Question: From NCERT 100% NCERT covered from Particular Keyword. NEET 2011 Explanations are 100% from NCERT | [Difficult level: Easy]
What will you look to identify the sex of the following?
(1) Male frog – a copulatory pad on the first digit of the hind limb
(2) Female cockroach – anal cerci
(3) Male shark – claspers bone on pelvic fins
(4) Female Ascaris – sharply curved posterior end
Answer:(3) Male shark – claspers bone on pelvic fins
👉Class – Chondrichthyes
They are marine animals with streamlined body
and have cartilaginous endoskeleton
(Figure 4.19). Mouth is located ventrally.
Notochord is persistent throughout life. Gill
slits are separate and without operculum (gill
cover). The skin is tough, containing minute
placoid scales. Teeth are modified placoid
scales which are backwardly directed. Their
jaws are very powerful. These animals are
predaceous. Due to the absence of air bladder,
they have to swim constantly to avoid sinking.
Heart is two-chambered (one auricle and one ventricle).
Some of them have electric organs (e.g., Torpedo) and
some possess poison sting (e.g., Trygon). They are
cold-blooded (poikilothermous) animals, i.e., they lack
the capacity to regulate their body temperature. Sexes
are separate. In males pelvic fins bear claspers. They
have internal fertilisation and many of them are
viviparous.
Examples: Scoliodon (Dog fish), Pristis (Saw fish),
Carcharodon (Great white shark), Trygon (Sting ray).
👉Morphology of Frog
Have you ever touched the skin of frog? The skin is smooth and slippery
due to the presence of mucus. The skin is always maintained in a moist
condition. The colour of dorsal side of body is generally olive green with
dark irregular spots. On the ventral side the skin is uniformly pale yellow.
The frog never drinks water but absorb it through the skin.
Body of a frog is divisible into head and trunk (Figure 7.19). A neck
and tail are absent. Above the mouth, a pair of nostrils is present. Eyes
are bulged and covered by a nictitating membrane that protects them
while in water. On either side of eyes a membranous
tympanum (ear) receives sound signals. The
forelimbs and hind limbs help in swimming,
walking, leaping and burrowing. The hind limbs end
in five digits and they are larger and muscular than
fore limbs that end in four digits. Feet have webbed
digits that help in swimming. Frogs exhibit sexual
dimorphism. Male frogs can be distinguished by the
presence of sound producing vocal sacs and also a
copulatory pad on the first digit of the fore limbs
which are absent in female frogs.
👉Morphology of Cockroach
The adults of the common species of cockroach, Periplaneta americana
are about 34-53 mm long with wings that extend beyond the tip of the
abdomen in males. The body of the cockroach is segmented and divisible
into three distinct regions – head, thorax and abdomen (Figure 7.14).
The entire body is covered by a hard chitinous exoskeleton (brown in
colour). In each segment, exoskeleton has hardened plates called sclerites
(tergites dorsally and sternites ventrally) that are joined to each other by
a thin and flexible articular membrane (arthrodial membrane).
Head is triangular in shape and lies anteriorly at right angles to the
longitudinal body axis. It is formed by the fusion of six segments and
shows great mobility in all directions due to flexible neck (Figure 7.15).
The head capsule bears a pair of compound eyes. A pair of thread like
antennae arise from membranous sockets lying in front of eyes. Antennae
have sensory receptors that help in monitoring the environment. Anterior
end of the head bears appendages forming biting and chewing type of
mouth parts. The mouthparts consisting of a labrum (upper lip), a pair
of mandibles, a pair of maxillae and a labium (lower lip). A median flexible
lobe, acting as tongue (hypopharynx), lies within the cavity enclosed by
the mouthparts (Figure 7.15b). 
Thorax consists of three parts – prothorax,
mesothorax and metathorax. The head is connected with thorax by a
short extension of the prothorax known as the neck. Each thoracic segment
bears a pair of walking legs. The first pair of wings arises from mesothorax
and the second pair from metathorax. Forewings (mesothoracic) called
tegmina are opaque dark and leathery and cover the hind wings when at
rest. The hind wings are transparent, membranous and are used in flight.
The abdomen in both males and females consists of 10 segments. In
females, the 7th sternum is boat shaped and together with the 8th and 9th
sterna forms a brood or genital pouch whose anterior part contains female
gonopore, spermathecal pores and collateral glands. In males, genital pouch
or chamber lies at the hind end of abdomen bounded dorsally by 9th and
10th terga and ventrally by the 9th sternum. It contains dorsal anus, ventral
male genital pore and gonapophysis. Males bear a pair of short, threadlike
anal styles which are absent in females. In both sexes, the 10th segment
bears a pair of jointed filamentous structures called anal cerci.
Anatomy Cockroach
👉The alimentary canal present in the body cavity
is divided into three regions: foregut, midgut
and hindgut (Figure 7.16). The mouth opens
into a short tubular pharynx, leading to a
narrow tubular passage called oesophagus.
