Education Is The Key To Success: Zoology - Paper I - For Class XI (Science Group) - Model papers With Solved MCQs 2020 -2021SSC Part 1 and 2

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Zoology - Paper I
For Class XI (Science Group)
Model papers 2020 -2021

Time: 01 hour

SECTION B (20 Marks)

NOTE: Attempt any THREE questions from Reasoning questions and THREE from Non-reasoning questions. All questions carry equal marks. (12 Marks)
(a) Reasoning Questions:
i. Why fats are solid and oils are liquid at room temperature?
Ans: Greater amount of saturated fatty acid in a liquid greater will be its chance to have solid state. Fats contain more amount of saturated fatty acid i.e. they do not contain any double bond between carbon atom. so it is solid at ordinary temperature, while oils contain more amount of unsaturated fatty acid i.e. they contain one or more than one-double bond between carbon atom (— C= C —). so it Is liquid at room temperature.

i. Why monosaccharides are sweet whereas polysaccharides are not?
Ans: Monosaccharides (like glucose, galactose and fructose) are white crystalline solids with sweet taste and are soluble in water.. They are also called simple sugars because they are made up of one unit of simple sugar and can not be hydrolysed further into simpler sugars. While Polysaccharides (like starch, cellulose and glycogen) are amorphous and insoluble in water. They are of high molecular weight carbohydrates and are tasteless or less sweeter than monosaccharides. Because These are long polymers of monosaccharide units and on hydrolysis yield mainly monosaccharides or products related to monosaccharides.

ii. Why are amphibians considered as unsuccessful land vertebrates?
Ans: Amphibians are regarded as unsuccessful land vertebrates because they failed to adapt completely to the land environment, as:

They are cold blooded and do not possess any exoskeleton.
They cannot cope with the extremes of temperature which has restricted their distribution, around the water bodies.
Their thin naked skin cannot prevent the continuous loss of water and hence makes them vulnerable to desiccation.
Their eggs are small and without a shell.
Fertilization is external and require water.
Larval stage have gills for respiration.

ii. Why reptiles are considered as successful land vertebrates?
Ans: Ans: Reptiles are considered as successful land vertebrates because:

They possess exoskeleton which prevent them from desiccation.
They have well Kidneys to reabsorb more water and produce concentrated urine.
Eggs are covered with amnion.
Fertilization Is internal and do not require water.
Limb with claws made them fit not only to move, dig and climb. but also to defend them against predators.
They have well developed lungs and hearts than amphibians, which help them to get more oxygen to live on land easily.

iii. Why are sponges considered as Parazoa?
Ans: Sponges which belong to phylum porifera are considered as Parazo, because its members lack a proper tissue organization.

iii. Why do we feel burning sensation of the tentacles of Jelly fish when it touches our skin?
Ans: We feel burning sensation of the tentacles of Jelly fish when it touches our skin because Jellyfish have special cells along their tentacles called cnidocytes. Within these cells are poisonous like structures full of venom, called nematocysts. The tentacles secrete this toxic material which penetrate in our skin in less time thus we feel burning sensation.

iv. Why are butterfly placed in class insecta where as scorpions are placed in class arachnida?
Ans: Arthropods of class Insecta have six (three pairs of legs) while class arachnids have eight legs (four pairs of legs). Another difference is that all insects have antennae on their heads and also have wings so they can fly whereas arachnids don't have antennae or wings, rather they are walking arthropods that's why butterfly is placed in class insecta where as scorpions are placed in class arachnida.

iv. Why honeybees and termites are regarded as social insects.
Ans: Honey bees and termites are regarded as social insects because they live in large colonies, with a marked division of labour. They work together in groups and keep the colony running by caring for their eggs and young ones, bringing in food, and also perform other tasks together.

v. Why in hydra the digestion is termed as mixed digestion?
Ans: The digestion in Hydra is extracellular as well as intracellular. During extracellular digestion food is not broken down into simpler form in gastrovascular cavity. So the semi-digested food particles are engulfed by the phagocytic action of the flagellated cells where they are completely digested in the food vacuole within the endodermal cell. This is called interacellular digestion. That's why in Hydra, the digestion is termed as mixed digestion.

vi. Why the fishes exhibit single circuit circulation?
Ans: The heart of a fish is two chambered, consisting of an atrium and a ventricle. Blood from the body circulation enters the atrium through a thin walled sinus venosus which opens into a muscular ventricle. When the ventricle contracts the blood is pumped into the ventral aorta via conus arteriosus. All these chambers have valves which prevent backward flow of blood. From the aorta, the venous blood passes into the afferent branchial arteries (4-5 pairs) into the gills for oxygenation. Since the blood flows through the heart only once during each circuit of the body, the fishes are said to possess a single circuit plan.

vi. Why marsupials are born in immature state?
Ans: Marsupials are viviparous and pouched mammals. They give birth to live young ones. Their eggs are not laid but retained and fertilized inside the body of the female. As the eggs do not contain enough yolk to feed the embryo for the entire period of development, hence marsupials are born in an immature form. The rest of the development of the new born tiny marsupial occurs outside the uterus in a special bag like pouch called marsupium.

(b) Non-Reasoning Questions:
i. Differentiate between cartilaginous and bony fishes.
Ans: Difference Between Cartilaginous And Bony Fishes

S.NO.	Cartilaginous Fish	Bony Fish
1.	Cartilaginous fish belongs to Class Chondrichthyes	Bony fish belongs to Class Osteichthyes
2.	They are marine fishes.	They are marine and fresh water fishes
3.	Their wide mouth is ventral in position	Mouth openning is present at the anterior tip.
4.	Body is covered by Placoid scales.	Body is covered by cycloid or clenoid scales
5.	Their tail fin is heterocercal.	Tail fin is usually homocercal or diphycercal.
6.	Gill slits on each side which are not covered over by the operculum.	The gills are covered over on each side, by a gill cover called operculum.
7.	e.g: Sharks, Scoliodon (Dog fish) Skates and Rays (like Ray-Torpedo) etc	e.g: Eel, Sea horse, Flying fish, Globe fish etc. Most of the delicious edible fishes also belong to this group, like: Perches (Pomfret), Hilsa (Pallah), Carps (Rohu), Mackrels (Surmai), Cat fishes (Khagga), and Salmon (Trout) etc.

i. Describe briefly levels of biological organization.
Ans: LEVELS OF BIOLOGICAL ORGANIZATION:
Living organisms are highly complex and organized. This complexity and organization is composed of grading of structures with each level based on the one below it, and providing the foundation for the one above it. These levels are called level of biological organization.
These levels are:

Atomic and Subatomic level
Molecular Level
Cell and organelles level
Tissue level
Organ and organ system level
Individual whole organism level

BROADER LEVELS OF ORGANIZATION:

Species
Population
Community
Ecosystem
Biosphere

Atomic and Subatomic level:
This is the smallest level of biological organization. The smallest possible unit of an element, which retains all the properties of that element. Further division of atom produces isolated subatomic particles, like proton, electron and neutron.

