Obelia

 Subject: Coelenterata : Obelia (sea fur)

Systematic position:- 

• Phylum :- Coelenterata or cnidaria ( Diploblastic, tissue organisation, coelenteron and cnidoblasts)
•  Class:- Hydroids (fixed polyps; medusa with ectodermal sense organs)
•   Order:- Hydroida( Fixed polyps; medusa with ectodermal sense organs)
•    Family:- Campanularidae( cup shaped hydrotheca)
•     Genus:- Obelia ( Free swimming and discoidal medusae)
•      Species:- geniculata (Colourless)

Habitat:- 

• Obelia is a marine, cosmopolitan, polymorphic, colonial and sedentary hydrozoan Coelenterate found attached on the stones, rocks, molluscan shells, ships, weeds, etc. In shallow coastal waters upto the depth of 80 metres.
• It is branched like a tree, so called zoophyte (zoo= animal ; phyte = plant) or sea fur.
• There are many species of Obelia but the most common species is O. geniculata.

Habits :- 

(1) Feeding :- 

• Obelia is carnivores and feeds upon the living insect larvae, small crustaceans and worms.
• Food is captured and paralysed with the help of stinging cells.
• Digestion is partly intercellular and partly intracellular.

(2) Reproduction:-

•  Obelia shows asexual as well as sexual reproduction.
• Asexual reproduction occurs by external budding.
• In Obelia reproductive zooids are meduse which are inside or dioecious but don't show sexual dimorphism.
• Fertilization is external.
• Development is indirect and includes a free swimming planula larva which brings about dispersal.
• Life history of Obelia shows alternation of generation.

(3) Respiration and Excretion :- 

• These occur through general body surface.

Morphology :-

(A) Shape, size , colour and symmetry:-  

• Obelia appears as a network of branched threads giving fur-like appearance, so called sea fur.
• It is about 25-30 mm in height, creamish- white or greyish in colour and radially symmetrical.

(B) Two types of filaments:-

• Obelia colony is formed of 2 types of filaments:-
• (a) Hydrorhizae:- These are horizontal branched which creep over the substratum and fix the colony to the substratum.
• (b) Hydrocauli:- These are upright branches.
• Each hydrocaulus grows in a scorpioid cymose manner.
• Each branch stops growing ends into a zooid and gives rise a new branch.
• Adjoining branches are on alternate sides.
• So it is formed of lower parts of all the true branches and grows in a zig zag manner.
• Each side branch and main hydrocaulus end into a terminal bud which later forms a polyp.

(C) Coelenteron:- 

• Coelenteron also called gastro-vascular cavity, Is the central cavity running through both types of filaments.
• It is bounded by 2 coats:-
• (a) Coenosarc:- It is inner and living coat.
• It is formed of two layers:-
• Inner gastrodermis lining the Coelenteron, and outer epidermal.
• Between the two cellular layers is a non- cellular and gelatinous mesoglea.
• (b) Perisarc :- It is outer and non-living coat.
• It is chitinous in nature and is secreted by myoepithelial cells is epidermis.
• In early stages, it is in contact with Coenosarc but later two are separated by a fluid-filled space  except at certain points.
• It is supportive and protective in function,so acts as exoskeleton.
• At the base of zooids and near the bends  of the hydrocaulus, Perisarc forms ring like grooves, called perisarcal annuli, which give flexibility to it , so it sways in water to withstand the wave action.

Polymorphism in Obelia :-

• Polymorphism us the phenomenon in which  a colonial organism is formed of many types of organisms (called zooids in coelenterates) which Differ in structure and function for the benefit of whole Colony.
• Obelia is a polymorphic (trimorphic) Coelenterate as the colony has three types of zooids which through are homologous zooids but are specialized in their morphology and physiology. 

So polymorphism is associated with division of labour.

(1) Hydrants or polyps ( nutritive and protective zooids)

(2) Blastostyles or Gonozooids(budding zooids)

(3) Medusae or Gonophores( sexual zooids)

(1) Hydranth or Polyp:-

(i) Position :-

•  These are more numerous in number than other zooids.
• These are distributed throughout the colony and are terminal in position.

(ii) Structure :-

(a) External structure:-

•  Polyp or Hydranth is a hollow and cylindrical zooid which is proximally continuous with the hydrocaulus.
• It's free distal end is produced into a conical process called oral cone or manubrium or hypostome having a termination and circular mouth.
• Oak cone is about one third of total length of zooid.
• Arising from the base of Hydranth, there is a ring of 24-30 solid, tapering and fillifo tentacles, each having batteries of  stinging cells.
• The tentacles are radially arranged to capture the food from all directions.
• Hydranth is protected by a cup-shaped and transparent cover called hydrotheca.
• So Obelia belongs to sub order Thecata while the hydranths of Bougainvillea and Tubularia have no theca, so placed in sub-order Athecata.
• It is formed by the expansion of Perisarc.
• Hydrotheca is open at the tip so Hydranth can be protruded.
• At its lower end, hydrotheca is produced inward to form a centrally- perforated circular shelplf which keeps a limit on the retraction of polyp.

(b) Coelenteron:- 

• Mouth of Polyp leads into a small cavity of manubrium, sometimes called gullet, which opens in the Coelenteron of body of Hydranth which in turn is continuous with that of hydrocaulus.

(c) Histology :- 

• Histologically , living Coenosarc of Hydranth is formed of 2 layers with a non-living and gelatinous mesoglea in between.
• So Obelia is a Diploblastic animal.

(A) Epidermis:- 

• It is outer and thinner layer.
• It is formed of 5 types of cells:-

(1) Myoepithelial or epitheliomuscular cells:-

• Position and structure:- 
• These forms the bulk of epidermis.
• These are colonial-shaped with their broader side outward.
• Their broader sides meet and form a continuous layer except when interrupted by sensory cells and cnidoblasts.

Each Myoepithelial cell is differentiated into 2 parts:-

Epithelial part and muscular part:-

• Epithelial part is outer and nucleated part having vacuolated cytoplasm, a layer of secretary granules in its outer part and two supporting fibrils called tonofibrils.
• Muscular part is inner and is produced into two or more tail or muscle processes having a contractile myoneme formed of myofilaments.
• Myonemes of these cells are arranged along the longitudinal axis so forming a kind of longitudinal muscles which when contract, make the  Hydranth small and thick.
• Functions:- These are protective, secretory and contractile in function.

(2) Interstitial cells:- 

Position and structure:- 

• These are groups of cells present in the spaces between the inner narrow ends of Myoepithelial cells.
• These are mainly present in the basal part tthe polyp.
• Each is spherical-shaped, about 5micrometer, with clear cytoplasm and nucleus having 1 to 2 nucleoli.
• Position:- 
• These act as reserve or undifferentiated cells which can differentiate into any type of cell depending upon their requirements, these are called totipotent cells.
• So these help in regeneration, budding and reproduction.
• Breton showed that these can renew cells within 45 days 

(3) Cnidoblasts:-

Position and structure:- 

• Cnidoblasts ,also called nematoblasts or stinging cells, are present among the Myoepithelial cells on the hypoblast and tentacles.
• These are peculiar cell-type of Coelenterates which are also called cnidarians while their  study is called Cnidology.
• These form ring-like groups called annular batteries on the tentacles.
• Each cnidoblast is pear shaped and about 16 micrometer in size.
• It has contractile cytoplasm, eccentric nucleus, a sensory trigger hair called cnidocil at it's free distal end and a sac like nematocyst inside.

• A namatocyst is differentiated into two parts :- 
• Capsule and thread tube.
• Capsule is oval-shaped, double walled , chitinous sac externally covered by a lid or operculum.
• It is filled with a poisonous fluid called hypnotoxic (a mixture of proteins and phenol).
• Thread tube is differentiated into basal butt and distal thread tube proper.
• Butt is again formed of proximal wider and funnal shaped part with no spines, called shaft, and distal and tapering part with three large-sized stylets or barbs and three spiral rows of spines or barbules, called spinneret.
• Thread tube proper is long tube of uniform diameter which ends into a hypodermic needle.
• Such nematocyst of Obelia are called penetrants or stenoteles.
• On the outer surface of capsule, there are a number of refractile rods, each giving rise to a contractile fibril extending upto the base of cnidoblast.
• Another coiled thread, called lasso, also extends the outer surface of the capsule to its base.
• These both prevent the protrusion of capsule.

Function:-

•  when the stinging. Cells are undischarged,spines and stylets of the butt are inward directed and thread tube proper is coiled around the butt as a watch spring.
• When stimulated, stimulus is first received by cnidocil and is conducted to contractile cytoplasm, the contraction of which causes the eversion of thread tube, so the spines and styles are now outward directed while the hypodermic needle is injected in the prey to release the hypnotoxin, which paralyses or kills the prey.So the stinging cells of Obelia are called penetrants or stenosis.
• It is now proposed that discharge of nematoblasts is probably due to rapid increase in Calcium level and intracapsular pressure inside the capsule of these cells.
• Their coordinated discharge is controlled by neural connections .
• So the nematoblasts are cells for offence and defence and are involved in food capturing and protection.
• Nematoblasts are independent effectors.
• These are stimulated by partly mechanical and partly Chemical stimuli.
• Once discharged, these are never withdrawn so these move in the Coelenteron and are digested.
• New nematoblasts are regenerated from interstitial cells in about 48 hours in the basal parts of the polyps .

4) Sensory cells:-

Position and structure:- 

• These are present among the Myoepithelial cells of epidermis, especially in hypostome and tentacles.
• Each is a columnar and neuro-sensonry cell.
• It has a sensory hair on other side and a few modulated nerve fibres on inner side which join the nerve fibres of nerve cells.

Functions:- 

• These are sensitive to externally stimuli like touch, temperature, light , Chemicals tc so also called receptors.

(5) Nerve cells:-.

Position and structure:- 

• Nerve cells, also called protoneurons, from an epidermal nerve net on outer border of mesoglea . 
• These are more developed in the tentacles.
• Each is an irregular cell and is differentiated into a central nucleated part called cell body and a number of nerve processes called neuritis .
• Depending upon the number of neurites, nerve cells may be bipolar or multipolar.
• But neurites are not differentiated into axon and dendron so nerve impulse can travel in any direction so form diffuse type nervous system.
• Neurites of adjacent nerve cells coil around one another to form a net , so called plexiform nervous system.
• But there is no continuity of their cytoplasm and nerve impulses are conducted only through synapses, so called synaptic nervous system.
• Function:- These form a part of sensory-neuro-motor system and conduct the nerve impulses.

(B) Gastrodermis:- 

• It is inner and thicker .
• It forms the bulk of body wall and is digestive, circulatory and muscular in function.

It is formed of following five types of cells:-

(1) Myoendothelial or Endothelio-muscular cells:-

Position and structure:- 

• These form the bulk of Gastrodermis .
• Each is long and columnar cell which is differentiated into 2 parts:-
• Endothelial part and muscular part.
• Endothelial part is inner and  nucleated part having vacuolated cytoplasm and either pseudopodia  or 2 flagella .
• Their inner free ends also have microvilli to absorb the digested food from the coelenteron.
• It's muscular part is outer and is produced into a muscle process having contractile fibrils called myonemes.
• Their myonemes are arranged perpendicular to longitudinal axis of hydranthand act as circular muscle fibres.
• When contract, these make the polyp long and thin .
• Around the mouth these muscle processes act as sphincter.
• Function:- These are nutritive, absorptive, muscular and circulatory in function.

(2) Gland cells:- 

Position and structure:- 

• These are modified Myoendothelial cells present only on manubrium and body of hydranth while these are absent on the tentacles.
• Each is columnar-shaped like the Myoendothelial cell but is smaller in size and lacks the muscle process.

Function:- 

• These secrete either mucus (those in manubrium and called mucous gland cells) or digestive enzymes ( those in the body and. Called enzymatic gland cells) so help in ingestion and intercellular digestion of food in coelenteron.

(3) Interstitial cells:-

• These are present in groups in the spaces between the outer ends of Myoendothelial cells.
• These resemble those of epidermis in their structure and function.

(4) Sensory cells:-

• These are present between the Myoendothelial cells of Gastrodermis.
• These resemble those e epidermis in their structure and function except that are less in number.

(5) Nerve cells:- 

• These form a gastrodermal nerve net on the inner border of mesoglea.
• These also resemble those of epidermis in their structure and function but are less in number
• Epidermal and gastrodermal nerve nets are interconnected by nerve fibres.

(C) Mesoglea:-

• Mesoglea , also called mesenchyme, is the middle homogeneous, non-cellular and gelatinous layer of uniform thickness.
• It is joint secretary product of both epidermis and Gastrodermis.

It helps in following functions:-

• It acts as middle lamella and provides binding surface for the attachment of muscle processes of both epidermis and Gastrodermis.
• It is elastic in nature and helps in extension of hydranth .
• It acts as the skeleton so provides mechanical support to hydranth

Plasmodium Vivax ( the malarial parasite)

Subject: Protozoa:-  Plasmodium Vivax ( the malarial parasite)

Systematic position:- 

• Kingdom:- Protists (Acellular eukaryote)
•  Phylum:- Protozoa (Heterotrophic and undergoes fission)
•   Super-Class:- Sporozoa (No organelles of locomotion)
•   Class- Coccidia (Mature trophozoite is intracellular)
•     Genus- Plasmodium (True malarial parasite)
•        Species- vivax ( causes benign tertian malaria as erythrocytic schizogony is completed in 48 hours)

Introduction:-

• Malaria is a widely known human disease. It is caused by infection with a pathogenic Protozoan parasite of blood, the plasmodium, whose 60 known species cause malaria in man and other animals.
• Four species of Plasmodium are known to cause different types of malaria fever in man.
• They are P. vivax , P. malariae and P. falciparum. Female Anopheles mosquitoes transmit Plasmodium from person to person , thus serving as carrier or vector host.
• It derives certain proteins from human blood and are important in its egg formation.
• Male feeds upon plant juices.
• P. vivax is mostly widely studied of Plasmodium. 
• Hence, the following description is mainly based upon it.

Distribution:-  

• Plasmodium vivax is cosmopolitan parasite.
• It is wide spread in tropical and temperate countries.
• Some species infect migratory birds.

Habitat:-

• Plasmodium is endoparasite, found in the blood of man:-
• Intracellular in R.B.Cs and parenchymal cells of liver.
• Also found in the alimentary canal and salivary glands of female Anopheles Mosquitoes.

Habits:-

• Being intracellular parasite, it depends for all vital activities on host.

Life cycle:-

• Life cycle of Plasmodium is complicated.
• It comprises several stages and requires two hosts for completion- a primary, definitive or principal host and a secondary, intermediate or vector host
• Such a two host life cycle is called digenetic.
• In human species of Plasmodium, intermediate host is always female Anopheles. 
• In human body, the parasite multiplies asexually, while is female Anopheles, it undergoes a sexual cycle followed by an Asexual multiplication called sporogony.

Asexual cycle and schizogony in man:- 

• The adult phase of Plasmodium is called trophozoite. 
• It occurs in R.B.Cs of man but before invading the R.B.Cs the paradises invade liver cells and undergoes extensive asexual multiplication by Schizogony. The life cycle of Plasmodium in man consists of two phases:-

(1) Exoerythrocytic or hepatic Schizogony

(2) Erythrocytic schizogony

Exoerythrocytic Schizogony:- 

(a) Inoculation or Infection:- 

• A healthy person acquires infection when a female Anopheles Mosquito, containing infective stage of parasite in their salivary glands.
• They feed upon human blood which they such, usually during night, by means of their piercing and sucking mouth parts.
• The mosquito punctures the host's skin by its proboscis and first introduces some saliva into the wound.
• Saliva contains an anticoagulant which prevents clotting of blood during sucking.
• This saliva carries thousands of sporozoites into the human blood.

(b) Structure of Sporozoites:- 

• A sporozoite has a spindle shaped, slightly curved or sickle shaped body tapering at either end .
• It is uninucleate organism, measuring 6 micro to 15 micro in length and 0.5-1 micro in width 
• Each has a covering of firm, but elastic pellicle, containing longitudinal contractile microtubules for its wriggling movements.
• It's Anterior end is marked by a minute aperture, the micropyle, followed an apical cap of connective rings.
• A pair of long and slender secretory organelles open into the cap 
• These is a single vesicular nucleus with a centrally located nucleolus and a mitochondrion with tubular cristae, scattered endoplasmic reticulum is also present.

(C) liver Schizogony:- 

• Within half an hour or so after inoculation into human blood, all Sporozoites disappear from the blood.
• As they reach into the liver with blood circulation, they make their way out from Blood capillaries and enter into the liver cells.
• Here they multiply asexually by Schizogony. 
• Liver Schizogony has two phases:- pre- erythrocytic and exo- erythrocytic.

(1) Pre- erythrocytic phase:- 

• In the liver cells, the parasite become spherical and are known as the cryptoschizoites.
• In the liver cell, the cryptozoite feeds on cytoplasm and grows into a rounded structure, the pre-erythrocytic schizont also known as cryptoschizont.
• The later divides into about 1000 minutes cryptomerozoites by a special type of fission called schizogony ( multiple fission).
• This Schizogony is called exo- erythrocytic, because it occurs away from blood R.B.Cs. 
• The schizont and the liver cell break up and liberate cryptomerozoites into the liver sinusoids.
• From the sinusoids, some of these cryptomerozoites invade fresh liver cells to continue Exoerythrocytic Schizogony, while other remain in blood stream and invade R.B.Cs to initiate the erythrocytic cycle.

(iii) Exo-erythrocytic phase:-

• Cryptomerozoites enter fresh liver cells to become metacryptozoites or phanerozoites. 
• The later are of two types- micrometscyptozoites and macrometacryptozoites.
• Each micro-metacryptozoite undergoes Schizogony, producing 100 to 10000 minute micro-metacryptozoite which pass into blood stream and invade R.B.Cs for fresh erythrocytic phase.
• Schizogony in each macrometacryptozoites, on the other hand, produces only about 64, relatively large macrometacryptomerozoites which invade fresh liver cells to continue Exo-erythrocytic cycle.
• Pre and exo-erythrocytic phases of parasite remain immune to the resistance of host and parasitea are not susceptible to the action of any anti-malarial drug.
• Also little damage to the host is done during these stages 

(iii) Pre-patent and incubation periods:- 

• The pre- erythrocytic phase is completed in about 8 to 10 days .
• This inverval between inoculation and initiation of erythrocytic phase is called Pre-patent period.
• The period between infection and appearance of first malarial symptom is the incubation period which is about 10-17 days.

