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Frequently asked questions (FAQS)
1. What are gymnosperms? Name some important
gymnosperms that are found in India.
Ans. Gymnosperms are group of plants with naked seeds.
The word gymnosperm has been derived from Greek words
where gymnos means naked and sperma means seeds. The
word gymnosperm was first used by Theophrastus in 300
B.C. Gymnosperms act as bridge between pteridophytes
and angiosperms. Gymnosperms flourished well during
Mesozoic era. Hence the Mesozoic era is called the age of
gymnosperms. However, most of the members of this group
have now become extinct and only few living forms are
known today. Some gymnosperms like Ginkgo biloba, Cycas,
Metasequoia are called living fossils, as these plants are found
both in living and fossil forms, and the number of fossil forms
is much more than the living forms.
In India there are about 16 genera and 53 species
of gymnosperms. They are Cycas from Cycadales, Abies,
Cedrus, Cephalotaxus, Cupressus, Juniperus, Larix, Picea,
Pinus, Podocarpus, Taxus, Tsuga from Coniferales, Ephedra
from Ephedrales and Gnetum from Gnetales. In addition
Ginkgo biloba is also growing in certain parts of India.
2. Discuss briefly the distribution of gymnosperms.
Ans. Gymnosperms are found both in tropical and temperate
regions. Some are found in arctic regions. The living
gymnosperms comprise 70 genera and 725 species. Of these,
majority belong to conifers or cone-bearing plants. The
conifers are mostly distributed in the cooler regions of Europe,
Asia and North America. They are dominant in upper timberline zone of mountain ranges including the Himalayas. The
living gymnosperms are widely distributed in the cold climates
where snow, rather than rain, is the source of water. The
only native gymnosperms which thrive in warm areas are the
cycads. In India, mostly the conifers thrive well in hilly areas.
Very few gymnosperms, except some cycads, grows in plains.
Cycas circinalis grow wild in some southern States. Some are
grown as ornamental plants in gardens, e.g. Araucaria.
3. Write a short note on the morphology of
gymnosperms.
Ans. Gymnosperms are tall, evergreen trees or shrubs. There
are no herbs. Certain species of Gnetum are twiners. The
plant body is a sporophyte and differentiated into root, stem
and leaves. Plants possess well-developed tap root system.
Roots often show symbiotic association with algae e.g. Cycas,
or with fungi e.g. Pinus. In Cycas coralloid roots are present
in addition to normal roots. The stem is aerial, erect, woody,
unbranched as in Cycas, or branched as in Pinus, Cedrus etc.
In some genera like Pinus, the branches are of two types,
long shoots or branches of unlimited growth and dwarf
shoots or branches of limited growth. The leaves are mostly
xerophytic, evergreen, and simple or compound, and vary in
size from small scaly leaf to more than six feet long leaves as
in Cycas. The leaves of Pinus are of two types; scale leaves
and foliage leaves. Scale leaves are minute, membranous,
brown and deciduous. Foliage leaves are present on dwarf
shoots only, and they are known as foliage spurs. They are
green, simple, needle-like or pinnately compound. The leaves
of Cycas exhibit circinate vernation, a characteristic feature
of ferns. The arrangement of leaves may be opposite and
decussate as in Gnetum, whorled as in Cedrus or spirally
arranged as in Taxus.
4. Name the tallest and the smallest gymnosperm.
Ans. Gymnosperms vary in their size from small herbs to
large gigantic trees. Sequoia sempervirens, a gymnosperm, is
the tallest living plant in the world, reaching a height of about
125 meters, and girth of about 30 meters. It is also known
as coast red-wood of California. Taxodium mucronatum and
Sequoiadendron giganticum with a girth of 125feet and 80feet
respectively, are the other gigantic gymnosperms. On the
contrary Zamia pygmaea, with the underground tuberous
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stem, is the smallest gymnosperm, about 25cm in height.
5. Discuss the internal structure of a gymnosperm
stem.
Ans. Anatomically the stem of gymnosperms shows an
epidermis, cortex and stele. The epidermis is singlelayered and is very soon replaced by periderm. Cortex is
parenchymatous. Based on the relative quantity of soft
tissue and mechanical tissue, gymnosperms are classified
into manoxylic and pycnoxylic types. In manoxylic forms, as
in Cycads, the wood is not compact, and has parenchyma.
In pycnoxylic forms wood is compact, and relatively less
amount of soft tissue is present. The stele is surrounded
by a typical epidermis followed by a layer of pericycle. The
vascular system consists of a number of vascular bundles
arranged in the form of a ring surrounded by central pith.
The bundles are collateral, endarch and open. Phloem
consists of only sieve tubes and phloem parenchyma.