Molecular Level:
Atoms may combine in specific ways to form molecules in a cell and molecules unite together to form a compound.
Molecules are of two types:

Simple molecules:
These molecules are small and are formed naturally in a systematic way. They may have low molecular weights.
Simple inorganic molecules are CO₂, H₂O etc.
Simple organic molecules are sugar, glycerol, fatty acid, amino acids, purines and pyrimidines etc.
Complex molecules:
These are large molecules wit high molecular weights. They are also called macromolecules.
In the bodies of living organisms, complex organic molecules are formed from simple organic molecules.
There are three types of complex molecules:
i. Carbohydrates
ii. Lipids
iii. Proteins

Level Of Cell And Organelles:
The body of all living organism is composed of cells. Cell is the smallest, basic, structural and functional unit of life. In a cell, many organelles are present which perform particular functions.

Tissue Level:
Cells of similar type form tissues, which perform a particular function, for example nervous tissues, connective tissues, xylem tissues etc.

Organ Level:
Various tissue types combine to make up an organ. Organ is a part of living organism that perform a special function of a body. For example the brain, stomach, intestine etc.

Organ System Level:
Several organs that collectively perform a single function form an organ system. For example, together, the brain, spinal cord, sense organs, and nerves form the nervous system.

Individual Whole Organism Level:
When different organ systems functioning together in a highly advanced co-ordination and co-operation in a body, They make up an individual whole organism.

BROADER LEVELS OF ORGANIZATION:
Species population:
Organism with similar character, having the same number of chromosomes which can interbreed with their opposite sex are called species.

Population:
Members of the same species living in close association in a given area are considered a population.

Community:
Populations of several species living and interacting in the same area form a community.

Ecosystem:
The interaction between living and non-living organism in a particular area, is known as ecosystem. Thus a community with it's environment, including land, water and atmosphere, constitute an ecosystem. e.g water ecosystem, land ecosystem etc.

Biosphere:
Finally, the entire surface region of the earth inhabited by living things is called the biosphere. Or The area where different ecosystem exist is called biosphere.

SUMMAY OF LEVEL OF BIOLOGICAL ORGANIZATION:

Sub-atom (Electron) ⟶ Atom ⟶ Molecule ⟶ Cell ⟶ Tissue ⟶ Organ ⟶ Syetem ⟶ Individual (Species) ⟶ Population ⟶ Community ⟶ Ecosystem ⟶ Biosphere

ii. Describe briefly factors affecting enzyme activity. (any two)
Ans: FACTORS AFFECTING ENZYME ACTIVITY
Following are the factors which affect the enzyme activity:

Concentration of substrate
Temperature
pH
Co-factors (Co-enzymes, activators and inhibitors)
Water
Radiation.

1) Concentration of Substrate:
The rate of reaction increases with an increase in the concentration of substrate until the available enzyme becomes saturated with substrate. At a very high concentration the substrate has no effect on the rate of reaction.
This may be due to two reasons:

Higher quantity of substrate than enzyme.
Accumulation of end product in high quantity.

Hence, concentration of substrate ia an important factor.

2) Effect of temperature:
Enzymes are sensitive to temperature. Each enzyme has its optimum temperature for its maximum activity, above and below this temperature its rate of reaction decreases. The optimum temperature for most of the enzymes is 30°C to 35°C and highly active at about 37°C. All are completely destroyed at 100°C, whereas at minimum i.e. 0°C, activity is reduced to minimum or inactive but enzymes are not destroyed.

3) Effect of pH:
The activity of enzyme varies considerably with pH because each enzyme works in a particular acidic or alkaline condition. There is generally a marked optimum pH for each enzyme e.g. pepsin of stomach has an optimum pH of 1.4. It is inactive in neutral or alkaline solution.

4) Co-factors (Co-enzymes, activators and inhibitors):
Enzyme action is frequently accelerated or inhibited by the presence of other substances called co-factors. Co-factors have been divided into three categories.
i) Co-enzymes:
If the co-factor is an organic molecule, its is called coenzyme. Without co-enzyme certain enzymes are unable to function e.g. CoA, NAD, FAD etc. Most vitamins are co-enzymes or raw materials from which coenzymes are made.

ii) Activators:
Inorganic substances which increase the activity of an enzyme are called activators. Magnesium (Mg⁺²) is an inorganic activators for the enzyme phosphatase and Zinc ion (Zn⁺²) is an activator for enzyme carbonic anhydrase found in RBCs.

iii) Inhibitors:
Substances which decrease the activity of an enzyme are called inhibitors. The inhibitors may act by combining directly with the enzyme or they may react with the activator, due to these substance activity of enzyme is stopped.
Inhibitors are of two types:

Competitive inhibitors:
Some inhibitors resemble the normal substrate molecule and compete for admission into the active site of enzymes, so they reduce the productivity of enzyme by blocking the substrate from entering into the active site. These are called competitive inhibitors.
If the inhibition is reversible, it can be overcome by increasing the concentration of substrate. In this way, substrate get the site of enzyme for attachment and reaction is proceed.
Non-competitive inhibitors:
When certain substances are attached to inactive part of enzyme (allosteric site, allo = other, steric = space or structure), the activity of enzyme is stopped. such inhibitors are called non-competitive inhibitors, This interaction causes the enzyme molecule to change its shape, rendering the active site unreceptive to the substrate, or leaving the enzyme less effective at catalyzing, for the conversion of substrate to product.

Feed-back inhibition:
When the product of a chemical reaction binds with the enzyme and causes inhibition of reaction, it is called feed back inhibition. It is attached competitively to the active site of the enzyme, then inhibition is reduced, as a result of which more product is formed.

In the same enzymatic reaction, the end product binds non-competitively at inactive site of the reaction. This binding stops the reaction and more products are formed.

5) Effect of Water:
Water is necessary for enzyme activity as it influences the rate of enzymatic activity. In germinating seeds, with the increase in amount of water, to some extent, enzymes become active and germination proceeds.

6) Radiation:
Enzymes are generally inactivated rapidly by exposure to ultraviolet light and also to X-rays, because it alters the shape of protein i.e. enzymes.

