GYMNOSPERMS - EPHEDRA

EPHEDRA

OCCURRENCE

Ephedra is an arid plant. It is found in Europe, Western and Central Asia and Central and South America. It is also found in arid areas of Pakistan. Ephedra is source of drug Ephedrine. It is used for the treatment of asthma, cough and hay-fever.

GENERAL STRUCTURE

The plant body of Ephedra is sporophyte. It is a bushy plant. Sometimes, it becomes a climber. It height is ranging from I to 25 feet. The body is divided into root stems and leaves.

1. Stem:

Stem and branches are slender and green in colour. It has longitudinal ridges and furrows. Stem becomes woody due to the limited secondary growth. In some cases underground rhizomes are also produced. The branches arise from axillary buds. Their arrangement gives the plants characteristic bushy and broom-like appearance, Apical meristem produces nodes and internodes. Meristematic tissues are also present at the base of each internode. Their activity further increases the length of stem. Sometimes, meristematic tissue becomes hard at the end of the growing season. Thus many branches fall These branches are replaced by axillary shoot. It gives bushy appearance to the plants. The ridges and furrows of the successive internodes alternate with each other.

2. Leaves:

The leaves are scale like. They are opposite and arranged in pairs. The leaves of each pair are joined with each other at their bases. It forms a small sheath around the stem.

3. Roots:

The primary root grows deep in the soil. It develops many secondary roots.

INTERNAL STRUCTURE OF STEM

The stem has ridges and furrows. So it has a wavy outline in transverse section.

1. Epidermis: Stem is covered by heavily cutinized epidermis. The epidermis has stomata. They are present in pits in the region of furrows. A group of sclerenchymatous cells is present below the epidermis in the region of each ridge.

2. Cortex: The cortex is wide. It is formed of parenchymatous cells. These cells have chloroplasts. Thus the cortex of stem is the main photosynthetic tissue of Ephedra. The cells of peripheral region of the cortex are loosely arranged and form palisade layer. The cells in the inner region of the cortex from the spongy tissue.

3. Stele: The central part of the stem is stele. It is surrounded by endodermis. Wide pith is present in the centre of the stele. The vascular bundles are collateral and endarch. They form a ring around the pith. The vascular bundles form a continuous ring due to narrowness of medullary rays. The xylem in Ephedra has true vessels like Angiosperms. Phloem consists of the usual phloem parenchyma and the sieve tubes. But they are without any companion cells. Secondary growth occurs due to the activity of cambium. It produces prominent annual rings.

4. Cork: Phellogen (cork cambium) is produced in the older stem. It forms periderm. The outer tissues of periderm are transformed into the bark.

REPRODUCTION

Ephedra is a dioecious plant. But some monoecious plants are also found.

MALE STROBILUS

Each male cone arises in the axil of a leaf. The male cones are small. They are 1-2 cm in length. Each cone has a central axis. This axis bears 2-12 pairs of thick bracts. Bracts are arranged in an opposite manner. These bracts are closely set on the axis. A single male microsporophyll is present in the axil of each bract. Two small scales are present at the base of each sporophyll. It has a single stamen. Stamen has short stalk (filament). This stalk bears two to six microsporangia (anthers) at the top. The anthers are united in a Each anther has two or three lobes. Each lobe has a pore at its tip for releases of microspore (pollen grain).

GERMINATION OF POLLEN GRAIN

Germination of pollen grain started before the release of pollen grain. Pollen grain divides into two cells. The smaller cell again divides to form two prothallial cells.

The larger cell becomes generative cell.

Generative cell divides into lower stalk and upper body cell. The upper cell divides to form two male gametes. Pollen grain is released at this stage. Two prothallial cells disintegrate just after the release of pollen grains. The pollen grains are dispersed by wind and insects. Pollen grains lodge on the ovule. It grows rapidly.

A pollen tube is produced. This tube carries the two male gametes, the tube nucleus and the nucleus of the stalk cell on its tip. Pollen tube passes through the neck cells and reaches the oosphere. It releases male gametes and one of them enters the oosphere. It fuses with the Ooshere.

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GYMNOSPERMS - CYCAS

CYCAS

Systematic position

Division: Gymnospermae 

Class :Cycadophyta 

Order : Cycadales 

Family Cycadaceae 

Genus : Cycas

Occurrence

Cycas has a limited distribution. It is found in south East Asia, South China, Southern India, South Japan and Australia. The plants grow under xerophytic conditions.

Cycas is also cultivated as an ornamental plant in the gardens and parks. Cycas plants live upto hundred years or more.

Cycas is called a living fossil.

PLANT BODY

The plant body is a sporophyte. It is differentiated into root, stem and leaves.

1. Stem: Stem is unbranched. It is covered by thick, woody, persistent leaf bases. It makes the stem rough.

The apex of the stem is ensheathed by a group of brown scales. The lower of stem is covered by pinnate compound leaves. The growth of the stem is very slow. It produces a cluster of leaves each year. Older leaves fall of after two years.

2. Leaves and scales: The leaves are produced in the axils of the scales near the apex. Each leaf is composed of a petiole, rachis and lateral pinnae.

The young leaves show cincinnati vernation. Scales are also produced each year. Therefore, the clusters of green leaves and scales alternate with each other. Scales are also persistent.

Scales and leaf bases cover the surface of the old stem.

 3. Roots: The primary root persists in Cycas. It becomes tuberous. Cycas produces coralloid roots.Coralloid roots are short tufts and dichotomously branched roots. These roots contain an endophytic alga in the inner part of their cortex. Sometimes, bacteria are also present in the cortex, Bacteria fix nitrogen,

INTERNAL STRUCTURE OF STEM

Stem is internally composed of outer epidermis, cortex and vascular bundles.

