Govt. Exams
Entrance Exams
In typical polygonum type, a functional megaspore undergoes three mitotic divisions producing an 8-nucleate, 7-celled embryo sac (3 antipodal, 2 synergid, 2 polar nuclei, 1 egg).
Seed dormancy is controlled by the balance between inhibitory hormones (ABA) and promoting hormones (gibberellins), along with environmental factors.
Polyembryony can occur through cleavage of the proembryo, budding from integuments or nucellus, or through apomixis. This is a diverse phenomenon.
Bryophytes produce both archegonia (female) and antheridia (male), allowing sexual reproduction; pteridophytes, gymnosperms also have these, but bryophytes are distinctively defined by them.
Marginal placentation occurs when ovules develop along the ventral suture (margins) of the carpel, commonly seen in legumes.
The transition from pteridophytes to gymnosperms shows complete terrestrial adaptation through development of pollen (no free sperm in water) and seeds (no gametophyte dependence).
Both dicots and monocots possess vascular tissue. They differ in cotyledon number (2 vs 1), bundle arrangement, and floral parts (mostly in whorls of 4-5 vs 3).
Flowers and fruits are the most recent evolutionary advancements (approximately 140-150 million years ago), making angiosperms the most evolved plants.
Spores are haploid products of meiosis; seeds contain a diploid embryo, endosperm, and seed coat. Seeds are more advanced structures for dispersal.
Angiosperms have stationary male gametes (non-motile sperm). Motile sperms are primitive characters found in bryophytes and some gymnosperms.
