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Showing posts with label BIOLOGY. Show all posts
Showing posts with label BIOLOGY. Show all posts

Wednesday, February 3, 2021

Respiration & Energy Transfer (Aerobic Respiration) - NEET


Respiration & Energy Transfer (Aerobic Respiration) 

  • Occurs: in Mitochondria.

  • Aerobic respiration is a biological process in which glucose is complete breakdown into energy in the presence of oxygen (O2).

  • The energy is released by splitting of a glucose molecule with the help of oxygen gas (O2).

  • However, in anaerobic respiration, the breakdown of glucose is incomplete. The end product of anaerobic respiration is lactic acid instead of carbon dioxide & water. This process occurs in oxygen debt. Hence, the amount of oxygen required to oxide lactic acid to carbon dioxide & water is not present. 

  • So, at the end of the chemical reaction, energy, water molecules, and carbon dioxide gas are released as the by-products of the reactions.

  • The 2900 kJ of energy is released during the process of breaking the glucose molecule and in turn, this energy is used to produce ATP- Adenosine triphosphate molecules, which are used by the system for various purposes.

  • The aerobic reaction process takes place in all multicellular organisms and plants.

  • Aerobic respiration produces 38 ATPs whereas, anaerobic respiration produces only 2 ATP molecules.


  • During the respiration process in plants, the oxygen (O2) gas enters the plant cells through the stomata, which is found in the epidermis of the leaves and stem of a plant. 

  • With the help of the photosynthesis process, all green plant synthesize their food and thus releases energy.

Aerobic Respiration:

  • It involves molecular oxygen as the final electron acceptor which is liberated during the oxidation of glucose.

  • The glucose is completely oxidized in this process which is operated through steps like a.) Glycolysis, b.) Production of acetyl CoA (connecting link reaction), c.) Kreb's cycle, d.) Electron transfer chain (ETC), e.) Terminal oxidation.

Conversion of  Pyruvic Acid to Acetyl CoA:

  • It is an oxidative decarboxylation reaction. This process occurs in the cytoplasm in the case of prokaryotes and in mitochondria in the case of eukaryotes. 

  • The glycolytic product i.e. pyruvic acid is converted into acetyl CoA. It is catalyzed by a multienzyme complex- pyruvate dehydrogenase complex (PDH).

  • Pyruvate dehydrogenase complex needs thiamin (vitamin B1) as a co-enzyme. It can not function in the absence of Vit. B1. Hence, thiamine deficiency causes pyruvic acidosis and lactic acidosis, life-threatening conditions.

  • Acetyl CoA is an important intermediate in lipid metabolism, cholesterol biosynthesis.

  • This enzyme is present in the mitochondria of eukaryotes and cytosol of prokaryotes.

  • This reaction is called the 'connecting link' reaction between Glycolysis & Krebs cycle.


  • It is a series of enzymatic reactions that occurs in all aerobic organisms to generate energy through the oxidization of acetate derived from carbohydrates, fats, and proteins into carbon dioxide (CO2).

  • It involves the oxidative metabolism of acetyl units and serves as the main source of cellular energy.

  • Some intermediates of the TCA cycle are used in synthesizing important biomolecules such as glutamate & aspartate.

Steps involved in Citric Acid Cycle (Krebs cycle):

Step I: Condensation

  • The first step is the condensation step combining the 2-carbon acetyl group (from acetyl CoA) with a 4-carbon oxaloacetate molecule to form a six-carbon molecule of citrate.

  • CoA is bound to a sulfhydryl (-SH) and diffuses away to eventually combine with another acetyl group.

  • This step is irreversible because it is highly exergonic.

  • The rate of this reaction is controlled by negative feedback and the amount of ATP available.

  • If the ATP level increase, the rate of this reaction decreases.

  • If the ATP is short supply, the rate increases.

Step II: Dehydration

  • Citrate loses 1-H2O (one-water molecule) and gains another as citrate is converted into its isomer, isocitrate.

Step III & IV: Oxidative Decarboxylation

  • In step III, isocitrate is oxidized, producing a 5-carbon molecule, alpha-ketoglutarate, together with a molecule of CO2 and 2-electrons, which reduces NAD+ to NADH.