1. The cortex is very wide. It is composed of parenchymatous cells. Parenchymatous tissue of the cortex

contains numerous mucilaginous canals.

2. Primary vascular bundles are present inside the cortex. They surround the central pith. These bundles are collateral. The primary medullary rays present between the adjacent bundles.

3. Cambium is present in the form of a narrow strip in each vascular bundle.

The xylem is endarch. The strength of the stem is mainly due to the presence of woody leaf bases on the surface.

4. Phellogen is produced in the periphery of the cortex. It produces cork (peridium) under the persistent leaf bases.

INTERNAL STRUCTURE OF THE LEAF

Each pinna of leaf has typical bifacial structure in transverse section.

1. Surface of leaf is covered by a single layered epidermis. The cells of the upper epidermis are slightly thick walled. But those of the lower epidermis are thin walled. Sunken stomata are present in the lower epidermis. A layer of hypodermis is present beneath the upper epidermis.

2. The mesophyll is differentiated into an upper palisade layer a lower spongy parenchyma. The cells of the mesophyll are rich in chloroplasts.

3. Each pinna is supplied by a single undivided vein. Transfusion tissues are present around mid ribs. They cause lateral conduction in the leaf. The vascular bundles are surrounded by pericycle and endodermis.

INTERNAL STRUCTURE OF ROOT

1. Epidermis: the surface of root is covered by a single layered epidermis.

2. Cortex: It is many layered thick and made up of thin walled parenchymatous cells.

3. Endodermis: The innermost layer of cortex is called as endodermis

4. Pericycle: Thin walled cells around the vascular bundle.

5. Stele : The young primary root is Diarch (vascular bundles are arranged in two groups) but in older roots it become Polyarch (vascular bundles are arranged in many groups). 

The xylem is exarch (Protoxylem is present towards the outside and metaxylem the towards centre. Phloem alternates with protoxylem elements.

6. Pith: is present in the centre of stele. It is composed thin walled parenchymatous cells. Root cap is present at the tip of root.

CORALLOID ROOTS

The structure is similar to that of primary root. In addition there is a conspicuous broad blue green zone in middle cortex.

This is the algal zone. It lies midway between the vascular bundle and epiblema. The cortical cells in this region get disorganized and are inhibited by blue green algae such as Nostoc and Anabaena.

In coralloid root the cortex is divided into three zones:Outer cortex, Middle cortex and Inner cortex.

The stele is diarch, triarch or tetrarch and

surrounded by an endodermis which is followed by pericycle.

REPRODUCTION

Cycas is dioecious. The male and female plants are separate. Sometimes, Cycas plants also reproduce vegetatively. It produces buds on the stem. These buds grow to form new plant.

MALE CONES

Male cones are produced on the male plants. Number of cones produced each year varies from one to many. Each male cone is fusiform in shape. Each cone has a central axis. It bears a number of spirally arranged microsporophyll. The microsporophylls are woody in texture.

They are wedge-shaped. The microsporangia (Pollen sacs) cover the lower surface of the microsporophylls.

The sporangia form sori. Each sorus has groups of two to six sporangia. Each sporophyll has several hundred sporangia. A large number of spores are produced in Cycas.

DEVELOPMENT  OF THE SPORANGIUM

1. Each sporangium develops from a single sporangial initial. This cell arise form the hypodermis of the sporophyll. This sporangial initial divides into an outer primary wall cell and an inner primary sporogenous cell.

2. The primary wall cell divides to produce a several layered wall. The number of layers in the wall varies from four to eight. The primary sporogenous divides to produce a mass of cell called sporogenous tissue or archesporium.

3. The outermost layer of the sporogenous tissue forms the tapetum. Some of the sporogenous cells increase in size and become the spore mother cells. But other cells disintegrate with the tapetum and nourish the spore mother cells.

4. The spore mother cells divide meiotically to form four microspores (pollen grain).

5. The sporangia become boat-shaped.

Each mature microspore has two layered wall, the exine and intine.

Exine is thickest at one end and becomes thinner towards the opposite end. The spores start germination before its liberation from the microsporangium.

GERMINATION OF MICROSPORE (POLLEN GRAIN)

The microspore cut off lateral prothalial cell towards one side of the spore. The larger cell then cuts off a small generative cell adjacent to the prothalial cell. It itself becomes tube cell. The microspore is liberated at this stage Spores are dispersed by wind.

FEMALE CONE

The female cones are produced on the female plants. Female cones of Cycas are very large. It is formed of megasporophylls.

Megasporophylls are loosely arranged to form crowns.

 Each megasporophyll is leaf like in form. The upper portion of the sporophyll is pinnate. Ovules (megasporangium) are arranged in two rows in the basal half of the sporophyll. The whole sporophyll and young ovules are covered by a dense mat of hairs. The ovules loose this hairy covering on maturity.

Each ovule is covered by a single massive integument. It has a narrow micropyle at the tip. Integument projects around the micropyle to form a small beak. Nucellus projects into the micropyle. But later the nucellar cells in this region disorganize to form a small cavity called pollen chamber. It plays an important part in early stages of fertilization. One of the nucellar cells increases in size and becomes megaspore mother cell. It undergoes meiosis to form four megaspores. Three megaspores degenerate. Only one becomes functional megaspore.

