Case Study Questions Class 11 Biology Chapter 8 Cell : The Unit of Life
CBSE Class 11 Case Study Questions Biology Cell : The Unit of Life. Important Case Study Questions for Class 11 Board Exam Students. Here we have arranged some Important Case Base Questions for students who are searching for Paragraph Based Questions Cell : The Unit of Life.
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CBSE Case Study Questions Class 11 Biology Cell : The Unit of Life
CASE 1
In 1838, Matthias Schleiden, a German botanist, examined a large number of plants and observed that all plants are composed of different kinds of cells which form the tissues of the plant. At about the same time, Theodore Schwann (1839), a British Zoologist, studied different types of animal cells and reported that cells had a thin outer layer which is today known as the ‘plasma membrane’. He also concluded, based on his studies on plant tissues, that the presence of cell wall is a unique character of the plant cells. On the basis of this, Schwann proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells.
Schleiden and Schwann together formulated the cell theory. This theory however, did not explain as to how new cells were formed. Rudolf Virchow (1855) first explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellula). He modified the hypothesis of Schleiden and Schwann to give the cell theory a final shape. Cell theory as understood today is: (i) all living organisms are composed of cells and products of cells. (ii) All cells arise from pre-existing cells.
1.) Identify the incorrect statement
Statement 1 – Theodore Schwann reported the presence of cell membrane
Statement 2 – Rudolph Virchowgive the cell theory a final shape.
Statement 3 – New cells arise from pre-existing cells.
Statement 4 – Living organisms are composed of cells and products of cells.
a.) Statement 1 and 3 are incorrect
b.) Statement 2 and 3 are incorrect
c.) Statement 4 is incorrect
d.) All statement are correct
2.) ____________ proposed the theory, which states that the bodies of animals and plants are composed of cells and products of cells.
a) Antony Von Leeuwenhoek
b) Matthias Schleiden (1838)
c) Rudolph Virchow (1855)
d.) Theodore Schwann (1839)
3.) Give the name of scientist who stated that the animal cell had a thin outer layer.
4.) Who was the first to explain that new cells arise from pre-existing cells and gave final shape to cell theory?
5.) What is mean by “Omnis cellula-e cellula”?
6.) Explain cell theory and give its postulates.
Answer key
1.) d
2.) d
3.) British Zoologist Theodore Schwann (1839) studied different types of animal cells and stated that animal cells had a thin outer layer which is today known as the ‘plasma membrane’.
4.) Rudolf Virchow (1855) explained that cells divided and new cells are formed from pre-existing cells.
5.) “Omnis cellula-e cellula” – means new cells develop by cell division of pre-existing cell.
6.) Schleiden and Schwann together formulated the cell theory. This theory however, did not explain as to how new cells were formed. Rudolf Virchow (1855) first explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellulae). He modified the hypothesis of Schleiden and Schwann to give the cell theory a final shape.
Cell theory postulates,
- All living organisms are composed of cells and products of cells.
- All cells arise from pre-existing cells.
CASE 2
The prokaryotic cells are represented by bacteria, blue-green algae, mycoplasma and PPLO (Pleuro Pneumonia like Organisms). They are generally smaller and multiply more rapidly than the eukaryotic cells. They may vary greatly in shape and size. The four basic shapes of bacteria are bacillus (rod like), coccus (spherical), vibrio (comma shaped) and spirillum (spiral).
The organisation of the prokaryotic cell is fundamentally similar even though prokaryotes exhibit a wide variety of shapes and functions. All prokaryotes have a cell wall surrounding the cell membrane except in mycoplasma. The fluid matrix filling the cell is the cytoplasm. There is no well-defined nucleus. The genetic material is basically naked, not enveloped by a nuclear membrane. In addition to the genomic DNA (the single chromosome/circular DNA), many bacteria have small circular DNA outside the genomic DNA. These smaller DNA are called plasmids. The plasmid DNA confers certain unique phenotypic characters to such bacteria. One such character is resistance to antibiotics. Nuclear membrane is found in eukaryotes. No organelles, like the ones in eukaryotes, are found in prokaryotic cells except for ribosomes. Prokaryotes have something unique in the form of inclusions. A specialised differentiated form of cell membrane called mesosome is the characteristic of prokaryotes. They are essentially infoldings of cell membrane.
1.) ______________ is the fluid matrix, which fills the prokaryotic cell.
a.) Cell sap
b) Cytoplasm
c.) Water
d.) Both a & b
2.) Identify incorrect statement
Statement 1 – In prokaryotic cell nucleus is absent.
Statement 2 – In prokaryotic cells genetic material appears naked.
Statement 3 – In prokaryotic cells genetic material not enveloped by a nuclear membrane.
Statement 4 – prokaryotic cells do not have a cell wall.
a.) Only 1
b) Only 4
c.) Both 2 & 3
d.) All of the above
3.) Give reason – why genetic material in prokaryotic cell is not enveloped in nuclear membrane?
4.) Define mesosome.
