Gaurav Gupta sir

2021-11-09 19:33:08 𝙋𝙃𝙔𝙇𝙐𝙈 𝙈𝙊𝙇𝙇𝙐𝙎𝘾𝘼:-

The phylum—Mollusca (Molluscs — soft bodied) includes the soft bodied, unsegmented, eucoelomate animals. These are called molluscs or shelled animals. Johnston (1650) coined .the term ‘Mollusca’. Mollusca is the second largest animal phylum and includes about 85,000 species.

The study of molluscs is called ‘Malacology’.

General Features
Some important general features ofphylum—mollusca are discussed below:-

i. Habit and Habitat Molluscs are mostly of marine forms (Sepia, Octopus, Chiton, etc.) Some are freshwater (e.g, Unio and Pila) and some are also terrestrial forms (e.g, Land snails). Few molluscs are parasites also, e.g., Glochidium larva, etc.

ii. Symmetry These are generally bilaterally symmetrical and some are asymmetrical due to torsion or twisting during growth.

iii. Germ Layers and Organisation They are triploblastic and possess organ system level of organisation.

iv. Body Form They have unsegmented, soft body covered by a calcareous shell, which is differentiated into head, muscular foot and visceral hump.

Mantle is a soft, spongy thick fold of skin over the visceral hump that secretes calcareous shell. The space between the hump and the mantle is called the mantle cavity in which feather like gills are present.

v. Skeleton Molluscsgenerally have shell as exoskeleton. In Octopus, shell is absent.

vi. Body Cavity The coelom is greatly reduced although they are eucoelomate.

vii. Locomotion The locomotory organ is muscular foot.

viii. Digestion The digestive tract is complete. The mouth contains a rasping organ called radula with file like transverse row of chitinous teeth. Anus opens into the mantle cavity.

ix. Respiration In terrestrial forms respiration occurs through lungs. In aquatic forms, respiration occurs through feather-like gills or ctenidia.

X.Excretion A pair of metanephridia (kidneys) or organs of Bojanus or Keber’s organs are present.

xi. Circulation Open type of circulation is present. The coelom is called haemocoel.

xii. Sense Organs These have eyes, statocyst, tentacles for equilibrium and receptors for touch, smell and taste.

xiii. Nervous System Few pairs of ganglia like cerebral, visceral and pedal with nerves is present.

xiv. Reproduction Molluscs reproduce sexually. Sexes are separate and mostly oviparous. Fertilisation is external or internal.

Development is either direct or indirect with larval stages like trochophore, glochidium and veliger. e.g., Chaetopleura(chiton), Dentalium (elephant tusk shell), Pila (apple snail), Patella, Aplysia (sea hare). Pinctada (pearl oyster) Sepia (cuttlefish), Loligo (squid), Octopus (devil fish).

Join for more Open / Comment

2021-11-09 19:02:40 Doubtnut ke Study Channels par ab sirf Instant doubt solving hi nahi
Milenge PDFs , Latest News , Previous Year Papers , Free Live Classes & aur bhi bhot kuch

Abhi join karein Doubtnut , Official Telegram Channel ko!!

Doubnut Official Channel
➤ https://t.me/Doubtnut

Doubtnut NEET
➤ https://t.me/Doubtnut_NEET

Doubtnut IIT JEE
➤https://t.me/DoubtnutIITJEE Open / Comment

2021-11-09 13:02:11 𝙋𝙃𝙔𝙇𝙐𝙈 𝘼𝙍𝙏𝙃𝙍𝙊𝙋𝙊𝘿𝘼:-

Phylum-Arthropoda (Arthron – jointed; podos — foot) include the first and simplest segmented animals. These are commonly called as jointed legged animals. It is the largest group of animal that include about 1,000,000 insect species, 1,02,248 spiders and scorpion species, 1,03,248 arachnoid species and 47,000 crustacean species representing about 80% of total known animal species.

General Features
Some important general features of phylum—arthropoda are discussed below:-

i. Habitat and Habit They may be aquatic or terrestrial. They may occur as free-living or parasitic forms e.g., Bed bugs, ticks, mosquitoes, etc.

ii. Body Parts Body is segmented externally. It has distinct head, thorax and abdomen. Head bears many fused segments and sense organs.

iii. Symmetry and Body Organisation Arthropods are bilaterally symmetrical. They are triploblastic with organ system level of organisation.

iv. Appendages They have jointed, paired appendages, which are present in some or all somites or segments. These perform various functions like walking, clinging, jumping, feeding, etc.

v. Exoskeleton The exoskeleton is formed of thick, tough and non-living chitinous cuticle.Exoskeleton protects animal from mechanical and chemical injuries, prevents desiccation and also helps in attachment.

vi. Locomotion Jointed appendages help in locomotion. Cilia are found to be absent in arthropod.

vii. Digestive System Alimentary canal is complete and well-developed, i.e., divided into foregut, midgut and hindgut.
viii. Respiration It occurs through general body surface, gills (e.g., Prawn), book lungs (e.g., Scorpion and spider), trachea (e.g., cockroach) and book gills (e.g., King crab).
head tall Antenna.