FEMALE GAMETOPHYTE

The megaspore (embryo sac) enlarges in size. Its nucleus undergoes many nuclear divisions. Thus several nuclei are formed in the megaspore. These nuclei occupy the peripheral region of the cytoplasm in the megaspore. Then the nuclei are surrounded by cell wall. Thus the megaspore becomes multicellular. It gives rise to the female gametophyte. The cells of the gametophyte develop numerous starch grains. The original megaspore wall persists around the prothalial tissue.

1. Three cells enlarge and function as archegonial initials at the micropylar end of the prothallus. Each archegonial initial divides into tipper neck cell and a lower central cell.

2. Neck cell divides to produce neck of the archegonium. The central cell enlarges. It forms the oosphere cell.

The whole interior of oosphere cell is filled with dense granular protoplasm. The wall of the oosphere cell is thick. The cells of the prothallus which surround the oosphere cell form the jacket layer.

3. The nucleus of the oosphere cell divides in two. The small ventral canal nucleus disintegrates. The other large nucleus becomes oosphere nucleus. It increases very much in size. The archegonium is now ready for fertilization.

4. The archegonial necks open in archegonial chamber Original megaspore wall ruptures above the archegonial chamber. The cellar tissue below the pollen chamber disintegrates. A passage is formed between the archegonial chamber and the pollen chamber.

5. A drop of mucilaginous fluid oozes out of the micropyle. The pollen grains are lodged on the micropyle. Pollen grain is trapped this mucilage and the pollen grain moves into the pollen chamber.

MALE GAMETOPHYTE

The pollen grain resumes its development after pollination. Generative cell divides into a stalk cell and a body cell. Both these cells represent an antheridium. A pollen tube grows out of the pollen grain.

It penetrates the nucellus. The pollen grain becomes dormant at this stage. This period lasts for about four months. After that the pollen grain resumes its activity,

Two blepharoplasts appear on the two sides of the nucleus. These blepharoplasts develop cilia. The body cell then divides into two antherozoids. The antherozoid develops thousands of cilia.

The nucleus of each antherozoid enlarged and completely fills the whole of the antherozoid. Antherozoids remain motile for several hours.

Pollen grain reaches the archegonial chamber by pollination. The wall of the pollen grain protrudes towards the archegonial chamber. The pollen grain bursts and release antherozoids into the archegonial chamber. Antherozoid enters the oosphere. Male nucleus unites with the oosphere nucleus. Fertilized oosphere secretes a thick wall and becomes the oospore. Oospore develops embryo.

Development of Embryo and Seed

Oospore divides into 200-300 cells. The cells of the central region disorganize to produce a cavity. This cavity is surrounded by two to three layers of cells. The cells in the lower region elongate very much to form suspensor. The cells at the tip of the suspensor develop into the embryo. The elongating suspensor pushes the developing embryo deep into the prothalial tissue. These tissues provide nutrition to the developing embryo. Whole of the nucellus is consumed during the development of the embryo. Some prothalial tissue persists in the seed and form endosperm. A thick pad of tissue develops near the micropylar end. It functions as coleorhiza. Coleorhiza protects the radical of the embryo. Ovule is transformed into the seed. Embryo has two cotyledons. They occupy the whole seed. The seeds germinate immediately Cotyledons remain within the seed on germination. It absorbs nutrients for the developing embryo.

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GYMNOSPERMS - PINUS

Pinus

Occurrence

The genus Pinus has about 90 species. It has world wide in distribution. They are mostly present in the temperate regions.

Four species of pinus are found in Pakistan: Pinus wallichiana; Pinus halepensis; Pinus roxburghii; Pinus gerardiana.

GENERAL STRUCTURE

The plant body is sporophyte. It is an evergreen tall tree. Plant body is divided into root, stem and leaves Stem: The main trunk is unbranched. It has branches confined to the apical region. These branches form a characteristic canopy. It is covered with a scaly bark. Its branches

are dimorphic.

(a)Branches of unlimited growth: The main branches have an unlimited growth.

They bear only scale leaves.

(b)Branches of limited growth: Branches of limited growth or dwarf branches are

produced in the axil of the scale leaves on the main branches. These are about

1-2cm long. These are covered by one or two scale leaves. These branches also bear foliage leaves. A dwarf shoot with its foliage leaves is called spur.

Leaf:

Pinus has two types of leaves: scale leaves and foliage leaves.

(a) Scale leaves: The scale leaves are small, membranous and brownish in colour. These are protective in function.

They are present on the main and dwarf shoots.

(b)Foliage leaves: The foliage leaves are

green and needle-like. They are found only on the dwarf shoots forming the spur.

Roots: Pinus has a well developed tap root. It remains short and grows on hard ground or rocks. The lateral roots are well developed. These roots spread over a large area. Young roots are infested with a fungus to form mycorrhizae.

Internal Structure of the Stem

Stem is differentiated internally into epidermis, cortex, vascular tissue and central pith

1. Epidermis:

The surface is covered by an epidermis. It consists of a single layer of cells. Outer walls of these cells are highly cutinized. Below the epidermis is a hypodermis which is formed of layers of lignified cells.

2. Cortex:

The cortex is formed of parenchymatous cells. Cortex has a large number of resin canals. Each resin canal is surrounded by a layer of resin secreting glandular epithelial cells.

3. Vascular bundle:

The vascular bundles are conjoint, collateral and open. They form a ring around the pith. In each vascular bundle the xylem is towards the inner side and phloem towards the outerside.

