The anther's microsporangia make pollen by meiosis of microspore mother cells; the mature pollen grain is a male gametophyte with a tough sporopollenin exine.
How it's asked: Wall layers and the role of tapetum, ploidy of each stage, exine and germ pores, two- vs three-celled shedding and pollen viability.
Why this is true
A typical anther is bilobed and dithecous, giving four microsporangia, each surrounded by four wall layers. The innermost layer, the tapetum, nourishes the developing pollen, so its cells are dense and often multinucleate. Sporogenous tissue in the centre produces diploid microspore mother cells (pollen mother cells), each of which undergoes meiosis to form a tetrad of haploid microspores; this is microsporogenesis. As the anther dries, the microspores separate and mature into pollen grains. Pollen must survive the journey to a stigma, so its outer exine is made of sporopollenin, one of the most resistant organic materials known, interrupted only at germ pores where sporopollenin is absent and the pollen tube emerges.
Key points
Microsporogenesis to mature pollen
- 1Sporogenous tissueCentre of microsporangium
Common traps
- The tapetum is the innermost wall layer and nourishes pollen; the endothecium helps dehiscence.
- Germ pores are where sporopollenin is absent, not where it is thickest.
Worked example
Fossil pollen grains millions of years old are recovered intact from sedimentary rock.
High-yield
Wall layers: epidermis, endothecium, middle layers, tapetum (nourishing). Exine = sporopollenin; intine = cellulose + pectin. Most angiosperms shed 2-celled pollen.
Quick check
Q1.Which layer of the microsporangium nourishes the developing pollen?
Q2.Pollen viability is only about 30 minutes in: