Plant Kingdom Test 8

The non-encased condition of their seeds stands in contrast to the seeds and ovules of flowering plants (angiosperms), which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or leaves, which are often modified to form cones, or solitary as in Yew, Torreya, Ginkgo.

Fruits are not formed in gymnosperms due to absence of ovary. The ovules of a gymnosperm do not develop in an ovary but are "naked". Seeds develop from the ovules that are found in the developed ovaries but in the case of gymnosperms, the ovules are located directly on the surface of the flower or cone.

• Gymnosperms are more ancient than angiosperms.
• They formed dominant vegetation on the earth about 200 million years ago, and have been replaced by the angiosperms with the changing time and climatic conditions.
• They are now maintaining their dominance only in the colder regions, where instead of rain, snow is the source of water.
• Only a few gymnosperms, like cycads thrive in warm weather.

Because Pinus is a gymnosperm plant, gymnosperm don't bear flower they only bear seeds.

Taxol is an anticancer drug. At present taxol is obtained mainly from the bark of the 'yew tree' (Taxus baccata) but scientists have found that the substance can be extracted from the needles of tree also.

Anemophily or wind pollination is a form of pollination whereby pollen is distributed by wind. Almost all gymnosperms are anemophilous, as are many plants in the order Poales, including grasses, sedges and rushes.

Coulter and Chamberlain (1910) divided the gymnosperms into seven orders. Some of the orders are quite extinct and not found in present day.
These orders are as follows:
(i) Cycadophyta

• Cycadofilicales - Extinct
• Bennettitales - Extinct
• Cycadales - Mesozoic to present day

(ii) Coniferophyta

• Cordaitales - Extinct
• Ginkgoales - Palaeozoic to present day
• Coniferales - Palaeozoic to present day
• Gnetales - Recent.

• Ginkgo is a genus of highly unusual non-flowering plants. The scientific name is also used as the English name.
• The order to which it belongs, Ginkgoales, first appeared in the Permian, 270 million years ago, possibly derived from "seed ferns" of the order Peltaspermales, and now only contains this single genus and species.
• The rate of evolution within the genus has been slow, and almost all its species had become extinct by the end of the Pliocene; the exception is the sole living species, Ginkgo biloba, which is only found in the wild in China, but is cultivated across the world.
• The relationships between ginkgos and other groups of plants are not fully resolved.

• Gymnosperms typically have one integument (unitegmic) while angiosperms typically have two (bitegmic).
• gymnosperms are orthotropous.
• The zygote develops into an embryo, whereas the ovule matures into a seed and the integument serves as the seed coat.
• Because the seeds are not enclosed in an ovary or fruit, gymnosperms are generally regarded as bearing 'naked' seeds.
• The 'naked' ovules do not mean that they do not have any protection.

• Diplontic life cycle: The life cycle characterized by gametic meiosis and diploid sporophyte is dominant, photosynthetic and independent generation of the plant.
• Diplontic life cycle is exhibited by some green algae, brown algae and all seed bearing plants i.e. gymnosperms and angiosperms.

• Pinus gerardiana, known as the chilgoza pine (means 40 nuts in one cone), noosa, or neoza, is a pine native to the northwestern Himalayas in eastern Afghanistan, Pakistan, and northwest India, growing at elevations between 1800 and 3350 metres.
• It often occurs in association with Cedrus deodara and Pinus wallichiana. Chilgoza pine is well known for its edible pine nuts, rich in carbohydrates and proteins. The seeds are locally called and marketed as "chilgoza", "neja" (singular) or "neje" (plural).

• Root of gymnosperm is a diploid cell which thus has 2n equals 24 chromosomes. Whereas, endosperm in gymnosperm is haploid in nature with 12 chromosomes.
• Haploid chromosome is the characteristic feature of haploid. Triploid endosperms are seen in angiosperms, formed as a result of double fertilisation.
• Reproductive organs form cones or strobilus except female organs of Cycas.
• Ovule is generally orthotropous, unitegmic with three layers.
• Endosperm is formed before fertilization and is always haploid. Double fertilization is absent.

Microsporangia are born on the abaxial or morphologically lower surface of microsporophylls. They may be numerous and grouped into sori as in Cycas or reduced to two as in Pinus.

• Angiosperms or flowering plants are those plants in which seeds are formed inside fruits and the sporophylls are organised into flowers.
• They are the most recently and highly evolved plants appeared on Earth about 130 million years ago.
• The plant body is differentiated into root, stem and leaves.
• At maturity the plants bear flowers, which produces fruits and seeds.
• The vascular tissues are arranged in the form of vascular bundles.
• Xylem contains vessels and phloem has sieve tubes and companion cells. 

Angiosperm has the maximum power of adaptation because it is the latest evolution in plant and hence it can only have maximum power of adaptation. 

• Main differences between pteridophytes and gymnosperms are that in pteridophytes secondary growth is absent but in gymnosperms it is present.
• Male gametes are ciliate in pteridophytes while they are absent in gymnosperms, they have seeds or ovules.

• Gymnosperm have lost of anthredia and it's role of filling pollen grain.
• Gymnosperms have their archegonium formed after pollination inside female conifer cones (megastrobili).

• The "endosperm" is a tissue in which the nutrient substances necessary for the development of the embryo are deposited.
• In gymnosperms, the endosperm is formed in the ovule during germination of the megaspore and is a gametophytic tissue, which consequently becomes the female prothallus or the gametophyte with a haploid set of chromosomes.
• The archegonia in gymnosperms develop from certain cells of the endosperm.

Megasporangium or ovule is borne on adaxial or upper surface of megasporophyll or ovuliferous scale and are generally orthotropous and unitegmic in gymnosperms but are bitegmic in the Gnetales.
Example: Gnetum

• The ovule of gymnosperms consists of a parenchymatous mass of cells called the nucellus or the megasporangium.
• The nucellus encloses a single diploid megaspore mother cell that undergoes meiosis to form a linear tetrad of 4 haploid megaspores, out of which only one remains functional, whereas the rest degenerate.
• The functional megaspore form female gametophyte. As the female gametophyte is formed prior to fertilization, therefore, endosperm is haploid in case of gymnosperm.

Heterospory is the production of two different types of spores by the sporophytes of land plants. Of all the options given in the question Selaginella, Pinus and Cycas all produce microspores and megaspores for reproduction. However, Pteridium on the other hand is homosporous.

Cycas is a group of gymnosperms which have top shaped multiciliated male gametes (largest male gamete) and the each mature seed of these plants contain one embryo and two cotyledons (dicotyledonous).

Siphonogamy is a condition in plants in which pollen tubes are developed for the transfer of the male cells to the eggs. The seed plants are siphonogamous, while in the lower plants the male cells usually swim to the eggs. As a consequence, the spermatophytes were sometimes called siphonogams.

• Plants are classified into two main groups, the bryophytes (nonvascular plants) and the tracheophytes (vascular plants).
• The tracheophytes include ferns, gymnosperms and angiosperms, and are characterized by specialized vascular tissues- the phloem and xylem.
• The study of living species suggests that angiosperms evolved from the gnetophytes, a group of gymnosperms. however, the oldest known angiosperms were a diverse group of plants called magnoliids from which dicots and monocots are evolved. Monocots are more advanced plants than dicot.

• Gymnosperms are woody plants that produce seeds, but, unlike the flowering plants (angiosperms), the seeds are not enclosed inside an ovary. This means that instead of developing inside a fruit, such as a berry or acorn, gymnosperm seeds are more exposed.
• Often they are housed in somewhat open structures called cones. (The seeds, or the structures that contain them, sometimes appear quite similar to fruits, though, as is the case with ginkgo and juniper trees.)

Two sporophytic, one gametophytic generation and sporophytic generation is dominant in gymnosperm.

Birbal Sahni revitalized Indian fossil plants and discovered Williamsonia sewardiana which thrived in Rajmahal, Bihar 140 million year ago.

• Gymnosperms are more ancient than angiosperms.
• They formed dominant vegetation on the earth about 200 million years ago, and have been replaced by the angiosperms with the changing time and climatic conditions.
• They are now maintaining their dominance only in the colder regions, where instead of rain, snow is the source of water.
• Only a few gymnosperms, like cycads thrive in warm whether. 

• Circinate vernation is the manner in which a fern frond emerges. As the fern frond is formed, it is tightly curled so that the tender growing tip of the frond is protected within a coil. As the lower parts of the frond expand and toughen up, they begin to photosynthesize, supporting the further growth and expansion of the frond.
• In the case of many fronds, long hairs or scales provide additional protection to the growing tips before they are fully uncoiled. Circinate vernation may also be observed in the extension of leaflets, in the compound leaves of Cycads. 
• Young leaves have circinate vernation like those of ferns and always covered with brown hairs called as ramenta. Scale leaves are small, dry, brown, triangular leaves covered with ramenta. They are non- photosynthetic and protect the stem apex.

• The phenomenon of the development of more than one embryo in one ovule, seed or fertilized ovum is called polyembryony.
• It occurs in both animals as well as plants.
• In plants, this phenomenon was first reported by Antoni van Leeuwenhoek (1719) in orange seeds.
• In several gymnosperms, polyembryony is so common that it might be regarded as an important character of this group.