  • This step is also regulated by negative feedback from ATP and NADH and by a positive effect of ADP.

  • Step III product: Alpha-ketoglutarate.

  • Step IV product: Succinyl CoA.

  • The enzymes that catalyze step IV is regulated by feedback inhibition of ATP, succinyl CoA, and NADH.

Step V: Substrate-level phosphorylation

  • A substrate group is substituted for CoA and a high-energy bond is formed.

  • This energy is used in the substrate-level phosphorylation (during the conversion of the succinyl group into succinate) to form either GTP (guanine triphosphate) or ATP.

  • There are two forms of enzymes, called isoenzymes, depending upon the types of animal tissue in which they are found.

  • One form is found in tissues that use large amounts of ATP, such as the heart and skeletal muscle.

  • The second form of the enzyme is found in tissues that have a large number of anabolic pathways, such as the liver. This form produces GTP.

  • GTP is energetically equivalent to ATP; however, its use is more restricted. In particular, protein synthesis primarily uses GTP. 

Step VI: Dehydrogenation

  • It converts succinate into fumarate.

  • 2-H atoms are transferred to FAD, producing FADH2.

  • The energy contained in the electrons of these atoms is insufficient to reduce NAD+ but adequate to reduce FAD.

  • Unlike NADH, this carrier remains attached to the enzymes and transfers the electrons to the electron transport chain directly.

  • This process is made possible by the localization of the enzyme catalyzing this step inside the inner membrane of the mitochondrion.

Step VII: Hydration

  • Water (H2O) is added to fumarate and malate is formed.

  • The last step of the citric acid cycle regenerates oxaloacetate by oxidizing malate.

  • Another molecule of NADH is produced.

Products of Krebs cycle:

  • 2-Carbon atoms come into the citric acid cycle from each acetyl group, representing 4 out of 6-carbons of one glucose-molecule.

  • 2- Carbon dioxide molecules are released at each turn of the cycle; however, these do not necessarily contain the most recently-added carbon atoms.

  • The 2- acetyl carbon atoms will eventually be released on later turns of the cycle; thus, all six- carbon atoms from the original glucose molecule are eventually incorporated carbon dioxide.

  • These carriers will connect with the last portion of aerobic respiration to produce ATP molecules.

  • 1- GTP/ ATP is also made in each cycle.

  • Several of the intermediate compounds in the citric acid cycle can be used in synthesizing non-essential amino acids; like alpha-ketoglutarate, oxaloacetate is used as precursors for the synthesis of fatty acids, glutamic acid, and aspartic acid respectively. Therefore, the cycle is referred to as an 'Amphibolic pathway' i.e. involving catabolism as well as anabolism.


Monday, February 1, 2021

Respiration & Energy Transfer (Anaerobic Respiration) - NEET


Respiration & Energy Transfer (Anaerobic Respiration) 

  • Maintenance of life requires a continuous supply of energy.
  • Respiration fulfills the continuous need for energy.

  • Respiration is a catabolic process wherein complex organic substrate is oxidized to simple components to generate biological energy.

Cellular respiration occurs in two different ways like 1.) anaerobic and 2.) aerobic respiration.

  • It is cellular respiration that does not involve oxygen at all.
  • It is completed through steps like glycolysis and conversion of glycolytic product to any suitable product like lactic acid, ethanol, etc.


  • It involves the breakdown of a glucose molecule into two pyruvic acid molecules.
  • This is a common step in anaerobic as well as aerobic respiration.
  • It is completed in two phases as preparatory phase and the pay-off phase.
  • The overall process of glycolysis is completed in ten steps.

1.) Preparatory phase:

  • The first five steps constitute the preparatory phase through which glucose is phosphorylated twice at the cost of two ATP molecules and a fructose 1,6-biphosphate is formed.

  • This molecule is split to form: 1.) a molecule of glyceraldehyde 3-phosphate & 2.) a molecule of dihydroxyacetone phosphate.

  • Both of these molecules are 3-carbon carbohydrates (trioses) and are isomers of each other.

  • Dihydroxyacetone phosphate is isomerized to the second molecule of glyceraldehyde-3-phosphate.

  • Thus, two molecules of glyceraldehyde-3-phosphate are formed, and here, the preparatory phase of glycolysis ends.

