You're viewing 2 free preview questions for Biology HL — subscribe to unlock 78 more, plus the Full Question Bank, Mock Papers & Worksheets.Upgrade

Gas Exchange · Paper 2 — Free Biology HL Practice Questions

What this topic covers

This theme is built on one repeated argument: structure exists because it does a job, and you can predict the job from the structure. Examiners test this exact logic at every scale — a motor protein's shape tells you which way it walks a microtubule, a red blood cell's missing nucleus tells you why it can pack more haemoglobin, a gill's countercurrent geometry tells you why it out-performs a lung-style parallel flow. Several chunks here — muscle and motility, enzyme kinetics, endosymbiotic theory, detailed phloem loading — exist only on the HL paper, and they're flagged below. Get the mechanism words right (troponin, not tropomyosin; ATP-binding, not hydrolysis) because that's where the marks actually sit.

Read the full Form and Function lesson notes →

1MasterySAQ-SRespiratory structures in animals and plants10 marksPaper 2~15 min

The shows a section through a human lung alveolus and a leaf mesophyll cell, both sites of gas exchange.

(a)

State one structural feature of the alveolus wall that reduces diffusion distance. [1 mark]

(b)

Explain how the arrangement of alveoli in the lung increases the rate of gas exchange. [2 marks]

(c)

The partial pressure of oxygen (

pO_2

) in the alveolar air is

13.3\,\text{kPa}

, and in the blood plasma entering the alveolar capillaries it is

5.3\,\text{kPa}

. The alveolar membrane has a surface area of

70\,\text{m}^2

and a thickness of

0.5\,\mu\text{m}

. Using Fick's law:

\text{rate of diffusion} = \frac{D \times A \times \Delta p}{t}

where the diffusion constant

D = 2.0 \times 10^{-5}

(arbitrary units), calculate the rate of oxygen diffusion across the alveolar membrane. Give your answer in arbitrary units. [3 marks]

(d)

A patient with pulmonary fibrosis has alveolar membrane thickness increased to

2.0\,\mu\text{m}

and effective surface area reduced to

40\,\text{m}^2

. Using your answer from (c), calculate the ratio of the healthy diffusion rate to the fibrotic diffusion rate, and hence evaluate the impact of pulmonary fibrosis on oxygen uptake. [4 marks]

Solutions

2MasterySAQ-SRespiratory structures in animals and plants5 marksPaper 2~8 min

A locust (an insect) and a human both use gas exchange systems — a tracheal system and lungs respectively.

(a)

State two ways in which the structure of the insect tracheal system differs from the human lung system. [2 marks]

(b)

In the locust, the tracheal tubes end in fluid-filled tracheoles. During intense activity, the fluid is withdrawn into the body tissues. Explain why this withdrawal increases the rate of oxygen delivery to muscle cells. [2 marks]

(c)

The tracheal system is highly efficient for gas exchange in small insects but becomes a limiting factor as body size increases. Explain why increasing body size reduces the effectiveness of the tracheal system for oxygen delivery. [1 mark]

Solutions

Questions 3-80

Unlock these questions with Premium

That's every free question here — 2 of 80.

+78 more questions, plus Mock Papers & Worksheets, are waiting in Premium.

Upgrade