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In standard bicarbonate-buffered media for animal cell culture, what carbon dioxide (CO₂) level is typically maintained in the incubator to support proper pH and metabolism?

Difficulty: Easy

2–5% CO₂
1–10% CO₂
10–15% CO₂
15–20% CO₂
0% CO₂ (ambient air only)

Correct Answer: 2–5% CO₂

Explanation:

Introduction / Context:
Most mammalian cell cultures use bicarbonate-buffered media (for example, DMEM, RPMI) and are maintained in CO₂ incubators. CO₂ equilibrates with bicarbonate and water to form carbonic acid, stabilizing pH near the physiological range.

Given Data / Assumptions:

Bicarbonate buffer system is present.
Typical incubator humidity is high and temperature is 37 °C (for human/rodent cells).
We seek the commonly used CO₂ range for stable pH (about 7.2–7.4).

Concept / Approach:
pH control in bicarbonate media depends on the Henderson–Hasselbalch relation: pH is set by the ratio of bicarbonate to dissolved CO₂. Around 5% CO₂ with appropriate bicarbonate concentration yields physiological pH.

Step-by-Step Solution:

Identify the buffer system: bicarbonate/CO₂.Recall standard practice: 5% CO₂ (commonly 4–6%).Select the option that encompasses this range: 2–5% CO₂.

Verification / Alternative check:
Most vendor datasheets recommend 5% CO₂ for bicarbonate-buffered formulations, confirming the 2–5% range as correct.

Why Other Options Are Wrong:

1–10%: overly broad; above about 7–8% would acidify most standard media.10–15% or 15–20%: typically too high and will depress pH.0%: insufficient for bicarbonate buffering; pH drifts upward.

Common Pitfalls:
Using the same CO₂ for all media; HEPES-buffered media can tolerate lower CO₂, but bicarbonate-based media need about 5% CO₂.

In standard bicarbonate-buffered media for animal cell culture, what carbon dioxide (CO₂) level is typically maintained in the incubator to support proper pH and metabolism?

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