Sexual Reproduction in Flowering Plants Test - 7

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. 

Both apomixis and vegetative reproduction produce progeny identical to the parent. Apomixis was defined by Hans Winkler as replacement of the normal sexual reproduction by asexual reproduction, without fertilization.

Honey bees convert nectar into honey by a process of regurgitation and evaporation. They store it as a primary food source in wax honeycombs inside the beehive.

A bisexual flower is a flower that contains all the four whorls such as petals, sepals, the male reproductive structure (stamen) and female reproductive structure (pistil/ carpel). Hence it is also called a complete or perfect flower. Petunia is a bisexual flower. Thus the correct answer is option A.

• 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. 

In an apomictic, seeds can be produced without fertilization. This process is called apomixis. An apomixis is a form of asexual reproduction that mimics sexual reproduction. It includes abnormal sexual reproduction in which egg or other cells like synergids and antipodals develop into an embryo without fertilization and meiosis. In apomicts, somatic cells can mix up and form the embryo under natural conditions. Somatic cells like nucellus can form an embryo in nucellar apomixis.

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

• The tapetum which is present along with the embryo to provide nourishment for the growing embryo. It is found in sporangium, particularly within the anther of flowering plants. It is important for the development of pollen grains. The cells are usually bigger and normally have more than one nucleus per cell.
• Sporogenous tissues are diploid in nature.
• Endothecium - secretes materials essential for the proper maturation of the pollen grains.
• Intine is the inner layer; outer tough layer of pollen is called as exine.

Each anther lobe develops two pollen sacs. Thus, a two-lobed anther develops four pollen sacs situated at four corners of the anther. The wall layers from the periphery to centre consist of: A single layer of epidermis A single layer of endothecium One to three middle layers A single layer of tapetum

Allogamy is also called cross-pollination which is favoured by Dicliny i.e., the presence of a separate male (staminate) and female (pistillate) flowers on the same plant.

a)Fusiform cells - present in the vascular cambium of both dicot root and dicot stem.

b)Trichoblast - present in the epidermis of root

c) Collocytes - present in the collenchymatous hypodermis, a part of cortex.

d)tylosis - balloon shaped strucutures present in the vessesls of heart wood,

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.

• Pollen grains represent the highly reduced haploid male gametophyte generation in flowering plants, consisting of just two or three cells when released from the anthers. Their role is to deliver twin sperm cells to the embryo sac to undergo fusion with the egg and central cell.
•  The female gametophyte of flowering plants, which produces the two female gametes – the egg cell and central cell – for double-fertilization by the two sperm cells of the male gametophyte

A fruit is the seed- bearing structure in flowering plants also referred to as angiosperms produced from the ovary after flowering. Rather, in some fruits, it is not the ovary that produces the fruit. In fact, other parts of the flower, just like the thalamus, inflorescence, and calyx are modified to become an area of the fruit.
 

• 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

A) Cleistogamy - It is a type of self-operating pollination technique of some plants. They are propagated by using non-opening, self-pollinating flowers. So they do not need any attractants and rewards. Thus it is the wrong answer.
B) Anemophily – it is wind pollination. Here pollen is distributed by wind. So they also do not need attractants/rewards. It is the wrong option.
C) Entomophily – it is insect pollination. Here pollen is carried by an insect. Insects are attracted by the attractants of plants and spores are distributed by them. So here attractants and rewards are required for pollination. Thus it is the correct option.
D) Hydrophily – Here pollen is distributed by the water flow. Thus it has no requirement for attractants and rewards. So it is the wrong option.

Endospermic seeds are those that have an endosperm in the mature seed. It is fleshy, oily, surrounds the embryo, and functions as the sole food storage organ. Inside the seed coat, a thin and papery cotyledon is present. Monocot plants have endospermic seeds.

Albuminous seeds are the seeds which have food stored in the special nourishing tissue called as endosperm that remains persistent till maturity. Cotyledons only act as food sucking organs and not food storage organs e.g., Castor seed. Non-albuminous seeds are the seeds which have the stored food and the cotyledons in a special structure called as a kernel. It does not remain until the embryo is mature. e.g. Pea seed.

In some seeds, remains of nucellus persist. This residual nucellus which persists in the seed is called perisperm, e.g., black pepper, coffee, castor, cardamom, Nymphaea.