Structural Organization in Plants and Animals Short Notes PDF in English for Class 11, NEET, AIIMS and Medical Exams

Structural Organization in Plants and Animals Short Notes PDF: Find below the important notes for the chapter, Structural Organization in Plants and Animals as per the NEET Biology syllabus. This is helpful for aspirants of NEET and other exams during last-minute revision. Important notes for NEET Biology- Structural Organization in Plants and Animals Short Notes PDF cover all the important topics and concepts useful for the exam.

Structural Organization in Plants and Animals Short Notes

Structural Organization in Plants and Animals Short Notes PDF

Structural Organization in Plants and Animals provides with a detailed description of the morphology and anatomy of both plants and animals. The topics covered under Structural Organization in Plants and Animals are:

  • Morphology of Flowering Plants
  • Anatomy of Flowering Plants
  • Structural Organization in Animals

Morphology of Flowering Plants

The study of various external features of the organism is known as morphology. The angiosperms are characterized by presence of roots, stems, leaves, flowers and fruits.

Flowering plants are the most diverse group of land plants with 300,000 known species. These are also known as angiosperms and produce seed-bearing fruits. It is believed that the flowering plant evolved from gymnosperms during the Triassic period and the first flowering plant emerged 140 million years ago.

Flowering Plants Parts

Flowering plants are divided into two parts:

  • Root system: The underground root system develops from the radicle embryo and helps in fixation of the plant as well as absorption of water and minerals.
  • Shoot system: The aerial shoot system develops from the plumule embryo. It contains root, stem, leaves as vegetative parts and flowers, fruits and seeds as reproductive parts. The Vegetative parts are involved in various vegetative functions like structural organization, fixation, absorption, nourishment, growth and maintenance of various components and reproducting parts are for sexual reproduction and germination of new plants.

Root System

The root is a brown, non-green and underground part of a plant. Root with their branches is collectively called a root system. There are three types of the root system:

  • Taproot System: The taproot is mainly found in dicotyledonous plants. The tap root develops from the radicle of embryo of a seed. In most of the plants, primary root persists and becomes stronger to form tap root. The first root forms by the elongation of radicle and is called primary root. It continuously grows and produces lateral roots called secondary roots. Mustard seeds, mangoes, grams and banyan are a few examples of dicotyledonous plants with taproot system.
  • Fibrous root System: The fibrous root is mainly found in ferns and in all monocotyledonous plants. This root develops from thin, moderately branching roots or primary roots, growing from the stem. The fibrous root system usually does not penetrate deep into the soil, therefore, on full maturity, these roots look like a mat or a carpet on the floor. Wheat, paddy, grass, carrots, onion, grass are a few examples of monocotyledonous plants with the fibrous root system.
  • Adventitious root System: The roots which originate from any part of the plant body other than the radicle is called the adventitious root system. This root system is mainly found in all monocotyledonous plants. In plants, the adventitious root system is used for various purposes, like mechanical support, vegetative propagation, etc. Banyan tree, maize, oak trees, horsetails are a few examples of monocotyledonous plants with the adventitious root system.
Regions of Root System

Regions of the Root

  • Root Cap (Calyptra): The root is covered at the apex by a thimble or cap-like structure called the root cap. It protects the root meristem from friction of the soil particles and also protect tender apex which allow the passage of root through cells, e.g., Lemna, Eichhornia.
  • Region of Meristematic Activity (Growing Point): It is a small (about 1 mm in length) thin-walled region having dense protoplasm. It lies partly within and partly beyond the root cap. Its cell divide regularly and repeatedly for elongation. It is responsible for the growth of the root.
  • Region of Elongation: It is situated behind the meristematic region (growing point). The cells elongate speedily and increases the length of the root. The cells of this region can absorb water and minerals from the soil.
  • Root Hair: It is the region where primary tissues differentiate into the root. The vascular tissues like xylem and phloem are formed. Root hair zone is the most important part of the root for absorption of water (most of the water) from the soil. The root hairs increase the exposed surface of the root for absorption.
  • Region of Maturation: This zone contains mature cells. It forms the permanent zone of the root and also gives out lateral roots from the interior part of this region, e.g., In dicots and gymnosperms.
Functions of Root
  • Fixation Root provides fixation to the plants with soil.
  • Absorption Roots absorb water and minerals from the soil and provide it to all parts of the body.
  • Storage Roots of many plants store food for the use of other plant parts and for animals.
  • Conduction Roots transport water and minerals in upward direction for the uses of stems and leaves.

