Diversity Among Animals Biology notes for fa fsc / 1st years/ class 11 chapter no 9 short questions, long question and pdf file for download google drive 2021.
Diversity Among Animals questions for class 11 2021
Why are certain animals called living fossils?
Living fossils are those animals that have characters of extinct animals or organisms. The closely related species have become extinct from the earth’s surface.
Sphenodon, a reptile called living fossil.
Q.2 ii) What is the reason for the formation of larva during the life cycle of many animals?
In some animals, eggs hatch into larvae because they have a moderate amount of yolk in their eggs. This yolk is not sufficient for the lete development of young to be like their adults. An organism in the larval stage is self-sufficient. Usually, it has special organs not characteristic of the adult form but lacks other organs characteristic of the adult. In many animals, the existence of the larval stage is determined by the differences in the modes of life.
Q.2 iii) What is the importance of polymorphism?
The existence of a single species in more than two morphological forms (individual types) is termed as polymorphism.
Importance of polymorphism:
- Polymorphism is a discontinuous genetic variation resulting in the occurrence of several different forms or types of individuals among the members of a single species. A discontinuous genetic variation divides the individuals of a population into two or more sharply distinct forms.
- Polymorphism usually functions to retain a variety of forms in a population living in a varied environment.
- The phenomenon of polymorphism is essentially one of a division of labour in which specific functions are assigned to different individuals.
- Polymorphism gave the colonies a competitive edge in protection and food gathering and eventual survival.
The individual is called zooids. Two major types of zooids are Polyps (tube-like body) and Medusae (Umbrella like body). Polyps are modified for feeding, protection, and asexual reproduction. Medusae are concerned with sexual reproduction.
This distribution of functions among diversified individuals and their subsequent modifications in coelenterates may have resulted from their initial simple organization and lack of organ specialization.
Q.2 iv) Cuttlefish, jellyfish, starfish are invertebrates and are not fishes. Why are many invertebrates called fish?
These are common names given by people made on random observation in early times and have no connection with the biological classification of animals. In the biological world, all living things are placed into groups depending on common characteristics. The animal kingdom is divided into two groups, the vertebrates and invertebrates. Invertebrates are a group of animals that have no backbone, unlike vertebrates fishes. Cuttlefish, jellyfish, starfish are invertebrates and called fishes because they live in a marine environment.
Q.2 v) What is the percentage of fishes and birds among the total vertebrate species numbering about 58933?
Fishes are the largest group of vertebrates and constitute about 48 % of the total vertebrates. The number of living fish species is more than 29000.
Birds make 17% of total vertebrates.
Q.2 vi) Why do reptiles excrete nitrogenous wastes in the form of uric acid crystals?
Reptiles live in water-deficient environments so to conserve maximum water they excrete uric acid crystals. The excretion of uric acid requires the least amount of water as compared to other nitrogenous wastes.
Differentiate the following
Q.3 i) Haemolymph and blood:
Haemolymph is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod body remaining in direct contact with the animal’s tissues. It is composed of a fluid plasma in which hemolymph cells called hemocytes are suspended.
Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells.
Q.3 ii) Proterostomes and Deuterostomes
|In protostome embryonic development, determinate and spiral cleavage take place||In deuterostomes, embryonic development, radical and indeterminate cleavage takes place|
|In protostomes, the first opening in the embryo is the mouth||In deuterostomes, the anus is the first opening in the embryo|
|The anus arises secondarily||In deuterostomes, the mouth arises secondarily|
|Protostomes are composed of a solid, ventral nerve cord.||Deuterostomes are composed of a hollow nerve cord and pharyngeal gill slits.|
|Protostomes include mollusks, annelids, and arthropods||Deuterostomes include echinoderms and all chordates|
Q.3 iii) Heart and pseudo-heart
The heart is a muscular organ about the size of a fist, located just behind and slightly left of the breastbone. The heart pumps blood through the network of arteries and veins called the cardiovascular system.
The circulatory system consists of a dorsal and ventral blood vessel, and 5 pairs of branches called pseudo hearts that connect the two vessels together behind the head region. The branches pump the blood toward the back of the worm through the ventral blood vessel, and blood returns through the dorsal blood vessel. Due to the pulsating action of the branches, which is similar to the action of hearts, they are termed as the pseudo heart.
