Class 8 Science Question Answers - Cell - Structure and Functions (Old Syllabus)

Q1: What is Cell? Define its components.

Ans: Cell is the structural unit of living organisms.

Components:

1. Cytoplasm is a jelly-like substance present between the cell membrane and nucleus.
2. Nucleus is spherical shaped component located in the centre of the cell. It acts as control centre of activities of cell.
3. Plasma membrane is a porous membrane surrounding the cytoplasm.

Q2: Define "Why plants need cell wall?"

Ans: Cell wall provides rigidity to plant cell. This provides plant cell protection against the variation of environmental condition like variation in temperature, humidity etc.
Q3: Compare plant and animal cell on basis of cellular components.

Ans: Comparison between plant and animal cell:

Q4: "Single cell organisms perform all the function that multicellular organisms perform." Define what functions are these. Also define who perform all these function in multicellular.

Ans: Single-celled organism performs all function that multicellular organisms perform. These functions are capturing and digestion of food, respiration, excretion, growth and reproduction.
In single-celled organism these function are performed by overall cell. However, in muticellular organism each function is performed by specific organ. 

Q. 5. Explain the position and functions of nucleus in a cell.
Ans. Nucleus is the most important component of the living cell. It is round or spherical in shape and situated in the centre of the cell. Nucleus is separated from cytoplasm by a membrane called nuclear membrane. This membrane is porous and allows the movement of materials between the cytoplasm and inside of the nucleus. There is a small and spherical body in the nucleus. It is called nucleolus. Nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance or transfer of characters from the parents to the offspring. Nucleus also acts as a control centre of the activities of the cell.