Gas Exchange (3.3.2)

Question 1

How are single-celled organisms adapted for efficient gas exchange?

Answer 1

• They have a large surface area to volume ratio and have a thin membrane that provides a short diffusion pathway
• Gas exchange can take place by diffusion across their body surface, so no gas exchange system needed

Question 2

How does the tracheal system work?

Answer 2

• Air enters the insect through spiracles and travels down the tracheae, which branch into smaller tracheoles, allowing direct gas exchange with cells

Question 3

How are insects adapted for efficient gas exchange?

Answer 3

• Tracheoles have thin walls providing short diffusion pathway
• The large number of tracheoles providing a large surface area

Question 4

How are insects adapted to control water loss?

Answer 4

• They have a small surface area to volume ratio, which reduces the surface are for evaporation
• They have a waterproof exoskeleton
• Spiracles can open and close to control water loss

Question 5

When do the spiracles open and close in insects?

Answer 5

• Spiracles open wider when carbon dioxide levels rise due to respiration
• During rest spiracles close to reduce water loss by evaporation

Question 6

How does muscle contraction in insects affect gas exchange?

Answer 6

• When an insect’s body muscles contract, they squeeze the tracheae, forcing air out
• When the muscles relax, the tracheae expand and air is drawn in
• This helps ventilate the tracheal system, increasing the efficiency of gas exchange

Question 7

How does anaerobic respiration in insects affect gas exchange?

Answer 7

• Lactic acid is produced in muscles during anaerobic respiration, lowering the water potential of surrounding fluid
• This causes fluid to move out of the tracheoles by osmosis
• Air then moves into the tracheoles to replace the lost fluid

Question 8

How are fish adapted for efficient gas exchange?

Answer 8

• Each gill has gill filaments, providing a large surface area. Gill filaments are covered with many lamellae, increasing the surface area further
• Very thin epithelial cells in the lamellae provide a short diffusion pathway
• Countercurrent system maintains a concentration gradient

Question 9

How are leaves adapted for gas exchange?

Answer 9

• Leaves are thin, providing a short diffusion pathway for gases
• Air spaces inside the leaf, allow rapid diffusion of gases to and from mesophyll cells
• A large number of mesophyll cells provide a large surface area, increasing the rate of diffusion

Question 9

When do plants respire and photosynthesise?

Answer 9

• Plants respire all the time. At night, there is a net uptake of oxygen and release of carbon dioxide
• Plants photosynthesise during the day. In daylight, there is a net uptake of carbon dioxide and release of oxygen

Question 9

Explain the countercurrent system in fish

Answer 9

• Blood and water flow in opposite directions across the gill lamellae
• This ensures blood always meets water with a higher oxygen concentration, maintaining a diffusion gradient along the entire length of the lamellae

Question 10

What is transpiration?

Answer 10

The evaporation of water from a plant’s surface

Question 11

What are the factors affecting the rate of transpiration?

Answer 11

• Light intensity
• Temperature
• Humidity
• Air movement

Question 12

How are xerophytes adapted to limit water loss by transpiration?

Answer 12

• Hairs on leaves trap a layer moist air around the stomata, reducing the water potential gradient and decreasing the rate of transpiration
• Curled leaves trap a layer of moist air, reducing the water potential gradient and decreasing the rate of transpiration
• Sunken stomata trap a layer of moist air in pits, reducing the water potential gradient and decreasing the rate of transpiration.
• [Thick waxy cuticle forms a waterproof barrier, creating a longer diffusion pathway and decreasing the rate of transpiration]

Question 13

How are the alveoli adapted for efficient gas exchange?

Answer 13

• Large number and rounded shape provide a very large surface area
• Alveolar epithelium consists of thin, flattened cells providing a short diffusion pathway
• Each alveolus is surrounded by a dense capillary network that maintains a steep concentration gradient by constantly removing oxygen and bringing in carbon dioxide

Question 14

Describe the gas exchange mechanism in mammals

Answer 14

• As you breathe in, air enters the trachea
• Splits into 2 bronchi
• Splits into smaller bronchioles
• Leads to alveoli
• The diaphragm, internal and external intercostal muscles work together to allow ventilation

Question 15

What are the two cell layers separating the blood and air?

Answer 15

A single layer of epithelial cells, the alveolar wall
A single layer of endothelial cells, the capillary wall

Question 16

What happens during inspiration?

Answer 16

• Diaphragm muscle contracts and external intercostal muscles contract
• The internal intercostal muscles relax
• This causes the volume of the thoracic cavity to increase
• The pressure inside the lungs decrease below atmospheric pressure
• Air enters from higher atmospheric pressure outside the lungs to lower atmospheric pressure inside the lungs
• Is an active process

Question 17

What happens during expiration?

Answer 17

• Diaphragm muscle relaxes and external intercostal muscles relax
• The internal intercostal muscles contract
• This causes the volume of the thoracic cavity to decrease
• The pressure inside the lungs increase above atmospheric pressure
• Air leaves from higher pressure inside the lungs to lower atmospheric pressure outside the lungs
• Is a passive process

Question 18

What is the formula of pulmonary ventilation?

Answer 18

• pulmonary ventilation = tidal volume x ventilation rate