A narrow strip of cambium is present between xylem and phloem. Pericycle is present outer to the ring of vascular bundles. A single layered thin walled endodermis is present outside the pericycle. Secondary growth takes place by the activity of cambium ring. There are distinct annual growth rings in the wood.

4. Bark:

Phellogen originates in the deeper layers of the cortex. It is present in the form of strips. It produces characteristic scaly bark.

INTERNAL STRUCTURE OF LEAF

A transverse section shows following internal parts of the leaf:

1. Epidermis:

Leaf is covered by thick walled epidermis. Epidermis is covered by a thick layer of cuticle. Sunken stomata are present below the general surface. Two or three layered hypodermis is present underneath the epidermis. Hypodermis is compose  of sclerenchymatous tissues. This hypodermis is the main strengthening tissue of the leaf.

2. Mesophyll:

The mesophyll of the leaf is parenchymatous. It is not differentiated into palisade and spongy parenchyma. Resin canals are present below the hypodermis. Each resin canal is lined by a layer of small epithelial cells. Each leaf is supplied by two branched veins.

3. Endodermis and vascular tissues:

Endodermis is present outside the pericycle. Pericycle surrounds the xylem Pericycle is formed of parenchymatous cells. Its cells adjacent to the phloem are called aluminous cells. The cells adjacent to the xylem are called tracheid cells.

These specialized cells form the transfusion tissue. They help in the lateral flow of nutrients.

INTERNAL STRUCTURE OF ROOT

young root is di- to pentarch. Xylem bundles are Y-shaped. Siwtil parenchymatous pith may be present or absent in the centre. The ring of vascular

bundles is surrounded by two to three layered pericycle. Pericycle is surrounded by endodermis. The cortex consists of a few layers of thin walled parenchymatous cells. Root hairs may be present or absent. Roots may be covered by mycorrhizal fungus.

REPRODUCTION

Pinus is monoecious. Plant develops both

male and female strobili on the same

plant. The strobili are monosporous. There is no vegetative reproduction in Pinus.

Male Cone

The male cones are much smaller. They are produced in clusters near the tip of

the long shoots. The male cones are

produced in the spring. Each male cone

has a central axis. It bears a number of

spirally arranged microsporophylls or stamens. Each microsporophyll has sac like microsporangia (pollen sacs) on the ventral side. Each microsporangium produces a large number of microspores (pollen grains). The wall of each microspore (pollen grain) consists of an inner intine and an outer exine. It has balloon like wings. The wings help in the dispersal of spores by wind.

DEVELOPMENT OF MICROSPORANGIUM (STAMEN)

1. A number of hypodermal cells act

sporangial initials. The sporangial initials divides to form outer wall initials and the inner archesporial initial.

2. The wall initials divide to form a many layered wall of the sporangium. The archesporial initials also increase in number by the repeated divisions. The

peripheral cells of the archesporium form the tapetum.

3. Some of the archesporial cells are transformed into microspore mother cells. The remaining archesporial cells and the tapetal layer provide nourishment to the developing microspore mother cells.

4. The microspore mother cell divides by meiosis to form four microspores or pollen grains. The exine of spore forms wings. The pollen grain divides in to smaller and larger cells.

The smaller cell again divides to form two small prothallial cells.

The larger cell becomes antheridial cell. The sporangium splits and microspores are released from the microsporangia at this stage.

MALE PROTHALLUS

1. The pollen grain has two prothalial cells and an antheridial cell. These

cells soon disintegrate. Further development of the pollen grain takes place at the surface of the nucellus.

2. The antheridial cell cut off second prothalial cells.

3. It also cut off generative cell adjacent to the prothallial cells.

4. The remaining large cell is known as the tube cell. Its nucleus is called tube nucleus. Tube nucleus controls the growth of the pollen tube.

5. Exine of the pollen grain ruptures.

6. Intine grows out to form the pollen tube. It grows through the nucellus. But its activity stops till spring. 

7. Female cone enlarges very much in size after pollination Outer ends of the ovuliferous scales increase very much. They meet each other to close the gaps in between them. The cone is covered with a lot of resinous secretions.

 Female cone

Female cones are produced in the axils of the scale leaves. The production of

female cones is initiated in the winter.

These become ready for pollination during the following spring. Each young female cone has a central axis. It bears spirally arranged scales. The scales are of two types. Some are thin membranous and are directly attached to the central axis. They are called bract scales. Woody ovuliferous scales are present on the ventral surface of each bract scale. The broader end of the ovuliferous scale has projection called the umbo. Each ovuliferous scale bears two ovules. They are situated side by side on upper side.

Each ovule (megasporangium) has a mass of nucellar tissue. They are surrounded by a single integument. The micropylar end

of the ovule is directed towards the

central axis. A single megaspore mother cell is differentiated in the nucellus near

the micropylar end. This megaspore mother cell undergoes meiosis to form four megaspores. Only the lower most megaspore remains functional. The others disintegrate Functional megaspore (embryo sac) increases in size. It occupied the major part of the nucellus. Pollination takes place at this stage.

FEMALE  PROTHALLUS

The megaspore divides many times to form female prothallus. Megaspore wall encloses the female prothallus. Three archegonia are produced towards the micropylar end.

Each archegonium develops from a single prothalial cell. Archegonia consist of a large venter and a short neck. The oosphere or egg is very large. It is bounded by the prothallial cells.

There is a small ventral canal cell below the neck.

The neck is without any neck canal cells.

The prothalial tissue enlarges very much in size. It crushes all nucellar tissue except a small amount near the micropylar end.

