Gaseous exchange biology notes for o level with questions grade 6 electricity experiments

The process of moving oxygen into the body and carbon dioxide out of the body is called breathing in or ventilation. Gaseous exchange involves the passage of carbon dioxide through a respiratory surface. Diffusion is the main transport process involved in gaseous exchange.

Small animals such as amoeba use their entire body surface for gaseous exchange. They have a high surface area /volume ratio. As organisms increase in size, the surface area/volume ratio decreases, hence there is need to have special respiratory system or organs.

The respiratory system consists of a network of tubes forming the tracheal system. The tubes open to the outside through pores called spiracles located on the sides of the thorax and the abdomen. The tubes called the trachea are lined with cuticle and have spiral rings which prevent the walls from collapsing inwards.

The trachea is divided into smaller tubes called tracheoles which are closely associated with the tissues. Some insects have air sacs connected to the trachea. These air sacs can be inflated or deflated in order to facilitate gaseous exchange

Amphibians live in two environments air and water and are therefore adapted to gaseous exchange in land and in water. They also show change of respiratory surfaces and organs as they develop from gills in tadpoles to lungs, skin and mouth in adults.

The lining of the mouth cavity and the lungs are used for Gaseous exchange when the frog is out of the water. Lungs are not very efficient since some of the oxygen in the air reaching them has already been taken up by the lining of the mouth cavity. When a frog is in water , it relies almost entirely on the skin for Gaseous exchange

The floor of the mouth is lowered and air is drawn in through the nostrils. When the nostrilsare closed and the floor of the mouth is raised, air is forced into the lungs (inspiration). When the floor of the mouth is lowered again, the pressure of the abdominal contents forces air out of the lungs through the nostrils (expiration)

Gaseous exchange in fish takes place between the gills and the surrounding water. The gills are located in the opercular cavity covered by a flap of skin called the operculum. Each gill consists of a number of thin leaf like lamellae projecting from a skeletal base (brachial arch) situated in the wall of the pharynx.

As the mouth opens, the floor of the mouth is lowered. Pressure inside the mouth is lowered and this causes water to be drawn into the bucal cavity. Meanwhile the operculum is closed, preventing water from entering or leaving through the opening.

As the mouth closes and the floor of the mouth is raised, pressure in the bucal cavity increases. Water is forced over the gills as the opercula are forced to open. As water passes over the gills, oxygen is absorbed and carbondioxide from the gills dissolves in the water.

The breathing system of a mammal consists of a pair of lungs which are thin walled elastic sacs lying in the thoracic cavity. The walls of the thorax consists of the ribs and the intercostal muscles while the floor consists of the diaphragm, a muscular flap of tissue between the thorax and the abdomen

Air enters the lungs through the trachea which is devided into two brochi, one to each lung. The trachea and bronchi have walls made up of rings of cartilage. Inside the lungs , each bronchus is divided into smaller tubes called bronchioles. The bronchioles terminate in saclike atria giving rise to numerous air sacs or alveoli. Each alveolus is a thin walled sac covered by numerous blood capillaries

 The walls of the alveoli and the capillaries are very thin and closely attached to each other. This makes diffusion of gases very efficient because the distance between the inside of the capillary and the inside of the alveolus is very small.

Blood from the tissues has a high concentration of carbondioxide and very little oxygen compared to alveolar air. The concentration gradient favours diffusion of carbondioxide into the alveolus and oxygen into the blood plasma in the capillaries. The oxygen is then picked by the haemoglobin of red blood cells and transported in combination with it as oxyhaemoglobin.