Drone Insect is a new addition to the concept of artificial pollination. Drone insect has been invented to turn the concept of artificial pollination into a real life working technology. The experiments have been successful enough to support the further work on the project. Japanese engineers in Tokyo have developed the drone insect for artificial pollination.
The National Institute of Advanced Industrial Science and Technology in Tokyo initiated the project of Drone Insect. The engineers discovered a specific type of sticky gel than can pick up the pollen grains from flowers and can release them at other place. The natural flies spread the pollen grains from one place to other. Population of natural flies is decreasing so the drone insect can be used as an artificial alternative.
Scientists all over the world are constantly working to increase the fertility of crops in an artificial way. The bottom panel of drone insect has specific type of gel and horse hairs. This bottom panel can pick up pollen grains from one flower and release them on another flower. The gel is so useful that it remained in working condition even after 8 years.
The gel was initially experimented on ants. Gel bearing ants picked up more pollen grains as compared to other normal ants. After that the gel is pasted on drone insect for experiments. The horse hairs were used as alternative to natural hairs on flies’ legs. Horse hairs bearing the specific gel picked up the pollen grains from one flower and released them on other. The results of experiment have been quite encouraging.
According to experts a lot of work has still to be done to make the concept a reality. These drone insects can be used as alternative to aid the decreasing population of natural flies, honey bees, and other flying insects. Drone insects are expected to increase the crops fertility after a few years of research.
Interesting Facts About Babies:
Here are some interesting facts about babies. Human body goes through various changes since its birth. Babies have some different body behaviors as compared to adults. Here are sixteen facts about babies.
- A new born baby sees in black and white.
- A baby cannot taste salt until it is 4 months old.
- Babies are born with the ability to swim.
- A baby in the womb can send stem cells to repair damaged organs of the mother.
- A baby has three times as many taste buds as adults.
- A baby’s brain uses 50% of the glucose in its body.
- A baby’s eyes are 100% their adult size when they are born.
- A new born baby can cry tears.
- A baby has 270 bones at birth.
- A new born baby is nearsighted.
- A baby can breathe and swallow at the same time.
- A baby does not have kneecaps.
- Babies have superhuman strength.
- If a baby continued to grow at the same rate as in its first year, then at 20 years of age it would be 30 feet tall.
- All babies have breasts and lactate.
- Babies sleep with their eyes open.
Tests for Lipids
Preliminary Tests for Lipids
|Poured one or two drops of original solution with the help of a dropper on a filter paper and allowed it to dry.||A fine greasy spot appeared on the filter paper||Lipids are present|
|Slowly heated 2-3 ml of original solution in a test tube.||No precipitate formation||Proteins are Absent|
|Took 2-3 drops of original solution and then added a few drops of iodine solution.||The solution does not turns its color||Carbohydrates are absent|
Confirmatory tests for Lipids
|2-3 ml of original solution in a test tube and add 3 ml of water then add few drops of Sudan III reagent. Shake properly and allow the solution to stand.||Formation of a red layer on the surface of solution in test tube||Lipids are present|
Oil Emulsion Test
|2.5 ml of O.S. added 2.5 ml of absolute alcohol and then added 5 ml of cold water. Then shake the mixture and allowed it to stand.||A white colored cloudy suspension (emulsion) is formed||Lipids are confirmed|
Prof. Imran Khan
Tests For Protein
Preliminary Tests for Protein
|Slowly heated 2-3 ml of original solution in a test tube.||White precipitate formation||Proteins are present.|
|Took 2-3 drops of original solution and then add a few drops of iodine solution.||The solution did not turns its color||Carbohydrates are absent|
|Poured one or two drops of original solution with the help of a dropper on a filter paper and allowed it to dry.||No greasy spot appeared on the filter paper||Lipids are absent|
Confirmatory Tests for Protein
|i) Took 2-3 ml of original solution and add 7-9 drops of Million’s reagent.
