31 Years NEET Previous Year Questions: Cell: The Unit of Life - 2 Free

• Plant cell wall possesses minute thread like cytoplasmic bridges between two adjacent cells are called as plasmodesmata.
• Plasmodesmata produce a continuum of the living material called symplasm.
• The cytoplasm of adjacent cells communicates through the pores by means of these cytoplasmic bridges.
• The plasmodesmata permit circulation of fluid and passage of solute between cells.

So, the correct answer is 'Plasmodesmata'

• Mitochondria are cylindrical or sausage-shaped double membranous organelles distributed in the cytoplasm.
• It is surrounded by two membranes designated as outer and inner membrane. A matrix lies inside the inner membrane.
• The matrix contains single circular dsDNA molecule, a few RNA molecules, 70S ribosomes, and the components required for the synthesis of proteins.
• Mitochondria are also known as semi-autonomous cell organelles because of its capability of self-duplication by the presence of DNA. 

• The main arena of various cellular activities of a cell occur is cytoplasm.
• Cytoplasm can be defined as a jellylike material present within the cell (inside the cell membrane) that surrounds the nucleus.
• All the cellular organelles such as mitochondria, the endoplasmic reticulum, and chloroplasts, are contained in the cytoplasm (all the cellular activities carried out here).

So, the correct answer is 'Cytoplasm'.

Correct answer is option B
Explanation for correct option:

• The fluid mosaic model of Singer and Nicolson (1972), is now widely accepted as best explaining the properties of the cell membrane. 
• This model assumes that there is a continuous bilayer of phospholipid molecules in which are embedded globular proteins. 
• The proteins have been compared to icebergs floating in a sea of the phospholipids bilayer.

Correct option is D

• If a nucleic acid sequence (DNA or RNA) is read same from 5' to 3' on one strand and 5' to 3' on its complementary strand, the sequence is called as palindromic sequence.
• In the question, the base sequence is same whether read from 5' to 3' upper strand (5' GAATTC 3') or 5' to 3' (5' GAATTC 3') on the lower strand. 

Correct Option:  B

Explanation:

• The contents synthesized by the endoplasmic reticulum are modified and packaged by the Golgi apparatus. 
• The proteins and lipids are glycosylated by the activity of glycosyltransferase and the glycans are attached to them.
• Glycosylation is a secondary protein processing mechanism. 
• It involves the modification of the carbohydrate portion of the glycoproteins.

The correct option is D:

Explanation of the correct option:

1. Ribosomes are found in all cells.
2. They are the site of protein synthesis.
3. Protein or peptide synthesis is carried out with an mRNA template.
4. The ribosomes then translate the genetically coded information in the mRNA to synthesize proteins.

Explanation of the incorrect options:

Option A:
Photosynthesis occurs in the chloroplasts to provide the plant with food and energy.

Option B:
Oxidative phosphorylation occurs in the mitochondria to produce energy for the cell's survival and functioning.

Option C: 
Pigments such as orange carotene, yellow xanthophylls, and various other red pigments are stored and synthesized in the chromoplasts.

• DNA molecule is wound around histone core to form nucleosomes.
• The nucleosomes actually represent the beads of beads-on-string structure visible under electron microscope. 

So, the correct answer is 'Nucleosomes'

Correct Option is B

• Mitochondria is surrounded by double membrane.
• The outer mitochondrial membrane is smooth whereas inner mitochondrial membrane is infolded into finger like projections called as cristae.

The inner membrane of mitochondria contains more than 151 different polypeptides, and has a very high protein-to- phospholipid ration.

Cell organelles, whose functions are coordinated, are considered together as an endomembrane system. The endomembrane system includes 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.

The nucleolus is the largest structure in the nucleus of eukaryotic cells. It is best known as the site of ribosome biogenesisRibosomal RNA is actively synthesized in the nucleolus. The nucleolus is also known as the ribosomal factory.Hence Ribosomal RNA is actively synthesized in Nucleolus.

So, the correct answer is 'Nucleolus'.