(Note: Out of six describe any two factors as mention in question)

ii. Describe characteristics or class Sarcodina.
Ans: Characteristics Of Class Sarcodina:

Their body wall is soft, due to which the shape of the body can be changed. In some, the body is covered by a shell e.g. Globigerina.
The members of this class have no specific organelles for locomotion.
From their outer surface of the body, psuedopodia are produced which help in locomotion and to capture the food.
The protoplasm is divided into ectoplasm and endoplasm.
Nucleus is one or more.
Excretion takes place by osmoregulatory vacuole in marine and in parasites vacuole is absent.
Some parasitic Amoebae (Entamoeba-histolytica) can cause human dysentery.
Marine shelled sarcodinians through geological time have deposited billions of skeletons, which now make layers on the bottom of the sea.
The "Radiolarian Ooze" and "Globigerina Ooze" are studied by oil prospectors because the presence of certain species (Foraminifera) gives clues to possible petroleum deposits.
e.g: Amoeba, Heliozoans and Foraminifera etc.

iii. Define Metamorphosis. Differentiate between complete and incomplete Metamorphosis.
Ans: Metamorphosis:
It is a set of changes which transforms a larva into its developed adult form. A larva is a creature which in some animals, comes out of the egg in an immature and undeveloped stage.

Difference Between Complete and Incomplete Metamorphosis.
Complete Metamorphosis:
Metamorphosis is said to be complete when a larva hatches out of the egg and develops into a resting stage the pupa which in turn transforms into an adult. e.g: Butterfly.
Incomplete Metamorphosis:
on the other hand incomplete metamorphosis is that in which a tiny, immature but adult like creature called nymph comes out of the egg and grows directly, into an adult. e.g: Cockroach.

iii. Write note on Pearl formation.
Ans: Pearl Formation:
A variety of molluscs called shell fish, together with crustaceans, are still an important source of food. Their shells are decorative and their inner lustrous layer which is a mixture of calcium carbonate and proteins is called Necre or mother of pearl.
In some bivalve molluscs, called Pearl Oyster, concentric layer of necre are deposited around any foreign particle that comes to lie between the mantle and the shell. This particle transforms into the most beautiful and precious jewellery item, the pearl.

iv. Write parasitic adaptations of flat worms.
Ans: Parasitic Adaptations Of Flat Worms:
The parasitic adaptations of flat worms are as follows:
1. Body Covering:
They have thick body covering which protect them against defence mechanisms (secretion) of host body.

2. Suckers And Hooks:
They have spines, suckers and hooks developed for proper attachment with the host body and sucking of food materials. They have replaced the locomotory organs which are not needed by parasitic animals.

3. Reduced Alimentary Canal:
Alimentary canal is reduced, even absent as in Taenia solium (Tape worm), because they absorb digested food from host body.

4. Reproduction:
Reproductive system is very much developed.

5. Nervous Sytem:
Neurosensory organs are not developed due to their passive mode of life.

iv: Write the examples of each of the following classes:
*Hydrozoa * Trematoda *Bivalvia *Polychaeta
Ans: Class: Hydrozoa
e.g: Hydra, Obelia, Physalia (portuguese man of war).

Class: Trematoda
e.g: Fasciola hepatica (sheep liver - fluke).

Class: Bivalvia
e.g: Unio, Mytilus and Pearl Oysters

Class: Polychaeta
e.g: Sabella (Peacock worm) and Nereis (Clam worm)

v. Write a short note on the functions of Liver.
Ans: Functions Of Liver:

Liver is a metabolic factory, detoxification center and storage organ.
It secrets and stores digestive juice called bile. It combines with food in duodenum and neutralizes its acidity. It also change fats into milky substance, after this emulsification, further digestion takes place by enzymes.
It excretes out the bile pigments and other waste products.
One of its functions is to maintain an appropriate quantity of level of nutrients in the body. It is performed in three ways.
a. Surplus amount of glucose is deposited in the liver cells after every meal. Here the glucose is transformed into glycogen in the presence of insulin, a hormone released from the pancreas. The glycogen can later be hydrolyzed through glucagon for energy to meet the body's energy requirements.
b. The amino acids are also stored after deamination (removal of NH+₂ group), which forms the urea.
c. The liver also processes fatty acids and stores the products as ketone bodies which later are released as nutrients for active muscles.
Liver also prevents certain poisons from harming the body by breaking them into harmless compounds.
In addition to these functions liver stores vitamins.
It produces necessary substances for coagulation of blood.
It keeps the composition of blood fairly constant.

v. Differentiate between inspiration and expiration.
Ans: Difference Between Inspiration And Expiration

S.NO.	Inspiration	Expiration
1.	The breathing process of taking in air into the lungs is called inspiration or inhalation	The breathing process of giving out of air from the lungs to the the atmosphere is called expiration or exhalation
2.	It is an active process	It is a passive process
3.	The volume of thoracic cavity is increased due to contraction of inter-costal muscles and diaphragm.	The volume of the thoracic cavity is reduced due to relaxation of external inter-costal muscles and diaphragm.
4.	Contraction of external intercostal muscles moves the ribs as well as sternum outward and upward	Contraction of internal inter-costal muscles, which move ribs as well as sternum inward and downward.
5.	Contraction of the diaphragm makes it flat	Relaxation of the diaphragm makes it dome shaped
6.	The size of chest cavity increases	The size of chest cavity increases
7.	Oxygen is taken into the lungs	Carbon dioxide is removed from the lungs

vi. Differentiate between arteries, veins, and capillaries.
Ans: CAPILLARIES:

The capillaries are the finest blood vessels of arteries and veins.
These are extremely narrow (7-10 μ in diameter), thin walled microscopic vessels.
They make a close contact between the circulatory system and the tissues in the form of capillary network.
These capillaries facilitates the diffusion of important materials easily by blood circulation. Active transport can also occur.
The walls of capillaries consist of a single layer of endothelium, which presents very little resistance to the diffusion of dissolved substances in or out.
The amount of the flow of blood in the capillaries are controlled by arterioles. It is under the influence of nervous system and hormones.

ARTERIES:

Arteries are the blood vessels which are involved in the transport of blood from the heart to various part of the body. All the arteries carry oxygenated blood except the pulmonary arteries which carry deoxygenated blood into the lungs for oxygenation.
The arteries are deep seated and do not collapse when empty.
The smaller arteries divide into small branches, called arterioles, which are connected to capillaries.
Arterioles contain sphincters at their capillary ends which regulate the flow of blood into the capillaries.
Arteries are thick walled vessels consisting of three layers.
i. Outer Layer (Tunica externa):
It composed of fibrous connective tissue having collagen fibers. They are pulsatile and maintain or resist the internal blood pressure.
ii. Middle layer (Tunica media):
It has smooth muscles and elastic fibers. These are elastic and by their contraction and relaxation, the cavity (lumen) of arteries can be decreased or increased. Th arteries have large cavity than veins.
iii. Inner Layer (Tunica interna or intima):
It consists of squamous endothelium.
Their lumen is small and does not contain semilunar valves. Blood flows rapidly with jerks in pulsations indicating the ventricular systole.