Shoot System

Shoot system is an aerial and erect part of plant body which grows upwards. It is usually above the soil and develops from plumule of the embryo. It consists of stem, branches, leaves, flowers, fruits and seeds.

The Stem

The stem is the ascending part of the axis bearing branches, leaves, flowers and fruits. It develops from the plumule of the embryo of a germinating seed. It shows distinction into nodes and internodes; where node is the region from where leaves are born and internodes are the region between two nodes. Its apex bears a terminal bud for growth in length. Young stems are usually green in colour and subsequently becomes woody and brown. The stem is modified into certain structures according to the function they perform.

  • Characteristics of Stem
    • Arises as a prolongation of plumule (one end of an embryo).
    • Grows and bends towards light (positively phototropic) and away from gravity (negatively geotropic).
    • Divided into nodes (point of attachment of leaf) and internodes (regions between two nodes).
    • Bears leaves, branches and flowers on nodes.
    • Bears vegetative buds which could be terminal (apical bud) for plant to grow upwards or axillary (bud in the axil of leaf) which give rise to lateral branches.
    • Bears floral buds (terminal or axillary) that grow into flowers.
  • Types of Stems
    • Aerial Stems: The aerial stems have two forms, i.e., reduced stem and erect stem. 
    • Subaerial Stem: In subaerial stems, some part lives underground, whereas, the remaining part of the stem is aerial.
    • Underground Stems: The stem of some plants lie below the soil surface. They are non-green, store food as means of perennation and vegetative propagation.
  • Modifications of Stems: Stems are variously modified into underground, sub aerial and aerial stems for performing functions like manufacturing and storing food, perennation (overcoming unfavorable climatic conditions), providing mechanical support and protection and for propagating vegetatively.
    • Underground modified Stems: It act as perennating structures by remaining leafless and dormant in winter but giving off aerial shoots under favourable conditions (next season). It stores food and become thick and fleshy. The various types of underground modified stems are:
      • Rhizome:  Ginger (Adrak), Curcuma domestica (turmeric).
      • Corm: Saffron (‘kesar’), Yam (‘zimikand’).
      • Bulb: Allium cepa (onion), Allium sativum (garlic).
      • Tuber: Solanum tuberosum (potato).
    • Subaerial modified Stem: Subaerial modified stems are weak, therefore lie prostrate on the ground or may get partially buried in the top soil. The plants bearing such stems are called creepers. Their stems serve the function of vegetative propagation. The various types of subaerial modified stems are:
      • Runner: Cynadon (lawn grass), Centella (brahmi booti), Oxalis, etc.
      • Stolons: Fragaria verica (strawberry), Jasminum (jasmine), Mentha piperita (peppermint).
      • Offsets: Pistia (water lettuce), Eichhomia (water hyacinth), etc.
      • Suckers: Mentha (podina), Chrysanthemum (guldaudi).
    • Aerial modified Stem: In this whole stem or its part (axillary or terminal bud) gets modified to perform definite functions. The various types of aerial modified stems are:
      • Tendrils: Thread like, spirally coiled, leafless structures
      • Thorns: Straight, pointed, hard structures
      • Phylloclade: Green, flattened or cylindrical fleshy stem, with nodes and internodes
      • Cladode: helps in photosynthesis
  • Functions of Stems
    • Support and orient the leaves in a manner that they are exposed to maximum sunlight and for efficient gaseous exchange during photosynthesis and respiration.
    • Conduct water and minerals Plants and animals from roots to leaves and manufactured food from leaves to different parts of the plant.
    • Bear flowers and fruits
    • Stems store food and water in some plants e.g. potato
    • The underground stems help tide over the unfavourable growing periods e.g. ginger.
    • Stem can be a means of vegetative propagation e.g. rose, and sugarcane.
    • In certain plants like xerophytes (desert plants) where leaves are reduced, the stem takes up the function of photosynthesis. These stems possess chlorophyll e.g. Opuntia.
    • In some plants the axillary bud modifies into thorn and protects the plants from grazing animals e.g. citrus, Duranta.
The Leaf

Leaf is a flattened and expanded lateral appendage of stem or branch developing from its node. It originates from leaf primordium formed by the shoot meristem and bears a bud in its axil called axillary bud. It is the seat of very important physiological processes like photosynthesis, transpiration and respiration. Besides protecting axillary buds, leaf can get modified into structures for storing food and water, climbing, and vegetative propagation.