Q.3 iv) Polymorphism and alternation of generation.
The existence of a single species in more than two morphological forms (individual types) is termed as polymorphism.
Alternation of generation:
Alternation of generation is the occurrence of two or more forms differently produced in the life cycle of a plant or animal usually involving the regular alternation of a sexual form with an asexual generation.
Q.3 v) Segmentation in earthworm and tapeworm
Segmentation in earthworm:
In earthworms, the body is metamerically segmented (metamerism) allows for each part of the worm to be somewhat independent, allowing the worm to continue to function even one its part is damaged. The segments also prevent the motion from being transferred through the coelom (body cavity), allowing for smoother motion.
Segmentation in tapeworm:
Tapeworms are bilaterally symmetrical. Their body is either segmented or superficially segmented and true segmentation is absent.
Q.3 vi) Haemocoel and coelom
|True coelom can be found in echinoderms and chordates.||Haemocoel is a type of primary body cavity found in arthropods and molluscs.|
|The fluid inside the coelom is called coelomic fluid.||The fluid inside the haemocoel is called haemocoelomic fluid.|
|The organisms that have coelom are called coelomates.||The organisms that have haemocoel are called haemo-coelomates.|
Q.3 vii) Healing and regeneration:
“Wound healing is a complex process in which the skin, and the tissues under it, repair themselves after injury.”
“Regeneration is the ability to recreate lost or damaged tissues, organs and limbs.”
Q.3 viii) Prototheria and metatheria
|Prototheria or Monotremata are the most primitive mammals and are also called as egg laying mammals.||Metatheria or marsupials are also called pouched mammals|
|They have certain characters of reptiles like they lay eggs but these eggs are kept in the uterus where they are fertilized and development takes place.||Females of these animals bear a pouch or marsupium on the ventral side of the belly in which young ones are kept after hatching as they are born in a very underdeveloped and immature stage.|
|These animals are more rightly called ovoviviparous. The young are given birth in an immature form and are nourished by the teats present on the ventral side of the body in females.||Teats of the mammary glands are present in the pouch from which the babies suckle milk.|
Australian platypus and echidna (spiny anteater)
Kangaroo, Opossum, Koala etc.
Q.3 ix) Perissodactyla and artiodactyla
|Perissodactyla are even hoofed mammals||Artiodactyla are even hoofed mammals.|
Horse, zebra etc.
Cow, goat, deer etc.
Q.3 x) Bilateral and radial symmetry
|Bilateral Symmetry||Radial Symmetry|
|All the animals in grade bilateria are bilateral symmetrical||In this group animals with radial symmetry have been included.|
|The animal can be divided into two equal parts by an imaginary line only in one plane.||The parts of the body are arranged around a central axis in such a way that any plane passing through the central axis divides the animal into halves that are almost mirror image of each other e.g. as in cnidaria (coelenterate).|
|All the animals included in grade bilateria are triploblastic.||All the animals which are included are diploblastic.|
|The animals belonging to phyla, Platyhelminthes, Nematoda, Annelida, Mollusca, Arthropoda, Echinodermata, hemichordata and Chordata are included in this grade.||The only phylum included in this grade is phylum Cnidaria|
Long Questions Biology Notes for kpk
Q.4 i) Describe the importance of classification in the animal kingdom. What are the different categories used for classification?
Importance Of classification in the animal kingdom:
Being a very diverse group, animals need to be classified for the convenience of study. In ancient times when the knowledge of cells and facility of microscopic studies were not available, scientists roughly divided the animals into two groups based on the presence or absence of the vertebral column.
Classification of animals is important because it allows scientists to identify, group, and properly name organisms through a standardized system, based on similarities found in the organism’s DNA/RNA (genetics), adaptations (Evolution), and embryonic development (Embryology) to other known organisms to better study and understand the new organism as a whole.
Categories used for classification:
The smallest and the basic unit of classification is species. Species is the group of reproductively isolated individuals which are similar in their internal and external characteristics. These individuals interbreed to produce fertile offsprings. Closely related species are placed in a genus. Genera similar to each other are grouped into a family. Many similar families make an order and orders having similarity are placed in a class. Related classes are combined into a phylum.