VEINS:

The veins carry deoxygenated blood from different parts of the body back to the heart except the pulmonary veins which transport oxygenated blood from the lungs to the heart. The veins are superficial and collapse when empty.
Veins are thin walled blood vessels.
They are also composed of the same three layers as that of arteries, but possess less muscles and less elastic fibers.
i. Outer Layer:
It consists of hard and fibrous connective tissue having collagen fibers.
ii. Middle layer:
It consists of smooth elastic tissues or muscles.
iii. Inner Layer:
It composed of endothelial layer.
Their lumen is large. Semilunar valves are present which prevent the back flow of blood. The pressure of blood flowing through them is low and are non-pulsatile. The blood flows slowly and smoothly.

vi. Define Lymphatic system. Write its functions.
Ans: Lymphatic System:
A system of blind vessels (lymphatics) that drains lymph (tissue fluid obtained from the blood plasma) from all over the body back into the blood stream is called lymphatic system. In addition to lymphatics and lymph it consists of lymph nodes, spleen, thymus, tonsils and some of the patches of tissues in vermiform appendix and small intestine.

Functions of Lymphatic system:
i. Drainage system:
Lymphatic vessels act as drainage channels for water and plasma proteins that have leaked away from blood at capillary bed and that must be delivered back to blood circulation, without which death can occur in 24 hours.

ii. Defense of the body:
The lymphatic system helps to maintain body resistance. Microorganisms, foreign cells, cellular debris in the lymph are removed by macrophages residing in the lymph nodes. These are also the site for differentiation of the B cells into antibody secreting cells.

iii. Absorption and delivery of fats:
Lymph capillaries called lacteal penetrate the villi of the small intestine where fats are absorbed and are changed into droplets. After that these fats delivered to the blood circulatory system.

vi. Bathing Of Tissue:
he lymphatic system bathe the tissues and keep them moist.

SECTION 'C' (08)

DESCRIPTIVE QUESTIONS

NOTE: Attempt any ONE question. All questions carry equal marks. Attempt all parts of a question. Draw labelled diagram where necessary.

Q.3: (a) Describe salient features of Phylum Annelida OR Arthropoda OR Mollusca. Classify the given phylum with characteristic and examples of any three classes. (5)
Ans: PHYLUM - ANNELIDA (SEGMENTED WORMS):
Examples: Pheretima (Earthworm), Leech, Neris
Definition:
"Bilateral, Protostomes, eucoclamate, eumetazoans whose long. and narrow body is divided into ring like (Annulus: little ring) true segments (Metamerical segmentation) are termed as Annelids."

Habitat:
Annelids live on land, in moist soil, in fresh water or in sea. Many annelids are active free swimming predators, some are aquatic filter feeder living in tubes buried in mud or parasites.

Characters Or salient Features:
Segmented body:
They have elongated and segmented body. The segment are complete i.e. externally and internally as well. These segments are known as metameres.

Symmetry:
They have bilaterally symmetrical body.

Triploblastic:
They are triploblastic animals i.e. the body develops from three-layers. of embryonic period outer ectoderm, middle mesoderm and inner endoderm.

Alimentary canal:
The alimentary canal is complete (i.e. mouth and anus present at terminal ends) elongated and tube-like structure. It extends from mouth to the anus.

Coelom:
These animals possess a true-coelom (true body cavity). It lies between the layers of mesoderm due to the presence of a true coelom they are called coelomates. The entire coelom is divided into compartments due to presence of septa.

Locomotion:
The locomotion of the body is taking place by small Chitinous chaetae also called setae . They are found along the segments in pairs. The setae are with or without parapodia.

Circulatory system:
They have closed-type of circulatory system i.e. the blood flows in blood vessels. The blood is red due to the presence of haemoglobin. The major blood vessels are dorsal and ventral blood vessels. The number of pulsatile hearts is two or more.

Respiratory system:
There is no special respiratory organ. The respiration takes place through, the moist skin by means of diffusion.

Excretion:
The excretion is by convoluted tube like organs, called nephredia in each segment a pair or more nephredia are present.

Nervous System:
Nervous system consists of a brain and double nerve cord, with a ganglion in each segment.

Reproduction:
The sexes are separate or occur in the same body (Heterophrodite or Hermaphrodite). Development may be direct or through trochophore larva. Regeneration is also common.

Metamerism:
The complete division (i.e internal and external) of the body is known an metamerism. It is of two types:

Homonemous: In this case always all the segments of body are equal.
Heteronemous: All the segments of the body are not equal.

Classes Of Phylum Annelida:

This phylum is divided into four classes:

Class - Polychaeta. e.g. Neris.
Class - Oligochaeta e.g. Earthworm.
Class - Hirudinea e.g. Leech.

I) Class - Polychaeta (With many setae):

The animals posses many setae with parapodia.
They are generally free living active swimmers, sedentary filter feeders and tubuculous forms. They are mostly marine.|
Their body is elongated and metamarically segmented.
From each segment on lateral side of the body a prominent flap like fleshy lobes are developed called parapodia. The parapodia bears the setae or chaetae on it which helps in locomotion.
Their head is distinct called protostomium. It possess eyes, tentacles. antennae and bristles or palps.
The sexes are separate. Fertilization is external.
Development is indirect and passes through trochophore larval stage.
e.g. Sabella (Peacock worm) and Nereis (Clam worm)

II) Class Oligochaeta (Few Setae):

The animal posses few setae.
The body is metamarically segmented consists of many segments.
The head is not prominent. Eyes and tentacles are also absent. Hence they re termed as non cephalized animal. Mouth is present on first segment. Which is covered by peristomium.
Some segments of the body are covered by a structure, called clitellum which is a reproductive device.
Locomation takes place by setae. Parapodia are absent.
All are hermaphrodite.
e.g. Pheretima (Earthworm)

III) Class Hirudinea (Leeches):

The animals of this class are ectoparasites. They live on the outer surface of their host body.
Their body is elongated and flattened at both sides.
The body consists of definite number of segments about 34 in number.
They do not have chaetea or appendages like other annelids.
They have suckers at both sides of their body. On the anterior sucker mouth is present, by the help of which they suck blood from the body of host. The suckers help in their attachment to the host body.
Anus is present on the posterior sucker.
Reproduction is sexual. Development of egg takes place in cocoon.

PHYLUM - MOLLUSCA (Soft body):
Examples: Octopus, Loligo, Nautilus.
Definition:
"There an soft bodied bilateral, prostomial, eucoclamate, eumetazoans whose body is enclosed within a thin layer of skin fold known as MANTLE. Usually they live in a shell."
"
Characters:
1. Soft and unsegmented body:
Thees animals have soft body without segments except Neopalina, which are segmented.

2. Mantle layer and shell:
Around their body a layer is present called mantle. It secrets a shell for the protection of the body.

3. Triploblastic:
Their body is triploblastic i e develops on the pattern of three layers, outer ectoderm, middle mesoderm and inner endoderm.

