Test: Hydra - 1 (Old NCERT) - NEET MCQ

The body cavity of the hydra is Known as coelenteron. Alternatively, it is also known as the cardiovascular cavity.

(a) Amoeba: There is no nervous system as there is no presence of neurons, but there is the presence of different types of sensors.

(b) Hydra: They have the anatomically simplest nervous system which is a nerve net formed by the nerve cell present the epidermis of hydra with no sign of brain.

(c) Sponge: They are the only multicellular animals without a nervous system. They do not have any nerve cells or sensory cells. However, touch or pressure to the outside of a sponge will cause a local contraction of its body.

(d) Cockroach: It belongs to the phylum Arthropoda. It has a well-developed nervous system with a nerve ring, nerve cord, and neuro-endocrine sympathetic system.

Hence, option B is correct.

Nematocysts are specialized stinging cells specific to Coelenterates that act as organs of offense and defense.
They are cell organelles that are found in specialized cells known as cnidocytes or cnidoblasts, which are modified epidermal interstitial cells.

Cross-section of Hydra Polyp, showing cnidocyte and nematocyst structure

• Nematocysts are cell organelles found in specialized cells called cnidocytes or cnidoblasts, which are modified epidermal interstitial cells.
• A Cnidoblast is an oval or rounded cell with a conspicuous nucleus lying on the basal side.
• Inside the cnidoblast is present an oval or pyriform sac or bladder that is filled with a toxin called hypnotoxin, which is a mixture of proteins and phenols. 

Tentacles and pseudopodia both help in movement.

• Mesogloes is gelatinous or jelly-like and has no fibers or cellular elements.
• In coelenterates and Porifera, mesogloea lies between the epidermis and gastrodermis and is attached to both layers
• The mesogloea may range from a thin, non-cellular membrane to a thick, non-fibrous, jelly-like material, and may contain cells that have migrated from other areas.

Hydra anatomy diagrams (a) Hydra regions, (b) epithelial bilayer of endoderm and ectoderm:

The correct option is C

Intercellular

The correct option is C

Explanation for correct option.

1. Digestion in hydra is intercellular.
2. The food is first trapped and then it gets digested in the gastrovascular cavity by the action of enzymes secreted by the cells of the gastrovascular cavity.
3. The animals of genius hydra belong to the class hydrozoa.
4. The food is caught by tentacles and then ingested through the mouth into the gastrovascular cavity(large digestive cavity)

Penetrants: Penetrants are of two types, stenotele found in Hydra and euryteles found in jellyfishes.

• They are the largest (16 microns in diameter) and the most complex nematocysts. It is pear-shaped and its thread tube is long and hollow, coiled transversely and bearing three large stylets and three rows of small spines at its stout base.
• The thread tube is open at the apex and when discharged, it darts out with such explosive force that it pierces the body of prey and injects the hypnotoxin that paralyzes the victim or kills it outright.

Locomotion in Hydra:

Regeneration in Hydra:

Tentacles capture prey in addition to this, sometimes also help in locomotion.

There's no role of tentacles in the case of digestion. 

Hydra breathe through general body surface because of not having any special organ to perform this activity.

Simplest type nervous system found in hydra that has non polarised nerve cells.

Nutrition is holozoic. Hydra is carnivorous and its favorite food is water fleas (Cyclops and Daphnia; Crustacea, Arthropoda).

Faecal matter is thrown out through mouth. Starch is not digested in coelenterates. Glycogen and fat are reserve food of Hydra. 

Digestion in Hydra takes place in two phases- the extracellular phase and the intracellular phase.
The preliminary digestion takes place outside the cells of the endodermis, that is, is an extracellular process, and the second phase takes place inside the cells or is an intracellular process.

Hence, option C is correct.

Hydra is a Cnidarian that is aquatic but is distributed in freshwater.
It exhibits radial symmetry as its divisible by an imaginary axis into two equal halves.
The presence of two layers of tissue makes the organism diploblastic.

Hence, option D is correct.

Some sea anemones i.e. hydra are known to have symbiotic algae living within their gastrodermal cells.

Some sea anemones contains both zoochlorellae and zooxanthellae.

Delamination: It involves splitting off the blastoderm into two layers by the appearance of grooves resulting in the formation of hypoblast. It is found in birds.

Formation of layers by gastrulation:
(a) Formation of endoderm
(b) Formation of embryonic disc and mesoderm
(c) Formation of ectoderm

Hydra is a minute freshwater coelenterate that consists of a stalk-like tubular body along with a  ring of tentacles around the mouth that is surrounded by 6-10 tentacles.

Hydrozoa, Cnidarians exhibit two basic body forms called polyp and medusa.

These Cnidarians, which exist in both forms exhibit alternation of generation (Metagenesis), i.e., polyps produce medusa asexually and medusa form the polyps sexually (e.g., Obelia).

The body wall consists of two cellular layers, an outer epidermis derived from the ectoderm and an inner gastrodermis derived from the endoderm.
In between them a thin non-cellular layer of a jelly-like substance called mesogloea is present.

• The gastrovascular cavity of the hydra helps in digestion and circulation.
• It is a cavity that has a single opening surrounded by tentacles. The cavity is lined by a diploblastic layer. The outer layer is the epidermis and the inner is the gastrodermis. The cavity is also known as coelenteron. 

Hence, option A is correct.

Nematocysts are produced by nematoblasts, or cnidoblasts, and are used for capturing and paralyzing prey or for defense. Each nematocyst contains a coiled, hollow thread that can have barbs or spines and often contains poison.

Hence, Option D is the correct answer.

• In species of Hydra oligactis, male is smaller and bears one to eight testes, while the larger female bears one or two ovaries.
• A testis is a slight conical elevation, arising from ectodermal interstitial cells and having a number of elongate cysts. At the base of a cystis is the primordial germ cell, which divides repeatedly by mitosis to form a variable number of spermatogonia, which grow into spermatocytes.
• The development of ovary is similar as of testis. The interstitial cells multiply to form the germ mother cells or oogonia.

They exhibit metagenesis but not metamorphosis.

In the hydra, respiration is accomplished via diffusion of molecules of oxygen and carbon dioxide through the skin. The hydra's simple cellular structure ensures that its body's skin layers are thin enough for diffusion to occur.