Plant Kingdom 3 Flashcards
Describe gymno sperms
Gymnosperms are very limited in distribution. They are mainly found in cold regions.In
India gymnosperms are found on the slope of Himaliayan mountains. As, they grow in
slopes of mountains so they have to face water scarcity hence most of the gymnosperms
are xerophyte.
it is the first seeded plant
-it is the first successful terrestrial plant
-In gymnosperm, embryo & seed formation take place but no fruit formation.
explain vascular tissue of gymnosperms
All gymnosperms are vascular plants. Therefore vascular tissue are present i.e. xylem &
phloem. Xylem lacks vessels & phloem lacks sieve tubes and companion cells.
Exceptionally in xylem of Gnetum, Ephedra, Welwitschia true vessels are present.
Early secondary growth(woody growth causing increase in girth) takes place in gymnosperm stem, so it becomes woody.
why are gymnoseprms called arborescent?
Most of the gymnosperms are arborescent (woody) and tree habit - but some are present
as shrub.
eg. Ephedra
Some gymnosperm are liana or woody climbers.
eg. Gnetum ula
differentiate between cycas and pinus?
Cycas:
- dioecious,short
-coralloid roots with association with BGA for nitrogen fixation
-unbranched stem
-pinnately compound leaves
-male cone is large
-female cone is loosely bound megasporophylls
-pollen grains are not winged
- pollination is through wind ( anemophily)
Pinus:
- monoecious, tall
-tap root with mycorrhizal asociatiion
-branched stem
-2 types of leaves: scaly leaves for protection, needle or foliage leaves for photosynthesis
-male cone is small
-female cone is compact
-pollen grains anre winged
-pollinating agent is through wind (anemophily)
what is sulphur shower
In pinus, the pollen grains and extremely small in size and yellow coloured. These are proeduced in large amounts, When these are reelased into the wind, it looks like a shower of yellow sulphur powder. Hence it is called sulphur shower
explain the formation of male gamete in gymnosperms
The strobilli (sing strobilus) bearing microsporophylls and microsporangia are called
microsporangiate cones or male strobilli or male cone.
(iv) Within microsporangium many microspore mother cells are present which undergo
meiosis and produce many haploid microspores. Germination of microspore takes place
with in microsporangium hence it is called endosporic germination.
(v) The microspore develop into pollen grain and then male gametophyte which is highly
reduced and is confined to made of only a limited number of cells (e.g. In Cycas-5 cells
and Pinus-6 cells are present in mature male gametophyte).
(vi) The development of pollen grains take place within the microsporangium.
explain the formation of femal egametophyte
The cones/strobilli bearing cluster group of megasporophylls with megasporangia are
called megasporangiate cones or female cones.
(ix)
In gymnosperm the megasporangium is made of a diploid tissue also called nucellus. It is
covered with integument (envelope) also hence this composite structure is called
integumented megasporangium or ovule.
(x) One cell of nucellus (2n) is differentiated into megaspore mother cell and undergoes
meiosis to form four haploid megaspores. Three of them degenerate, pass on cytoplasm to the functional female megaspore and only one
megaspore remains functional.
(xi) The functional megaspore germinate inside the megasporangium (endosporic germination) and developes into a multicellular female gametophyte also called
endosperm(n).
(xii) The female gametophyte (endosperm) produces two or more archegonia or female sex
organs in one ovule.
(xiii) This multicellular but less developed female gametophyte is retained within
megasporangium (ovule).
explain pollination in gymnoseprms
The pollen grain are released from the microsporangium and are carried in air currents
(wind pollination = Anemophily) and come in contact with the opening (micropyle) of
ovules on megasporophylls.
(xv) Each pollen grain produces pollen tube carrying two male gametes which grows towards
archegonia in the ovule and release (discharge) its content (two male gametes) near the
mouth of archegonia.
(xvi) One male gamete fuses with female gamete and another male gamete degenerates. The
fertilisation is performed which results in zygote and then embryo formation within the
ovule.
Now fertilized ovule having embryo is called seed.
(xviii) These seed are not covered with ovary wall or fruit wall so they are called naked seeds.
The ovule actually secrete certain chemicals whcih forms a bulging drop like structures in the opening(micropyle). The pollen grains falls on the drop and then grows pollen tube.
what are the 3 types of fertilisation
(i) Zoodiogamy- male gametes are motile, it rached female gemate via water
-algae/bryo/pterido
(ii) Zoodio-siphonogamy- male gametes are motile, they rech female gamete via water
lower gymnosperms
(iii) Siphonogamy- male gametes are non motile, they reach female gamete via pollen tube
high gymnosperms, angiosperms
why is polyembryony
Polyembryony is commonly found in gymnosperm i.e. occurence of more
than one embryos with in seed.
summarise life cycle of gymnsoperms
Life cycle of Gymnosperm & angiosperm is diplontic because gametophytic generation is short
lived. Gametophyte is very reduced & depends on its sporophyte.
differentitate between poloidy of gymnosperm endosperm and angiosperm endosperm
(i) gymnsperm endosperm: haploid because it is formed bfr fertilisation
(ii) angiosperm endosperm: triploid(3n) because it is formed after fertilisation.
both endosperms are for nutrition
whata re the two orders of gymnsoeprms
(A) Cycadophyta (Lower Gymnosperm)
The characters of this group are similar to ferns
The plants of this group are megaphyllous or macrophyllous
Male gametes are motile
(B) Coniferophyta (Higher Gymnosperm)
explain different classes of order: cyacodphyta
(i) Cyacdofillicales/pteridospermae
- similar to ferns c/a seed fern
-extinct
-first plant to have seed habit
(ii) Benettitales
- extinct grp
(i) Cycas (Order Cycadales)
Living fossil
Fern palm or Sago palm because sago is obtained from its stem.
Ovule, egg, male gametes and male cone of Cycas are largest in plant kingdom.
In embryo of Cycas two cotyledons are present.
Cycas is known as “Relic of past” because it has many primitive characters of ferns
like presence of circinately coiled leaves and motile male gametes (sperms).
In Cycas female cone is absent.
In Cycas male gametes are motile, multiciliated and top shaped.
explain different classes os order: coniferophyta
(i)
Ginkgoales :-
It is the oldest order of coniferophyta.
eg. Ginkgo biloba - living fossil.
Note : Exceptionally Ginkgo biloba
belongs to higher gymnosperm
but its male gametes are motile.
(ii) Coniferales :-
(a) Conifers are included in this group.
(b)
It is the largest group of gymnosperm
Examples of Coniferales -
(a) Pinus (Pines) :- Known as chir pine, different species of Pinus give us chilgoja (edible
seed) and turpentine oil.
(b) Cedrus deodara - It is known as Devdar.
(c) Sequoia - The plants in this genus are very heavy. Therefore they are called father of
forest. It is called Red wood tree or Sherman tree. It is the tallest gymnosperm.
(d) metasequoia- living fossil
(iii) Gnetales -
(a) They are the most advanced gymnosperms.
(b) Exceptionally members of this group have vessels in xylem.
e.g. Gnetum
Welwitschia
Ephedra