4. Foot:
At the ventral side of the body a special structure muscular foot is present, which helps in locomotion.

5. Head:
The head is distinct, contains mouth. eyes and tentacles.

6. Radula:
In some animals a special structure is developed in the mouth, called radula. It is used for scraping, tearing and pulling of food.

7. Coelom:
It is reduced in the form of pockets which is filled by the coelomic fluid and acts a hydro-static skeleton.

8. Digestive system:
They have complete alimentary canal which may be straight or coiled.

9. Open type circulatory system:
Circulatory system is of open type, but the cephalopoda have closed type of circulatory system. Heart is present.

Open type: Blood vessels are absent. The body cavity is divided into chambers.
Closed type: Blood vessels are present.

10. Nervous system:
They contain well-developed nervous system with paired ganglia, connectives and nerves.

11. Respiration:
Respiration takes place by gills in aquatic animals or by rudimentary lung in terrestrial animals.

12. Excretion:
Excretion is by rudimentary kidneys.

13. Reproduction:
Reproductive organs are found either in the same or separate bodies. The fertilization is external which takes place in water. Their development takes place through the TROCHOPHORE LARVA-, hence development is indirect.

Classes of Phylum Molluscs:
Phylum Molluscs is divided into six classes:

Class - Monoplacophora e.g Neopalina.
Class - Amphineura e.g. Chitin.
Class - Plecypoda (Bivalvia) e.g. Olio, Oyster.
Class - Scaphopoda e.g. Dentalium.
Class - Gastropoda e.g. snails, Slugs, Limpets, Cowries.
Class - Cephalopod e.g. Octopus, Sepia (Squid).

1. Class - Bivalvia or Plecypoda (Shell with 2 halves):

This class is also called Lamalli-branchiata. The characters of this class are as follows:
The head is not distinct. Radula is also absent.
Mantle consists of two parts. It produces a shell. The shell consists of two pieces. It can be opened or closed.
The foot is large. It comes out front opened shell and it is used for locomotion or burrowing in sand.
Respiration takes place by gills, which are thin and plate like.
At the lower side of the body two tubes like structures are produced, called siphons. One siphon is for the entrance of water and other for the discharge of water e.g. Clams, Oysters.

2. Class Gastropoda (Foot on visceral mass):

On ventral side of their body a distinct head is present. On the same side a large foot is produced.
The head has eyes, mouth and tentacles.
From the mantle a spiral shaped single shell is produced.
In the mouth a special structure is present, called radula. It is used to scrap food particles from rocks or to make holes in the shells of other mollusca.
Respiration takes place either by gills or through the wall of mantle. e.g. Snails, Limpets. Cowries.
Many of them become asymmetrical because of TORSION. During this process the entire mass is twisted at 180°.

3. Class Cephalopoda (Foot on the head):

This is the most advanced class of phylum mollusca. All animals are marine in nature. The characters of these animals are as follows.
The head is distinct. It has a pair of large eyes. Internal Shell is reduced or absent.
The foot is modified into eight or ten tentacles which are used to capture the prey.
Siphon is present which 'discharge the blue color water when frightened by enemies.
In the tentacles or arms suckers are preset.
Two or four pairs of gills are present for respiration.
Examples: Octopus, Sepia (cattle fish).

PHYLUM — ARTHROPODA (Jointed legs):
Examples: Cockroach. Prawn. Centipede.
Definition:
"Bilateral and prostomial, eucoclamate, eumetazoa with metamerically segmented body and posses jointed legs.
It is the largest phylum of animal kingdom. It Include, King crab, Scorpion, Spider, Crabs, Millipedes, Centipedes and Insects."

Habitat: They are terrestrial ans found everywhere on the earth wherever the life is possible, even in the oil wells.

Important Characters:
1. Segmented body:
The animals of Arthropods have metamerically segmented body.

2. Exoskeleton:
The body is covered by an outer covering called exoskeleton. It is made up of proteins and chitin.

3. Triploblastic:
Their body is triploblastic i.e. based on three layers, outer ectoderm, middle mesoderm and inner endoderm.

4. From the body jointed legs or appendages are produced. The antennae, jaws, legs and swimming organs are in pairs.

5. Circulatory system:
Circulatory system is of open type i.e. blood vessels are absent and the blood flows freely throughout the body. The blood is colorless.

6. Haemocoel:
The body cavity is known as haemocoel, because the blood flows through it. The true blood cavity coelom is very small and contains reproductive organs.

7. Digestive system:
The digestive system consists of a tube like structure, which extends from mouth to the anus and is divided into three parts:

(i) Fore gut
(ii) Mid gut
(iii) Hind gut

8. Respiration:
In terrestrial, respiration take place by trachea or book lungs. In animals it is by trachea.

9. Nervous system:
Nervous system consists of a brain in the anterior region (head) and a double ventral nerve cord in the lower region of the body.

10. Body structure:
The body of these animals is divided into head, thorax and abdomen. In some animals head and thorax is fused to form cephalothorax.

11. Excretion:
In insects and other animals excretion take place by malpighian tubules. In some animals green glands are the excretory organs.

12. Reproduction:
Sex organs are found in separate bodies. Fertilization is internal. The animals are heterophrodite. The sexual dimorphism is also present.

Classification or Phylum Arthropoda:
Phylum Arthropoda is divided into five classes:

Class Merostomata (with mouth plates).
e.g. Limulus, King Crab.
Class Arachnida (spider like animals).
e.g. Scorpions, Spiders.
Class Crustacea (with carpaee).
e.g. Crab, Sacculina, Prawn, shrimps and lobsters.
Class Myriapoda (with many legs).
e.g. Centipedes, Millipede.
Class Insecta or Hexapoda (with six legs).
e.g. Butterfly, Mosquito, Cockroach, A few ants, Termites, Honey bees

1. Class Merostomata (mouth plates):

It is a small group of marine arthropods in which mouth is surrounded by many small plates.
The body of these animals is divided into cephalothorax and abdomen.
The cephalothorax is covered by a horse-shoe shaped covering called carapace.
From the lower region of cephalothorax legs are produced.
Abdomen is unsegmented. It produces a tail like structure from its lower end, called telson e.g. Limulus (King cab).

2. Class Arachnida (spider like):

It is a group of terrestrial arthropods with four pairs of walking legs.
In this class Scorpions, Spiders, mites and ticks are included included.

Characters:

Their body is consists of two pairs, cephalothorax and abdomen. Antennae are absent.
They have four pairs of legs.
They respire by the help of book lungs, tracheae or general body surface.
Scorpions have poison sting at the end of their narrow segmented posterior abdomen, with the help of which it paralyses its prey.
Spiders are predators . They possess silk glands which secrete a protein that on exposure to air forms silk threads used in building nest and spider's webs for trapping the preys.
Ticks and mites are parasites. Ticks cause Rock ,mountain spotted fever and allergic reactions in human being and other animals.