  • Characteristics of Leaf
    • The leaf arises from the node.
    • It is exogenous in origin.
    • It has a bud at its axis.
    • The growth of the leaf is limited.
    • The leaves do not bear an apical bud.
  • Parts of Leaf
    • Leaf Base (Hypopodium): Lower most part of leaf by which it is attached to the stem node. 
    • Petiole (Mesopodium): Is the stalk of leaf. Leaf can be petiolate ( with petiole) as in many dicots or sessile ( without petiole) as in most monocots.
    • Lamina or leaf blade (Epipodium): It is a green, thin, flattened and expanded part of leaf with veins and veinlets traversing through its surface.
  • Modifications of Leaves
    • Leaf Tendrils: Here leaves or leaflets get modified to form thin wiry, closely coiled sensitive structure called the tendril that helps the plant to climb the support.
    • Spines: The leaves are modified into sharp and pointed structures which protect the plant and help in reducing transpiration.
    • Phyllode: The petiole of compound leaf becomes flattened leaf like and helps in photosynthesis; the leaflets gradually disappear.
    • Insect-catching leaves: They help in trapping insects.
  • Venation in Leaves
    • Reticulate venation: When the veinlets form a network, the venation is called reticulate. It is found in dicot leaves. 
    • Parallel Venation: When the veins run parallel to each other within a lamina, the venation is termed as parallel, e.g. Calophyllum, Zingiber officinale, etc.
  • Functions of Leaves
    • Photosynthesis
    • Exchange of gases
    • Transpiration
    • Guttation

The flower is the reproductive unit in the angiosperms. It is meant for sexual reproduction. Morphologically, it is considered as a shoot bearing nodes and modified floral leaves. A flowers is called modified shoot because the position of the buds of both flower and shoot which is same and can be in terminal or axillary in position.

  • Structure of Flower

A flower arises in the axil of a leaf like structure called bract. Flowers with bracts are called bracteate and those without bracts are called ebracteate. The terminal part of the axis of the flower is the receptacle or thalamus. The receptacle contains sepals, petals, stamens and carpels. If the leaves are present on the pedical, they are called bracteoles.

Structure of Flower

  • Parts of Flower
    • Calyx: It is the outermost whorl of a flower. It is made up of units like sepals.
    • Corolla: It is composed of petals. Petals are usually brightly coloured to attract insects for pollination.
    • Androecium: It is the third whorl of flower composed of stamens or microsporangium.
    • Gynoecium: Gynoecium is the female reproductive part of the flower and is made up of one or more carpels or megasporangium.
  • Functions of Flower
    • Help in the process of reproduction.
    • Produce diaspores without fertilization.
    • The gametophytes develop inside the flower.
    • The flowers attract insects and birds which then act as a medium to transfer the pollen from the anther of one flower to the stigma of some other flower.
    • The ovary of the flower develops into a fruit that contains seed.

The fruit is the characteristic feature of flowering plants, which is a ripened or mature ovary and the seed is what the ovules develop into after fertilization. The fruit that develops without fertilization is known as parthenocarpic.

  • Types of Fruits
    • Simple Fruits: A simple fruit develops from the single simple or compound ovary of a flower. These can be dry fruits (pericarp dry) or succulent fruits (pericarp fleshy).
    • Aggregate (Etaerio) Fruits: An aggregate fruit is a group of fruitlets which develops from a flower having polycarpellary apocarpous (free) gynoecium. The aggregate fruit is also called etaerio.
    • Multiple (Composite) Fruits: A composite (multiple) fruit develops from an entire inflorescence. The multiple fruit is composed of a number of closely associated fruits (which may or may not get fused) along with its peduncle. Hence, these fruits are pseudocarps and are also called inflorescence fruits. Pomology is the branch of horticulture that deals with the study of fruits and their cultivation.
The Seed

Seed is a ripened ovule which contains an embryo or tiny plant with sufficient reserve food for the development of embyo. The ovules after fertilisation develops into seeds. A seed is made up of seed coats and an embryo. The embryo is made up of a radicle, an embryonal axis and one (wheat and maize) or two cotyledons (gram and pea).