IX. Circulation The circulatory system is open type, i.e., blood flows in the haemocoel instead of blood vessels.

x. Excretion The excretory organs are Malpighian tubules (opening into duct) or green glands opening ‘ directly to the exterior.

xi. Nervous System The nervous system consists of a nerve ring and a double ganglionated ventral nerve cord.

xii. Sense Organs Arthropods have simple eyes called ocelli and compound eyes. Aquatic forms have statocysts for balancing.

xiii. Reproduction Arthropods reproduce by sexual methods. Fertilization is usually internal type. They are generally oviparous but few are viviparous, i.e., scorpion. Development may be direct or indirect involving metamorphosis. Open / Comment

2021-11-08 20:28:39 Doubtnut ke Study Channels par ab sirf Instant doubt solving hi nahi
Milenge PDFs , Latest News , Previous Year Papers , Free Live Classes & aur bhi bhot kuch

Abhi join karein Doubtnut , Official Telegram Channel ko!!

Doubnut Official Channel
➤ https://t.me/Doubtnut

Doubtnut NEET
➤ https://t.me/Doubtnut_NEET

Doubtnut IIT JEE
➤https://t.me/DoubtnutIITJEE Open / Comment

2021-11-07 20:18:09 𝙋𝙃𝙔𝙇𝙐𝙈 𝘼𝙎𝘾𝙃𝙀𝙇𝙈𝙄𝙉𝙏𝙃𝙀𝙎:-

Phylum—Aschelminthes or Nemathelminthes or Nematoda (Nema — thread; helminth — worms) includes roundworms. They are commonly called as nematodes.

General Feature
Some important general features of phylum- aschelminthes are discussed 𝙗𝙚𝙡𝙤𝙬:-

i. Habitat and Habit They are mostly free living and may occur in water or within the soil. There are several parasitic species which live within the body of animals or plants, e.g., Guinea worms, whipworms, eyeworms, etc.

ii. Symmetry They show bilateral symmetry and have organ system level of organisation.

iii. Germ Layers They are triploblastic animals and have tube within tube body plan.

iv. Body Walt The body wall contains an outer cuticle, syncytial epidermis and a muscle layer. Circular muscles are absent.

v. Body Cavity Aschelminthes are pseudocoelomates as the cavity present between the body wall and gut is not lined by mesodermal epithelium.

Circulatory and respiratory systems are also seem to be absent in Aschelminthes.

vi. Digestive System Alimentary canal is complete with a well-developed muscular pharynx.

vii. Excretory System It consists of a pair of gland cells or intracellular canals or both.

viii. Nervous System It contains a nerve ring around the pharynx with dorsal and ventral longitudinal nerve cords running throughout the length of the body.

ix. Reproduction Nematodes reproduce only by sexual method. Sexes are separate and exhibit sexual dimorphism. The males are generally smaller than the females to aid copulation.

x. Fertilisation It is internal. The fertilised eggs develop directly or indirectly through larvae that undergo moulting and finally grow into adults. Open / Comment

2021-11-07 18:44:56 Doubtnut ke Study Channels par ab sirf Instant doubt solving hi nahi
Milenge PDFs , Latest News , Previous Year Papers , Free Live Classes & aur bhi bhot kuch

Abhi join karein Doubtnut , Official Telegram Channel ko!!

Doubnut Official Channel
➤ https://t.me/Doubtnut

Doubtnut NEET
➤ https://t.me/Doubtnut_NEET

Doubtnut IIT JEE
➤https://t.me/DoubtnutIITJEE Open / Comment

2021-11-06 19:47:01 Important Points of NCERT :

Environmental protection act:- 1986

Air Act:- 1981(amended in 1987)

1990:- Delhi ranked 4th out of 41 most polluted cities in the World.

