a thin plasma membrane, which cannot withstand the turgor pressure and bursts.
WBBSE Class Nine Life Science
Question 17. Mention one structural and one functional difference between cell wall and cell membrane.
Answer:
Structural and functional differences between the cell wall and cell membrane are-
WBBSE Class Nine Life Science
Question 18 Distinguish between cytoplasm and protoplasm.
Answer:
Distinguishing features between cytoplasm and protoplasm are
Question 19 What is hyaloplasm or cytosol? Mention its function.
Answer:
Hyaloplasm And Its Functions:-
Hyaloplasm: The colourless, viscous matrix of a living cell without the cell organelles, is called hyaloplasm or cytosol.
Function: Hyaloplasm provides space for all cellular functions within it.
WBBSE Class Nine Life Science
Question 20 What is meant by ectoplasm and endoplasm?
Answer:
Ectoplasm:
The transparent, amorphous, homogeneous portion of cytoplasm with low viscosity, present close to the cell membrane, is called ectoplasm.
Endoplasm:
The denser, granular, non-homogeneous portion of cytoplasm with greater viscosity, present at the inner portion of a cell, is called endoplasm.
Question 21 Mention the constituents of cytoplasm.
Answer:
Constituents Of Cytoplasm:-
In eukaryotic cells, the cytoplasm contains a matrix and different cell organelles. Matrix also contains 90% water and different types of organic and inorganic matter, such as nutrient molecules, different enzymes, mineral salts, etc. The cytoplasm of prokaryotic cells contains all the above materials except membrane-bound cell organelles.
WB Class 9 Life Science Question Answer
Question 22 name two protists with multiple nuclei.
Answer:
Protists With Multiple Nuclei:
Paramoecium and Opalina are two protists with multiple nuclei.
Question 23 Name a human cell which has multiple nuclei and one which has no nucleus.
Answer:
Voluntary muscle fibres have many nuclei, whereas, matured red blood cells do not have any nuclei in humans.
Question 24 Name four different parts of a nucleus. Similar question, Which are the components of a nucleus?
Answer:
Four structural components of a nucleus are- the nuclear membrane, nucleoplasm, nuclear reticulum and nucleolus.
Question 25 What is nucleoplasm or karyolymph? Mention its function.
Answer:
Nucleoplasm:
The transparent, viscous and granular matrix of the nucleus that holds chromatin reticula, is called nucleoplasm or karyolymph.
Function: Nucleoplasm acts as a site for the synthesis of DNA and RNA. It also transports essential materials involve in vital metabolism and cell function.
WB Class 9 Life Science Question Answer
Question 26 What is chromatin reticular? Mention its function.
Answer:
Chromatin reticular:
Chromatin reticula are the network of several fine thread-like structures, made up of DNA and histone protein, spread in the nucleoplasm of a eukaryotic cell.
Function: DNA in chromatin material regulate protein synthesis and carry hereditary characteristics from parents to offspring giving rise to chromosomes before cell division.
Question 27 What is a chromosome? Mention its function.
Answer:
Chromosome And Its Function
Chromosome: A chromosome is a fine thread-like, 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.
WB Class 9 Life Science Question Answer
Question 28 What is meant by euchromatin and heterochromatin?
Answer:
Euchromatin:
The portions of chromatin faintly stained reticular which are with chromosomal stain are called euchromatin. Heterochromatin: The portions of chromatin reticula which are intensely stained with chromosomal stain, are called heterochromatin.
Question 29 What is a gene? Where does it occur?
Answer:
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:
The gene occurs in DNA within the chromosomes of eukaryotic cells. In prokaryotic cells, it occurs in their naked DNA.
WB Class 9 Life Science Question Answer
Question 30 Why is the nucleus called the ‘brain of a cell’? Name two animal cells which have multiple nuclei.
Answer:
The brain of a cell:
The nucleus controls all metabolic and genetic activities of a living cell. The nucleus of a cell is therefore as important for it as the brain of our body. So, nucleus is popularly known as the ‘brain of a cell.
Multinucleated animal cell:
A protozoan named Opalina and voluntary muscle cells of our body have many nuclei.
Question 31 Mention two differences between the nucleus and nucleolus.
Answer:
The differences between the nucleus and nucleolus are:
WB Class 9 Life Science Question Answer
Question 32 Distinguish between true nucleus and nucleoid.
