Sign In Sign-Up

Welcome!

Close

Would you like to make this site your homepage? It's fast and easy...

Yes, Please make this my home page!

No Thanks

  Don't show this to me again.

Close

The material of which living organisms are made of is called protoplasm.

From the biological stand point, following are the features which distinguish living from non-living things.

Metabolism is a word used to describe all the chemical changes with in an organism which are necessary for life. The word metabolite refer to the substance which undergo various changes during metabolism. One of the important consequences of metabolism is production of energy for doing work.

Living things grow. Most animals grow until they reach maturity. Plants usually continue to increase in size throughout their life span.

Living things are sensitive to their environment. This means that they detect and respond to events in the world around them.

Living things are able to reproduce. It is the process in which living organism produce young ones of their own kind.

Living things move in a directed and controlled way. Animals usually move their whole bodies and often have special locomotory organs. Plants also move in a directed and controlled manner but generally part of their bodies move. Consequently, their movements are not locomotory.

Living things feed. Food is the material from which organisms obtain energy. The scientific study of food and different ways in which organism feed is called Nutrition. There are two important types of nutrition.

1. Autotrophic
2. Heterotrophic

Living things respire. Respiration is a complex sequence of chemical reactions which results in release of energy from food. These reactions are vital to life because they provide the power for the numerous chemical and physical processes with in living organisms.

Living things excrete. Excretion is the removal form the body of waste products which result from the normal life processes.

The holy Quran throws adequate light on the origin of life. The most important in the teaching of Quran is that Allah is the ultimate creator of everything. There are several verses of Quran in this regard. A few are quoted below.

Man had believed since ancient times that living organisms arise from, clay, earth and other non-living matter and not from pre-existing parents of their own kind. This old belief that living beings can spontaneously develop from the non-living is termed as abiogenesis.

According to this theory living organisms can arise from pre-existing living organisms.

Following are a few experiments which Redi performed and which led to concepts of biogenesis.

Some dead snakes were placed in a box. It was noticed that flies gathered round the dead snakes. After three days maggots appeared in their bodies and they devoured their flesh, leaving behind only the bones. After eighteen days maggots became inactive, assumed an egg like shape and transformed into pupae. Some of these pupae were then transferred to separate glass containers covered with sheet of paper.

After eight days, it was observed that a fly emerged from every pupae and all such flies were similar to those which were seen initially to settle on the body of the dead snakes.

From this it was concluded that the flies had laid eggs on dead snakes. Those eggs gave rise to maggots which formed pupae and ultimately files emerged from them.

Redi took eight bottles. He put dead snakes and fishes in them. Of these eight bottles, four were kept open and four covered.

After a few days, maggots appeared in the first four bottles only. No maggots appeared in the bottles kept covered.

This showed that if the flies were prevented from entering bottles, the maggots did not appear.

Some pieces of meat were put in a bottle whose mouth was covered with gauze. Thus air could enter the bottle while flies remained out. As further precaution this bottle was placed in a box, the wall of which were made of a netting.

No maggots appeared on the piece of meat even after many days inspite of the fact that entry of air was possible.

These experiments provided evidence supporting the idea that only living beings give rise to living beings.

In the beginning, the universe was an intensely hot point where mass and energy were indistinguishable. About 15 billion year ago, there was Big Bang (huge explosion). The universe started expanding and the temperature dropped drastically. In time about 4.6 billion years ago our earth and other planets appeared as a part of Solar System. The primitive atmosphere of earth was rich in hydrogen. Soon gases from the very hot and liquid core of the earth added more elements to this atmosphere. It is currently believed that the earth atmosphere at this stage consisted of carbon monoxide, carbon dioxide, hydrogen, nitrogen and water vapours. It hardly had free oxygen. With the passage of some more time the atmospheric temperature dropped further. This allowed condensation and heavy rains which caused formation of oceans. Thunder and lightning sparks together with ultra violet radiation caused reactions of the atmospheric gases. This led to formation of simple organic molecules. These molecules come down with rain and accumulated in the oceans, lakes, rivers and the soil over a very long period of time. Biologists believe that these molecules had enough chance to interact with the environment and produce amino acids and proteins which are the building blocks of the life.

