biology

Potato dextrose agar

Potato dextrose agar is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Potato dextrose agar rather than just read about it. In short: Potato dextrose agar (BAM Media M127) and potato dextrose broth are common microbiological growth media made from potato infusion and dextrose. Potato dextrose agar (abbreviated "PDA") is the most widely used medium for growing fungi and bacteria.

Key takeaways

Potato dextrose agar belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Potato dextrose agar to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Potato dextrose agar from memory before moving on to harder problems.

Reference excerpt

Potato dextrose agar (BAM Media M127) and potato dextrose broth are common microbiological growth media made from potato infusion and dextrose. Potato dextrose agar (abbreviated "PDA") is the most widely used medium for growing fungi and bacteria. PDA has the capability to culture various bacteria and fungi found in the soil. This agar can be acidified with an organic acid or loaded with antibiotics such as chloramphenicol to inhibit unwanted bacterial growth. PDA is used in the food industry to test for fungi that can spoil food products. It is also used in the pharmaceutical industry to screen compound libraries for potential antifungal agents. Potato dextrose agar is a versatile growing medium for bacteria and fungi (yeasts and molds). This agar is used for a broad range of fungi but there are other agars that are more selective for specific types of fungi. These agars include but are not limited to malt extract agar and sabouraud agar. Malt extract agar is more acidic than PDA and is commonly used to cultivate penicillium species. Sabouraud agar is also slightly acidic with pH 5.6-6.0 which is similar to PDA. It is most often used for the isolation of pathogenic fungi such as dermatophytes.

Typical composition

Potato infusion can be made by boiling 200 grams (7.1 oz) of sliced (washed but unpeeled) potatoes in ~ 1 litre (0.22 imp gal; 0.26 US gal) distilled water for 30 minutes and then decanting or straining the broth through cheesecloth. Distilled water is added such that the total volume of the suspension is 1 litre (0.22 imp gal; 0.26 US gal). 20 grams (0.71 oz) dextrose and 20 grams (0.71 oz) agar powder is then added and the medium is sterilized by autoclaving at 15 pounds per square inch (100 kPa) for 15 minutes. A similar growth medium, potato dextrose broth (abbreviated "PDB"), is formulated identically to PDA, omitting the agar. Common organisms that can be cultured on PDB are yeasts such as Candida albicans and Saccharomyces cerevisiae and molds such as Aspergillus niger.

References

Further reading Atlas, R.M.: Handbook of Microbiological Media, second edition. Lawrence C. Parks (1997)

Illustrations

Worked examples

Example 1 — a first encounter with Potato dextrose agar

Start with the simplest possible case. Write down what Potato dextrose agar claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Potato dextrose agar before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Potato dextrose agar ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Potato dextrose agar

In research: Potato dextrose agar appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Potato dextrose agar in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Potato dextrose agar is common in secondary-school and first-year university syllabi. It links to neighbouring topics Microbiological media, Potatoes, so understanding it makes those chapters shorter.
In everyday life: Look for Potato dextrose agar outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Potato dextrose agar in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Potato dextrose agar means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Potato dextrose agar out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Potato dextrose agar in simple terms?

Why does Potato dextrose agar matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Potato dextrose agar?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Potato dextrose agar.