Answer:
Distinguishing features between the true nucleus and nucleoid are:
Question 33 Why mitochondrion is called the powerhouse of a cell?
Answer:
The main energy-generating reactions of respiration, i.e. Kreb’s cycle and electron transport occurs in the mitochondrion. Through these reactions, energy is liberated from food by oxidation and is stored in ATP. These ATP molecules are kept in the mitochondrial matrix for future utilisation. Therefore, the mitochondrion is called the power house of cell.
WB Class 9 Life Science Question Answer
Question 34 Apart from energy generation, which other functions does mitochondrion perform in a cell?
Answer:
Different functions of mitochondrion are as follows:
1. Mitochondria can synthesise amino acids to make their own protein as they have their own DNA.
2. They help in the metabolism of fatty acids and synthesise cytochrome and many other biomolecules.
Question 35 What is F, particle?
Answer:
At the inner surface of the inner membrane of mitochondria, there remain attached a number of tiny, tennis racket-shaped protein particles, which take part in ATP synthesis. These are called F particles. These are also known as Fernandez- Moran subunits or oxysome.
Question 36 What are stroma lamellae?
Answer:
Stroma Lamellae:-
Inside the chloroplast, the stacks of grana remain attached to each other by some thin membranous extensions of thylakoids. These are called stroma lamellae.
WB Class 9 Life Science Question Answer
Question 37 What is a quant some?
Answer:
Quant Some:-
On the inner membrane of each thylakoid of granum of a chloroplastid, there remain attached numerous chlorophyll-packed granules. These granules are called quantosomes. These are the site of light reactions. Nowadays, quantosomes are called antenna complexes.
Question 38 What is a pyrenoid?
Answer:
Pyrenoid:-
The tiny cavity inside the chloroplast of algae, which helps in photosynthesis by condensing CO2 is called pyrenoid. These cavities often store starch and protein.
Question 39 Why water turns red when beetroot is boiled in it but remains unchanged when the carrot is boiled in it?
Answer:
The pigment present in beetroot is betacyanin which is water soluble. So when beetroot 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, the colour of the water remains unchanged.
Question 40 What is meant by a semi-autonomous organelle? Give example.
Answer:
Semi-Autonomous Organelle:-
Semi-autonomous organelle: Certain cell organelles have their own DNA and ribosome, by which they can synthesise necessary proteins and can perform self-replication. These organelles are called semi-self-dependent organelles.
Example: Mitochondria and plastiḍs are two self-dependent organelles.
West Bengal Board Class 9 Life Science Book Solution
Question 41 Distinguish between smooth endoplasmic reticulum and rough endoplasmic reticulum.
Answer:
Distinguishing features between smooth ER and rough ER are:
Question 42 What is meant by a zone of exclusion?
Answer:
Zone Of Exclusion:-
The portion of the cytoplasm that surrounds the Golgi body does not have any cell organelle or ergastic substances. This region of cytoplasm appears more transparent than the rest. This portion of cytoplasm adjacent to the Golgi body is called the ‘zone of exclusion.
Question 43 What is dictyosome? Mention its function.
Answer:
Dictyosome: Golgi body of a plant cell is known as a dictyosome.
Function: It takes part in the formation of middle lamella during cytokinesis of cell division. It also helps in cellular secretion.
Question 44 What is the GERL system?
Answer:
GERL System:-
Golgi Body (G), Endoplasmic reticulum (ER) and Lysosome (L) unite to maintain a close functional relationship to establish GERL system. This system helps to intake (endocytosis) of materials into the cells for synthesis and recycling and to transport or secrete (exocytosis) different materials from cells.
Question 45 What do you mean by primary lysosome? Define secondary lysosome.
Answer:
Primary lysosome: Newly produced lysosomes are called as primary lysosomes. These lysosomes do not take part in digestion as their enzymes remain in inactive,granular form.
Secondary lysosome: Secondary lysosomes actively take part in digestion in the presence of different hydrolytic enzymes like protease, lipase, nucleosidase and phosphatase.
West Bengal Board Class 9 Life Science Book Solution
Question 46 What is primordial utricle? Where does it occur?
Answer:
Primordial utricle: The central vacuole of plant cells enlarge and pushes the whole of the protoplasm back to the cell membrane as a thin strip. This thin layer of protoplasm is called the primordial utricle.
