(A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

Question

Q. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true. Assertion (A) : The stirrer facilitates the even mixing of oxygen availability in a bioreactor. Reason (R) : Stirred-tank bioreactors generally have a flat base.

CBSECBSE Class XII Board 2024MCQ· 1mImportance★★★★★

🔒 Locked · start free trial →

You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.

Start your 14-day free trial to unlock the full solution →

Concept understanding — Bioreactor Scale-Up

Imagine you have a small kitchen blender that makes a perfect smoothie for one person. Now, your job is to make the same smoothie for a thousand people — but you can only use a giant industrial vat. You cannot just multiply every ingredient by a thousand and press the same button. The giant vat will not mix the same way; the heat will build up differently; the blades will not reach every corner. The smoothie might come out burnt, lumpy, or uneven.

That, in essence, is the core problem of bioreactor scale-up.

The Everyday Intuition

A bioreactor is a large, controlled tank where living cells (like yeast, bacteria, or animal cells) are grown to produce something useful — medicines, vaccines, enzymes, or even beer. In a lab, scientists work with tiny flasks or small reactors (a few litres). They figure out the perfect conditions: the right temperature, the right amount of oxygen, the right stirring speed, and the right nutrients.

But when you want to produce that medicine for millions of patients, you cannot just use a thousand tiny flasks. You need one giant reactor — maybe 10,000 litres or more. The challenge is: how do you take the small-scale success and make it work at a large scale without ruining the product?

This is bioreactor scale-up. It is the art and science of transferring a biological process from a small, well-controlled lab environment to a large, industrial-sized reactor while keeping the cells happy and the product quality identical.

The Precise Meaning

In technical terms, bioreactor scale-up is the process of increasing the volume of a bioreactor while maintaining the same environmental conditions that the cells need to grow and produce the desired substance. It is not about simply making everything bigger. It is about recreating the same micro-environment for every single cell, even when the reactor is a hundred times larger.

Why can't you just scale up by multiplying? Because physical forces do not scale linearly. Consider these three key problems:

Mixing: In a small flask, a gentle swirl mixes everything instantly. In a giant tank, the liquid at the top may be perfectly stirred, but the liquid near the bottom may be stagnant. Cells at the bottom might starve or suffocate.
Oxygen transfer: Cells need oxygen to breathe. In a small reactor, oxygen dissolves easily from the air. In a large reactor, the surface area relative to volume is much smaller. You need to pump in air and stir vigorously to get enough oxygen to the cells — but too much stirring can physically tear the cells apart.
Heat removal: Cells generate heat as they grow. In a small flask, the heat escapes through the glass walls. In a large tank, the heat builds up inside. Without proper cooling, the temperature can rise and kill the cells.

Important

The central rule of scale-up is: You cannot keep all parameters the same. You must choose one or two key parameters to hold constant (like the rate of oxygen transfer or the mixing time) and let others change. The choice depends on what the cells need most.

Why It Matters (The Real-World Impact)

Bioreactor scale-up is not a theoretical exercise. It is the bridge between a lab discovery and a life-saving product reaching the market. If scale-up fails, the product fails — and that can mean millions of rupees wasted, or worse, a medicine shortage.

Consider the production of insulin, vaccines, or monoclonal antibodies. These are made by genetically engineered cells. The process that works in a 5-litre lab reactor must be successfully transferred to a 10,000-litre production reactor. If the cells stop producing the protein at large scale, or if the protein gets contaminated, the entire batch is lost.

The NCERT textbook (Class 12 Biology, Chapter 11: Biotechnology – Principles and Processes) puts it this way: "The process of scaling up is a critical step in the commercialisation of a biotechnological product. It involves moving from a laboratory-scale process to a pilot plant and then to a full-scale production plant."

The Steps in a Nutshell

Scale-up is usually done in stages, not in one giant leap: …

Start your 14-day free trial to unlock the full solution →

The stirrer in a bioreactor ensures uniform oxygen distribution, but the reason given about a flat base is factually incorrect — stirred-tank bioreactors typically have a curved or rounded base, not a flat one.