Class Crustacea (with carapace):

In this class, Crabs, Lobsters, Prawns, shrimps, Crayfish are included. They are found in fresh and sea water (marine). Some are also terrestrial creatures.

Characters: Their characters are as follows:

The body is consists of three parts head, thorax and abdomen. In many cases, e.g. prawn, shrimps etc head and thorax become fused to form cephalothorax.
The body is covered over by a single plate of exoskeleton called carapace.
From head two pairs of antennae are produced.
Compound eyes are present.
A pair of mandibles is produced from the head function as jaws.
Respiration takes place by gills or through the body surface.
They usually bears five pairs of walking legs.

Class Myriapoda (many legs):

These are terrestrial arthropods leading a hidden life in the soil.
Their body consists of two parts, a head and a very long trunk.
The truck is elongated and consisting of many similar segments.
The head bears a pair of antennae and trunk is provided with paired lateral appendages.
Respiration takes place by trachea.
In sub-class Chilopoda Centipedes included. In these animals each segment has one pair of legs.
In sub-class Diplopoda Millipede included. Each segment of their body contains two pairs of legs.

Class Insecta or Hexapoda (six legs):

This is the largest class of the animal kingdom. It includes more than 90% of the arthropod species.
Members of this large group are called insects and their study is called entomology.
The body of insects is divided into three parts. head, thorax and abdomen.
From the head a pair of antennae is produced.
Mouth parts are modified according to their function such as:
a) Biting and chewing type e.g. Cockroach.
b) Piercing and sucking type e.g. Mosquito.
c) Chewing and lapping type e.g. Honey bee.
d) Sponging type e.g. Housefly.
e) Siphoning type e.g. Butterfly
Thorax is made up of three segments, .prothorax, mesothorax and metathorax.
From Ventral region of thorax, three pairs of legs are produced for walking.
From Dorsal region of thorax two pairs of wings are produced for flying.
Respiration takes place by trachea. 1n aquatic insects gills are present.
Excretion occurs by malphigian tubules.
Usually sexual reproduction takes place, but in some insects parthenogenesis is also common, in which eggs develops into an adult without fertilization.
In some insects complete metamorphosis occurs e.g. butterfly and in some insects incomplete metamorphosis takes place e.g. cockroach, grasshopper.
They have open type of circulatory system
Insects are of two types:
(i) Pterygota: These insects have wings e.g. Butterfly.
(ii) Apterygota: These insects are without wings e.g. Ants.

Social life of Insects:
some insects live in the form of a group or colony. They constitute a social colony. these insects are called social insects for example: bees, ants and termites.

Disease Carrier:
Many insects are harmful to mankind. Mosquitoes and Flies transmit many diseases e.g. Malaria, Dysentery, Cholera etc. Rat fleas transmit plague disease in man.
(Note: Describe characters of any three classes with Its phylum as mentioned in question)

3(b) Describe the characteristics of class Aves OR Mammalia. Mention the names and examples of their sub-classes. (3)
Ans: CLASS - AVES (BIRDS):
A bird can be defined as a feather covered bipedal flying vertebrate possessing wings. The study of birds is known as Ornithology. Their size and weight is from a 2 gms West Indian humming bird to a 150 kg Ostrich.

Important Charatters:
1. Endotherms or Homeotherms (warm blooded animals):
They are Homeotherms (warm-blooded animals). They can regulate and maintain their body temperature.

2. Presence of skeleton:
They have hollow bony skeleton with backbone.

3. Presence of Feathers:
Their body is covered by feathers.

4. Wings:
The forelimbs are modified into wings, which are the flying organs.

5. Hollow bones:
In flying birds the bones are hollow, thin and light in weight, which. help in flying.

6. Mouth parts:
Mouth parts are modified into beak which are of various types. Teeth are absent.

7. Digestive system:
They have special digestive system. The food is stored in the crop, and then it is masticated in the gizzard. The birds also swallow some stones, which help in the grinding of food.

8. Respiration:
Respiration takes place by lungs. The lungs also contain air sacs for the storage of air.

9. Syrinx (voice box):
They have a special voice organ, called syrinx. It is present at the junction of trachea and bronchi.

10. Heart:
The heart is advanced. It consists of auricles and two ventricles. The two ventricles separate the oxygenated and deoxygenated bloods from each other.

11. Eyes:
They have large eyes with eyelids.

12. Internal ears:
They have only internal ears.

13. Mobility of Neck:
Their neck has great mobility due to monocondylous nature. It helps in feeding. nest-building, preening and defence.

14. Egg laying animals:
They are egg laying animals. The egg is covered by egg shell. Fertilization is internal.

15. Antidotes animals:
They are amniotes animals. In the egg a protective membrane amnion is present.

CLASSIFICATION OF BIRDS:
Birds are classtafied into two subclasses.

Sub class Ratitae (Sternum raft like):
e.g. Ostrich, Rhea, Emu and Cassowary, Kiwi and Penguin.
Sub class Carinatae (Sternum with keel):
e.g:
(a) Common birds: sparrow, pigeons, myna, bulbul, hoopoes, crow, oves, parrots, fowls, cuckoo and ducks.
(b) Kites, falcon and owl are the common birds of prey.
(c) Ducks, Sea Gulls Terns and Cranes are common migratory birds.
(d) Peacock and Houbara are among the most beautiful birds of Pakistan.

CLASS - MAMMALIA:
Important Cbaraaers:
I. Homeotherms (warm blooded animals):
They are homeotherms i.e. warm-blooded animals.

2. Skeleton:
They have bony skeleton with vertebral column.

3 Body hairs:
The body is cowered by hairs.

4. Sebaceous and sweat glands:
The skin a contains sebaceous and sweat glands.

5. Body structure:
The body consists of head, neck and trunk. The body cavity internally divides into upper thorax and lower abdomen by a partition called diaphragm.

6. Circulatory system:
Heart consists of four chambers, two auricles and two ventricles. Due to the presence of two ventricles the oxygenated and deoxygenated bloods remain separate from each other.

7. Ears:
External ear (pinna) is present with internal and middle ear.

8. Eyes:
Eyes are with eye lids. Eye lashes and eye brows are also present.

9. Mammary glands:
They have mammary glands. which produce milk in female to provide noursiment to the young ones.

10. Respiration:
Respiration take place by lungs.

11. Excretion:
Excretion is by kidneys.

12. Teeth:
Teeth though few are thecodont (lodged in sockets of the Jaws) and heterodont (of different shapes) being differentiated into 4 types i.e. incisors, canines, premolars and molars.

13. Fertilization:
Fertilization is internal. The fertilization of egg takes place in oviduct. The development of embryo takes place in uterus. There is a duct between mother and developing embryo. called placenta, through which food and oxygen is supplied. Mother takes care of her young ones after the birth. It is termed as parental care.

