Caskets of life - class-IX

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Select the correct option:

Lipids are arranged within the membrane with

  1. Polar heads toward inner side and the hydrophobic tails toward outerside

  2. Both heads and tails toward outerside

  3. Heads toward outerside and tail towards inside

  4. Both heads and tails toward innerside

Correct Option: C

In lipid bilayer, lipids are arranged with the polar head towards the outer side and the hydrophobic/ non-polar tails towards the inner side.

Select the correct option:

The best material for the study of structure of cell membrane is

  1. RBC of human

  2. Liver cell

  3. Kidney cell

  4. Muscle cell

Correct Option: A

RBCs lack a nucleus and may other cell organelles thus they are best suited to study cell membrane without any complication.

So, the correct answer is 'RBC of human'.

Select the correct option:Who gave the lamellar or sandwich model of cell membrane?

  1. Singer and Nicolson

  2. Danielli and Davson

  3. J. Robertson

  4. None of these

Correct Option: B

In $1935$, Danielli and Davson proposed that cell membrane is made of a double layer of phospholipid molecules sandwiched between two single layers of proteins. The three layers are held together by electrostatic forces while phospholipid layers are kept adhered by vander Waal's forces.

So, the correct answwer is 'Danielli and Davson'.

Nucleolus contains

  1. Genetic instructions

  2. Ribosome assembly line

  3. Protein synthesis machinery

  4. Enzymes for polysaccharide formation

Correct Option: B
The nucleolus, whose primary function is to assemble ribosomes is the largest structure in the cell nucleus. The nucleolus takes up around 25% of the volume of the nucleus. It is made up of proteins and ribonucleic acids (RNA). Its main function is to synthesize ribosomal RNA (rRNA) which helps in the synthesis of proteins. It has a ribosome assembly line.
So the correct answer is 'Ribosome assembly line'.

What is true of fluid mosaic model?

  1. Phospholipid monolayer is present over protein layer

  2. Phospholipid bilayer is present over protein layer

  3. Protein embedded in phospholipid bilayer

  4. Phospholipid layer is sandwitched between two protein layers.

Correct Option: C
  • The fluid mosaic model of the biomembrane or cell membrane was proposed by SJ Singer and GL Nicolson in the year 1972.
  • According to this model, the protein molecules are embedded in the phospholipid bilayer.
  • Thus, the proteins are seen as icebergs in the sea of lipids.
  • The lipid bilayer of the cell membrane provides fluidity, flexibility and elasticity to the membrane. 
  • So, the correct answer is 'Protein embedded in phospholipid bilayer'.

Which of the following show selective permeability?

  1. Cell membrane

  2. Cell wall

  3. Cytoplasm

  4. Protoplasm

Correct Option: A
  • The cell membrane or plasmalemma is a phospholipid bilayer that are selectively permeable membranes which separate the interior of the cells (cell organelles and cytoplasm) from the outside environment or the extracellular space.
  •  A selectively permeable can be defined as a cell membrane which allows only certain molecules or ions to pass through the membrane by active or passive transport.
  • So, the correct answer is 'Cell membrane'.

Which one of the following pairs of structures distinguishes a nerve cell from other types of cell ?

  1. Nucleus and mitochondria

  2. Perikaryon and dendrites

  3. Vacuoles and fibres

  4. Flagellum and medullary sheath

Correct Option: B
The vacuole is membrane bound organelle present in all plant and fungal cells and some protist, animal and bacterial cells. The flagellum is an appendage, that protrudes from the cell body of certain prokaryotic and some eukaryotic cells. Nucleus and mitochondria are membrane bound organelles present in almost all cells. 
Perikaryon, also called cyton is the bulbous end of a neuron containing cell nucleus. Dendrites are the short cytoplasmic processes of the cell body of the neuron, which receives stimulus from other neurons.
So, the correct answer is option B.

Cell membranes consist mainly of a

  1. Carbohydrate bilayer and proteins

  2. Protein bilayer and phospholipids

  3. Lipid bilayer and proteins

  4. None of these

Correct Option: C
In the fluid mosaic model of the cell membrane, proposed by Singer-Nicolson in 1972, the phospholipid bilayer has integrated as well as peripheral proteins embedded in it. The integrated proteins are found on the inside and span across the bilayer, while the peripheral proteins are found at the periphery of the lipid layers.

