F4 Biology teaching notes Ch 7: 2nd Term NE 2

Uptake of oxygen by the blood	Removal of carbon dioxide into the air sacs
1      Inhaled air flows into the air sacs. 2      Oxygen in the inhaled air dissolves in the         (1) water film lining the air sacs. 3      Since the oxygen concentration in the water film is (2) lower / higher than that in the blood, oxygen (3) diffuses across the walls of the air sacs and the capillaries into the blood.	1      Since the carbon dioxide concentration in the blood is (4) lower / higher than that in the water film lining the air sacs, carbon dioxide diffuses across the walls of the capillaries and the air sacs into the air in the (5) air sacs. 2      Carbon dioxide is removed from the body when we exhale呼出.

B

What are the adaptive features of air sacs for gas exchange?

                   (Book 1B, p. 7-11)        CE-2009-II, CE-2007-II, CE-2005-I-A Q.4, CE-2004-I Q.1(c)

Feature of air sac	Adaptation
Large in number	Provides a very large (6) surface area for the diffusion of gases
Thin walls (the layer of epithelial cells is (7) one-cell thick)	Reduces the diffusion (8) distance
(9) Moist inner surface	Allows gases to dissolve before diffusing across the walls of the air sacs
Richly supplied with (10) capillaries	Allows rapid transport of gases, which helps maintain a steep (11) concentration gradient of gases between the air sacs and the blood
Lying close to the capillaries	Reduces the (12) diffusion distance

C		What is the difference in composition between inhaled air and exhaled
		air? (Book 1B, p. 7-12)  CE-2003-I Q.1(a)

	Inhaled air	Exhaled air	Reason for the difference
Oxygen	21%	16%	Oxygen in inhaled air diffuses from the air sacs into the blood during gas exchange. It is then used by the body cells for (13) respiration
Carbon dioxide	0.03%	4%	Carbon dioxide produced by body cells during respiration diffuses from the blood into the air sacs during gas exchange.
(14) Nitrogen	78%	78%	It is not used or produced by body cells.
Water vapour	Variable	Saturated	Air is moistened by the (14) mucus lining the respiratory tract and the water film lining the air sacs.
Other gases	1%	1%	They are not used or produced by body cells.

Ø   Exhaled air is warmer than inhaled air because exhaled air is warmed by the blood in the

(13) capillaries.