Companion cells are absent. Xylem consists of trachieds
and xylem parenchyma only. Vessels are absent except
in Gnetales. The xylem is either endarch or mesarch.
Secondary growth is seen in all the members. It is usually
normal. However, anomalous secondary growth may be
found in Cycas and Gnetum. Normal secondary growth
takes place due to the activity of fascicular cambium, which
produces the typical annual rings. Parenchymatous pith is
present in the central region of the stem. In some cases
mucilage ducts or resin canals are found both in the pith and
cortex.
6. Discuss briefly the general structure of a
gymnospermic leaf.
Ans. Gymnosperm leaves exhibit xerophytic characters.
Anatomically gymnospermic leaves consist of epidermis
which is always covered by a cuticle. The stomata are
sunken and often present on pits. The mesophyll may be
differentiated into palisade and spongy parenchyma as in
Cycas or undifferentiated with arm parenchyma as in Pinus.
In some members, as in Cycas with a single veined leaf, a
transfusion tissue is present to help in lateral conduction,
necessitated by the absence of side veins. The stomata are
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either syndetocheilic or haplocheilic. In syndetocheilic type,
guard cell and subsidary cells originate from same mother
cell. For haplocheilic type, the guard cells and subsidiary
cells originate from the different mother cells. Haplocheilic
stomata are considered to be primitive compared to
syndetocheilic. In Gnetum both types of stomata can be
seen. Stomata may be distributed on both sides of leaf as in
Pinus, Ginkgo or confined to lower side as in Cycas.
7. Give the general organisation of a gymnospermic
ovule.
Ans. In gymnosperms, ovules are naked and born on
megasporophylls. The ovule consists of central mass of
parenchymatous tissue called nucellus. The nucellus is
surrounded by integument, which covers the whole nucellus
except at the top, where it leaves a small passage called
microphyle. The integument is differentiated into an outer
fleshy layer, middle stony layer and the inner fleshy layer.
The apex of the nucellus develops into pollen chamber,
where pollen grains undergo period of rest after pollination.
The development of female gametophyte begins with the
differentiation of megaspore mother cell in the nucellus. Its
development is either monosporic or tetrasporic. Megaspore
mother cell undergoes meiosis to form linear tetrad of four
megaspores, out of which, upper three cells degenerate,
and the lower most remains as functional megaspore.
The functional megaspore then develops into female
gametophyte. Archegonia are formed towards the micropylar
end of the female gametophyte. In Gnetum archegonia
are not formed. A few nuclei at the microphylar end, of the
female gametophyte act as egg, which is an angiospermic
character. The archegonia of gymnosperms do not have neck
canal cells and Venter canal cells.
8. Discuss briefly the germination of microspores in
gymnosperms.
Ans In gymnosperms, pollen grains or microspores are
unicellular. In Pinus pollen grains are winged. Microspores
develop into male gametophyte. During the germination
of microspores, one or two prothalial cells are cut off at
one end, leaving large antheridial cell, which divides into
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generative cell and larger tube cell. The generative cell
divides into stalk cell and body cell. Body cell produces two
male sperms. The tube cell forms the pollen tube, which acts
as carrier of sperms.
9. How does pollination occur in gymnosperms?
Ans. In gymnosperms pollination is anemophilous. The ovule
secretes mucilaginous substance, which oozes out from the
micropyle of the ovule and forms pollination drop, which
traps pollen grains. The pollen grains are drawn on due to
drying of pollination drop. Further changes take place in the
pollen chamber. The pollen tube grows through the tissue of
the nucellus, until it reaches the neck of the archegonia.
10. What is the difference between simple and
cleavage polyembryony?
Ans. Polyembryony is the characteristic feature of
gymnosperms. In cycads, more than one archegonia are
fertilized, resulting in the formation of more than one
embryo. This phenomenon is known as simple polyembryony.
In conifers, polyembryony is due to the separation of four
embryonal cells, and each of them develops into an embryo.
This phenomenon is called cleavage polyembryony. It occurs
in Pinus, but only one embryo attains maturity and rest
degenerate. In gymnosperms, embryo is differentiated into
root, stem and leaf.
