7.4 Exercise Problems

Q1. Draw a neat diagram of the digestive system of frog.

Answer: 

Q14. Mention the function of the Ureters in frog

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

Exemplar Section

VERY SHORT ANSWER TYPE QUESTIONS

Q1. Identify the sex of a frog in which sound producing vocal sacs are present

Answer: Male frog

Q2. Name the process by which a tadpole develops into an adult frog.

Answer: By metamorphosis a tadpole develops into an adult frog.

Q3. A muscle fibre tapers at both ends and does not show striations. Name the muscle fibre. 

Answer: Smooth muscle fibre

Q4. Name the different cell junctions found in tissues.

Answer: a. Tight Junctions
b. Adhering Junctions
c. Gap Junctions

Q5. Give two identifying features of an adult male frog.

Answer: a. Vocal Sacs
b. Thumb pads/copulatory pads in thumb

Q6. The digestive system of frog is made of the following parts. Arrange them in an order beginning from mouth.
Mouth, oesophagus, buccal cavity, stomach, intestine, cloaca, rectum, cloacal aperture

Answer: Mouth, buccal cavity, oesophagus, stomach, intestine, rectum, cloaca and cloacal aperture.

Q7. What is the difference between cutaneous and pulmonary respiration?

Answer: Frogs respire on land and in the water by two different methods. In water, skin acts as aquatic respiratory organ (cutaneous respiration). Dissolved oxygen in the water is exchanged through the skin by diffusion. On land, the buccal cavity, skin and lungs act as the respiratory organs. The respiration by lungs is called pulmonary respiration.

Q8. Special venous connection between liver and intestine and between kidney and intestine is found in frog, what are they called?

Answer: Hepatic portal system and renal portal system respectively.

SHORT ANSWER TYPE QUESTIONS

Q1. Frogs are beneficial for mankind, justify the statement.

Answer: Frogs are beneficial for mankind as they can eat some crop pests and protect crop. Frogs maintain ecological balance as they are an important component of food chain and food web in the ecosystem. They are edible in some countries.

Q2. The body of sponges does not possess tissue level of organisation though it is made of thousands of cells. Comment.

Answer: Though all members of Animalia are multicellular, all of them do not exhibit the same pattern of organisation of cells. For example, in sponges, the cells are arranged as loose cell aggregates, i.e. they exhibit cellular level of organisation. Some division of labour (activities) occur among the cells. Hence, the body of sponges does not possess tissue level of organisation.

Q3. Structural organisation in animals attains different levels as cell – organ – organ system. What is missing in this chain? Mention the significance of such an organisation.

Answer: Tissue is missing in this chain. In multicellular animals, a group of similar cells along with intercellular substances perform a specific function. Such an organisation is called tissue. 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.

Q4. Stratified epithelial cells have limited role in secretion. Justify their role in our skin.

Answer: Stratified epithelium is made of more than one layer of cells and thus has a limited role in secretion and absorption. Their main function is to provide protection against chemical and mechanical stresses. They cover the dry surface of the skin.

Q5. How does a gap junction facilitate intercellular communication?

Answer: Gap junctions facilitate the cells to communicate with each other by connecting the cytoplasm of adjoining cells, for rapid transfer of ions, small molecules and sometimes big molecules.

Q6. Why are blood, bone and cartilage called connective tissue?

Answer: Blood, bone and cartilage are called connective tissue because of their special function of linking and supporting other tissues/organs of the body.

Q7. Why are neurons called excitable cells? Mention special features of the membrane of the neuron?

Answer: Neurons are called excitable cells because when a neuron is suitably stimulated, an electrical disturbance is generated which swiftly travels along its plasma membrane. Arrival of the disturbance at the neuron’s endings, or output zone, triggers events that may cause stimulation or inhibition of adjacent neurons and other cells.

Q8. Common name of some animals are given in Column A, write their scientific name in Column B.
\(
\begin{array}{lll}
& \text { Column A } & & \text { Column B } \\
\text { a. } & \text { Tiger } & & ? \\
\text { b. } & \text { Peacock } & & ? \\
\text { c. } & \text { Housefly } & &  ?
\end{array}
\)

Answer: 

\(
\begin{array}{lll}
\text { a. } & \text { Tiger } & \text { Panthera tigris } \\
\hline \text { b. } & \text { Peacock } & \text { Pavo cristatus } \\
\hline \text { c. } & \text { Housefly } & \text { Musca domestica } \\
\hline
\end{array}
\)

Q9. Frog is a poikilotherm, exhibits camouflage and undergoes aestivation and hibernation, how are all these beneficial to it?

Answer: Frog have the ability to change colour which hides them from their enemies (camouflage). This protective coloration is called mimicry. Frogs are not seen during peak summer and winter. During this period they take shelter in deep burrows to protect them from extreme heat and cold. This is called as summer sleep (aestivation) and winter sleep (hibernation).

