NCERT Class 11-Biology: Exemplar Chapter –3 Plant Kingdom Part 4

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Question 8:

How are the male and female gametophytes of pteridophytes and gymnosperms different from each other?

Answer:

Male and female gametophytes of pteridophytes are free living while in gymnosperms male and female gametophyte do not have free-living existence. They remain within the sporangia retained on sporophytes

Pteridophytes

(i)Flagellated male gamete

(ii)Water is essential for fertilization

(iii)Pollen tubes are not formed

(iv)Archegonia with neck canal cells

Gymnosperms

(a)Non-flagellated male gamete

(b)Water is not essential

(c)Pollen tubes are formed

(d)Neck canal cells are absent

Question 9:

In which plant will you look for mycorrhiza and coralloid roots? Also explain what these terms mean.

Answer:

In Pinus, mycorrhizal roots are found and in Cycas coralloid roots are found.Coralloid roots grow upwards and are highly branched. These are associated with green algae and help in nitrogen fixation.

Mycorrhizal roots have association with fungus and this relationship makes available the nutrients and water to the plant.

Long Answer Type Questions

Question 1:

Gametophyte is a dominant phase in the life cycle of a bryophyte. Explain.

Answer:

Gametophyte is a haploid multicellur adult stage in a bryophytes’s life cycle. It bears male reproductive structure (antheridia) and female strurtrue called rchegonia, and thus produces hapliid gametes antherozoids (male gamete) and egg cell (female gamete ) respecitvelyIn mosses, liverworts and hornworts the gametophye is a dominant form and thus most familiar phases of life cycle of the bryophyte. The moss gametophye originate from a haplod spore. Initial phase of grwoth 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 multicelluar rhizoids. They may possess root like leaf like or steam structures.

Question 2:

With the help of a schematic diagram describe the haplo-diptontic life cycle pattern of a plant group.

Answer:

In a sexually reproducing plant there is an alternation of generation between a haploid and a diploid phase of plant bodies. The haploid plant body is termed gametophyte while the diploid plant body is called sporophyte. The gametophyte produces gametes by mitosis while the haploid spores are produced by sporophyte following meiosis (reduction division). Two gamete fuse together to produce a zygote which develops into the diploid sporophyte.

A schematic

A Schematic

A schematic

In a haplo-diptontic life cycle pattern, such as in bryophyte or pteridophyte both the phases of life are multicellular. However, in bryophytes, the gametophytes are small, photosynthetic, and independent and represent dominant phase. The partly or totally dependent sporophyte is physically attached to the gametophyte. The (n) spores dispersed by sporophyte germinate into individual gametophytic plants. However, in pteridophytes the 2n (diploid) phase is dominant, well organized, independent while the n phase though also free-living and independent is short lived and photosynthetic. In both of these groups of plants the mobile male gametes, antherozoid produced by sex organ antheridium, travel to archegonium (bearing an egg cell) via the medium of water. Egg cell is non-motile hence the reproduction is oogamous.

Egg cell

Egg Cell

Egg cell

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