Test: Sexual Reproduction in Flowering Plants (October 27) - NEET MCQ

•Flemming in 1882 characterized the animal mitochondria cytologically.

•Ubisch discovered orbicules (also called ubisch bodies) secreted from the Tapetum and how these ubisch bodies help in exine formation. 

•Strasburger while working on Monotropa, observed the actual fusion of the male gamete with the female gamete (i.e. egg) and discovered syngamy.

•Nawaschin while working on Lilium and Fritillaria confirmed syngamy and gave the concept of Triple fusion and double fertilisation.

• Emasculation is the process of removing anthers from bisexual flowers without affecting the female reproductive part (pistil). 
• Emasculation is performed by plant breeders in bisexual flowers to obtain a desired variety of a plant by dusting the pollen grains from the required variety onto the stigma of the emasculated flower

Polyembryony has been defined as the occurrence of more than one embryo in a seed. However, the additional embryos may not always mature. They may become arrested at very early stages and may degenerate during the course of seed development. Except for a few taxa like Citrus and Mangifera, polyembryony occurs only as an abnormal feature. Polyembryony in angiosperms may arise by
(i) Cleavage of proembryo. It is widespread in gymnosperms 
(ii) Formation of embryos by cells of the embryo sac other than egg as in Aristolochia, Poa etc. 
(iii) Development of more than one embryo sac within the same ovule example Casuarina 
(iv) Activation of some sporophytic cells of the ovule as in Citrus. 

• Simple Polyembryony is the occurrence of more than one embryo in the same seed.

• Adventive Polyembryony is a kind of Apomixis in which there is a formation of extra embryos due to sporophytic budding. One or more diploid sporophytic cells, either nucellus or integuments undergo stages of embryogeny and eventually develop into mature embryos.

• Cleavage Polyembryony involves the cleavage of an embryo in which a single fertilized egg forms a number of embryos. The zygote divides several times irregularly to form a mass of cells which can develop into embryos.

Hence, the formation of an extra embryo from nucellus or integument is called adventive polyembryony. 

Pollen wall consists of two layers: outer layer exine and inner layer intine.

Exine is made up of sporopollenin which is one of the most resistant known biological materials. Exine is thin in the beginning but it becomes very thick with maturity. However, exine is discontinuous or ruptured at some places. These are the called the germ pores (or germinal furrow) through which pollen tube comes out during germination on the stigma.

The androecium is the third whorl of a flower whose individual unit is called the stamen. It is the male reproductive organ whorl. 

A. Anthers are the parts of the stamen in which pollen grains are formed.

B. Stamens are the male reproductive structures, collectively called the androecium.

C. Filaments are the parts of stamens that connect the anthers to the thalamus.

D. Tepals are the units of the whorl called perianth

Female gametophyte or embryo sac of angiosperms develops upto 8-nudeate, 7-celled prior to fertilisation. There is a three celled apparatus (one egg cell or oosphere and two synergids), three antipodal cells and two polar nuclei. The two polar nuclei fuse to form a diploid secondary nucleus.