FSc Notes Biology Part 1 Chapter 4 The Cell

FSc Notes Biology Part 1 Chapter 4 The Cell 1st Year Biology Notes Online Taleem Ilmi Hub Class 11

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Q 1. State salient features of cell theory.

Ans. The salient features of cell theory are:

1. All organisms are composed of one or more cells.
2. All cells arise from pre-existing cells.
3. Cell is the basic structural as well as functional unit for all organisms.

Q 2. What are the basic components of cell?

Ans. A cell consist of following basic components:

1. Plasma membrane, also a cell wall in plant cell.
2. Cytoplasm, containing cell organelles.
3. Nucleus, with nuclear or chromatin material.

Q 3. What is the chemical composition of plasma membrane?

Ans. Cell membrane is chemically composed of lipids and proteins, 60-80% are protein, while 20-40% are lipids. In addition there is a small quantity of carbohydrates.

Q 4. Differentiate between unit membrane and fluid mosaic model of membrane.

Ans. Unit Membrane: It was proposed earlier by J.D. Robertson in 1959 that cell membranes is composed of lipid bi-layer sandwiched between inner and outer layers of protein. This basic structure is called the unit membrane and is present  in all the cellular organelles.

Fluid Mosaic Model: The protein layers are not continuous and are not confined to the surface of the membrane but are embedded in lipid layers in a mosaic manner. This discovery which was given by S-Singer and Nicolson in 1972 led to the proposal of fluid mosaic model. This model at present is the most accepted one.

Q 5. What is the basic function of cell wall?

Ans. Cell wall is very important. It provides a definite shape to cell and keeps it rigid. It does not act as a barrier to the materials passing through it.

Q 6. What is cytosol?

Ans. The soluble part of the cytoplasm is called cytosol.

Q 7. What is the main function of cytoplasm?

Ans. The main function of cytoplasm is to act as a store house of vital chemicals. Is is also a site for certain metabolic processes such as glycolysis.

Q 8. Who was the first person to study ribosomes?

Ans. Palade (1955) was the first person to study them.

Q 9. What is polysome?

Ans. A group of ribosomes attached to mRNA is known as polysome.

Q 10.Who first isolated lysosomes?

Ans. These were isolated as a separate component for the first time by De Duve (1949).

Q 11. Who discovered Golgi apparatus?

Ans. Golgi apparatus was discovered by Golgi in 1898.

Q 12. What are the functions of Golgi apparatus?

Ans. Functions of Golgi Apparatus:

1. Cell Secretions: Golgi complex is concerned with cell secretions. Secretions are products formed within the cell on ribosomes and then passed to the outside through endoplasmic reticulum and Golgi apparatus. The secretions are converted into finished products and are packed inside membrane, before export. Exp: In mammals, the secrete granules containing enzymes that help in digestion. The Golgi complex has a role in information of these granules.
2. Transportation: The proteins or enzymes which have to be transported out of the cell pass through the Golgi apparatus.
3. Modification of Proteins and Lipids: The most important function of this apparatus is to modify the proteins and lipids by adding carbohydrates and converting them into glyco-proteins and glycolipids.

Q 13. What is autophagy? How it is beneficial for the cell?

Ans. Autophagy: Self eating process of cell is called autophagy.

Benefits: Lysosomes are also involved in the autpphagy. During this process some old, worn out parts of cell, such as old mitochondria are digested . In this way, materials of cell may be recycled and cell may be renewed. Their enzymes can also result in degeneration of cell, as may occur during some developmental processes. Lysosomes also release enzymes for extra cellular digestion.

Q 14. What are lysosomes? What is the main function of lysosomes?

Ans. Lysosomes: Lysosomes are cytoplasmic organelles and are different from others due to their morphology. Lysosomes(Lyso = splitting, soma = body) are found in eukaryotic cells.

Function of Lysosomes: Any foreign that gains entry into the cell is immediately engulfed by the lysosome and is completely broken into simple digestible pieces. The process is known as phagocytosis. They are most abundant in those animal cell which exhibit phagocytic activity. They are bounded by single membrane and are simple sacs rich in acid phosphatese and several other hydrolytic enzymes.

Q 15. Differentiate between primary lysosome and secondary lysosome.