Occurrence: Primordial utricle is seen in matured plant cells along the inner periphery of the cell membrane.
Question 47 Why is the ribosome called the protein factory? What does ‘S’ indicate in describing ribosome?
Answer:
Ribosome-the protein factory: Ribosome plays a very important role in protein synthesis. It is, therefore, called the protein factory of a cell. >> Significance of ‘S’: While describing the structure of the ribosome, ‘S’ indicates the Svedberg unit. It denotes the sedimentation coefficient of any cellular component.
Question 48 Why are lysosomes called suicidal bags?
Answer:
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.
West Bengal Board Class 9 Life Science Book Solution
Question 49 Compare the ribosome of prokaryotic and eukaryotic cells.
Answer:
Ribosomes of prokaryotic and eukaryotic cells may be compared as follows:
1. Ribosomes of prokaryotic cells are smaller than that of the eukaryotic cells.
2. The sedimentation coefficient of the prokaryotic ribosomes is 70S, with two subunits of 50S and 30S; whereas, eukaryotic ribosomes are 80S and their two subunits are 60S and 40S.
3. Prokaryotic ribosomes remain scattered in the cytoplasm but eukaryotic ribosomes remain free in the cytoplasm as well as attached on the surface of rough endoplasmic reticula and nuclear membrane.
Question 50 State the difference between mitoribosome and mitoribosome.
Answer:
Difference Between Mitoribosome And Mitoribosome:-
Cytoribosomes are those ribosomes which are present in the cell cytoplasm. It is 70S type in prokaryotic cell and 80S type in eukaryotic cell. Mitoribosomes are the special type of ribosomes present in the mitochondrial matrix. These are 55S type.
West Bengal Board Class 9 Life Science Book Solution
Question 51 What is polysome and monosome?
Answer:
Polysome And Monosome:-
Polysome: In eukaryotic cells, many ribosomes cling to mRNA molecules during protein synthesis. This chain of ribosomes is called a polysome. Another name of it is orgasm.
Monosome: In prokaryotic cells, ribosomes remain freely scattered in cytoplasm as unrelated units. Such single ribosomes are known as monosome. In eukaryotic cytoplasm some monosomes are also found.
Question 52 Mention the differences between ribosome and lysosome.
Answer:
Differences between ribosome and lysosome are:
Question 53 What is ‘the cartwheel model?
Answer:
Cartwheel Model:-
The transverse section of a centriole appears like a cartwheel. At the centre, there remains a ring. from which radiates nine equidistant triplets of microtubules along the periphery. This structural design of centriole is designated as the ‘Carl wheel’ model.
Question 54 What is the main function of the centrosome? Why neurones are incapable of dividing?
Answer:
The main function of the centrosome is to prepare spindle fibres during cell division.
Centrosome within a neurone remains in an inactive state and cannot form spindle fibre. Therefore, neurones are incapable of division.
West Bengal Board Class 9 Life Science Book Solution
Question 55 Mention the differences between centriole and centromere.
Answer:
Differences between centriole and centromere are:
Question 56 Mention two differences between centrosome and ribosome.
Answer:
Differences between centriole and centromere are:
Question 57 What is a microtubule? Mention its functions.
Answer:
Microtubule: The fine, microscopic, tubular protein structures, which remain scattered in the cytoplasm as cytoskeletal elements, are called microtubules.
Function:
1. Formation of the cytoskeleton.
2. Formation of spindle fibres during cell division.
3. Takes part in the formation of cilia and flagella.
West Bengal Board Class 9 Life Science Book Solution
Question 58 What are orgastic materials? Give an example.
Answer:
Ergastic materials: The non-living particles present in the cytoplasm of animal cells are together known as ergastic materials. These are produced during the metabolic activities of cells.
Example: Glycogen is an example of orgastic material.
Question 59 Mention the relation between centriole and microtubule.
Answer:
Relation Between Centriole And Microtubule:-
Each centriole is made up of nine equidistant, triplet microtubules. The spindle fibres, which extend from the centriole during cell division are none other than these microtubules.
Question 60. What is meant by prokaryotic cell?
Answer:
Prokaryotic Cell:-
The primitive cells without a true and organised, nucleus and any of the membrane-bound cytoplasmic organelles are called prokaryotic cells. In these cells, genetic activities are controlled by a naked circular DNA, eg-bacterial cell.
