(i) Nephridia are segmentally arranged excretory organs present in earthworms.
(ii) On the basis of their location, three types of nephridia are found in earthworms. They are:
(a) Septal nephridia: These are present on both sides of the inter-segmental septa behind the 15th segment and they open into the intestine.
(b) Integumentary nephridia: These lie attached to the body wall from the third segment to the last segment, which opens on the body surface.
(c) Pharyngeal nephridia: These are present as three paired tufts in fourth, fifth, and sixth segments.
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.
What is the site of gaseous exchange in an insect?
What are nuclear pores? State their function.
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?
Describe the structure of the following with the help of labelled diagrams.
(i) Nucleus
(ii) Centrosome
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