Question
Which one of the following living organisms completely lacks a cell wall? [CBSE AIPMT 2014]
(a) Cyanobacteria
(b) Sea-fan (Gorgonia)
(c) Saccharomyces
(d) Blue-green algae
Answer/Explanation
Ans. (b)
Sea-fan (Gorgonia) belongs to: kingdom -Animalia, phylum-Cnidaria and orderGorgonacea. As, it is on animal, thus it lacks cell wall unlike cyanobacteria or blue-green algae (kingdom-Monera) have cell wall which is composed of peptidoglycan. Saccharomyces is a genus of kingdom fungi which includes many species of yeast. Their cell wall is made up of chitin.
Question
Select the taxon mentioned that represents both marine and freshwater species [CBSE AIPMT 2014]
(a) Echinoderms
(b) Ctenophora
(c) Cephalochordata
(d) Cnidaria
Answer/Explanation
Ans. (d)
Cnidarian members are found both in freshwater and marine environments, while members of Ctenophora Cephalochordata and Echinodermata are found exclusively in marine environment.
Question
In which animal nerve cell is present but brain is absent? [CBSE AIPMT 2002]
(a) Sponge
(b) Earthworm
(c) Cockroach
(d) Hydra
Answer/Explanation
Ans. (d)
The neurons of Hydra synapse with each other and other body cells. As a result, it responds to external stimuli. However, there is no brain in Hydra to coordinate the responses.
Question
In Hydra, waste material of food digestion and nitrogenous waste material are removed from [CBSE AIPMT 2001]
(a) mouth and mouth
(b) body wall and body wall
(c) mouth and body wall
(d) mouth and tentacles
Answer/Explanation
Ans. (c)
In Hydra, undigested residues are egested from coelentron through mouth, while nitrogenous excretory product (ammonia) is removed through general body surface.
Hydra are solitary, sessile, freshwater coelenterates. They are found in lakes, ponds stream. Hydra is an ammonotelic animal i.e., it excretes waste material in the form of ammonia.
Question
13 Most appropriate term to describe the life cycle of Obelia is [CBSE AIPMT 1998]
(a) neoteny
(b) metagenesis
(c) metamorphosis
(d) All of these
Answer/Explanation
Ans. (b)
True alternation of generations is alternation between haploid gametophyte and diploid sporophyte phase. In Obelia, the asexual polypoid phase is alternate with sexual medusoid phase and this type of life cycle is called metagenesis.
Neoteny It is also called Juvenilisation, is one of the two ways by which paedomorphism can arise.
Paedomorphism It is the retention by adults of traits previously seen only in young, and is a subject studied in the development biology.
Metamorphosis It is a biological process by which an animal physically develops after birth or notching, involving a conspicous and relatively abrupt change in the animal body structure through cell growth and differentiation. e.g., in some insects, molluses etc.
Question
Point out a non-parasite [CBSE AIPMT 1994]
(a) tapeworm
(b) mosquito
(c) leech
(d) sea anemone
Answer/Explanation
Ans. (d)
Sea anemone is a coelenterate found in marine water, attached to the empty shell of gastropods already occupied by hermit crab, this association is symbiosis not parasitism.
Tapeworm, mosquito and leech are parasites.
Question
Special character of coelenterates is [CBSE AIPMT 1994]
(a) polymorphism
(b) nematocysts
(c) flame cells
(d) hermaphroditism
Answer/Explanation
Ans. (b)
The most characteristic feature of coelenterates is the presence of nematocysts or stinging cells.
Nematocysts are mainly concerned with food capture, defence and attachment.
Question
Which one of the following animals possesses nerve cells but no nerves? [CBSE AIPMT 1993]
(a) Hydra
(b) Tapeworm
(c) Earthworm
(d) Frog’s tadpole
Answer/Explanation
Ans. (a)
Hydra has nerve cells but no nerves. Hydra possesses a very primitive nervous system consisting of a synaptic network of bipolar and multipolar nerve cells.
Question
Budding is a normal mode of asexual reproduction in [CBSE AIPMT 1993]
(a) starfish and Hydra
(b) Hydra and sponges
(c) tapeworm and Hydra
(d) sponge and starfish
Answer/Explanation
Ans. (b)
Hydra and sponges reproduce asexually by exogenous budding, a type of vegetative propagation.
Question
Jelly fish belongs to class [CBSE AIPMT 1989]
(a) Hydrozoa
(b) Scyphozoa
(c) Anthozoa
(d) None of these
Answer/Explanation
Ans. (b)
Aurelia(jellyfish) belongs to
class-Scyphozoa of phylum-Cnidaria. It is without skeleton.
Question
Organ pipe coral is [CBSE AIPMT 1988]
(a) Tubipora
(b) Astraea
(c) Helipora
(d) Fungia
Answer/Explanation
Ans. (a)
Organ pipe coral is the common name of Tubipora. This is coelenterate and comes under class-Anthrozoa.