Frog

Topic: Respiration in Amphibians; Subtopic: Modes of Respiration in Frogs

Keyword Definitions:

• Cutaneous respiration: Exchange of gases through the skin, common in amphibians.

• Buccal respiration: Breathing by movements of the mouth cavity to draw air in and out.

• Pulmonary respiration: Respiration through lungs involving inhalation and exhalation of air.

• Amphibians: Vertebrates that can live both in water and on land, such as frogs.

• Gaseous exchange: Movement of oxygen and carbon dioxide between organism and environment.

Lead Question – 2025

Frogs respire in water by skin and buccal cavity and on land by skin, buccal cavity and lungs. Choose the correct answer from the following:

(1) The statement is true for water but false for land
(2) The statement is true for both the environment
(3) The statement is false for water but true for land
(4) The statement is false for both the environment

Explanation: The correct answer is (2). Frogs show cutaneous and buccal respiration in water because lungs collapse underwater. On land, they perform cutaneous, buccal, and pulmonary respiration. Thus, both parts of the statement are true, demonstrating amphibian adaptation for dual respiration modes in aquatic and terrestrial environments.

1. Which of the following organs is used by frogs during hibernation for respiration?

(1) Lungs
(2) Gills
(3) Skin
(4) Buccal cavity

Explanation: The correct answer is (3). During hibernation, frogs remain buried in mud where only the skin performs gas exchange. The moist skin enables diffusion of oxygen and carbon dioxide directly with surrounding water or damp soil, allowing survival without active lung function.

2. Which type of respiration is absent in adult frogs?

(1) Buccal
(2) Pulmonary
(3) Branchial
(4) Cutaneous

Explanation: The correct answer is (3). Branchial respiration occurs only in tadpoles through gills. Adult frogs lose gills during metamorphosis and shift to skin, buccal cavity, and lungs for respiration depending on their environment.

3. When a frog is completely submerged in water, which of the following occurs?

(1) Lungs remain active
(2) Skin performs respiration
(3) Buccal cavity becomes dry
(4) Gills reappear temporarily

Explanation: The correct answer is (2). Frogs submerged underwater rely entirely on cutaneous respiration. The moist skin acts as a respiratory surface for gas diffusion since lungs are ineffective under water pressure.

4. Assertion-Reason Type
Assertion (A): Frogs can survive long periods underwater.
Reason (R): Their skin is thin, moist, and richly supplied with blood vessels for gas exchange.

(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is not the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true

Explanation: The correct answer is (1). Frogs survive underwater by cutaneous respiration. Their skin’s thin, moist surface with capillaries enables oxygen absorption and CO₂ release, perfectly explaining their underwater survival ability.

5. Match the following:
A. Cutaneous respiration
B. Buccal respiration
C. Pulmonary respiration
D. Branchial respiration

I. Skin
II. Mouth cavity
III. Lungs
IV. Gills

(1) A-I, B-II, C-III, D-IV
(2) A-II, B-I, C-IV, D-III
(3) A-I, B-IV, C-II, D-III
(4) A-IV, B-I, C-II, D-III

Explanation: The correct answer is (1). Frogs perform cutaneous respiration through skin, buccal respiration through mouth cavity, pulmonary respiration through lungs, and branchial respiration through gills (in tadpoles). These distinct modes help amphibians adapt to multiple habitats.

6. Which of the following is TRUE for respiration in tadpoles?

(1) Pulmonary respiration only
(2) Buccal respiration only
(3) Cutaneous respiration only
(4) Branchial respiration only

Explanation: The correct answer is (4). Tadpoles respire through gills, exhibiting branchial respiration similar to fish. As metamorphosis proceeds, lungs develop and gills degenerate, preparing the adult frog for life on land.

7. Fill in the blanks:
During summer estivation, frogs respire mainly through _______.

(1) Lungs
(2) Skin
(3) Mouth cavity
(4) Gills

Explanation: The correct answer is (2). During estivation and hibernation, frogs remain inactive and rely on cutaneous respiration through their moist skin, which maintains sufficient oxygen exchange for survival in dormancy.