The first life form, perhaps was sphere of naked protein or RNA in the beginning and was capable of making its copies. At some stage a membrane assembled around the sphere giving rise to the first cell. There is now agreement that this first life form respired anaerobically because the earth atmosphere lacked free oxygen, obtained energy by ingestion of organic molecules like a heterotroph and reproduced asexually.

Robert Hooke, a British scientist discovered cell for the first time in 1665. Cell is the basic unit of living organisms.

This theory was put forward by two German biologists M.J.Schleiden (1838) and T.Schwann (1839). According to this theory:

1. All living bodies are composed of cells and cell products.
2. Cell is the structural and functional unit of living organisms.
3. New cells arise from pre-existing cells.

Plant cell is divided into following parts.

Animal cell consist of following parts.

Plant cell is surrounded by cell wall but this wall is absent in animal cell. It is made up of cellulose.

It is present in both the animal and plant cells. In animal cells it is outermost boundary but in plant cells it lies inside the cell wall. It is semi-impermeable membrane, and composed of lipid bilayer and protein.

It is the region of cell between cell membrane and nuclear membrane. It consist on water electrolytes, enzymes, nutrients and certain structures called organelles which are associated with the living activities.

Organelle is a discrete sub cellular structure with a particular function. The largest organelle is the nucleus, the other examples are chloroplast, mitochondria, golgi apparatus, vacuole and ribosomes. Organelles allow division of labour with in the cell. Following are some of the major organelles. It is present in both plants and animal cells.

Mitochondria are generally rod like organelles consist on double layer membrane. They are self replicative.

Mitochondria play important role in respiration of cell. They contain enzymes which help in production of energy. As producers of energy they are called power house of the cell.

It is an organelle of plant and animal cells discovered by Camillo Golgi in 1898. It is associated with endoplasmic recticulum but lacks ribosomes. It consist of sticks of flattened membrane-bounded rac(cioternae) associated with vesicles (golgi vesicles).

1. Formation of zymogen granules.
2. Synthesis and transport of secretory polysaccharides. e.g., cellulose in cell wall or cell plate formation.
3. Formation of nucleus in goblet cells.
4. Assembly of glycoproteins.
5. Synthesis of neurotransmitters.
6. Formation of lyrosomes.

A system of flattened membrane-bounded racs(cisternae) running through the cytoplasm of all encaryotic cells and continuous with the nuclear envelope. Its surface is often covered with ribosome forming rough endoplasmic recticulum. ER lacking ribosome is called smooth ER.

1. Transportation within the cell.
2. Lipid synthesis.

It is the smallest organelle found in one animal and plant cells. Ribosomes are often bound to endoplasmic recticulum or may occur free in the cytoplasm. It is found in large numbers in all cells. It is composed of RNA and protein.

1. Protein Synthesis

The centrosome occurs only in the animal cell or in lower plant cells.

This organelle is important in spindle formation during cell division.

The nucleus is the largest cell organelle. It is an organelle of plant and animal cells containing the genetic information (DNA) and hence controlling the cell’s activities. It is surrounded by a double layer nuclear membrane. The fluid present in side the nucleus is called nucleoplasm. It contain network of fine chromatic threads which become visible as chromosome when cell prepares to divide. The hereditary material called deoxyribonucleic acid (DNA) is located on chromosomes.

Nucleus control all the activities of cells.

Plastids are small bodies and are found in plant cell only. They contain different pigments important among them is chlorophyll.

It is involved in the process of photosynthesis.

The chemical reactions that takes place in cells. The molecules taking part in these reactions are called metabolites. Some metabolites are synthesized with in the organism, while other have to be taken as food. Metabolic reactions occurs in small steps, comprising a metabolic pathway. Metabolic reactions involve the breaking down of molecules to provide energy are catabolism, and the building up of more complex molecules and structure from simpler molecules are anabolism.

Cells increase in number by division. During this process the nucleus divide first (Karyokinesis) which is followed by the division of cytoplasm (Cytokinesis). There are two main types of Cell divisions.

1. Mitosis
2. Meiosis

The division in which the parent cell divide into two daughter cells in a way that the number of chromosomes in the daughter cell remains the same as in the parent cell.

Although mitosis is a continuous process, it can be divided into four stages, which are:

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

1. During early prophase chromosome become visible as thread like structure.
2. Each chromosome at this stage is already doubled i.e., it contain two chromatids.
3. The nuclear membrane disappear gradually.
4. Contrioles move towards opposite poles of the cells and give rise to spindle fibers.

