BSc 1st Year Botany Sporophyte in Bryophytes Sample Model Practice Question Answer Papers

BSc 1st Year Botany Evolution of Sporophyte in Bryophytes Sample Model Practice Question Answer Papers: BSc is a three-year program in most of the universities. Some of the universities also offer BSc Honours. After getting enrolled for BSc, there are certain things you require the most to get better grades/marks in BSc. Out of those, there are BSc Study Material, BSc Sample Model Practice Mock Question Answer Papers along with BSc Previous Year Papers. At gurujistudy.com you can easily get all these study material and notes for free. Here in this post, we are happy to provide you BSc 1st Year Botany Evolution of Sporophyte in Bryophytes Sample Model Practice Question Answer Papers.

BSc 1st Year Botany Sporophyte in Bryophytes Question Answers

Q. 1. Explain progressive development of Sporophyte in Bryophytes.

Ans. The sporophyte in bryophytes develops from zygote. The sporophyte of bryophytes usually lacks lateral appendages and is incapable of self nutrition. It obtains its nutrition whole or partially from the parent gametophytes to which it remains organically attached throughout its life. The chief function of sporophytes in bryophytes is the production and dispersal of spores. In form it varies from only a spherical spore producing capsule as in Riccia to an elaborate object differentiated into foot seta and capsule as in Mosses. The function of foot is anchoring and food absorbing, the seta helps in conduction.

Usually the series starts with the simples sporophyte of Riccia runs through that of Marchantia, Pellia, Anthoceros and Funaria (Moss).

Regarding the evolution of sporophytes in Bryophytes two different lines of evolution have been suggested by different workers:

(1) The progressive evolution Or Theory of sterilization.

(2) Theory of reprogressive evolution Or Reduction theory.

(I) Theory of sterilization

Bower (1890) said that there is a progressive elaboration and on in the structure of the sporophytes. The fundamental principle upon the formulated his argument as the “progressive sterilization of potentially fertile cells of sporogenous tissue”. He tried to explain the evolution of sporophyte in the bryophytes on the basis of progressive elaboration. This theory of Bower was further supported by Caver (1910) and Campbell (1918-40). According to this theory Riccia sporophyte is most primitive and the sporophytes of Funaria is most evolved as follows:

1. Riccia sporophyte

In Riccia the zygote by divisions becomes multicellular structure. At this stage the embryo divide by pericilinal wall into outer amphithecium and inner endothecium. In this case the endothecium is the first cell generation (archesporium) of the sporogenous tissue or we may say that in Riccia archesporium is formed from entire endothecium and is centrally situated. The amphithecium forms as single layered jacket. As a result of repeated divisions the archesporium transforms into sporogenous cells which functions as spore mother cells. Most of the spore mother cells from the spores haploid after reduction division except a few celled as nurse cells which degenerate afterwards and serve as a nutritive tissue.

The sporophyte in case of Riccia represents the simplest structure among bryophytes as it has only a capsule with jacket and spores. There is no foot, seta, and no sterilization of sporogenous tissue in the capsule.

2. Marchantia Sporophyte

In Marchantia the zygote divides by successive division and differentiated into four superimposed tiers of four cells each. It divides periclinally into amphithecium and endothecium and in Marchantia the archesporium develops from endothecium which is centrally situated. The archesporium divides and redivides and form a massive sporogenous tissue. The sporogenous cells elongate, some remaining undivided to form elaters, others divide transversely by five successive divisions thus sporogenous cells forms a transverse row of 32 spore mother cell. The spore mother cell divides by meiosis and forms four haploid spores In this way each sporogenous cell either gives one elaters of 28 spores.

The foot is bulbous structure towards the base of archeogonium, it help in absorption and anchoring. The seta is short, thick stalk connecting foot and capsule. The capsule is a spherical structure at the distal end of sporogonium. It has sterile jacket layer of cell. Inside the wall there are spores and elaters. The elaters are long, narrow, spindle shaped cells pointed at each end, and with two spiral thickening on their walls. These elaters are hygroscopic in nature. The exine being thick and warty. Inside the walls of spore there is a haploid nucleus one cytoplasm along with some chloroplast.

The capsule of Marchantia has specialized both as spore producing and spore distributing body. It illustrates a further step in progressive sterilization of sporogenous tissue.

3. Pellia sporophyte

In Pellia, the archesporium formed from entire endothecium. The sporogenous cells in the centre form elaterophore and rest spore mother cells. Archesporium remain surrounded by two or more layers of jacket.

Thus, a fully mature capsule consists of foot, seta and capsule. The capsule is spherical in outline. Inside capsule there are present spores elaters and elaterophore. When capsule is fully mature, seta suddenly elongate and capsule comes out in air.

A maturity the wall of capsule splits longitudinally but into four valves only. The elaters and elaterophore help in dispersal of spores.

4. Anthoceros sporophytes

This illustrates a further step of progressive sterilization of potentially fertile tissue. In this case the entire endothecium remain sterile and forms a central region the columella.

In Anthoceros the zygote divides to form the octant. The upper four cells of the octant give rise to capsule. The cells divide once or twice transversely and then the periclinally differentiating into amphithecium and endothecium.

The archesporium in Anthoceros develops from amphithecium instead of endothecium. The endothecium forms the central sterile columella. The archesporium is superficial in position and over arches the apex of columella. The sporogenous cells from the spore mother cells and Pseudoelaters. The spore mother cells as a result of reduction division form spores.

The mature sporophyte or sporogonium is an exact cylindrical structure, consists of a bulbous foot and smooth slender, erect cylindrical capsule which may project 2 or 3 centimeter but sometimes upto 15 cm above surface of gametophytic thallus. The foot absorbs food from gametophyte. The capsule is made up of several tissues. It has a central column of sterile cell the columella, columella surrounded by the sporogenous tissue which consists of spores and elaters. The wall of capsule is 2 to 5 layered, with an outer layer of epidermis which have stomata.

5. Funaria sporophyte

In Funaria the zygote as a result of division form eight outer cells encircling the four inner cells. The outer cells form the amphithecium and inner cells forms endothecium. The endothecium cells divide by periclinal divisions to form a outer endothecium and inner endothecium cells. The inner endothecium cells give rise to columella while the outer endothecium cells forms the archesporium. Archesporium is superficial in position and surrounds the columella from all sides. The entire archesporium or sporogenous cells form the spore mother cells. The spore mother cells divide by meiosis and form haploid spores. No elaters are formed in Funaria.

The mature capsule when seen in longitudinal section consists of a cap like operculum at top. Below operculum, peristomes with peristomial teeth are present. There is present a well developed central columella surrounded by a spore sac. Adjacent to the spore sac the air spaces are present. The wall of the capsule is multilayered. The lower part of capsule or apophysis has conducting strand and epidermis of this region possesses the stomata.

Thus, from the above discusion it is clear that Bower’s theory of sterilization offer a possible explanation. The theory has been accepted by most of the Botanists in the present days.

(II) Reduction theory

According to this theory of evolution of the sporophyte has downward direction. The main supporters of this theory are Kashyap (1919), Chruck (1919), Goebel (1930) and Evans (1939). They believe and an example of retrogressive evolution. The reduction is accompanied by simplification of the structure of sporophyte in the series. According view, the structure of sporophyte of Riccia will be considered as a highly evolved through reduced as a result of progressive simplification.

BSc 1st Year Sample Model Practice Mock Test Question Answer Papers