Question 61. What is meant by eukaryotic cells?
Answer:
Eukaryotic Cells:-
The cells with true and various membrane-bound cell organelles, in which genetic activities are controlled by chromosome-borne DNA, are called eukaryotic cells, e.g-algal cell.
Question 62. Mention similarities between prokaryotic and eukaryotic cells.
Answer:
Similarities between prokaryotic and eukaryotic cells are:
1. Both these cells have cytoplasm.
2. Both cells have their own cellular components for cellular respiration.
3. In a bath the cell’s DNA acts as the genetic material. [4] Both these cells undergo cell division.
Question 63. If there is no cell organelle present, can we treat a eukaryotic cell as prokaryotic?
Answer:
Only due to the absence of cell organelles, a eukaryotic cell cannot be treated as prokaryotic.
Because:
1. In prokaryotic cells, mesosomes take part in cellular respiration. The absence of mitochondria in the eukaryotic cells will lead to the death of the cell due to lack of respiratory organelle.
2. The structure of the cell wall is different in prokaryotic and eukaryotic cells.
3. The method of cell division is also different in these two types of cells.
Question 64. Mention three basic features of a plant cell.
Answer:
The basic features of a plant cell are:
1. Plant cells have dead cell walls beyond the cell membrane.
2. These cells possess plastids in the cytoplasm.
3. The vacuoles are large and lesser in number.
4. Plant cells do not possess centrosomes.
Question 65. Schematically represents the structure of a plant cell.
Answer:
Schematic representation of the structure of plant cell is:
Question 66. Schematically represents the structure of an animal cell.
Answer:
Schematic representation of the structure of animal cells is:
Question 67. Mention the three basic features of an animal cell.
Answer:
The basic features of an animal cell are:
1. The outermost coating of an animal cell is a lipoprotein cell membrane.
2. These cells possess centrosomes in the cytoplasm.
3. Animal cells have many small vacuoles.
4. Animal cells possess centrosomes.
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Question 68 Mention the similarities between plant cells and animal cells.
Answer:
Similarities between plant and animal cells are:
1. Both are structural and functional units in plants and animals.
2. Both cells possess mitochondria for cellular respiration, ribosomes for protein synthesis and Golgi bodies for cellular secretion.
3. Both plant and animal cells possess endoplasmic reticula and vacuoles.
Chapter 2 Levels Of Organization Of Life Cell Answer In A Single Word Or Sentence
Question 1. What do you mean by cell organelles?
Answer: The intracellular components of a cell, which take part in different cellular functions, are called cell organelles.
Question 2 Which is denoted as the structural and functional unit of life?
Answer: The cell is denoted as the structural and functional unit of life.
Question 3 Who proposed the concept of ‘Origin of a cell from another cell’?
Answer: Scientist Rudolf Virchow
Question 4 Which is the largest cell of any of the multicellular plants?
Answer: Bark fibre of Rami plant [55cm long]
Question 5 Name the longest unicellular plant.
Answer: Acetabularia [5-10cm long]
Question 6 Which is the longest cell of the human body?
Answer: Neurone [1m approx.]
Question 7 Which is the smallest cell in the living world?
Answer: Mycoplasma gallisepticum[0.1 micron]
Question 8 Which is the largest cell present on earth?
Answer: Ostrich egg is the largest cell (170mm x 135 mm) present on Earth.
Question 9 What is the outer coating of an animal cell?
Answer: Cell membrane
Question 10 Who named the cell membrane?
Answer: Scientists Nageli and Cramer
Question 11 Who proposed the ‘Fluid mosaic model’ of the cell membrane?
Answer: Scientist Singer and Nicolson
Question 12 Give an example of the cell membrane that is visible under the naked eye.
Answer: The thin membrane that can be seen just below the shell of a boiled egg.
Question 13 Which cell organelle is present in between the cell wall and protoplasm of a plant cell?
Answer: The cell membrane is present in between the cell wall and the protoplasm of a plant cell.
Question 14 Besides cytoplasm and nucleus, which is another basic cellular component, present in all living cells?
Answer: Besides cytoplasm and nucleus, cell membrane is another basic cellular component, present in all living cells.
Question 15 Which component of the cell membrane behaves like a fluid?
Answer: The lipid bilayer of the cell membrane behaves like a fluid.
