In flowering plants, the mature female gametophyte is commonly referred to as the embryo sac or megagametophyte. In most angiosperms, including common garden varieties, the mature female gametophyte contains seven haploid cells. These cells typically include one egg cell (female gamete), two synergids, three antipodal cells, and one central cell containing two polar nuclei. This structure is characteristic of the typical angiosperm embryo sac, but there can be variations in some species.

Sporopollenin is a complex biopolymer found in the cell walls of spores and pollen grains of vascular plants, including both gymnosperms and angiosperms. It is one of the toughest organic materials known and is highly resistant to chemical and biological degradation, making it essential for the survival and reproductive success of plants.

The significance of sporopollenin lies in its chemical nature and physical properties:

1. Protection: Sporopollenin provides a protective barrier for the delicate reproductive cells (gametes) contained within pollen grains and spores. It shields them from various environmental stresses such as desiccation, UV radiation, and microbial attack, thus ensuring the viability of these cells during dispersal and germination.

2. Resistance: Its exceptional resistance to degradation ensures the long-term preservation of pollen grains and spores in sediments, contributing to the formation of fossil records used in paleobotany and evolutionary studies.

3. Allergenicity: Sporopollenin is also responsible for triggering allergic reactions in susceptible individuals when airborne pollen grains are inhaled. Its inert nature means that it can persist in the environment for extended periods, causing seasonal allergies in many people.

4. Chemical composition: Sporopollenin is primarily composed of biopolymers such as long-chain fatty acids, phenolic compounds, and carotenoids. Its precise chemical composition can vary between plant species, but it generally consists of a highly cross-linked network of organic molecules, imparting strength and resilience to the cell wall.

Overall, sporopollenin plays a crucial role in the reproductive biology of plants, facilitating the dispersal of reproductive cells and ensuring the success of plant reproduction in diverse environmental conditions.