2.Erythrocytic Schizogony:- 

• This cycle occurs in R.B.Cs and begins when a cryptomerozoites or micro-metacryptomerozoite enters into an R.B.Cs . 

It includes the following stages:-

(i) Trophozoite stage:-  

• Inside the corpuscle, the parasite become rounded and grow.
• During the growth period it is called trophozoite.

(ii) Signet ring stage:- 

• As the trophozoite grows in size, a large non-contractile vacuole appeara in the centre, pushing the cytoplasm and nucleus to a thin peripheral layer.
• This stage is clinically referred to as signet ring stage as it resembles the signet ring.

(iii) Amoeboid stage:-  

• The signet ring trophozoite developes into an active amoeboid trophozoite.
• Now, the trophocytes starts feeding more actively upon cytoplasm of host R.B.Cs with the help of pseudopodia.
• It secretes out digestive enzymes which liquify, the cytoplasm of R.B.Cs by its partial digestion.
• The haemoglobin is not digested 
• It gets decomposed into a brownish black pigmentz the haematin, which lies in the cytoplasm of trophozoite.
• In about 36 hours, the young trophozoite grows into an adult, occupying almost the entire R.B.Cs.
• Besides plasmolemma, endoplasmic reticulum, mitochondria, food vacuole, Golgi complex, nucleus etc, a concentric structure of unknown significance has been recently observed in this trophozoite by electron microscopy by Garnham, 1966 and Zinska , 1969.
• The host R.B.Cs gets somewhat enlarged and irregular in shape.
• At this time, small red eosinophilic granules appear in the cytoplasm of the host corpuscle which are known as Schuffner's granules.

(iv) Schizont :- 

• The amoeboid trophozoite, after active feeding becomes rounded, grows in size and becomes Schizont.
• It now undergoes Schizogony.
• It's nucleus undergoes repeated mitotic divisions, forming. 12-24 daughter nuclei, which get arranged at the periphery and cytoplasm masses surrounding them.
• Each cytoplasmic mass with one nucleus becomes an oval shaped merozoite.
• They are shorter and thicker than the Sporozoite.
• A part of the cytoplasm of the Schizont is not used in the formation of merozoite.
• This residual cytoplasm contains the haematin and metabolic wastes or toxins produced by the parasites.
• The merozoite arranged themselves around the residual cytoplasm like the petals of rose flower.
• This stage is called rosette stage.
• One complete erythrocytic cycle takes 48 hours in P. vivax.
• The residual cytoplasm and haematin are eaten up by  special cells, the phagocytes in the spleen, kidney and liver.
• The interval between inoculation of Sporozoites into human blood and first attack of the fever is called incubation period.
• Repeated erythrocytic cycles results, not only in intermittent attack of fever, but also in a large scale destruction of R.B.Cs, weakening the patient to a considerable extent.
• In P.vivax, the erythrocytic Schizogony takes 48 hours and therefore the fever recurs rhythmically every third day.
• Destruction of R.B.Cs in erythrocytic Schizogony releases toxins and makes the patient feel chilly.

(v) Formation of gametocytes:- 

• After a number of erythrocytic cycles, some merozoite, invading fresh R.B.Cs, grow not into normal schizont, but into a different kind of rounded form called gametocytes or gamonts.
• These show sexual dimorphism, being of two types.
• The male or microgametocyte is smaller and contains a large diffused nucleus.
• The gametocytes donot divide, but remain as intracellular parasitrs within their host's blood corpuscles, until they either die or are ingested by the vector, in which they continue their Development.

(2) Sexual cycle of Plasmodium in mosquito :-

(i) Infection of mosquito:-

• When a female Anopheles Mosquito sucks blood of the infected person, it receives  R.B.Cs containing different stages of erythrocytic cycle, including gametocytes.
• In its gut, all stages except the gametocytes are digested
• Gametocytes however survive.
• They break the corpuscle and become free in the stomach of mosquito.
• Their becoming active depends upon temperature.
• While the trophozoite and merozoites are active at high temperature (98.6°F) of the human body, the gametocytes need low temperature for further change and therefore, become active only in cold blooded mosquito host.
• The Development of the gametocytes in the mosquito's stomach involves two imo events.

(1) Sexual cycle and

(2)  Sporogony

Sexual cycle:-

(a) Gametogony or Gametogenesis:-

• Gametogony or Gametogenesis means the Development of gametes.
• Male and female gametes are dissimilar. 
• Such gametes are called heterogametes.

Formation of male gametes:-

•  The male or microgametocyte undergoes Spermatogenesis.
• The nucleus of each rapidly divides by meiosis, into 6 to 8 haploid nuclei.
• The later migrate to the periphery.
• The cytoplasm gathers around these nuclei.
• Suddenly each cytoplasmic mass, together with nucleus shoots out from the surface of the microgametocyte in the form of a 20 micro to 25 micro long, whip-like microgametes or sperms.
• This process is called as exflagellation. 
• Soon they become free from the residual cytoplasm and start creeping by lashing movements.

Formation of female gametes:-

• A macrogametocyte forms a single female gamete or macrogamete or ovum.
• It's nucleus casts off one or  two small pieces, which leave the Gametocyte with a bit or cytoplasm.
• This converts the macrogametocyte into a microgamete.

(b) Fertilization:- 

• The megagamete developes a small cytoplasmic projection, the come of reception, on one side.
• The nucleus moves into this cone.
• One male gamete penetrates the female gametes through this cone.
• The nuclei and cytoplasm of the gametes fuse to produce a diploid zygotic nucleus or synkaryon.
• Syngamy is heterogamy  or anisogamy as the uniting male and female gametes are dissimilar.
• Zygotes are formed in the stomach of mosquito about 9 or 10 days after the blood meal.

(iii) Ookinete:-

• The zygote, when formed is rounded and motionless.
• After remaining inactive for sometime, each zygote starts elongating and undergoes certain changes so that, in about 9to 10 hours, it becomes 15 micro to 20 micro long and 3 micro thick, worm-like motile organism called vermicular or Ookinete.
• The later has dense cytoplasm, a single pseudopodium -like blunt extension, one irregular nucleus, mitochondria, ribosomes, microtubules and 2 or more, non-contractile vacuoles.
• The Ookinete pierces through the wall of stomach and comes to rest just beneath it's outermost layer.
• Here , it reassumed sphere shape and soon becomes enclosed inside a cyst, about 8 micro to 10 micro in diameter.
• The cyst-wall is derived partly from zygote and partly by tissues of stomach wall.
• Encysted zygote is called oocyst or sporont.
• Just one or two days after fertilization, 50 or more oocysts appear upon the surface of the stomach of the infected mosquito.

(3) Sporogony:- 

• Each oocyte undergoes asexual multiplication known as Sporogony.
• It's nucleus divides repeatedly by mitosis, forming about 10000 minute daughter nuclei within 2-3 days.
• At the same time ,the cytoplasm developes large vacuoles and takes up a sponge- like structure, in which numerous irregular cytoplasmic developes large vacuoles and takes up a sponge -like structure, in which numerous irregular cytoplasmic mass are formed connected by protoplamic strands.
• Each cytoplasmic mass becomes elongated and spindle shaped.
• Together with its nucleus, it now projects into the adjacent vacuole.
• These spindle shaped bodies are called sporozoites.
• Each sporozoite has tapering ends and a broad middle part containing a single nucleus.
• By their pressure, the oocyst ruptures.
• Floating freely in haemocoel or body cavity, these reach the salivary glands of the host and become lodged in its common salivary duct in large numbers.
• In mosquito, whole sexual cycle is completed with 10-20 days depending upon temperature.
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Some characters of P.vivax:- 

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• Geographical distribution:- Tropical and sub-tropical regions
• Prepatent period:- 8 days
• Duration of erythrocytic cycle :- 48 days
• No. Of metacryptozoites formed per Schizont:- 10000
• Incubation period :-14 days
• Signet ring form in R.B.Cs:- large ring with vacuole and usually one chromatin dot.
• Haematin:- Dark brown granules and rodless
• Schizont:- Larger than normal erythrocyte.
• Gametocyte in R.B.Cs:- Rounded to oval
• Microgametes formed:- 4 to 8
• Duration of mosquito cycle:- 10 days
• Type of malaria:- Benign tertian, death rate low.

Some characters of P.malariae:- 

• Geographical distribution:- Tropical and sub-tropical regions
• Prepatent period:- 7-12 days
• Duration of erythrocytic cycle:-  72 hours
• No. Of metacryptozoites formed per Schizont :- 2000
• Incubation period:-  18-24 days
• Signet ring form in R.B.Cs:- Usually one ring and one chromatin dot.
• Haematin:- Dark brown to black as coarse granules
• Schizont:- Slightly smaller than normal erythrocyte.
• Gametocyte in R.B.Cs:- Oval or circular
• Microgametes formed:- 2 to 5
• Duration of mosquito cycle:- 25-28 days
• Type of malaria:- Quartan, severe.

