Ch.8 Gas exchange in humans

Question 1

Most organisms obtain energy from the oxidation of food in a process called __________

Answer 1

respiration

Question 2

What is gas exchange?

Answer 2

The exchange of respiratory gases between the cells of an organism and the environment is called gas exchange.

Question 3

How does gas exchange take place in unicellular organisms?

Answer 3

Unicellular organisms are small and therefore have a large surface area to volume ratio. Gas exchange takes place effectively by diffusion across their cell surfaces, which is covered only by a cell membrane.

In other words, the cell membrane works as the respiratory surface.

Question 4

Is diffusion over the body surface an adequate method for gas exchange in multicellular organisms?

Answer 4

No.
∵multicellular organisms are relatively large
∴ small surface area to volume ratio

& most body cells are far from the external environment

Question 5

Human have evolved a _________________ to move air into and out of the body for effective gas exchange.

Answer 5

breathing system

Question 6

The breathing system works closely with the ______________________, which delivers oxygen to all the body cells and removes carbon dioxide from them

Answer 6

circulatory system

Question 7

What features does nostrils and nasal cavity have to condition the incoming air?

Answer 7

• the nostrils are lined with hairs to filter out dust and other particles from the air
• the wall of the nasal cavity is lined with mucus-secreting cells, which secrete mucus. The mucus traps dust particles and bacteria. It moistens the incoming air as well
• The wall of the nasal cavity is also lined with ciliated epithelial cells. The cilia extending out from these cells beat in a wave like manner. This beating action sweeps the mucus towards the throat (pharynx). The mucus is then either swallowed or coughed out.
• the nasal cavity is well supplied with blood capillaries. The blood in the capillaries helps warm the incoming air.

Question 8

What is the pharynx?

Answer 8

The pharynx is a part shared by the breathing system and the digestive system. Both food and respiratory gases pass through it. From the pharynx, air passes into the larynx of the breathing system, while food and drink enter the oesophagus of the digestive system.

Question 9

What happen to the larynx when we swallow?

Answer 9

When we swallow, the larynx rises. A flap of tissue called the epiglottis automatically covers the entrance to the trachea (the glottis). This stops food and drink from entering the trachea, and thus prevents choking.

Question 10

The larynx is also called the voice box. Within the larynx, there are two thin elastic membranes called the ____________________. When air is forced through the vocal cords, they vibrate to produce sound.

Answer 10

vocal cords

Question 11

What’s the use of the C-shapes rings of cartilage in the wall of the trachea?

Answer 11

These cartilage rings keep the trachea open for air to pass through freely. Without the support of the cartilage, the trachea would collapse with the fall in air pressure when we bbreathe in.

The open side of the C-shaped rings is next to the oesophagus. This allows the oesophagus to expand when food passes down it.

Question 12

How are bronchi supported?

Answer 12

By complete rings of cartilage.

Question 13

Does the bronchioles have cartilage?

Answer 13

NO

Question 14

What’s the use of the ciliated epithelial cells and mucus-secreting cells lined in the inner walls of the trachea, bronchi, and some larger bronchioles?

Answer 14

The inner walls of the trachea, bronchi and some larger bronchiles are also lined with ciliated epithelial cells and mucus-secreting cells. The secreted mucus traps dust particles and bacteria in the air. The beating action of the cilia sweeps the mucus upwards towards the phraynx, where the mucus is either swallowed or coughed out.

Question 15

These is a dense network of _____________________ surrounding the air sacs. These capillaries are supplied with blood from the ________________________ and are drained by the ________________________. As blood flows through these capillaries, it exchanges respiratory gaes with air inside the air sacs.

Answer 15

blood capilarries
pulmanoary arteries
pulmonary veins

Question 16

What’s the use of the diaphagm?

Answer 16

It seperates the thoracic cavity from the abdominal cavity.

Question 17

Each lung is enclosed by two ________________. The inner membrane is attached to the lung, while the outer membrane lines the horacic cavity. The narrow space between these two membranes is the _____________________.

Answer 17

pleural membrane
pleural cavity

Question 18

What does the pleural membranes secrete? Why does it secrete that?

Answer 18

The pleural membranes secrete pleural fluid into the pleural cavity to reduce friction between the lungs and the cage during breathing movements.

Question 19

How does oxygen diffuses into the blood?

Answer 19

When we breathe in, fresh air reaches the air sacs. Oxygen in the incoming air dissolves in the water film on the inner surface of the air sacs. As the oxygen concentration of the water film is higher than the blood of the capillaries, oxygen diffuses across the walls of the air sacs and the capillaries into the blood. It then combines with haemoglobin in the red blood cells.

Question 20

How does carbon dioxide diffuses out of the blood?

Answer 20

As the carbon dioxide concentration of the blood is higher than the air in the air sacs, carbon dioxide diffuses across the walls of the capillaries and the air sacs into the air in the air sacs. It is then removed in the air we breathe out (exhaled air)

Question 21

How are the air sacs adpated for gas exchange?

