Which gas is produced by plants at night?

Appeared in: MNS 2015

Explanation

Plants perform cellular respiration continuously, both day and night, to generate energy for survival.
Cellular respiration consumes oxygen and releases carbon dioxide as a waste product.
At night, in the absence of sunlight, photosynthesis ceases, so there is no oxygen production.
Therefore, the net gas produced by plants at night is carbon dioxide from the ongoing process of respiration.

Option A: Oxygen is the primary gas produced during photosynthesis, a process that requires sunlight and therefore does not happen at night.
Option C: Plants absorb nitrogen compounds from the soil through their roots to build essential molecules like proteins and DNA. They do not produce or release nitrogen gas into the atmosphere.
Option D: Hydrogen gas is not a product of the standard metabolic processes of photosynthesis or respiration in plants.

Clinical Relevance

Nursing practice connection: Knowing Plant Metabolism: Photosynthesis and Cellular Respiration helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Understanding basic biological processes like plant respiration is part of the general scientific literacy that forms the foundation for a healthcare professional's knowledge.
This knowledge helps debunk common myths, such as the belief that having plants in a hospital room or bedroom at night is dangerous. The amount of CO2 produced is negligible and poses no risk to human health.
What if the question asked about the net gas produced over a full 24-hour cycle? The answer would be Oxygen. A healthy, growing plant produces significantly more oxygen during daytime photosynthesis than it consumes during 24 hours of respiration.

How to Approach the Question

First, identify the key components of the question: the action ('produced'), the subject ('plants'), and the timing ('at night').
Recall the two main metabolic processes in plants: photosynthesis and cellular respiration.
Differentiate the conditions for each process. Photosynthesis requires sunlight, so it only occurs during the day.
Recognize that cellular respiration is a continuous process, happening both day and night, to provide the plant with a constant supply of energy.
Compare the gas exchange for each process: Photosynthesis consumes CO2 and produces O2. Respiration consumes O2 and produces CO2.
Conclude that at night, with photosynthesis halted, the only active process producing a gas is respiration, which releases carbon dioxide.

Concept Tested & Keywords

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E6 Parks TextBook of Preventive & Social Medicine part 2 — Subpart B (pp 233-449 of 464) p. 48-50

Practise the full MNS 2015

Attempt every question from this paper in a timed mock, then review the full solution for each one.