NOTE
B I O L O G Y
STRUCTURAL ORGANISATION
IN ANIMALS
FROG - EXCRETORY SYSTEM, NERVOUS SYSTEM,
REPRODUCTIVE SYSTEM, ENDOCRINE GLANDS
Key Takeaways
Frog (Rana tigrina)
• Excretory system • Reproductive system
• Nervous system • Development in frogs
○ Central nervous system • Endocrine glands in frogs
○ Peripheral nervous system • Importance of frogs
Prerequisites
Anatomy of frog
Reproductive
Digestive system Circulatory system Excretory system
system
Respiratory Lymphatic Nervous
system system system
Excretory System
• Frogs excrete nitrogenous wastes in the form of urea and hence are known as ureotelic
animals.
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Structure of the excretory system
Pair of kidneys Ureters
• Compact, dark red, bean-shaped • Two ureters emerge from the
structures kidneys and pass urea into
• Present on either sides of the the urinary bladder.
vertebral column • In males, the ureter acts as a
• Collects urea from the blood and urinogenital duct that opens
passes it into the ureters into the cloaca.
• In females, the ureter and
oviduct open separately into
the cloaca.
Urinary bladder
• Ureters lead to the urinary
Excretory system of a frog
bladder
• Stores urine
Nephron/Uriniferous
tubules Cloaca
• Present in large numbers in the kidney • Opening for the removal of
urea
• Structural and functional unit of the kidney
• Filter blood to remove nitrogenous waste
Passage of urea
Kidney
Ureters
Urinary Bladder
Cloaca
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03
Nervous System
Parts of the nervous system
Central nervous system Peripheral nervous system
(CNS) (PNS)
Brain Cranial nerves
• Protected by the cranium/ • 10 pairs arise from the
brain box brain
Spinal cord Spinal nerves
Parts of the brain
(a) Forebrain
• Olfactory lobes: Control the sense of smell
Olfactory lobe • Paired cerebral hemispheres: Control the
functions of the body
Cerebral hemispheres • Unpaired diencephalon: Acts as a relay
centre for sensory and motor signals
Diencephalon
Optic lobe (b) Midbrain
• Pair of optic lobes: Helps in vision
Cerebellum
Medulla oblongata
(c) Hindbrain
• Cerebellum: Controls muscle movement
and balance
• Medulla oblongata: Connects the brain
and spinal cord
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04
Did you know?
Vocal sacs, present only in males, help in the amplification of the voice that helps to attract the
female frog.
Reproductive System
Male reproductive system
Parts of the male reproductive system
A pair of testes
• Yellowish and ovoid in
appearance
• Attached to the kidneys by
the mesorchium (double
fold of peritoneum)
• Produces sperm
Vasa efferentia
• 10–12 in number
• Arise from the testes
• Enter the kidneys and open
into the Bidder’s canal
Urogenital tract
Cloaca
• Opens to the exterior of Male reproductive system
the body through the cloacal
aperture
• Passes urine, sperm, and
faecal matter
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Passage of sperm in the male reproductive system
Testes (Produce sperm)
Vasa efferentia
Bidder’s canal
Urogenital tract
Cloaca
Female reproductive system
Ovaries
• Situated near the kidneys
• Produce about 2500–3000
ova at a time
Oviduct
• Carries ova from the ovary
to the oviduct
Cloacal chamber
Female reproductive system
Fertilisation
• Fertilisation is external as ova and sperms are released into water.
• The egg and sperm fuse together to form the zygote.
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Did you know?
Copulatory pad
Male frogs have a structure on the first digit of the forelimb
known as the copulatory pad. This structure helps the male
grasp the female during copulation.
Development in Frogs
• After fertilisation, the zygote divides to form an embryo and then the tadpole hatches out.
Metamorphosis
• The process by which an immature larva transforms into the adult form is known as
metamorphosis.
Zygote Embryo
Tadpoles
• Look more like fish
• Have gills for respiration and tail
for movement
• Eat plants and algae from water
Frog Froglet
As the tadpole develops into the froglet and mature frog, the
following changes occur:
• Front and hind legs develop
• Tail shortens
• Lungs develop
Different stages of development of frog
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Tadpoles Frogs
They have gills. They lose their gills and breathe through
the lungs.
They have tails. They lose their tails when they become frogs.
They cannot live on land. They can live on land.
Endocrine Glands in Frogs
• Endocrine glands secrete hormones that help in the chemical coordination of the body.
Thymus
Gonad
Pituitary body Adrenal gland
(present on the kidneys)
Thyroid
Pancreas
Endocrine glands in a frog
Importance of Frogs
• They play a role as bioindicators.
○ They are sensitive to environmental changes like pollution.
○ Pollution can cause developmental malformations in frogs.
• They are an important part of the food chain and food web.
• They help in protecting crops by feeding on harmful insects.
• They serve as a food source.
○ In some cultures, muscular frog legs are consumed.
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08
Summary Sheet
Reproductive system Anatomy of frog Excretory system
Male reproductive system Kidneys (nephrons)
Testes (Produce sperm) Ureters
Vasa efferentia Bladder
Bidder’s canal Cloaca
Urogenital tract
Cloaca
Female reproductive system Endocrine system Nervous system
Pair of ovaries Thymus CNS
Oviduct Adrenal gland Brain
Cloacal chambers Pancreas Spinal cord
Pituitary gland PNS
Thyroid Cranial nerves
Gonad Spinal nerves
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