8. Choose the correct statements:
Statement I: Frogs respire only through lungs on land.
Statement II: Frogs also use buccal cavity and skin on land.

(1) Both statements are correct
(2) Only Statement I is correct
(3) Only Statement II is correct
(4) Both statements are incorrect

Explanation: The correct answer is (3). On land, frogs use lungs as the major organ, but buccal cavity and skin also assist in respiration, particularly when metabolic activity is low or during rest.

9. In which of the following conditions would a frog depend entirely on skin for respiration?

(1) During active jumping
(2) While submerged in water
(3) While feeding
(4) During sound production

Explanation: The correct answer is (2). When underwater, lungs are inactive and cutaneous respiration occurs. The moist skin enables gas exchange directly with water, ensuring oxygen uptake and carbon dioxide removal.

10. The structure that assists in both sound production and respiration in frogs is:

(1) Buccal cavity
(2) Glottis
(3) Nostrils
(4) Eustachian tube

Explanation: The correct answer is (2). The glottis connects the buccal cavity and lungs, controlling airflow for respiration and helping produce sound. Air passing through vocal cords creates croaking, an adaptation linked to respiratory function.

Topic: Reproductive System of Frog; Subtopic: Copulatory Pad in Male Frog

Keyword Definitions:

• Copulatory Pad: Thickened, glandular pad found on male frog’s forelimb digits that helps grip the female during amplexus.

• Amplexus: The mating embrace of frogs where the male holds the female to fertilize eggs externally.

• Forelimb: The front limb of a frog used for support, movement, and grasping during reproduction.

Lead Question - 2025

Which of the following statement is correct about location of the male frog copulatory pad?

(1) First and second digit of fore limb

(2) First digit of hind limb

(3) Second digit of fore limb

(4) First digit of the fore limb

Explanation:

In male frogs, the copulatory pad is present on the first digit of the forelimb. It becomes thick and dark during the breeding season, assisting in firm grip during amplexus. This structure is a secondary sexual character, influenced by androgen hormones, helping the male hold the female securely while fertilizing eggs externally. Hence, option (4) is correct.

Guessed Questions:

1. The copulatory pad in male frogs develops under the influence of which hormone?

(1) Estrogen

(2) Androgen

(3) Oxytocin

(4) Progesterone

Explanation:

Androgens, secreted by testes, are responsible for development of male secondary sexual characters, including the copulatory pad. These hormones enhance glandular activity, causing thickening and pigmentation. During breeding season, these pads help male frogs grip females during amplexus for successful external fertilization. Thus, the correct answer is (2) Androgen.

2. Which structure helps in external fertilization in frogs?

(1) Vocal sac

(2) Copulatory pad

(3) Nictitating membrane

(4) Tympanum

Explanation:

External fertilization in frogs occurs in water, and the copulatory pad enables the male to firmly grasp the female during amplexus, ensuring proper alignment for gamete release. It plays a vital role in reproductive success. Hence, the correct answer is (2) Copulatory pad.

3. The copulatory pad in male frog is absent during:

(1) Breeding season

(2) Non-breeding season

(3) Monsoon season

(4) Rainy season

Explanation:

Copulatory pads are seasonal structures that regress during non-breeding periods due to reduced androgen levels. They reappear in the breeding season under hormonal influence, aiding in reproduction. Therefore, they are absent during the non-breeding season. Correct answer: (2) Non-breeding season.

4. The number of copulatory pads in a male frog is:

(1) One

(2) Two

(3) Three

(4) Four

Explanation:

Male frogs possess a pair of copulatory pads — one on each forelimb, particularly on the first digit. These pads provide grip during amplexus, ensuring reproductive efficiency. Their seasonal development signifies sexual maturity. Thus, the correct answer is (2) Two.

5. The copulatory pad in frog helps in:

(1) Sound production

(2) Amplexus

(3) Respiration

(4) Swimming

Explanation:

The copulatory pad helps male frogs hold onto females during amplexus for successful external fertilization. It prevents slipping and ensures proper egg-sperm contact. Its structure supports effective mating. Thus, the correct answer is (2) Amplexus.