Some characters of P.ovale:- 

• Geographical distribution:- West Africa and South America
• Prepatent period:- 9 days
• Duration of erythrocytic cycle:- 48 hours
• No. Of metacryptozoites formed per Schizont:- 15000
• Incubation period:- 14 days
• Signet ring form in R.B.Cs:- Usually one ring and one dot
• Haematin:- Dark brown less aboundant coarse granules
• Schizont:- Much smaller than a normal erythrocyte.
• Gametocyte in R.B.Cs:- Rounded or oval
• Duration of mosquito cycle:- 16 days
• Type of malaria:- Ovale or mild tertian severe

Some characters of P. falciparum:-

• Geographical distribution:- Tropical, sub-tropical and warmer temperate regions.
• Prepatent period:- 5-6 days
• Duration of erythrocytic cycle:- 36-48 hours
• No. Of metacryptozoites formed per Schizont:- 40000
• Incubation period:- 12 days
• Signet ring form in R.B.Cs:- Small ring situated at edge of R.B.Cs. sometimes 2 chromatin dots.
• Haematin:- Dark brown coarse granules in a compact mass.
• Schizont:- Smaller than a normal erythrocyte. 
• Gametocyte in R.B.Cs:-Sausage or crescent shaped
• Microgametes formed:- 4 to 8
• Duration of mosquito cycle:- 10-20 days
• Type of malaria:-Malignant tertian, death rate high

PORIFERA : Scypha (sycon)

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 Porifera : Scypha (Sycon)

Systematic position:-

Phylum:- PORIFERA

Class :- CALCISPONGIAE

Order :-HETEROCOELA

Family:-SYCETTIDAE

Genus:- Scypha

Habitat:- 

• Marine, colonial, branched and sedentary sponge of cosmopolitan distribution.
• Attached to rocks etc. Just below low tides upto depth of 100 metres in area with strong wave action.
• Commonly called Urn-shaped (due to base like shape) or crown sponge ( due to presence of a crawn like oscular fringe).
• Commonly found species of Scypha are : S. ciliatum, S. elegans and S. raphanus.

Habits:-

 1.) Locomotion:-  

• Absent due to sedentary mode of life.

2.) Feeding:-

•  Omnivores and holozoic . 
• Feeds upon planktons like protozoans, diatoms, bacteria and dead organic particles. 
• Food is drawn inside the sponge body along with a respiratory cum nutritive water current maintained by constant buy uncoordinated beating of flagella of collar cells.
• Digestion is intracellular.

3.) Reproduction:- 

• shows both asexual and sexual reproduction.
• Asexual reproduction occurs by external budding.
• Scypha is monoecious or bisexual or hermaphrodite but always shows cross fertilization due to protogynous condition.
• Fertilization is internal.
• Development is indirect and include a free swimming and ciliated amphiblastula larva for dispersal.

4.) Regeneration:- 

• H.V. Witson reported very hight power of restorative regeneration is Scypha.

Morphology:-

A.) Shape, size, colour and symmetry:-

•  vase like shape,  
• 20-25mm in height,
•  5-6 mm in diameter.
•  Greyish or light brown coloured and 
• radially symmetrical

B.) External appearance:-

• Body surface is with a regular arrangements of polygonal elevations having groups of needle and spear shaped calcareous spicules so giving bristly appearance.
• These elevations are seperated by narrow grooves having groups of small apertures called dermal ostia or inhalent or incurrent pores which lead into a central cavity, called spongocoel, through a system of interconnected canals 
• The spongocoel opens out by a single, wide and circular aperture called osculum or exhalent or excitement pore present at the distal free end of Scypha.
• Osculum is guarded by a funnel shaped collar of long monoaxon spicules called oscular of, which prevents the entry of other animals inside the sponge body through osculum.

Canal system of Sycon:-

Definition:-

 Canal system also called aquiferous system, is a system of interconnected canals of different types present inside the sponge body.

Components of Syconoid canal system:- Scypha has Syconoid canal system and is formed of following parts:-

Dermal Ostia:- 

• Also called inhalent or incurrent pores.
• These are groups of small circular apertures present in the grooves lying between the polygonal elevations of the body surface.
• These are present in a thin pore membrane which closes the incurrent canal externally.
• Dermal Ostia are surrounded by contractile cells, called myocytes, which regulate their opening and closing.
• These act as mouths for ingoing water current.

b) Incurrent canals:-

•  also called inhalent or afferent canals.
• These are narrow be squarish canals.
• Formed by invaginations of surface ectopinacoderm and end blindly on the inner side just outer to spongocoel.

c) Prosopyles(pros.= Near; Pyle= gate) 

• These are short, narrow canals(each about 5mm) which connect the incurrent canals with the radial canals.
• These are intercellular and not intracellular as in Leucosolenia.

d) Radial canals:-

•  Also called flagellated canals.
• These are wider and octagonal canals.
• Each is externally closed just inner to the polygonal surface elevation while internally opens in the excurrent canal by apopyle.
• It is lined by a layer of flagellated cells called collar cells or choanocyte these are formed by evagination of wall of spongocoel of Asconoid canal system.
• The incurrent and radial canals lie parallel and alternate to each other both vertically and radially.
• The arrangement of these canals is such that each radial canal is surrounded by four Incurrent canals and vice versa

e) Apopyle (app=away; Pyle= gate) 

• Also called internal Ostia.
• These are openings of radial canals into excurrent canals.
• Each apopyle is a large circular aperture in the centre of a thin partition called diaphragm lying between the radial canal and excurrent canal.
• It's size can be regulated by contractile cells, called myocytes, which is surrounded by apopyle and regulate it's opening and closing.

f) Excurrent canals:-

• Also called exhalent or efferent canals.
• These are small , wide chambers in which radial canals open. 
• These are lined by pinacocytes and internally open in the spongocoel by wide aperture called gastral ostium.

g) Spongocoel:-

•  Also called paragastric cavity or atrium or cloaca.
• It is narrow and tubular cavity present in the centre of each branch of Sycon.
• It is also lined by flat and polygonal pinacocytes.
• Spongocoels of different branches are continuous at the base.

h) Osculum:-

•  Also called exhalent or Excurrent aperture.
• It is large circular aperture at the tip of each branch.
• It is guarded by a group of monoaxon, needle or spear shaped spicules which collectively form an oscular fringe.
• It is also surrounded by contractile cells, myocytes, which form a kind of sphincter which regulates it's opening and closing

Physiology of canal system:-

• The flagella of collar cells of radial canals undergo constant but uncoordinated beating and maintain a water current which follows following path:-
• Outside water( Dermal Ostia) -- > incurrent canal ( Prosopyles) -- > Radial canals (Apopyles) -- > Excurrent canals ( Gastral Ostia ) --> Spongocoel (Osculum) --> outside.

This ingoing water current helps in following metabolic functione of a sedentary sycon:-

1. Brings food for nutrition.
2. Brings oxygen for respiration
3. Brings sperms of another sponge for reproduction

The outgoing water current also helps in:-

1. Carries out undigested food for egestion
2. Carries out nitrogenous wastes for excretion.

Histology of Sycon:- 

• Histologically the sponge is diploblastic (develops from two primary germ layers).
• Even body wall of adult Sycon is formed of 2layers :
• A) Dermal layer or Pinacoderm
• B) Gastral later or Choanoderm

A) Dermal layer or Pinacoderm:- 

• It is formed of single layer of large, highly contractile, thin, flat, ectodermal in origin and polygonal cells called pinacocytes.
• These pinacocytes are cemented together like the tiles in a floor.
• Each cell has a nucleus in its central swollen part.
• Dermal layer is differentiated into 2 types:-
• Exopinacoderm:-  which covers the outer surface of the body
• Endopinacoderm:-which lines incurrent canals, Excurrent canals and spongocoel.

• Functions:- It provides protection from mechanical injuries and entry of germs.
• It keeps a limit to semi-fluid mesoglea and prevente it's dispersion in water.
• Due to its contractile nature, it shortens it's sponge body to great extent.

Modifications of Pinacocytes:-

• To perform special functions, pinacocytes are modified into following cell types:-
• Porocytes:- also called pore cells.
• These are thin walled, tubular cells present in the inner lining of incurrent canals.
• These are open at both the ends and have tubular intracellular canals called Prosopyles, which connect incurrent canal to radial canal.
• These are present only in young sponge but are absent in the adult sponge.

Myocytes:-

•  These are elongated, fusiform shaped highly contractile cells which are present around the aperture like dermal Ostia, apopyle and oscula.
• These act as sphincter to regulate the opening and closing of these aperture.
• Scleroblasts:- These are modified pinacocytes which means migrate into mesoglea and form calcareous spicules, so are also called calcoblasts

• B) Gastral layer or Choanoderm:- it is the inner lines only radial canals.
• It is formed of large, loosely arranged and flagellated cells called collar cells or choanocytes.

Structure:-

•  Each choanocytes is an oval or rounded cell having vacuolated cytoplasm, single nucleus and a long , whit like vibratile flagellum on its inner side.
• Flagellum arises from a cytoplasmic granules, called centroblepharoplast, a combination of centrioles and blepharoplast.
• It is connected to a darkly stained chromatin body called parabasal body, present on the nucleus, by a fine fibril called rhizoplast.
• These are endodermal in origin.
• The basal part of the flagellum is surrounded by a thin, transparent and contractile collar formed or 20-30 cytoplasmic processes, called microvilli which are about 0.03 to 0.10 micrometer and interconnected by a fibre like material.