  • Types of Seeds
    • Monocotyledonous seeds: The embryo consists of an embryo axis and has only one cotyledon. The monocotyledonous is also known as monocot seeds. Grains including rice, millet, wheat and other plants like onions, corn, ginger banana, palm tree, are examples of monocot seeds.
    • Dicotyledonous seeds:  The embryo consists of an embryo axis and has two cotyledons. The dicotyledons are also known as dicots or dicot seeds. Legumes including beans, lentils, pea, peanuts, and tomato are examples of dicot seeds.

Anatomy of Flowering Plants

Anatomy is the study of internal structure of plants. Study of plant anatomy includes histology study of organization and structure of tissues. Anatomy is the study of a flowering plant’s internal composition by cutting them in sections. It helps to understand the functioning of plants after careful analysis by anatomists.

Tissues and Tissue Systems

A tissue is a group of cells having a common origin and usually performing a common function. A plant is made up of different kinds of tissues. Tissues are classified into two main groups, namely, meristematic and permanent tissues based on whether the cells being formed are capable of dividing or not. Plants tissues are of two types:

  • Meristematic Tissues: The cells in meristematic tissues can divide themselves. The cell division happens in meristems. They are responsible for the growth of plants. As per the anatomy of flowering plants chapter, each plant has different kinds of meristems, which are broadly classified as:
    • Apical Meristem: This meristem happens to be at the tip of shoots & roots and produce primary tissue. It increases the plant length and consists of axillary bud, which helps with the formation of leaves.
    • Intercalary Meristem: It is the meristem present between the mature tissues. It produces primary tissues that are intercalary meristems. It is present in grasses and helps in regenerating the parts removed by herbivores.
    • Lateral Meristem: This meristem is present in the mature region of shoots and roots of various plants. It produces secondary tissues and appears after primary meristem and is solely responsible for secondary growth.

Meristematic Tissues

  • Permanent Tissues: The cells of the permanent tissues do not generally divide further. Permanent tissues having all cells similar in structure and function are called simple tissues. Permanent tissues having many different types of cells are called complex tissues.
    • Simple Tissues: A simple tissue is made of only one type of cells. The various simple tissues in plants are:
      • Parenchyma: The cells of the parenchyma are generally isodiametric. They may be spherical, oval, round, polygonal or elongated in shape. Their walls are thin and made up of cellulose. The parenchyma performs various functions like photosynthesis, storage, secretion.
      • Collenchyma: These are tightly packed living cells and are thick at the corners. They provide technical support in the growing plants
      • Sclerenchyma: Sclerenchyma consists of long, narrow cells with thick and lignified cell walls having a few or numerous pits. They are usually dead and without protoplasts. On the basis of variation in form, structure, origin and development, sclerenchyma may be either fibres or sclereids.
    • Complex Tissues: The complex tissues are made of more than one type of cells and these work together as a unit. The complex tissues in plants are:
      • Xylem: It is a conducting tissue for movement of minerals and water from roots to leaves and stem. It is mainly composed of vessels, tracheids, xylem parenchyma, and xylem fibres
      • Phloem: It helps with the transportation of food from leaves to various plant parts. It is composed of companion cells, sieve tube elements, phloem fibres, and phloem parenchyma.

Epidermal Tissue Systems

The epidermal tissue system forms the outer-most covering of the whole plant body and comprises epidermal cells, stomata and the epidermal appendages – the trichomes and hairs. It comprises of:

  • Epidermis: Outermost layer of the plant’s body.
  • Cuticle: A thick waxy layer covering epidermis to prevent water loss.
  • Epidermal Hair: Helps with absorbing minerals from soil and water. 
  • Stomata: Helps in regulating the process of gaseous exchange and transpiration. 
  • Trichomes: Prevents water loss during transpiration.

