Structural Organisation in Animals

What to remember

• The four basic animal tissues are epithelial, connective, muscular and neural. Epithelium covers and lines; connective tissue binds and supports; muscle contracts; neural tissue conducts impulses.
• Cell junctions: tight junctions seal, adhering junctions cement, and gap junctions connect cytoplasm for rapid transfer of ions and small molecules.
• The frog (Rana tigrina) has a three-chambered heart, is ureotelic, and has external fertilisation with a tadpole larva.
• The cockroach (Periplaneta americana) has an open circulatory system, tracheal respiration, uricotelic excretion by Malpighian tubules, mosaic vision, and paurometabolous development through nymphs.

Epithelial tissue

Epithelial tissue has a free surface facing a body fluid or the outside. Its cells are tightly packed with little intercellular matrix. It is of two main types: simple (single layer) and compound (many layers).

Glandular epithelium may be unicellular, such as goblet cells that secrete mucus, or multicellular, such as the salivary gland. Exocrine glands secrete mucus, saliva, earwax, oil, milk and digestive enzymes through ducts. Endocrine glands have no ducts and secrete hormones directly into the fluid bathing the gland.

Compound epithelium is made of two or more layers of cells. It has a protective role against chemical and mechanical stress and has a limited role in secretion and absorption. It covers the dry surface of the skin, the moist surface of the buccal cavity and pharynx, and the inner lining of the ducts of salivary glands and pancreatic ducts.

Cell junctions:

Connective tissue

Connective tissue links and supports other tissues and organs. It has cells, fibres and a ground substance (matrix).

Muscular tissue

Neural tissue

Neural tissue exerts the greatest control over the body. Neurons are excitable cells that receive and conduct impulses. Neuroglia make up more than half the volume of neural tissue. They protect and support neurons.

Organ and organ system

Cells make tissues, tissues make organs, and organs form organ systems that work together. Frog and cockroach below show how the systems are arranged.

Frog (Rana tigrina)

Frogs live in freshwater and on land, so they are amphibians. They are poikilothermic (cold-blooded). They change colour to match the surroundings, which is protective colouration. They show hibernation (winter sleep) and aestivation (summer sleep). The body has a head and a trunk but no neck or tail. The skin is smooth, slippery and moist because of mucus. The dorsal surface is olive green with dark irregular spots. The ventral surface is pale yellow. The forelimbs have four digits. The hind limbs are long, have five webbed digits and help in swimming.

Sexual dimorphism: the male has vocal sacs and a copulatory pad on the first digit of the forelimb. The female lacks both.

The cloaca receives faecal matter, urine and sperms or eggs and passes them to the exterior. A mature female lays about 2500 to 3000 ova at a time. Fertilisation is external, in water. Development is indirect: the tadpole larva undergoes metamorphosis to form the adult frog.

Cockroach (Periplaneta americana)

The cockroach is brown or black and about 34 to 53 mm long. The body is segmented and has a head, thorax and abdomen. The exoskeleton is chitinous and has hardened plates called sclerites: tergites (dorsal), sternites (ventral) and pleurites (lateral), joined by a thin arthrodial membrane.

• Head: triangular, formed by fusion of six segments, and very mobile because of a flexible neck. It has a pair of compound eyes, a pair of antennae and mouthparts.
• Mouthparts: labrum (upper lip), a pair of mandibles, a pair of maxillae, labium (lower lip) and a tongue-like hypopharynx.
• Thorax: prothorax, mesothorax and metathorax. Each has a pair of walking legs. The forewings (tegmina) are on the mesothorax and are opaque. The hind wings are on the metathorax and are transparent and membranous, used in flight.
• Abdomen: 10 segments in both sexes. Anal cerci are present in both sexes on the 10th segment. The male has a pair of short, thread-like anal styles that the female lacks. In the female the 7th sternum is boat-shaped and with the 8th and 9th sterna forms a brood or genital pouch.

Development: fertilised eggs are encased in a capsule called the ootheca. An ootheca is dark reddish to blackish brown, about 8 mm long, and holds an average of 14 to 16 eggs. The female drops or glues it in a safe crevice. The young are nymphs, which look like adults but are smaller. The nymph moults about 13 times to reach the adult stage. The next-to-last nymphal stage has wing pads. Wings are present only in the adult. This is paurometabolous development.

