Explain rice growth in submerged conditions
Relate aerenchyma, ethanol fermentation in roots and faster stem growth to rice adaptation when roots are submerged.
Section 12.2 · Respiration
A Level; Cambridge International Biology 9700, 2028–2030. Written practice is self-checked; practical investigations need supervised work and human subject-teacher review remains pending.
Before you begin
- ATP transfers energy for cellular work, and enzymes control metabolic reactions.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which low-yield pathway can rice roots use when oxygen is limited?
What you will learn
- Describe aerenchyma development in rice roots
- Explain the roles of fermentation and stem growth during submergence
Build the explanation
When rice roots are submerged, oxygen availability in the soil can be limited. Aerenchyma, air spaces that develop in roots, help gases move within the plant. Root cells can use ethanol fermentation in oxygen-limited conditions to regenerate NAD so glycolysis can continue. Faster stem growth can help shoots reach above the water surface, improving access to air and light. These are the syllabus-limited features used to explain rice growth in submerged conditions.
Apply it carefully
Do not describe fermentation as a high-yield replacement for aerobic respiration; its energy yield per glucose is low. Aerenchyma supports internal gas movement, while stem growth changes the plant's position relative to the water surface. Avoid adding unlisted adaptations as if they were required by this learning outcome.
Pause and explain
How can faster stem growth help a submerged rice plant?
Worked example
What is the role of aerenchyma in submerged rice roots?
Show the worked solution
- Identify what the air spaces allow to move.
- They support gas movement within the plant.
Answer Aerenchyma provides air spaces that help gases move within submerged rice roots.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain how three syllabus features help rice grow when roots are submerged.
Give me a hint
Include air-space development, root metabolism and stem response.
Compare my reasoning
- Aerenchyma forms air spaces that help gases move within roots.
- Ethanol fermentation supports glycolysis under limited oxygen; faster stem growth can help shoots reach above water.
Aerenchyma develops in roots and supports gas movement within the plant. In oxygen-limited roots, ethanol fermentation regenerates NAD for glycolysis. Faster stem growth can help shoots reach above the water surface, improving access to air and light.
Look for these in your work
- Aerenchyma function stated
- Fermentation role stated
- Stem response linked to emergence
A student says root fermentation supplies as much energy as aerobic respiration. Correct this and explain why it may still be useful temporarily.
Give me a hint
Separate pathway yield from NAD recycling.
Compare my reasoning
- Fermentation yields much less energy per glucose.
- It regenerates NAD so glycolysis can continue when oxygen is limited.
Root ethanol fermentation has a much lower energy yield per glucose than aerobic respiration, but it regenerates NAD so glycolysis can continue temporarily when oxygen is limited.
Look for these in your work
- Yield comparison correct
- NAD recycling role stated
- Conditions qualified
A flooded rice plant has aerenchyma but its stem cannot grow quickly. Explain which benefit may be reduced while avoiding a claim that the plant must die.
Give me a hint
Link stem growth to position, not to guaranteed survival.
Compare my reasoning
- Aerenchyma still supports internal gas movement.
- Slower stem growth may delay access of shoots to air and light above the water.
Aerenchyma can still support internal gas movement, but slower stem growth may delay the shoot reaching above water, limiting access to air and light. This evidence alone does not establish that the plant must die.
Look for these in your work
- Aerenchyma role preserved
- Stem-growth benefit identified
- Outcome not overclaimed
Common mistakes
- Calling ethanol fermentation an efficient energy source
- Confusing aerenchyma with an external root opening
- Treating faster stem growth as guaranteed survival
What can you explain now?
Which low-yield pathway can rice roots use when oxygen is limited?
Compare with the explanation
Ethanol fermentation
Fermentation regenerates NAD so glycolysis can continue.
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Make it stick
How do aerenchyma, fermentation and stem growth support rice in submerged conditions?
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