ii) Prepared the same mixture and boiled
|Formation of white precipitates
Appearance of brick red color
|Proteins are present
Proteins are present
|5 ml O.S. + 3 drops of 1% solution of ninhydrin in ethanol is added to 1 ml of the solution and the solution heated for five minutes in a boiling water bath.||formation of red, blue or purple color||Proteins are present|
|2.5 ml original solution and add 2.5 ml of 5% of NaOH solution. Then mixed it by shaking thoroughly, and added 1-2 drops of 1 % copper sulphate solution and shake well.||Violet, red or pink color appeared||Proteins are confirmed|
Prof. Imran Khan
Tests For Carbohydrates
Preliminary Tests for Carbohydrates
|Heating||Slowly heated some original solution in a test tube.||No precipitate formation||Proteins are absent|
|Iodine Test||2-3 drops of original solution and then add a few drops of iodine solution.||The solution turns Blue-Black in coloration||Carbohydrates are present|
|Poured one or two drops of original solution with the help of a dropper on a filter paper and allowed it to dry.||No greasy spot appears on the filter paper||Lipids are absent|
Confirmatory Tests for Carbohydrates
|Benedict’s Test||7 drops of original solution + 2-3 ml of Benedict’s solution + gentle heating||Blue color of the solution changes into green, then yellow to orange at last brick red precipitates are formed||Carbohydrates are present|
|Took 2 ml of O.S. in a test tube. Two drops of the Molisch reagent (a solution of -napthol in 95% ethanol) was added. Then poured slowly into a tube containing two ml of concentrated sulfuric acid so that two layers form.||The formation of a purple product at the interface of the two layers.
|Carbohydrates are confirmed|
Prof. Imran Khan
Riccia Systematic Position
Riccia belongs to the family Ricciaceae of the order Marchantiales. Majority of the species of this genus are terrestrial but some species are aquatic as these are found growing actually in the water. The following seven species have been commonly reported from the North Western Himalayas and the Punjab plains in Pakistan:Riccia robusta;R. melanospora; R, cruciata; R. sanguinea,’ R. himalayansis; R.pathankotensis, Riccia robusta; R sanguinea and R. pathankotensis are very common in the Punjab plains found growing on the moist soil in places like river beds, banks of rivers and canals, and along the streams.
Riccia is a thallose liverwort in which the vegetative plant, which is a gametophyte, generally forms rosettes due to the crowded growth of the thallus lobes this crowded growth of the various lobes is due to the repeated dichotomies of the thallus The thallus lobes arc flat growing horizontally on the soil and each lobe has a small not that the apex where the growing point is situated. The lobes are thicker in the middle and gradually become thinner towards the margins. A deep cleft or furrow is commonly present in the middle of each lobe on the dorsal side; the sex organs are found embedded in this furrow. The lobes in Riccia fluitans, which is an aquatic species, are narrow and ribbon-like having repeated dichotomous branches which do not form any rosetts, Numerous unicellular rhizoids are found attached to the ventral side of the thallus, these rhizoids are generally crowded in the middle part of the thallus and are of two types i.e., smooth and tuberculate as in Marchantia. The ventral side also bears scales which are formed of a single layer of cells and are arranged in two rows in the older parts of the thallus while in the younger parts these scales are in one row and in the apical region are crowded below the notch for the protection of the growing point,
INTERNAL STRUCTURE OF THE THALLUS
The thallus of Riccia has a simple structure and is formed of parenchymatous cells which are bounded on both sides by the upper and lower epidermis. Internally the thallus is differentiated into two regions, upper assimilatory region and the lower storage region. The storage region is formed of compactly arranged parenchymatous cells which are either colourless or contain only few chloroplasts, but these cells are rich in starch grains. Some of the cells of the lower epidermis grow out and elongate forming the rhizoids, while certain cells divide and produce the single layered scales. In the majority of species the assimilatory region is formed of vertical rows of cells which are about six to eight cells in height and are separated by large air spaces, the cells of these filaments are rich in chloroplasts as these form the main photosynthetic tissue. The cells of the upper epidermis are also loosely placed having spaces in between them which function as pores through which the underlying air spaces communicate out for the exchange of gases. Some species the assimilatory region is spongy being formed of irregularly placed air spaces which are separated from each other by single layered partitions whose cells are rich in chloroplasts.
Riccia plants, like other liverworts, multiply vegetatively by the decay or death of the Older parts which results in the separation of younger branches, each of which grows into an independent plant. In certain species (R. fluitans) small adventitious lateral branches may be produced from the ventral side of the thallus, these adventitious branches on detachment give rise to new plants, Formation of vegetative reproductive gemma-like multicellular bodies at the apices of rhizoids have also been reported in certain species.