Cell membrane of prokaryotes is structurally similar to that of eukaryotes. So, it does not differ in E. coli and Chlamydomonas.
E.coli (bacteria) is a prokaryote while Chlamydomonas (algae) is a eukaryote. Ribosomes of both groups differ being 70S in prokaryotes and 80S in eukaryotes. Prokaryotic chromosomes lack histone protein unlike eukaryotic ones. Cell wall organization also differs as bacterial cell wall is rich in muramic acid while algal cell wall is cellulosic. It is the cell membrane which has similar organization in both the groups.

Ribosomes are amembraneous (ie. without membrane) cell organelle composed of rRNA and protein. These are found in both prokaryotic and eukaryotic cells. In prokaryotes, ribosomes are 70S type while in eukaryotes, it is 80S type.

Nostoc is prokaryote while rest are eukaryotes. Nuclear membrane is absent in prokaryotes.

Fluid mosaic membrane model was proposed by Singer and Nicholson in 1972. It is most accepted model of structure of biomembrane.

Ribosome are small naked (non membrane bound) particles made of r-RNA and proteins. Ribosomes are also seen in the organelles like mitochondria and chloroplasts. They are the cell’s protein factories and are found on RER and scattered in the cytoplasm as polyribosomes. Ribosomes are the sites at which information carried in the genetic code is converted into protein molecules.

Centrioles serve as basal bodies for cilia and flagella. They are concerned with spindle formation during cell division. Lysosomes are membrane-bound organelles containing many hydrolytic enzymes, which are optimally active at an acid pH (near pH 5). Thylakoids are membrane-bound organelles found within chloroplasts. The thylakoid membrane, forms many flattened, fluid-filled tubules that enclose a single convoluted compartment. These tubules tend to stack on top of each other to forma structure called a granum

Correct option is C

• Endoplasmic reticulum is the cell organelle present within the cytoplasm of an eukaryotic cell.
• Based on the ribosomes attachment, the endoplasmic reticulum is of 2 types.
• Smooth endoplasmic reticulum (SER) and rough endoplasmic reticulum (RER). The Smooth ER has no ribosomes attached to it, while the rough ER has ribosomes attached. These ribosomes helps in the protein synthesis.
• Additionally, other than protein synthesis endoplasmic reticulum also helps in protein folding, modification and their transport. It is also involved in the synthesis of lipids.
• Therefore, rough endoplasmic reticulum and protein synthesis is the correct match with respect to the function.

Golgi apparatus plays a major role in post translational modification of proteins forming glycoprotein and glycosidation of lipid forming glycolipids. A number of proteins and lipids synthesised on endoplasmic reticulum (rough and smooth respectively) are modified in the cisternae of the Golgi apparatus before they are released from it trans face.

The smooth endoplasmic reticulum is the major site for synthesis of lipid. In animal cells lipid like steroidal hormones are synthesised in SER.

 The correct answer is (A) A layer surrounding the cell wall of bacteria.
A carbohydrate-protein layer that is covered on many of the eukaryotic cells and prokaryotic cells is called the glycocalyx. In prokaryotes particularly it is covered on the cell wall of bacteria. Many of the eukaryotic cells use glycocalyx to recognize the cell. To protect from the host factors bacterial cells are covered with glycocalyx. The glycocalyx in bacterial cells has the ability to establish an infection.

Chromoplasts are non-photosynthetic coloured plastides which synthesise and stored carotenoid pigmentes. They, therefore, appear orange red and yellow where as amyloplast (store starch), aleuroplast (store proteins) and elaioplast (store oil droplets and fats) are leucoplasts, colourless plastids.

In fig., (A) shows the cell organelle mitochondria. The mitochondria are bounded by two membranes, i.e., outer membrane and inner membrane. Mitochondria are referred as “powerhouse” of the cell as they produce 95% of ATP. This energy is produced during the break down of food molecules which involve glycolysis, oxidative decarboxylation and oxidative phosphorylation (krebs cycle and respiratory chain). 

Correct option is D.
The capsule is the protective covering of the bacterial cell made up of polymers of simple sugars (polysaccharides). Most capsules are hydrophilic and may help the bacterium avoid desiccation. It protects a bacterial cell from ingestion and destruction by white blood cells (phagocytosis) and helps it to hide from host immune system.