Class mammalia is divided into three snb classes:

Sub-Class Prototheria (Egg laying mammals):
e.g. Echidna, the spiny anteater (Trashing glossus) and duck billed Platypus (Ornithorhynchus)
Sub-Class Metatheria (Pouched mammals):
e.g. Kangaroo, Koala bear and Opossum.
Sub-Class Eutheria (Placental mammals):
e.g Man, horse, Elephant, Whale, Bat, Rabbits, Giraffe and Bear etc.

Q 4: (a) Define digestion. Describe the digestive system of man with its mechanism. (5)
Ans: DIGESTION:
When a large complex insoluble organic food substances are converted into smaller simple soluble molecules by the action of enzymes. The process is called digestion.

DIGESTIVE SYSTEM (NUTRITION) IN MAN:
In man, there is a tube like alimentary canal which extends from mouth to the anus. In this alimentary canal, digestion and absorption of food take place, after absorption the food is used to provide energy.

Part of Alimentary Canal:

The alimentary canal of a man consists of the following parts:
Mouth
Buccal cavity
Pharynx
Oesophagus
Stomach
Small Intestine consist of (Duodenum, Jejunum, Ileum)
Large Intestine consists of 3 parts (Caecum, Colon, Rectum)
Anus

Digestive glands

Liver
Pancreas

(I) MOUTH AND BUCCAL CAVITY:

Mouth is an opening through which the food enters the buccal cavity. The buccal cavity is a chamber surrounded by two jaws. Upper Jaw and Lower Jaw.
In these jaws, teeth are present which are of different types. It is called heterodont. These teeth are fixed in the gums and are known as thecodont. In human beings, there are two sets of teeth in entire life. The teeth which appear during early age are known as milky teeth. These teeth are replaced by parmanent teeth. Such type of dentition is termed as Diphyodont.
In short, the human denten is
Heterodont
Thecodont
Diphyodont
Different types of teeth are as follows:
Incisors: These are front tech used for cutting and biting.
Canines: Canines are side teeth used for stretching the food and tearing the meat.
Premolars And Molars: These are back teeth used for chewing and grinding the food material. With the help these teeth, the food is properly masticated.

Dental formula:
C: ²/₂, I: ¹/₁, pm: ³/₂, m: ³/₃

Salivary Glands:
In the buccal cavity there arc 3 pairs of salivay glands. These glands are:

Parotid glands: Situated below the ear (Pinna) on the inner side of the buccal cavity.
Sublingual glands: Situated under the tongue.
Submandibular glands: Situated below the jaws materials.

Function:
Saliva contains:

Water And Mucus: due to which, the food becomes soft and lubricated. It can easily be swallowed.
Salts: These are used to kill the germs.
Amylase or Ptyaline Enzyme: Which takes part in the digestion of starch, and convert Starch into Carbohydrates.

PHARYNX:

At the end of the buccal cavity small part pharynx is present which opens into Oesophagus.
In the pharynx there is an Opening known as glottis. it leads into respiratory tract.
The glottis has valve known as epiglottis.
Function:
When food passes through the pharynx the glottis is closed by epiglottis so the food particles cannot enter the glottis.

OESOPHAGUS:

Pharynx opens into oesophagus.
It is a narrow tube like structure, which passes through the neck and then opens into stomach.
Function:
No enzyme is secreted in oesophagus. Only mucus is present to lubricate the inner wall.

STOMACH:

Stomach is present in the upper region of abdomen.
It is a sac like structure. It has three parts .
(i) Cardiac Part: in which oesophagus opens. Its opening has a valve known as cardiac sphinctor. It allows small amount of food to enter in the stomach.
(ii) Middle Part is known as fundus, which secretess digestive enzymes.
(iii) Lower Part is known as pyloric part, which is connected with duodenum. This part also contains a valve, called pyloric sphinctor. It allows to fine particles of food to pass into duodenum.

Function:
In the stomach gastric glands are present which secrete gastric juice under the influence of gastric hormone. The gastric juice contains:

Mucus: It forms a covering on the wall of stomach to protect from the action of enzymes and HCl.
HCl: It kills bacteria and other germs hence antiseptic. It also provides the acidic medium for action of enzyme.
Pepsinogen: It is an inactive enzyme which is changed into pepsin enzyme by the help of HCl. It converts protein into peptones.
Renin: It is present in the infants and babies to convert milk into curd but in adult body it is not secreted. HCl performs the function of rennin enzymes.

Protein -------Pepsin-------> Peptones

Thus It performs three functions: storage of food, mechanical digestion by peristalsis and the chemical digestion of food by enzymes, which is reduced to a creamy paste called chyme.

SMALL INTESTINE:
It consists of 3 parts:
Duodenum:

The stomach open into duodenum. It is a very important part. It receives bile duct from liver and pancreatic duct from pancreas. Both open collectively in the duodenum, called hepato-pancreatic duct.
Function:
The chyme on entering the duodenum meets the bile from the liver and the pancreatic juice from the pancreas.

Function OF Bile:

Bile performs two functions, after mixing with food material.
Bile secretes salts such as Sodium carbonate. Sodium glycocholate etc, neutralize the acid of the gastric juice and make the chyme alkaline.
It acts upon fats and emulsified it into small fat globules.
Bile pigments: bilirubin (red) and biliverdin (green) are excretory products formed by the breakdown of haemoglobin of worn out R.B.Cs in the liver.

Function Of Pancreatic juice:
The pancreatic juice contains enzymes which help in the digestion of food. These enzymes are:

Trypsisogen: This inactive enzyme is converted into trypsin enzyme, which is very active. It changes peptones into Polypeptide.
Chymotrypsin: It converts casein (milk proteins) into short chain amino acids.
Amylase: It converts carbohydrates into maltose and disacchrides.
Lipase: It converts emulsified fats into fatty acids and glycerol.

Jejunum:
From duodenum, the digested food is shifted into jejunum. It also secretes important enzymes.

Erypsin: It converts polypeptides into amino acids.
Maltase: It converts maltose sugar into glucose.
Lactase: It converts milk sugar lactose into glucose and galactose.
Sucrose: It convert sucrose into glucose.
Lipase: It converts fats into fatty acids and glycerol. In this way. the food is almost completely digested.

From jejunum diluted food chyle (digested food in the true solution form) passes into ileum.