Riccia plants may be monoecious or dioecious depending upon the species. Both the male (antheridia) and female (archegonia) reproductive organs are produced in acropetalous order on the dorsal side of the thallus in the median furrow. In the monoecious species the antheridia are generally produced earlier than the archegonia.
Antheridia are found in a linear row on the dorsal side of the thallus embedded in the median furrow.Each antheridium is a globular structure having a very short insignificant stalk. The wall of the antheridium consists of a single layer of cells and encloses a mass of androcytes or antherozoid mother cells. At maturity the contents of each androcyte are transformed into a typical coiled biflagellate antherozoid. When the antherozoids are produced the original walls of the androcytes become gelatinous thus producing a mucilaginous mass in which the antherozoids float freely. The antherozoids are released in the surrounding water by the bursting of the antheridial wall and then these swim freely in the water.
DEVELOPMENT OF THE ANTHERIDIUM
Each antheridium develops near the apex from a superficial cell which divides transversely into a lower basal cell and an outer cell. The basal cell divides further producing the basal part of the antheridial stalk which remains embedded in the thallus tissue. The outer cell divides transversely producing a row of four cells, The two lower cells of this row by further transverse and vertical divisions produce a short stalk of the antheridium. In the upper two cells of the row two vertical divisions take place at right angle to each other producing a group of eight ceils or octants. Periclinal divisions then take place in these octants producing outer jacket initials and inner androgonial initials. The jacket initials by further anticlinal divisions only produce the single layered wall of the antheridium; while the androgonial initials by further transverse and vertical divisions produce a mass of androgonial cells which are enclosed by the single layered wall. The last division in each androgonial cell is diagonal thus producing two androcytes (antherozoid mother cells). The contents of each androcyte are transformed into an antherozoid. As the development of the antheridia is going on the surrounding vegetative tissue grows up and the antheridia become embedded in the dorsal furrow. The thallus continues its growth at the apex while the development of the antheridia is going on, therefore, the mature antheridia are lying some distance back from the apex.
The archegonia, like the antheridia, are also embedded in the mid-dorsal furrow of the thallus and are arranged in acropetalous order i.e., the younge archegonia lie towards the growing point while the older ones are towards the hinder region. Each archegonium is a flask-shaped structure having a multi-cellular stalk. The basal swollen portion of the archegonium is known as the venter and the upper elongated portion as the neck. The wall of the neck consists of a single layer of cells which are arranged in six vertical rows. The canal of the neck contains a row of four neck canal cells and is closed at the tip by four lid cells. The wall of the venter is also formed of a single layer of cells which are arranged in several vertical rows. The venter contains a lower larger cell, the egg or oosphere, and a smaller upper cell known as the ventral canal cell. The necks of the mature archegonia protrude out above the general surface of the thallus, When the archegonia are mature the ventral canal cell and the neck canal cells disorganise forming mucilaginous mass which swells by absorbing water and comes out the neck by pushing apart the lid cells thus forming an opening for the entry of antherozoids.
DEVELOPMENT OF THE ARCHEGONIUM
Each archegonium develops from a superficial cell situated on the dorsal side about three or four cells away from the growing point. This archegoniai initial divides by a transverse division into an upper primary cell and a lower primary stalk cell. The primary stalk cell by further transverse and longitudinal divisions produces a short multicellular stalk. ln the primary archegonial cell three excentric vertical divisions take place resulting in the production of three peripheral cells around an axial cell. A vertical division takes place in each peripheral cell resulting in the production of six jacket initials. The axial cell cuts of a small cover cell at the tip.A transverse division takes place in all the cells resulting in the production of a lower and an upper group of cells. The upper group of Peripheral cells divides by transverse divisions only producing the single layered wall of the neck in which the cells remain arranged in six vertical rows. The lower group of Peripheral cells by further anticlinal divisions produces a single layered wall of the venter. In the meantime the axial cell by a transverse division has divided into an upper neck canal initial and a lower central cell. The neck canal initials produce a row of four neck canal cells. The central cell divides Producing an egg or oosphere towards the base and a small ventral canal cell towards the upper side.
