Phylum - Porifera - NEET-Biology

 Phylum Porifera

Fig: Phylum Porifera = Pore Bearing

Important Characteristics:

• Phylum Porifera = Pore-bearing animals.

• Sponges are primitive multicellular animals with a cellular grade of organization. 

• They have no fixed body shape & no plane of symmetry. 

• Whole sponges can be regenerated from a few separated cells.

• Sponges can almost be regarded not as individuals but as colonies of separate cells.

• Sponges are free-living aquatic (mostly marine) & having neither nerves nor muscles.

• Body wall with two layers of loosely arranged cells and mesenchyme in between (diploblastic).

• Reproduction occurs by asexual (external & internal buds) or sexual methods.

• The body-wall encloses a large cavity, the spongocoel & in most cases also contain numerous small canals. 

• Either the spongocoel or canals are lined by special collar cells or choanocytes with flagella.

• The ceaseless beating of flagella maintains s steady current of water through the canals to bring in food & oxygen & remove waters.

• Almost all sponges possess an internal skeleton. It may consist of tiny siliceous spicules or of fine spongin fibers or of both.

• Example: Sycon (Scypha), Spongilla (Freshwater sponge), Euspongia (Bath sponge)

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Phylum Platyhelminthes (Flatworms) - NEET-Biology

 Phylum Platyhelminthes (Flatworms)

Important Characteristics:

• Acoelomate, triploblastic, bilaterally symmetrical organisms.

• Possess a mouth but no anus- Blind sac body plan.

• Digestive, skeletal, circulatory & respiratory systems are absent, parenchymal gland serves as hydroskeleton.

• The body is soft & dorso-ventrally flattened. It may be leaf-like ribbon-like. It is without segmentation.

• Possess the organ-system level of organization.

• The organ-system level of organization.

• The organ-system is packed in a characterize connective tissue, called parenchyma.

• The nervous system is ladder-like. It comprises the brain & two main longitudinal nerve-chords connected at intervals by transverse commissures.

• The excretory system includes characteristics of flame-cells leading into tubules that open out by one or more excretory pores.

•  Hermaphroditic, often with elaborate precautions for minimizing self-fertilization.

• Fertilization is internal. Life history often includes larval stages.

• Asexual reproduction by transverse fission occurs in some forms.

• Example- Taenia (Tapeworm), Fasciola (Liver fluke)

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Phylum Annelida - NEET-Biology

 Phylum Annelida

Fig: Leech (Hirudinaria)

Characteristics:

• Triploblastic, coelomate, bilaterally symmetrical & metamorphically segmented animals.

• In earthworm, each segment has a separate coelom which acts as a hydraulic skeleton.

• During muscular contraction, the body wall pushes against each compartment wall. This allows separate regions to contract independently & elongate during locomotion.

• The body is elongated, cylindrical, or flattened.

• It is divided into segments by ring-like grooves, the annuli. This character gives the phylum its name.

• The segmented worms are triploblastic, i.e. they develop from the three germ layers.

• The body-cavity is a true coelom, as it is lined by a mesodermal epithelium.

• It is divided by vertical septa into compartments.

• A closed circulatory system present.

• Segmented nephridia for excretion & osmoregulation.

• Typically, there is a trochophore larva during development.

• Example: Nereis, Pheretima (Earthworm), & Hirudinaria (Bloodsucking leech).

Fig: Earthworm (Pheretima)

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Phylum Arthropoda -Biology

Phylum Arthropoda

Fig: Apis (Honey Bee)

Important Characteristics:

• It is the largest phylum of Animalia.

• Exhibit organ-system level of organization.

• Bilaterally symmetrical, triploblastic, segmented & coelomate animals.

• Metamorphic segmentation as in annelids but segmented not separated from each other by septa.

• All arthropods have an exoskeleton of a chitinous cuticle. 

• Cuticle shed periodically to allow for growth.

• The process of casting off of skin or integument is known as ecdysis or molting.

• The body is divisible into the head, thorax & abdomen or divisible into cephalothorax and abdomen.

• They have jointed appendages (arthos-joint, poda- appendages).

• Arthropods have an open circulatory system. The body cavity is known as hemocoel (hemocoel), is filled with fluid hemolymph.

• Respiration takes place through the general body surface & gills in crustacean; through trachea in insects, Diplopoda, Chilopoda; through book lungs in Arachnida.

