The sino-atrial (SA) node is a specialised bundle of neurons located in the upper part of the right atrium of the heart. The cardiac impulse originating from the SA node triggers a sequence of electrical events in the heart, thereby controlling the sequence of muscle contraction that pumps blood out of the heart. Since the SA node initiates and maintains the rhythmicity of the heart, it is known as the natural pacemaker of the human body.
What is meant by double circulation? What is its significance?
Name the components of the formed elements in the blood and mention one major function of each of them.
What is the difference between lymph and blood?
Which of the following is not correct?
(a) Robert Brown discovered the cell.
(b) Schleiden and Schwann formulated the cell theory.
(c) Virchow explained that cells are formed from pre-existing cells.
(d) A unicellular organism carries out its life activities within a single cell.
How do you distinguish between a skeletal muscle and a cardiac muscle?
Define sliding filament theory of muscle contraction.
Define a taxon. Give some examples of taxa at different hierarchical levels.
How do neutral solutes move across the plasma membrane? Can the polar molecules also move across it in the same way? If not, then how are these transported across the membrane?
Both lysosomes and vacuoles are endomembrane structures, yet they differ in terms of their functions. Comment.
Describe the structure of the following with the help of labelled diagrams.
(i) Nucleus
(ii) Centrosome
Multicellular organisms have division of labour. Explain.
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