POLLINATION

Each ovule secretes a mucilaginous drop at the micropylar end. A gap is produced between the ends of the ovuliferous scales. It forms a passage for the entry of pollen grains. Wind carried pollen grains. The mucilage drop entangles the pollen grain. Pollen grain is carried through the micropyle to the surface of the nucellus.

Formation of Embryo and Seed

Diploid nucleus divides thrice to form eight cells. The lower four cells becomes proembryonal cells. The upper four nuclei are separated by incomplete cell walls. Four proembryonal divides to produce three tiers of cells:

1. Embryonal cell: The cells of the lower tier become embryonic cells. The four embryonic cells separate from each other

Each develops into a separate embryo

independently. Each embryonal cell forms secondary suspensor cells. The formation of more than one embryo from a single fertilized oosphere is called polyembryony. Only one embryo reaches maturity. The rest are aborted.

1. Suspensor cells: The cells of the middle

tier become suspensor cells. Suspensor cells elongate very much. it pushes the developing embryos into the prothaliat

tissue for nutrition.

2. Rosette cells: The cells of the upper most tiers are called the rosette cells. These cells do not take part in the development of the embryo.

A fully developed embryo is in the forma short straight axis. Its radicle is present towards the micropylar end. Plumule is present towards the inner side. Plumule is surrounded by ten cotyledons. The unutilized prothalial tissue forms the endosperm. The persistent nucellus tissues near the micropylar end form the perisperm.

The integument becomes hard testa. Some part of the ovuliferous scale fuses with the developing seed. It makes a large wing for dispersal of seed. The axis of the female cone rapidly increases. It produces gaps in ovuliferous scales. The cone becomes woody for the dispersal of seeds.

GERMINATION OF SEED

The radicle grows out. it splits the testa at the micropylar end. This radicle grows down into the soil and forms the primary root. The hypocotyl elongates to form a loop. Then it becomes straight, It carries with it the plumule and the cotyledons. The testa is also carried up with the cotyledons.

GYMNOSPERMS

GYMNOSPERMS

“Gymnosperms are a group of plants that produce seeds not enclosed within the ovary or fruit. “

The word “Gymnosperm” comes from the Greek words “gymnos”(naked) and “sperma”(seed), hence known as “Naked seeds.” Gymnosperms are the seed-producing plants, but unlike angiosperms, they produce seeds without fruits. These plants develop on the surface of scales or leaves, or at the end of stalks forming a cone-like structure.

Gymnosperms belong to kingdom plantae and sub-kingdom ‘Embryophyta’. The fossil evidence suggested that they originated during the Paleozoic era, about 390 million years ago.

Characteristics of Gymnosperms

Following are the important characteristics of gymnosperms:

1. They do not produce flowers.
2. Seeds are not formed inside a fruit. They are naked.
3. They are found in colder regions where snowfall occurs.
4. They develop needle-like leaves.
5. They are perennial or woody, forming trees or bushes.
6. They are not differentiated into ovary, style and stigma.
7. Since stigma is absent, they are pollinated directly by the wind.
8. The male gametophytes produce two gametes, but only one of them is functional.
9. They form cones with reproductive structures.
10. The seeds contain endosperm that stores food for the growth and development of the plant.
11. These plants have vascular tissues which help in transportation of nutrients and water.
12. Xylem does not have vessels, and the phloem has no companion cells and sieve tubes.

Classification:-

• Gymnosperms consist of four main phyla: the Coniferophyta, Cycadophyta, Gingkophyta and Gnetophyta.
•  Conifers are the dominant plant of the gymnosperms, having needle-like leaves and living in areas where the weather is cold and dry.
•  Cycads live in warm climates, have large, compound leaves, and are unusual in that they are pollinated by beetles rather than wind.
• Ginkgo biloba is the only remaining species of the Gingkophyta and is usually resistant to pollution.
• Gnetophytes are the gymnosperms believed to be most closely related to the angiosperms because of the presence of vessel elements within their stems.

Evolution of Gymnosperms

• Gymnosperms are believed to have evolved from the paleozoic to the mesozoic eras.
• There are 3 groups of extinct plants that played important roles in the evolution of modern gymnosperms
• They are progymnosperms, aneurophytales, and a groups of primitive gymnosperms: archaeopteridales.
• In middle devonian period, progymnosperms arose from the trimerophytes which were extant until the lower carboniferous period.
• The cordaitales were trees and shrubs during the carboniferous and permian periods both in swamp and dry land which had slender leaves.
•  They also had vascular cambium tissues and ovulate cones.
•  The cordaitales apparently gave rise to the phylum ginkgophyta, which persists to present day and others which have relatives to cycadophyta, gnetophyta and coniferophyta.
•  Voltziales is an extinct order of trees that gave rise species related to modern conifers.
• Pteridosperms were the first seed plants, with integuments protecting ovules to various degrees
• Another extinct group of Pteridosperms are the Bennettitales, which resemble present cycads.
• The Archaeopteridales may have given rise to the Cordaitales and the Voltziales.
• The Archaeopteridales arose from the Aneurophytales.
• Progymnosperms gave rise to aneurophytales that gave rise to pteridosperms and archaepteridales.
•  Aneurophytales were homosporous, producing many identical spores and had three dimensional branching
• Unlike the progymnosperms, the pteridosperms produced seeds appearing in the late devonian period.

Diversity of Gymnosperms

Modern gymnosperms are classified into four phyla. The first three (the Coniferophyta, Cycadophyta, and Gingkophyta) are similar in their production of secondary cambium (cells that generate the vascular system of the trunk or stem and are partially specialized for water transportation) and their pattern of seed development. However, these three phyla are not closely related phylogenetically to each other. The fourth phylum (the Gnetophyta) are considered the closest group to angiosperms because they produce true xylem tissue.