6. During breeding season, the male frog’s copulatory pad becomes:

(1) Rough and dark

(2) Smooth and white

(3) Transparent

(4) Soft and light-colored

Explanation:

The copulatory pad thickens, darkens, and becomes glandular during breeding season due to hormonal stimulation. These changes improve grip during mating. It is an adaptive structure for reproductive success. Hence, the correct answer is (1) Rough and dark.

Assertion-Reason Question

7. Assertion (A): Male frog possesses copulatory pads.

Reason (R): These pads help in amplexus during reproduction.

(1) Both A and R are true, and R is the correct explanation of A

(2) Both A and R are true, but R is not the correct explanation of A

(3) A is true but R is false

(4) A is false but R is true

Explanation:

Both assertion and reason are true. The male frog has copulatory pads that provide grip during amplexus, ensuring egg and sperm release are synchronized. The reason correctly explains the assertion. Hence, option (1) is correct.

Matching Type Question

8. Match the following:

List I (Structure) — List II (Function)

A. Copulatory pad — 1. Grasping female

B. Vocal sac — 2. Sound production

C. Nictitating membrane — 3. Eye protection

D. Tympanum — 4. Hearing

(1) A-1, B-2, C-3, D-4

(2) A-2, B-1, C-3, D-4

(3) A-3, B-2, C-4, D-1

(4) A-4, B-3, C-2, D-1

Explanation:

The copulatory pad helps in grasping females during amplexus, vocal sacs produce sound, nictitating membrane protects eyes underwater, and tympanum aids in hearing. Therefore, the correct match is (1) A-1, B-2, C-3, D-4.

Fill in the Blanks Question

9. The copulatory pad in male frogs develops on the ______ digit of the forelimb.

(1) First

(2) Second

(3) Third

(4) Fourth

Explanation:

The copulatory pad develops on the first digit of the male frog’s forelimb. It thickens and darkens during breeding, assisting in grasping the female securely for reproduction. Hence, the correct answer is (1) First.

Choose the Correct Statements (Statement I & II)

10. Statement I: Copulatory pad helps in the process of amplexus.

Statement II: It is a characteristic feature of female frogs.

(1) Both Statement I and II are correct

(2) Both Statement I and II are incorrect

(3) Statement I is correct but Statement II is incorrect

(4) Statement I is incorrect but Statement II is correct

Explanation:

Statement I is true since the copulatory pad aids amplexus during reproduction. Statement II is false because the pad is a male-specific structure. It assists in gripping the female during mating. Therefore, option (3) is correct. 

Subtopic: Cardiac Physiology

Keyword Definitions:

Poikilotherm: Organisms whose body temperature varies with the environment.

Coronary Circulation: Blood flow through vessels supplying the heart muscle.

Myogenic: Originating from the muscle itself, not nerve impulses.

Autoexcitable: Ability to generate spontaneous impulses.

Cardiac Muscle: Specialized muscle tissue forming the heart.

Depolarization: Loss of membrane potential leading to contraction.

Repolarization: Restoration of resting membrane potential.

Sinoatrial Node (SA Node): Pacemaker of the heart initiating impulses.

Atria: Upper chambers of the heart receiving blood.

Ventricles: Lower chambers pumping blood out of the heart.

Clinical Significance: Understanding heart activity helps in diagnosing cardiac disorders.

Lead Question - 2017

Frog’s heart when taken out of the body continues to beat for sometime. Select the best option from the following statements.

(a) Frog is a poikilotherm

(b) Frog does not have any coronary circulation

(c) Heart is “myogenic” in nature

(d) Heart is autoexcitable

Options:

(A) c and d

(B) Only c

(C) Only d

(D) a and b

Explanation: The frog’s heart continues beating outside the body because it is myogenic, meaning impulses originate from cardiac muscle itself, and autoexcitable, meaning it can spontaneously generate impulses without nerve stimulation. Therefore, both statements (c) and (d) are correct. Answer: A.

1. MCQ - Single Correct Answer

Which part of the human heart acts as the primary pacemaker?