Question 16 Which type of proteins in the cell membrane are called intrinsic proteins?
Answer: The protein molecules, which remain submerged in the lipid bi-layer of the cell membrane, are called intrinsic proteins.
Question 17 Which type of proteins in the cell membrane are called extrinsic proteins?
Answer: The protein molecules, which remain attached to the surface of the lipid bi-layer of the cell membrane, are called extrinsic proteins.
Question 18 Who proposed the famous ‘Unit membrane model’ of the cell membrane?
Answer: Scientist Robertson
Question 19 Name the rigid, thick and non-living protective layer present outside the plasma membrane of bacterial and plant cells.
Answer: The rigid, thick and non-living protective layer, present outside the plasma membrane of bacterial and plant cell, is known as cell wall.
Question 20 What is the outer coating of a plant cell?
Answer: Cell wall
Question 21 Which cells of higher plants do not possess cell walls?
Answer: Germ cells (male and female gametes) of higher plants do not possess cell walls.
Question 22 Mention the structural components of the primary cell wall of a plant cell.
Answer: Cellulose, hemicellulose, pectin
Question 23 Which type of cell wall creates wood?
Answer: Secondary cell wall
Question 24 Who first proposed that Protoplasm is the basis of life’?
Answer: Scientist Thomas Henry Huxley
Question 25 Who coined the term ‘cytoplasm’?
Answer: First the term ‘cytoplasm’ was coined by Rudolf von Kölliker. It was finally described by Strasburger.
Question 26 Which part of a cell acts as the site of different cellular reactions?
Answer: The protoplasm acts as the site of different cellular reactions.
Question 27 What is a tonoplast?
Answer: The thin cytoplasmic layer surrounding the vacuoles is called the tonoplast.
Question 28 How do different intracellular organelles remain evenly distributed within the cell?
Answer: Continuous flow of cytoplasm distributes different intracellular organelles evenly within the cell.
Question 29 Which portion of protoplasm has the maximum density?
Answer: Within protoplasm, the nucleus has the maximum density.
Question 30 Name one macro and one micro-element present in the cytoplasm.
Answer: Macro-element-Carbon [C] and Micro- element-Copper [Cu]
Question 31 Name the cytoplasm of muscle cell.
Answer: Sarcoplasm
Question 32 How do you denote the nucleus of a prokaryotic cell?
Answer: Nucleoid
Question 33 How do you denote a multinucleate plant cell?
Answer: Coenocyte
Question 34 How do you denote a multinucleate animal cell?
Answer: Cyncytium
Question 35 Name one non-nucleate plant cell and one animal cell.
Answer: Sieve tube cells in plants and matured RBCs of mammals in animals
Question 36 Mention a similarity between matured RBC of human blood and the sieve tube of a mango tree.
Answer: Both matured RBCs of human blood and the sieve tube of a mango tree are devoid of nuclei.
Question 37 What is the name of the densest part of a nucleus?
Answer: The densest part of a nucleus is called nucleolus.
Question 38 Name the matrix, where DNA and RNA are synthesised within an eukaryotic cell.
Answer: DNA and RNA are synthesised within the nucleoplasm of an eukaryotic cell.
Question 39 Which membrane separates cytoplasm and nucleoplasm?
Answer: Nuclear membrane separates cytoplasm and nucleoplasm.
Question 40 Which cell organelles maintain direct contact with the nuclear membrane?
Answer: Endoplasmic reticula and ribosomes maintain direct contact with the nuclear membrane.
Question 41 How do different larger intracellular molecules move in and out through the nuclear membrane?
Answer: Different larger intracellular molecules move in and out through the pores of the nuclear membrane.
Question 42 What is the name of the inward projections of the inner membrane of mitochondria?
Answer: The inward projections of the inner membrane of the mitochondria are called cristae.
Question 43 Which cell organelle is called the ‘power house’ of a cell?
Answer: The mitochondrion is called the ‘ powerhouse of a cell.
Question 44 Which cell organelle is involved in cellular respiration?
Answer: Mitochondrion is involved in cellular respiration.
Question 45 Which cell organelle is also known as a chondriosome?
Answer: Mitochondrion is also known as chondriosome.
Question 46 Which double membrane-bound cell organelles are present exclusively in plant cells?
Answer: Plastids are the double membrane-bound cell organelles, present exclusively in plant cells.