2.) Pay-off phase:

  • Both the molecules of glyceraldehyde-3-phosphate are converted to two molecules of 1, 3-biphosphoglycerate by oxidation and phosphorylation.

  • Phosphorylation is brought about with the help of inorganic phosphate (Pi) and not ATP.

  • Both molecules of 1, 3-biphosphoglycerate are converted into two molecules of pyruvic acid through series of reactions accompanied by the release of energy.

  • This released energy is used to produce ATP (4 molecules) by substrate-level phosphorylation.

  • 2 ATP/glucose is the net outcome.

  • Energy is also converted by the formation of 2-NADH molecules.

B.) Lactic Acid Fermentation (In Muscle):

  • In muscles, the NADH+H ion produced during glycolysis is reoxidized to NAD+ by donating one proton and two electrons to pyruvic acid which yields lactic acid. 


  • In this reaction pyruvate is converted into a 3-carbon molecule called lactic acid.


  •  No production of carbon dioxide (CO2).


  • The only benefit is serves is that it allows glycolysis to continue with the small gain of ATP generated. 


  • Skeletal muscles usually derive their energy by anaerobic respiration. 


  •  After vigorous exercise lactic acid accumulates, leading to muscle fatigue. 


  • During rest, however, the lactic acid is reconvereted to pyruvic acid and is channeled back into the aerobic respiration pathway.

C.) Alcoholic Fermentation (In Yeast):

  • In yeast, the pyruvate is decarboxylated to acetaldehyde.


  • The acetaldehyde is then reduced by NADH+H ion to ethanol.


  • Carbon dioxide (CO2) is also produced in this process.


  • Accumulation of ethanol by fermentation in a culture of yeast may stop further multiplication and lead to the death of cells.


  • In the presence of oxygen (O2) however, yeast can respire aerobically.


  • Examples of food produced are alcoholic drinks, bread, cakes, etc.







Wednesday, January 13, 2021

Plant Tissue - NEET (Botany)

Plant Tissue-NEET (Botany)

Plant Tissue
A group of cells having essentially a common function and origin is called a tissue. The plant tissue is made up of a group of cells. These cells may be either similar or dissimilar in structure, function, and origin. Plant of higher-level shows this level of cellular organization.

Fig: Plant Tissue Flowchart

Plant tissues are broadly categorized into three tissue systems. This classification is based on parts of the plants that are present.

  • Epidermis Tissue: cells formed from the outermost surface of the leaves.

  • Vascular Tissue: involved in transporting fluid and nutrients internally.
  • Ground Tissue: involved in producing nutrients by photosynthesis and preserve nutrients.

Plant tissues are grouped as two types based on their ability to divide:

A. Meristematic Tissue. 
B. Permanent Tissue.


  • It is a group of young cells, which consists of continually dividing cells and helps in the increase of length and width of the plant.
  • These are living cells with the ability to divide into the regions where they are present.
  • These are polyhedral or isodiametric in shape without intercellular spaces.
  • The cell wall is thin, elastic, mainly composed of cellulose.
  • Protoplasm is dense with a distinct nucleus at the center and vacuoles if present, are very small.
  • Cells show a high rate of metabolism.
  • It is involved in the movement of water and nutrition within the plants.
  • These tissues are responsible for both the primary and secondary growth of the plant.
  • It is the outermost tissue, functions by providing protection from mechanical injury.
  • It gives rise to the epidermis layer, cortex, endodermis, ground tissue, and vascular tissue.

Classification of Meristem:

Following criteria are used for the classification of meristems viz. origin, function, and position as follows:

A. Origin:

Primordial Meristem or Promeristem

  • It is also called an embryonic meristem.
  • It is usually occupying a very minute are at the tip of the root and shoot.

Primary Meristem

  • It originates from the primordial meristem and occurs in the plant body from the beginning, at the root and shoot apices.
  • Cells are dividing and different permanent tissues are produced from primary meristems.

Secondary Meristem

  • It develops from living permanent tissues during later stages of plant growth; hence are called secondary meristems.
  • This tissue occurs in the mature regions of the root and shoot of many plants. 

