Page 209 - Biology_F5

Biology for Advanced Level Secondary Schools

behaviour, either by basking in the sun
Activity 3.16: Dissection of a frog to to warm themselves or by hiding under
display the urinogenital system
cover to cool their body. Most of them
Materials are tetrapods, with claws on their toes.
Fresh male or female frog or toad, Reptiles such as snakes and some lizards
dissection kit, dissecting tray or dish, a
FOR ONLINE READING ONLY
piece of thread, chloroform, water, and are legless, although they are descendants
cotton wool. of four-limbed ancestors.

Procedure Distinctive features of class Reptilia
(a) Dissect the frog or toad in a usual Reptiles possess the following unique
way to open up the body cavity. features, which differentiate them from
(b) Deflect the alimentary canal to your other chordates:
right hand side and pin it to fully, (a) They have dry skin with horny scales
display the urinogenital system. or scutes.

Questions (b) They have two pairs of pentadactyl
1. With reasons, state the sex of your limbs, except some members, such as
specimen. snakes, which have no limbs.
2. Describe the displayed urinogenital (c) They undergo internal fertilisation and
system. Compare what you have their fertilised yolky eggs are laid on
displayed and that of Figure 3.64 land or retained until hatching.
and Figure 3.65. (d) They lay amniotic eggs that have a
3. Outline the role (s) of each of the leathery shell to prevent rapid water loss.
labelled parts. (e) Their eyes are located at the front of
4. How does the urethra of a male the head to facilitate binocular vision.
differ from that of a female? Some reptiles can move each eye
independently, and this helps them to
Class Reptilia find food and escape from predators.
The class comprises a group of animals
including turtles, crocodiles, alligators, Structure of a lizard
chameleons, tortoises, snakes, and lizards. Lizards have dry scaly skin, and most of
Most of them have four limbs, while others them have clawed feet and external ear
do not have limbs. Reptiles are found in openings. Most lizards are small, with
diverse habitats, such as deserts, mountains, four legs and a long tail that, in many
rocks, treetops and in water. They are mostly species. It is fragile and easily broken but
terrestrial with few aquatic members such regenerate later (Figure 3.70). The legs of
as turtles and terrapins. They are cold- some lizards such as glass lizard or a slow
blooded (ectothermic) vertebrates. Their worm are greatly shortened or vestigial,
body temperature fluctuates according to making snake-like in appearance. They
the environmental temperature. Reptiles are distinguished from true snakes by their
regulate their body temperature by movable eyelids and external ears.

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