Thinking Process

Cyanobacteria are also known as blue green algae. These are primitive prokaryotes.

Answer

(c) Monera Kingdom-Monera is one group which exclusively includes all forms of bacteria. All bacteria are prokaryotes and do not have well defined nucleus and other cell organelles.

The other options Protista, Algae and Plantae include eukaryotic and unicellular or multicellular organism.

Answer

(c) Anisogamy Sexual reproduction is lower group of plants like algae exhibit great variation in mode of sexual and asexual reproduction. Some algae produce gametes which are not similar in shape, size and structure, when they fuse, it is called Anisogamy. e.g., Chlamydomonas.

The other options are incorrect because oogamy is the fusion of big oospore female with small male gamete. Isogamy is fusion of similar gametes. Zoogamy is sexual reproduction of animals.

Answer

(c) Phaeophyceae In the members of class-Phaeophyceae, the plant body is usually attached to the substratum by a hold fast and has a stalk called stipe and a leaf like photosynthetic organ called frond.

Answer

(d) Bryophyta is a group of plants which have gametophytic haploid thalloid body. The motile male gamete are produced in special male reproductive structure called antheridia.

These gametes need thin film of water to move and reach to the female reproductive organ called archegonia. Whereas, pteridophytes, gymnosperm and monocots show division of labour and their body shows higher level of organisation.

Answer

(c) Prothallus is usually a gametophytic stage in the life of a Pteridophyte. Spore germinates to form a prothalium, it is short lived inconspicuous heart shaped structure with a number of rhizoids developed beneath and sex organs, archegonium and antheridium.

Answer

(d) Gymnosperms include medium sized trees or tall trees and shrubs. Leaves of these plants are well adapted to with stand extremes of temperature, humidity and wind. Reproductive organs are usually in the form of cones or strobili.

The male cone are made up of microsporophyll and female cones are made up of megasporophyll. The presence of sporophyll (micro and megasporophyll) shows the development of seed habit but seeds develop from naked ovule and are not covered.

Other examples are incorrect because monocots and dicots belong to angiosperms which have well developed covered seeds. Whereas, pteridophytes do not have microsporphylls and are not adapted to the above said conditions.

Answer

(b)Embryo sac in angiosperm is a female gametophyte. It contains 2 synergids, 1 egg cell, 3 antipodal cells and one secondary nucleus.

Vascular bundle

Structure of female gametophyte of an angiosperm

Thinking Process

The ploidy of an angiospermic plant is $2 n$. Reduction division (meiosis) occurs at the time of gamete formation to produce male and female gametes, i.e., pollen and egg cell. Since, the double fertilisation is feature of angiosperms, related to the ploidy of endosperm.

Answer

(c)Endosperm is a product of triple fusion. One male nuclei $(n=18)$ fuses with diploid secondary nucleus $(2 n=36)$, so it becomes triploid structure $(3 n=54)$. So, ploidy of endosperm is (3n) and chromosomes will be 54 .

Thinking Process

Mosses and liverworts and simplest terrestrial plants evolved from algal ancesters. Protonema is one cell thick, filamental structure developed in early developmental stage of bryophyte which resemble with filamentous algae.

Answer

(a) The germination of haploid spores of mosses produced by sporophyte after reduction division these haploid spores when germinate, form the Protonema. This structure later develops into an independent gametophytic plant.

Answer

(d) Sequoia sempervirens is a gymnspermic plant. It is a group of plants having thick, woody, branched stems. These plants also have some xeric adaptations which help them survive in adverse climatic conditions.

The other examples are incorrect because pteridophytes is primitive group, no tree is included in this. Ferns are included in Pteridophytes. Angiosperms are different form gymnosperms in seed habit and adaptations.

Answer

The members of Phaeophyceae (brown algae) store mannitol as a reserve food material.

Answer

(a) Haplontic life cycle It is exhibited by Volvox, Spirogyra and Chlamydomonas. The dominant photosynthetic phase in these plants is gamotophytic phase which develops from a haploid spores after a mitotic cell division of zygote.

(b) Diplontic life cycle is found in gymnosperms and angiosperms. The dominant phase is diploid sporophyte plant develop from zygote.

(c) Haplodiplontic life cycle It is an intermediate conditions exhibited by bryophytes and pteridophytes. Here haploid gametophytic stage alternates with diploid sporophytic stage.

Adult

Haplodiplontic life cycle

Answer

Roots are represented by root like structure called rhizoids in less developed lower plants (bryophytes and pteridophytes). The plant tissue system in these is not differentiated into true leaf, stem and roots as it is found in higher plants (gymnosperm and angiosperm).

Thinking Process

In plants both haploid and diploid cells can divide by mitosis. This ability leads to the formation of different plant body-haploid or diploid. Haploid plant body produces gametes by mitosis. This plant body is gametophyte.