The system of the naming of animals is called binomial nomenclature. In this system, scientific or zoological names are assigned to animals. Common names of animals may be similar but no two species in the world can have a similar scientific name. In binomial nomenclature an animal is assigned two names: first is the name of the genus to which it belongs and the second is its specific name (i.e. the name of the species of animals).
As a rule, the first “generic name” is always written with a capital letter and the second “specific name” with a small letter. Similarly, the scientific name is always written in italics or otherwise underlined. The scientific name of a human being is Homo sapiens.
Classification of Animals:
This group includes all those animals, which possess a backbone vertebral column. Vertebrata included fishes, amphibians, reptiles, birds and mammals.
All those animals which do not possess backbone were included in this group. Invertebrata was divided into following phyla.
- 1. Phylum Porifera
- 2. Phylum Coelenterata
- 3. Phylum Platyhelminthes
- 4. Phylum Aschelminthes
- 5. Phylum Annelida
- 6. Phylum Mollusca
- 7. Phylum Arthropoda
- 8. Phylum Echinodermata
- 9. Phylum Chordata (excluding subphylum Vertebrata)
Few invertebrate animals which do not fit any of the above-mentioned phyla are classified into “phylum Ctenophora” and “minor phyla” but the number of animals and their species present in these phyla are so much less than they are generally ignored. They are inhabitants of deep seas and we know very little about them.
Classification from phylum to species:
Each phylum is divided into the following lower categories as below:
Except for the genus, the above categories can further be divided using prefix sub or super like superphylum and subphylum, superclass and subclass superorder and suborder etc.
Q.4 ii) Draw a pedigree tree for the living phyla of animals?
Q.4 iii) What are the salient features of phylum Annelida? Describe their economic importance as well.
Important Characteristics of phylum Annelida:
- The body of annelids is divided into different segments. The body is metamerically segmented i.e. the organs are repeated in every segment.
- The body of annelids is bilaterally symmetrical.
- They are coelomates having a true coelom.
- The body may be cylindrical as in earthworm or dorso-ventrally compressed as in nereis.
- They are triploblastic.
- They have a closed circulatory system.
- In earthworm four to five pairs of hearts called pseudo-hearts are present, which contract rhythmically to keep the blood moving in the system.
- Colour of the blood is red due to haemoglobin dissolved in the plasma.
- The digestive system is well developed, especially in free-living species. Different digestive organs are well-formed.
- The excretory system consists of metamerically arranged nephridia. Nephridium opens to the exterior through nephridiopore.
- The body is covered with a glandular epidermis which secretes mucus and keeps the skin moist.
- Locomotory organs are setae or parapodia.
- Respiration is through the general surface but some annelids like nerves have gills under parapodia.
- The body is covered with a cuticle.
- Annelids are mostly hermaphrodite i.e. the same animal contains both types of sex organs, ovaries and testes but cross-fertilization is common.
- Trochophore larva is formed during the life cycle of some annelids, especially in marine species.
- They are found everywhere in damp soil, fresh and marine water and some species are parasitic too.
- In annelids like an earthworm, every segment of the body contains blood vessels, epidermal structures (like setae etc.), nervous and excretory organs. This pattern is repeated in most of the segment with some variation.
Economic importance of phylum Annelida:
Annelids are an economically very important group of invertebrates. Earthworm makes the soil porous and fertile which increases the production of crops. Animals of this group are an integral part of the food chains both in an aquatic and terrestrial environment. Leech is a parasite of cattle damages their health and growth. Many molluscs like octopus and cuttlefish are eaten as seafood.
Examples of phylum Annelida:
Pheritema Posthuma (earthworm), Hirudinaria medicinalis (medicinal leech), Series etc.
Q.4 iv) Describe the parasitic adaptations in phylum Platyhelminthes?
The body of all the animals included in this phylum is dorsoventrally flattened, i.e. leaf-like or paper-like hence called flatworms. They are bilaterally symmetrical. They are the first triploblastic metazoa and are acoelomates. Their bodies are either unsegmented or superficially segmented, and true segmentation is absent.
