2004 SPM Sample answers

a) An athlete has just completed a 400 metre track event. His leg muscles are painful due to muscle fatigue. The athlete then carries out the following actions.

· Wears a track suit

· Takes a few long deep breaths

· Walks freely as a ‘cooling down’ activity.

Explain why the athlete carries out these actions.

b) Human and fish respiratory systems are adapted to function in their respective habitats. Compare and explain the adaptations.

Answer

a) The athlete wears a track suit so that there is no sudden decrease in temperature in his muscles.

A sudden decrease in temperature will cause the accumulation of lactic acid and muscles pain/cramp.

He draws a deep breath several times to oxidize lactic acid that has been accumulated and pays back the oxygen debt.

He walks freely so that his muscles take time to oxidize 1/6 of lactic acid to carbon dioxide, water and energy and 5/6 of the lactic acid is converted back to glucose.

b)

	Human	Fish
Organ	Human’s respiratory structure is the lungs	Fish’s respiratory structure is the gills
Habitat	Human lives on land	Fish lives in the water
Function	Lungs do not need a medium to function	Gills need flow of water through the gills for gaseous exchange
Adaptation	Human lungs have a lot of alveoli and covered with a large network of blood capillaries. Gaseous exchange occur by diffusion through the alveoli	Water is drank in and flows through the gills for absorption of oxygen to blood capillaries which are cross linked with the filaments of gills. Then water flows out through the operculum and absorbs carbon dioxide from the blood capillaries to the water to be released
Characteristics	Total surface area is big with 700 million alveoli/ many alveoli to increase total surface area for diffusion Thin alveolar wall which helps in the diffusion of gases, The wall of the alveolus is moist whereby respiratory gases can dissolve in it, The alveolus is well supplied by blood capillaries to facilitate diffusion and transportation of the gases.	Has thin epithelial wall of gill filaments to facilitate diffusion of gases. Many plate like projections (lamella) at gill filaments to increase the total surface area for diffusion A network of blood capillaries in the gill filaments to facilitate diffusion and transportation of the gases.