Let’s think about what a bioreactor actually does. In any large-scale fermentation or cell culture process, the goal is to create a controlled environment where microorganisms or cells can grow and produce a desired product — be it an antibiotic, an enzyme, or a vaccine. One of the biggest challenges inside a bioreactor is making sure every single cell gets enough oxygen. Oxygen is poorly soluble in water, and in a large tank, it tends to stay near the surface unless something actively pushes it down and spreads it around. That’s where the stirrer — also called an impeller — comes in.

The stirrer’s job is to keep the contents of the bioreactor well-mixed. It breaks up air bubbles into smaller ones, increases the surface area for oxygen transfer, and circulates the liquid so that oxygen-rich medium reaches cells at the bottom and sides of the tank. Without proper stirring, cells near the top would get plenty of oxygen while those deeper down would suffocate — leading to uneven growth and poor yields. So Assertion (A) is absolutely correct: the stirrer does facilitate even mixing of oxygen availability. …

Start your 14-day free trial to unlock the full solution →

Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2026Set A1 markMCQ
$Q. In which of the following is the large volume of culture processed to produce appreciable quantities of products?$
(a) Distillation unit
(b) Bioreactor
(c) PCR
(d) Electrophoresis unit
›Reveal solutionSolution

A bioreactor processes large volumes of culture; the correct option is (b).

A bioreactor is a large vessel (often thousands of litres) in which raw materials are biologically converted into specific products (enzymes, proteins, etc.) using microbial, plant, animal or human cells. It provides optimum conditions — temperature, pH, substrate, salts, vitamins, oxygen — for large-scale produc …

Start your 14-day free trial to see the full solution →
CBSE 2026Set ANNUAL1 mark
$Q. Large scale production of biotechnological products involve use of ............ .$
›Reveal solutionSolution

Large-scale production of biotechnological products (enzymes, hormones, antibiotics, etc.) requires bioreactors, which provide optimum growth conditions for large volumes (100–1000 litres) of culture.

Once a gene of interest is cloned into a suitable host, the host cells must be grown on a large scale to produce the desired biotechnological product commercially. This is done in bioreactors, vessels in which raw materials are biologically converted by microbes, plant, animal, or human cells into specific products, …

Start your 14-day free trial to see the full solution →
CBSE 2026Set ANNUAL1 markMCQ
$Q. Assertion (A) : In bioreactors, raw materials are biologically converted into desired products. Reason (R) : In bioreactors optimum growth conditions for microbes such as temperature, pH, substrate, salt etc. are available.$
(a) Assertion (A) and Reason (R) both are true and Reason (R) is the correct explanation of Assertion (A).
(b) Assertion (A) and Reason (R) both are true, but Reason (R) is not the correct explanation of Assertion (A).
(c) Assertion (A) is true, but Reason (R) is false.
(d) Assertion (A) is false, but Reason (R) is true.
›Reveal solutionSolution

Bioreactors do biologically convert raw materials into desired products (A), and they are able to do so specifically because they maintain the optimum growth conditions (temperature, pH, substrate, salts, etc.) microbes/cells need (R), which correctly explains A.

A bioreactor is a large vessel in which raw materials are biologically converted, using microbial, plant, animal, or human cells (or their enzyme systems), into specific products such as enzymes, hormones, antibodies or antibiotics — confirming Assertion (A). This large-scale, efficient conversion is possible precisely because a bioreactor provides and continuously monitors the optimum conditions …

Start your 14-day free trial to see the full solution →
CBSE 2025Set ANNUAL1 mark
$Q. Simple shake flasks are more effective than stirred-tank bioreactors for producing large quantities of recombinant proteins.$
›Reveal solutionSolution

Small-scale culture in shake flasks cannot supply enough product; large-scale industrial production of proteins/biomolecules needs bioreactors with controlled aeration, mixing and nutrient/oxygen supply.