Parasitic adaptations in phylum Platyhelminthes:
- In parasitic forms the cilia are absent and a thick coat of cuticle is present for protection.
- Organs of attachment are present in the form of hooks or suckers.
- The digestive system in parasitic forms, it is either poorly developed (Class Trematoda) or completely absent (Class Cestoda).
- No circulatory or respiratory system is present.
- Class Trematoda (liver flukes) and Class Cestoda (tapeworms) being parasitic do not show any regeneration. All the members of this phylum are solitary i.e. not found in colonies.
- In Cestodes (Tapeworms) the digestive system is completely absent. Tapeworm absorbs digested food from the wall of the intestine of the host where they remain attached with the help of scolex (head) which is provided with hooks and suckers.
- The excretory system is with few flame cells (flame cell is a structure with thin elastic walls with a nucleus and a cavity containing many long cilia flickering like a flame) attached with ducts which open at the excretory pore.
- The nervous system is with a pair of anterior cerebral ganglia and a ventral ganglion connected by nerve ring and one or three nerve cords.
- They are hermaphrodite i.e. both sex organs are found in the same animal. The reproductive system is well developed with gonads, their ducts and copulatory organs. Eggs are small with yolk and are produced in very large numbers.
- Self and cross both types of fertilization is present among Platyhelminthes. Fertilization is always internal. The fertilized eggs are passed out which either directly grow into a new individual as in planaria and tapeworm or a different type of larvae are formed as in liver fluke.
Q.4 v) Compare the structure of the heart in different phyla of the animal kingdom and especially in different classes of vertebrates.
- In invertebrates, no true heart structure is present, however, some invertebrates, such as in annelids; earthworms, have a closed circulatory system in which blood is pumped throughout the body by the contraction. In earthworm four to five pairs of hearts called pseudo-hearts are present, which contract rhythmically to keep the blood moving in the system.
- The open circulatory system is common to molluscs and arthropods. Open circulatory systems (evolved in crustaceans, insects, molluscs and other invertebrates) pump blood into a hemocoel with the blood diffusing back to the circulatory system between cells. Blood is pumped by a heart into the body cavities, where tissues are surrounded by the blood.
- The hearts of fishes are two-chambered, they have only one atrium and one ventricle. Fish have a single systemic circuit for blood, where the heart pumps the blood to the gills to be re-oxygenated (gill circulation), after which the blood flows to the rest of the body and back to the heart.
- The amphibians have a 3 chambered heart. The heart has a divided atrium segment. The right atrium receives blood from the systemic circulation, while the left atrium receives blood from the lungs. Amphibians are unique in that they have a third circuit that brings deoxygenated blood to the skin for the gas exchange to occur; this is called pulmocutaneous circulation.
- Reptiles have a 3 1/2 chambered heart. In the 3 1/2 chambered heart, the ventricle is partially divided. This separation decreases the mixing of left side oxygenated blood with deoxygenated blood of the right ventricle.
- Both birds and mammals have 4 chambered hearts. Both the atrial and ventricular regions of the heart are divided. This allows complete separation of the pulmonary circuit from the systemic circuit.
Q.4 vi) Discuss the distinguishing characters of phylum Arthropoda. How will you evaluate the economic importance of class Insecta?
Phylum Arthropoda includes all those animals that have jointed appendages. This is the most successful group and the largest phylum of the animals.
General characteristics of phylum Arthropoda:
1. Triploblastic, bilaterally symmetrical:
Arthropods are triploblastic and bilaterally symmetrical. The body is metamerically segmented.
2. Jointed appendages:
They have jointed limbs and generally, every segment of the body has a pair of legs (limbs or appendages).
The body is covered with an exoskeleton in the form of thick cuticle chemically made of chitin. The exoskeleton provides not only protection but also a surface for the attachment of muscles with the help of which arthropods show active locomotion by swimming, crawling, walking or flying. The chitinous exoskeleton is considered one of the reasons for their success among the animal kingdom.
4. Body differentiation:
A body can be differentiated into three regions; head, thorax and abdomen. The body cavity is haemocoel.
5. Circulatory system:
The circulatory system is of open type. Blood does not contain any respiratory pigment. Blood is called hemolymph because (it does not carry oxygen) it only carries food to different tissues of the body.