1. During this phase each chromosome arranges itself on the equator of the spindle.
2. Each chromosome is attach to separate spindle fiber by its centromare.

1. In this process the centromare divide and chromatids of each chromosome separate from each other and began to move towards opposite poles.

1. This is a stage when the chromatids (now called chromosomes) reach the poles and their movement ceases.
2. Nuclear membrane is formed around each set of chromosomes.

Soon the cytoplasm of the cell divides and two daughter cells arise. The nucleus of daughter cell contain the same number of chromosomes as the parent cell.

1. It provides a mean for asexual reproduction.
2. It takes place during the growth.
3. Damaged cells are replaced by new cells which are formed by mitosis.

The process of cell division leading to the production of daughter nuclei with half the genetic compliment of the parent cell. Meiosis consist of the two divisions during which the chromosomes replicates only once.

Fist meiotic division is divided into following phases.

Homologous chromosomes come together and forms pair. In each homologous pair there are four chromatids. Homologous chromosome exchange their parts at certain places. This exchange is called crossing over. The nuclear membrane disappears and spindle fibers are formed.

During this phase pairs of homologous chromosomes arrange themselves on the equator of the spindle. Unlike mitosis, it is the homologous pair and not the individual chromosome attach at the separate fibers of the spindle.

The members of the homologous pairs now begin to separate and move towards the opposite poles.

In this phase chromosome come to rest at the poles. The nuclear membrane is formed around each set of chromosomes resulting in formation of two daughter nuclei. The nucleolus reappears. On completion of nuclear division, division of cytoplasm takes place and two cells are formed.

Second meiotic division is almost similar to mitosis. During prophase spindle are formed and the nuclear membrane disappears. In metaphase chromosome arrange themselves on the equator. Their chromatids separate from each other in anaphase and migrate to the opposite poles. In Telophase the nuclear membrane reappears around each set of chromatids (now called chromosomes) and cytoplasm divides forming two daughter cells. So at the end of meiosis four daughter cells are produced in total each possessing a haploid nucleus.

Unicellular organisms consist of single cell. They are capable of independent existence by making use of their organelles. Such organism represent the unicellular organization of life. Wile some cells have stayed at this level of organization other lives have also developed. In some cases cells have come together to form loose assemblies.

A group of cells specialized for a particular function.

A part of an organism that is made up of a number of tissues specialized to carry out a particular function e.g., lung, stomach etc.

Cell ® Tissue ® Organ ® Organization ® Organism

In plants there are two basic types of tissues which are as follows:

These tissues contain cells have the ability to divide. Meristematic cells are smaller in size with thin walls. Apical meristem are present at the tip of roots and stems, and they are responsible for primary growth. The lateral meristem is responsible for secondary growth.

These tissues are formed from meristematic cells. They don’t have ability to divide. Their walls become thick to give them definite shape. Following are the types of permanent tissues.

The cells of dermal tissues are uniform in shape and size, they form outer layer of root, stem and leaf.

They consist of thin walled parenchymatous cells which are formed from meristematic tissues.

These cells are basically meant for storing food but they also prepare some food.

When cell reach a maximum size their cell wall become thick due to deposition of special material and become dead. The tissue is of various shapes and provide rigidity and support to the plant. Sclerenchyma (thick walled lignified elongated) and collenchyma (living cell with thick outer walls with a few and small intercellular spaces) are examples of supporting tissues.

This tissue consist of elongated cells with thick or thin wall. Xylem and phloem are the examples of conducting tissues.

XYLEM conduct water and mineral salts from roots to leaves.

PHLOEM conducts food from leaves to the different parts of the plant body.

Following are the important animal tissues.

The cells of this tissue occur in single layer and are present very close together. This tissue forms layer and lines tubular organs of the body.

1. Protection
2. Secretion
3. Absorption

These tissues provide support to other tissues and organs and bind them together e.g., fatty tissues, tendons and cartilages are examples of connectives tissues. Blood is also a special type of connective tissue.

This tissue is formed of muscle fiber. Each muscle fiber is elongated cell which has ability to contract and relax.

This tissue cause movement of body and body parts.