Fertilization takes place in the presence of water the antherozoids liberated in the surrounding water swim towards the archegonia, being attracted chemotactically by the mucilage coming out of the archegonia. Several antherozoids may enter a single archegonium but only one of them fuses with the egg for fertilization. The male and female nuclei fuse together producing a single diploid nucleus. The fertilized oosphere secretes a wall and becomes the oospore which develops into the sporogonium. The mature sporogonium in Riccia is of very simple structure. it is globular or rounded in shape and is enclosed in the enlarged venter of the archegonium. This sporogonium is not differentiated into foot, seta and capsule as in other liverworts. The of the mature capsule consists of a single layer of cells surrounding a mass of spore mother cells. The mature sporogonia are embedded in the tissue of the thallus and are visible to the naked eye as small black dots on the thallus. The nucleus of each spore mother cell undergoes meiosis (reduction division) producing four haploid nuclei, and each spore mother cell then divides into four uninucleate parts, each of which is transformed into a single haploid spore. The four spores produced from each spore mother cell remain held together in tetrads for a long time.
The wall of each mature spore is very unevenly thickened and it consists Of three layers, the outer exosporium which is thin, hard and cutinised; the middle mesosporium which is very thick and soft; and the inner endosporium which is membranous. All the spore mother cells in a sporogonium are generally transformed into spores there are no sterile cells or elaters. In certain species few sport mother cells do not produce spores but disorganise producing a mucilaginous fluid, The original wall of the sporogonium disorganises producing a mucilaginous fluid before the maturation of spores. The mature spores are actually enclosed by the outer layer of the enlarged venter which is Often mistaken as the sporogonium wall. The spores are released by the bursting of the wall of the enlarged venter which is comparable to the calyptra of other liverworts The release of spores is delayed for a long time till the decay Of the vegetative tissue which may take even a year or so after the maturation of spores.
DEVELOPMENT OF THE SPOROGONIUM
The oospore increases very much in size filling the whole cavity of the venter. enlarged oospore then divides by two vertical and one transverse division, all at right angle to each other, producing a group of eight cells or octants. These octants divide further producing a group of about 20-30 cells. Then the periclinal divisions take place in. These ceils resulting in the production of an outer layer of jacket initials or amphithecium and an inner mass of archesporial initials or endothecium. The cells of the amphithecium by further anticline! divisions give rise to a single layered wall of the sporogonium; while the cells cf the endothecium by repeated divisions produce a mass of archesporial cells. When the development of the sporogonium is initiated periclinal divisions take place in all the wall cells of the venter making the venter wall double layered. The venter goes on increasing in size along with the developing sporogonium, and in this way the mature sporogoniurn remains enclosed in the double layered wall of venter. The cells of inner layer of the venter wall the sporogonial wall along with some spore mother cells disorganize producing a viscous liquid.Each spore mother cell produces the four spore the unsual method after the reduction division of its nucleus, spore mass is enclosed in the outer layer and not by the sporogonium wall which has disorganised. As all stated the mature spores are released by the bursting of this wall after a long time when the tissue of the thallus has decayed
GERMINATION OF SPORES
When a spore falls on a suitable place, it germinates by the production of a long tube. This germ tube is produced by the rupture of the outer hard exosporium and mesosporium, and then the endosporium forming the germ tube. The protoplasmic of the flow into the tip of this germ tube which becomes separated from rest of the by the formation of a septum.
ALTERNATION OF GENERATION
The vegetative plant or thallus in Riccia, is a gametophyte, whose cells are haploid. This gamete producesmale(antherozoids) and female (oosphere) gamete surrounding vegetative tissue. The apical growth of the thallus continues and the mature archegonia come to lie near the hinder portion. Sometimes all the developmental stages can be traced in the single thallus due to the production of archegonia in an acropetalous succession, antheridia and archegonia respectively. The union of these gametes or fertilization results in the production of an oospore which is diploid. The oospore develops into the sporogonium or the sporophyte which represents the asexual stage as it produces the spores asexually. The spores are haploid as these have been produced after the reduction division in the spore mother cells. The spores germination give rise to the gametophyte. For the completion of the whole life cycle the gametophyte produces the sporophyte, this sporophyte produces the gametophyte again, and these two generation regularly alternate with each other.
The root may be defined as the cylindrical plant organ which is devoid of chlorophyll, bearing no buds or leaves, and tending to grow downwards away from light. It develops from radicle part of the embryo. The main functions of roots are anchorage and absorption of food from the soil. The root also perform certain special functions, e.g., store food, absorb moisture from air, provide shelter to nitrogen fixing bacteria, provide extra support to the plant, for which the roots undergo various types of modifications.