The ground Tissue Systems

  • All tissues except epidermis and vascular bundles constitute the ground tissue.
  • It consists of simple tissues such as parenchyma, collenchyma and sclerenchyma.
  • Parenchymatous cells are usually present in cortex, pericycle, pith and medullary rays, in the primary stems and roots.
  • In leaves, the ground tissue consists of thin-walled chloroplast containing cells and is called mesophyll.

The Vascular Tissue Systems

  • It consists of complex tissues of xylem and phloem.
  • Dicots have cambium present between xylem and phloem of vascular bundle.
  • Cambium forms secondary vascular tissues.
  • Dicots have an open vascular bundle.
  • Monocots have a closed type of vascular bundle, i.e. cambium is absent.
  • Roots have a radial arrangement of vascular bundles, i.e. xylem and phloem are present alternatively.
  • Stem and leaves have a conjoint arrangement of vascular bundles, i.e. xylem and phloem are present at the same radius.

Dicotyledonous Root

  • Epiblema is the outermost layer, which contains root hair.
  • Several layers of cortex present, that ends with innermost layer endodermis, which contains waxy material called suberin forming Casparian strips.
  • Next is pericycle, which gives rise to lateral roots and vascular cambium.
  • Two to six vascular bundles are present.
  • Radial and exarch vascular bundles.

Monocotyledonous Root

  • It has a wide cortex.
  • It has highly thickened endodermis with visibility of Casparian strips in young roots only.
  • There are more than 6 xylem and phloem bundles.
  • A well-developed pith is present.
  • No secondary growth is possible.

Dicotyledonous Stem

  • The outermost layer is the epidermis with cuticle
  • Trichomes and stomata may be present on the epidermis
  • The cortex consists of three layers; outermost hypodermis (collenchymatous), middle parenchymatous cortical layer and the endodermis containing starch grains
  • Below endodermis, pericycle and radially located medullary rays are present
  • Vascular bundles are arranged as a ring
  • Vascular bundles conjoint, open and with endarch protoxylem

Monocotyledonous Stem

  • Similar cells are there in ground tissues.
  • Closed vascular bundles are scattered throughout the ground tissue.
  • No secondary growth is possible.

Dicotyledonous Leaf

  • It is also known as a dorsiventral leaf.
  • Fewer stomata on the upper side of it is completely absent.
  • There are more stomata present on the abaxial epidermis.
  • The epidermis covers both the upper and lower surface.
  • Mesophyll cells are parenchymatous and perform photosynthesis.
  • The kidney-shaped guard on the stomata.

Monocotyledonous Leaf

  • It is also known as an isobilateral leaf.
  • Presence of stomata on both surfaces of the epidermis.
  • The mesophyll is not differentiated between palisade and spongy parenchyma cells.
  • Vascular bundles are of the same size.
  • Stomata guard is bell-shaped.

Secondary Growth

  • Secondary growth is due to dividing lateral meristems; vascular and cork cambium.
  • It is characterised by an increase in the thickness (girth).
  • In the dicot stem, a ring of cambium is formed from intrafascicular cambium present between xylem and phloem and the medullary cells present adjoining the two vascular bundles that become meristematic.
  • Cambium is very active during spring and forms earlywood or springwood, which has more xylary elements, light in colour and with low density.
  • The peripheral region of secondary xylem conducts water and lighter in colour and known as sapwood.
  • Cork cambium develops in the outer cortex region. It is also known as phellogen.
  • Phellogen divides on both sides, differentiating into outer cells are called phellem or cork and the inner cells are known as phelloderm or secondary cortex.
  • All the tissue exterior to vascular cambium are called bark including secondary phloem.
  • Secondary growth is absent in monocots but present in gymnosperms.

Structural Organization in Animals

All complex animals consist of only four basic types of tissues. These tissues are organised in specific proportion and pattern to form an organ like stomach, lung, heart and kidney. When two or more organs perform a common function by their physical and/or chemical interaction, they together form organ system, e.g., digestive system, respiratory system, etc. Cells, tissues, organs and organ systems split up the work in a way that exhibits division of labour and contribute to the survival of the body as a whole.