Function:-

•  By constant but uncoordinated beating of their flagella, choanocytes maintain a water current for nutrition, respiration, excretion etc. It also secretes mesoglea.

Mesoglea:-

•  Also called mesenchyme or mesohyl.
• It is middle, transparent, non living and gelatinous layer between the Pinacoderm and Choanoderm of body wall of sponge.
• It's matrix is of proteinaceous nature and is mainly secreted by Choanoderm.
• It is of uniform thickness except inner to incurrent canals and outer to Excurrent canals where it thickens greatly to form Gastral cortex and dermal cortex respectively.
• It also has  many free wandering cells on the basis of which mesoglea is called collenchyma or parenchyma.
• These cells of mesoglea are derived either from Pinacoderm or from Choanoderm and are of 2 types:-
• Scleroblasts:-These are modified pinacocytes which means migrate into mesoglea and form calcareous spicules, so are also called calcoblasts
• Amoebocytes:- These are amoeboid shaped cells and are mainly derived from Choanoderm. 
• These move freely in mesoglea.

On the basis of their function, these are of following types:-

• Collencytes or connective tissue cells :- These give rise fine and branched pseudopodia which collectively form a network. These secrete the collagen fibres
• Chromocytes or Pigment cells:- These have loose pseudopodia while their cytoplasm has pigment granules so these give colour to sponge
• Trophocytes or Nourishing cells:- These also have loose pseudopodia and are adapted to ingest, digest and distribute food.
• Thesocytes or Storage cells:- These also have loose pseudopodia and store the reserve food as glycogen, far, glycoproteins or lipoprotein.
• Phagocytes:- These also have loose pseudopodia and engulf and remove the damaged tissue
• Archaeocytes or Embryonic cell gland cells:- These are large sized amoebocytes having blunt pseudopodia. These are undifferentiated or reserve cells and can differentiate into any other cell type depending upon requirement,so these are also called totipotent cells. These also help in regeneration while the gametes forming archaeocytes are called gonocytes.
• Desmocytes or fibre cells:- these are long and slender cells which is present around the longitudinal channels and help in extension of sponge body.

Skeleton of Sycon:-

• Scypha has an endoskeleton of large number of microscopic , crystalline, calcareous and needle-like structures called sclerites or spicules present in the mesenchyme of the body wall . These are always calcareous in nature

1) Types and orientation of Spicules:- 

• On the basis of their number of axes and rays, spicules of Scypha are of two types which are oriented in a characteristic way:-

(a) Monoaxons:-

•  These have only one axis and are of three types:-
• Long, short and spear-like or cube like.
• On the basis of their growth, monoaxon may be monoactinal (or uniradiate) called styles, or diactinal (or biradiate) called rhabds.
• Long monoaxon spicules surrounded and guard the Osculum by forming an oscular fringe.
• Short monoaxons mostly lie parallel to the radial canals.
• Spear-shaped spicules, called oxeotea, are partly embedded in the dermal cortex while partly project out over the polygonal elevations to partly cover and protect the dermal Ostia.

(b) Tetraxons:- 

• These have four aces of growth and are of 2types: tetraradiate and triradiate spicules.
• Tetraradiate Spicules have 4 rays.
• These generally occur in the Gastral cortex along with the triradiate spicules.
• Their one ray projects into the spongocoel.
• Triradiate Spicules are formed by the loss of one ray from the tetraradiate Spicules 
• These generally lie along the radial canals with one ray directed inward.

• (ii) Development of spicules:- Spicules are secreted by special amoebocyte called sclerocytes of mesenchyme which are derived from the modified pinacocytes called scleroblasts of Pinacoderm.
• One scleroblasts secrets only one ray of a spicule so a Monoaxon spicule is secreted by one scleroblast while a triradiate and tetraradiate Spicules is secreted by three and four scleroblasts respectively.
• Scleroblasts secreting calcareous spicules of Scypha are called calcoblasts.

(iii) Development of a Monoaxon spicule:- 

• A scleroblast becomes binucleate.
• A minute and slender axial filament of organic matter is laid between two nuclei which is further deposited with calcium carbonate matter and finally a sheath of organic matter.
• Two nuclei are pushed apart by the growth of spicule and finally the scleroblast is divided into two sclerocytes.
• Inner sclerocytes is called founder as it is responsible for laying and lengthening of the spicule, while outer sclerocytes is called thickener as it deposits additional layers of calcium carbonate so increasing the thickness of spicules.
• CaCO3 used is extracted from the surrounding sea water.
• When the spicule is fully formed, both the sclerocytes leave the spicule, the founder first and the thickener later.

• Development of a triradiate spicule:- A triradiate spicule is secreted by three scleroblast while come together in the form of a figure of a trifoil.
• Each scleroblast becomes binucleate.
• A minute Spicule is laid between two nuclei of each scleroblast.
• Later these spicules act as three rays which finally meet at their inner ends to form a small triradiate spicule.
• Each scleroblast is also finally divided into two sclerocytes so forming a sextet.
• Three thickeners lie at the tip of triradiate spicule and increase the length of rays, while three founders remain joined for some time at the junction of three rays and increase their thickness by adding more layers of CaCO3.

Development of Tetraradiate Spicules:- 

• In the formation of Tetraradiate Spicules, the fourth ray is added to developing triradiate spicule by an additional scleroblast.

(iii) Chemical composition:-

•  Each calcareous spicule is formed of:-
• CaCO3 - 87%
• MgCO3 - 7%
• Water -.   3%
• Small amounts of other minerals.
• An axial thread of organic matter, called spiculin.

(IV) Functions of skeleton:- 

• It provides mechanical support to soft body of sponge.
• It gives definite shape to the sponge.
• It protects the sponge from the wave actions of sea water 
• It helps in resisting external pressure.
• It protects the sponge from other animals due to bristly nature.
• It increases the stiffness of sponge tissue.

Physiology of Sycon:-

• Movement:- Being sedentary in its habitat, Scypha has no active organs for locomotion.
• It has only local contractile powers which are restricted to within 3 to  4 mm of the point of strong stimulus.
• These reactions are slow responses and become noticeable only after one to several minutes of exposure to stimuli.
• As sensory and nerve cells are absent in the sponge body, so these contractile cells acr as independent effectors. 
• The movements of amoebocyte are amoeboid or pseudopodial and not muscular.
• The pinacocytes are highly contractile cells.

Nutrition:- 

• Food:- Scypha is omnivorous Nd holozoic .
• It feeds upon planktons like protozoans, bacteria, diatoms and dead organic Matter.
• So Scypha is microphagous in its feeding.

Ingestion:- 

• Scypha is a filter-feeder. 
• The collar cells or choanocytes maintain a water current by constant but uncoordinated beating of their flagella.
• As the flageller beating is directed towards apopyle, which develops a negative pressure in the radial canals 
• So draw a water current which enters the sponge body through dermal Ostia and reaches the radial canal after passing through the incurrent canals and Prosopyles.
• This incoming water current brings fine food particles along with it as dermal Ostia are very minute apertures, the size of which is further regulated by myocytes.
• The flagella of choanocytes beat from their base to tip, so the water also flows in the same direction. 
• The microvilli of collar of choanocytes act as a filter and the food particles are trapped by these microvilli. 
• The cyclotic flow of protoplasm moves these food partly are trapped by these microvilli.
•  The cyclotic flow of protoplasts moves these food particles towards the base of microvilli from where these are ingested in the food vacuolate by the choanocytes or directly by underlying amoebocyte with the help of pseudopodia. 
• Larger food particles may be ingested by the Pinacocytes lining the incurrent canals.

(iii) Digestion:-

•  Digestion of Scypha is intracellular and occurs in the food vacuole which fuses with the primary lysosome with hydrolytic enzyme to form heterophagosome.
• Medium in the food vacuole is first acidic but finally alkaline. 
• Food vacuole has all the three types of enzymes, Viz. Proteases, carbohydrase and lipase for the Digestion of protein, carbohydrates and fats respectively. 
• But it is not confirmed whether these enzyme's are secreted by Scypha or by bacteria.

Digestion:-

-

•  It may occur by cell to cell diffusion but is generated brought about by special amoebocyte called trophocytes which move about in the mesoglea and distribute nutrients to various cells.

(V) Storage:-

• Reserve food is stored as glycogen, fats , glycoprotein or lipoprotein in the special amoebocytes called thesocytes.

(vi) Egestion :-

•  Choanocytes or amoebocyte, involved in intracellular digestion, throw the indigestible food particles in the radial canals from where these are expelled out along with the outgoing water current.

(vii) Respiration:-

•  Scypha is aerobic in respiration. 
• In this, respiration occurs through general body surface as there are no special respiratory organs and cells of both dermal and Gastral layers are in direct contact with water.
•  This permits direct exchange of gases between oxygen and carbon dioxide of body cells on the principal of diffusion.
•  Wave action ensures the constant supply of well oxygenated water whose importance is evident from that if the dermal Ostia are blocked with debris particles, then the sponges dies.
•  The rate of consumption of oxygen by Scypha has been found to range from 0.04 mL to 0.16 mL per gram of fresh weight per hour.
•  The upper half of the sponge consumes about 10 to 50% more oxygen per gram per hour than the basal half.

