Directions: In the following questions, a statement of assertion is followed by a statement of reason.
Mark the correct choice as:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.
Q.1. Assertion: Radial symmetry in animal helps in detecting food and danger.
Reason: It enables the animal to respond to stimuli from any direction.
AnswerAnswer: (a) Radial symmetry is advantageous for an animal in responding to stimuli from any direction thereby allowing it to detect food and danger easily.
Q.2. Assertion: Animals that have an exoskeleton, lacks an endoskeleton.
Reason: Skeleton cells in the embryonic stage migrate to either stage and produce exoskeleton
or endoskeleton but never both.
AnswerAnswer: (d) Many animals have an endoskeleton and exoskeleton such as Chelon-turtle or Testudo-tortoise. Exoskeleton of other animals include chitinous plate, calcareous shell, horny scales, feathers, hair, claws, nails, hoofs, horns and antlers.
Q.3. Assertion : Cold blooded animals do not have fat layer.
Reason : Cold blooded animals use their fat for metabolic process during hibernation. [AIIMS 1997]
AnswerAnswer: (c) Cold blooded animals do not need to stay warm and can let their body temperatures get closer to that of their surroundings. Thus, they do not need to have extra insulation.
Q.4. Assertion : The skeleton of sponges is made up of spicules.
Reason : Composition of spicules help in classification of sponges.
AnswerAnswer: (b) Spicules help in making skeleton of sponges. These are made up of silica, calcium or spongin substances. The structure of spicules also help in classification of sponges.
Q.5. Assertion : Sponges belong to Porifera.
Reason : Sponges have canal system.
AnswerAnswer: (b) Sponges belong to Porifera and they have characteristic canal system.
Q.6. Assertion : Sponges have body organization of “cellular level”.
Reason : There is some physiological division of labour.
AnswerAnswer: (b) Sponges are multicellular but they have cellular level of body organization i.e., true tissue, movable parts, or appendages are not formed. Although, there is some physiological division of labour, accompanied with structural differentiation amongst body cells. But here, similar cells are arranged neither in permanent layer nor masses to form tissues.
Q.7. Assertion: Sponges exhibit cellular level of organization.
Reason: In sponges, cells are arranged as loose cell aggregates.
AnswerAnswer: (a) All members of animalia are multicellular, but all of them do not exhibit the same pattern of organization of cells. In sponges, the cells are arranged as loose cell aggregates, i.e., they exhibit cellular level of organisation while, higher animals have tissue or further organ system level of organization.
Q.8. Assertion: Leucosolenia shows ascon type of canal system.
Reason: Water passes through ostia → spongocoel → osculum in Leucosolenia.
AnswerAnswer:(a) Leucosolenia shows simplest type of canal system. In this, surrounding water enters the canal system through ostia. This water of sea enters into the spongocoel and is pushed out readily through osculum. Course taken by the water current in the body of sponge may be shown as under.
Ingressing → Spongocoel → To outside
Q.9. Assertion: Sponges do not show any animal nature.
Reason: Sponges are sessile having specialized structures for capturing food or eliminating wastes.
AnswerAnswer:(d) Robert Grant (1857) was the first to recognise and prove the true animal nature of sponges. The animal nature of sponges was well established on the following grounds-
(i) Sponges feed on in water solid particles. Their mode of nutrition is truly holozoic.
(ii) Sponge cells are devoid of cellulose cell walls.
(iii) Life cycle of sponges include swimming ciliated larval stages resembling those of other marine animals. Sponges are sessile and digestion is very simple without any apparent way of capturing food or eliminating wastes.
Q.10. Assertion: In ctenophores, digestion is chiefly extracellular.
Reason: Digestive tract is incomplete in ctenophores.
AnswerAnswer:(d) Digestive tract in ctenophores consists of mouth, pharynx or stomodaeum, stomach or infundibulum, anal canals and two anal pores. Since there are mouth and anal pores present, the digestive tract is complete. Thus, digestion is both extracellular and intracellular.
Q.11. Assertion: Cnidoblasts are present on the tentacles and the body in cnidarians.
Reason: Cnidoblasts are used for anchorage, defence and capture of the prey.
AnswerAnswer:(b) Cnidoblast cells are present on the tentacles and the body of cnidarians. A cnidoblast (also called nematoblast) has nematocyst known as ‘stinging organ’ (consisting of capsule, shaft and thread tube) used for anchorage, defence and offence.
Q.12. Assertion: Coelenterates are known as Radiata.
Reason: These are bilaterally symmetrical organism.
AnswerAnswer: (c) Coelenterata is the phylum of acoelomate and radially symmetrical lower invertebrates. Due to their radial body symmetry, they are also known as radiata. Bilateral symmetry starts from the phylum platyhelminthes.
Q.13. Assertion: Hydra is green in colour.
Reason: Green colour is due to the presence of chlorophyll in their body wall.
AnswerAnswer:(c) H. viridis is green in colour. Its bright green colour is not because of chlorophyll containing chloroplasts, but due to the presence of symbiotic zoochlorallae, Chlorella vulgaris, a unicellular green alga, that lives in its gastrodermal cells.
Q.14. Assertion: Nerve cells in coelenterata have complete co-ordination in their body.
Reason: True nerve cells occur for the first time in coelenterate.
AnswerAnswer:(a) Coelenterates possess a very primitive type of nervous system. This system is composed of many nerve cells. In coelenterates, separate mechanisms for digestion, respiration, excretion and reproduction etc. have evolved for the first time. Thus, there is a constant need to maintain coordination between these systems. Nerve cells are developed for this purpose, for the first time in coelenterates.
Q.15. Assertion: Obelia is dimorphic in nature.
Reason: Polyp and gonangia form are exhibited by Obelia.
AnswerAnswer:(a) Hydroid colony of Obelia is dimorphic, exhibiting two types of individuals or zooids which differ both morphologically as well as physiologically. These two zooids are-
(i) Polyps – the nutritive zooid of the colony
(ii) Gonangium – the reproductive zooid.