Answer

Haplo diplontic type of life cycle is exhibited by Ectocarpus, Polysiphonia and Kelps. Here, diploid saprophytic phase alternate with haploid gametophytic phase.

In Fucus, the main plant body is saprophytic and it shows diplontic type of life cycle.

Answer

In bryophytes the male sex organ is antheridium and female sex organ is archegonium. The gametophyte (n) in bryophyte bears the primiture sex organs in the form of antheridium (male) which produce flagellate antherozoids which are male gamete and need thin film of water to swim and reach female reproductive organ (archegonium).

Archegonia is female part which has single egg cell. Both these reproductive parts are born on male and female, anthridiophore and archegoniophores borne on haploid gametophyte.

Thinking Process

Amphibians can live their life in water as well as on terrestrial habitat. Think of plant and animal species that can live this mode of life.

Answer

Bryophytes are amphibian of plant kingdom. It is a group of primitive plant having a dominant gametophytic plant body. These plants can live in soil but depend on water for movement of male gametes called antherozoids to reach archegonium (female organ having egg cell) so that fertilisation can take place.

Answer

The structures are as given

Thinking Process

Formation of two types of spores is an evolutionary advancement of sexuality in plant over primitive form of plants.

Answer

Heterospory is production of spores of two different sizes and sexes by the sporophytes of land plants. Two types of spores are produced by heterosporic plants.

Small spores are microspores which germinate into male gametophyte and large spores are macrospores which develop into female gametophyte.

In evolution of plants pteridophytes are intermediate between bryophytes and gymnosperms. All bryophytes are homosporous and all gymnosperms are heterosporous. This condition is advanced as sexual dimorphism result in cross fertilisation.

Primitive or earlier pteridophytes are homosporous later pteriodophytes are heterosporous e.g., Dryopteris, Pteris-homosporous Selaginella, Salvinia-heterosporous.

Answer

Seed habit The differentiation of spores into microspores and megaspores and their dependence on the parent sporophyte for the nutrition, are the certain features in the life cycle of Selaginella, which have been considered as the essential pre-requite for formation of seed, the characteristic of spermatophyte.

The evolution of heterospory and seed habits in Selaginella is evident by the following characters

(i) Reduction to a single functional megaspore per sporangium.

(ii) Retention and germination of megaspore within megasporangium

(iii) Development of protective layer and nutritive tissue called tapetum is present.

(iv) Development of embryosac with in the sporangium.

(v) Modification of distal end of mega sporangium to capture pollen grain.

(vi) Pollination and siphonogamy.

(vii) Temporary suspension of growth of embryo (dormancy period).

Thinking Process

Similarity between phylogenetic characters of two plants shows that advanced group of plants have evolved from the primitive one.

Answer

Cycas as the relic of past Cycas is an evergreen plant which looks like a palm. It has unbranched stem and large compound leaf. It exhibit phylogenetic relationship with pteridophyte. Its evolutionary characters are

(i) Slow growth

(ii) Shedding of seed when the embryo is still immature.

(iii) Little secondary growth and manoxylic wood.

(iv) Leaf like megasporophyllus.

(v) Flagellate sperms even when pollen tube is present.

(vi) Persistent leaf bases.

(vii) Circinate ptysix.

(viii) Arrangement of microsporangia is well defined archegonia.

Thinking Process

Presence of seed and woody stem is the characteristic feature of gymnosperms. The development of seed plants have evolved from few plants like Selaginella (pteridophyte) whose life cycle clearly shows the development of seed habit. Compare the life cycle of this pteridophyte with Cycas.

Answer

Heterospory, i.e., production of two types of spores smaller microspores and larger megaspore was first reported in Selaginella a pteridophyte. In Selaginella, the smaller microspores are destined to produce male gametophytes and the larger megaspores to female gametophyte.

The male gametophyte produces male gametes, whereas the female gametophyte produces archegonia and also provides nourishment to the developing embryo.

The phenomenon of heterospory, thus lead to the reduction of gametophyte, in situ germination of spores, retention of megagametophyte in the megasporangia and finally to the seed development. Thus, the heterospory in Selaginella forms the base for seed habit development in gymnosperms.

Answer

The life cycle of fern (Dryopteris) clearly shows the alternation of generation. The gametophytic stage $(n)$ alternates with the sporophytic stage (2n) figure given shows its complete life cycle.

Prothallus The prothallus of the fern is multicellular, free living, thalloid, haploid and autotrophic structure. It develops from the spores produced by sporophyte after reduction division.

These spore germinate with a germtube with an apical cell and forms a filament of 3-6 cells and one or two rhizoids at the base which later develops into gametophytic plant.

