Plant Kingdom 2 Flashcards
describe bryophytes
Bryophytes include the various mosses and liverworts that are found
commonly growing in moist shaded areas in the hills. Bryophytes are also called amphibians of the plant kingdom because
these plants can live in soil but are dependent on water for sexual
reproduction. They usually occur in damp, humid and shaded localities.
They play an important role in plant succession on bare rocks/soil.( they are pioneer organisms after lichens)
explain the strcuture of bryophytes
They lack true roots, true leaves and true stem. But they possess root like strcutred called rhizoids for absorption and attatching to substratum. These rhizoids may be multicellular or unicellular. It is thallus-like and prostrate or erect. Prostate means the leaf life structure is parallel to the ground while erect means leaf like part is perendicular to ground. . The
main plant body of the bryophyte is haploid. It produces gametes, hence
is called a gametophyte
explain sex organs and gametes
The sex organs in bryophytes are multicellular.
The male sex organ is called antheridium. They produce biflagellate
comma shaped antherozoids. The female sex organ called archegonium is flask-shaped
and produces a single egg.
explain sexual repro in bryphytes
The antherozoids are released into water where
they come in contact with archegonium. An antherozoid fuses with the
egg to produce the zygote. Zygotes do not undergo reduction division
immediately. They produce a multicellular body called a sporophyte.
The sporophyte is not free-living but attached to the photosynthetic
gametophyte and derives nourishment from it. Some cells of the
sporophyte undergo reduction division (meiosis) to produce haploid
spores. These spores germinate to produce gametophyte.
Spore mother cells are present inside the capsule of sporophyte. Now meiosis takes place
in spore mother cells and leads to the formation of spores. After release from the capsule,
the spores geminate.
explain structure of sporophyte of bryophytes
(i) foot- attachment to gameotphytic body
(ii) seta- stem like structure
(iii) capsule- terminal strcuture containing spore mother cells
all these are diploid
(iv) calyptra- outer covering on the sporophyte. it is made of gametophytic cells.
hence haploid
explain the economic importance of bryophytes
Bryophytes in general are of little economic importance but some
mosses provide food for herbaceous mammals, birds and other animals.
Species of Sphagnum, a moss, provide peat that have long been used as
fuel, and as packing material for trans-shipment of living material because
of their capacity to hold water. Mosses along with lichens are the first
organisms to colonise rocks and hence, are of great ecological importance.
They decompose rocks making the substrate suitable for the growth of
higher plants. Since mosses form dense mats on the soil, they reduce the
impact of falling rain and prevent soil erosion. The bryophytes are divided
into liverworts and mosses.
describe liverworts
The liverworts grow usually in moist, shady habitats such as banks of
streams, marshy ground, damp soil, bark of trees and deep in the woods.
The plant body of a liverwort is thalloid, e.g., Marchantia. The thallus is
dorsiventral and closely appressed to the substrate. The leafy members
have tiny leaf-like appendages in two rows on the stem-like structures.
explain asexual reproduction in liverworts
Asexual reproduction in liverworts takes place by fragmentation of
thalli, or by the formation of specialised structures called gemmae
(sing. gemma). Gemmae are green, multicellular, asexual buds, which
develop in small receptacles called gemma cups located on the thalli.
The gemmae become detached from the parent body and germinate to
form new individuals. During sexual reproduction, male and female sex organs are produced either on the same or on different thalli.
all liverworts are monoecious except marchantia which is diocious. The formation of gemmae is charcateristic feature of marchantia.
explain the two stages of gemtophytic life cycle of mosses
The predominant stage of the life cycle of a moss is the gametophyte which
consists of two stages. The first stage is the protonema stage, which
develops directly from a spore. It is a creeping, green, branched and
frequently filamentous stage. The second stage is the leafy stage, which
develops from the secondary protonema as a lateral bud. They consist of
upright, slender axes bearing spirally arranged leaves. They are attached
to the soil through multicellular and branched rhizoids. This stage bears
the sex organs.
explain reproduction in mosses
Vegetative reproduction in mosses is by fragmentation and budding
in the secondary protonema. In sexual reproduction, the sex organs
antheridia and archegonia are produced at the apex of the leafy shoots.
After fertilisation, the zygote develops into a sporophyte, consisting of a
foot, seta and capsule. The sporophyte in mosses is more elaborate than
that in liverworts. The capsule contains spores. Spores are formed after
meiosis. The mosses have an elaborate mechanism of spore dispersal.
Common examples of mosses are Funaria, Polytrichum and Sphagnum
explain the uses of pteriodphytes
The Pteridophytes include horsetails and ferns. Pteridophytes are used
for medicinal purposes and as soil-binders. They are also frequently grown
as ornamentals. Evolutionarily, they are the first terrestrial plants to
possess vascular tissues – xylem and phloem. The pteridophytes are found in cool, damp,
shady places though some may flourish well in sandy-soil conditions.
describe sructural features of pteridophytes
However, in pteridophytes, the
main plant body is a sporophyte which is differentiated into true root,
stem and leaves (Figure 3.3). These organs possess well-differentiated
vascular tissues. The leaves in pteridophyta are small (microphylls) as
in Selaginella or large (macrophylls) as in ferns.
define:
(i) sporophylls
(ii) strobili/ strobilus
The sporophytes bear
sporangia that are subtended by leaf-like appendages called
sporophylls. In some cases sporophylls may form distinct compact
structures called strobili or cones (Selaginella, Equisetum).
The
sporangia produce spores by meiosis in spore mother cells.
explain the gametophyte of pterdiophytes
The spores
germinate to give rise to inconspicuous, small but multicellular, free-living, mostly photosynthetic thalloid gametophytes called
prothallus. These gametophytes require cool, damp, shady places to
grow. Because of this specific restricted requirement and the need for
water for fertilisation, the spread of living pteridophytes is limited and
restricted to narrow geographical regions.
explain sexual reproduction in pteridophytes
The gametophytes bear male
and female sex organs called antheridia and archegonia, respectively.
Water is required for transfer of antherozoids – the male gametes released
from the antheridia, to the mouth of archegonium. Fusion of male gamete
with the egg present in the archegonium result in the formation of zygote.
Zygote thereafter produces a multicellular well-differentiated sporophyte
which is the dominant phase of the pteridophytes.