B. Position:

Apical Meristem:

  • It is produced from promeristem and forms a growing point of apices of roots, shoots, and their lateral branches.
  • It brings about an increase in the length of the plant body and is called apical initials.
  • Shoot apical meristem is terminal in position whereas in root it is subterminal i.e. located below the root cap.
  • Intercalary meristematic tissue is present in the top or base area of the node.
  • Their activity is mainly seen in monocots.
  • They are short-lived.

Lateral Meristem:

  • It is present along the sides of a central axis of organs.
  • It takes part in increasing the girth of stem or root, eg. intrafascicular cambium.
  • It is found in vascular bundles of gymnosperms and dicot angiosperms.

C. Functions:

  • The young growing root of the plant has Protoderm that forms a protective covering like epidermis around the various organs.
  • Meristem called Procambium is involved in developing primary vascular tissue while the other structures like cortex, endodermis, pericycle medullary rays, pith are formed from the region of the ground meristem. These three groups of meristem are based on the functions.
  • This is a group of cells that have lost the capacity of division and acquired permanent size, shape, and functions.
  • They are offer elasticity, flexibility, and strength to the plant.

Depending upon the types of cells, there are two types as simple and complex permanent tissues.


  • These are made up of only one type of cells carrying similar functions.
  • This tissue is either living or dead.
  • The types of simple permanent tissues: Parenchyma, Collenchyma, Sclerenchyma.

A. Parenchyma:

  • Cells in this tissue are thin-walled, isodiametric, round, oval to polygonal, or elongated in shape.
  • The cell wall is composed of cellulose.
  • The cells are living with a prominent nucleus and cytoplasm with large vacuoles.
  • This is less specialized permanent tissue.
  • The parenchyma has distinct intercellular spaces. Sometimes, cells may show a compact arrangement.
  • The cytoplasm of adjacent cells is interconnected through plasmodesmata and thus forms a continuous tissue.
  • These cells are distributed in all the parts of the plant body viz. epidermis, cortex, pericycle, pith, mesophyll cells, endosperm, xylem, and phloem.


  • The cells stores food, water, help in gaseous exchange, increase buoyancy, perform photosynthesis, and different functions in the plant body.
  • Differentiation in parenchyma cells develops vascular cambium and cork cambium at the time of secondary growth.
  • Some parenchymatous cells perform as storage chambers for starch in vegetables and fruits.

Fig: Parenchyma tissue

B. Collenchyma:
  • It is a simple permanent tissue made up of living cells.
  • The cell wall is cellulosic but shows uneven deposition of cellulose and pectin especially at corners.
  • The cell wall may show the presence of pits. 
  • The cells are similar to parenchyma containing cytoplasm, nucleus, and vacuoles but small in size and without intercellular gaps. Thus appears to be compactly packed.
  • Shape: either circular, oval, or angular in the transverse section.
  • Collenchyma is usually absent in monocots and roots of the dicot plant.


  • Collenchyma is living mechanical tissue and serves different functions in plants.
  • It gives mechanical strength to young stems and parts like the petiole of the leaf.
  • It allows bending and pulling action in plant parts and also prevents tearing of leaf.
  • Growth of organs and elongation.

Fig: Collenchyma tissue

C. Sclerenchyma:
  • It is simple permanent tissue made up of compactly arranged thick-walled dead cells.
  • The cells are living at the time of production but at maturity they become dead.
  • As cells are devoid of cytoplasm their thickened walls are due to uniform deposition of lignin.
  • The cells remain interconnected through several pits.

It is of two types: 1.) Fibers & 2.) Sclerids.

1.) Fibers

  • It is a thread-like, elongated, and narrow structures with tapering and interlocking end walls.
  • These are mostly in bundles, pits are narrow, unbranched, and oblique.
  • They provide mechanical strength.

2.) Sclerids:

  • It is usually broad, with blunt end walls.
  • These occur singly or in loose groups and their pits are deep branched and straight.
  • These are developed due to the secondary thickening of parenchyma cells and provide stiffness only.


  • This tissue functions as the main mechanical tissue.
  • It permits bending, shearing, and pulling.
  • It gives rigidity to leaves and prevents them from falling.
  • It also gives rigidity to epicarps and seeds.
  • Commercial fibers are also produced from sclerenchyma fibers. e.g. jute, flax, hemp.