Question 47 Which type of plastid is present in the cells of leaves and tender twigs of green plants?
Answer: Chloroplastid is present in the cells of leaves and tender twigs of green plants.
Question 48 Which type of plastid is present in the cells of carrot root?
Answer: Chromoplastid is present in the cells of carrot root.
Question 49 Which type of plastid is present in the cells of potatoes?
Answer: Leucoplastid is present in the cells of potatoes.
Question 50 Which cell organelle is directly involved in photosynthesis in green plants?
Answer: Chloroplastid is directly involved in photosynthesis in green plants.
Question 51 Which structural elements constitute an endoplasmic reticulum?
Answer: Wide flat, sac-like cisternae, long, branched and tube-like structures and tiny spherical vesicles constitute the endoplasmic reticulum.
Question 52 Which type of endoplasmic reticulum carries ribosomes?
Answer: Rough endoplasmic reticulum carries ribosomes.
Question 53 Name two cell organelles with single-layered membranes.
Answer: Golgi body and lysosome
Question 54 Which structural components constitute a Golgi complex?
Answer: Flat sac-like cisternae, small spherical vesicles, large saccular vacuoles and fine connecting tubules constitute the Golgi complex.
Question 55 Which component of the Golgi apparatus appears like a flat sac?
Answer: Cisterna of the Golgi apparatus appears like a flat sac.
Question 56 What is the full form of the GERL system?
Answer: The full form of the GERL system is the Golgi Endoplasmic Reticulum Lysosome system.
Question 57 Which cell organelle is also known as mitochondrion?
Answer: Golgi body is also known as the mitochondrion.
Question 58 What is the other name of the Golgi body?
Answer: Golgi body in animal cell is also known as the dictyosome in plant cells.
Question 59 Which single membrane-bound cell organelle takes part in intracellular digestion?
Answer: Lysosome is the single membrane-bound cell organelle which takes part in intracellular digestion.
Question 60 Which two cell organelles are involved in the intracellular digestion of food?
Answer: Vacuole and lysosome take part in the intracellular digestion of food.
Question 61 Which cell organelle stores food particles within Amoeba?
Answer: Food vacuoles store food particles within Amoeba.
Question 62 Which cell organelle maintains the turgidity of a plant cell?
Answer: Vacuoles maintain the turgidity of a plant cell.
Question 63 Which membrane-less cell organelle is involved in protein synthesis within the living cell?
Answer: Ribosome is the membrane-less cell organelle, involved in protein synthesis within a living cell.
Question 64 Which macromolecule is involved in the formation of a polyribosome chain?
Answer: RNA molecule is involved in the formation of a polyribosome chain.
Question 65 Which cell organelle acts as the hub of several microtubules?
Answer: Centrosome acts as the hub of several microtubules.
Question 66 What are the structural constituents of a centriole?
Answer: Protein microtubules are the structural constituents of a centriole.
Question 67 Which cell organelle is present only in animal cells?
Answer: Centrosome is present only in animal cells.
Question 68 Name a photosynthetic organism with a centrosome.
Answer: Chlamydomonas is a photosynthetic organism with a centrosome.
Question 69 What constitutes a microtubule?
Answer: Several fine, rod-shaped protein microfilaments constitute a microtubule.
Question 70 Which is the only cell organelle present in a prokaryotic cell?
Answer: The only cell organelle present in a prokaryotic cell is the ribosome.
Question 71 Name a prokaryotic and a eukaryotic organism.
Answer: Bacteria is an example of a prokaryotic and Amoeba is an example of an eukaryotic organism.
Chapter 2 Levels Of Organization Of Life Cell Fill In The Blanks
1. An Egg/ Ovum is the biggest cell in the human body.
2. Middle lamella of the cell wall is formed from the Cell plate during cell division.
3. Trophoplasm is the cytoplasm with yolk and fat as stored material for nutrition.
4. The term Syncytium is used for a multinucleated animal cell.
5. Oxysome is also known as an F0-F1 particle.
6. Mitochondrion and plastid are two semi-autonomous cell organelles as they have their own DNA
7. Discs of thylakoids are stacked into a Granum
8. Colourless, immature plastids are known as Proplastids
9. Golgi body is the cell organelle that helps in the formation of the acrosome of spermatozoa.
10. Lysosome with undigested food materials is also named as Residual body
11. The 70S type of ribosome is found in a Prokaryotic type of cell.
12. Total number of microtubule triplets in each centriole is 9/Nine
Chapter 2 Levels Of Organization Of Life Cell True Or False
Question 1. Extrinsic proteins are also called ‘tunnel proteins.
