Class 8, CBSE Guide and CBSE Science Sample Questions - 

Chapter 8 Ncert Science, Cell - Structure and Functions

Class 8, Ncert Science

Cell - Structure and Functions

CBSE Guide - CBSE Notes - Solutions of CBSE Questions

CBSE Questions with Short Answers

Question.1: Define Prokaryotes and Eukaryotes.

Answer:

Prokaryote: The cells having nuclear material without nuclear membrane are termed as prokaryotic cells. An organism with these kinds of cells is called a Prokaryote e.g. Bacteria and Blue Green Algae.

Eukaryote: The cells having well organized nucleus with a nuclear membrane are termed as eukaryotic cells. All organisms other than Bacteria and Blue Green Algae are Eukaryotes.

Question.2: What is Protoplasm?

Answer: The entire content of a living cell is known as protoplasm. It includes cytoplasm and the nucleus. 

Question.3: Give three examples of unicellular organisms.

Answer: Amoeba, Paramecium and Chlamydomonas.

Question.4: Name the cell organelle which is found only in plant cell.

Answer: Plastids.

Question.5: What is the smallest cell size?

Answer: The smallest cell is 0.1 to 0.5 micrometer in Bacteria.

Question.6: What is the largest cell?

Answer: The largest cell is 170mm x 130mm, is the egg of an Ostrich.





CBSE Questions with Long Answers

Question.7: Why cell is known as structural and functional unit of life?

Answer: Refer to the answer of Q.No.8 (NCERT Textbook Exercise) above.

Question.8: Why are the mitochondria known as the power house of the cell?

Answer: Mitochondria are rod shaped and very minute bodies present in cytoplasm. They are concerned with release of energy from food during respiration. Because of this they are often referred to as the power house of the cell.

Question.9: Why plasma membrane is called a selectively permeable membrane?

Answer: A cell bound by a semi-permeable membrane called plasma membrane that enables it to exchange only certain materials with its surroundings. Plasma membrane permits the entry and exit of some material in the cell. It also prevents movement of some other material. Therefore, ‘Plasma Membrane’ is called as ‘selectively permeable membrane’. 

Question.10: Write a short note on the ‘shape of cells’ or ‘cell shape’.

Answer: Cells exhibit a variety of shapes. Some cells have a definite shape while some keep on changing its shape. For example- White Blood Cell (WBC) present in our bodies, Amoeba continuously changes their shape. However, most of the cells maintain a constant shape and the different shapes are related to their specific functions. For example- blood cells are spherical, muscle cells have spindle shape, and nerve cells are long and branched. It is mainly the cell membrane which provides the shape to the cells of plants and animals.

Question.11: Write short notes on the following:

(a)        Gene

(b)        Chromosomes

(c)        Organelles

(d)        Vacuole

(e)        Tissues

(f)          Plastids.

Answer:

(a)     Gene: Gene is a unit of inheritance in living organisms. Nucleus contains thread-like structures called chromosomes which carry genes in them. Genes are composed of DNA (Deoxyribonucleic acid), except in some viruses. They achieved their effects by directing the synthesis of proteins.

(b)    Chromosome: These are the microscopic thread-like parts present in the nucleus of a cell that carries hereditary information in the form of genes.  

(c)      Organelles: The various tiny components of a cell present in the cytoplasm are known as organelles. These are - Mitochondria, Golgi bodies, Ribosome etc.

(d)        Vacuole: A vacuole is a clear space generally stored in the cytoplasm. Big size vacuole is found in the plant cell whereas; in animal cells they are very small. In protozoa, vacuoles are cytoplasmic organs performing many functions such as digestion, excretion etc.

(e)       Tissues: Each organ is further made up of smaller parts called tissues. A tissue is a group of similar cells performing a specific function.

(f)         Plastids: Plastids are found in the plant cells but are absent in animal cells. They are found scattered in the cytoplasm of the leaf cells. Plastids are of three types -

  1. Chloroplast
  2. Leucoplast and
  3. Chromoplast

Among these three types chloroplast is the most important as they contain chlorophyll which is a necessary element for photosynthesis. Because of this reason plastids are also said as ‘Kitchen of plant cells’. 

Question.12: Why Plastids are said as ‘Kitchen of plant cells’?

Answer: See the answer of the Q.No.5 (f).

Question.13: Differentiate between Plant cell and animal cell.

Answer: The differentiation between plant and animal cells is given in the following table:

Animal Cell

Plant Cell

(a)  Cell wall is absent.

(b)  These cells do not contain Chloroplasts.

(c)  Chromosomes are present in the nucleus.

(d)  Vacuoles are less and of smaller size.

(a)  Plant cells have rigid cell walls.

(b)  Chloroplasts are present.

(c)  Chromosomes are present.

(d)  Vacuoles are larger and more in numbers.

 Question.14: Write a short note on ‘Nucleus of a cell’?

Answer: Refer to the answer of Q.No.3 (b) Solutions of Ncert Cbse Science, Chapter 8 Cell - Structure and Functions: Exercise Questions

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