NEET traps

• Simple squamous lines blood vessels and air sacs. Simple cuboidal has a brush border in the proximal tubule. Simple columnar lines the intestine.
• Exocrine glands have ducts. Endocrine glands do not.
• Tight junctions seal. Gap junctions communicate. Adhering junctions cement.
• Tendons join muscle to bone. Ligaments join bone to bone.
• Cartilage has chondrocytes and chondroitin salts. Bone has osteocytes and calcium salts.
• Skeletal and cardiac muscles are striated. Smooth muscle is not. Skeletal is voluntary; the other two are involuntary.
• Frog: vocal sacs and copulatory pad belong to the male. Cockroach: anal styles belong to the male, while anal cerci are present in both sexes.
• Frog is ureotelic. Cockroach is uricotelic.
• Frog heart has three chambers and blood vessels form a closed system. Cockroach circulation is open and does not carry oxygen, because tracheae do.
• Frog has no external ear. Cockroach compound eyes give mosaic vision.

One-liners

• Goblet cells are unicellular exocrine glands.
• Ciliated epithelium lines the bronchioles and fallopian tubes.
• Areolar tissue has fibroblasts, macrophages and mast cells.
• Adipose tissue stores fat.
• Smooth muscle cells are fusiform.
• Intercalated discs are present in cardiac muscle.
• Neuroglia make up more than half of neural tissue volume.
• Rana tigrina is a poikilotherm.
• Frog respires through skin, buccal cavity and lungs.
• The frog heart has a sinus venosus.
• A frog lacks an external ear.
• Bidder's canal is present in the male frog's kidney.
• The cockroach gizzard has six chitinous teeth.
• Cockroach spiracles are present in 10 pairs.
• The cockroach nymph moults about 13 times.

Practice questions

1. The epithelium lining the air sacs of the lungs is

   1. simple columnar
   2. simple squamous
   3. simple cuboidal
   4. ciliated columnar
   Answer

   B. simple squamous

   Flat, thin cells allow diffusion across the air sac wall.

2. Which junctions plug cell edges and prevent leakage across the tissue?

   1. Tight junctions
   2. Plasmodesmata
   3. Adhering junctions
   4. Gap junctions
   Answer

   A. Tight junctions

   Tight junctions seal the spaces between epithelial cells.

3. Tendons connect

   1. cartilage to bone
   2. bone to bone
   3. skin to muscle
   4. skeletal muscle to bone
   Answer

   D. skeletal muscle to bone

   Tendons are dense regular connective tissue joining muscle to bone; ligaments join bone to bone.

4. Cells enclosed in small cavities of the matrix of cartilage are called

   1. fibroblasts
   2. mast cells
   3. chondrocytes
   4. osteocytes
   Answer

   C. chondrocytes

   Chondrocytes lie in lacunae of the chondroitin-rich matrix.

5. Intercalated discs are present in

   1. skeletal muscle
   2. all muscle types
   3. cardiac muscle
   4. smooth muscle
   Answer

   C. cardiac muscle

   Cardiac muscle cells are joined by intercalated discs for rapid, coordinated contraction.

6. Which cells protect and support neurons and form more than half of the neural tissue volume?

   1. Chondrocytes
   2. Neuroglia
   3. Neurons
   4. Fibroblasts
   Answer

   B. Neuroglia

   Neuroglia make up more than half of the volume of neural tissue.

7. The heart of a frog has

   1. two atria and one ventricle
   2. one atrium and two ventricles
   3. one atrium and one ventricle
   4. two atria and two ventricles
   Answer

   A. two atria and one ventricle

   The frog heart is three-chambered.

8. In a male frog, the vasa efferentia open into

   1. the oviduct
   2. the urinary bladder
   3. the cloaca directly
   4. Bidder's canal
   Answer

   D. Bidder's canal

   Vasa efferentia enter the kidney and open into Bidder's canal, which joins the urinogenital duct.

