Problem 31 - Objective Biology for NEET

Question

What could be the length of bacterial cell? (a) 3 to \(5 \mathrm{~mm}\) (b) 3 to \(5 \mu \mathrm{m}\) (c) \(3.5 \mathrm{~cm}\) (d) None of these

Step-by-Step Solution

Answer

The most plausible length range for a bacterial cell is 3 to 5 µm.

Step 1: Understanding the Scale

First of all, recognize the relative scale of the units. Millimeters, micrometers, and centimeters are units of length in the metric system. The scale from large to small goes as follows: centimeters (cm), millimeters (mm), and then micrometers (µm). This means that a micrometer is smaller than a millimeter, which is smaller than a centimeter.

Step 2: Compare Options to Average Size of Bacterial Cells

Bacterial cells are generally measured in micrometers, and they are typically a few micrometers in length. This averages out to a range of about 1-10 micrometers. Option (b), which presents a length range of 3 to 5 micrometers, fits within this range. Comparing this to the other options, option (a) and option (c) are far larger in scale and are therefore not plausible sizes for bacterial cells.

Step 3: Select the Final Answer

Considering these comparisons, it becomes clear that option (b) is the most plausible range for the length of a bacterial cell. Thus, the correct answer is option (b) 3 to 5 µm.

Key Concepts

Metric Units Comparison

Understanding metric units is vital when studying the size of bacterial cells. The metric system includes units used to measure length, such as centimeters (cm), millimeters (mm), and micrometers (µm). Knowing the order of these units from large to small can aid in comprehending measurements:

• Centimeter (cm) is larger than a millimeter.
• Millimeter (mm) is larger than a micrometer.
• Micrometer (µm) is the smallest of these three units.

It helps to visualize these conversions: 1 cm equals 10 mm, and 1 mm equals 1000 µm. Therefore, micrometers are most suitable for measuring tiny objects, such as bacterial cells. This hierarchy and conversion play a crucial role in scientific fields, where precise measurements are essential.

Scale of Measurement

When measuring bacterial cells, the scale of measurement is an essential concept. This scale helps us determine the appropriate unit to use based on the object's size. For example:

• Centimeters are typically used for measuring everyday objects like a pencil or a book.
• Millimeters help measure smaller objects, such as the thickness of a credit card.
• Micrometers (µm), however, are used for extremely small entities like bacteria or the width of a human hair.

By understanding these scales, it becomes evident why options such as 3 to 5 millimeters or centimeters are unsuitable for measuring bacteria. Bacteria typically require measurements in micrometers due to their minuscule size.

Average Size of Bacteria

Knowing the average size of bacteria is crucial to understanding how we measure them. Bacteria are microscopic and are generally measured in micrometers (µm). The average bacterial cell is about 1 to 10 µm in length:

• Most bacteria fall within this range, depending on the species.
• Some can be a bit smaller, while others slightly larger, but they still remain within micrometer dimensions.

In the exercise, the correct choice was the 3 to 5 µm option because this falls well within the expected average size range for bacteria. Recognizing these typical sizes and the limitations of other metric units in this context ensures accurate understanding and application of these measurements in scientific study.