Illuem (Absorption of food):

In the Ileum. absorption of digested food takes place. In the ileum, there are small projections known as villi.
The villi contain epithelial cells and lacteals. Lacteals are special cells connected with lymph vessels. Villi also have blood capillaries.
The glucose and amino acids are absorbed by villi. These are diffused into the blood. This blood carries them to the liver by hepatic portal vein. This glucose is used in supplying energy and its extra amount is converted into compound, glycogen. The glycogen is stored in the liver or in muscles of the body.
Amino acids provide energy and their extra amount is converted into glycogen by the removal of Nitrogen. Epithelial cells of villi absorb the fatty acids and glycerol. These are transferred to the lacteals, then into lymph vessels.
In these vessels, the fatty acids and glycerol are changed into simple droplets, after that these compounds are also migrated into blood vessels which carry them into the liver. These are either used to provide energy or stored in the body as reserve food in the form of solid fats (glycogon).

LARGE INTESTINE:
Large intestine consists of three parts.

Caecum
Colon
Rectum

Caecum:

It is present at the junction of ileum and colon. In this part, special bacteria are present which help in the digestion of cellulose, it is converted into sugar and it is thee absorbed in the body.
At the end of Caecum a small part called appendix is situated it has no function in digestion. Some times food particles are diffused into the appendix, causing pain. Such an appendix is removed by operation but removal does not cause any problem.

Colon:

It is very important part of large intestine. It consists of 3 parts.
(i) Ascending Part
(ii) Transverse Part
(iii) Descending Part
In the colon, undigested food is stored. The inns cells of colon, absorb a large amount of water, sugar and minerals from this food material. These substances are used again by the body and then undigested food is transferred into the rectum.

Rectum:
In the rectum, purely undigested food comes and it is expelled periodically out of the through the anus after re-absorption of water.

DIGESTIVE GLANDS:
Liver and pancreas are two important glands which are closely related to digestion.
LIVER:

Liver is the largest gland as well as the largest organ of the body.
A pear shaped gall bladder lies on the under surface of the liver.
It stores bile which is secreted by the liver cells.
The bile is collected by two hepatic ducts which join the cystic duct coming from the gall bladder forming a common bile duct which joins the pancreatic duct and opens into duodenum.

PANCREAS:

The pancreas lies behind the stomach horizontally within the curve of the duodenum.
It is exocrine as well as endocrine in function.
The exocrine part produces pancreatic juice and the endocrine part produces insulin and glucagon hormones.

(b) Draw labelled diagram of digestive system of man. (3)

Q5. (a) What is Cardiac cycle. Describe structure and function of human heart. (5)
Ans: Cardiac Cycle:
Heart muscles are myogenic. Their rhythmical contractions arise from within the muscle tissue itself without any external stimuli. Following one contraction, the next will not start till the whole has relaxed. There is a short pause between two contractions. The sequence of events which take place during the completion of one heart beat is called cardiac cycle.
The resting period of the heart chambers is known as diastole and the period during which they contract is known as systole.
The right atrium in its diastolic phase, receives deoxygenated blood from the vena cava and the left atrium receives oxygenated blood from the lungs. These chambers become distended and extend a pressure on the atrio-ventricular valves, by which they are pushed open. When the atrial diastole ends, the two atria contract simultaneously. This event is known as atrial-systole and the blood contained with in the atria is pumped into the respective ventricles.
Immediately, the ventricles contract. This event is termed as ventricular systole during which atrio-ventricular valves are closed and the aortic, pulmonary valves are opened. The blood is pumped into the respective aortae (The right ventricle opens into pulmonary arch and the left opens into aortic arch).
The volume of blood pumped per minute by the left ventricle into the systemic circuit is called cardiac output.

HEART OF MAN:

The heart is a pumping organ of the body. It helps to circulate the blood throughout the body. The blood is red in colour due to the presence of haemoglobin.
The heart is a muscular, hollow organ. It is present in a cavity of thorax, called pericardial cavity.
It is covered by protective covering called pericardium, which consists of two layers. Its outer layer is called parietal and the inner one is known as visceral.
The space between these two layers is filled with fluid called pericardial fluid. This fluid protects the heart from shocks and jerks
. The heart of man consists of four chambers:
(i) Right atrium or Right auricle
(ii) Left atrium or left auricle
(iii) Right ventricle
(iv) Left ventricle

RIGHT AND LEFT ATRIA (Auricles):

The two upper, thin walled atria (auricles) form the anterior part of the heart.
The two atria are separated from each other by a septum, called Inter-auricular septum.
In the right atrium there are two Two large veins, superior and inferior vena cava enter separately and bring deoxygenated blood from all parts of the body.
In the left atrium, two pulmonary veins open by separate aperture and bring oxygenated blood from the lungs.
In this way in the right atrium, in the right atrium deoxygenated and in the left atrium, oxygenated blood is collected.

RIGHT AND LEFT VENTRICLES:

The two thick walled ventricles form the lower part of the heart.
They are also separated from each other by a septum called inter-ventricular septum.
The right atrium opens into the right ventricle by an aperture called right auriculo-ventricular aperture. This aperture is guarded by a tricuspid valve, which allows the blood to flow from the right atrium into the right ventricle but not in the backward direction.
The left atrium also opens into the left ventricle by an aperture, called left auriculo-ventricular aperture. It is guarded by a bicuspid valve, which allows the blood to flow from the left atrium into the left ventricle but not in the backward direction.
Internally. the walls of ventricles are raised into conical processes, called papillary muscles. The tricuspid and bicuspid valves are attached to the papillary muscles by fine threads, known a chordac-tendineae. These threads control the movement of valves.
From the right ventricle pulmonary aorta arises. Its opening has three valves. called semilunar valves. These valves permit the flow of blood from the ventricle into the pulmonary aorta, but not in the backward direction.
From the left ventricle an arch called aortic arch or systemic arch arises. Its opening also has semilunar valves, which allow the flow of blood from the ventricle into the aortic arch but not in the backward direction.

ACTION OF HEART:
From all parts of the body, the deoxygauted blond is collected by pre-cavals and post-caval which open into the right atrium. In the left atrium oxygenated blood comes from lungs through pulmonary veins. When the atria are full of blood. they contract at the same time and blood comes into the ventricles. The right ventricle receives the deoxygenated blood and the left ventricle receives oxygenated blood.

When the Ventricles are filled with blood, they also contract at the same time. The bicuspid and tricuspid valves prevent the backward flow of blood into the atria (auricles). When ventricles contract, the chordae-tendineae do not allow the valves to be pushed back into the atria.

When Ventricles contracts, the semilunar valves allows the blood to flow into aortic arch and pulmonary artery. From the right ventricle, the blood comes into pulmonary artery which carries this deoxygenated blood of the lungs where oxygenation takes place. From the left ventricle, the blood flows into aortic arch (systemic arch) which supplies oxygenated blood to different parts of the body.

In this way, two systems of circulation work in the body of man. One is pulmonary circulation, in which the circulation takes place between the heart and the lungs. The second circulation is systemic circulation, which takes place between the heart and other parts of the body through the systemic or aortic arch. This is known as complete double circuit circulation.

(b) Draw labelled diagram of internal structure of human heart. (3)