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AQA a-level biology 🧬🔬 > Exchange and transport - GAS EXCHANGE > Flashcards

Exchange and transport - GAS EXCHANGE Flashcards

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1
Q

What is Fick’s Law?

A

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

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2
Q

Why are most exchange surfaces internal to the body?

A
  • Very thin hence would not be supported and are easily damaged
  • Site of water and heat loss that could cause dehyration
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3
Q

Where does gas exchange occur in humans?

A

In the alveoli

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4
Q

Describe the pathway of oxygen to the alveoli

A
  • Oxygen diffuses across epithelial (outside) cell of alveolus
  • Into capillary across endothelial (inside) cells
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5
Q

How are the alveoli adapted for efficient gas exchange?

A
  • 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
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6
Q

Structure to function of the diaphragm

A
  • Dome shaped muscle
  • Separates contents of thorax from abdomen
  • Controls movement of air in and out of lungs for ventilation
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7
Q

Function of ribs?

A
  • Protect the lungs
  • Can be moved by intercostal muscles between them
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8
Q

Function of intercostal muscles?

A
  • Control movement of air in and out of lungs
  • Internal and external work as antagonistic pair
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9
Q

Describe the action of the intercostal muscles during inhalation

A
  • External intercostal muscles contract
  • Internal intercostal muscles relax
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10
Q

Describe the action of the intercostal muscles during exhalation

A
  • External intercostal muscles relax
  • Internal intercostal muscles contract
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11
Q

Function of pleural membrane?

A
  • Separates thorax from lungs
  • Forms a continuous envelope around the lungs, creating an airtight seal
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12
Q

Function of pleural fluid?

A
  • Lubricates the surface of the lungs
  • So it doesn’t stick to the inside of the chest
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13
Q

Describe the process of inspiration in humans

A
  • 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
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14
Q

What is the pulmonary ventilation rate?

A

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

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15
Q

What is the formula for pulmonary ventilation rate?

A

PVR = tidal volume x breathing rate

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16
Q

What is tidal volume?

A

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

17
Q

What is breathing rate?

A

Number of breaths taken in 1 minute

18
Q

What is vital capacity?

A

The net volume of air in one breath

19
Q

What is residual volume?

A

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

20
Q

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?

A
  • Deeper breaths for increased tidal volume
  • Take more breaths per minute to increase breathing rate
21
Q

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

A
  • Counter current mechanism
  • Large surface area
  • Dense capillary network
  • Thin walls
22
Q

What is the counter current mechanism?

A
  • 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
23
Q

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

A
  • 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.
24
Q

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

A
  • 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
25
Q

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

A

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

26
Q

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

A
  • 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
27
Q

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

A
  • Hard exoskeleton made of chitin
  • Holes in exoskeleton that may contribute to water loss
28
Q

What are the spiracles in insects?

A
  • Site of entry and exit of respiratory gases
  • Can be opened or closed by sphincters
29
Q

What are the tracheae and tracheoles?

A
  • 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
30
Q

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

A
  1. Along a diffusion gradient
  2. Ends of tracheoles are filled with water
  3. Mass transport
31
Q

Describe and explain passive ventilation

A
  • Oxygen concentration gradient maintained as oxygen is used in aerobic respiration, so more oxygen diffuses in
32
Q

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

A
  • 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
33
Q

How is water loss reduced in insects?

A
  • Waterproof coating
  • Smaller surface area:volume ratio to minimise area from which water is lost
  • Guard cells open and close spiracles
34
Q

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

A
  • Abdominal pumping
  • Moisture in tracheoles
  • More spiracles
35
Q

Explain why insect spiracles are often surrounded by hairs

A

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

36
Q

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

A
  • Oxygen used in aerobic respiration
  • When spiracles are closed, no new oxygen can enter tracheae
37
Q

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

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

AQA a-level biology 🧬🔬 (32 decks)

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