Pollen grain (2-celled and 3-celled)पराग कण (2-कोशिकीय व 3-कोशिकीय)

NCERT Fig 1.5 · Class 12 Biology · Chapter 1 · interactive diagram

Parts and their functions

• Exine (बाह्यचोल) — Hard outer wall made of SPOROPOLLENIN — one of the most resistant organic materials known: survives high temperature, strong acids and alkalis; no enzyme can degrade it. That is why pollen is well preserved as fossils.
• Germ pore (जनन छिद्र) — Gap in the exine where sporopollenin is ABSENT. The pollen tube comes out through a germ pore.
• Intine (अंतःचोल) — Thin, continuous inner wall made of cellulose and pectin.
• Vegetative cell (कायिक कोशिका) — The bigger cell; has abundant food reserve and a large, irregularly shaped nucleus. Forms the pollen tube.
• Vegetative nucleus (कायिक केंद्रक) — Large, irregularly shaped nucleus of the vegetative cell (also called tube nucleus).
• Generative cell (जनन कोशिका) — Small, spindle-shaped cell with dense cytoplasm and a nucleus; floats in the cytoplasm of the vegetative cell. It divides mitotically to give the 2 male gametes.
• Two male gametes (दो नर युग्मक) — Formed when the generative cell divides. In over 60% of angiosperms pollen is shed at the 2-celled stage (division happens later in the pollen tube); in the rest it is shed at this 3-celled stage.

Steps

1. 2-celled pollen grain: vegetative cell + generative cell (how pollen is shed in over 60% of angiosperms).
2. 3-celled pollen grain: the generative cell has divided into 2 male gametes.

Original diagram drawn by Simple Learning Hub, based on NCERT Fig 1.5. Report a mistake