All buses run on CNG by- 2002

Water Act:- 1974

Chipko movement(Garhwal Himalayas):- 1974

JFM(Joint Forest Management):- the 1980s

Montreal Protocol (Canada):- 1987 (amended in 1989)

The Earth Summit:- 1992 (Rio de Janeiro)

World Summit:- 2002 (Johannesburg S.A)

IUCN Red List (2004):- 784 species extinct in last 500 years.

Joint Forest Management (JFM):- 1980's.

1st recombinant DNA:- 1972.

1st restriction endonuclease:- 1963.

1997:-An American company got patent rights on Basmati rice.

1990:- 4 year old girl got ADA deficiency Open / Comment

2021-11-06 18:33:42 Doubtnut ke Study Channels par ab sirf Instant doubt solving hi nahi
Milenge PDFs , Latest News , Previous Year Papers , Free Live Classes & aur bhi bhot kuch

Abhi join karein Doubtnut , Official Telegram Channel ko!!

Doubnut Official Channel
➤ https://t.me/Doubtnut

Doubtnut NEET
➤ https://t.me/Doubtnut_NEET

Doubtnut IIT JEE
➤ https://t.me/DoubtnutIITJEE Open / Comment

2021-11-06 08:56:01 The best JEE preparation is now on your finger tips and that too at the most amazing prices. Enroll now and get access to everything you need to ace IIT JEE, including video lectures by the Dream Team, QBank, PrepTests. Use my code < DP7315 > to get an additional ₹500 Off.

https://prepladder.com/app/singlePackJEE Open / Comment

2021-11-05 20:44:24 𝙋𝙃𝙔𝙇𝙐𝙈 𝘾𝙉𝙄𝘿𝘼𝙍𝙄𝘼/𝘾𝙊𝙀𝙇𝙀𝙉𝙏𝙍𝘼𝙏𝘼

There are about 9000 species of cnidarians. The name Cnidaria (Knide — nettle or sting cells) is derived from the stinging cell or cnidoblasts present on the ectoderm of tentacles and body of these animals.

General Features
Some important general features of phylum coelen- terata are discussed 𝙗𝙚𝙡𝙤𝙬:-

i. Habit and Habitat Cnidarians are exclusively of marine forms (Obelia, Aurelia, Physalia, Metridium), but few of them are freshwater form (e.g. Hydra). They are either sedentary (fixed) or free swimming forms.

ii.Body Organisation and Body Wall They have tissue grade organisation. Coelenterates are diploblastic. The layers of body wall contain several types of cells, such as interestitial cells, sensory cells, nerve cells, epitheliomuscular cells, stinging cells (cnidoblasts), etc.

iii. Coelentric Cavity A coelenteron or gastro- vascular cavity is present, which is blind at one end and opens as mouth or hypostome at other end. Mouth is used both for ingestion and egestion.

iv. Tentacles The mouth is surrounded by many thin, long, slender hollow structures called tentacles. Their function is to paralyse and capture the prey, attachment, defense and offence.

v. Skeleton A horny or calcareous exoskeleton as well as endoskeleton is present in many cases. The coelenterate with exoskeleton of calcium carbonate are called corals.

vi. Digestion In coelenteron or gastrovascular cavity, both intracellular and extracellular digestion occurs.

vii. Respiration and Excretion Exchange of gases and excretion occurs directly as all the cells are in direct contact with water.

viii.Sensation Sensory cells occur in the body wall such as statocyst for balancing and ocelli for photosensitivity.

ix. Nervous System It is in the form of a nerve net, i.e., the unipolar neurons are loosely arranged in the body wall.

Polymorphism Cnidarians are mainly of two types of individuals, i.e., polyp (cup-shaped) and medusa (umbrella-shaped). Polyp is sessile, cylindrical structure with mouth and tentacles facing upwards, e.g., Hydra, Adamsia, etc. Medusa is free swimming zooid with mouth and tentacles facing downwards, e.g., Aurelia or jelly fish. Medusae may form polyps after sexual reproduction while polyps form medusae through vegetative budding. Many variations occur in zooid forms. This phenomenon is called polymorphism, which helps in division of labour.

xi. Reproduction Coelenterates reproduce both by asexual and sexual methods. In many cnidarians, the polyps usually reproduce asexually by budding to give rise to a medusae. The medusae bear gonads or sex organs and reproduce sexually to form polyps.

xii. Fertilisation It may be external or internal.

xiii. Alternation of Generation The cnidarians complete their life cycle through two phases, i.e., asexually reproducing polyp phase and’ sexually reproducing medusa phase. Those cnidarians which exist in both forms exhibit alternation of generation (metagenesis). Open / Comment