Answer: False
Question 2. We can observe the presence of mucopeptide in plant cell walls.
Answer: False
Question 3. Plasmodesmata are present in animal cells.
Answer: False
Question 4. Both micronucleus and macronucleus can be seen in a Paramoecium cell.
Answer: True
Question 5. Perinuclear space is the space between the two units of the nuclear membrane.
Answer: True
Question 6. Chromosomes are only visible in the dividing cells.
Answer: True
Question 7. The Fernandez-Moran subunit is the other name for oxysome.
Answer: True
Question 8. Aleuroplast is a type of leucoplast which stores proteins.
Answer: True
Question 9. Anthocyanin and betacyanin are two fat-soluble pigments.
Answer: False
Question 10. Spherosome is also known as ‘plant lysosome.
Answer: True
Question 11. 55S type of ribosomes is found in mitochondria.
Answer: True
Question 12. A ribosome has two subunits of Parson.
Answer: False
Question 13. Peridinium is an example of prokaryotic organism.
Answer: True
Chapter 2 Levels Of Organization Of Life Cell Match The Columns
Find The Odd One Out
Question 1. Hyaloplasm, Nucleoplasm, Nucleolus, Chromatin.
Answer: Hyaloplasm
Question 2. Cisternae, Desmosome, Tubule, Vesicle
Answer: Dosmosome
Question 3. Mesosome, Nucleoid, Mitochondria, Ribosome
Answer: Mitochondria
Question 4. Grana, Stroma, Thylakoid, Cristae
Answer: Cristae
Question 5. Egg of ostrich, Neurone, Root hairs, Plastid
Answer: Plastid
Question 6. Cell wall, Plastid, Dictyosome, Lysosome
Answer: Lysosome
Question 7. Plastid, Ribosome, Semiautonomous cell organalles, Mitochondria
Answer: Ribosome
Question 8. Cell wall, Plasmodesmata, Centrosome, Plastid
Answer: Centrosome
Question 9. Naked DNA, Eukauyotes, Nucleoid, Mesosome
Answer: Eukaryote
Question 10. Golgi apparatus, ER, Lysosome, Centrosome
Answer: Centrosome
Question 11. Golgi apparatus, Ribosome, Lysosome, Parenchyma
Answer: Parenchyma
Fill In The Blanks By Looking At The First Pair
1 Unit membrane model: Robertson:: Fluid Mosaic model: Singer and Nicolson
2 Cell wall :: Permeable :: Plasma membrane : Semipermeable
3 Solid food: Phagocytosis:: Liquid food: Pinocytosis
4 Protein factory: Ribosome:: Power house: Mitochondria
5 Food synthesis: chloroplast:: Storage food: Leucoplast
6 Amyloplast: Storage of starchy cellulose:: Elaioplast: Storage of lipids
7 Golgi apparatus: Secretion:: Mitochondria: Respiration
8 Brain of the cell: Nucleus:: Suicidal bag: Lysosome
9 Eukaryotic ribosome: 80S :: Prokaryotic :: ribosome: 70S
Among The Four Concepts Given, Three Of Them Belong To One. Find That
Question 1 Integral membrane protein, Glycoprotein, Cell membrane, Glycolipid
Answer: Cell membrane
Question 2 Ectoplasm, Nucleoplasm, Protoplasm, Cytoplasm
Answer: Protoplasm
Question 3 Ectoplasm, Endoplasm, Tonoplasm, Cytoplasm
Answer: Cytoplasm
Question 4 Nucleolus, Nucleus, Nucleoplasm, Nuclear reticulum
Answer: Nucleus
Question 5 Cristae, Mitochondria, F, particle, DNA
Answer: Mitochondria
Question 6 Plastid, Chloroplast, Chromoplast, Leucoplast
Answer: Plastid
Question 7 ER, Golgi apparatus, GERL, Lysosome
Answer: GERL
Question 8 Protein synthesis, Monosome, Polysome,
Answer: Ribosome
Question 9 Chloroplast, Golgi apparatus, Eukaryotic cell, Mitochondria.
Answer: Eukaryotic cell