5.) Give the any two characteristic of prokaryotic cells.
6.) Enlist the shapes of bacteria are generally occurs.
Answer key
1.) b
2) b
3.) In prokaryotic cell well-defined nucleus is absent. Hence all genetic material appears naked and not enveloped by a nuclear membrane.
4.) Mesosome – A specialised differentiated form of cell membrane called mesosome is the characteristic of prokaryotes. They are essentially infoldings of cell membrane
5.) Characteristic of prokaryotic cells;
- There is no well-defined nucleus.
- The genetic material is basically naked, not enveloped by a nuclear membrane.
- Cellulose is the fluid matrix, which fills the prokaryotic cell.
- The prokaryotic cells are generally smaller and multiply more rapidly than the eukaryotic cells.
- All prokaryotes have a cell wall surrounding the cell membrane except in mycoplasma.
6.) The four basic shapes of bacteria are bacillus (rod like), coccus (spherical), vibrio (comma shaped) and spirillum (spiral).
CASE 3
Studies showed that the cell membrane is mainly composed of lipids and proteins. The major lipids are phospholipids that are arranged in a bilayer. Also, the lipids are arranged within the membrane with the polar head towards the outer sides and the hydrophobic tails towards the inner part. This ensures that the nonpolar tail of saturated hydrocarbons is protected from the aqueous environment. In addition to phospholipids membrane also contains cholesterol.
The ratio of protein and lipid varies considerably in different cell types. In human beings, the membrane of the erythrocyte has approximately 52 per cent protein and 40 per cent lipids.
Depending on the ease of extraction, membrane proteins can be classified as integral and peripheral. Peripheral proteins lie on the surface of membrane while the integral proteins are partially or totally buried in the membrane.
An improved model of the structure of cell membrane was proposed by Singer and Nicolson (1972) widely accepted as fluid mosaic model. According to this, the quasi-fluid nature of lipid enables lateral movement of proteins within the overall bilayer. This ability to move within the membrane is measured as its fluidity.
One of the most important functions of the plasma membrane is the transport of the molecules across it. The membrane is selectively permeable to some molecules present on either side of it. Many molecules can move briefly across the membrane without any requirement of energy and this is called the passive transport. Neutral solutes may move across the membrane by the process of simple diffusion along the concentration gradient, i.e., from higher concentration to the lower. Water may also move across this membrane from higher to lower concentration. Movement of water by diffusion is called osmosis. As the polar molecules cannot pass through the nonpolar lipid bilayer, they require a carrier protein of the membrane to facilitate their transport across the membrane. A few ions or molecules are transported across the membrane against their concentration gradient, i.e., from lower to the higher concentration. Such a transport is an energy dependent process, in which ATP is utilised and is called active transport, e.g., Na+/K+ Pump.
1.) _______________ is the major constituent of the cell membrane.
a) Phospholipids
b) Lipoproteins
c) Proteins
d) Carbohydrates
2.) The lipids arranged within membrane in such way, that the polar head oflipids towards the ___________ sides and the hydrophobic tails towards the ________side.
a) inner , outer
b) outer , inner
c) outer , outer
d) inner , inner
3.) In cell membrane, the tail of phospholipid is _________________.
a.) Polar and hydrophilic
b) Non-polar and hydrophilic
c) Polar and hydrophobic
d) Non-polar and hydrophobic
4.) Define simple diffusion.
5.) Give the classification of membrane protein.
6.) What is the ratio of protein and lipid present in cell membrane of erythrocyte?
Answer key
1.) c
2.) b
3.) d
4.) Simple diffusion it is defined as the movement of the neutral solute across the membrane along with the concentration gradient, i.e., from higher concentration to the lower.
5.) Depending on the ease of extraction, membrane proteins can be classified as integral and peripheral. Peripheral proteins lie on the surface of membrane while the integral proteins are partially or totally buried in the membrane.
6.) The ratio of protein and lipid varies considerably in different cell types. In human beings, the membrane of the erythrocyte has approximately 52 per cent protein and 40 per cent lipids.
CASE 4
The membranous organelles is distinct in terms of its structure and function, many of these are considered together as an endomembrane system because their functions are coordinated. The endomembrane system include endoplasmic reticulum (ER), Golgi complex, lysosomes and vacuoles. Since the functions of the mitochondria, chloroplast and peroxisomes are not coordinated with the above components, these are not considered as part of the endomembrane system.
Electron microscopic studies of eukaryotic cells reveal the presence of a network or reticulum of tiny tubular structures scattered in the cytoplasm that is called the endoplasmic reticulum (ER). Hence, ER divides the intracellular space into two distinct compartments, i.e., luminal (inside ER) and extra luminal (cytoplasm) compartments. The ER often shows ribosomes attached to their outer surface. The endoplasmic reticulum bearing ribosomes on their surface is called rough endoplasmic reticulum (RER). In the absence of ribosomes they appear smooth and are called smooth endoplasmic reticulum (SER). RER is frequently observed in the cells actively involved in protein synthesis and secretion. They are extensive and continuous with the outer membrane of the nucleus. The smooth endoplasmic reticulum is the major site for synthesis of lipid. In animal cells lipid-like steroidal hormones are synthesised in SER.
