Use the Following Information to Answer the Question

question 24

Multiple Choice

Use the following information to answer the question.
Nitrogenase, the enzyme that catalyzes nitrogen fixation, is inhibited whenever free oxygen (O₂) reaches a critical concentration. Consequently, nitrogen fixation cannot occur in cells wherein photosynthesis produces free O₂. Consider the colonial aquatic cyanobacterium, Anabaena, whose heterocysts are described as having "...a thickened cell wall that restricts entry of O₂ produced by neighboring cells. Intercellular connections allow heterocysts to transport fixed nitrogen to neighboring cells in exchange for carbohydrates."
Think about this description of the colonial aquatic cyanobacterium, Anabaena. Which of the following questions below is important for understanding how nitrogen (N₂) enters heterocysts, and how oxygen (O₂) is kept out of heterocysts?

• A) If carbohydrates can enter the heterocysts from neighboring cells via the "intercellular connections," how is it that O₂ doesn't also enter via this route?
• B) If the cell walls of Anabaena photosynthetic cells are permeable to O₂ and carbon dioxide (CO₂), are they also permeable to N₂?
• C) If the nuclei of the photosynthetic cells contain the genes that code for nitrogen fixation, how can these cells fail to perform nitrogen fixation?
• D) If the nuclei of the heterocysts contain the genes that code for photosynthesis, how can these cells fail to perform photosynthesis?

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Definitions:

AASB 138

An Australian Accounting Standards Board standard that prescribes the accounting treatment for intangible assets not covered by other AASB standards.

Research Phase

The research phase is a stage in the development process where efforts are undertaken to acquire new knowledge or understanding without any specific application or usage in mind.

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Knowledge based on scientific methods and empirical evidence, including theories, laws, and facts about the natural world.

AASB 138

The Australian Accounting Standards Board standard that specifies the accounting for intangible assets that are not dealt with specifically in another AASB standard.