This tissue is formed of cells called Neurons. Nerve cells are specialized to conduct message in the form of electric current. Nervous system consist of this tissue.

Organism consist of single cell are called unicellular organisms. Chlamydomonas and amoeba are examples of unicellular organisms.

It is a unicellular green fresh water plant which is visible under microscope. From an evolutionary view point it is considered to be the simplest aquatic plant. It is spherical slightly elongated or pear shaped.

It is surrounded by the cell wall which is made up of cellulose. On its interior and it has an out growth called apical papilla.

A pair of flagella occurs on apical papilla. By the means of flagella it moves from one place to another.

Inside the cell wall there is a cell membrane which is made up of lipid bilayer and proteins.

It is the region of cell between cell membrane and the nucleus. The cytoplasm contain many structures. Following are some of them.

The chloroplast helps in synthesis of food by the process of photosynthesis.

Two contractile vacuoles are present in the cytoplasm at the base of flagella. They remove matter and excess of water from the body.

A spherical body called pyrenoid is present in the chloroplast. It is believed that carbohydrates are accumulated in this pyrenoid.

A red eye spot is present near the interior tip of the organism. It is very sensitive to light and helps plant to distinguish between bright light and

Cytoplasm contain a big nucleus which control all the function of the cell.

It is unicellular animal found in stagnant pools and ponds. It is microscopic in size measuring about 0.25 mm. It does not possess a definite shape because it lacks pellicle.

The structure of amoeba is very simple. Following are some important structures:

It is surrounded by a cell membrane.

Cytoplasm is very clear. It is differentiated into two parts. The outer portion which is clear and transparent is called ectoplasm. The inner viscous, translucent and granular part is called endoplasm. The endoplasm contain many food vacuoles of different size in contractile vacuole and spherical nucleus. Organelles such as endoplasmic recticulum and mitochondria are also present in the endoplasm.

The animal moves by producing finger like projections called pseudopodia. The pseudopodia are also used to capture food particles. Amoeba respire by exchanging gases with the surrounding water through its surface.

Living organisms consist on many cells are called multicellular organisms. Brassica and frog are representative examples of multicellular plants and animal respectively.

Brassica campestris is the botanical name of mustard (sarson).

The plant body is divided into two categories on functional basis

The vegetative parts are those which do not directly take part in sexual reproduction. These parts are root, stem and leaves.

The reproductive parts consist of sex organs which are directly related to sexual reproduction. These are flowers.

1. It is underground part of the plant.
2. It develops from the radicle of the seed.
3. Chlorophyll is absent in the root.
4. Its movement is positively geotropic and negatively phototropic.

The first part of the root which arise from the radicle is known as the primary root. During its growth it gives rise to secondary and tertiary roots. The tips of all roots bear a cap, the root cap. Behind the root cap are present fine thin root hairs.

1. Absorption of water and mineral salts.
2. Fixation.

The transverse section of root shows the different layers of cells from outer to inner side.

The outer part of root is epidermis which protect the roots. Root hairs are outgrowths of epidermal cells.

Cortex primarily consist of parenchyma cells. Parenchyma cells store food materials.

With in the cortex is central cylinder called the stele. The stele of root is surrounded on the outside by layer of cells called endodermis.

Next to the endodermis is a layer of cells called pericycle. Branch root arise from pericycle. Then central part of the stele is occupied by star shaped xylem. In between arms of xylem is phloem. Rest of the stele is made up of parenchyma cells.

It develops from the plumule of the seed.

It is axial part of the plant body.

Some of its parts contain chlorophyll.

Its movement is positively phototropic and negatively geotropic.

It bears branches, leaves and flowers. The point on the stem which give rise to leaf is known as node. The part of stem between adjacent nodes is called internode.

1. The stem and the branches transport water and mineral salts from roots to leaves.
2. It also transport prepared food from leaves to all parts of the plant body.
3. Stem supports the leaves and the branches.
4. The stem bear leaves and flowers.

In the transverse section of stem of brassica following layers of cells can be observed from outside to inside.

Stem is surrounded by single layer of cell called epidermis.

Next to the epidermis is cortex. The cortex is made up of parenchyma and collenchyma cells. Food material is stored in the cortex.

