Cell Biology and Structure

 Choanocytes are cells which lines the spongocoel in sponges.

 The epidermis does not contain blood vessels

 Option (2) is correct.

Animal cell is prokaryotic in nature - False statement. Animal cell has a well defined nucleus. So it is an eukaryote and not a prokaryote (without nucleus) . Therefore, (B) is the correct answer. 

Reason: DNA (Deoxyribonucleic acid) is present in the nucleus of the cell. Along with nucleus, DNA is also present in mitochondria and chloroplast (in plants) but not in golgi apparatus, ribosomes and vacuole.. Mitochondria and chloroplast are referred to as strange organelles in the sense that they have their own DNA and ribosomes involved in protein synthesis. Therefore, both organelles are able to make some of their own protein. Therefore (C) is correct answer. 

Reason: Presence of chromosomes, presence of mitochondria (power house of the cell) and presence of lysosomes are similar in both plants and animals. The difference between the two lies in the nature of vacuoles. Vacuoles are small sized animal cells while large size in plant cells. The central vacuole of some plant cells may occupy 50 - 90% of the cell volume. In plant cells, vacuoles are full of cell sap (which is made up mostly of water containing various dissolved sugar, salts and other chemicals) and provides turgidity and rigidity to the cell. Many substances of unimportant in life of plant cell are stored in vacuoles. 

Endoplasmic Reticulum - is a large network of membrane bound tubes and sheets. It looks like long tubules or round or oblong bags (Vesicles). They are of two types viz. Rough ER and Smooth ER. It always forms a network system in a cell. 

Nucleus - plays a central role by determining the way the cell will develop and what form it will exhibit at maturity, by directing the chemical activities of cell. This is because nucleus enclose chromosomes which are composed of DNA and protein. Fundamental segments of DNA are called genes which regulate the process of development of a cell. 

Cytoplasm - is the fluid content inside the plasma membrane but outside the nuclear membrane. It also contains many specialized cell organelles. It is water like substance of cell. If we stain cheek cells or onion peel cells with methylene blue nucleus will take up the stain & appear as a dense structure whereas cytoplasm does not take up the stain. 

Nucleoid: In bacteria (prokaryotes), the nuclear region of the cell is poorly defined due to the absence of nuclear membrane. Such an undefined nuclear region containing only nucleic acids is called a Nucleoid. 

Plastid - are present only in plant cells. Plastid containing pigment chlorophyll are known as chloroplasts which are important for photosynthesis in plants. Photosynthesis does not occur in animals. 

Reason: Cells vary in shape and size. The smallest cell, a type of bacterium known as Mycoplasma, measures 0.0001 mm in diameter. Amongst the largest cells are nerve cells. These cells can exceed 3 m in length. Along with the differences in size, cells are present in different shapes. In humans outermost skin cells are flat while nerve cells are elongated. In multicellular organisms shape and size of the cell is mainly dependent on its job or functions.For example - flat skin cells pack tightly into a layer that protects the underlying tissue from invasion by bacteria. The numerous extensions from a nerve cell enable it to connect to several other nerve cells in order to send and receive messages rapidly. 

Golgi apparatus consists of a system of membrane bound vesicles arranged approximately parallel to each other in bundles or stacks, called cisterns. These membranes often have connections with the membrane of endoplasmic reticulum and therefore constitute another portion of a complex cellular membrane system. 

Mitochondria - is a membrane bound organelle and prokaryotes do not have membrane bound organelles. 

Lysosomes - do not carry genetic information. They act as a waste disposal system in the cell. Lysosomes help to keep the cell clean by digesting any foreign material as well as worn out cell organelles. This is the reason why they are also known as “suicidal bags” Therefore the correct answer for this question is a Lysosome.