Respiration Ex

1. Compare and contrast how the structure of the leaves in plants and the lungs in mammals allow them to be effective gas exchange surfaces.

Similarities between lungs and leaves as gas exchange surfaces:
1. Large surface area to volume ratio for rapid diffusion of gases.
2. Layer of moisture lining both the inside of the alveolar wall and the outside of mesophyll cells where gases can dissolve.
3. Both are thin structures: The leaf is only made up of a few layer of cells, while the alveolar walls are one-cell thick, reducing diffusion distance and hence increase rate of diffusion of gases into the cells of the leaf and blood.
4. Presence of air spaces in both lungs (alveoli) and leaves (intercellular air spaces) where air moves in and out of these spaces and then into the cells or blood.

Differences between lungs and leaves:
1. Lungs have capillaries which transport oxygen in blood away, and bring in more carbon dioxide, maintaining a diffusion gradient, while leaves do not have capillaries.
2. Air enters the alveoli via branching airways while air enters the leaf via openings known as stomata.
3. Movement of air into and out of the alveoli is due to breathing movements brought about by the action of the intercostal muscles, ribcage and diaphragm, where air flows in and out due to a pressure gradient, while air movement in the leaves is due to diffusion of gases through the stomatal openings down a concentration gradient.

2. The two graphs show the oxygen uptake and the lactic acid concentration in the blood of a man before, during and after a short period of physical exercise.

(a)(i) Explain the increase in lactic acid concentration in the blood at the beginning of exercise. [2]

(ii) Write a word equation for the production of this lactic acid. [1]

(b)(i) State the biological term used to represent the shaded area on graph A. [1]

(ii) Explain why the volume of oxygen in the shaded region is related to the amount of lactic acid in the blood. [2]

(c)(i) Describe the effect of lactic acid during exercise. [1]

(ii) Suggest why this lactic acid is not excreted out of the body? [1]

(d) Name another organism, besides the human being, which produces lactic acid and explain why the organism produces it. [1]

(a) (i) Sufficient oxygen cannot be delivered to the muscles fast enough to keep pace with the requirement for oxygen for aerobic respiration;
Cells respire anaerobically producing lactic acid which accumulates and diffuse into the blood stream;
(ii) Glucose –(lack of oxygen)→ lactic acid + small amounts of energy;

(b) (i) Oxygen debt;
(ii) Lactic acid is toxic to the body cells and needs to be converted to glucose;
The required volume of oxygen shown by the shaded region is used to oxidise lactic acid to produce energy to convert remaining lactic acid into glucose;

(c) (i) It causes muscle fatigue;
(ii) It contains a large amount of unutilised energy which would be lost if excreted;

(d) Any ONE situation there is absence of oxygen, hence organism carries out anaerobic respiration producing lactic acid:
e.g. Mammals which dive for long periods (whales, seals); muscles of any named mammal during strenuous activity; lactobacillus during yoghurt and cheese production; Reject mention of yeast (produces ethanol).