Animal Tissues

The structure of the cells vary according to their function. Tissues are an integrated group of cells which perform similar functions and possess similar cellular structure. These tissues provide a basic framework in multicellular animals. Therefore, the tissues are different and are broadly classified into four types: 

  • Epithelial Tissue: Epithelial tissue is made up of layers of tightly packed cells that line the surfaces of the body for protection, secretion, and absorption. Epithelial tissue is classified into two types – simple epithelium and compound epithelium. Moreover, epithelial tissue can be classified based on its shape as well – cuboidal, squamous, columnar. Examples of epithelial tissue include the skin, the lining of the mouth and nose, and the lining of the digestive system.
  • Connective tissue: Connective tissue is made up of many different types of cells that are all involved in structure and support of the body. Bone, blood, fat, and cartilage are all connective tissues. Connective tissue can be densely packed together, as bone cells are, or loosely packed, as adipose tissue (fat cells) are.
  • Muscular tissue: Muscle tissue is made up of cells contain contractile filaments that move past each other and change the size of the cell. There are three types of muscle tissue: smooth muscle which is found in the inner linings of organs; skeletal muscle, which is attached to bone and moves the body; and cardiac muscle which is found only in the heart.
  • Nervous tissue: Nervous tissue is made up of the nerve cells (neurons) that together form the nervous system, including the brain and spinal cord. Nervous tissues have the greatest control over the body’s responsiveness to changing conditions.

Organ and Organ Systems

A collection of tissues form an organ; a group of organs that work together to perform one or more functions is called an organ system. Every organ is composed of one or more type of tissues. A group of organs working together to perform a common function is called an organ system. Excretory system, reproductive system, endocrine system, circulatory system, respiratory system are examples of organ systems.

Structural Organization of Earthworm

  • Earthworms have a reddish brown color with a cylindrical body.
  • The body is also elongated and is pointed in the anterior region, while the posterior region is rounded.
  • The body is segmented and there are about 100 to 120 metameres or short segments.
  • There is a dark median mid-dorsal blood vessel that is seen on the dorsal surface of the body.
  • The ventral surface of the body has genital openings or pores.
  • Peristomium is the first body segment that also has the mouth. The last segment has the anus.
  • A single pair of male genital pores is present on the 18th segment. 
  • Except for the first segment, last segment, and clitellum, all other segments have S-shaped setae that are present embedded. These setae help in the locomotion.

Structural Organization of Earthworm

  • The body of the earthworm is covered externally by a thin noncellular cuticle. This is followed by an epidermal layer, two muscle layers, and inner coelomic epithelium.
  • The epidermis has columnar epithelial cells, which are present in a single layer. There are also some secretory gland cells present.
  • Earthworms show a closed blood vascular system. It means that blood flows in closed blood vessels. The circulatory system consists of blood, blood vessels, capillaries, and heart.
  • Blood is circulated in one direction due to the contractions.
  • The 4th, 5th and 6th segments have the blood glands, which produce the blood cells and haemoglobin.
  • There is no Respiratory system present in earthworms. The exchange happens through the moist body surface.
  • There are ganglia that are arranged in a segment-wise manner on the ventral paired nerve cord.
  • The excretory system consists of coiled tubules called nephridia. They are arranged on the segments of the body.
  • Earthworms have both the male and female reproductive organs in the same body. Hence they are called hermaphrodite or bisexual. They have two pairs of testes in the 10th and 11th segments. In between the 12th and 13th segments, there is a pair of ovaries.
  • Sac-like structures called spermathecae (four pairs) are found in the 6th and 9th segments.