Answer

The male and female gametophytes of pteridophytes and gymnosperms different from each other are

Thinking Process

Symbiosis is a phenomenon of interaction of two living organisms in such a way that both the associated partners derive some benefit from each other in such a way that both co-exist and flourish well.

Answer

Mycorrhiza (Myco’s = fungus, rize = roots) is a symbiotic association between fungus and the roots of vascular plants. The fungus colonizes the roots of the host either intra or inter cellularly. It helps in the nutrient absorption from soil for the plant. Mycorrhizal associations are present in conifers, i.e., Pinus, Cedrus, Abies and Picea.

Coralloid roots is develop in Cycas. It is produced in clusters at the base of the stem and protrudes out over the ground. It is dichotomously branched and greenish in colour. It contains algal zone in cortex. This algal zone contains blue green algae like Anabaena and Nostoc which grow in symbiotic association with coralloid roots.

Answer

Gametophyte is a haploid multicellular adult stage in a bryophyte’s life cycle. It bears male reproductive structure (antheridia) and female reproductive structure called archegonia, and thus produce haploid gametes antherozoids (male gamete) and egg cell (female gamete) respectively.

In mosses, liverworts and hornworts the gametophyte is a dominant form and thus most familiar phase of life cycle of the bryophyte. The moss gametophyte originate from a haploid spore. Initial phase of growth forms protonema in moss.

The protonema further develops into a main plant body of bryophyte which is thallus like prostrate and erect, attached to substratum by unicellular or multicellular rhizoids. They may possess root like, leaf like or stem like structures.

Answer

Haplo diplontic life cycle (is also referred as diplohaplontic, diplo biontic or dibiontic) shows multicellular diploid and haploid stages as dipicted in the following figure.

Schematic diagram represent the life cycle of a pteridophyte (homosporous one) haplo-diplontic type of life cycle

Life Cycle of a Pteridophyte The life cycle of a pteridophyte consists of two morphologically distinct phases

(i) The gametophytic phase

(ii) The sporophytic phase

These two phases come one after another in the life cycle of a pteridophyte. This phenomenon is called alternation of generation. The gametophyte is haploid with single set of chromosomes. It produces male sex organs antheridia and female sex organs archegonia.

(i) The antheridia may be embedded or projecting type. Each antheridium has single layered sterile jacket enclosing a mass of androcytes.

(ii) The androcytes are flask-shaped, sessile or shortly stalked and differentiated into globular venter and tubular neck.

(iii) The archegonium contains large egg, which is non-motile.

(iv) The antherozoids after liberation from antheridium, reaches up to the archegonium fuses with the egg and forms a diploid structure known as zygotes.

(v) The diploid zygote is the first cell of sporophytic generation. It is retained inside the archegonium and forms the embryo.

(vi) The embryo grows and develop to form sporophyte which is differentiated into roots, stem and leaves.

(vii) At maturity the plant bears sporangia, which encloses spore mother cells.

(viii) Each spore mother cell gives rise to four haploid spores which are usually arranged in tetrads.

(ix) The sporophytic generation ends with the production of spores.

(x) Each spore is the first cell of gametophytic generation. It germinates to produce gametophyte and completes its life cycle.

Answer

(b) Is correct, lichen is a symbiotic association between an alga and a fungi, which live together for their mutual benefit. If both are separated from each other then they will die. The fungus holds water, provides protection and ideal housing to the alga.

The alga in turn supplies carbohydrate food for the fungus. If the alga is capable of fixing nitrogen (e.g., Nostoc), it supplies fixed nitrogen to the fungus. The kind of mutual interdependence helps lichens to grow on dry, barren rocks, where the other plants fail to exist. Morever, the algae or the fungi alone cannot grow in such places. Thus, both the partners cannot survive without each other.

Thinking Process

Double fertilisation and triple fusion is characteristic feature of all angiosperms. It is an advancement in sexual reproductions.

Answer

An angiospermic plants sexually reproduces by the formation of male and female gametes. The male gamete is a pollen which contain two male nuclei and female gamete is egg cell produced in ovule (female gametophyte).

The pollen grains germinate on the stigma of a flower and the resulting pollen tube grow through the tissues of stigma and style and reach near the egg apparatus. The two male gametes are discharged within the embryo sac. One of the male gamete fuses with the egg cell to form a diploid zygote.

This fusion is known as fertilisation or syngamy. The second male gamete fuses with the diploid secondary nucleus and forms the triploid Primary Endosperm Nucleus (PEN). This fusion is known as triple fusion.

Because of the involvement of two fusion, this event in angiosperms is termed as double fertilisation. The zygote then develops into embryo and PEN develops into endosperm which provides nourishment to the developing embryo.

Answer

(a)

(b)

(c)