Three types of chromosomes are shown in the figure given above. Answer the following questions.
(a) Identify and name the types of chromosomes, A, Band C.
(b) What forms the basis for such a classification of chromosomes?
(c) What are kinetochores?

Nucleus as a cell organelle was described by Robert Brown (1831). The interphase nucleus under an electron microscope shows a double-layered nuclear membrane, which encloses the nuclear matrix/nucleoplasm.
(a) Name the organelle that is not membrane-bound and present in the nuclear matrix.
(b) Mention its function.
(c) What is perinuclear space?
(d) Name a human cell that lacks a nucleus.

The EM picture of endoplasmic reticulum is given above. Answer the following questions
(a) Identify the rough endoplasmic reticulum and smooth endoplasmic reticulum from among the parts labelled in the above diagram.
(b) Name the two compartments of the intracellular space as divided by the endoplasmic reticulum.
(c) Write the function of SER in animal cells.

Eukaryotic cells have a number of membrane-bound cell organelles that are distinct in their structure and functions. Yet, some of the cell organelles are described together as forming an endomembrane system.
(a) Name the cell organelles included in the en do membrane system.
(b) Why are they considered so?

Cell wall is a non-living rigid structure that forms an outer covering for the plasma membrane in some protists, fungi and plants. It protects the cell from mechanical injuries and infections and helps in cell-to-cell interactions.
(a) name the three layers in the cell wall of a mature plant cell.
(b) Mention any three components of cell wall of algae.

The improved model of the structure of cell membrane proposed by Singer and Nicolson (1972), is called fluid mosaic model. The fluid nature of the membrane is important from the point of view of certain functions.
(a) What is meant by fluidity of membrane?
(b) Mention any four functions for which the fluid nature of the membrane is necessary.

Detailed electron microscopic and other chemical investigations have shown that the cell membrane is composed of lipids, proteins and some carbohydrates.
(a) What per cent of the membrane of human erythrocytes consists of lipids?
(b) Name the major lipid component of membranes.
(c) How are the lipids arranged in the membranes?
(d) What are the two types of membrane proteins based on the ease with which they are extracted?

The prokaryotic cells have certain specialised, differentiated infoldings of the cell membrane. They serve certain specific functions.
(a) What term is given to these infoldings?
(b) Name the three different forms of such infoldings.
(c) Mention two of their functions during cell division.

The diagram given above shows the diagrammatic representation of a typical eukaryotic cell.
(a) Identify the following parts
(i) Mitochondria
(ii) Endoplasmic reticulum
(iii) Golgi bodies
(iv) Nucleolus
(b) Name the following:
(i) The longest cells in a human body.
(ii) The organisms with the smallest cells

All organisms are composed of cell(s), i.e. organisms are unicellular or multicellular. The discovery of microscope and its improvement leading to the electron microscope has revealed all the structural details of cells.
(a) Why are cells considered the fundamental structural and functional units of life?
(b) Mention two characteristic features of unicellular organisms.
(c) Name the scientist who
(i) first observed and described living cells.
(ii) showed that cell wall is a unique character of plant cells.