Next to the cortex is a ring of vascular bundles. Each vascular bundle consist of xylem and phloem. Xylem is located towards inside. Phloem is located towards outside. In between xylem and phloem is region consisting 2 – 3 layers of cells called meristematic cells. This layer is combium. The center of stem is occupied by the pith. Pith is made up of parenchymatons cells and store food.

Leaves grow out on stem and its branches from the nodes. Generally, the leaf of brassica consist of two parts. The lower stalk part is tutiole and upper green expanded portion is the lamina. There is a swollen vein in the middle of the leaf which is known as mid rib. The leaves are arranged on stem and the branches in such a way that their upper surface remain directly exposed to the sunlight.

There is a layer of upper and lower epidermis on the upper and lower surfaces of leaves respectively. Lower epidermis contains stomata.

These tissues are present in between the upper and lower epidermis. On the upper side are the layers of palisade mesophylls. On lower side is the layer of spongy mesophyll. Photosynthesis takes place in palisade mesophyll, while spongy mesophyll store water.

Running through the leaf are vascular tissues or veins, surrounded by layer of endodermis. Xylem is located towards upper side and phloem towards the lower side.

The arrangement of flower on the floral axis is called inflorescence.

The flower in brassica is situated on stalk known as pedicel.

The tip of pedicel is slightly flattened and known as thalamus. The floral leaves are arranged in four whorls on the thalamus. These whorls starting from the outer most to the central on are in the following order.

This is the outermost whorl and consist of four free sepals. The most important function of the calyx is that it covers the inner parts of the flower and protect them from sunlight and rain.

This is second whorl and composed of four free yellow petals.

This is the third whorl of the flower. It consist of six stamens. Each stamen consist of anther and filament. The anther contain numerous pollen grains. There are nacteries at the base of the androecium.

This is fourth whorl occupying the central position in the flower. The individual member of gynoecium is called Carpel. Each carpel consist of three parts.

1. Stigma
2. Style
3. Ovary

In the ovary are present many ovules which ripen after fertilization into seed. The ovary ripen and is converted into fruit after fertilization.

Phylum : Chordata

Sub phylum : Vertebrata

Class : Amphibia

Biological name : Rana Fegrina

Frog lives both in water or on land. It swims in water and moves by jumping when on land. There is a membranous skin between its toes in each foot, but hand has only four fingers because the thumb is very rudimentary. In male frog first finger is thicker than others.

Neck and tail are absent in mature frog. The conical head has two large bulging eyes. Behind each eye is a circular area called tympanic membrane. They help in hearing. At the tip of snout are two small openings called external nostrils by which frog respire. The skin of frog is loose and slippery due to secretion produced by glands present on skin.

Frogs are found in abundance in rainy season during which they lay eggs. They hibernate during the winter season by burying themselves in the mud and stay throughout the winter.

The organs involved in the breakdown of complex food into simpler form constitute the digestive system. The digestive system composed of alimentary canal and digestive glands associated with alimentary canal. The alimentary canal consist of mouth, buccal cavity, pharynx, oesophagus, stomach, duodenum, ileum, rectum cloaca and anus.

Food enters the buccal cavity through mouth. Frog has upper and lower jaws. Upper jaw is fixed while lower jaw is movable. At the margin of upper jaw there are many small teeth called maxillary teeth. They are not meant for chewing but prevent it from slipping out of the mouth. The tongue of frog is bifurcated and attached in front to the floor of buccal cavity and being free behind. This allow the animal to throw it outward. Frog feeds mainly on insects. On seeing the prey it suddenly throws out its tongue. The prey sticks to it because a sticky substance is secreted by glands present on tongue.

Buccal cavity opens into a short and narrow pharynx. Behind it communicates with oesophagus.

From oesophagus food comes into the stomach. The stomach stores food, produces gastric juice and it also grinds food.

The intestine is a long narrow tube. It is divisible into small and large intestine. The partially digested food from stomach enters into the small intestine, where its digestion is completed and digested food is absorbed into the blood. The undigested food enters into the large intestine from where it is expelled out as feaces through a cloacal opening.

Liver is a large gland located adjacent to the stomach. Its secretion is known as bile. Between lobes of the liver is a pouch like structure called gall bladder which stores bile. On its way this duct passes through pancreas and join the pancreatic duct. The pancreas lies in the folds of the small intestine. Its secretion pancreatic juice is carried by pancreatic duct. The pancreatic duct and bile duct join to form common hepatopancreatic duct which open into the small intestine.