• Excretion is brought about by green glands in aquatic forms & Malpighian tubules in terrestrial forms.

• Sexes usually separate; Fertilization internal; oviparous or ovoviviparous; development direct or indirect.

• Example: Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect).

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Phylum Mollusca - NEET-Biology

 Phylum Mollusca

Fig: Apple snail (Pila)

Characteristics:

• Mollusca is the second-largest animal phylum & includes snails, slugs, oysters, cuttlefish, octopuses, and many other familiar animals.

• Exhibit organ-system level of body organization.

• Bilaterally symmetrical, triploblastic & coelomate animals.

• The body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot & visceral hump.

• Most mollusks have a rasping tongue-like radula for feeding.

• Except for cephalopods, all mollusks have such as open circulatory system.

• Nitrogenous wastes are removed from the body by the nephridium.

• Mostly dioecious.

• Fertilization is both external & internal, oviparous with indirect development.

• Embryo developed into a free-swimming larva called a trochophore.

• Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devilfish), Aplysia, Dentalium (Tusk shell), Chaetopleura (Chiton)

Fig: Octopus (Devilfish)

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Fundamental Duties - NCERT Solution-Political

Fundamental Duties

• Incorporated in Part IV-A, article 51-A of the constitution of India.

• Inserted by the Constitution 42nd Amendment Act, 1976.

• It was part of a large number of changes brought about during the internal emergency (1975 - 77).

• But after the end of the Emergency, when the new Parliament reviewed the whole position & in most cases restored the pre-emergency position, article 51-A was one emerged unscathed because it was considered by all parties to be an unexceptionable charter of principles which citizens could usefully absorb & practice.

• The inclusion of Fundamental Duties in our Constitution also brings it in line with Article 29 (1) of the Universal Declaration of Human Rights which says: "Everyone has the duties to the community in which alone the free & full development of the personality is possible."

• The exercise of fundamental rights entails duties to the community which ensures the free and full development of human personality.

• Added on the recommendations of the Swaran Singh Committee. These are based on the Japanese model.

• Originally 10 duties, but now 11 in number, it was added by the 86th Amendment Act, 2002.

List of Fundamental Duties:

According to Article 51-A, it shall be the duty of every citizen of India:

• To abide by the Constitution & respect its ideals & institutions, the National Flag & the National Anthem;

• To cherish & follow the noble ideals that inspired the national struggle for freedom;

• To uphold & protect the sovereignty, unity & integrity of India;

• To defend the country & render national service when called upon to do so;

• To promote harmony & the spirit of common brotherhood amongst all the people of India transcending religious, linguistic & regional, or sectional diversities & to renounce practices derogatory to the dignity of women;

• To value & preserve the rich heritage of the country's composite culture;

• To protect & improve the natural environment including forests, lakes, rivers & wildlife, and to have compassion for living creatures;

• To develop scientific temper, humanism & the spirit of inquiry & reform;

• To safeguard public property & to abjure violence;

• To strive towards excellence in all spheres of individual & collective activity so that the nation constantly rises to higher levels of endeavor & achievements;

• To provide opportunities for education to his child or ward between the age of 6 - 14 years. This duty was added by the 86th Constitutional Amendment Act, 2002.

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Chromosomal Basis of Inheritance - CSIR NET

Chromosomal Basis of Inheritance

In 1902, Walter S. Sutton and T. Boveri proposed the chromosomal theory of heredity.

• The theory provides a way to explain how cellular transmission or chromosomes passes genetic determinant (i.e. genes) from parent to offspring.

According to this view:

• The chromosome contains the genetic material (genes) that is transmitted from parent to offspring.

• Chromosomes are replicated & passed along generation after generation from parent to offspring.

• The nuclei of most eukaryotic cells contain chromosomes that are found in homologous pairs (i.e. they are diploid).

• One member of each pair segregates into one daughter nucleus & the other segregates into different daughter nucleus. Therefore, gametes contain one set of chromosomes (i.e. they are haploid).

• During gamete formation, different types of chromosomes segregate independently of each other.

• Each parent contributes one set of chromosomes to its offspring. Hence, the chromosome theory of inheritance describes the relationship between Mendel's Law & chromosomal transmission.

Fig: Segregation of homologous chromosome during meiosis explains Mendel's law of segregation

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