Back to: O level Biology NOTES Uganda syllabus

PHYLUM: CHORDATA

Chordate refers to animals which possess a notochord.

Main characteristics

  • The presence of a notochord during the early stages of development.
  • They have bilateral symmetry.
  • The body is composed of head, trunk and usually a tail at some stage of development.
  • Possess a hollow dorsal nerve cord.
  • They have pharyngeal clefts.
  • They limbs originate from different body segments.

This phylum mainly consists of the vertebrates and they are divided into 5 classes. The 5 classes include the following;

  1. Pisces (fishes) e.g. tilapia and the Nile perch,
  2. Amphibia, e.g. frogs and toads
  3. Reptilia e.g. snakes, lizards, crocodiles
  4. Aves -birds
  5. Mammalia e.g. man and whale

CLASS: PISCES

This class contains fish.

.Characteristics of organisms in class Pisces

  • They live in water
  • They have a streamlined body
  • They scales on their skin
  • They breathe using gills
  • They have fins for swimming.
  • They have eggs that are fertilized outside the body (externally)
  • They are ectothermic –they rely on external conditions to maintain their body temperature.

The fish is further sub divided into two sub classes, namely chondrichthyes and osteichthyes.

Sub class: chondrichthyes

Chondrichthyes are also referred to as Elasmobranches. These are cartilaginous fish. They include sharks, rays, dogfish and skates.

Subclass: Osteichthyes

Osteichthyes are also known as teleosts. Teleosts are bony fish.Examples of bony fishes include tilapia and herring. The figure below shows a tilapia fish

fish
diff

CLASS: AMPHIBIA

This class includes then ewt, salamander, toad and frog. The word amphibian comes from two greek words: amphi-(both) and bios (life). This means that amphibians spend part of their life (as larvae or tadpoles) in water, and part of their life as adults on land. Amphibians live on land but require water for breeding.

frog

Distinguishing characteristics

  • Amphibians have a soft moist skin without scales.
  • They have a bony skeleton.
  • They have two pairs of pentadactyl limbs. A pentadactyl is one which has five digits
  • They have visceral clefts at the larval stages which are used as gills for gaseous exchange. Adult amphibians use lungs for gaseous exchange.
  • Amphibians have middle and an inner ear but no external ear. However, they have a tympanic membrane also called the ear drum
  • The egg of amphibians are laid in water and fertilized externally.
  • An amphibian has a three-chambered heart with two auricles and a ventricle.
  • They are poikilothermic / ectothermic.

CLASS: REPTILIA

Reptiles are mainly terrestrial with the exception of the turtlewhich lives in water.Examples of reptiles include the lizard, snake, crocodile, tortoise and turtle.

Distinguishing characteristics

  • Reptiles have dry skin with horny scales
  • Their skeleton is made up of bones
  • Most reptiles have pentadactyl limbs
  • Some reptiles have a middle and inner ear. Snakes have no middle ear.
  • Reptiles do not have an external ear.
  • They use lungs for carrying out gaseous exchange
  • Their eggs are fertilized internally and laid on land. Some snakes give birth to live young ones
  • Some reptiles have a three-chambered heart; two auricles and one ventricle. Others have four chambered heart for example crocodile.
  • Reptiles are poikilothermic.

CLASS: REPTILIA

Reptiles are mainly terrestrial with the exception of the turtlewhich lives in water.Examples of reptiles include the lizard, snake, crocodile, tortoise and turtle.

Distinguishing characteristics

  • Reptiles have dry skin with horny scales
  • Their skeleton is made up of bones
  • Most reptiles have pentadactyl limbs
  • Some reptiles have a middle and inner ear. Snakes have no middle ear.
  • Reptiles do not have an external ear.
  • They use lungs for carrying out gaseous exchange
  • Their eggs are fertilized internally and laid on land. Some snakes give birth to live young ones
  • Some reptiles have a three-chambered heart; two auricles and one ventricle. Others have four chambered heart for example crocodile.
  • Reptiles are poikilothermic.

CLASS: AVES

Aves refer to birds. There exists a wide variety of birds. Examples of birds include eagle, ducks, flamingo, heron, dove etc.

parts a bird

Distinguishing characteristics

  • The skin of birds is covered by feathers, except the legs which are covered by horny scales. The feathers keep the bird warm and also used for flight.
  • They have skeleton is made of hollow bones. The hollow and light bones reduce weight and enable flight.
  • They have two pairs of pentadactyl limbs. The fore limbs modified into wings for flight while the hind are feet for walking or swimming.
  • They have middle and inner ear but no external one. However, the have tympanic membrane.
  • They use lungs for gaseous exchange.
  • They have beak for feeding.
  • They have internal fertilization. They lay eggs in calcareous shells.
  • Their hearts have four chambers.
  • They are ectothermic.
  • They show parental care.

CLASS: MAMMALIA

Mammals comprise a wide variety of animals. They mostly occupy terrestrial habitats except few which occupy aquatic habitats. Examples of terrestrial mammals are cows pigs, goats, monkeys, rats, lions etc. and the aquatic mammals are seals, dolphins and whales.

Distinguishing characteristics

  • The skins of mammals are covered by hairs or fur.
  • The skin has sweat glands called sebaceous glands.
  • They have an endoskeleton made up of bones.
  • They use lungs for breathing or gaseous exchange.
  • They have two pairs of pentadactyl limbs.
  • They have an external, middle and inner ear.
  • They have four types of teeth for feeding.
  • They have four chambered heart.
  • Theyhave muscular diaphragm which separates the thoracic organs from the abdominal organs.
  • Their brains are well developed thus intelligent.
  • They are homoeothermic.
  • They have internal fertilization.
  • They have mammary glands.
  • Give birth to live young ones except the platypus

Class Mammalia is divided into 3 sub classes;

  1. MonotremaThese are the egg laying mammals. They include the spiny anti eaters, and the duck billed platypus.
  2. MetatheriaThese are the marsupials which keep their immature young ones in the pouch where they continue to grow. They include the Kangaroos, Wallaby, Koala bear, etc.
  3. EutheriaThey have placenta. They give birth to fully developed young ones and suckle the mammary glands. They include man, rats, cows, goats, etc.