Q10. Write the functions in brief in column B, appropriate to the structures given in column A.

Answer:

\(
\begin{array}{|l|l|l|l|}
\hline \text { a. } & \text { Nictitating membrane } & \text { i. } & \text { Protects them while in water. } \\
\hline \text { b. } & \text { Tympanum } & \text { ii. } & \text { Receives sound signals } \\
\hline \text { c. } & \text { Copulatory pad } & \text { iii. } & \text { Hold the female during copulation } \\
\hline
\end{array}
\)

Q11. Write the appropriate type of tissues in column B according to the functions mentioned in column A.

Answer: 

\(
\begin{array}{|l|l|l|l|}
\hline \text { a. } & \text { Secretion and absorption } & \text { i. } & \text { Cuboidal epithelium } \\
\hline \text { b. } & \text { Protective covering } & \text { ii. } & \text { Compound epithelium } \\
\hline \text { c. } & \text { Linking and supporting framework } & \text { iii. } & \text { Connective tissue } \\
\hline
\end{array}
\)

Q12. Using appropriate examples, differentiate between false and true body segmentation.

Answer: (i) Metamerism: In some animals, the body is externally and internally divided into segments with a serial repetition of at least some organs. For example, in earthworm, the body shows this pattern called metameric segmentation and the phenomenon is known as metamerism or true segmentation.
Metamerism is found in 3 animal phylums—Annelida, Arthropoda and chordata.
(ii) Pseudometamerism or false segmentation: In tapeworm, the body is externally divisible into parts called proglottis. They develop from the neck but are not embryonic in origin, this segmentation is called pseudometamerism.

Q13. What is special about tissue present in the heart? 

Answer: Cardiac muscle tissue is a contractile tissue present only in the heart. Cell junctions fuse the plasma membranes of cardiac muscle cells and make them stick together. Communication junctions (intercalated discs) at some fusion points allow the cells to contract as a unit, i.e. when one cell receives a signal to contract, its neighbours are also stimulated to contract.

LONG ANSWER TYPE QUESTIONS

Q1. Classify and describe epithelial tissue on the basis of structural modifications of cells.

Answer: There are two types of epithelial tissues namely simple epithelium and compound epithelium. Simple epithelium is composed of a single layer of cells and functions as a lining for body cavities, ducts, and tubes. The compound epithelium consists of two or more cell layers and has protective function as it does in our skin. On the basis of structural modification of the cells, simple epithelium is further divided into three types. These are

• (i) Squamous,
• (ii) Cuboidal and
• (iii) Columnar
• The squamous epithelium is made of a single thin layer of flattened cells with irregular boundaries. They are found in the walls of blood vessels and air sacs of lungs and are involved in functions like forming a diffusion boundary. The cuboidal epithelium is composed of a single layer of cube-like cells. This is commonly found in ducts of glands and tubular parts of nephrons in kidneys and its main functions are secretion and absorption. The epithelium of proximal convoluted tubule (PCT) of nephron in the kidney has microvilli. The columnar epithelium is composed of a single layer of tall and slender cells. Their nuclei are located at the base. Free surface may have microvilli. They are found in the lining of stomach and intestine and help in secretion and absorption.
• Compound epithelium is made of more than one layer (multi-layered) of cells and thus has a limited role in secretion and absorption. Their main function is to provide protection against chemical and mechanical stresses. They cover the dry surface of the skin, the moist surface of buccal cavity, pharynx, inner lining of ducts of salivary glands and of pancreatic ducts.

Q2. Write down the common features of the connective tissue. On the basis of structure and function, differentiate between bones and cartilages.

Answer: Connective tissues are most abundant and widely distributed in the body of complex animals. They are named connective tissues because of their special function of linking and supporting other tissues/organs of the body. They range from soft connective tissues to specialised types, which include cartilage, bone, adipose, and blood. In all connective tissues except blood, the cells secrete fibres of structural proteins called collagen or elastin. The fibres provide strength, elasticity and flexibility to the tissue. These cells also
secrete modified polysaccharides, which accumulate between cells and fibres and act as matrix (ground substance).

• The intercellular material of cartilage is solid and pliable and resists compression. Cells of this tissue (chondrocytes) are enclosed in small cavities within the matrix secreted by them. Most of the cartilages in vertebrate embryos are replaced by bones in adults. Cartilage is present in the tip of nose, outer ear joints, between adjacent bones of the vertebral column, limbs and hands in adults.
• Bones have a hard and non-pliable ground substance rich in calcium salts and collagen fibres which give bone its strength. It is the main tissue that provides structural frame to the body. Bones support and protect softer tissues and organs. The bone cells (osteocytes) are present in the spaces called lacunae. Limb bones, such as the long bones of the legs, serve weight-bearing functions. They also interact with skeletal muscles attached to them to bring about movements. The bone marrow in some bones is the site of production of blood cells.

Q3. Draw a neat and well labelled diagram of male reproductive system of a frog.

Answer: