31 Years NEET Previous Year Questions: Cell: The Unit of Life - 3 Free

Fluid mosaic model of plasma membrane proposes that plasma membrane comprises of a phospholipid bilayer wherein icebergs of proteins floating in sea of phospholipids.

A chromatid is one of two identical halves of a chromosome. Sister chromatids are 2 identical halves which are joined by the centromere in a chromosome. A chromomere is serially arranged beads of a chromosome that have resulted from the supercoiling of a continuous DNA thread. It is more distinct during prophase. Telomere is a cap-like structure present at the end of each strand of DNA. It protects the chromosome from sticking to another chromosome. It also protects the genetic material during cell division. It occurs 4 times in a chromosome.

Thus, the correct answer is 'Telomere.'

Golgi bodies take part in elaboration and secretion of complex biochemicals.  Mitochondria are the site of ATP  synthesis. Ribosomes are produced in nucleolus.

Mitotic spindles are composed of microtubules which are made of tubulin dimers. Actin and myosin are the contractile proteins of muscle fibres. Myoglobin is oxygen carrying pigment found in muscle.

Raphides are needle-shaped crystals of calcium carbonate or calcium oxalate found in specialized plant cells called idioblasts. It is believed that the raphides are a defense mechanism against plant predators, as they are likely to tear the soft tissues of the throat or esophagus of a plant predator chewing on the plant’s leaves. They are non-nitrogenous substances.

Prokaryotes have simple flagella without microtubules whereas eukaryotes have complex cilia and flagella which consists of microtubules arranged in 9+2 fashion (an outer ring of nine pairs surrounding 1 center pair). Further in prokaryotes the arrangement is 9+0.

The thylakoid membranes possess the chlorophylls. The outer membrane is permeable to a number of solutes. Inner membrane  has a number of carrier proteins. Stroma forms the matrix containing the enzyme for Calvin cycle.

Endoplasmic reticulum transport proteins and enzymes to their destinations i.e. within the cell and outside the cell.

The incorrect statement according to the fluid mosaic model is b) Proteins can also undergo flip-flop movements in the lipid bilayer.

Explanation: While proteins can move laterally within the lipid bilayer, the "flip-flop" movement of proteins between the inner and outer leaflets of the bilayer is not considered to be a significant part of the fluid mosaic model. This is because the hydrophobic nature of the transmembrane proteins would require significant energy to move across the hydrophilic phospholipid head groups.

Why other options are correct:

• a) Proteins in cell membranes can travel within the lipid bilayer: 

  The fluid mosaic model emphasizes the lateral diffusion of both lipids and proteins within the membrane, allowing them to move freely within the bilayer. 

• c) Proteins can remain confined within certain domains of the membrane: 

  The fluid mosaic model acknowledges that not all proteins are completely free to move. Some proteins are anchored to specific cytoskeletal elements or have other constraints that limit their mobility, confining them to specific membrane domains. 

• d) Many proteins remain completely embedded within the lipid bilayer: 

  Integral proteins are embedded within the lipid bilayer, spanning the membrane completely. These proteins are permanently attached to the membrane and cannot easily be removed without disrupting the bilayer. 

Correct Answer :- a

Explanation : Resolution power is the ability of the lens to make the contents of a specimen very clear to observe.

To get good resolution the illumination light should have the shortest wavelength for clear vision.

Blue light has good wave lent to study a cell.

During anaphase APC (anaphase promoting complex) develops. It degenerates proteins binding the two chromatids in the region of centromere.
As a result the centromere of each chromosome divides. This converts the two chromatids into daughter chromosomes.

Protein synthesis in an animal cell occurs on ribosomes present in cytoplasm as well as in mitcohondria because mitochondria and chloroplast also have their own DNA, RNA and ribosome so can synthesize half of their required proteins.

The enzymes of electron transport system are present in inner mitochondrial membrane.

Electron microscope uses a beam of electron which has wavelength much higher than that of photons.
The magnification power of electron microscope is also more than that of light microscope.
Hence, a major breakthrough in the studies of cell came with the development of electron microscope because the resolution power of microscope is much higher than that of light microscope.

Both chloroplasts and mitochoridria have an internal compartment, the thylakoid space bounded by double membrane 

The biological membranes are made up of lipids and proteins. The various lipids present in the membrane are phospholipids, cerebrosides, gangliosides, cholesterol, glycolipids etc. Proline is an amino acid which is generally known as chain breaker because of its structure. Proline is generally absent in membrane proteins. Proline usually occurs in regions where protein chain makes sharp turns. 
So, the correct answer is 'Proline'

Keeping in view the ‘Fluid mosaic model” for the structure of cell membrane, the movement of lipids and proteins from one lipid monolayer to the other, lipid can rarely flip-flop, protein can not. The fluid mosaic model is the most important and widely accepted latest model for plasma membrane was given by Singer and Nicolson in 1972. According the them it is “ protein iceberg in a sea of lipids”. 

Polysome (Polyribosome) is a complex formed by several ribosomes attached to a single mRNA molecule in the process of translation. 

Cellulose is a major component of cell wall of Pythium. Pythium is a genus of parasitic Oomycete. Because this group of organisms were once classified as fungi, they are sometimes still treated as such. Pythium, like others in the family Pythiaceae, are usually characterized by their production of coenocytic hyphae, hyphae without separations. Oogonia generally contain a   single Oospore. Antheridia contain an elongated and club shaped antheridium. 

The two subunits of ribosome remain united at a critical ion level of magnesium. The presence of magnesium and its amount plays an important role in the appearance and structure of the ribosomes. If magnesium is absent in medium, the large particles fall apart to present a group of smaller particles. 

Vacuole in a plant cell is membrane bound and contains water and excretory substance. Vacuole is a space within the cytoplasm of living cell that is filled with air, water or other liquid, cell sap or food particles. In plant cells, there is usually one large vacuole bounded by a single layered membrane (tonoplast or vacuole membrane); animal cells usually have several small vacuoles. 

Plasmodesmata are connections between adjacent cells. Plasmodesmata are narrow channels that act as intercellular cytoplasmic bridges to facilitate communication and transport of materials between plant cells. Plasmodesmata are formed during cell division, when traces of the endoplasmic reticulum become caught in the new wall that divides the parent cell.

The cytoskeleton is made up of three kinds of protein filaments actin filaments (also called microfilaments), intermediate filaments and microtubules whose major constituents are actin and tubulin respectively.

Stroma in the chloroplasts of higher plant contains light independent reactions enzymes. Within the stroma are stacks of thylakoids, the sub-organelles which are the site of photosynthesis.

Middle lamella is mainly composed of calcium pectate. Calcium is deposited in plants cell walls during their formation - it is required for the stability and function of cell membranes and acts as a type of ‘cementing agent’ in the cell walls in the form of calcium pectate’. Calcium pectate is like a glue binding adjacent cells together so if inadequate calcium is not transported during cell formation, tissues become less stable and prone to disintegration.