9. The main nitrogenous waste of a frog is

   1. creatinine
   2. uric acid
   3. ammonia
   4. urea
   Answer

   D. urea

   The frog is ureotelic.

10. The ear of a frog consists of

    1. an external ear and an internal ear
    2. a middle ear only
    3. an internal ear and a tympanum only
    4. a pinna and a tympanum
    Answer

    C. an internal ear and a tympanum only

    Frogs have no external ear; the tympanum receives sound.

11. The abdomen of a cockroach has how many segments?

    1. 10
    2. 9
    3. 8
    4. 12
    Answer

    A. 10

    The abdomen has 10 segments in both sexes.

12. Grinding of food in a cockroach takes place in the

    1. hepatic caeca
    2. gizzard
    3. crop
    4. ileum
    Answer

    B. gizzard

    The gizzard has six chitinous teeth that grind food.

13. Malpighian tubules of the cockroach open at the junction of the

    1. ileum and colon
    2. foregut and midgut
    3. midgut and hindgut
    4. crop and gizzard
    Answer

    C. midgut and hindgut

    A ring of 6 to 8 Malpighian tubules lies at the midgut-hindgut junction.

14. The number of pairs of spiracles in a cockroach is

    1. 2
    2. 10
    3. 8
    4. 12
    Answer

    B. 10

    There are 10 pairs of spiracles on the sides of the body.

15. An ootheca of Periplaneta americana contains an average of about

    1. 14 to 16 eggs
    2. 140 to 160 eggs
    3. 40 to 60 eggs
    4. 4 to 6 eggs
    Answer

    A. 14 to 16 eggs

    An ootheca is about 8 mm long and holds about 14 to 16 eggs.

16. A cockroach nymph moults about how many times before reaching the adult stage?

    1. 3
    2. 6
    3. 26
    4. 13
    Answer

    D. 13

    The nymph moults about 13 times.

17. Given below are two statements: Statement I: Compound epithelium has a protective function. Statement II: Glandular epithelium can be unicellular or multicellular. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    A. Both Statement I and Statement II are correct

    Both are correct; goblet cells are unicellular and salivary glands are multicellular.

18. Given below are two statements: Statement I: Exocrine glands release their secretions through ducts. Statement II: Endocrine glands release hormones through ducts. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    Endocrine glands are ductless.

19. Given below are two statements: Statement I: Gap junctions cement neighbouring cells together. Statement II: Adhering junctions connect the cytoplasm of adjoining cells. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    B. Both Statement I and Statement II are incorrect

    Adhering junctions cement cells; gap junctions connect cytoplasm. Both are reversed, so both are incorrect.

20. Given below are two statements: Statement I: Ligaments attach skeletal muscles to bones. Statement II: Cartilage matrix is rich in calcium salts. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    B. Both Statement I and Statement II are incorrect

    Ligaments join bone to bone; cartilage matrix has chondroitin salts, bone has calcium salts.

21. Which of the following statements are correct? 1. Skeletal muscles are striated and voluntary. 2. Smooth muscle fibres are striated and involuntary. 3. Cardiac muscles are striated and involuntary.

    1. 1 and 2 only
    2. 2 and 3 only
    3. 1, 2 and 3
    4. 1 and 3 only
    Answer

    D. 1 and 3 only

    Smooth muscle is non-striated.

22. Given below are two statements: Statement I: The alimentary canal of a frog is long because the frog is herbivorous. Statement II: The skin of a frog is kept moist by mucus. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    D. Statement I is incorrect but Statement II is correct

    The alimentary canal is short because frogs are carnivores; the skin is moist with mucus.

23. Given below are two statements: Statement I: In a male frog the ureter acts as a urinogenital duct. Statement II: In a female frog the ureters and oviducts open separately into the cloaca. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    A. Both Statement I and Statement II are correct

    Both are correct.

24. Given below are two statements: Statement I: Both sexes of the cockroach have anal styles. Statement II: Anal cerci are present only in males. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    B. Both Statement I and Statement II are incorrect

    Anal styles occur only in males; anal cerci occur in both sexes.

25. Which of the following statements are correct? 1. The cockroach has an open circulatory system. 2. The haemolymph has colourless plasma and haemocytes. 3. The haemolymph carries oxygen to the tissues.