(a) AV Node

(b) Purkinje Fibers

(c) SA Node

(d) Bundle of His

Explanation: The SA Node generates spontaneous impulses that initiate the heartbeat. It is located in the right atrium and sets the rhythm of cardiac contractions. Answer: c.

2. MCQ - Single Correct Answer

Which ion primarily initiates cardiac muscle contraction?

(a) Sodium

(b) Potassium

(c) Calcium

(d) Magnesium

Explanation: Calcium ions entering during the plateau phase trigger contraction by binding to troponin, enabling actin-myosin interaction. Sodium initiates depolarization, but calcium sustains contraction. Answer: c.

3. MCQ - Single Correct Answer (Clinical)

A patient shows irregular heartbeat due to SA node damage. Which condition is expected?

(a) Bradycardia

(b) Tachycardia

(c) Atrial Fibrillation

(d) Ventricular Hypertrophy

Explanation: Damage to the SA Node slows impulse generation, leading to bradycardia or slow heart rate. AV node may take over partially, but rhythm is irregular. Answer: a.

4. MCQ - Single Correct Answer

Which structure ensures unidirectional blood flow in the heart?

(a) SA Node

(b) AV Valves

(c) Purkinje Fibers

(d) Coronary Arteries

Explanation: AV Valves (tricuspid and mitral) prevent backflow from ventricles to atria, ensuring unidirectional flow during contractions. Valve closure produces the first heart sound. Answer: b.

5. MCQ - Single Correct Answer

Which is true regarding frog heart circulation?

(a) Double circulation

(b) Single circulation

(c) Pulmonary only

(d) Systemic only

Explanation: The frog heart exhibits double circulation with oxygenated and deoxygenated blood partially separated in a three-chambered heart. This supports both pulmonary and systemic circuits. Answer: a.

6. MCQ - Single Correct Answer (Clinical)

During heart block, which conduction pathway fails?

(a) SA Node

(b) AV Node

(c) Purkinje Fibers

(d) Sinoatrial Fibers

Explanation: In AV block, impulses fail to pass from atria to ventricles, delaying or stopping ventricular contraction. SA Node may remain functional but conduction is impaired. Answer: b.

7. MCQ - Assertion-Reason

Assertion (A): Cardiac muscle is myogenic.

Reason (R): Heart requires continuous nerve stimulation to beat.

(a) Both A and R are true, R is correct explanation of A

(b) Both A and R are true, R is not correct explanation of A

(c) A is true, R is false

(d) A is false, R is true

Explanation: Cardiac muscle is myogenic (A true) and beats without nerve stimulation, making reason false. Therefore, correct option is c. Answer: c.

8. MCQ - Matching Type

Match the following:

1. SA Node - (a) Impulse conduction to ventricles

2. AV Node - (b) Pacemaker

3. Purkinje Fibers - (c) Ventricular contraction

Options:

(A) 1-b, 2-a, 3-c

(B) 1-a, 2-b, 3-c

(C) 1-b, 2-c, 3-a

(D) 1-c, 2-a, 3-b

Explanation: SA Node is the pacemaker, AV Node conducts impulses to ventricles, and Purkinje fibers stimulate ventricular contraction. Correct matching: 1-b, 2-a, 3-c. Answer: A.

9. MCQ - Fill in the Blanks

The duration between two successive heartbeats is called __________.

(a) Cardiac Output

(b) Heart Rate

(c) Cardiac Cycle

(d) Stroke Volume

Explanation: The cardiac cycle is the complete sequence of atrial and ventricular contraction and relaxation between two successive heartbeats. It includes systole and diastole phases. Answer: c.

10. MCQ - Choose Correct Statements

Select correct statements about cardiac muscle:

1. It is striated

2. It is voluntary

3. Intercalated discs are present

4. Always requires nerve impulses

Options:

(A) 1 and 3

(B) 2 and 4

(C) 1, 2, and 3

(D) All 1,2,3,4

Explanation: Cardiac muscle is striated with intercalated discs for synchronized contraction. It is involuntary and myogenic, not requiring constant nerve impulses. Correct statements are 1 and 3. Answer: A.