Ans. Primary Lysosome: The hydrolytic enzymes are synthesized on Rough Endoplasmic Reticulum and are future processed in the Golgi apparatus. These processed enzymes are budded off as Golgi vesicles and are called as primary lysosomes.

Secondary Lysosomes: The phagocytic vacuoles fuse with the primary lysosomes to form digestive vacuoles. These digestive vacuoles and autophagosomes are known as secondary lysosomes.

Q 16. Differentiate between Gel and Sol.

Ans. Gel: Viscous colloidal solution of cytoplasm is called gel. Peripheral parts of cell are gel like.

Sol: Non-viscous colloidal solution of cytoplasm is called sol. Central parts of cell are sol.

 

Q 17. What are storage disease?

Ans. Several congenital disease have been found to be due to accumulation within the cell of substances such as glycogen or various glycolipids. These are also called storage disease and are produced by a mutation that effect one of the lysosomal enzymes involved in the catabolism of a certain substance.

Q 18. Who first isolated peroxisomes?

Ans. De Duve and coworkers isolated in 1965 particles from liver and other tissues which were enriched with some oxidative enzymes, such as peroxidase, catalase, glycolic acid oxidase and some other enzymes.

Q 19. Briefly describe the structure of peroxisomes.

Ans. These are single membrane enclosed endoplasmic organelle found both in animal and plants cells. These are characterized by containing H2O2 - producing oxidases and catalase. They are approximately 0.5 micro meter in diameter. They have also been found in protozoa, yeast and many cell types of higher plants.

Q 20. What is the function of peroxisomes?

Ans. This organelle is specifically involved in the formation and decomposition of hydrogen peroxide in the cell.

Q 21. What are glyoxisomes?

Ans. Plants contain an organelle, which in addition to glycolic acid oxidase and catalase, also possess a number of enzymes that are not found in animal cells. This organelle called glyoxisomes are most abundant in plant seedlings, which rely upon stored fatty acids to provide them with the energy and material to begin the formation of the cell.

Q 22. What is the basic function of vacuole?

Ans. The plant vacuole is the major contributor to the turgor that provides support to the individual plant cell and contributes to the rigidity of the leaves and younger parts of the plant.

Q 23. What are the main proteins present in cytoskeleton?

Ans. The main proteins that are present in cytoskeleton are tubulin actin, myosin, tropomyosin and others which are also found in muscles.

Q 24. What are the functions of centriole?

Ans. Centrioles play an important part in the location of furrowing during cell division and in the formation of cilia.

Q 25. Justify that mitochondria is a self replicating organelle.

Ans. The presence of ribosomes and DNA indicates that some proteins are synthesized in them. It is a self replicating organelle.

Q 26. What are F1 particles?

Ans. The inner surface of cristae in the mitochondrial matrix has small knob like structure known as F1 particles.

Q 27. What are plastids?

Ans. Membrane bounded, mostly pigment containing bodies present in the cell and are called plastids. Plastids are present in plant cells only.

Q 28. What is stroma and what is its function?

Ans. Stroma:  Stroma covers most of the volume of chloroplast. Stroma is a fluid which surrounds a thylakoids. It contains proteins, some ribosomes and a small circular DNA.

Function of Stroma: It is the part of the chloroplast where CO2 is fixed to manufacture sugars. Some proteins are also synthesized in this part.

Q 29. Why granum appears green?

Ans. On the layer of thylakoids, chlorophyll molecules are arranged and that is why granum appears to be green.

Q 30. What is intergranum?

Ans. Each granum is inter connected with others by the non-green part called intergranum.

Q 31. What are the functions of chromoplast?

Ans. They impart colors to the plant other than green. They are present in the petal of the flower and in the ripened fruit. They help in the pollination and dispersal of seed.

Q 32. What are lecoplasts? What is its function?

Ans. Leucoplasts: They are colorless. They are triangular, tubular or of some other shape.

Function: They are found in the underground parts of the plant and store food.

Q 33. How nuclear pores are formed? What is its function?

Ans. The outer and inner membranes are continuous at certain points resulting in the formation of pores, the nuclear pores. The nuclear pores allow the exchange of materials between the nucleus and the cytoplasm.

Q 34. What is the function of chromosomes?

Ans. All the information necessary to control the activities of the cell is located on the chromosomes in the form of genes, which are transferred from one generation to the other. The number of chromosomes in all individuals of the same species remain constant generation after generation.

