Answer: Option B. -> rounded structure inside nucleus having r RNA.
:
B
Nucleolus is a rounded structure inside nucleus having r – RNA.

Answer: Option C. -> Assertion [A] is True and Reason [R] is True and is a correct explanation of [A].
:
C
Mitochondria is a double membrane-bound organelle found in most eukaryotic cells. The most prominent role of mitochondria is to produce the energy currency of the cell which is the ATP.Therefore, Mitochondria are also called "The Powerhouse of the Cell”.

Answer: Option A. -> Selectively permeable
:
A
plasma memebrane is selectively permeable as it allows the diffusion of only certain substances.

Answer: Option A. -> Carbohydrates
:
A
Amyloplasts stores carbohydrates.

Answer: Option A. -> Both Assertion and Reason are true and Reason is the correct explanation of Assertion
:
A
Eukaryotic cells (particularly) animal and lower plant cells) have the ability to adopt averiety of shapes and carry out directed movements because they have a network of proteinfibres that support the shape of the cell and anchor organelles to fixed location. This network is called cytoskeleton. Later is made up ofactin filaments, which are made of two strands of the fibrous protein twisted together and usually occur in bundles.
(i)Actin Filaments are ubiquitous, and are concentrated below the plasma membrane in bundles known
as stressfibres, which may have a contractile function.
(ii)Microtubules, which are composed of 13 stacks of tubulin protein subunits arranged side by side to
form a tube. Microtubules are comparatively stiff cytoskeletal elements that serve to organize
metabolism and intracellular transport in the non-dividing cell.
(iii)Intermediate filaments,which are composed of overlapping staggered tetramers of protein. This
molecular arrangement allows for a rope-like structure that imparts tremendous mechanical
strength to the cell.

Answer: Option A. -> Both Assertion and Reason are true and reason is the correct explanation of Assertion
:
A
Mitochondria and chloroplast are semi-autonomous cell organelles, which contain their own DNA and protein synthesizing machinery. They arise from pre-existing organelles and their functions are partially controlled by the nucleus of a cell and partially themselves.

Answer: Option D. -> Golgi apparatus
:
D
The Golgi apparatus looks like a stack of hollow pancakes; the mitochondria are long, lysosomes are round .

Answer: Option C. -> to regulate the assembly of microtubules
:
C
The centrosome regulates the assembly of microfilaments.

Answer: Option B. -> Singer and Nicolson 
:
B
The fluid-mosaic model was proposed by singer and nicolson to explain the structure of plasma membrane.

Answer: Option D. -> Murein
:
D
Cell wall in bacteria is made up of peptidoglycan or murein.