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The Cell - Cell Theory and Discovery

Grade 6ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The cell is the basic structural and functional unit of all living organisms. All living things are composed of one or more cells.

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Robert Hooke in 16651665 discovered the cell while observing a thin slice of cork under a self-designed microscope. He noticed box-like compartments resembling a honeycomb and named them 'cells'.

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Anton van Leeuwenhoek in 16741674 was the first to observe free-living cells in pond water (like bacteria and protozoa) using an improved microscope.

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The Cell Theory was proposed by Matthias Schleiden (18381838) and Theodor Schwann (18391839), later expanded by Rudolf Virchow (18551855).

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The three main points of Cell Theory are: 1. All living organisms are made up of cells. 2. The cell is the fundamental unit of life. 3. All cells arise from pre-existing cells (Omnis cellula e cellulaOmnis\ cellula\ e\ cellula).

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Most cells are microscopic and measured in micrometres (μm\mu m). The size of a typical cell ranges from 10 μm10\ \mu m to 100 μm100\ \mu m.

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Cells vary in shape (spherical, spindle-shaped, elongated, or branched) depending on the specific function they perform.

📐Formulae

Total Magnification=MagnificationObjective Lens×MagnificationOcular (Eyepiece) LensTotal\ Magnification = Magnification_{Objective\ Lens} \times Magnification_{Ocular\ (Eyepiece)\ Lens}

1 μm=10−6 m=11000 mm1\ \mu m = 10^{-6}\ m = \frac{1}{1000}\ mm

💡Examples

Problem 1:

A student is observing a cheek cell using a compound microscope. If the eyepiece has a power of 15×15 \times and the objective lens has a power of 40×40 \times, calculate the total magnification.

Solution:

Total Magnification=15×40=600×Total\ Magnification = 15 \times 40 = 600 \times

Explanation:

To find the total magnification of a microscope, we multiply the magnifying power of the ocular lens (eyepiece) by the magnifying power of the objective lens.

Problem 2:

Who provided the evidence that all cells come from pre-existing cells, and in which year?

Solution:

Rudolf Virchow in 18551855.

Explanation:

While Schleiden and Schwann established that plants and animals are made of cells, it was Virchow who completed the theory by explaining the origin of new cells.

Problem 3:

Identify the smallest and largest known cells.

Solution:

Smallest: MycoplasmaMycoplasma (PPLO) measuring about 0.1 μm0.1\ \mu m. Largest: Ostrich egg measuring about 170 mm×130 mm170\ mm \times 130\ mm.

Explanation:

Cell size varies greatly in nature; MycoplasmaMycoplasma represents the lower limit of cellular life, while the ostrich egg is a single cell containing a large amount of yolk.