Exchange and transport - GAS EXCHANGE

Question 1

What is Fick’s Law?

Answer 1

Rate of diffusion = (Surface area x change in concentration)/length of diffusion path

Question 2

Why are most exchange surfaces internal to the body?

Answer 2

• Very thin hence would not be supported and are easily damaged
• Site of water and heat loss that could cause dehyration

Question 3

Where does gas exchange occur in humans?

Answer 3

In the alveoli

Question 4

Describe the pathway of oxygen to the alveoli

Answer 4

• Oxygen diffuses across epithelial (outside) cell of alveolus
• Into capillary across endothelial (inside) cells

Question 5

How are the alveoli adapted for efficient gas exchange?

Answer 5

• Walls of capillaries and alveoli are very thin/short diffusion distance
• Large surface area
• RBCs are slowed/more time for diffusion
• RBCs are flattened/reduces diffusion distance
• Ventilation and heart pumping/large concentration gradient maintained

Question 6

Structure to function of the diaphragm

Answer 6

• Dome shaped muscle
• Separates contents of thorax from abdomen
• Controls movement of air in and out of lungs for ventilation

Question 7

Function of ribs?

Answer 7

• Protect the lungs
• Can be moved by intercostal muscles between them

Question 8

Function of intercostal muscles?

Answer 8

• Control movement of air in and out of lungs
• Internal and external work as antagonistic pair

Question 9

Describe the action of the intercostal muscles during inhalation

Answer 9

• External intercostal muscles contract
• Internal intercostal muscles relax

Question 10

Describe the action of the intercostal muscles during exhalation

Answer 10

• External intercostal muscles relax
• Internal intercostal muscles contract

Question 11

Function of pleural membrane?

Answer 11

• Separates thorax from lungs
• Forms a continuous envelope around the lungs, creating an airtight seal

Question 12

Function of pleural fluid?

Answer 12

• Lubricates the surface of the lungs
• So it doesn’t stick to the inside of the chest

Question 13

Describe the process of inspiration in humans

Answer 13

• External intercostal muscles contract
• Internal intercostal muscles relax
• Ribs pulled upwards and outwards/volume in thorax increases
• Diaphragm muscles contract and flatten/volume in thorax increases
• Atmospheric pressure greater than pulmonary pressure so air is drawn into lungs

Question 14

What is the pulmonary ventilation rate?

Answer 14

The total volume of air that is moved into the lungs per minute

Question 15

What is the formula for pulmonary ventilation rate?

Answer 15

PVR = tidal volume x breathing rate

Question 16

What is tidal volume?

Answer 16

The volume of air normally taken in at rest in one breath

Question 17

What is breathing rate?

Answer 17

Number of breaths taken in 1 minute

Question 18

What is vital capacity?

Answer 18

The net volume of air in one breath

Question 19

What is residual volume?

Answer 19

The volume of air in the lungs that does not change/cannot be expelled

Question 20

When we exercise, the pulmonary ventilation rate (PV) increases because we need to supply oxygen more rapidly to the muscles for faster respiration. In what two ways can the PV be increased?

Answer 20

• Deeper breaths for increased tidal volume
• Take more breaths per minute to increase breathing rate

Question 21

How are the gills specialised for efficient gas exchange in fish?

Answer 21

• Counter current mechanism
• Large surface area
• Dense capillary network
• Thin walls

Question 22

What is the counter current mechanism?

Answer 22

• Unidirectional flow of medium-tidal ventilation against transport medium
• Maintains constant concentration gradient across the length of a gill lamellae and so maximised oxygen uptake

Question 23

Why is it important that a continuous flow of water is maintained over the gills?

Answer 23

• Prevents filaments and lamellae sticking together, which would decrease the surface area and reduce gas exchange
• Gas exchange is maintained due to low partial pressure of oxygen in water.

Question 24

What is the mechanism for bony fish to maintain constant flow of water across gills?

Answer 24

• Fish mouth opens and opercular valve shut
• Floor of mouth is lowered
• Water enters due to decreased pressure
• Mouth closes and opercular valve opens
• Floor raised which results in increased pressure
• Increased pressure forces water over the gills

Question 25

What is the benefit to bony fish of the buccal-opercular pump?

Answer 25

The buccal-opercular pump is useful to the fish as they do not need to move around for gas exchange as flow of water is maintained over the gills

Question 26

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them

Answer 26

- Many alveoli increases surface area for increased diffusion - Many capillaries provide large surface area so faster diffusion - Alveoli/capillaries only one cell thick for shorter diffusion distance - High concentration gradient due to dense capillary network maintained for constant diffusion - Moisture in alveoli dissolves gases for faster diffusion

Question 27

What factors limit ability of insects to exchange gases with air?

Answer 27

- Hard exoskeleton made of chitin - Holes in exoskeleton that may contribute to water loss

Question 28

What are the spiracles in insects?

Answer 28

- Site of entry and exit of respiratory gases - Can be opened or closed by sphincters

Question 29

What are the tracheae and tracheoles?

Answer 29

- Trachea are tubes supported by spirals of chitin, hence are impermeable to gas - Tracheoles are minute tubes that contain no chitin and are therefore very permeable to gas

Question 30

What are the 3 ways respiratory gases can move in and out (insects) ?

Answer 30

1. Along a diffusion gradient 2. Ends of tracheoles are filled with water 3. Mass transport

Question 31

Describe and explain passive ventilation

Answer 31

- Oxygen concentration gradient maintained as oxygen is used in aerobic respiration, so more oxygen diffuses in

Question 32

What is abdominal pumping and how does it increase rate of gas exchange?

Answer 32

- Muscle contraction - Raises pressure in body, by decreasing volume -Air is pushed out the body - Air moves down the pressure gradient to atmosphere - Muscles relax, pressure in body falls and air moves in

Question 33

How is water loss reduced in insects?

Answer 33

- Waterproof coating - Smaller surface area:volume ratio to minimise area from which water is lost - Guard cells open and close spiracles

Question 34

Describe 3 ways an insect can increase the rate of gas exchange in its body

Answer 34

- Abdominal pumping - Moisture in tracheoles - More spiracles

Question 35

Explain why insect spiracles are often surrounded by hairs

Answer 35

To prevent loss of water particles out the spiracles by trapping or wafting them.

Question 36

Explain what causes the oxygen concentration in the tracheae to fall when the spiracles are closed (PPQ 2 marks)

Answer 36

- Oxygen used in aerobic respiration - When spiracles are closed, no new oxygen can enter tracheae

Question 37

Explain the movement of oxygen into the gas exchange system of an insect when it is at rest (PPQ 3 marks)

Answer 37

- Spiracles open, and oxygen enters into the tracheae down the concentration gradient - Oxygen used by cells respiring aerobically - More oxygen diffuses in