3.3.2 Gas exchange

Question 1

Describe gas exchange in single-celled organisms

Answer 1

1. Diffusion is the main mode of exchange of material for single-celled organisms.
   They use diffusion to absorb and release gases.
2. Due to their small size, single-celled organisms have a high surface area where
   gas exchange can occur. They also developed a thin surface which make the
   diffusion pathway shorter.

Question 2

Describe the gas exchange mechanism in insects

Answer 2

1. Insects developed a tracheal system for gas exchange.
2. Trachea contains pores in its surface called spiracles. It is through these
   spiracles that air moves.
3. Oxygen moves into the cell, down a concentration gradient (concentration of
   oxygen outside the cell is higher than inside the cell).
4. To reach individual cells of the insect’s body, the trachea branch off into smaller
   tracheoles.
5. Like oxygen, carbon dioxide also moves down a concentration gradient, from the
   inside of the cell, to the spiracles. Eventually, carbon dioxide will be released into
   the atmosphere.
6. Rhythmic abdominal movements facilitate the moving in and out of air in the
   spiracles.

Question 3

Describe the gas exchange mechanism in fish

Answer 3

1. Since fish live underwater, it is much harder to obtain oxygen from the
   environment because of the lower oxygen concentration in water than in air.
2. Fish developed gills which serve as the exchange organ. The gills contain thin
   plates, called gill filaments. These thin plates increase the surface area for gas
   exchange.
3. To increase the surface area further, tiny structures called lamellae are present in
   the surface of the gill filaments.
4. The respiratory system of a fish is well connected to the circulatory system to
   facilitate transport of material. A lot of blood capillaries are contained in the
   lamellae.
5. Movement of gases is from high concentration to low concentration.
6. A counter-current system happens in the lamellae to facilitate blood flow in one
   direction, and the water flow in the opposite direction. In this way, transfer of
   oxygen across a concentration gradient (from high oxygen-containing water to the
   low oxygen-containing blood) becomes more efficient.

Question 4

Define pulmonary ventilation

Answer 4

Pulmonary ventilation happens by inhaling or breathing in air through a nasal
cavity. As the air passes through the cavity it is warmed to body temperature

Question 5

What do the lungs contain to facilitate gas exchange ?

Answer 5

The lungs contain a number of parts that facilitate the gas exchange

Question 6

What is the trachea , bronchi and bronchioles function ?

Answer 6

○ Trachea - It functions to funnel the inhaled air into the lungs, while also
facilitating the removal of inhaled air out of the lungs.
○ Bronchi - These are smaller passages where air enters the lungs from the
trachea.
○ Bronchioles - The bronchi further divide into smaller, and smaller passages
called bronchioles.

Question 7

What is the function of alveolar ducts and alveoli ?

Answer 7

○ Alveolar ducts - At the end of
each bronchiole, grape-like
structures are present called
alveolar ducts. Each of these
ducts contain about a hundred
alveolar sacs. Each of these sac
contains about 30 alveoli.
○ Alveoli - These structures
contain thin-walled cells that are
directly connected to capillaries.
Oxygen are transferred down a
concentration gradient from the
alveoli, into the blood cells. At
the same time, carbon dioxide is
transferred from the blood cells
to the alveoli.

Question 8

How do dicotyledonous plants work ?

Answer 8

1. Diffusion is the main mode of
   exchange of material for single-celled
   organism. They use this means to
   absorb and release gases.
2. Due to their small size, single-celled
   organisms have a high surface area
   where gas exchange can occur. They
   also developed a thin surface which
   make the diffusion pathway shorter.
3. There are mesophyll cells (middle
   leaf) which serves for gas exchange.
   These cells contain pores called
   stomata that open to allow gas
   exchange, and close to control loss of
   water. The closing and opening of
   these pores is controlled by guard
   cells.

Question 9

What do plant cells use to minimize water loss ?

Answer 9

Stomata closed by guard cells
Swollen when water enters causes them to open
Dehydrated guard cells lose water become flaccid stomata close

Question 10

What features do xerophytes have to prevent water loss ?

Answer 10

○ To prevent further loss of water, they
have hairs in their epidermis to trap
moist air around the stomata.
○ The stomata are sunken in pits capable
of trapping moist air. This
configuration also lowers the
concentration gradient of water
between the air and the leaf, lessening
the tendency for water to evaporate
away.
○ Relatively, these xerophytes have a
lower number of stomata to lessen
sites where water can escape.
○ The leaves have a waxy cuticle to
reduce evaporation rate.