1.) Endomembrane system facilitate the ______________
a) Coordinated functions of cell organelles with in the cell
b) Coordinated functions of membranous organelles with in the cell
c) Coordinated functions of plasma membrane with in the cell
d) Both a and b
2.) Endoplasmic reticulum is the ____________________
a) Tiny tubular secretion scattered in the cytoplasm
b) tiny tubular structures embedded in membrane
c) Tiny tubular structures scattered in the cytoplasm
d) Tiny tubular structures scattered in the vacuoles
3) Define Rough endoplasmic reticulum and Smooth endoplasmic reticulum.
4) Give the functions of Endoplasmic reticulum.
5) Enlist the name of membranous organelles which comes under endomembrane system and why?
Answer key
1.) b
2.) c
3.) Rough endoplasmic reticulum: The ER which shows ribosomes attached to their outer surface which gives rough appearance, suchribosomebearing ER is called as rough endoplasmic reticulum (RER). In the absence of ribosomes they appear smooth and are called smooth endoplasmic reticulum (SER).
4.) Functions of endoplasmic reticulum:
- Protein synthesis
- Synthesis of lipids
- Synthesis of steroids
- Synthesis of hormones
5.) Membranous organelles are distinct in terms of structure and function, many of these are considered together as an endomembrane system because their functions are coordinated. The endomembrane system include endoplasmic reticulum (ER), Golgi complex, lysosomes and vacuoles
CASE 5
Camillo Golgi (1898) first observed densely stained reticular structures near the nucleus. These were later named Golgi bodies after him. They consist of many flat, disc-shaped sacs or cisternae of 0.5µm to 1.0µm diameter. These are stacked parallel to each other. Varied number of cisternae are present in a Golgi complex. The Golgi cisternae are concentrically arranged near the nucleus with distinct convex cis or the forming face and concave trans or the maturing face. The cis and the trans faces of the organelle are entirely different, but interconnected. The Golgi apparatus principally performs the function of packaging materials, to be delivered either to the intra-cellular targets or secreted outside the cell. Materials to be packaged in the form of vesicles from the ER fuse with the cis face of the Golgi apparatus and move towards the maturing face. A number of proteins synthesised by ribosomes on the endoplasmic reticulum are modified in the cisternae of the Golgi apparatus before they are released from its Trans face. Golgi apparatus is the important site of formation of glycoproteins and glycolipids. It is also involved in the formation of lysosomes.
Mitochondria unless specifically stained, are not easily visible under the microscope. The number of mitochondria per cell is variable depending on the physiological activity of the cells. In terms of shape and size also, considerable degree of variability is observed. Typically it is sausage-shaped or cylindrical having a diameter of 0.2-1.0µm (average 0.5µm) and length 1.0-4.1µm. Each mitochondrion is a double membrane-bound structure with the outer membrane and the inner membrane dividing its lumen distinctly into two aqueous compartments, i.e., the outer compartment and the inner compartment. The inner compartment is filled with a dense homogeneous substance called the matrix. The outer membrane forms the continuous limiting boundary of the organelle. The inner membrane forms a number of infoldings called the cristae towards the matrix. The cristae increase the surface area. The two membranes have their own specific enzymes associated with the mitochondrial function. Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP, hence they are called ‘power houses’ of the cell. The matrix also possesses single circular DNA molecule, a few RNA molecules, ribosomes (70S) and the components required for the synthesis of proteins. The mitochondria divide by fission.
1.) Golgi cisternae formed faces of the Golgi apparatus are ____________
a) Similar
b) Different
c) Interconnected
d) Both b and c
2.) In mitochondria, on the inner membrane number of infoldings present, are called as __________
a) Matrix
b) Follicles
c) Cristae
d) Cisternae
3.) Name the method by which mitochondria divides to form new mitochondria.
4.) Name site which releases the proteins, synthesised by ribosomes on the endoplasmic reticulum.
5.) Give the functions of Golgi apparatus.
6.) Why the Golgi apparatus remains in close association with the ribosomes?
Answer key
1.) d
2.) c
3.) The mitochondria divide by fission.
4.) Proteins synthesised by ribosomes on the endoplasmic reticulum are modified in the cisternae of the Golgi apparatus and then they are released from its Trans face.
5.) Functions of Golgi apparatus:
- Storage, modification and packaging of products
- Involved in formation of lysosomes
- Golgi apparatus is the important site of formation of glycoproteins and glycolipids.
- performs the function of packaging materials, to be delivered either to the intra-cellular targets
6.) A number of proteins synthesised by ribosomes on the endoplasmic reticulum are modified in the cisternae of the Golgi apparatus before they are released from its Trans face. Golgi apparatus is the important site of formation of glycoproteins and glycolipids.