NCERT Solutions For Class 11 Biology Structural Organisation in Animals

Epithelial tissue is a tissue made of one or more layers of compactly arranged cells that covers external surface and internal free surface of body organs and which is underlined by a basement membrane. The various types of epithelial tissue along with the diagram are given below:
(i) Simple epithelium : It is composed of single layer of cells which rest on basement membrane. Simple epithelium generally occurs over secretory and absorptive surfaces and forms lining of body cavities, ducts and tubes. Simple epithelium is of several types.

 

(a) Squamous epithelium: It consists of single layer of flat cells, tightly linked together and have centrally located oval or spherical nucleus. It is also called pavement epithelium. It is found in walls of blood vessels, air sacs of lungs, and lining of eye lens.

(b) Cuboidal epithelium: Cells of cuboidal epithelium are as tall as wide, with centrally placed nucleus. Its main functions are secretion and absorption. It lines sweat gland, thyroid follicles, salivary glands. Brush bordered cuboidal epithelium, i.e., cells having microvilli on their free surface lines proximal part of uriniferous tubule, pancreatic duct, testis and ovary.

(c) Columnar epithelium: Cells are with basally located nucleus. It helps in secretion and absorption. It occurs in lining of intestine, stomach, gall bladder.

(d) Ciliated epithelium: Free surface of columnar and cuboidal cells are covered with cilia. Cilia help in moving fluids, particles, mucus, etc. in a specific direction. It occurs in the inner surface of Fallopian tubules, nasal passage, bronchioles.

 

(e) Pseudostratified epithelium: It consists of single layer of cells but some cells are shorter than others. Due to difference in size of cells, the epithelium appears 2-3 layered. Pseudostratified columnar epithelium occurs in urethra and parotid salivary gland. Pseudostratified columnar ciliated epithelium (only larger cells ciliated) occurs in lining layer of nasal’ chambers, trachea and large bronchi. It helps in moving mucus and foreign particles.

(ii) Compoundepithelium/stratifiedepithelium: It is multilayered epithelium where cells of only the lowermost or basal layer are in contact with basement membrane. It provides protection against mechanical and chemical stresses and has limited role in secretion and absorption. It covers dry surface of skin, moist surface of buccal cavity, pharynx, etc. Different types of compound epithelium are:

(a) Stratified squamous epithelium: The cells of outer layer are flattened and squamous while the inner layers are cuboidal cells. It is of two types: Non- keratinised lining oesophagus, pharynx, buccal cavity, cornea, vagina and anal canal and keratinised (comified): forming epidermis of skin, hair, horn and nail.

(b) Stratified cuboidal epithelium: The outer layer of cuboidal cells and basal layer of columnar cells. It lines ducts of sweat glands, large salivary and pancreatic ducts.

(c) Stratified columnar epithelium: Both upper and basal layers are made of columnar cells, e.g., epiglottis covering, part of urethra.

 

(d) Stratified ciliated columnar epithelium: Outer layer consists of ciliated columnar cells and basal layer of columnar cells, e.g., larynx.

(iii) Transitional Epithelium: This is stratified epithelium which contains cuboidal or columnar shaped cells, which are thin and stretchable. No basement membrane is present as it would impede stretchability. It lines the inner surface of renal calyces, urinary bladder, ureter. Because of its t distribution, it is also called urothelium.

(iv) Glandular epithelium: It consists of specialised epithelial cells which synthesise intracellular macromolecules (protein in pancreas, lipids in adrenal glands, glycoprotein in salivary glands and all the three in mammary glands) and pour out the same in the form of a useful fluid secretion which is different from blood or any other extracellular fluid. Glands can be unicellular or multicellular on the basis of number of cells.

(a) Unicellular glands: Single-celled, e.g., goblet (mucous) cells of respiratory tract and alimentary canal.

(b) Multicellular glands: Consist of cluster of cells, e.g., Salivary glands.

On the basis of presence or absence of duct glands can be:

(a) Exocrine glands : These glands pour their secretion through a duct. They secrete milk, saliva, mucus, earwax. e.g., goblet cells, salivary glands, tear glands, gastric glands, intestinal glands.

(b) Endocrine glands: They are ductless glands, which pour their secretions into blood or lymph for reaching the target region. Their secretion is called hormone e.g., pituitary gland, thyroid gland, parathyroid glands, adrenal glands.

(c) Heterocrine glands: Both exocrine and endocrine, e.g., pancreas.

On basis of mode of secretion glands can be:

(a) Merocrine: Secretion is discharged

through diffusion, e g., goblet cells, sweat glands.

(b) Apocrine glands: Glandular secretion accumulates in the terminal part of the cell which is pinched off, e.g., mammary glands.

(c) Holocrine glands : The cell filled with secretory product disintegrates during discharge of the product, e.g., sebaceous gland.

(v) Modified epithelium : It is of following types:

(a) Germinal epithelium (generally cuboidal, produces gametes), (b) Glandular epithelium (columnar or cuboidal secretes chemicals and mucus), (c) Sensory epithelium or neuroepithelium. Epithelial cells having sensory hair on free surface and connected with nerve fibres on the other surface (generally columnar, receives and conveys stimuli), e.g, nasal epithelium, taste buds, retina, sensory spots of internal ear. (d) Pigmented epithelium – The cells possess melanin granules, e.g, retinal layer in contact with choroid of eye.

 

 

Solution: (i) Cockroach.
(ii) Four pairs.
(iii) In cockroaches, two large ovaries lie laterally in the 2nd – 6th abdominal segments’.
(iv) Abdomen of a cockroach consists of 10 segments.
(v) Malpighian tubules are present at the junction of midgut and hindgut in cockroach.

