Tag: unit of living - cell

• Inside the cell wall, if present, do not contain muramic acid (therefore, no peptidoglycan). 
• A eukaryotic cell has 80S ribosomes present in the cytoplasm. 
• Membrane-bound organelles are present, like, mitochondria, ER, Golgi apparatus, chloroplasts, etc. 
• Mitochondria are semi-autonomous organelles, which are double membrane-bound and have their own ribosomes (70S) and DNA (circular).
  
• So, (A) statement is not true for the eukaryotic cells.

Gene silencing by dsRNA makes use of the naturally occurring cell machinery that is involved in the processing of miRNA in eukaryotic cells. It does not provide any defense mechanism. So the correct answer is ' RNAi silencing takes place in all eukaryotic cells for cellular defense'.

Carbon dioxide, has two atoms of oxygen and one atom of carbon, making it the smallest one among the given options. Phospholipids are amphipathic molecules, having phosphate head group and fatty acid tails. DNA polymerase is polypeptide enzyme while ribosomes are the assemblage of rRNA and proteins. 
The correct answer is option A.

• Cytoplasm is a semifluid matrix present within a cell surrounding the nucleus (i.e without the nucleoplasm) which is enclosed by a cell membrane.
• They are the nonnuclear content of protoplasm in which all of the cell organelles are embedded.
  
• A cytoplasmic membrane or cell membrane is a phospholipid bilayer that separates the cell from the external environment.
  
• Protoplasm is the living substance of a cell that is enclosed by a plasma membrane and includes the nucleoplasm.
• So, the correct answer is 'Cytoplasm'.

The characteristics of a eukaryotic plant cell are

Organelles are small, specialised structures which perform a specific function within the cell. Organelles are enclosed by their own membrane.  They are found in eukaryotic cells. Their function is from generating energy to the cell to controlling of cell's growth and reproduction.

Centrifugation of cells is a sedimentation process used to separate certain organelles for analysis of specific parts of cells. a sample of tissue is lysed to break the cell membranes and mix up the contents of the cell. However, while the procedures may break many of the membranes of the cell including the plasma membrane and endoplasmic reticulum, it leaves certain  organelles such as mitochondria, nuclei, Golgi apparatus, peroxisomes and lysosomes intact in a homogeneous extract. During the process, particles of different densities or size sediment at different rates. The largest and most dense particle sediments first followed by less dense and smaller particles. Hence the cellular organelle concentrated on the top of the centrifuged mixture will be the mitochondria due to its less density and small size. Thus, the correct answer is option C.

• A mesokaryotic (meso= in between, karyon= nucleus) cell shows intermediate resemblance to both eukaryotic and prokaryotic cell.
  
• It contains well-developed nucleus but it undergoes cell division by amitosis (because the mitotic spindle is not formed).
• This condition in a cell was first distinguished by Dodge in the year 1966.
• So, the correct answer is 'Dodge'.

In eukaryotic cells, the nucleus is bound by a double membrane or nuclear envelope. It possesses openings at certain intervals called as 'nuclear pore'. Nuclear pores are large protein complexes regulates the exchange of material between nucleus and cytoplasm, i.e., nucleo-cytoplasmic exchange of materials.