Biology Class 11 NCERT Solutions: Chapter 8 Cell the Unit of Life Part 2

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Q: 7. Name two cell-organelles that are double membrane bound. What are the characteristics of these two organelles? State their functions and draw labelled diagrams of both.


Mitochondria and chloroplasts are the two organelles that are double-membrane-bound.

Q 7 Mitochondria and Chloroplasts are the two Organelles tha …

Mitochondria and Chloroplasts Are Double-Membrane-Boond

Characteristics of the mitochondria

Mitochondria are double- membrane-bound structures. The membrane of a mitochondrion is divided into the inner and outer membranes, distinctly divided into two aqueous compartments – outer and inner compartments. The outer membrane is very porous (containing the organelle), while the inner membrane is deeply folded. These folds are known as cristae. Cristae increase the surface area inside the cell. They are the sites for ATP-generating chemical reactions. The membrane of a mitochondrion contains specific enzymes meant for specific mitochondrial functions. Hence, the mitochondria are the sites for aerobic respiration. They have their own DNA and ribosomes. Thus, they are able to make their own proteins. This is why they are considered as semi-autonomous organelles

Characteristics of chloroplasts

Chloroplasts are double-membrane-bound structures.

They are divided into outer and inner membranes, further divided into two distinct regions:

(i) Grana are stacks of flattened discs containing chlorophyll molecules. The flattened membranous sacs are called thylakoids. The thylakoids of adjacent grana are connected by membranous tubules called stroma lamellae.

(ii) Stroma is a homogenous mixture in which grana are embedded. It contains several enzymes that are used for the synthesis of carbohydrates and proteins. It also contains its own DNA and ribosomes.

Q 7 2 Stroma is a homogeneous mixture in which grana are emb …

Stroma is a Mixture in Which Grana Are Embedded

Functions of the mitochondria:

(i) They are the sites for cellular respiration.

(ii) They provide energy in the form of ATP for all vital activities of living cells.

(iii) They have their own DNA and ribosomes. Hence, they are regarded as semi- autonomous organelles.

(iv) They have several enzymes, intermediately required for the synthesis of various chemicals such as fatty acids, steroids, and amino acids.

Functions of chloroplasts:

(i) They trap solar energy and utilise it for manufacturing food for plants. Hence, they are involved in the process of photosynthesis.

(ii) They contain the enzymes required for the synthesis of carbohydrates and proteins.

Q: 8. What are the characteristics of prokaryotic cells?


Prokaryotic cell is a unicellular organism lacking membrane-bound organelles. The characteristics of prokaryotic cells are as follows:

The characteristics of prokaryotic cells

The Characteristics of Prokaryotic Cells

(i) Most of them are unicellular.

(ii) They are generally small in size. The size of a prokaryotic cell varies from.

(iii) The nuclear region of a prokaryotic cell is poorly defined because of the absence of a nuclear membrane. Hence, a prokaryotic cell lacks a true nucleus.

(iv) The genetic materials of prokaryotic cells are naked. They contain single, circular chromosomes. In addition to the genomic DNA, they have a small, circular plasmid DNA.

(v) They have specialised membranous structures called Mesosome. Mesosome are formed by the invagination of the cell membrane. These extensions help in the synthesis of the cell wall, replication of DNA. They also help in the equal distribution of chromosomes into the daughter cells.

(vi) Membrane-bound cell organelles such as mitochondria, plastids, and endoplasmic reticulum are absent from a prokaryotic cell.

(vii) Most prokaryotic cells contain a three-layered structure – outermost glycocalyx, middle cell wall, and the innermost plasma membrane. This structure acts as a protective unit.

Examples of prokaryotic cells include blue green algae, bacteria, etc.

Q: 9. Multicellular organisms have division of labour. Explain.


Multicellular organisms are made up of millions and trillions of cells. All these cells perform specific functions. All the cells specialised for performing similar functions are grouped together as tissues in the body. Hence, a particular function is carried out by a group of cells at a definite place in the body. Similarly, different functions are carried out by different groups of cells in an organism. This is known as division of labour in multicellular organisms.

Image shows the division of labour

Image Shows the Division of Labour

Q: 10. Cell is the basic unit of life. Discuss in brief.


Cells are the basic units of life capable of doing all the required biochemical processes that a normal cell has to do in order to live. The basic needs for the survival of all living organisms are the same. All living organisms need to respire, digest food for obtaining energy, and get rid of metabolic wastes.

Cells are capable of performing all the metabolic functions of the body. Hence, cells are called the functional units of life.

Image shows the structure of cell

Image Shows the Structure of Cell

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