(iv) Excretion:-

•  Scypha is ammonotelic but it has no special excretory structures so ammonia of dermal cells lost by diffusion through the body surface in the surrounding sea water while ammonia of Gastral cells is released in the outgoing water current.
•  These wastes are carried away from the sponge by wave action.
• Some science say that the metabolic wastes are taken up by amoebocyte which generally release them into the Spongocoel to be carried out along with the outgoing water current.

(V) Nervous system and behaviour:-

•  Scypha has no special sensory or nerve cells so there is no coordinated actions of the whole body but the cells are sensitive and react individually.
•  This sensitivity is maximally developed at the oscular rim but in other parts the stimuli can be conducted only upto 3 to 4 mm from the point of stimulation so the reactions to stimuli are very slow.
•  These slow and local reactions of sponges are sufficiently to fulfill the needs of sedentary scycon having only cellular organisation.
• The sensitive cells have been found to behave as independent effectors.
•  Some kind of coordination has been reported among the myocytes surrounding the aperture like dermal Ostia, Apopyles and Osculum. These myocytes , surrounding a common aperture, contra simultaneously.
• Tuzet and M Pavan's Dr Ceccatty suggested that the collencytes may act as neurons and form a kind of diffused nervous system connecting the pinacocytes, choanocytes and myocardial.
•  These neurons may receive and conducting the stimuli.

Reproduction:- 

(1) Definition:-

•  Reproduction is the ability of all living organism to produce young ones similar to themselves in many characters. 
• It not only halos in survive but also helps in continuity of that race and group immortality.

(2) Types:-

 On the basis of presence or absence of gametes, reproduction is of two types:- 

(A) Asexual reproduction and 

(B) Sexual reproduction

(A) Asexuality reproduction:-

•   It does not involve formation and fusion of gametes.
•  Scypha reproduces asexually by external budding.
•  In this, multicellular outgrowth, called bud, arise from the base of sponge and develops an Osculum at it's distal end.
•  It may separate from the parent and fix at a new substratum to form a new sponge but may remain attached to the parental body and may develop secondary buds to form a kind of colony.

(B) Sexual reproduction:-

•  It involves formation and fusion of gametes.

(a) Sexes:-

•  Scypha is a bisexual or monoecious and hermaphrodite but it always shows cross fertilization due to protogynous condition.

(b) Gonads:-

•  Gonads in Scypha are temporary as special sex organs are absent. 
• Archaeocytes or sometimes any amoebocyte or sometimes even choanocytes act as gonocytes or gonads to form the gametes.
•  For this the choanocytes lose flagellum, withdraw collar and move into the mesoglea to form the gametes.

(c) Gametogenesis:-

•  It involves formation of gametes.

(1) Spermatogenesis :-

 It involves formation of spermatozoa.

•  In this archaeocytes or amoebocyte or even choanocytes acts as sperm mother cell or spermatogonium.
•  It gets covered by one or more flattened cover cells which are either derived from amoebocytes or formed by the division of spermatogonium .
•  The complex structure so formed is called sperm-nest or spermatocyst.
•  The spermatogonium divides mitotically to form 4-8 spermatocyst, each of which undergoes meiosis to form sperms.
• Each sperm is formed of a rounded or oval head and a long vibratile tail.
•  The tail shows lashing movements which move the sperm in water in search of ovum.

(2) Oogenesis:-

•  It involves formation of ova.
•  In this, archaeocytes or amoebocyte or even choanocytes acts as egg mother cell or oogonium or ovocyte. It migrates in the radical canal, undergoes two mitotic divisions to form 4 oocytes.
•  Each oocyte passes through choanocytes to reach the mesoglea, enlarges in size by engulfing other cells or by receiving nutrition from nutritive trophocytes.
•  When mature oocyte undergoes meiosis and forms one ovum and two polar bodies. 
• During oogenesis, oogonium shows the amoeboid movements.
•  A ripe ovum is a large rounded cell having a large nucleus with a well developed nucleolus.
•  It lies in the wall of radial canal where waits for the sperm of another sponge.

(d) Fertilization :-

•  It involves fusion of gametes and is internal as the egg is fertilised in situ.
•  On maturity, spermatocyst ruptures and sperms are released in the radial canal and are discharged out in the sea water along with outgoing water current through Osculum. 
• The free sperms along with ingoing water current enter into another sponge and reach radial canals.
•  A sperm is taken either by wandering amoebocyte or a choanocytes for which the choanocytes loses its flagellum, withdraws the collar and sinks in the mesoglea to carry the sperm to waiting ovum.
•  Such a choanocytes is called sperm  transient or carrier cell.
• During fertilization, when sperm transient cell comes in contact with ovum, then the later develops a conical depression to receive sperm. Head of sperm swells up and is surrounded by a capsule while it's tail is lost.
•  The capsule with sperm head enters the ovum and forms the zygote.
•  So fertilization in Scypha is internal.
•  Later the zygote us surrounded by a brood capsule formed by aggregation of amoebocytes.

Development of Embryogeny:-

• Development of Scypha started within the brood capsule and occurs in situ.
•  It involves following steps:-

(a) Cleavage :-

•  It involves the transformation of a single celled zygote into a single layered hollow spherical blastula large by rapid mitotic divisions of Zygote.
• Cleavage in Scypha is holoblastic and unequal.
•  It starts when the Zygote lies in the mesoglea of the sponge.
•  First three cleavages are vertical or meridional and produce a pyramidal disc of eight cells called blastomeres.
•  Fourth cleavage is horizontal or equatorial and slightly above the equator so producing a sixteen celled stage.
•  At this stage, the blastomeres are arranged in two tiers, each formed of 8 blastomeres.

 Depending upon size, blastomeres are of two types:- 

(1) Micrometres:-

•  It forms the upper tier of 8 cells . These will form the Choanoderm.

(2) Macromeres:-

•  It forms the lower tier of 8 cells.
•  These lie towards the parent Choanoderm.
•  These will form the Dermal layer.
• The Macromeres donot divide for some time while Micrometres divide by rapid mitosis to increase their number, become columnar and develop inward directed flagella.
•  Later , a blastocoel or segmented cavity is developed between the tiers of blastomeres.
•  The Embryo is now called blastula.
• (b) Formation of stomoblastula:- Macromeres become rounded, granular and develop a blastopore between them which communicates with the blastocoel.
•  Blastopore acts as mouth and is used to ingest the surrounding amoebocyte for nutrition.
•  This feeding blastula like larva is called stomoblastula and is the parasite on its parent.
•  It's wall is formed of many small, elongated and flagellated Micrometres and 8 spherical and granular Macromeres 
• (c) Formation of amphiblastula:- Stomoblastula undergoes inversion so the flagella of micromere are now directed outward.
•  Now the Macromeres multiply grow on all sides and close the mouth.
•  Now Embryo elongates, ruptures the brood capsule and is released outside through radial canals, Excurrent canal, spongocoel and Osculum.
•  This free larva is more or less oval shaped.
•  It's wall is half flagellated of small and narrow flagellated Micromeres and half non-flagellated of large Macromeres and is called amphiblastula.
•  It is formed in the development of most of the members of O. Calcarea .
•  It swims freely in sea water keeping its flagellated pole forward, so helps in dispersal of a sedentary adult sponge.

(d) Formation of Gastrula :-

•  After a brief free-swimming period, flagellated half gets surrounded by non-flagellated micromeres.
•  This produces a two layered Gastrula larva having a newly formed cavity which opens out by blastopore at the invagination end.
•  In Gastrula, outer layer is formed of non-flagellated and granular Macromeres while inner layer is formed of small and flagellated Micromeres.
•  So gastrulation is opposite to inversion.

Metamorphosis:-

•  Metamorphosis involves the transformation of Gastrula larva into a young sponge.
•  During this, gastrula fixes itself to some substratum by its blastoporal endz elongates and becomes cylindrical.
•  Blastopore is closed by growth of both cell- layers while free end develops a perforation called Osculum.
•  During metamorphosis outer non-flagellated Macromeres flattern to form dermal layer of Pinacocytes and their derivatives like myocytes porocytes and calcoblasts while inner flagellated Micromeres form Gastral layer of choanocytes and line whole of central cavity representing future spongocoel.
•  Certain dermal cells act as porocyte and develop intracellular Prosopyles which act as dermal Ostia. 
• Young sponge now resembles the adult Asconoid Leucosolenia and is called Olynthus stage .
•  Mesoglea is developed between the dermal and Gastral layers and is mainly secreted by Choanoderm, so the sponge wall thickens .

 Now this Olynthus stage is transformed into young Syconoid Scypha by following changes:- 

•  (1)  Incurrent canals are formed by invagination of dermal layer.
• (2) Radial canals are formed by evagination of Gastral layer. The  formation of radial canals start from the middle of the body.
• (3) incurrent canals GT external bounded by pore membrane having intercellular dermal Ostia.
• (4) Choanocytes are restricted in only radial canals.
• (5) Scleroblasts and various amoebocyte are developed in mesoglea. Scleroblasts and myocytes are derived from the dermal layer while archaeocytes and other amoebocyte are Developed from the Gastral layer. So the mesenchymal cells are derived both the Embryonic layers.

