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

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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