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Biology : Term 3 Grade 11
Gaseous exchange in plants and animals
The need for gaseous exchange
-​ Cellular respiration: process of breaking down glucose to release energy.
-​ Living cells require oxygen as a raw material for cellular respiration.
-​ Co2 is released as a waste product.
-​ gasses need to be exchanged between the organism and its environment.
●​ Gaseous exchange: the diffusion of oxygen and carbon dioxide in and out of an
organism.
●​ Breathing (ventilation): movement of air in and out of the lungs.
●​ Gaseous exchange surface: surface through which gaseous exchange takes place.

Adaptations increasing efficiency in gaseous exchange organs
●​ Large surface area: Increases the area through which gaseous exchange can occur.
●​ Thin surface: Thin and permeable so that gases can diffuse quickly through the
surface.
●​ Moisture: Oxygen and carbon dioxide must dissolve in fluid for them to be able to
diffuse through the gaseous exchange surface.
●​ Good ventilation: Diffusion only occurs down a concentration gradient. In order to
maintain a concentration gradient, the gaseous exchange surface needs to be well-
ventilated.
●​ Protection: Internal organs are well protected from damage and desiccation (example
the ribs in Vertebrates)
●​ Efficient transport system: Gaseous exchange surfaces are richly supplied with a
network of blood vessels- transport gases around body- Oxygen needs to be
continuously removed from the respiratory surface and transported to where it is
needed to maintain a diffusion gradient. Similarly, carbon dioxide needs to be
transported to the gaseous exchange surface for release.

Gaseous exchange in dicotyledonous plants
-​ Plants =low metabolic rate.
-​ require less oxygen and less energy per unit volume than animals.
-​ stomata :Flowering plants have small gaseous exchange pores ->open during the
day and are closed at night= When open they connect the intercellular air spaces in
the plant with the atmosphere.
●​ Carbon dioxide diffuses into the leaf through the stomata.
●​ The mesophyll cells use up the carbon dioxide during photosynthesis, creating a
concentration gradient down which carbon dioxide diffuses.
●​ Oxygen and water vapour diffuse out of the mesophyll cells. They create a
concentration gradient and diffuse out of the leaf through the stomata.
●​ Plants use some of the oxygen produced during photosynthesis for cellular
respiration, so they do not need to get it from the environment. Oxygen moves by
diffusion through the intercellular air spaces to respiring cells that require oxygen.

GASEOUS EXCHANGE IN EARTHWORMS:

-​ Pseudohearts: five heart-like structures found in an earthworm that circulate blood

, -​ occurs by diffusion over the whole surface of the body.
-​ The surface of the skin is kept moist by the mucous glands in the skin + moist soil
-​ No special organs for gaseous exchange are required because the cylindrical bodies
of the earthworms give them a high surface area to volume ratio.
-​ Their low activity = low metabolism and low oxygen requirement.
●​ Oxygen dissolves in the moisture of the skin-> diffuses into the blood capillaries
found in the epidermis of the skin.
●​ The large number of capillaries provide a large surface area + a short distance for
diffusion.
●​ The pumping action of the pseudohearts of the earthworm circulates the blood with
its dissolved oxygen



●​ Cuticle: a waterproof, wax-like layer that covers the body of insects
●​ Tracheal system: System of spiracles and tracheae in the body of the insect for
gaseous exchange.
●​ Spiracles: openings on the outside of an insects’s exoskeleton that lead to the
tracheae
●​ Tracheae: Tubes on the inside of an insect’s body that transports gases to the
different parts of the body
●​ Gills: the breathing organs of a fish
●​ Operculum: bony flap that covers the gills in fish; opens and closes to allow water
over the gills.

Gaseous exchange in locusts

-​ Life on land causes the need for oxygen and the need for water.
-​ Locusts have a waterproof cuticle covered with wax on the outer surface of their
bodies to prevent desiccation.
-​ The cuticle makes their bodies nearly impermeable to gases, so oxygen cannot
diffuse through the body surface.
-​ Instead, insects have a tracheal system for gaseous exchange.
-​ The tracheal system consists of small holes called spiracles in the cuticle through
which gas diffuses into the body.
-​ The spiracles lead to internal air-filled tubes called tracheae and tracheoles.
-​ These trachea carry air directly to respiring tissue, such as wing muscles.