Q 35. What are the functions of glyoxysomes?

Ans. 1.One of the primary activities in these germinating seedlings is the conversion of stored fatty acids to carbohydrates. This is achieved through a cycle, glyoxlate cycle, the enzymes of which are located in the glyoxysomes and the process is called gluconeogenesis.

2. Glyoxysomes are the sites for breakdown of fatty acids to succinate.

Q 36. What is the difference between thylakoids and grana?

Ans. Thylakoids: Thylakoids are flattened vesicles which arrange themselves to form grana and intergrana.

Grana: A granum appears to be a pile of thylakoids stacked on each other like coins. On an average, there are 50 or more thylakoids piled to form one granum. Membranes of the gran are sites where sunlight energy is trapped and where ATP is formed.

Q 37. What is nucleolus? What is its function?

Ans. Nucleolus:  It is darkly stained body within the nucleus, and is without any membranes to separate it from the rest of the nuclear material. They are composed of two regions:

1. The peripheral granular area composed of precursors of ribosomal subunits.
2. The central fibril area consisting of large molecules weight RNA and rDNA.

Q 38. Why mitochondria is called power house of the cell?

Ans. Mitochondria extract energy from different components of food and convert it in form of ATP. This energy is used for various cellular activities. The spent energy is in form of ADP is regenerated by mitochondria into ATP. As mitochondria are involved in manufacture and supply of energy to the cell. So they are called power house of the cell.

Q 39. What is Tay Sach's disease?

Ans. Tay Sach's disease is because of absence of Hexoseaminidase enzyme that is involved in the catabolism of lipids. Accumulation of lipids in brain cells lead to mental retardation and even death.

Q 40. Differentiate between Microtubules, Microfilaments and intermediate filaments.

Ans.

Microtubules: 

They are long, unbranched, slender proteins structures.

Functions: Several cell organelles are derived from special assemblies of microtubulues for e.g., cilia, flagella, basal bodies and centrioles.

Assembly and dis-assembly of spindle structure during mitosis.

Microfilaments:

These are considerably more slender cylinders made up of contractile actin protein, linked to the inner surface of plasma membrane.

Functions: They are involved in the internal cell motion like movement of cyclosis and amoeboid movements.

Intermediate Filaments: 

They have diameter in between those of Microtubules and Microfilaments.

Functions: They are involved in maintenance of cell shape and integration of cellular compartments.

Q 41. What is the difference between chlorophyll and hemoglobin?

Ans. Chlorophyll: Chlorophyll has Mg+2 as the central atom in its molecule.

Haemoglobin: Haemoglobin has Fe+2 as the central atom in its molecule.

Q 42. What is the difference between chromatids and chromosomes?

Ans. Chromosomes: Chromosomes are thread like structures consisting of chromatids and centromere.

Chromatids: Chromatids is exact replica of the chromosome.

Q 43. Briefly describe the structure of cell wall of plant cells.

Ans. The outer most boundary in most of the plant cells is called cell wall. It is secreted by the protoplasm of the cell and consists of :

Primary Wall: The primary wall is composed of cellulose deposition of pectin and hemi-celluloses. It is true wall and develops into newly growing cells.

Secondary Wall: It is formed on the inner surface and is completely thick and rigid. It is composed of silica, waxes, cutin, lignin, etc.

Middle Lamella: It is formed in between primary walls of the neighboring cells.

Q 44. Differentiate between phagocytosis and pinocytosis.

Ans. Phagocytosis: The cell membrane helps to take in or engulf solid particles by infolding in the form of vacuoles.

Pinocytosis: The cell membrane helps to take in or engulf liquid particles by infolding in the form of vacuoles.

Q 45. What are the basic functions performed by plasma membrane?

Ans. Transport of Materials: Cell membrane offers a barrier between the cell contents and their surrounding, allowing only selective substances to pass through like lipid soluble substance, glucose, small gas molecules and water can pass through while ions cannot.

Endocytosis: In many animal cells, the cell membranes helps to take in materials by infolding in the form of vacuoles. This can either be phagocytosis or pinocytosis.

Transport Nerve Impulses: In neuron the cell membrane transmits nerve impulses from one part of the body to another to keep coordination.

Q 46. Differentiate between active and passive transport.

Ans. Passive Transport: The substances from the area of high concentration to the area of low concentration. It does not require energy.

Active Transport: The substances move from the area of low concentration to the area of the high concentration. It is uphill movement which requires energy.

Q 47. Describe different types of functions performed by animal and plant cells.

Ans.

Animal Cells:

Muscle Cells: They contract and relax.

Nerve Cells: They transmit impulses.

Gland Cells: They secrete their secretions.

Red Blood: Cells: They carry oxygen.

White Blood Cells: They defend the body against pathogens.

Stomach Cells: They secrete gastric juice.

Plant Cells:

Xylem Cells: They conduct water and mineral salts from soil to the aerial parts of the plant.

Phloem Cells: They trans-locate food.

Sclerenchymatous Cells: They give support to plants.

Collenchymatous Cells: They give support to young plants.

Chrolenchymatous Cells: They carry out photosynthesis.

Parechymatous Cells: They store surplus food.

Meristematic Cells: They produce new cells for growth and development of the plant.

Q 48. What is the difference between animal and plant cells?

Ans.  Animal Cells                                  Plant cells
         Nucleus is central                             Nucleus is peripheral.
         Small sized vacuole.                         Large vacuole present in center.
         No cell wall.                                    Cell wall present.
         Chloroplast absent                           Chloroplast present.
         Centriole and lysosomes present.      Centriole ans lysosomes absent.
         Flagellum present.                            Flagellum absent.
         Glyoxysome absent.                         Glyoxysome present.

Q 49. Differentiate between Prokaryotic and Eukaryotic cell.

Ans. Prokaryotic Cell                         

• No well defined nucleus.
• Nuclear material DNA and chromosomes and are directly submerged in cytoplasm without nuclear covering.
• Organisms possessing prokaryotic cell are celled prokaryotes.
• They lack many of the membrane bounded organelles like mitochondria, endoplasmic reticulum, chloroplasts, Golgi apparatus.
• Prokayotes have small sized ribosomes.
• Prokaryotic cell has cell wall composed of polysaccharides chains bounded covalently to shorter chains of amino acids forming peptidoglycan or murein. The cell wall is regarded as sacculus.

Eukaryotic Cell:

• They have well defined nucleus.
• Nuclear material DNA and chromosomes are enclosed in double nuclear membrane.
• Organisms possessing eukaryotic cells are called eukaryote.
• Eukaryotic cells are rich in membrane bounded organelles. They possess mitochondria, endoplasmic reticulum, chloroplast and Golgi apparatus.
• Eukaryotes have large sized ribosomes.
• Eukaryotic cells have cellulose in their cell wall.

Q 50. Differentiate between Rough Endoplasmic Reticulum and Smooth Endoplasmic Reticulum.

Ans.  Rough Endoplasmic Reticulum:

• Rough Endoplasmic Reticulum is marked by the presence of ribosomes on its membranes.
• It is involved in the synthesis of protein.

Smooth Endoplasmic Reticulum:

• Smooth Endoplasmic Reticulum is without ribosomes.
• It helps in the metabolism of lipids and other molecules. They also detoxify harmful drugs. They also transmit impulses. They are also involved in the transport of materials from one cell to another.

Q 51. Differentiate between Cristac and Cisternae.

Ans. Cristac:
The inner membrane of mitochondria forms infolding into chamber or matrix. These infolds are celled cristae.
Cisternae:
The material present in Endoplasmic reticulum and golgi apparatus is separated from the cytoplasmic materials by structures that are spherical or tubular membranes called cisternae.

Q 52. Describe the emergence and implication of cell theory/

Ans.   
Robert Hook   Was the first who discovered and named the cell, by studying a thin section of cork. Published the report in "Micrographia". He stated, cell is an empty space bounded by thick wall.

Lorenz Oken    Believed "all living beings originate from or consist of vesicles or cells".

Jean Baptist de-Lamarck    Expressed no body can have life if its constituent parts are not cellular tissue or formed by cellular tissue.

Robert Brown    Reported the presence of nucleus, thus changed the ideas about the cell being an empty space.

Theodor Schwann and Schleiden   Presented cell theory.

Rudolph Virchow      Opposed the ideas of abiogenesis and hypothesized, "omnis cellula e cellula", mew cells are formed formed only by division of previously existing living cells.

Louis Pasteur          Provided experimental proof for Virchow's hypothesis by demonstrating than micro-organisms could be formed only from existing bacteria.

August Weismann      Stated "all presently living cells have a common origin because they have basic similarities in structure and molecules".

Q 53. Compare different cytoskeleton of cell.

Ans. Feature      Microtubules         Microfilaments      Intermediate Filaments
         Size          Long, unbranched       Short, Slender         Diameter between both types
                          and slenderic
         Protein       Tubulin                      Actin                        Actin
          Role          Assembly &              Internal cell              Maintenance of cell shape
                           dis-assembly of                                        Integration of cellular compartments
                           spindles during
                            mitosis.
                           From cilia, flagella,
                           basal bodies and centrioles

Q 54. Write note on plastids?

Ans. Plastids:

• These are membranes bounded mostly pigment containing bodies present only in plant cells.
• These are three main types of plastids.

Feature               Chloroplasts             Chromoplasts             Leucoplasts
Color of pigment   Green                         Other than green           Colorless
Location               Green parts of plant    Petals of flower and      Underground parts of plant
                                                               in ripened fruits
Morphology         Double membrane                                           Triangular, tubular or of some
                           containing matrix and                                        other shape
                            thylakoids
Main Function      Absorbs the light         Impart color to              Storage of food
                           energy and utilize it to    different parts
                           manufacture food          Help in pollination
                                                              Dispersal of seeds

Q 55. Describe various movements involved in the transport of materials across cell membrane.

Ans. Movements involved in the transport of materials:
Cell membrane plays an important role in the movement of materials from and to the cell. There are two main processes which are involved in the transport of materials:

• Non-facilitated Transport: 

Non Polar molecules like oil droplets, phospholipids, fatty acids etc., move across the membrane freely through the lipid bi-layer. This is called non-facilitated transport.

• Facilitated Transport: 

The movement of ionic materials like water molecules oxygen carbon dioxide or radicals is carried out across the cell membrane only with the help of proteins. So it is called facilitated transport. There are two types of facilitated transport.

• Active Transport: 

The transport of molecules across the membrane against concentration gradient with the expenditure of energy is called active transport.

• Passive Transport: 

The transport of molecules across the membrane along concentration gradient without utilizing energy is called passive transport. There are two types of passive transport.

• Diffusion: 

Soluble materials are in constant motion and moves from an area of higher concentration to an area of lower concentration across the membranes by a process called diffusion.

• Osmosis: 

The movement of water molecules from an area of its higher concentration to an area of lower concentration through differentially permeable membrane is called osmosis.

• Exocytosis: 

If the transportation takes place from the cell to the exterior or to the other cells then such a process is known as exocytosis. By exocytosis either the waste products or secretions move across the membrane.

• Endocytosis: 

The inward movement of the materials by infolding of the cell membrane in the form of vacuole or vesicle is known as endocytosis. There are two types of endocytosis.

• Phagocytosis: 

If the large solid particles are taken in then such a process is called phagocytosis.

• Pinocytosis:  

The ingestion of liquid materials into the cell is called pinocytosis.

Q 56. State various structural modifications in a cell involved in secretion.

Ans. Secretions are the products produced within the cell on ribosomes and then passed to the outside through endoplasmic reticulum and golgi apparatus. The secretions are converted into finished product and are packed inside membrane, before export.

Q 57. List the processes blocked by mitochondrial failure in a cell.

Ans.  Process blocked by mitochondrial failure in a cell.

1. Krebs cycle.
2. Electron transport chain.
3. Fatty acid metabolism.
   

Q 58. What will happen if a chromosome loses its centromere?

Ans. The loss of centromere will cause:

1. A change in the physical composition.
2. Separation of chromosome.
3. Degeneration of chromosome,

Q 59. How does autophagy help in converting a tadpole larva into an adult amphibian?

Ans. Autophagy is involved in breakdown of cell organelles of tail of tadpole larva. Autophagy is followed by autolysis by which cell is destroyed. In this way tail would disappear.

Q 60. Is there any similarity between bacterial and plant cell wall? 
Ans. No, Peptidoglycan found in bacterial cell wall and cellulose found in plant cell wall are carbohydrates.

 

Written By: Asad Hussain