Peculiarity in development:-

• Development of Scypha is characterized by certain peculiar features like:-
• (1) Blastula of Scypha is called Stomoblastula as it has mouth to ingest amoebocytes.
• (2)Blastula undergoes inversion.
• (3) Development includes a partly flagellated and partly non-flagellated amphiblastula larva.
• (4) Gastrulation occurs by invagination.
• (5) Most peculiar feature of development of Scypha is that the flagellated Micromeres and non-flagellated Macromeres form the Gastral and dermal layer respectively.
•  It is exactly reverse to the mode of Development in higher animals in which the flagellated and non- flagellated cells of gastrula give rise to outer ectoderm and inner endoderm respectively.
•  So two layers of a sponge gastrula cannot be called ectoderm and endoderm, and two layers of adult sponge cannot be named epidermis and gastrodermis as in coelenterates.

Class 7: chapter 15 (Light )

Subject: Light class 7 notes

Introduction:-

Light enable us to see world.

Luminous objects:- Produce their own light. Example:- Sun.

Illuminous objects:- Donot produce their own light. Example:- chair.

Capable of reflecting light to our eyes coming from luminous objects.

Light:- A form of energy which enable us to see things around us.

Speed of light is 300000 km/s.

Light travels along straight lines.

Ray of light:- Straight line path of light is called ray of light.

Beam of light:- Bunch of rays of light is called beam of light.

Reflection of light:- Bouncing back off a ray of light into the same medium after striking a polished surface such as mirror.

Light reflected from an object reaches our eye and then we see things around us.

Incident ray:-  Ray of light that strikes the surface.

Reflected ray:- Ray of light sent back be surface after reflection.

Normal:- Perpendicular to the surface at the point of incident. It is an imaginary line.

Angle of incidence:- Angle between Incident ray and normal.

Angle of reflection:- Angle between reflected ray and normal.

Laws of Reflection:- Incident ray, reflected ray and normal all lie on same plane.

Angle of incidence = Angle of reflection

Plane mirror:-Mirror with a flat reflective surface.

Real image:- Image is formed when reflected rays actually meet.

Can be obtained on screen.

Virtual image:- image formed when reflected rays appear to meet . It cannot obtained on screen.

Lateral inversion:- Left side of object appears right and vice versa. This is called lateral inversion.

Image formed by Plane mirror :- 

Virtual and erect

Same size as that of object.

Image formed behind mirror.

Distance of image behind mirror is same as distance of object from the mirror.

Spherical mirror :-Mirror having spherical reflective surface.

Real image:- Image formed when reflected rays actually meet.

Virtual image:- Image formed when reflected rays appear to meet.

Lens:- Transparent optical medium bounded by two surfaces, at least one being spherical.

Types of lens:-

 Convex lens:- Converging lens which is thicker at middle and thinner at edges.

Concave lens:- Diverging lens which is thinner at middle and thicker at edges.

Application of concave mirror:- 

Used by doctor for examine eyes, ears, nose and throat.

Used by dentists to see enlarge image of teeth.

Reflector of torches, headlights of cars and scooter are concave in shape.

Sunlight:- White light made up of seven colours.

Prism:- Transparent element with three rectangular and two triangular surfaces is called prism.

Dispersion of light:- Splitting of light into its constituent colours. Example:- Rainbow

Spectrum:- Pattern of colours obtained after dispersion is called spectrum.

Resume

 Shivam Chawla

Mobile : 91-8930507948

                 91-9728195136

Email : chawlas914@gmail.com

Career Objective :

• Seeking a challenging role, where teamwork as well as individual contributions are demanded and recognised . Be part of an energetic group of peers and share the organisation's vision and also grow along with the organisation.

Strength :

• I am Innovative, enthusiastic, hardworking and sincere with good communication skills and leadership qualities. I am capable in motivating team and play an effective role in organisation.

Educational Qualification:-

• 8th 

Skills:- 

• Driving 

Hobbies:- 

• Gardening,
• Reading books.

Strength:

• Punctual,
• Hard working,
• Responsible,
• To be positive in all kind of circumstances

Positive assets :

• Positive thinking
• Quick learner

Personal Profile : 

Date of birth       : 9 August 2000

Father's name     : Bharat Bhushan

Nationality           : Indian

Language known: Hindi

Marital status.    : Unmarried

Permanent address : 8/1 Guru Nanak pura, Kacha camp , Panipat ( 132103)

Declaration :

• I hereby declare that all the information provided by me is true to the best of my knowledge and belief.

Place : Panipat

(Shivam)

Personal blog

Simran Chawla

Mobile : 91-9728195136

Email : chawlas914@gmail.com

Career Objective :

• Seeking a challenging role, where teamwork as well as individual contributions are demanded and recognised . Be part of an energetic group of peers and share the organisation's vision and also grow along with the organisation.

Strength :

• I am Innovative, enthusiastic, hardworking and sincere with good communication skills and leadership qualities. I am capable in motivating team and play an effective role in organisation.

Educational Qualification:-

• MSc Chemistry (2022)
• BSc Medical Science (2019)
• 12 th passes (2016)
• 10th passes (2014)

Computer qualifications:-

• Basic computer course grade "A" 2014
• Computer education ( level 1) grade "A" KUK 2017

National exam:- 

• Akash Talent Hunt Exam , Panipat (2013)

Internship program:-

• For five days by INSPIRE in Hisar , 2014

Applied for :- Teaching

• Science (Grade IX,X)
• Chemistry (Grade XI, XII)

Hobbies:- 

• Singing,
• Gardening,
• Reading books.
• Strength:
• Punctual,
• Hard working,
• Responsible,
• To be positive in all kind of circumstances

Positive assets :

• Positive thinking
• Quick learner

Personal Profile : 

Date of birth        :10 July 1998 

Father's name     : Bharat Bhushan

Nationality           : Indian

Language known: English and Hindi

Marital status.    : Unmarried

Permanent address :8/1 Guru Nanak Pura, Panipat (Haryana) 132103

Declaration :

• I hereby declare that all the information provided by me is true to the best of my knowledge and belief.

Place : Panipat

(Simran Chawla)

How do organism reproduce

 

How organism Reproduce?

Reproduction:- Re= again ; production = to produce.

A biological process by which an organism produce another organism similar to itself.

Not essential for life of individual like respiration.

Function/ importance:- 

Necessary for continuing of species.

Do organism create exact copies of themselves?

No. They produce similar but not exact copies (Identical copies) of themselves because their DNA is not same.

We know chromosomes in nucleus a cell contain information for inheritance of features in the form of DNA molecules 

DNA :- Deoxyribo Nucleic acid

DNA is the information source for making proteins.

If the information is changed , different proteins will be made.

Thus, different proteins will lead to altered body designs.

Write basic event in reproduction.

Creation of DNA copy.

How cell build copies of DNA?

By using chemical reactions.

Mechanisms:- Semi Conservative mode of DNA replication.

Enzyme involved:-

DNA polymerase

Helicase and gyrase.

DNA ligase

Primate etc.

After DNA replication, other cellular apparatus creates and two cells divides to give rise to two cells.

Since no biochemical reactions is absolutely reliable, so some variation generates each and every time in DNA replication and so organism can't be identical and so NO organism can't be identical.( Case of sexual reproduction)

Advantage of Variation:-

Organism will be capture of adopting changing environment.

Natural rule of Selection:-

Only useful variations will be selected by nature and other will be eliminated.

Types of reproduction:-

Two types:-

Asexual reproduction

Sexual reproduction

Asexual reproduction:- 

Uniparental

Simple and fast process

Produce identical offsprings and are called clones.

No role in evolution 

Does not involve formation of gametes.

Fusion of gametes takes place.

Involves mitosis.

Sexual reproduction:-

Biparental

Complex and slow process

Produce similar offsprings with some variation

Important role in evolution.

Involves formation of gametes.

Fusion of gametes takes place.

Involves meiosis and mitosis.

Modes of asexual reproduction used by single celled organisms:-

Six types:- 

1. Fission

2. Fragmentation

3. Budding

4. Regeneration

5. Spore formation

6. Vegetative propagation.

Fission:- splitting of parental cell into two or more daughter cells.

Two types:-

Binary fission

Multiple fission

Binary fission:- seen in Amoeba, Paramecium (protozoan) and bacteria.

Parental cell split into two daughter cells.

It can be simple/ irregular, longitudinal, transversal depending upon the plane of division.

In Leishmania splitting of parent cell take place in longitudinal plane w.r.t. flagellum at its end.

Multiple fission:-

Seen in malarial parasite, Plasmodium.

Splitting of a parent cell into numerous daughter cells, each of which grow into an adult.

Fragmentation:- seen in lower multicellular organisms which have relatively simple body organisation.

Seen in Spirogyra.

In this parent body breaks into two or more fragments and each fragment grows into a new individual.

Regeneration:- 

Mode of asexual reproduction in which missing part  of ab organism is repaired by proliferation of cells.

Seen in Planaria.

All these changes takes place in an organised sequence referred to as development.

Budding:-

Seen in Hydra .

In this mode of asexual reproduction, a bud is develops as an outgrowth due to repeated cell division at one specific site 

These buds develop into tiny individuals and when fully mature, detach from parent body and become new independent  individuals.