Structural Organization of Cockroach

Structural Organization of Cockroach

  • Cockroaches are brown or black bodied animals that are included in class Insecta of Phylum Arthropoda.
  • They have long antenna, legs and flat extension of the upper body wall that conceals head.
  • They are pests because they destroy food and contaminate it with their smelly excreta and also transmit various types of bacterial diseases.
  • Their body is segmented into three distinct regions – head, thorax and abdomen. The complete body is covered by a hard chitinous exoskeleton.
  • The exoskeleton in each segment has sclerites (hardened plates) which are joined to each other by a thin and flexible articular membrane (Arthrodial membrane).
  • The triangular-shaped head lies anteriorly at right angles to the longitudinal axis formed by the fusion of six segments. The head has a pair of compound eyes.
  • A pair of thread-like antennae(having sensory receptors) emerge from membranous sockets present in front of the eyes.
  • Mouthparts consist of the labrum, a pair of mandibles, a pair of maxillae and a labium. A median flexible lobe serving as a tongue lies enclosed within the cavity by the mouthparts.
  • Thorax consists of the – prothorax, mesothorax and metathorax. Each of the thoracic segment has a pair of walking legs.
  • The sense organs are antennae, eyes, maxillary palps, labial palps, anal cerci, etc.
  • Male reproductive system consists of a pair of testes lying one on each lateral side in the 4th-6th abdominal segments.
  • From each testis arises a thin vas deferens, which opens into ejaculatory duct through seminal vesicle and the ejaculatory duct opens into male gonopore situated ventral to anus.
  • In the 6th-7th abdominal segments there is an accessory reproductive gland.
  • The sperms are stored in the seminal vesicles and are glued together to form spermatophores.
  • The female reproductive system consists of two large ovaries in the 2nd – 6th abdominal segments.
  • Each ovary is formed of a group of eight ovarian tubules or ovarioles, containing a chain of developing ova.
  • Oviducts of each ovary unite into a single median oviduct.
  • Sperms are transferred through spermatophores.
  • Their fertilized eggs are encased in dark reddish to blackish brown capsule called oothecae.

Structural Organization of Frog (Amphibia)

Structural Organization of Frog

  • Frogs are amphibians belonging to Phylum Chordata.
  • The common Indian frog goes by the scientific name, Rana tigrina.
  • Their lives begin in water when they are eggs. From the eggs, tadpoles emerge, which also live in water. When these tadpoles fully develop they begin to live on land.
  • A frog is a poikilotherm, which means that it is a cold-blooded animal. The body temperature is not constant and varies according to their surrounding environment.
  • The body of the frog is divisible into head and trunk.
  • Neck and tail are absent in a frog.
  • The skin of the frog has mucus, which makes the skin moist, smooth and slippery.
  • The skin of the frog has the ability to absorb water.
  • The head of a frog is triangular in shape with a blunt snout.
  • The eyes of a frog have a nictitating membrane that gives protection when the frog is in water.
  • On the sides of the eyes, a membranous tympanum (ear) is present that receives the sound signals.
  • A frog has two forelimbs and two hind limbs.
  • Sexual dimorphism is seen in frogs, with the male species having vocal sacs and copulatory pad. These are absent in female frogs.
  • Inside the body cavity of a frog, there are many organ systems present such as the circulatory system, digestive system, respiratory system, nervous system, excretory system, and reproductive system.
  • Digestive System is well developed and has the alimentary canal and digestive glands.
  • The alimentary canal of the frog is not long, but it is short.
  • Liver and gallbladder organs are also present along with the pancreas.
  • Food is digested in the stomach by the action of HCL and other gastric juices that are secreted.
  • Any undigested food waste goes into the rectum and is passed out through the cloaca.
  • The circulatory system of a frog is very well developed. In fact, just like humans, frogs also have a lymphatic system.
  • Blood is opaque and sticky and is red in color due to the presence of haemoglobin.
  • The skin of the frog has a role to play in the respiration process. It acts as the aquatic respiratory organ, as oxygen gets diffused through the skin when a frog is in water.
  • The nervous system is very well organized and consists of the central nervous system and the peripheral nervous system.
  • The brain is enclosed in a cranium and there are ten pairs of cranial nerves that emerge out of the brain. The brain is divided into three parts – forebrain, midbrain, and hindbrain.
  • The spinal cord is enclosed in the vertebral column.
  • Control and coordination are evolved to a higher extent in frogs.
  • Excretory System consists of a pair of kidneys, ureters, urinary bladder and cloaca.
  • Both male and female frogs have their own reproductive system where gametes for reproduction are produced.
  • Male frog has testes which produce sperms and eject it through the cloaca.
  • In a female frog, a pair of ovaries produce ovum and pass it to oviduct which opens into the cloaca.
  • The cloaca is a common pathway for excretion and reproduction.
  • A female frog can lay about 2500 to 3000 eggs at a time.
  • External fertilization is seen in frogs and occurs in water.


पौधों और जानवरों में संरचनात्मक संगठन Short Notes in Hindi

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