Cell Biology and Structure

• Golgi apparatus is not present in Prokaryotes, because prokaryotic cells lack a nucleus and membrane-bound structures such as mitochondria, lysosomes, Golgi apparatus. while eukaryotic cells have a nucleus and membrane-bound structures.

Prokaryotes do not possess membrane-bound organelles and well-defined nucleus. Nucleoid is a region in a prokaryotic cell, where most of the genetic material resides. It is not a well-defined membrane-bound region. 
Eukaryotes possess a well-defined nucleus and membrane-bound organelles as mitochondria, Golgi complex, etc. Nucleus is bound with double membrane in eukaryotic cells in which most of the genetic material is present. 

Prokaryotic cells are primitive cells. They do not have well defined membrane bound nucleus. Nuclear material of a prokaryotic cell consists of a single chromosome which is in direct contact with cytoplasm. Here, the undefined nuclear region in the cytoplasm is called as nucleoid, i.e., there is no nuclear membrane. 

Bacteria and plant cells possess DNA, RNA and cell wall. Bacteria being a prokaryote, lacks membrane bounded nucleus. Their genetic material is present in undefined nuclear region in the cytoplasm is called as nucleoid. while plant is a eukaryote, which has organized nucleus with double wall nuclear membrane.

Animal cell, plant cell and bacterium have plasma membrane, cytoplasm and ribosomes as common parts. Cell organelles and nucleus are absent in bacterial cell but present in animal and plant cells.

Prokaryotic cells are primitive cells. They do not possess many membrane bound organelles as mitochondria, lysosomes etc. They also do not have well defined membrane bound nucleus. Nuclear material of a prokaryotic cell consists of a single chromosome which is in direct contact with cytoplasm. Here, the undefined nuclear region in the cytoplasm is called as nucleoid, i.e., there is no nuclear membrane. 

In the prokaryotic cell, there is no definite nucleus with a nuclear membrane. But the genetic material is distributed throughout the cytoplasm of the cell. Along with some of them may have cell wall and mitochondria.

• Pilus refers to a thin and rigid hair-like appendage that protrudes from the cell surface of bacteria (prokaryotic cell) and is responsible for bacterial conjugation.
• They are absent in eukaryotic cells.
• The ribosomes present in a bacteria and the cellular organelles (mitochondria and chloroplasts) are 70S type and those present in a eukaryotic cell (both plants and animals) are 80S type.
• So, the correct answer is 'a and b are wrong, c is correct'.

Plant and animal cells have several differences and similarities. For example, animal cells do not have a cell wall or chloroplasts but plant cells do. Animal cells are mostly round and irregular in shape while plant cells have fixed, rectangular shapes.

Ascaris meglocephala (horse round worm ) has chromosome number 2n = 2. 

• Tissue is a cellular organizational level intermediate between cells and a complete organ. 
• A tissue is an ensemble of similar cells from the same origin that together carry out a specific function. 
• Organs are then formed by the functional grouping together of multiple tissues.
  
  

The living organisms are made up of the cells in which the atom forms the basis of all the structures in the cells like the proteins, lipids, fats, nucleic acids, etc. The living organisms are composed of cells, tissues, and ATP as the common source of energy. The non-living things are made up of the atoms which form the material. 

The living organisms are composed of cells which form the tissues. The tissues when damaged are repaired and replaced by the new cells. Irritability is the ability of an organism to respond to the external stimulus. The organism exhibit movement on receiving the stimulus from the internal or the external environment. The most common example of irritability is shown by the Mimosa plant which folds the leaflets on stimulus with touch.