So, the correct answer is 'lipid bilayer and proteins',

According to widely accepted, "Fluid mosaic model" cell membranes are semi-fluid, where lipids and integral proteins can diffuse randomly. In recent years, this model has been modified in several respects. In this regard, which of the following statements is incorrect? 

  1. Proteins in cell membranes can travel within the lipid bilayer.

  2. Proteins can remain confined within certain domains of the memberane.

  3. Proteins can also undergo flip-flop movements in the lipid bilayer.

  4. Many proteins remain completely embedded within the lipid bilayer.

Correct Option: D
  • As per the fluid mosaic model for membrane structure, the fatty acyl chains in the interior of the membrane form a fluid hydrophobic region. 
  • Integral membrane proteins float in the sea of lipid held by hydrophobic interactions with their non polar amino acid side chains. 
  • Both the proteins and lipids are free to move laterally in the plane of lipid bilayer but movement of either from one face of the bilayer to the other is restricted. 
  • This view has been changed now and it is generally accepted that proteins may also show flip flop movement. Although it occurs rarely. 
  • When individual protein molecules and multiprotein complexes in freeze fractured biological membranes are visualized with the electron microscope, some proteins appear on only one face of the membrane; others span the full thickness of the bilayer and protrude from both inner and outer membrane surfaces. 
  • Among the latter, are some proteins that conduct solutes or signals across the membrane. There are no proteins completely embedded within the interior of membranes.
So, the correct answer is 'Many proteins remain completely embedded within the lipid bilayer'.

A cell weighing 1 mg grows to double its initial mass before dividing into two daughter cells of equal mass. Assuming no death, at the end of 100 divisions what will be the ratio of the mass of the entire populations of these cells to that of the mass of the Earth? Assume that mass of the Earth is $10^{24}Kg$ and $2^{10}$ is approximately equal to $1000$.

  1. $10^{-28}$

  2. $10^{-3}$

  3. $1$

  4. $10^3$

Correct Option: D

Hybridoma cells are

  1. nervous cells of frog

  2. hybrid cells resulting from myeloma cells

  3. only cells having oncogenes

  4. product of spore formation in bacteria.

Correct Option: B

Choose the correct answers from the alternatives given.
Slime molds have:

  1. pseudoplasmodia

  2. feeding stages consisting of solitary, individual cells

  3. spores that develop into free-living amoeboid cells

  4. spores that develop into flagellated gametes

Correct Option: D

The haploid spores are produced from the mass by meiosis, these spores are developed or germinated into flagellated gametes. 

So, the correct option is 'spores that develop into flagellated gametes'.

To observe Amoeba and Paramecium in a water drop, the drop was taken on a glass slide. If both the organisms were clearly seen, then the stain used must be ________.

  1. Methylene blue

  2. Iodine

  3. Safranin

  4. Eosin

Correct Option: A

Microorganisms can be observed under microscope using particular stain. To observe Amoeba and Paramecium in a water drop, the drop was taken on a glass slide. If both the organisms were clearly seen, then the stain used must be Methylene blue or thionin. Both these stains are LTP, that is Lipid transfer protein. They are used to observe animal cells like amoeba and paramecium through hybridization membranes like water. This stain makes the nucleus of amoeba and paramecium visible under microscope.

Thus, the correct answer is 'Methylene blue.'

Shape of Paramecium is 

  1. Circular

  2. Oval

  3. Rectangular

  4. Square

Correct Option: B

The Paramecium is a unicellular ciliated protozoan. It looks an oval, slipper-shaped micro-organism when observed under a microscope, rounded at the front/top and pointed at the back or bottom. It can also be seen by naked eyes.

Choose the correct answers from the alternatives given.
Which one of the following protists is not correctly linked to the type of movement it shows?

  1. Amoeboids-pseudopodia

  2. Ciliates-cilia

  3. Zooflagellates-flagella

  4. Sporozoa-flexing the pellicle

Correct Option: D

Sporozoa do not have flagella, cilia, or pseudopodia and they show gliding movement, amoeboids show movement by pseudopodia, ciliates by cilia and zooflagellates show by flagella, the pellicle is shown by paramecium.

So, the correct option is 'Sporozoa-flexing the pellicle'.

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