Conversion of complex form of food into a simpler form by the action of the different enzymes.

The pulmonary respiratory system of frog consist on following parts.

1. External nostrils
2. Internal nostrils
3. Buccal cavity
4. Laryngotracheal chamber
5. Bronchi
6. Lungs

The frog has two lungs which balloon like structure. Their outer surface is smooth but the inner surface has numerous folds which increase the area for gaseous exchange. The lungs are richly supplied with blood vessels. Each lung has bronchus at its upper end. Two bronchi open into larynx.

During respiration air is taken in by the external nostrils. It passes into the buccal cavity through the internal nostrils. From here it enters the glottis and passing through the larynx and bronchi finally reaches the lungs. In the lungs exchange of gases between blood and air takes place.

Circulatory system of frog consist of following parts:

1. Heart
2. Arteries
3. Veins
4. Capillaries

1. Transport of nutrients.
2. Transport of waste products.
3. Transport of hormones.
4. Transport of respiratory gases.

The heart is an organ which can be compared with a pump. Its continuous beat makes the blood to circulate in the body. Frog’s heart has five chambers namely:

1. Sinus venosus
2. Right auricleThese three chambers are thin walled.
3. Left auricle
4. Ventricle:It is thick walled and muscular.
5. Truncus arteriosus :It is tubular part and arises from the ventricle.

In heart flow of blood is continuous and is in two directions. The oxygenated blood from the lungs enters the left auricle through pulmonary vein. The deoxygenated blood from all other parts of the body enters the sinus venosus. From sinus venosus it reaches the right auricle. When the two auricles contract the blood is pushed into single ventricle. When ventricle contracts blood is pumped into the truncus arteriosus. From here

1. it enters the pulmonary arteries which supply the blood to the lungs for oxygenation, and
2. other vessels which take it to all parts of the body.

The various chambers of the heart are guarded by valves which prevent the back flow of the blood. The heart receive two types of blood simultaneously. One type is rich in oxygen and arrives from lungs and other is poor in oxygen and comes from the rest of the body. These two types of blood are kept separate in the two auricles. As soon as blood enters the ventricle it would tend to mixed here. However the flow of the blood into the ventricle is rapid which prevent extensive mixing of pure and impure blood except when two streams are in contact. Furthermore a special valve in truncus arteriosus keeps the two streams separate.

Arterial system can be simply stated to comprise following three main components.

They supply deoxygenated blood to lungs and skin where it give carbon dioxide and pick up oxygen.

These vessels arise from the truncus arteriosus and supply the oxygenated blood to various parts of the head region such as brain, tongue, head muscles, eyes, ears etc.

These supply oxygenated blood to all other parts of the body except the head and lungs. A major vessel of this system is aorta which give off branches to various parts of the body such as fore limbs, digestive system, liver, pancreas, kidneys, genital organs and muscles.

The blood returns from various parts of the body by vein into the sinus venosus of the heart. The venous system consist of following major components.

1. Blood after oxygenation in the lungs is collected in pulmonary vein which bring it to the left auricle of the heart.
2. The deoxygenated blood from head and fore limb is collected through several veins which join together and form precavals. These open into the sinus venosus from where the blood is pumped into the right auricle of the heart.
3. Blood from lower parts of the body such as stomach, intestine, liver, pancreas, genital organs, muscles, hind limbs is collected through vein which join together and form post caval. The post caval also open into the sinus venosus which empties into the right auricle.

It is necessary to mention here that the blood from the digestive system is not carried directly to the heart. It first enters the liver by hepatic portal vein which break up into the capillaries in liver to allow transfer of some of the digested food into the liver for storage. From the liver it enters the post caval which carries it to sinus venosus. The blood from the hind limbs follows two routes towards the heart.

1. It can be collected in an abdominal vein which join the hepatic portal vein in the liver and drain blood into the post caval vein.
2. The alternated route from the hind limb is by the way of a renal portal vein. This vein begins in capillaries in the hind limbs and breaks up into capillaries in the kidneys. From the kidneys this blood enter the post caval by renal vein and ultimately return to the heart.

The removal of metabolic waste matter from the body is known as excretion. This function is performed by kidneys which filter out the excretory matter from the blood and pass it out in the form of urine.