Answer 21

• Air sacs are very numerous. They provide a large surface area for diffusion of gases
• the inner surfaces of the air sacs are moist. They are covered with a film of watery mucus secrete by special cells in the walls of the air sacs. This allows oxygen to dissolve in the water film and diffuse across the walls of the air sacs.
• the walls of the air sac are very thin. They are made up of only one layer of epithelial cells. This provides a short distance for diffusion of gases.
• Air sacs are surrounded by a dense network of blood capillaries. The continuous blood flow readily transports the gases to and from the air sacs. This maintains a steep concentration gradientof gases between the blood and the air sacs, which increases the diffusion of gases.
• the walls of the air sacs lie close to the walls of the blood capillaries, which are also one-cell thick. This reduces the distance that gases need to diffuse.

Question 22

Most cells in the human body are far away from the air sacs where gas exchange takes place. A transport system is needed to transport respiratory gases between the air sacs and cells in body tissues, using _______________ as transport medium

Answer 22

blood

Question 23

___________ is transported by the blood from the air sacs int he lungs to body cells for respiration

Answer 23

oxygen

Question 24

______________________________ produced during respiration is transported by the blood to air sacs in the lungs for removal

Answer 24

carbon dioxide

Question 25

Most oxygen (>98%) transported in the blood is carried by _____________________. The remaning oxygen is transported as ______________ in blood plasma.

Answer 25

red blood cells dissolved oxygen

Question 26

What adaptations does red blood cells have for carrying oxygen?

Answer 26

- red blood cells are packed with haemoglobin molecules. Haemoglobin is an iron-containing protein that can bind with oxygen. It serves as an oxygen carrier. - red blood cells have a biconcave disc shape. This shape provides a larger surface area to volume ratio to facilitate the diffusion of oxygen into and out of the cells. It also shortens the distance for oxygen to reach and leave haemoglobin in the cells. - mature red blood cells do not have a nucleus. This enables them to hold more haemoglobin and thus carry more oxygen

Question 27

How does haemoglobin function in relation to oxygen transport in the body?

Answer 27

When the oxygen concentration is high, such as in the air sacs of the lungs, haemoglobin combines with oxygen to form oxyhaemoglobin. When the oxygen concentration is low, such as in body tissues, oxyhaemoglobin breaks down and oxygen is released.

Question 28

What happens to oxygen in the lungs and how does it affect blood color?

Answer 28

The oxygen concentration in the air sacs is high. This is because when we breathe in, fresh air enters the air sacs. Oxygen in the air sacs thus diffuses into red blood cells. It then binds to haemoglobin, forming oxyhaemoglobin. Oxyhaemoglobin gives the blood its bright red colour. The oxygenated blood is transported to the heart, and is then transported to different body tissues.

Question 29

How does the oxygen function in body tissues?

Answer 29

The body cells continuously take up oxygen from the blood for respiration. The oxygen concentration in body tissues is low. Under a low oxygen concentration, oxyhaemoglobin in red blood cells breaks down into oxygen and haemoglobin. The oxygen then diffuses into the body cells and is used for respiration. After releasing most of its oxygen, the blood becomes deoxygenated and is dark purplish red in colour.

Question 30

How is carbon dioxide transported?

Answer 30

Most carbon dioxide (~70%) is transported as hydrogencarbonate ions in the plasma. The formation and breakdown of hydrogencarbonate ions take place in the red blood cells catalyse by a specific enzyme.

Question 31

How does the carbon dioxide function in body tissues?

Answer 31

The carbon dioxide concentration in body tissues is high, as carbon dioxide is produced continuously by the cells during respiration. When carbon dioxide diffuses into the blood, most of it enters the red blood cells. It then reacts with water in the red blood cells, forming hydrogencarbonate ions. Hydrogencarbonate ions diffuse from the red blood cells into the plasma, and are carried to the air sacs.

Question 32

How does the carbon dioxide function in the air sacs?

Answer 32

The carbon dioxide concentration in the air sacs is low. This is becuase when we breathe out, air is removed from the air sacs. At a low carbon idoxide concentration, the hydrogencarbonate ions in the plasma enter red blood cells, and breakd down into carbon dioxide and water. Carbon dioxide diffuses from the blood into the air sacs, and is then exhaled

Question 33

What is ventilation?

Answer 33

The movement of air into and out of the lungs

Question 34

The act os breathing includes breathing in (inhalation) and breathing out (exhalation). The lungs contain no muscles and are not able to expand on their own. Breathing is brought about mainly by the actions of ___________________________ and the _____________.

Answer 34

Intercostal muscles diaphragm

Question 35

When does inhalation occur?

Answer 35

Inhalation occurs when the pressure in the lungs is lower than atmospheric pressure.

Question 36

When does exhalation occur?

Answer 36

Exhalation occurs when the pressure in the lungs is higher than atmospheric pressure.