Coniferophyta (conifers - pine, spruce, redwood)

These are the most commonly known species among the gymnosperms family.They are evergreen hence they do not shed their leaves in the winter. These are mainly characterised by male and female cones which form needle-like structures. Coniferous trees are usually found in temperate zones where the average temperature is 10℃. Giant sequoia, pines, cedar and redwood are one of the many examples of Conifers.

Cycadophyta ( cycads)

Cycads are dioecious (meaning: individual plants are either all male or female). Cycads are seed-bearing plants where the majority of the members are now extinct. They had flourished during the Jurassic and late Triassic era. Nowadays, the plants are considered as relics from the past.

These plants usually have large compound leaves, thick trunks and small leaflets which are attached to a single central stem. They range in height anywhere between a few centimetres to several meters.

Cycads are usually found in the tropics and subtropics. Some members have adapted to dry arid conditions, and some also have adapted to oxygen-poor swampy environments.

Ginkgophyta ( ginko bolona)

Another class of Gymnosperms, Ginkgophyta, has only one living species. All other members of this class are now extinct.

The Ginkgo trees are characterised by their large size and their fan-like leaves. Also, Ginkgo trees have a large number of applications ranging from medicine to cooking. Ginkgo leaves are ingested as a remedy for memory-related disorders like Alzheimer’s.

Ginkgo trees are also very resistant to pollution, and they are resilient against diseases and insect infestations. In fact, they are so resilient that after the nuclear bombs fell on Hiroshima, six Ginkgo trees were the only living things to survive within a kilometre or two of the blast radius.

Gnetophyta (Ephedra)

Just like any other member of gymnosperms, Gnetophytes are also relics from the past. Today, only three members of this genus exist.

Gnetophytes usually consist of tropical plants, trees, and shrubs. They are characterised by flowery leaves that have a soft coating. This coating reveals an ancestral connection with the angiosperms.

Gnetophytes differ from other members of this class as they possess vessel elements in their xylem.

Origin of seed habit

Seed habit is known to be the most successful method in the evolution of sexual reproduction in plants.

The first seed was found to be Gymnosperms that was first appeared during the Devonian period in the time line. Soon it started appear on the land plants. As like the Gymnosperms seed habit has been found to be emerged during the Devonian period and now dominating every land plants.

Seeds are specialized structure resultant of gamete fusion. It has several advantages including late rejuvenation, safety besides others.

This means that primitive plants do not have the capacity to produce seed. Hence evolution has taken a direction and all advanced plant now bear seeds.

So seed habit is the ability to produce seed like propagules. This has many intermediary steps including heterospory (which has started in advanced pteridophytes), integument development (started in progymnosperms) and development of seed coat (started in gymnosperms).

GEOLOGICAL TIME SCALE

FOSSILISATION AND FOSSIL GYMNOSPERMS

Gymnosperms means (Greek gymnos = naked; sperma = seed. i.e., the plants with naked seeds. Gymnosperms are phanerogams or spermatophytes without ovary and fruit. Their seeds or ovules are naked or exposed, without a fruit wall. They are therefore considered as fruitless flowering plants and are referred to as "Phanerogams without ovary. Gymnosperm seeds develop either on the surface of scale or leaf-like appendages of cones, or at the end of short stalks (Ginkgo). The word gymnosperm is coined by Theophrastus in 300 B.C. and called them "plants with naked seeds". Palaeobotany is the study of plant fossils preserved in rocks.

The word "Fossil" has been defined as "any evidence of prehistoric life. The first mention of a fossil plant was made by a German scholar Albertus Magnus in the thirteenth century.

Fossils (from Latin fossus, literally having been dug up) are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous (fossil-containing) rock formations and sedimentary layers (strata) is known as the fossil record.

The process of preservation of living beings or their parts in form of fossils is called fossilization. 'Birbal Sahni' is known as father of Indian Palaeobotany.

(His main contribution is Pentoxifylline of Jurassic gymnosperms from Raj Mahal hills in Bihar).

BirbalSahni Institute of Paleobotany is situated on Trans-Gomati River bank, Lucknow (India).

The essential conditions for fossilization is that whole organism be buried alive soon after death without decay by bacteria, fungi etc. This is the reason why only small number of plants get fossilized.

GYMNOSPERMS LIFE CYCLE

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KAPPA PARTICLES IN PARAMECIUM

KAPPA PARTICLES IN PARAMECIUM

Sonneborn in 1938 discovered certain strains in paramecium which showed a killer trait due to presence of a cytoplasmic factor called Kappa. The killer strain can destroy the sensitivite strains growing in culture which do not have Kappa by liberating a toxic substance paramecin. Killer strains are not killed by their own paramecin.

Paramecin has two kinds of nuclei, a small micronucleus and a very large macronucleus which is highly polyploid and irregular in shape and behaviour during cell division. Only the micronucleus behave according to mendelian principles. Paramecium has three modes of reproduction. The first is a simple mitotic division called binary fission. The second method is conjugation here two protozoans divide meiotically to form four micronuclei in each cell; out of these, three nuclei degenerates and only one remains which divides by mitosis to produce two genetically identical haploid nuclei in each paramecium. During conjugation only one of the two  haploid nuclei is exchanged through a cytoplasmic bridge formed between the two ciliates. The cells than separates as two Exconjugants.

