NCERT Class 11-Biology: Chapter –8 the Unit of Life Part 5

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Question 4:

Structure and function are correlatable in living organisms. Can you justify this by taking plasma membrane as an example?

Answer:

Structure and function are correlatable in living organisms.

Taking a look at the structure of RBCs-

RBCs

RBCs

RBCs

It is called biconcave shape. The function of RBCs is to pass through capillaries and carry more oxygen and this shape helps it to absorb more oxygen.

Taking a look at the structure of plasma membrane –

It is made up of proteins, carbohydrates and lipids. The lipids arranged with their hydrophilic polar head directed outwards and non-polar hydrophobic tails directed inwards providing fluidity to the membrane. This provides the cell membrane its selective permeability.

Question 5:

Eukaryotic cells have organelles which may

a. not be bound by a membrane

b. bound by a single membrane

c. bound by a double membrane

Group the various sub-cellular organelles into these three categories.

Answer:

a. Non-membrane bound cell organelles – Ribosomes, Centriole, nucleolus, Cytoskeletal structures

b. Single membrane bound cell organelles – Endoplasmic reticulum, Golgi bodies, lycosomes, vacuoles, Thylakoid.

c. Double membrane bound cell organelles – Plastids, Mitochondrias and nucleus.

Question 6:

The genomic content of the nucleus is constant for a given species whereas the extra chromosomal DNA is found to be variable among the members of a population. Explain.

Answer:

  • The genomic content of the nucleus is constant for a given species whereas the extra chromosomal DNA is found to be variable among the members of a population.

  • For example, all the human cells have 46 chromosomes. This is constant in all the humans. But mitochondria in different humans contain different amount of extra chromosomal DNA.

  • Similarly, in bacteria, the amount of genomic DNA is same but the extra genomic DNA contained in plastids and mitochondria are different.

Question 7:

Justify the statement, “Mitochondria are power houses of the cell”

Answer:

  • Each mitochondrion has 2 membranes – the outer and the inner membrane.

  • These membranes have their own specific enzymes associated with the mitochondrial functions.

  • Mitochondria are the sites of aerobic respiration.

  • They produce cellular energy in the form of ATP, hence they are called ‘power houses’ of the cell

Question 8:

Is there a species specific or region specific type of plastids? How does one distinguish one from the other?

Answer:

  • Plastids are species specific or region specific. They bear some specific pigments, thus imparting specific colours to the plants.

  • Based on the type of pigments plastids can be classified into chloroplasts, chromoplasts and leucoplasts.

  • The chloroplasts impart green colour as they contain chlorophyll and carotenoid pigments which are responsible for trapping light energy essential for photosynthesis.

  • The chromoplasts contain fat soluble carotenoid pigments like carotene, xanthophylls and others are present. This gives the part of the plant a yellow, orange or red colour.

  • The leucoplasts are the colourless plastids of varied shapes and sizes with stored nutrients: Amyloplasts store carbohydrates (starch), e.g., potato; elaioplasts store oils and fats whereas the aleuroplasts store proteins.

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