IB DP Biology- D4.3 Climate change- IB Style Questions For HL Paper 1A -FA 2025
▶️ Answer/Explanation
✅ Answer: (A) The burning of fossil fuels, releasing greenhouse gases into the atmosphere.
Question
Which gas is the main contributor to the greenhouse effect?
▶️Answer/Explanation
- Water vapour is the most abundant and significant greenhouse gas. It acts as a feedback mechanism: as the Earth’s temperature rises, more water vapour is evaporated, which then enhances the greenhouse effect.
- Although human activities don’t directly release much water vapour, they increase the concentration of other greenhouse gases, which leads to higher temperatures and subsequently more water vapour in the atmosphere.
Breakdown of the gases:
A. Ozone: Ozone plays a role in the greenhouse effect but is less significant compared to water vapour. It primarily absorbs UV radiation in the stratosphere.
B. Methane: Methane is a potent greenhouse gas but is present in much lower concentrations than water vapour.
C. Nitrogen oxide: Nitrogen oxides contribute to warming but have a lesser effect than the primary greenhouse gases like water vapour and methane.
Question
The graph shows atmospheric oxygen levels over time.
About 2.5 billion years ago, a significant rise in atmospheric oxygen occurred. What was the cause of this rise?
A. Photosynthesis by non-vascular land plants
B. Photosynthesis by vascular land plants
C. Oxygen produced by photosynthetic bacteria being released from the ocean into the atmosphere
D. Volcanic activity
▶️Answer/Explanation
Answer: C. Oxygen produced by photosynthetic bacteria being released from the ocean into the atmosphere
Explanation:
- The significant rise in atmospheric oxygen about 2.5 billion years ago is primarily attributed to the oxygen produced by photosynthetic bacteria, particularly cyanobacteria.
- These bacteria, through photosynthesis, began to release oxygen into the atmosphere.
- This event, known as the Great Oxygenation Event, dramatically increased oxygen levels in the atmosphere and set the stage for the evolution of aerobic organisms.
Other options are incorrect:
A. Photosynthesis by non-vascular land plants: While photosynthesis by plants later contributed to oxygen production, land plants evolved much later and were not the primary source of the rise in oxygen 2.5 billion years ago.
B. Photosynthesis by vascular land plants: Similarly, vascular plants came much later in Earth’s history and were not responsible for the early rise in oxygen.
D. Volcanic activity: Volcanic activity can release gases like carbon dioxide and sulfur dioxide, but it does not significantly contribute to the increase in atmospheric oxygen.