1. A pair of kidney
2. A pair of ureter
3. Urinary bladder
4. Cloaca

The kidneys of frog are elongated organs and are attached to the dorsal body wall of body cavity. The urine is carried from the kidney by pairs of ureters which empty into the cloaca. From the cloaca, it is either passed out directly through the cloacal aperture or stored for some time in a bag, the urinary bladder.

Sexes are separate in frog. The reproductive system consist of gonads and their ducts. The gonads produce germ cells and the ducts pass them out of the body. The male gonad is known as the testis and the female gonad is called ovary. The gonad are paired structures and are located near kidneys. The sex cell of male is sperm and that of female is ovum. The ova are released from the ovary into the body cavity from where they enter the oviduct through the oviduct funnel. They are liberated into water through the cloaca in the breeding season.

The male produces sperms during the breeding season. Sperms are released from the testes and reach the cloaca through a pair of duct called vas-deference from where they are passed out. In the male the vas-deference are also called urinogenital duct, because they transport both sperm and urine.

The nervous system of frog is composed of two parts i.e., the central nervous system and the peripheral nervous system. The central nervous system includes brain and spinal cord. Where as peripheral nervous system consist of cranial and spinal nerves.

The brain is located in the skull. It consist of the following parts.

The most interior region comprises the olfactory lobes.

They are associated with the sense of smell and transfer of olfactory sensation to the cerebral hemispheres.

Immediately behind the olfactory lobes there are two large out growths called the cerebral hemispheres.

It is higher control center and control important function like memory, thoughts, planning etc.

Behind the cerebral hemisphere are located two prominent out growths the optic lobes.

They are associated with eyes and vision.

The part between the optic lobes and cerebral hemisphere is diencephalon. On the dorsal surface of the diencephalon is present a pineal body while pituitary gland is attached to its ventral side.

The diencephalon receives variety of messages from the internal and external environment of the body and also controls the secretion of hormones from the pituitary gland.

The last part of brain consist of the cerebellum and medulla oblongata.

The cerebellum and the medulla oblongata control and coordinate body movement and maintain balance of the body. The medulla also controls respiration, circulation and digestion.

The spinal cord start from the posterior end of medulla oblongata. It passes from the skull through a hole and enters the canal of vertebral column.

The nerves arise from spinal cord are spinal nerves. Through these nerves spinal cord connects brain with the different parts of the body.

Receptors are specialized cells which receive stimulus. Following are some of the important receptors.

1. Sense of touch® Receptors in skin
2. Sense of smell® Olfactory reception
3. Sense of sight® Rods and cones
4. Sense of hearing® Receptors in ear
5. Sense of taste® Taste buds on tongue

It is an organ of hearing. Its outermost part is tympanic membrane. On the inner side of this is a cavity known as tympanic cavity. The cavity contains rod like small bone known as columella auris. Its one end is attached to the tympanic membrane and other with the internal ear.

The internal ear is very delicate organ. Consist of semicircular canal. These canals are filled with a fluid and sensory cells are located at special places in these canals. When sound waves strike the tympanic membrane it set into vibration. This in turn influence the stapes and the internal ear.

Thus sound waves stimulate the hearing receptors in the ear. The internal ear in addition to hearing also keep the balance of the body.

The frog has two eyes on each side of the head. From outer side to inner side eye ball consist of following layers.

This is the outermost coat which is transparent in its interior 1/3 part called cornea. The posterior 2/3 part is opaque and called sclerotic.

It is the middle layer of the eye which is highly vescular and pigmented. On interior side it forms iris, and other structure. This layer supply nutrients to retina.

This is the innermost layer of the eye. It is also known as sensory layer of an eye. It has sensory cells rods and cones which receive light stimulus.

The fluid present between cornea and lens.

A biconvex lens is present just behind the aqueous humor.

A jelly like transparent fluid present first behind the lens. It maintain the shape of the eye ball.

The rays of light enters through the cornea, a transparent outer layer and passes through the aqueous humor, lens and vitreous humor and strikes on retina. Retina has photoreceptors rods and cones. There is a point on retina called yellow spot where concentration of cones is higher. Most clear image is formed at this point. Optic nerve take the sensory message from eye to the brain.

Top