Chapter 7 Structural Organisation in Animals

(i) The common name of Periplaneta americana is the American cockroach.

(ii) Four pairs of spermathecae are present between sixth and the ninth segments. They help in receiving and storing the spermatozoa during copulation.

(iii) In a cockroach, the pair of ovaries is located between 12th and 13th abdominal segments.

(iv) In both sexes, the abdomen of a cockroach consists of ten segments.

(v) Malphigian tubules are excretory organs of cockroaches. They form a part of the alimentary canal.

(i) Nephridia are segmentally arranged excretory organs present in earthworms.

(ii) On the basis of their location, three types of nephridia are found in earthworms. They are:

(a) Septal nephridia: These are present on both sides of the inter-segmental septa behind the 15th segment and they open into the intestine.

(b) Integumentary nephridia: These lie attached to the body wall from the third segment to the last segment, which opens on the body surface.

(c) Pharyngeal nephridia: These are present as three paired tufts in fourth, fifth, and sixth segments.

 (a)

(b)

Components of blood include erythrocytes (RBCs), leucocytes (WBCs), and thrombocytes (platelets). These components form 45% of blood. They are suspended in the remaining fluid portion, called plasma.

Mammalian erythrocytes are biconcave, coloured cells devoid of a nucleus. They help in transporting respiratory gases.

Leucocytes or white blood cells are nucleated cells. They can be divided into two types, granulocytes (neutrophils, eosinophils, and basophils) and agranulocytes (lymphocytes and monocytes). They help fight against various disease-causing agents entering the body.

Thrombocytes are cell fragments produced from megarkaryocytes of the bone. They play a major role during blood coagulation.

Chondriocytes:

They are cells of cartilages, and are present in small cavities within the matrix secreted by them.

Axons:

They are long, slender projections of neurons that help in carrying nerve impulses away from the neuron body. Axons aggregate in bundles which make up the nerves.

Ciliated epithelium:

It consists of simple columnar or cuboidal epithelium with cilia on their free surfaces. It is present on the inner surface of the oviducts and bronchioles. Where it helps in the movement of eggs or mucus in specific directions.

Epithelial tissue lines the surface of a body and forms a protective covering. Epithelium cells are packed tightly together with little intercellular matrix.

Epithelial tissue in the body is of two types.

(a) Simple epithelium: It consists of a single layer of cells where cells are in direct contact with the basement membrane. It is further sub-divided into the following types:

(i) Simple squamous epithelium: It consists of a single layer of flat cells with irregular boundaries. It is found in the walls of the blood vessels and in the lining of alveoli.

(ii) Simple cuboidal epithelium: It consists of a single layer of cube-like cells. It is present in regions where secretion and absorption of substances takes place such as the proximal convoluted tubule region of the nephron.

(iii) Simple columnar epithelium: It consists of a single layer of tall, slender cells with their nuclei present at the base of the cells. They may bear micro-villi on the free surfaces. Columnar epithelium forms the lining of the stomach and intestines, and is involved in the function of secretion and absorption.

(iv) Ciliated epithelium: It consists of columnar or cuboidal cells with cilia on their free surfaces. They are present in bronchioles and oviducts from where they direct mucus and eggs in specific directions.

(v) Glandular epithelium:It consists of columnar or cuboidal cells involved in the secretion of substances. Glands are of two types, unicellular glands (goblet cells of the alimentary canal) and multicellular glands (salivary glands). They can be classified as exocrine (ductless glands) and endocrine glands (duct glands) by the method through which they release enzymes.

(b)

Compound epithelium: It consists of many layers of cells. It is involved mainly in the function of providing protection and has a limited role in secretion and absorption.

Dry surface of the skin or moist inner lining of the buccal cavity, pharynx, pancreatic ducts, and the inner lining of ducts of salivary glands are some of the examples of compound epithelium

(a)

(b)

(c)

(d)

(e)

(a) Areolar tissue, blood, and tendons are examples of connective tissues. Neuron is an example of neural tissue.

(b) RBCs, WBCs, and platelets are the three most important components of blood (fluid connective tissue) while Cartilage is skeletal connective tissue.

(c) Exocrine, endocrine, and salivary glands are examples of simple glandular epithelium. Ligament is a connective tissue.

(d) Maxilla, mandible, and labrum are mouthparts of a cockroach; white antennae are present in the head constituent of region of cockroaches.

(e) Prothorax, Mesothorax and metathorax are parts of thorax of cockroach and present in the legs of a cockroach.

Earthworm (Pheretima) have closed blood vascular systems, which consists of the heart, blood vessels, and capillaries. The heart pumps blood for circulating it in one direction. Blood is supplied by smaller blood cells to the gut, nerve cord and the body wall. Blood glands are present in the 4th, 5th, and 6th segments, which produce blood cells and haemoglobin dissolved in blood plasma. Blood cells in earthworms are phagocytic in nature.

(a) Ureters in frogs: A ureter acts as a urinogenital duct, which carries sperms along with urine in male frogs.

(b) Malphigian tubules: Malphigian tubules are excretory organs in cockroaches.

(c) Body wall in earthworms: In earthworms, the body wall consists of muscle layers. It helps in movement and burrowing.