  • This tissue is heterogeneous comprising more than one type of cell and all function as a single unit.
  • This tissue is involved in conducting the sap and food from source to sink area.
  • This type of complex permanent tissue: Xylem, Phloem.
Fig: Complex Permanent Tissue

A. Xylem:
  • It is dead complex tissue.
  • The xylem also provides mechanical strength to the plant body.
  • Tracheids and Vessels conduct water and minerals. These are known as hadrome = the part of the xylem mestome that conducts water and nutrients.
  • In pteridophytes and gymnosperms, tracheids are conducting elements and vessels in angiosperms, Selaginella (Pteridophyte) and Gnetum (Gymnosperm) show the presence of vessels.

1.) Tracheids:

  • It is elongated, tubular, and dead cells.
  • The ends are oblique and tapering.
  • The cell walls are uniformly thickened and dignified. This provides mechanical strength.
  • It contributes 95% of the wood in Gymnosperms and 5% in Angiosperms.
  • The different types of thickening patterns are seen on their walls such as annular (in the form of rings), spiral (in the form of spring/helix), scalariform (ladder-like), pitted is the most advanced type (small circular area) which may be simple or bordered.

2.) Vessels:

  • It is longer than tracheids with perforated or dissolved ends and formed by the union of several vessels end to end.
  • These are involved in the conduction of water and minerals.
  • Their lumen is wider than tracheids and the thickening is due to lignin and similar to tracheids.
  • In monocot, vessels are rounded.
  • In Dicot angiosperm, vessels are angular.
  • The first formed xylem vessels (protoxylem) are small and have either annular or spiral thickening.
  • The later formed xylem vessels (metaxylem) have reticulate or pitted thickenings.
  • Endarch: When protoxylem is arranged towards pith and metaxylem towards the periphery. E.g. in the stem.

  • Exarch: When metaxylem is arranged towards pith and protoxylem towards the periphery. E.g. in the roots.

Fig: Tracheids & Vessels (Xylem tissue)

3.) Xylem Parenchyma (Only living tissue):
  • The cells are small associated with tracheids and vessels.
  • This is the only living tissue among the complex tissue.
  • The function is to store food (starch) and tannins.
  • It is involved in lateral or radial conduction of water or sap.

4.) Xylem Fibers:

  • The tissue is sclerenchymatous cells and serves mainly mechanical support.
  • These are called wood fibers.
  • Shape: elongated, narrow, spindle.
  • Cells are tapering at both ends and their walls are lignified.

B. Phloem (Bast):

  • This is a living tissue. It is called as bast.
  • Phloem is responsible for the conduction of organic food material from a source (generally leaf) to a sink (other plant parts).
  • It was named leptome by Haberlandt as similar to the xylem.
  • Based on origin, it is first formed (Proto) and lately formed (Meta) phloem.
  • It is composed of sieve cells, sieve tubes, companion cells, phloem parenchyma, and phloem fibers.

1.) Sieve tubes:

  • It is a long tubular conducting channel of phloem.
  • These are placed end to end with bulging at end walls.
  • The sieve tube has a sieve plate formed by septa with small pores.
  • The sieve plates connect the protoplast of the adjacent sieve tube cells.
  • The sieve tube cell is connected to a companion cell through phloem parenchyma by plasmodesmata.
  • Sieve cells are found in the lower plants like pteridophytes and gymnosperms.
  • The cells are narrow, elongated with tapering ends and a sieve are located laterally.

2.) Companion cells:

  • This is narrow elongated and living.
  • These cells are laterally associated with sieve tube elements.
  • The companion cells have dense cytoplasm and prominent nucleus.
  • The nucleus of the companion cell regulates the functions of the sieve tube cells through simple pits.
  • From an original point of view, the sieve tube cells and companion cells are derived from the same cell.
  • The death of the one results in the death of the other type.

Fig: Sieve tubes & Companion cells

3.) Phloem Parenchyma:
  • The cells are living, elongated found associated with sieve tube and companion cells.
  • The chief function is to store food, latex, resins, mucilage, etc.
  • The cells carry out lateral conduction of food material.

