Exercises
Draw a neat diagram of digestive system of frog.
Answer
(A diagram is required. Key labelled parts are described below.)
The digestive system of a frog consists of the following parts in order:
Alimentary canal: Mouth
⇒ Buccal cavity (tongue attached in front, teeth present)
⇒ Pharynx
⇒ Oesophagus (short)
⇒ Stomach (J-shaped; gastric glands secrete pepsin and HCl)
⇒ Small intestine (duodenum + ileum; receives bile from liver and juice from pancreas)
⇒ Large intestine
⇒ Cloaca
⇒ Cloacal aperture.
Digestive glands: Liver (bilobed; produces bile stored in gall bladder) and Pancreas (between stomach and duodenum; produces digestive enzymes). These open into the duodenum.
Mention the function of the Ureters in frog.
Answer
In a male frog, the ureters serve a dual function – they act as urinogenital ducts, carrying both urine (from the kidneys) and sperms (from the testes) to the cloaca. In a female frog, the ureters carry only urine from the kidneys to the cloaca. The cloaca is a common chamber that receives products from the digestive, excretory, and reproductive systems, opening to the outside through the cloacal aperture.
Important Extra Questions
What are the four types of animal tissues? Give brief functions of each.
Answer
The four basic types of animal tissues are:
(i) Epithelial tissue: Covers body surfaces, lines body cavities and organs. Functions: protection, secretion, absorption, excretion, and sensation. Types include squamous, cuboidal, columnar, ciliated, and glandular epithelium.
(ii) Connective tissue: Binds and supports other tissues. Includes loose connective tissue (areolar), dense connective tissue (tendons, ligaments), specialised connective tissue (cartilage, bone, blood). Functions: structural support, transport (blood), storage (fat).
(iii) Muscular tissue: Responsible for movement. Types: skeletal (voluntary, striated), smooth (involuntary, non-striated, in visceral organs), and cardiac (involuntary, striated, only in heart).
(iv) Neural (nervous) tissue: Made of neurons (nerve cells) and glial cells (support cells). Functions: rapid communication; conducts nerve impulses; coordinates body activities; processes information.
Describe the morphology and anatomy of an earthworm briefly.
Answer
Morphology: An earthworm (Pheretima posthuma) has a long, cylindrical, bilaterally symmetrical body, divided into 100–120 segments (metameres). The first segment is called the peristomium (bears the mouth); the last is called the pygidium (bears the anus). Segments 14–16 are covered by a thick band called the clitellum. Each segment has a set of S-shaped setae for locomotion. The dorsal surface is darker.
Anatomy: The body wall consists of cuticle, epidermis, circular muscles, and longitudinal muscles. The coelom is true coelom, lined by coelomic epithelium. The digestive system runs the full length. The vascular system is closed with dorsal and ventral blood vessels connected by lateral vessels; haemoglobin is dissolved in the blood. Excretion is by nephridia. The nervous system consists of a ventral nerve cord with a pair of ganglia per segment.
What is the role of the nephridia in earthworms?
Answer
Nephridia are the excretory organs of earthworms. They are tubular structures that collect metabolic wastes (nitrogenous compounds) and excess water from the coelomic fluid and blood, and eliminate them to the outside through the body surface or into the gut. There are three types: septal nephridia (on septa), integumentary nephridia (in body wall), and pharyngeal nephridia (in segments 4–6). They maintain osmotic and ionic balance of the body.
How does a cockroach breathe? Describe the tracheal system.
Answer
A cockroach breathes through a system of tracheae (air tubes), not through lungs or gills. The tracheal system consists of a network of chitinous air tubes that open to the outside through 10 pairs of spiracles (lateral openings on the thorax and abdomen). Air enters through spiracles
⇒ into tracheae
⇒ into smaller tracheoles
⇒ directly to tissues. There is no blood pigment; oxygen is delivered directly to cells. The tracheoles are in direct contact with cells for efficient gas exchange. Muscular contractions of the abdomen help pump air in and out.
Name the parts of the frog's heart and describe the flow of blood through it.
Answer
The frog's heart is three-chambered: two atria (right and left) and one ventricle. There is also a sinus venosus (receives deoxygenated blood from the body) and a conus arteriosus (leads blood out from the ventricle). Deoxygenated blood from the body enters the right atrium via the sinus venosus. Oxygenated blood from the lungs (pulmonary veins) enters the left atrium. Both atria open into the single ventricle. The ventricle pumps blood into the conus arteriosus, which divides into different arches supplying oxygenated blood to various organs and the skin. Despite a single ventricle, mixing of blood is minimal due to the spiral valve in the conus.