The third method of reproduction is called autogamy. Here a single paramecium divides meiotically and by the same process that occurs in conjugation, two identical haploid nuclei are formed which fuse to form a diploid organism. As there was no genetic exchange, the diploid paramecium is Homozygous.

One noteworthy feature of the sensitive strains is that they are not killed by paramecin while they are in the process of conjugation. This has an advantage because it allows the investigator to perform cross between the killer and sensitive strains. The two strains can be distinguished morphologically as killers have granular cytoplasm and sensitive are clear. When a cross is made between killer and a sensitive paramecium (each made homozygous by autogamy), there is exchange of genetic material through conjugation. This is followed by separation of the two genetically identical Exconjugants. It is found that killer Exconjugants produce only killer paramecia and the sensitivite traits are not controlled by mendelian genes.

If the heterozygous (KK) killer Exconjugants is inbred to another heterozygous killer, it produce three-Quarter killer (1KK and 2kk) and one quarter sensitivites (kk). But if the sensitivite Exconjugant (Kk) is crossed to another heterozygous sensitivite, it results in all sensitivite progeny even through their genotypes are in the ratio of 1KK:2Kk:1kk. The results suggest non-chromosomal inheritance of killer trait.

The final proof regarding inheritance of killer trait was obtained by modifying the experiment in the following way. The cross between killer and sensitivite was prolonged, allowing enough time for exchange of cytoplasm to take place. In this way, some of the Kappa particles could move  from killer into the sensitivite strain. Att the resulting progeny of such a cross consisted of killers thus confirming the cytoplasmic inheritance of Kappa particles.

The below experiment can be performed in such a way that paramecia divide very rapidly by controlling the nutrient conditions. Under such conditions, a Homozygous killer strains (kk) containing Kappa particles can produce a few individuals that are sensitivite and without Kappa particles. The explanation is that Kappa particles cannot multiply as rapidly as the cells and become fewer in number in comparison with the number of paramecium cells. Due to their reduced number Kappa particles are not passed on to some members of the progeny at all.

It was found that although Kappa particles are transmitted cytoplasmically, yet they require a dominant K gene for maintenance. The K gene cannot initiate the presence of Kappa particles about 0.2 micron in diameter and have ability to reproduce independent of the nucleus. They have their own DNA, can multiply and produce the substance paramecin.

Fig : Conjugation in Paramecium demonstrating extranuclear inheritance of Killer trait

Fig : exchange of nuclear genes

Fig : exchange of both nuclear genes and cytoplasm

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CYTOPLASMIC INHERITANCE

CYTOPLASMIC INHERITANCE

• Discovered by Correns.
• Inheritance of characters which are controlled by cytogene or cytoplasm is called cytoplasmic inheritance.

There are 3 types of cytoplasmic inheritance:-
1. Maternal inheritance.
2. Organellar Inheritance.
3. Inheritance involving infectious particles.

• Genes which are present in cytoplasm called 'cytogene' or 'plasmagene' or 'extra nuclear gene'.
• Total cytogene present in cytoplasm is called 'plasmon'.
• A gene which is located in the nucleus is called 'karyogene'.
• Inheritance of cytogene in organisms occurs only through the female. Because female gamete has karyoplasm, simultaneously it has cytogene because of more cytoplasm.
• The male gamete of higher plant is called male nucleus. It has very minute [equivelent to nil] cytoplasm. So male gamete only inherited karyogene.
• Thus, inheritance of cytogene occurs only through female. (Also called maternal inheritance).
• If there is a reciprocal cross in this condition, then results may be affected.
• Cytoplasmic inheritance involving essential organelles like, Chroloplast and mitochondria called as organellar inheritance.

Example of Organellar Inheritance: (true examples of cytoplasmic inheritance).

1. plastid inheritance in Mirabilia jalapa- cytoplasmic inheritance was first discovered by Correns in Mirabilia jalapa. In Mirabilis jalapa branch (leaf) colour is decided by type of plastid present in leaf cells. So it is an example of cytoplasmic inheritance.

2. Male sterility in maize plant- Gene of male sterelity is present in mitochondria. If normal male plant crossed with a female plant which has genes of male sterility then all the generation of male become sterile because a particular gene was present with female which has inherited by female.

3. Albinism in plant- Gene of albinism found in chloroplast. Gene of albinism in maize is lethal.

CYTOPLASMIC INHERITANCE- maternal effects in Limnea shell coiling.

Shell Coiling In fresh water Snail (Lymnaea peregra).

• In snails (gastropods)the shell is spirally coiled.
• Snails exhibit two types of coiling of their shell:

fig : A sinistral (left) and a dextral (right) shell

• Shell coiled to right is dextral.
• Shell coiled to left is sinistral.
• This direction of coiling is genetically controlled. The gene for dextral coiling is dominant 'D' and for sinistral coiling is recessive 'd'. So, that the dextral is 'DD' and sinistral is 'dd'.

• Boycott and Driver(1923) showed that the character of coiling is determined by the gene of the mother and not by the individual's own gene.

• Shell coiling in the hermaphroditic snail Limnaea peregra may be right-handed (dextral) or left-handed (sinistral).
• The coiling depends on the genotype of egg donor parent, regardless of the phenotype of that parent.
• Shell coiling in snail is controlled by D (dextral) and d (sinistral) alleles. The genotype of progeny depends on genotype of mother. If mother is "DD", the Dd offspring are dextral but the "Dd" progeny of "dd" mother has sinistral coiling.