    1. 1 and 2 only
    2. 2 and 3 only
    3. 1 and 3 only
    4. 1, 2 and 3
    Answer

    A. 1 and 2 only

    Oxygen is carried by tracheae, not haemolymph.

26. Given below are two statements: Statement I: The nymphs of a cockroach resemble the adults. Statement II: Functional wings are present in the nymphal stages. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    Wings are present only in the adult; the next-to-last nymph has wing pads.

27. Assertion (A): The skin of a frog must remain moist. Reason (R): Frogs respire through the skin and dissolved oxygen must pass across a moist surface.

    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
    Answer

    A. Both A and R are true and R is the correct explanation of A

    Cutaneous respiration needs moisture.

28. Assertion (A): The cockroach has an open circulatory system. Reason (R): The cockroach respires through tracheae.

    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
    Answer

    B. Both A and R are true but R is not the correct explanation of A

    Both true, but tracheal respiration is not the reason for an open system.

29. Assertion (A): Cardiac muscles contract rapidly in a coordinated manner. Reason (R): Cardiac muscle fibres are non-striated.

    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
    Answer

    C. A is true but R is false

    Cardiac muscle is striated and has intercalated discs; R is false.

30. Assertion (A): Tight junctions allow rapid transfer of ions between cells. Reason (R): Gap junctions connect the cytoplasm of adjoining cells.

    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
    Answer

    D. A is false but R is true

    Rapid transfer of ions is a function of gap junctions, so A is false; R is true.

31. Assertion (A): The alimentary canal of a frog is short. Reason (R): Frogs are carnivores.

    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
    Answer

    A. Both A and R are true and R is the correct explanation of A

    Carnivores need less digestion time, so a short canal is typical.

32. Assertion (A): The gizzard of a cockroach is lined with cuticle and has six teeth. Reason (R): The gizzard secretes the digestive enzymes of the cockroach.

    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
    Answer

    C. A is true but R is false

    The gizzard grinds food; it does not secrete enzymes.

33. Match List I with List II. List I: a. Simple squamous b. Simple cuboidal c. Simple columnar d. Ciliated epithelium List II: i. Lining of stomach and intestine ii. Walls of blood vessels iii. Ducts of glands iv. Fallopian tubes

    1. a-iii, b-ii, c-i, d-iv
    2. a-ii, b-iii, c-iv, d-i
    3. a-i, b-iii, c-ii, d-iv
    4. a-ii, b-iii, c-i, d-iv
    Answer

    D. a-ii, b-iii, c-i, d-iv

    Squamous lines vessels; cuboidal lines gland ducts; columnar lines stomach and intestine; ciliated lines fallopian tubes.

34. Match List I with List II. List I: a. Tendon b. Ligament c. Areolar tissue d. Adipose tissue List II: i. Fat storage ii. Muscle to bone iii. Beneath skin with loose fibres iv. Bone to bone

    1. a-i, b-iv, c-iii, d-ii
    2. a-iv, b-ii, c-iii, d-i
    3. a-ii, b-iv, c-i, d-iii
    4. a-ii, b-iv, c-iii, d-i
    Answer

    D. a-ii, b-iv, c-iii, d-i

    Tendon joins muscle to bone; ligament joins bone to bone; areolar is loose; adipose stores fat.

35. Match List I with List II. List I: a. Skeletal muscle b. Smooth muscle c. Cardiac muscle d. Neuroglia List II: i. Intercalated discs ii. Supports neurons iii. Striated and voluntary iv. Fusiform, non-striated

    1. a-i, b-iv, c-iii, d-ii
    2. a-iii, b-iv, c-i, d-ii
    3. a-iii, b-iv, c-ii, d-i
    4. a-iv, b-iii, c-i, d-ii
    Answer

    B. a-iii, b-iv, c-i, d-ii

    Skeletal muscle is striated and voluntary; smooth muscle is fusiform; cardiac has intercalated discs; neuroglia support neurons.