Generally, the roots are positively geotropic and negatively phototropic i.e., they grow downward into the soil and away from light. They are also Positively Thermotropic and exhibit Positive Hydrotropism, i.e. they bend in the direction of temperature that is most favourable for the growth, and have a tendency to grow in the direction of moisture supply.
When a seed germinates, the embryonal root (radicle) gradually elongates and forms the Primary Root. The primary root may give off branches, the Secondary Roots which in turn branch off to produce Tertiray and Quarternary Roots.
In dicotyledonous plants the primary root becomes the main root and is termed as a Tap Root. Monocotyledonous plants generally, lack tap root. In these plants the root formedfrom the radicle is short lived and from the base of the stem strong and vigorous roots develop. These roots are known as Adventitious Roots (roots developing from or the plant other than the radicle). In some members of Poaceae (grasses), additional embryonal roots known as Seminal Roots arise from the base of the radicle. These roots come out just after the radicle during germination.
A root, whether tap or adventitious, have the same different regions. Each root tip possesses a protective covering, the Root Cap. The root-cap protects the actively dividing cells and controls the direction. Root-cap is absent in aquatic plants. Below The root-cap, Zone of Cell is present this zone consists of meristelnatic cells (actively dividing cells). This region gradually passes into Region of Elongation. The cells of this region are columnar and are slightly thick walled. This region in turn merges into Region of Maturation. The cells of this region has root-hairs, which are extensions of epidermal cells. The cells of this region starts differentiating and permanent tissue of the root is produced, This region gradually passes into Mature Zone where the differentiation of the cells occur and tissues like Epidermis, Cortex and Stele can be recognized.
The roots and its branches together constitute the Root System.
Two main types of root systems are found in plants.
- Tap Root System
- Adventitious Root System
Tap Root System:
In this the root developing the radicle persists throughout the life of the plant. Such root is Tap Root or Primary Root. This root branch off to produce Secondary, Tertiary and Quaternary branches. The primary root along with subsequent branches constitutes Tap Root System.
The tap root system is of two types:
Racemose tap root system:
The primary root continues to grow and penetrates the soil to considerable depth and is very prominent. The secondary and tertiary roots are smaller as compared to the primary root. The older secondary branches lie close to the soil surface while the younger secondary branches are present near the tip portion of the primary root. This type of root system is found in deep-feeding dicots, e.g., Oak. Such plants are known as Deep-Feeders.
Cymose tap root system:
The primary root persists throughout the life of the plant but does not go deep into the soil and stops its growth after sometimes. Secondary roots developing from primary roots are quite strong but they also invade upper layers of the soil like primary root. This type of root system is found in surface-feeding plants. The plants having this type of root system are called Surface-Feeders.
Modifications of Tap Roots
In many plants the tap roots may get swollen due to storage of reserve food material in them. The stem proper in these modifications is very much reduced. A part of the hypocotyls may also be involved in storage of food. Due to storage of food the tap roots assume various shapes which determine a particular type of root.
Three main modifications are recognized:
(i). Conical Tap Root:
This root is broad at the base and gradually taper towards the apex, e.g Carrot, Radish.
(ii). Napiform Tap root:
The root is very much swollen above and abruptly tapers towards its lower end, as in Turnip. In Titrnip the swollen portion is mostly hypocotyl while the narrow portion is the root proper. In Beet, swollen portion is contributed by the hypocotyl and the root.
(iii). Fusiform Tap Root:
The tap root assumes a shape of a spindle, i.e., swollen in the middle and tapering towards the ends, e.g., English Radish. In English Radish the upper and middle portions are hypocotyl and lower part is root proper.
Special Types of Tap Roots
(i). Nodulated roots:
These roots are characteristics of the members of the family Leguminaceae. The root system resemble a typical tap-root system except for the presence of small globular swellings mostly restricted to secondary roots. These are known as Nodules or Tubercles. These provide shelter to nitrogen fixing bacteria.
(ii). Buttress roots:
These are laterally compressed and vertically elongated roots that provides extra support to stem, e.g., in Almond plants.
Adventitious Root System:
The adventitious roots are those roots which are not developed from the radicle but are formed from any other part of the plant. Adventitious roots arising from any part of the plants together constitute a system called Adventitious Root system.