When genes are cloned to produce large quantities of useful proteins such as recombinant insulin, growth hormone or industrial enzymes, the desired gene is expressed in a suitable host organism (bacteria/yeast) which is then grown in large volumes (typically 100–1000 litres) of culture medium to obtain a sufficiently large biomass/yield of the product. Small shake flasks used in the laboratory can only support very limited culture volumes and provide poor control over oxygen, nutrients, pH and temperature, so they are unsuitable for large-scale product …

Start your 14-day free trial to see the full solution →
CBSE 2024Set 57/3/11 markMCQ
$Q. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true. Assertion (A) : The stirrer facilitates the even mixing of oxygen availability in a bioreactor. Reason (R) : Stirred-tank bioreactors generally have a flat base.$
›Reveal solutionSolution

The stirrer in a bioreactor ensures uniform oxygen distribution, but the reason given about a flat base is factually incorrect — stirred-tank bioreactors typically have a curved or rounded base, not a flat one.

Let’s think about what a bioreactor actually does. In any large-scale fermentation or cell culture process, the goal is to create a controlled environment where microorganisms or cells can grow and produce a desired product — be it an antibiotic, an enzyme, or a vaccine. One of the biggest challenges inside a bioreactor is making sure every single cell gets enough oxygen. Oxygen is poorly soluble in water, and in a large tank, it tends to stay near the surface unless something actively pushes it down and spreads it around. That’s where the stirrer — also called an impeller — comes in.

The stirrer’s job is to keep the contents of the bioreactor well-mixed. It breaks up air bubbles into smaller ones, increases the surface area for oxygen transfer, and circulates the liquid so that oxygen-rich medium reaches cells at the bottom and sides of the tank. Without proper stirring, cells near the top would get plenty of oxygen while those deeper down would suffocate — leading to uneven growth and poor yields. So Assertion (A) is absolutely correct: the stirrer does facilitate even mixing of oxygen availability. …
Start your 14-day free trial to see the full solution →
CBSE 2021Set D1 markMCQ
$Q. Bio-reactors in optimal conditions produce$
(a) Product
(b) Organism
(c) Medium
(d) All of these
›Reveal solutionSolution

A bioreactor under optimal conditions yields the desired product.

A bioreactor is a large vessel in which raw materials are biologically converted into specific products (enzymes, proteins, antibiotics, etc.) using microbial, plant, animal or human cells. It maintains optimal conditions of temperature, pH, substrate, salts, vitamins and oxygen (e.g. through a stirred-tank or sparged system). Th …

Start your 14-day free trial to see the full solution →
CBSE 2019Set ANNUAL1 mark
$Q. Define bioreactor.$
›Reveal solutionSolution

A bioreactor is the large-scale controlled vessel where microbes/cells are cultured to manufacture a biotechnological product commercially.

A bioreactor is a vessel in which raw materials are biologically converted, by living cells or their enzymes, into specific products, or in which a single cell/organism is multiplied to generate large quantities of biomass. Unlike a small laboratory flask culture, a bioreactor is designed and engineered to provide the most favourable, tightly controlled growth conditions — including optimum temperature, pH, substrate (nutrient) concentration, oxygen supply (aeration) and adequate mixing/agitation — for the specific culture involved, and to do so on a large, i …

Start your 14-day free trial to see the full solution →
CBSE 2019Set ANNUAL1 markMCQ
$Q. Bio reactors provide optimal conditions to produce desired-$
(a) Product
(b) Organism
(c) Medium
(d) All of these
›Reveal solutionSolution

Bioreactors give optimal conditions to maximise the desired product.

A bioreactor is a vessel in which raw materials are biologically converted into specific products (enzymes, antibiotics, proteins, etc.) using microbes, plant or animal cells. It supplies optimal growth conditions — temperature, pH, dissolv …

Start your 14-day free trial to see the full solution →

🎓Unlock everything free for 14 days

Unlock everything free for 14 days