36. Match List I with List II. List I: a. Hepatic portal system b. Renal portal system c. Sinus venosus d. Conus arteriosus List II: i. Ventricle to arterial trunk ii. Liver and intestine iii. Kidney and lower body iv. Joins the right atrium

    1. a-ii, b-iii, c-i, d-iv
    2. a-ii, b-i, c-iv, d-iii
    3. a-ii, b-iii, c-iv, d-i
    4. a-iii, b-ii, c-iv, d-i
    Answer

    C. a-ii, b-iii, c-iv, d-i

    Hepatic portal links liver and intestine; renal portal links kidney and lower body; sinus venosus joins the right atrium; conus arteriosus leaves the ventricle.

37. Match List I with List II. List I: a. Gizzard b. Malpighian tubules c. Spiracles d. Ommatidia List II: i. Excretion ii. Gas exchange openings iii. Grinding iv. Mosaic vision

    1. a-iii, b-i, c-ii, d-iv
    2. a-ii, b-i, c-iii, d-iv
    3. a-iii, b-i, c-iv, d-ii
    4. a-i, b-iii, c-ii, d-iv
    Answer

    A. a-iii, b-i, c-ii, d-iv

    Gizzard grinds; Malpighian tubules excrete; spiracles admit air; ommatidia give mosaic vision.

38. Match List I with List II. List I: a. Tergite b. Sternite c. Arthrodial membrane d. Tegmina List II: i. Ventral plate ii. Joins sclerites iii. Dorsal plate iv. Forewings

    1. a-i, b-iii, c-ii, d-iv
    2. a-iii, b-i, c-iv, d-ii
    3. a-iii, b-ii, c-i, d-iv
    4. a-iii, b-i, c-ii, d-iv
    Answer

    D. a-iii, b-i, c-ii, d-iv

    Tergite is dorsal, sternite ventral; arthrodial membrane joins sclerites; tegmina are forewings.

39. A tissue section shows tall pillar-like cells with nuclei near the base and microvilli on the free surface, lining the intestine. The tissue is

    1. simple squamous epithelium
    2. simple columnar epithelium
    3. smooth muscle
    4. dense regular connective tissue
    Answer

    B. simple columnar epithelium

    Tall, pillar-like cells with microvilli are simple columnar epithelium.

40. A tissue is solid but pliable. Its cells lie in cavities of a matrix containing chondroitin salts. The tissue is

    1. bone
    2. areolar tissue
    3. cartilage
    4. adipose tissue
    Answer

    C. cartilage

    Cartilage has chondrocytes in a pliable chondroitin-rich matrix; bone matrix is hard with calcium salts.

41. A frog is kept in very dry air for a long time and weakens. The most likely reason is

    1. the skin dries and cutaneous respiration fails
    2. the lungs become larger
    3. hibernation begins in summer
    4. the tympanum is damaged
    Answer

    A. the skin dries and cutaneous respiration fails

    Frogs depend on a moist skin for gas exchange.

42. If all the spiracles of a cockroach are blocked, which process is directly affected?

    1. Excretion by Malpighian tubules
    2. Entry of air into the tracheal system
    3. Circulation of haemolymph
    4. Grinding of food
    Answer

    B. Entry of air into the tracheal system

    Air enters the tracheae through spiracles.

43. Which pair of features identifies a male frog?

    1. Vocal sacs and anal styles
    2. A copulatory pad on the hind limb and anal cerci
    3. Anal styles and a boat-shaped sternum
    4. Vocal sacs and a copulatory pad on the first digit of the forelimb
    Answer

    D. Vocal sacs and a copulatory pad on the first digit of the forelimb

    Vocal sacs and the forelimb copulatory pad are present only in male frogs.

44. In a cockroach, wing pads are first seen in

    1. the ootheca wall
    2. the egg
    3. the next-to-last nymphal stage
    4. the first nymphal stage
    Answer

    C. the next-to-last nymphal stage

    The next-to-last nymphal stage has wing pads; wings appear in the adult.

45. During winter hibernation, a frog buried in mud exchanges gases mainly through its

    1. buccal cavity
    2. gills
    3. lungs
    4. skin
    Answer

    D. skin

    During hibernation and aestivation, gas exchange occurs through the skin.