Modifications of Adventitious Roots:
As compared to tap roots the adventitious roots undergo more diverse modifications. These modifications provide some advantage to the plants.
Different modifications met among the adventitious roots are as follows:-
(i) Fibrous: These are hair-like roots present in the form of clusters and these arise from the base of the stem (wheat), from nodes (grasses–Cynodon dactylon) or from leaves (Bryophyllurn).
(ii) Stilt Roots: These arise from the first few nodes of-the stem and run obliquely towards the soil surface. These help the plant to fix it more firmly in the soil, e.g., in Maize, Sugar-cane.
(iii) Prop or Pillar Roots: these roots arise from stem branches and grow vertically downward. These roots increase In girth with the increase in girth of branches. These roots provide support to the plant. In Banyan, these roots are quite thick and look like pillars.
(iv) Pneumatophores or Respiratory roots are found in Mangrove Plants, i.e., such plants which grow in marshy places. The waterlogged soil does not contain air. Special roots arise from the underground roots which have tiny pores called Pneumatophores through which the roots take oxygen for respiration.
(v) Epiphytic Roots: Such roots are found in some epiphytic orchids. These roots possess special spongy tissues at their apices. The tissue is termed as Velamen. It has the capability of absorbing and retaining the moisture so these roots help in absorbing Inoisture from the air.
(vi) Climbing Roots: Some plants have roots which twine around the support liketendrils, e.g., in sonle species of FiC11S and Hcdera helix.
(vii) Clinging Roots: These roots penetrate into the cracks and crevices of the support and hold the plant firnlly, e,g. in Betel plant and Epiphytic orchid species.
(viii) Assimilatory Roots: These roots arc green due to presence of chlorophyll and can perform photosynthestis.
(ix) Parasitic roots: These roots are produced by parasitic plants and thesepenetrate into the food channels of the host plant and draw food for the plant, e.g., in Cascuta.
(x) Reproductive roots: In many plants adventitious buds develop on roots. If these are separated and put into the soil, they establish new plants, e.g., in Dhalia, sweet Potato.
(xi) Floating roots: In some aquatic plant the roots ari.se from the nodes. These roots are spongy in nature and look like a cotton ball. These roots provide buoyancy and help the plant in floating.
(xii) Root Tubers: In som plants the underground adventitious roots become tuberous due to accumulation of food in thenl. These are called root tubers, e.g., in sweet Potato.
(xiii) Fasciculated roots: In some plants, e.g., in Dahlia and Asparagus, adventitious roots occur in a cluster and swollen. These are called fasciculated roots.
(xiv) Nodulose Roots: In some plants apices of the adventitious roots become swollen due to storage of food and appear like beads. Such roots are called nodulose roots, e.g., in Costus speciosus.
(xv) Annulated Roots: In this type, the roots give an appearance of, as if discs have been arranged in stacks, e.g.,in Ipecac.
(xvi) Contractile Roots: Certain plants with underground stems possess special roots that can contract and move the rhizome, bulb or corm more deeply into the soil, e.g., Gladiolus and Polygonatunt.
Chick Embryo Development
The chick egg has different accessory coverings around it, which are secreted, by the female reproductive tract. The following steps occur during the chick embryo development.
Fertilization takes place when the egg is entering the oviduct. Therefore, fertilization is internal. The shell is formed around the egg when it passes through the shell gland (uterus).
After the egg is laid, the development stops unless the temperature of the egg is kept nearly up to the body temperature of mother. The eggs can also be incubated artificially by regulating the temperature between 36-38°C. At this temperature development completes on 21st day and the egg is hatched.
Immediately after fertilization, a series of mitotic divisions occurs in the true egg (the so-called yolk of the egg). This is called cleavage. In chick, the cleavage occurs only in a disc-like portion of active cytoplasm present at the surface of the yolk. That is why it is called discoidal cleavage. First two divisions are vertical. The third division is horizontal which separates the disc-like cytoplasmic portion from yolk. After this, the divisions become irregular and many cells are formed. Each cell is called blastomere.
As a result of cleavage, a circular disc-like mass of cells called blastoderm is formed over the yolk. This mass consists of two or more layers of closely packed cells. The cells in the centre of disc are smaller while cells at the periphery are larger and flattened. Embryo at this stage is called morulla.
