Photosynthesis and respiration comparedIB MYP Biology: Flashcards

Exam questions on Photosynthesis and respiration compared

1. A sealed glass bottle garden in a flat in Singapore contains soil, several small green plants and a few snails. It has been kept in a bright room for two years without ever being opened, and everything in it is still alive.
   Explain how the gases in the sealed bottle stay balanced so that the plants and snails stay alive.2 marks
2. Large areas of tropical rainforest are being cleared for farmland, and the trees are often burned. Scientists are measuring the effect on the gases in the atmosphere. Every living organism uses oxygen in respiration, yet the oxygen level in the atmosphere has stayed at about 21% for a very long time.
   Explain why the oxygen level in the atmosphere stays roughly constant even though all living organisms use oxygen.2 marks
3. A student investigates respiration in bean seeds using hydrogencarbonate indicator, which is red in normal air, turns yellow when the carbon dioxide level rises and turns purple when it falls. She puts 10 germinating bean seeds on a gauze platform above 10 cm³ of indicator in tube 1, and 10 boiled bean seeds on a gauze platform above 10 cm³ of indicator in tube 2. She seals both tubes with bungs and keeps them in a dark cupboard at 20 °C for four hours. Afterwards the indicator in tube 1 is yellow and the indicator in tube 2 is still red.
   Explain the colour change of the indicator in tube 1.3 marks