11. Discuss briefly the formation of seed in
gymnosperms after fertilization
Ans. In gymnosperms, after fertilization, the ovule develops
into seed. The inner fleshy layer of ovule turns into tegmen
and middle stony layer forms testa of the seed coat, which
protect inner embryo. Embryo is developed at the end of
long suspensor which is pushed down into the food laden
endosperm that develops before fertilization. Female
gametophyte, soon after it has absorbed the food from
the nucellus, becomes endosperm. As there is no double
fertilization or triple fusion, the endosperm is a haploid
tissue. The whole of the nucellus except a small portion is
crushed. The remaining small part of the nucellus persists
in the seed in the form a narrow film, or cap, known as
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perisperm. Since there is no closed ovary, true fruits, like
that of angiosperms are not found in the gymnosperms. The
developed ovules remain naked. Middle stony layer of the
integument becomes extremely hard and protects the female
gametophyte and embryo. Cotyledons may be one or two as
in Cycas or a whorl of many as in Pinus. They become green
while still enclosed within the seeds. The seed generally
undergo a period of dormancy. However, the seed of Ginkgo
and Cycas germinate without undergoing period of rest.
12. Point out the similarities between gymnosperms
and pteridophytes.
Ans. Gymnosperms form a heterogeneous plant group
with several evolutionary trends which have been operating
since past to present day. Evolutionary trends reveal that
gymnosperms form a bridge between pteridophytes and
angiosperms. Gymnosperms resemble with pteridophytes in
the following features.
i). Both the plant groups show heterologous alternation of
generation. Sporophytic generation is dominant, independent
and large at maturity while the gametophytic generation
shows progressive reduction and dependence.
ii).Sporophytes of both the plant groups is distinguished
into root, stem and leave, and possess well marked vascular
system.
iii) Many cycads resemble ferns in having large compound
leaves and circinate venation.
iv).Both heterosporous pteridophytes and gymnosperms
possess endosporic gametophytes.
v).Male gametes of cycads (Cycas) and Ginkgo are motile like
that of pteridophytes.
vi).Female sex organs are archegonia in both pteridophytes
and gymnosperms.
vii).Male gametophytes of heterosporous pteridophytes and
majority of gymnosperms are highly reduced and posses only
two prothalial cells.
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viii).Endosperm develops before fertilization, as a result of
free nuclear division in the tissue of female gametophyte in
both gymnosperms and pteridophytes.
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following features.
1. Plants of both the groups are woody and perennial.
ix).Embryogeny is endoscopic in many pteridophytes, and
majority of gymnosperms
2. The stele is eustelic both in gymnosperms and
angiosperms.
13. Enumerate the differences between gymnosperms
and pteridophytes.
3. Both show secondary growth except monocots.
4. Both are heterosporic and endosporic.
Ans. Gymnosperms differ from pteridophytes in the
following features.
5. Megaspore is retained in megasporangium resulting in the
formation of seed.
I). Gymnosperms are commonly large sized trees, shrubs
or climbers. Pteridophytes on the other hand, are smaller in
size.
6. The male gametophytes are highly reduced.
II). Gymnosperms posses tap roots; where as roots of
pteridophytes are adventitious.
8. The sperms are non-motile except in Cycas.
III). Gymnosperms have eustelic organisation, whereas in
pteridophytes eustele is not found.
15. Enumerate the main differences between
gymnosperms and angiosperms.
IV). Gymnosperms undergo secondary growth, whereas
pteridophytes lack secondary growth.
V). In gymnosperms male and female gametophytes are
simple, non-green and dependent on sporophytes. They
are very much reduced in comparison to gametophytes of
pteridophytes.
VI). In gymnosperms megaspore remains in
megasporangium, whereas in pteridophytes they shed
from the sporangia and develop into independent female
prothallus.
VII). In gymnosperms, neck canal cells and venter canal
cells are absent, whereas archegonia of pteridophytes, are
provided with neck canal cells and venter canal cells.
VIII). Seed formation is not common in pteridophytes except
in Selaginella, whereas in gymnosperms seeds are produced.
14. Point out the similarities between gymnosperms
and angiosperms.
Ans. Gymnosperms resemble with angiosperms in the
7. Pollen tube acts as carrier of sperms.
9. The plants show distinct alternation of generation
Ans. Gymnosperms differ from angiosperms in the following
features.
1.Majority of angiosperms are herbaceous, whereas
gymnosperms are mostly woody.
2.Angiosperms may be annuals, biannual or perennials
whereas gymnosperms are mostly perennials.
3.In angiosperms, xylem possesses vessels and phloem
bears companion cells, whereas in gymnosperms (except
in Gnetales) xylem in devoid of vessels and phloem lacks
companion cells.
4.In gymnosperms cones are unisexual, whereas in
angiosperms the flowers are usually bisexual.
5.In gymnosperms ovules are naked, whereas in
angiosperms they are enclosed by the carpels.
6.Gymnosperms do not show double fertilization or
triple fusion, whereas in angiosperms it very common
phenomenon.
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7.Angiospermic seeds are enclosed within the ovaries
that develop fruit, whereas in gymnosperms seeds are
exposed.
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