The Morula is short lived and soon changes into Blastula. Now the blastoderm splits into two layers; the upper epiblast and the lower hypoblast. The cavity between these two layers is called Blastocoele. And soon after Segmental cavity appears between hypoblast and central area of yolk due to detachment of cells from it. Now two spaces are formed, one between epiblast and hyponlast and second between hypoblast and yolk. The peripheral area of blastoderm where cells are still attached to the yolk is called zone of junction. The embryo is now called blastula.
Formation of germ layers (ectoderm, endoderm and mesoderm) by rearrangement of cells is called gastrulation. Epiblast is the presumptive ectoderm and mesoderm whereas hypoblast is the presumptive endoderm. The hypoblast grows outward around the yolk and form endodermal lining. A pool of fluid develops between central cells of hypoblast and yolk. Thus the blastoderm is raised of from the centre. At this time the central area of the circular blastoderm looks translucent (seeing from upper side) and is called area pellucida, whereas its peripheral area (zone of junction) looks like a dark ring and is called area opaca.
Now a midline thickening called primitive streak is formed on the epiblast because of inward migration of cells to form mesoderm below. This streak is formed at medial region (central region) to caudal end (posterior end) and grows in length rapidly. As a result, shape of the blastoderm is changed from circular to pear-shape. At the cephalic end (anterior end) of the primitive streak, an aggregate of cells form a thickening called the primitive node or Hensen’s node or notochordal cells. The inward migration of cells from epiblast to hypoblast continues and primitive streak changes into a groove called primitive groove. The thickened margins of primitive groove are called primitive ridges. Embryo is now called gastrula.
The cells begin to push in from the Hensen’s node to form a rod-like structure called notochord in the midline beneath the ectoderm. Notochord is visible in the chick embryo of 18 hours. The notochord is committed to form the backbone.
The marginal area (area opaca) where the germ layers (ectoderm, mesoderm and endoderm) are peripherally merging with the yolk is called germ wall. The cavity between yolk and endoderm (which is first called gastrocoele) is now called primitive gut.
The dorsal mesoderm also form group of cells called somites, which are visible in 25-26 hours embryo. Mesoderm found at the periphery of embryo is called lateral plate mesoderm. It splits into two sheet-like layers; the upper somatic mesoderm and the lower splanchnic mesoderm. The cavity between these two layers is called coelom.
On the dorsal surface of gastrula, a band of ectoderm becomes thick and is called neural plate. It is visible in embryo of 18 hours. At 21-22 hours, the neural plate folds and a neural groove is formed in the mid-dorsal line. This folding of neural plate is clearly visible at 24 hours. The embryo is now called neurula. The anterior end of the groove is widest and is the future brain whereas the rest of the portion forms spinal cord in future. Now the neural plate sinks down and the margins of the groove called neural folds grow towards each other and meet in the mid-dorsal line. As a result, the neural groove is converted into neural tube. The cavity inside the neural tube is called neurocoele and the small openings at its both ends are called neuropores. The process of formation of neural tube is called neurulation. The neural tube develops into central nervous system of chick.
POINTS TO REMEMBER in Chick Embryo Development
|Ectoderm||forms skin and nervous system|
|Mesoderm||forms circulatory system, reproductive system etc.|
|Endoderm||forms digestive system and respiratory system|
|Notochord||Replaced by backbone|
|Neural tube||forms brain and spinal cord|
|Somatic mesoderm||forms the future body wall|
|Splanchnic mesoderm||forms circulatory system and future gut wall|
Adiantum Taxonomic Position
Adiantum is widely distributed fern with 200 known species. It grows in mild climate. Moist and shady places are liked by Adiantum as habitat.
Morpholigical features of Adiantum (External Structure)
Body of Adiantum can be divided into root, stem and leaves.
The stem of Adiantum is underground, so it is called as rhizome. It does not grow deep inside the soil. Its rhizome grows horizontally near the soil surface. Scales, called palea covered the surface of rhizome.
Leaves of Adiantum are called fronds. These leaves are large, about 4-6 inches in length and are bipinnately compound. Leaflets of first order are called pinnae and leaflets of second order are called pinnules. Main axis of leaf on which leaflets are produced is rachis. Rachis is of black color and shiny. Due to this characteristics color and shine of rachis, Adiantum is also known as Maiden hair fern.
