Case Study
Passage with linked questions
Case Set 1
Case AnalysisPassage
Riya was observing a transverse section of an anther under a compound microscope during her biology practical. She noticed that the anther had a distinct bilobed structure with four microsporangia, two in each lobe. The outermost layer appeared thin and protective, followed by the endothecium, then middle layers, and finally the innermost nutritive layer surrounding a mass of homogenous cells at the centre. Her teacher explained that these central cells would undergo a special type of cell division to produce microspores, which would eventually develop into pollen grains. Riya was fascinated to learn that the innermost wall layer plays a critical role in nourishing developing pollen and often contains cells with more than one nucleus.
Question 1: Name the innermost wall layer of the microsporangium and state its primary function.
- The innermost wall layer is called the tapetum.
- Its primary function is to nourish the developing pollen grains (microspores).
Question 2: What is the name of the central homogenous cells Riya observed, and what process do they undergo to form microspores?
- The central homogenous cells are called sporogenous tissue.
- They undergo meiotic divisions (microsporogenesis) to form microspore tetrads.
Question 3: How do tapetal cells become bi-nucleate? Describe the structure of a mature pollen grain, mentioning the role of each wall layer.
- Tapetal cells become bi-nucleate either by cell fusion or by nuclear division without cytokinesis (endomitosis).
- A mature pollen grain has two wall layers: the outer exine made of sporopollenin, which is highly resistant and helps in protection and fossilisation; it has germ pores for pollen tube emergence.
- The inner layer is the intine, made of cellulose and pectin, which is thin and continuous.
- The pollen grain contains a vegetative cell (large, with food reserves) and a generative cell (small, spindle-shaped, gives rise to two male gametes).