Understanding Litmus and its Origin

Litmus is a widely used natural indicator. It is commonly used in chemistry laboratories to test whether a solution is acidic or basic (alkaline). Litmus paper, which is paper impregnated with litmus dye, is a very common form.

The question asks about the biological source from which litmus is derived.

The Source of Litmus: Lichens

Litmus is extracted from certain species of lichens. Lichens are fascinating organisms that are actually a symbiotic association between a fungus and an alga (or cyanobacterium). This unique relationship allows them to survive in harsh environments.

• Specific lichen species, primarily from the genera Roccella, Dendrographa, and Lecanora, are processed to obtain the litmus dye.
• The dye is then used to create litmus solutions or impregnate paper to make litmus paper.

When used as an acid-base indicator, litmus exhibits distinct color changes:

• In acidic solutions (pH < 7), litmus turns red.
• In basic (alkaline) solutions (pH > 7), litmus turns blue.
• In neutral solutions (pH = 7), litmus remains purple (or red/blue depending on the form used).

Why Other Options Are Not the Source of Litmus

Let's consider the other options provided:

• Fungi: While fungi are one component of lichens, litmus is not derived solely from fungi alone. It's a product extracted from the entire lichen organism.
• Bacteria: Bacteria are single-celled microorganisms and are not the source material for litmus indicator.
• Termite: Termites are insects known for eating wood, but they have no connection to the production or derivation of litmus.

Therefore, the correct and specific biological source for litmus is lichens.

Statement Analysis

Let's evaluate the options based on our understanding:

• Option 1: Fungi - Incorrect. While part of lichens, not the sole source.
• Option 2: Lichens - Correct. Litmus is directly derived from certain species of lichens.
• Option 3: Bacteria - Incorrect. Bacteria are not the source of litmus.
• Option 4: Termite - Incorrect. Termites are insects, not related to litmus production.

Based on scientific knowledge, litmus is a natural dye extracted from lichens.

Revision Table: Litmus Key Facts

Additional Information: Acid-Base Indicators

Acid-base indicators are weak acids or weak bases that change color in response to changes in pH. They are essential tools in chemistry for determining the approximate pH of a solution or finding the endpoint of a titration.

• Indicators work because their acidic and basic forms have different colors.
• The color change happens over a specific pH range, known as the indicator's transition range.
• Litmus is one of the oldest and most well-known indicators. Other common indicators include phenolphthalein, methyl orange, and universal indicator (a mixture of several indicators).

Understanding the source and behavior of indicators like litmus is fundamental in studying acids, bases, and pH.