Roots are produced from under side of rhizome. These are adventitious roots.
Anatomy of Adiantum (Internal structure of Adiantum)
Anatomy of Rhizome
Rhizome is wavy in outline. Outermost layer of rhizome is epidermis that is composed of thin walled cells. Outer to this, thick cuticle is present. Beneath the epidermis, well developed cortex is present. Cortex is formed by parenchyma cells with intercellular spaces. In some species of Adiantum, beneath the epidermis, there is a layer of sclerenchyma cells (hypodermis). In other species, sclerenchyma cells are scattered among the parenchyma cells in cortex region. Internal to cortex there is well developed stele. An outer endodermis is present just beneath the cortex. Then there is outer phloem beneath the outer endodermis. Inside the outer phloem, xylem tissue is present. Then there is inner phloem and inner endodermis respectively. Centre of rhizome is occupied by pith.
Anatomy of Adiantum Leaf (Internal structure of Adiantum leaf)
Transverse section of petiole of leaf is almost round in outline. Outermost layer is epidermis. Next to epidermis is hypodermis, composed of sclerenchyma cells. Then there is gound tissue of parenchyma cells and xylem and phloem.
Leafblade is covered with epidermis from both sides, upper epidermis and lower epidermis. Stomata are present in lower epidermis. Epidermis also contains chloroplast and is covered with thin cuticle layer. Mesophyll cells are limited in extent, therefore epidermis performs major role in photosynthesis. Centre of leaf is occupied by xylem and phloem. Phloem faces the lower epidermis and xylem faces the upper epidermis. Completer vascular tissue is surrounded by sheath of sclerenchyma cells.
Anatomy of Adiantum Root (Internal structure of Adiantum Root)
Outermost layer is epidermis that surrounds cortex region. Cortex contains sclerenchyma cells. Beneath the cortex well developed thick walled cells form endodermis. Endodermis also contain casparian strip, which checks the movement of water and minerals. Stele is protostele (without pith). Just outer to stele and beneath the endodermis there is a layer of parenchyma cells called pericycle.
Reproduction of Adiantum (Life Cycle)
Life cycle of Adiantum contains two generations i.e. sporophyte and gametophyte. Both of these generations are independent.
Sporophyte of Adiantum produces vegetative leaves at start. At later stages, fertile leaves also start producing along with vegetative leaves. Fertile leaves produce sori on their underside. Sori are group of sporangia. These sori are covered with a flap of tisse called false indusium.
A mature sporangium is flattene, spherical or ellipsoidal. It consists of a stalk and upper swollen portion called capsule. Capsule is covered with single layered wall. Wall consists of two portions Annulus and Stomium. Annulus portion contains cells with thick radial and inner tangential cell walls. Stomium consists of cell with thin cell walls. This is the site for bursting of sporangia. Inside sporangia, spores are produce by meiosis of spore mother cells. Many spores are produce inside sporangia. Spore wall contains two layers exine and intine.
When spores get mature, the wall of sporangia burst. Sporangium becomes dry, so the cells of annulus region contracts which exerts pressure on stomium cells. Stomium is weak region of wall of sporangia, so sporangia get burst from this region. Bursting of sporangia caused the dispersal of spores. After falling on suitable place, spore germinates. During germination, exine of spore bursts and intine elongate into a tube like structure. The apical portion of tube give rise to new generation of Adiantum the gametophyte generation.
Gametophyte of Adiantum:
Gametophyte of Adiantum has heart like shape. It has a notch, where growing point reside. Gametophyte of Adiantum is many cell thick from centre and only one cell thick at margins. Rhizoids are produce from underside of Gametophyte for anchorage and absorption of water and nutrients. Gametophyte contains chloroplast, so carried out photosynthesis. Gametophyte is independent. Two kinds of organs antheridia and archegonia are produce on gametophyte.
Archegonia is flask shaped structure with two portions i.e. ventre and neck. Ventre contain egg while neck contains neck canal cells. Antheridia are globose structures, in which many antherozoids are produced. Antherozoids when get mature has two flagella for movement in water.
Antherozoids after releasing from antheridia travel through water chemotactically towards archegonia. Antherozoids fertilize the egg inside archegonia. Resultant zygote develops into embryo. Embryo starts divisions to form sporophyte. Sporophyte remains dependent on gametophyte at start but soon it becomes independent.