CARBON DIOXIDE SENSITIVITY IN DROSOPHILA

Carbon dioxide is used as an anaesthetic for Drosophila and normal flies can with stand high CO2 concentrations without any adverse effect. But some strains of Drosophila are sensitive to CO2 so that within a few minutes they become paralysed and die. Reciprocal crosses between CO2 sensitive and resistance flies gave differing results.

If a CO2 sensitive female is crossed with a normal (resistant) male, almost all the offspring are sensitive. But the reciprocal cross of a sensitive male with a normal female yields almost all normal offspring indicating extra nuclear inheritance of this trait.

There is mostly maternal transmission although some transmission through sperm may also take place. Moreover, normal flies can be induced to become sensitive by injecting a cell free filtrate of haemolyph obtain from sensitive flies.

The casual agent for CO2 sensitivity has been observed in electron micrographs to be a virus-like particle called sigma. In flies that have been induced to become sensitive, sigma enters the egg cytoplasm and is transmitted maternally.

In the naturally occuring sensitive strains, sigma particles become incorporated into the nucleus (without associating with a specific chromosome) of the egg or some of the sperms and are transmitted in a non-mendelian manner. They are self-reproducing independent bodies and can mutate.

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MULTIPLE FACTORS (Blood Group)

Blood

Blood is a fluid connective tissue. The quantity of blood in the humans body is 7% of total weight. This is a dissolution of base whose pH value 7.4, there is an average of 5-6 litres of blood in the human body. Female contains half a litre of blood less in comparison to male.

History

At the beginning of the 20th century an Austrian scientist, Karl Landsteiner, noted that the RBCs of some individuals were agglutinated by the serum from other individuals. He made a note of the patterns of agglutination and showed that blood could be divided into groups. This marked the discovery of the first blood group system, ABO, and earned Landsteiner a Nobel Prize.

Landsteiner explained that the reactions between the RBCs and serum were related to the presence of markers (antigens) on the RBCs and antibodies in the serum. Agglutination occurred when the RBC antigens were bound by the antibodies in the serum. He called the antigens A and B, and depending upon which antigen the RBC expressed, blood either belonged to blood group A or blood group B. A third blood group contained RBCs that reacted as if they lacked the properties of A and B, and this group was later called "O" after the German word "Ohne", which means "without". The following year the fourth blood group, AB, was added to the ABO blood group system. These RBCs expressed both A and B antigens.

In 1910, scientists proved that the RBCs antigens were inherited, and that the A and B antigens were inherited codominantly over O. There was initially some confusion over how a person's blood type was determined, but the puzzle was solved in 1924 by Bernstein's "three allele model".

The ABO blood group antigens are encoded by one genetic locus, the ABO locus, which has three alternative (allelic) forms—A, B, and O. A child receives one of the three alleles from each parent, giving rise to six possible genotypes and four possible blood types (phenotypes).

Blood contains:-

1. Plasma

2. Blood cells/corpuscles

a. Red blood cells carry oxygen b.white blood cells fight infection  c.Platelet stop bleeding in injuries

A. Plasma

• Water-90%
• Protein, salts, glucose-10%
• This is the liquid part of blood 55% of the blood plasma.
• It's 90% part is water, 7% Proteins, 0.9% salts and 0.1% is glucose, remaining substances are in a very low quantity.

The function of plasma:-

• Transportation of digested food, hormones, excretory products etc. From the body take place through the plasma.

SERUM- when fibrinogen and protein is extracted out of plasma the remaining plasma is called 'Serum'. 

B. Blood corpuscles

This is the remaining 45% part of the blood, this is divided into three parts-

1. Red blood corpuscles (RBCs)

2. White blood corpuscles (WBCs)

3. Blood platelets

A.Red blood corpuscles (RBCs) or Erythrocytes-

• Red blood corpuscles of a mammal is biconcave.
• There is no nucleus in it, exception camel and lama.
• RBCs formed in Bone marrow (At the embryonic stage it's formation takes place in the liver).
• It's life spanis from 90-120 days.
• It's distraction takes place in the liver and spleen, therefore, the liver is called Grave of RBCs.
• It's contains Haemoglobin [haemo- iron(Fe2+) and globin- protein (combine to O2 and CO2), in which haemo iron containing compound is found and due to this the colour of iron is red.
• Globin is a proteinous compound which is extremely capable of combining with oxygen and carbon dioxide.
• The Iron compound found in haemoglobin in haemin.
• Anaemia disease is caused due to deficiency of haemoglobin.
• At the time of sleeping RBCs reduce by 5% and people who are at the height of 4200 meters RBCs increases by 30% in them.

B. White Blood corpuscles (WBCs) or Leucocytes-

• White blood corpuscles in shape and constitution this is similar to an amoeba.
• It's formation takes place in Bone marrow, Lymph node and sometimes in liver and spleen.
• It's life span is 3-5 days.
• It's formation of antibodies which protect from disease/infection.
• Nucleus present in it WBCs.

C. Blood platelets or Thrombocytes-

• It is found only in the blood of human.
• It's formation takes place in Bone marrow.
• It dies in blood.
• Its main function is to help in clotting of blood.
• If the quantity of WBCs is less in blood it causes Dengue.

Function of BLOOD:-

1. To control the temperature of the body and to protect the body from disease.

2. Clotting of blood.

3. Transportation of O2, CO2, Digested food, conduction of hormones etc.

4. To help in establishing coordination among different parts.

MULTIPLE FACTORS

INHERITANCE OF BLOOD GROUP AND RHESUS FACTOR:-

EXAMPLES:-

NOTE:- There are four types blood group and this system is called ABO system. ABO blood group system are determined by three alleles.

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