6. Respiratory organs:
Respiration takes place in aquatic forms through gills and in terrestrial forms (especially insects) through the trachea. The trachea is air tubes which divide repeatedly to form numerous fine branches distributed to all the tissues of the body. They communicate with the exterior through openings on each side of the body known as Spiracles. Arachnids, a group of arthropods including scorpion, spider etc. respire through special structures, arranged side by side like books in a bookshelf, hence called book lungs.
7. Excretory organs:
Excretion takes place either through Malpighian tubules (in insects) or green gland or coxal gland (in crustacean).
8. Reproduction in arthropods:
Fertilization is internal. Sexes are generally separate. Sexual dimorphism is generally present i.e. male and female can be differentiated from each other based on their morphology. During development, they exhibit either complete metamorphosis or incomplete metamorphosis. Some insects like honey bees, ants, termites etc. show social behaviour. They live in colonies and divide their work among different groups.
9. Nervous system:
The nervous system in arthropods is well developed. It consists of a pair of cerebral ganglia (simple brain) connected to a double nerve cord. A ganglion is present in each segment and nerves arising from these ganglia connect the whole body. The responses are well coordinated. Sensory organs are eyes and antennae.
All the changes occurring from the fertilization of an egg to the formation of an adult are collectively called metamorphosis. During metamorphosis, a larva undergoes a series of changes called ecdysis or moulting in which it casts off (removes) its skin many times to attain its maximum size.
Economic Importance of Insects:
- Insect plays a major role in human life both in primary production and in decomposition and serves as a major food source for many vertebrates directly or indirectly.
- Insects are used as a source of food for humans e.g. (grasshopper) and palm weevil. They are a highly digestible protein and energy source. Also, they are the principal food for many birds and reptile
- The survival of insect-pollinated plants depends on them. Bees are not important pollinator. In Africa and other parts of the world, pollination is largely done by flies and butterflies.
- Insects act as a pest to plant, some insects that eat plant leaves affect the growth of the plant thereby reducing the crop yield and production of the plant.
- Some insects take man as host thereby causing injuries that even serve for secondary infection. The insect that lives as a parasite on the other animal causing diseases, reduces the meat value and a decrease in the value of hides and skin.
- The insect has provided biologists with outstanding material for genetic, physiological, development and ecological studies.
Q.4 vii) Describe class Pisces in detail.
Class Pisces (Fishes):
Fishes are aquatic vertebrates which respire through gills and perform locomotion with the help of fins. Fishes are the largest group of vertebrates and constitute about 48 % of the total vertebrates. The number of living fish species is more than 29000.
Division of class pieces:
They are divided into three classes.
a. Class Cyclostomata or Agnatha:
- These are the most primitive jawless fishes having a circular mouth.
- These fishes have a long, eel-like body.
- Skin is naked i.e. without scales.
- They lack paired fins (appendages).
- Seven pairs of gills are found which open separately to the outside and are not covered with an operculum.
- Their skeleton is of lower grade, fibrous cartilage.
- They do not possess a stomach because of their parasitic way of life.
- The mouth is adapted for sucking.
- Sexes are separate.
Marinus (lamprey) and Maxine (hagfish).
b. Class Chondrichthyes: ( Cartilaginous fishes):
- Their skeleton is made of cartilage.
- They have streamlined bodies.
- All the Chondrichthyes live in a marine environment.
- Their mouth is ventral.
- Their body is covered with placoid scales which are very small and numerous and give the skin a touch of sandpaper.
- The circulatory system is with many pairs of aortic arches.
- They have heterocercal tails in which the dorsal lobe is longer than the ventral lobe.
- Respiration takes place through 5- 7 pairs of gills. Gills are not covered with an operculum and open separately.
- Most of them are carnivorous and sharks are very active hunters.
- A swim bladder is absent.
- Sexes are separate and many of them are viviparous.
Sharks, rays and chimaeras.
c. Class Osteichthyes: (Bony Fishes):
These fishes have a skeleton made of bone hence called bony fishes. They are the most successful group of fishes and inhabit all types of aquatic habitats.