 

 (a) Chondrocytes – Chondrocytes are the only cells found in cartilage. They are present in spaces called lacunae and they produce and maintain the matrix of cartilage. Bending ability of cartilage is due to chondrocytes. Cartilage is present at tip of the nose, pinna of ear, epiglottis etc.
(b) Axon – Axon is one of the processes of the neuron, which is the structural and functional unit of the nervous system. The part of cyton – n’here axon arises is axon hillock and the axon ends in a group of branches called terminal arborizations. It conducts impulses away from the cyton. Neurons (nerve cells)
are present in the brain and spinal cord.
(c) Ciliated epithelium – If the columnar or cuboidal cells bear cilia on their free surface they are called ciliated epithelium. Their function is to move particles or mucus in a specific direction over the epithelium. They are mainly present in the inner surface of hollow organs like bronchioles and Fallopian tubes.

 

 (i) Nephridia are excretory organs of earthworm, which perform the function of excretion and osmoregulation. Nephridia regulate the volume and composition of the body fluids. A nephridium is a coiled tubular and microscopic structure which starts out as a funnel that collects excess fluid from coelomic chamber. The funnel connects with a tubular wastes through a pore to the surface in the body wall or into the digestive tube.

 

(ii) In earthworm, nephridia are present in all segments except the first two. There are three types of nephridia on the basis of their location:

(a) Septal nephridia, present on both the sides of intersegmental septa from segment 15 to the last that open into intestine.

(b) Integumentary nephridia, attached to lining of the body wall of segment 3 to the last that open on the body surface and

(c) Pharyngeal nephridia, present as three paired tufts in the 4th, 5th and 6th segments.

Blood is a fluid connective tissue. It is composed of plasma (fluid) and blood cells (corpuscles). Cellular components of blood (blood corpuscles) constitute about 45% of blood volume.
Three types of blood cells are:
(i) Erythrocytes or red blood cells: They are most abundant blood cells. Normal RBC count is 5-5.5 million/mm3 in males and 4.5-5 million/mm3 in females) RBCs help in transport of gases and maintain blood pH.
(ii) Leucocytes or white blood cells: The normal WBC count is 5000-6000/mm3 of blood. They are involved in immune response of body and act as soldiers and scavangers.
(iii) Thrombocytes or blood platelets: There are about 2,50,000 platelets/mm3 of blood. They are involved in blood clotting.

 

(a) Differences between prostomium and peristomium are

(b) Differences between septal and pharyngeal nephridia are:

(a) Neuron: Areolar tissue, blood and tendon are connective tissues while neuron is a part a nervous tissue.
(b) Cartilage: RBC, WBC and platelets are parts of vascular connective tissue while cartilage is skeletal connective tissue.
(c) Ligament: Ligament is a connective tissue.
(d) Antennae: Maxilla, mandible and labrum are mouth parts of cockroach while antennae are sense organs.
(e) Protonema: Protonema is a filamentous juvenile stage in life cycle of Bryophytes, while mesothorax, metathorax and coxa are appendages of cockroach.

 

 (a) – (iii), (b) – (iv), (c) – (v), (d) – (ii), (e) – (i), (f) – (vii), (g) – (vi)

 

Earthworm possesses a closed type of blood vascular system, as the blood flows through closed blood vessels. Blood is red in colour due to respiratory pigment haemoglobin. Prominent blood vessels in earthworm includes dorsal, ventral, sub- neural, lateral oesophageal and supra- oesophageal blood vessels. There are four pairs of tubular hearts, provided with valves. The anterior two pairs of hearts, known as lateral hearts lie in the 7th and 9th segments and connect the dorsal blood vessel with the ventral blood vessel. They receive blood from the dorsal blood vessel and convey it to the ventral blood vessel. The posterior two pairs of hearts are called latero-oesophageal hearts and are situated in the 12th and 13th segments. The latero-oesophageal hearts apart from connecting the dorsal and ventral blood vessels are also joined with the supra oesophageal blood vessel. Latero-oesophageal hearts carry blood from the dorsal vessel and the supra oesophageal vessel to the ventral blood vessel.Contractions keep blood circulating in one direction. Blood glands are present in the 4th, 5th and 6lh segments which produce blood cells and haemoglobin which is dissolved in blood plasma. Blood cells are phagocytic in nature.

 

(a) Differences between simple and compound epithelium are as follows:

(b) Differences between cardiac and striated muscles are as follows:

(c) Differences between dense regular and dense irregular connective tissues are as follows:

(d) Differences between adipose tissue and blood tissue are as follows:

(e) Differences between simple gland and compound gland are as follows:

 

(a) Ureters in frog: Ureter is a transparent duct which arise from outer portion of kidney. In the “male frogs, ureter acts as urinogenital duct which runs backwards from kidneys and opens into the cloaca. It carries both urine and spermatozoa from kidney to the cloaca. In female, ureter conducts only urine from kidneys to the cloaca.
(b) Malpighian tubules: Malpighian tubules are excretory organs present in cockroach. These are present at junction of mid gut and hindgut. These are fine, long, unbranched, yellowish and blind tubules and are 100-150 in number. They help in the removal of excretory products from haemolymph.
(c) Body wall in earthworm: It consists of cuticle, epidermis, muscular layer and parietal peritoneum.
(i) It maintains the characteristic shape of’ the body.
(ii) It protects the internal organs.
(iii) The cuticle prevents excessive evaporation.
(iv) It serves as an ideal respiratory organ.

(v) The receptor cells play a vital sensory function.
(vi) The albumen helps in the formation of cocoon. It also serves as a food for the developing earthworm inside the cocoon.
(vii) Setae and muscles are responsible for locomotion.
(viii) Excretory matter is passed out through nephridiopores.