4.) Phloem Fibers (only Dead tissue):

  • These are the only dead tissue among the phloem. These are sclerenchymatous. 
  • It is generally absent in the primary phloem but present in the secondary phloem.
  • These cells are with lignified walls and provide mechanical support.
  • They are used in making ropes and rough clothes.


Thursday, October 1, 2020

Class Chondrichthyans - NEET - Biology

Class Chondrichthyans

Fig: Rhinocodon

  • They have a skeleton that is composed predominantly of cartilage, often impregnated with calcium.

Important characteristics:

  • Marine animals having cartilaginous endoskeleton.
  • The notochord is persistent throughout life.
  • Gill slits are separate & operculum (gill cover) is not present.
  • The skin is tough, containing minute placoid scales.
  • The stomach is J-shaped.
  • The swim bladder & lungs are absent and the liver is filled with oil to provide buoyancy to the body while swimming.
  • Due to the absence of an air bladder (fish maw), they have to swim constantly to avoid sinking. If they stop swimming, they will sink (fall) like a stone.
  • The heart is two-chambered (one auricle & one ventricle).
  • Kidneys opisthonephric. Excretion ureotelic. Cloaca present.
  • Fertilization is external. Sexes are separate.
  • The pectoral fins of the shark are called claspers & used for copulation.
There are three ways in which sharks reproduce;
  • Oviparous= in which the female lays eggs which takes a few months to develop.
  • Ovoviviparous= where the eggs are hatched in the oviduct & the embryo develops in the uterus.
  • Viviparous= in which the gestation period of the embryo is about one year.
Examples: Rhinocodon (whale shark), Carcharodon (great white shark), Trygon (stingrays), Torpedo (electric rays), Scoliodon (dogfish), Pristis (sawfish).
Fig: Stingrays


Class Reptilia- NEET-Biology

 Class Reptilia

Fig: Sphenodon (Tuatara)

  • Reptilia= Creeping or crawling mode of locomotion.
  • It is considered the first animal on the land with the ability to live & multiply on land, with the help of their amniotic eggs.
  • Most of them are tetrapods, with four-legs or like-like appendages.

Important characteristics:

  • The skin is covered with scutes or scales & it has a high level of keratin, which prevents water loss through the skin.
  • Glands are usually absent.
  • Snakes & lizards shed their scales as skin cast (sloughing) routinely.
  • They are considered tetrapods with sets of paired limbs. In some reptiles, like snakes, worm lizards, the legs are absent, but it is believed that these animals evolve from some tetrapod ancestor.
  • Unlike amphibians, reptiles do not pass through an embryonic stage with gills. These animals breathe with well-developed lungs, right from birth. Most of them have two lungs, except for some snakes, which posses only a single lung.
  • All reptiles have three-chambered hearts, except crocodiles, which have four-chambered (2 atria, 2 ventricles), like mammals & birds. The three chambers in reptiles consist of two atria to receive blood & one partially divided ventricle for pumping blood.
  • Reptiles do not have external ear openings. The tympanum represents the ear.
  • Most of the reptiles lay eggs, but some of them give birth to young ones, by hatching the eggs inside the body of the mother.
  • Their characteristics also include internal fertilization, in this process sperm gets deposited into the reproductive tract of the female directly.
  • Being cold-blooded, the body temperature of the reptiles vary with the surrounding atmosphere.
  • Sexes are separate. Fertilization is internal.
  • They are oviparous & development is direct.
  • Example: Sphenodon (Tuatara), Varanus (Komodo dragon), Draco (Flying lizard), Ophiophagus (King cobra), Hydrophis (Sea snake), Crocodylus (Indian freshwater crocodile).
Fig: Ophiophagus (King cobra)


Phylum - Porifera - NEET-Biology

 Phylum Porifera

Fig: Phylum Porifera = Pore Bearing

Important Characteristics:

  • 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 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. 
  • 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)


Phylum Platyhelminthes (Flatworms) - NEET-Biology

 Phylum Platyhelminthes (Flatworms)

Important Characteristics:

  • Acoelomate, triploblastic, bilaterally symmetrical organisms.
  • 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 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)


Wednesday, September 30, 2020

Phylum Annelida - NEET-Biology

 Phylum Annelida

Fig: Leech (Hirudinaria)


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