- Their body is covered with scales of different types; Median fins i.e. dorsal fin, anal fin, caudal fin and paired fins i.e. pectoral and pelvic fins are present in bony fishes.
- A specific organ swim bladder is found which is hydrostatic in function and provides buoyancy to the fish in the water.
- They respire through well-developed gills which are covered with a bony cover called an operculum.
- Jaws may be with or without teeth.
- The brain is developed with 10 pairs of cranial nerves.
- The heart consists of an auricle and a ventricle. Blood contains haemoglobin as a respiratory pigment and its colour is red.
- Sexes are separate and except few species the fertilization is external.
- Majority of bony fishes are oviparous but some are ovoviviparous and viviparous.
Q.4 viii) What adaptations are found in birds for aerial life? Describe the evolutionary history of birds with special reference to the fossil birds.
Aerial adaptations in birds:
- To overcome the air resistance the bodies of the birds are streamlined.
- Limbs are adapted for flying. The forelimbs are modified into wings and hindlimbs for perching.
- The skeleton of the bird is hollow to reduce weight. These bones are known as pneumatic bones and they have filled the air to support flight.
- Many bones like the bony tail of the early bird which are not necessary are lost throughout evolution.
- Toothed jaws of early birds have been replaced with a lightweight beak.
- The breastbone has also been adapted for attachment of powerful and large flight muscles.
- The feathers of birds have hooklets known as barbules at the vanes that zip the vanes of individual feathers together. This gives the feathers the strength that needs to hold the airfoil.
- These barbules of the feathers are to maintain the shape and function of the feather.
- The non-conducting covering of feathers insulates the body perfectly and prevents loss of heat which enables the bird to endure the intense cold at high altitudes and also to maintain a constant temperature.
- The smooth, closely fitting and backwardly directed contour feathers make the body streamlined helping them to pass through the air by reducing the friction to the minimum.
- A large amount of energy consumed during flight has led to the evolution of a unidirectional pulmonary system that provides large quantities of oxygen required for the high respiratory rates. The lungs have extensions known as air sacs which extend into the bone also.
The evolutionary history of birds:
The evolutionary history of birds is very interesting. In 1861, from the rocks of the Jurassic period, a fossil of a bird was found which was given the name of Archeopteryx; the lizard tailed bird. It is of the size of a crow. Interesting about it is that it has characters of both reptiles and birds so can be considered transitional species between the two groups.
Birds Characters of archeopteryx:
- Well developed contour and flight feathers covering the body.
- Forelimbs modified into flying wings.
- Tail with two rows of feathers.
- Skull large with a single occipital condyle.
- Jaws elongated to form a beak.
Reptilian characters of Archaeopteryx:
- Presence of scales on the legs.
- Bones solid and heavy without air spaces.
- Jaws with teeth present in sockets.
- Along, the tapering lizard-like tail consists of 20 caudal vertebrae.
- Nine to ten cervical vertebrae.
- No fusion of trunk and sacral vertebrae.
- Sternum not keeled. Free cervical and abdominal ribs are also present.
- Simple brain with cylindrical cerebral hemisphere and unexpanded cerebellum.
- Forelimbs with three clawed fingers.
The above evidence proves that Archaeopteryx was a connecting link between reptiles and birds. Birds gradually evolved and became one of the most successful groups of vertebrates
Q.4 ix) Write short notes on the following.
- a) Binomial nomenclature
- b) Coral reef
- c) Parazoa
- d) Poikilothermic animals
Answer: a. Binomial nomenclature:
“The system of the naming of animals is called binomial nomenclature.”
In this system, scientific or zoological names are assigned to animals. Common names of animals may be similar but no two species in the world can have a similar scientific name.
- In binomial nomenclature an animal is assigned two names: first is the name of the genus to which it belongs and the second is its specific name (i.e. the name of the species of animals).
- The first “generic name” is always written with a capital letter and the second “specific name” with a small letter.
- The scientific name is always written in italics or otherwise underlined.
i. Homo sapiens for humans
ii. Rana tigrina for frog
b) Coral reefs:
“A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.”
Types of coral reefs:
Coral reefs are of four basic types:
1. Fringing Reef or Shore reef:
Fringing Reef or Shore reef is the simplest type. They are flat in structure and extend from coast to a few meters and sometimes to half a kilometre as a bench or platform.