Vegetative propagation:-

Mode of reproduction in which new plants are formed from vegetative parts of plants like root , stem etc.

Advantage:-

Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds.

Method is useful for propagation of seedless plants like banana , rose and Jasmine.

All plants produce are genetically similar to parent plant to have all its characteristics.

Example:- Buds produced in notches along the leaf margin of Bryophyllum fall on the soil and develop into new plants.

Spore formation:-

Seen in Rhizopus, Chlamydomonas, Sponges, Penicillium.

On bread, thread like structure grows which is nothing but Rhizopus.

It contain two parts:-

Hyphae

Blob on a stick.

Blob are sporangia which contain cells or spores.

Spores developes into new Rhizopus individuals.

The spores are covered with thick walls that protect them.

When it comes in contact with moist surface the wall ruptures and begin to grow.

Tissue culture:-

New plants grown by separating cells from growing tip of a plant.

The cells are then places in an artificial medium where they divide rapidly to form a group of cells called callus.

The callus is then transferred to another medium containing hormones for growth and differentiation.

The plant let's are placed in soil so that they can grow into mature plants.

Using tissue culture,many plants can be grown from one parent in disease free conditions.

Technique is commonly used for ornamental plants.

Sexual reproduction:-

Involves two parents.

When reproduction takes place as a result of fussion of male and female gametes , this is called sexual reproduction.

Fusion of two gametes results in formation of zygote.

Sexual reproduction in flowering plants:-

Pistil/ Carpel :- 

Comprises of

- Stigma

-style

-ovary

Group of Pistil is called Gynoecium.

Female reproductive part .

Stamen:- 

Comprises of 

- Anther

-Filament

Group of stamen is called androecium.

Male reproductive part.

Petals:-

Coloured attractive modified shoot.

Attract pollinators such as insects.

Group of petals is called corolla.

Sepals:- 

Green coloured modified shoot.

Perform photosynthesis.

Group of sepals is cay calyx.

Note:- Stamens and Carpels are reproductive parts of flower which contain germ cells.

Types of flower:-

Two types :-

Unisexual

Bisexual.

Unisexual:-

Contains either stamen or pistils.

Example:- Papaya, Watermelon.

Bisexual:-

Contains both Stamens and Carpels.

Stamens is male reproductive part and produces pollen grains (yellow)

Carpel is female reproductive part and placed centrally.

It consists 3 parts

-Stigma:- Terminal and sticky

-Style:-middle , elongated

-Ovary:-bottom part , swollen.

Contain ovules

Each ovule contain an egg cell.

Fertilisation:- 

The process of fusion of male germ cell produce by pollen grain and female gamete present in ovule is called fertilization.

Pollination:-

The transfer of pollen grains from.anther to stigma of same flower or of different flower is called pollination.

Types of pollination:-

Two types

Self pollination

Cross pollination

Self pollination:- 

Transfer of pollen from anther to stigma of same flower.

Seen in bisexual and cleistogamous flowers ( Flowers which  donot open)

Cross pollination:-

Transfer of pollen grains from anther to stigma of different flowers. 

Seem in some bisexual and all unisexual flowers.

What happens after pollination?

After pollination, the pollen grains reaches to ovary through pollen tube 

It than reaches to ovule and finally to egg.

On reaching egg, it get fused with it to form zygote.

This is called fertilization.

Post fertilization events:-

Zygote divides many times to form an embryo within ovule.

Ovule develops a tough coat and is gradually converted into seed.

Ovary ripen to form fruit.

Meanwhile, petals , sepals, stamens, style and stigma may shrivel and fall off.

Germination:- 

Seed contains future plant or embryo which develops into a seedling under appropriate conditions.

This process is known as germination.

Reproduction in Human beings:-

General process of growth:-

Increase in size (height).

Increase in body weight.

Acquire teeth {Deciduous (milky) and permanent (second set)}

Changes after puberty:-

Thick hair growth in new body parts such as armpits and genital area between thighs.

Thin hair appear on legs , arms and face.

Skin become oily and pimple develops.

Aspects of sexual maturation:-

In girls :-

 breast size begin to increase;

Menstrual begin;

Voice become high pitch.

In boys:-

Penis become large and erect

Voice begin to crack.

Thick hair growth on face.

Puberty:- the period in which rate at which general body growth behind to slow down, reproductive tissues begin to mature is called puberty.

Why does the body show sexual maturation at this age?

For creation of germ cells to participate in sexual.

Note:- if animals are to participate in the process of mating, their state of sexual maturity must be identified by other individual.

For transfer of germ cells between two people there is a need of specialised organs for sexual act.

In male , it is penis.

In female, it is vagina.

Male reproductive system:-

Male reproductive system comprises of :-

1.Primary sex organ:-

-Testis ( 1 pair, produce sperm and testosterone)

2.Secondary sex organ/ accessory sex organ:-

-Epididymis

-Seminal vesicle

-Prostate gland

-Cowper's gland.

3.Duct ( Help in conduction of sperm)

-Vas deferens

-Urino genital duct (Common passage for urine  and sperm conduction)

4.External genital

-Penis (Help in insemination)

Ques:- testes are located outside the abdominal cavity in scrotum . Why?

Because sperm formation require a 2°lowet temperature than the normal body temperature.

Name the hormones that regulate formation of sperms and also bring changes in appearance seen in boys at the time of puberty.

Testosterone

Define sperm.

Tiny body that consists of genetic material a long tail that help them to move towards the female germ cell.

What is the role of seminal vesicle and prostate gland? Also write role of Cowper's gland.

Seminal vesicle:-

Secretion contain prostaglandins.

Activate sperm

Cause construction in femal reproductive gland.

Prostate gland:-

Provide nutrition to sperm

Protect sperm from acidic medium of vagina.

Provide basic pH for sperm (7.4)

Cowper's gland:-

Secrete mucus.

Help in lubrication during copulation.

Sperm + secretion from three gland:- semen.

Female reproductive system:-

It consists of:-

1. Primary sex organ

-Ovary ( produce egg and female sex hormone)

2. Uterus , Fallopian tube , vagina.

3. Glands :- Mammary gland.

4. External genitalia:- Valva

Ovary:- When a girl is born, the ovary already contain thousands of immature eggs.

On reaching puberty, some of these starts maturing.

One egg is produced every month by one of ovaries in alternate manner.

Fallopian tube:-The egg is carried from ovary to womb through oviduct.

It comprises of Infundibulum, ampulla and Isthamus.

Site of fertilization.

Uterus:- 

Two fallopian tubes unite into an elastic bag like structure called uterus .

Site of Implantation of zygote.

After implantation, it get divided to form foetus.

Placenta:-

During pregnancy mother's uterus prepare itself every month to receive and nurture growing embryo.

Lining thickens and is richly supplied with blood to nourish the growing embryo.

The lining is called placenta.

Vagina and Cervix:-

The uterus opens into vagina through cervix.

From where embryo get Nutrition?

From mother's blood through placenta

Development of Embryo:-

Placenta contains villi on embryo's side of tissue.

On the mother's side are blood spaces which surround the villi.

Villi provide large surface area for glucose and oxygen to pass from mother to embryo.

Waste generated by developing embryo  also be removed by transferring them into mother's blood through placenta.

Gastation period:-

The development of child inside the mother's body take approx nine months 

This period is called gastation period.

What happens when egg is not fertilised?

If the egg is not fertilised, it lives for about one day.

So after that it slowly breaks down and comes out through vagina as blood and mucous..

This cycle takes place every month and is known as menstruation.

It usually last for about two to eight days .

Note:- Since the ovary release an egg every month , the uterus prepare itself every month to receive a fertilised egg.

Thus it's lining becomes thick and spongy for nourishing the embryo if fertilization has taken place.

Reproductive health:-

It is a state of complete Physical, mental and social well being in all aspects of reproduction.

Parent should have adequate knowledge on the following:-

-knowledge of reproductive process and organs.

Care of mother and child.

What point to be remembered to ensure good care of mother and child?

Proper nutrition diet to pragnent woman as well as lactating woman.

Proper age difference between children.

Planning a body at right age of mother ( between 20-35 years) . Restrict the number of children not to add over population.

Avoid unwanted pregnancy.

Family planning:-

Necessary to limit the huge increase in polulation.

Overpopulation can give rise to serious problems like lack of food, employment and education which in turn affect the economy and also survival of population.

Knowledge on STD ( Sexually Transmitted disease)

Transmission of disease via sexual connection.

This include:-

Bacterial infection (Gonorrhoea , Syphilis)

Viral infection (Warts, AIDs)

AIDs :- Acquired immuno-deficiency syndrome

HIV :- Human Immunodeficiency Virus.

Precautions from STD spread:- 

Use Condom

Wash before and after intercourse.

Ways to prevent unwanted pregnancy:-

Condom:- Balloon like  elastic covering that tightly fits over the penis.

Collect ejaculated sperm during intercourse 

Oral contraceptive pills:-

Does not allow ovulation to occur.

Surgical method:-

Vasectomy:- Removal of a small portion of vas deferens.

Tubectomy:- removal of a small portion of fallopian tube.

Copper-T :-A loop or copper T are placed in uterus to prevent pragnency.

Side-Effect:- cause irritation in uterus.

Thank you :-)