This in turn opens into a sac like structure
called crop used for storing of food. The crop
is followed by gizzard or proventriculus. It has
an outer layer of thick circular muscles and
thick inner cuticle forming six highly chitinous
plate called teeth. Gizzard helps in grinding the
food particles. The entire foregut is lined by
cuticle. A ring of 6-8 blind tubules called
hepatic or gastric caeca is present at the
junction of foregut and midgut, which secrete
digestive juice. At the junction of midgut and
hindgut is present another ring of 100-150
yellow coloured thin filamentous Malpighian
tubules. They help in removal of excretory
products from haemolymph. The hindgut is
broader than midgut and is differentiated into
ileum, colon and rectum. The rectum opens
out through anus.
👉Blood vascular system of cockroach is an
open type (Figure 7.17). Blood vessels are
poorly developed and open into space
(haemocoel). Visceral organs located in the
haemocoel are bathed in blood (haemolymph).
The haemolymph is composed of colourless
plasma and haemocytes. Heart of cockroach
consists of elongated muscular tube lying
along mid dorsal line of thorax and abdomen.
It is differentiated into funnel shaped chambers
with ostia on either side. Blood from sinuses
enter heart through ostia and is pumped
anteriorly to sinuses again.
👉The respiratory system consists of a
network of trachea, that open through 10 pairs
of small holes called spiracles present on the
lateral side of the body. Thin branching tubes
(tracheal tubes subdivided into tracheoles)
carry oxygen from the air to all the parts. The
opening of the spiracles is regulated by the sphincters. Exchange of gases
take place at the tracheoles by diffusion.
👉Excretion is performed by Malpighian tubules. Each tubule is lined
by glandular and ciliated cells. They absorb nitrogenous waste products
and convert them into uric acid which is excreted out through the hindgut.
Therefore, this insect is called uricotelic. In addition, the fat body,
nephrocytes and urecose glands also help in excretion.
👉The nervous system of cockroach consists of a series of fused,
segmentally arranged ganglia joined by paired longitudinal connectives
on the ventral side. Three ganglia lie in the thorax, and six in the abdomen.
The nervous system of cockroach is spread throughout the body. The
head holds a bit of a nervous system while the rest is situated along the
ventral (belly-side) part of its body. So, now you understand that if the
head of a cockroach is cut off, it will still live for as long as one week. In
the head region, the brain is represented by supra-oesophageal ganglion
which supplies nerves to antennae and compound eyes. In cockroach,
the sense organs are antennae, eyes, maxillary palps, labial palps, anal
cerci, etc. The compound eyes are situated at the dorsal surface of the
head. Each eye consists of about 2000 hexagonal ommatidia
(sing.: ommatidium). With the help of several ommatidia, a cockroach can
receive several images of an object. This kind of vision is known as mosaic
vision with more sensitivity but less resolution, being common during
night (hence called nocturnal vision).
👉Reproduction ;Cockroaches are dioecious and both sexes have well developed
reproductive organs (Figure 7.18). 
Male reproductive system consists of
Male reproductive system consists of
a pair of testes one lying on each lateral side in the 4th -6th abdominal
segments. From each testis arises a thin vas deferens, which opens into
ejaculatory duct through seminal vesicle. The ejaculatory duct opens into
male gonopore situated ventral to anus. A characteristic mushroomshaped
gland is present in the 6th-7th abdominal segments which functions
as an accessory reproductive gland. The external genitalia are represented
by male gonapophysis or phallomere (chitinous asymmetrical structures,
surrounding the male gonopore). The sperms are stored in the seminal
vesicles and are glued together in the form of bundles called
spermatophores which are discharged during copulation. The female
reproductive sysytem consists of two large ovaries, lying laterally in the
2nd – 6th abdominal segments. Each ovary is formed of a group of eight
ovarian tubules or ovarioles, containing a chain of developing ova.
Oviducts of each ovary unite into a single median oviduct (also called
vagina) which opens into the genital chamber. A pair of spermatheca is
present in the 6th segment which opens into the genital chamber.
Sperms are transferred through spermatophores. Their fertilised eggs
are encased in capsules called oothecae. Ootheca is a dark reddish to
blackish brown capsule, about 3/8" (8 mm) long. They are dropped or
glued to a suitable surface, usually in a crack or crevice of high relative
humidity near a food source. On an average, females produce 9-10
oothecae, each containing 14-16 eggs. The development of P. americana
is paurometabolous, meaning there is development through nymphal
stage. The nymphs look very much like adults. The nymph grows by
moulting about 13 times to reach the adult form. The next to last nymphal
stage has wing pads but only adult cockroaches have wings.
👉Phylum – Aschelminthes
The body of the aschelminthes is circular in
cross-section, hence, the name roundworms
(Figure 4.10). They may be freeliving, aquatic
and terrestrial or parasitic in plants and animals.
Roundworms have organ-system level of body
organisation. They are bilaterally symmetrical,
triploblastic and pseudocoelomate animals.
Alimentary canal is complete with a welldeveloped
muscular pharynx. An excretory
tube removes body wastes from the body cavity
through the excretory pore. Sexes are separate
(dioecious), i.e., males and females are distinct.
Often females are longer than males. Fertilisation
is internal and development may be direct (the
young ones resemble the adult) or indirect.
Examples : Ascaris (Roundworm), Wuchereria
(Filaria worm), Ancylostoma (Hookworm).