2. Platform Reef or Table Reef:
Platform Reef or Table Reef is a flat structure without a lagoon. It rests on the shallow ponds of continental shelves. They may appear between the coast and a barrier reef.
3. Barrier reef:
Barrier reef does not have any connection with the land. A strip of seawater is always present between this reef and mainland called lagoon. This strip maybe about 180 feet to 3 miles wide.
4. Great barrier reef:
The Great Barrier Reef of Australia is the best-known example which is 1250 miles (2012 kilometres) long.
Economic and ecological importance of coral reefs:
Coral reefs are economically very important. Reefs provide an efficient ecosystem to a great variety of marine life. Many invertebrates living in reefs provide food to fishes. Reefs also provide good breeding habitats for fishes and in this way, reefs help to maintain fish populations which in turn provide fish meat for human beings. Corals being very brightly coloured are used as an ornament or for manufacturing jewellery.
c. Phylum Porifera:
All the members of this phylum are aquatic, mostly marine. They are the most primitive metazoans and are commonly called sponges.
Characteristics of Phylum Porifera:
- Animals of this phylum bear small holes or pores all over the body. These pores are called Ostia. Their bodies are made of groups of cells but the tissues and organs are not present.
- The body of Porifera is tubular which is opened at its anterior end called the osculum.
- The cavity present in the body is called spongocoel. Walls of the tube are made of two layers of cells. The outer layer, pinacoderm is made of the flattened cells called pinacocytes whereas the inner layer choanoderm is made of flagellated collar cells called choanocytes.
- Flagella of these cells keep beating to create water currents which not only bring food to the spongocoel but also remove excretory material from it. It contains special mobile cells called amoebocytes which are not only nutritive but ova and sperms also develop from certain amoeboid cells.
- The Ostia are part of a canal system in which water circulates and brings food to the body. This food is digested inside the body cell (intracellular digestion) as well as in the spongocoel (extracellular digestion).
- Food of Porifera includes phytoplankton, zooplankton, protozoans, crustacean and other small organisms but the major part (80 %) of the food is composed of dead decaying organic matter.
- Sponges are sessile (stationary) and do not contain any locomotory organs.
- Their dispersal takes place during asexual reproduction by budding and gemmule formation or by sexual reproduction through the formation of eggs and sperms.
- The process of excretion takes place by diffusion.
- Sponges also lack any nervous system. Neurosensory cells and neurons are found which are believed to coordinate the flow of water.
- All sponges except class mykospongida have a skeleton. The skeleton may consist of carbonate of lime or silicon in the form of spicules or spongin (a fibrous protein) in the form of fibres
Economic importance of sponges:
- Sponges are economically important animals as they are used for washing and bathing by human beings from ancient times. Even after the production and availability of artificial sponges, still, natural sponges have their demand in the market and they make a considerable proportion of the total business all over the world.
- Sponges found in the warm waters of the Mediterranean Sea are commercially more important.
- Sponges are used in surgical operations because of their ability to absorb blood and other fluids.
- Sponges are used to reduce noise pollution and to make the buildings soundproof, sponges are used to absorb sound waves.
Examples of sponges:
Sycon (a common marine sponge), Spongilla (a freshwater sponge), Leucosolenia (a tubular marine sponge), Euplectella or Venus flower basket (a very beautiful, delicate, siliceous sponge appear to be made of glass framework) etc.
“Poikilotherms are cold-blooded animals whose body temperature tends to fluctuate with that of a temperature of its environment.”
“A poikilotherm is an organism whose internal temperature varies considerably.”
It is the opposite of a homeotherm, an organism which maintains thermal homeostasis. Usually, the variation is a consequence of variation in the ambient environmental temperature. Many terrestrial ectotherms are poikilothermic. However, some ectotherms remain in temperature-constant environments to the point that they are able to maintain a constant internal temperature (i.e. are homeothermic ).
Poikilothermic animals include types of vertebrate animals, specifically fish, amphibians, and reptiles, as well as a large number of invertebrate animals. The naked mole-rat is the only mammal that is currently thought to be poikilothermic
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