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Organization of the Organism - Levels of organisation

Grade 11IGCSEBiology

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

🔑Concepts

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Levels of organisation follow a specific hierarchy: Organelles→Cells→Tissues→Organs→Organ Systems→OrganismOrganelles \rightarrow Cells \rightarrow Tissues \rightarrow Organs \rightarrow Organ\ Systems \rightarrow Organism.

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A cell is the basic functional and structural unit of all living organisms. Examples include specialized cells like Ciliated cellsCiliated\ cells (movement of mucus) and Root hair cellsRoot\ hair\ cells (absorption of H2OH_2O and mineral ions).

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A tissue is a group of cells with similar structures, working together to perform a shared function. Examples include XylemXylem (transport of water) and Muscle tissueMuscle\ tissue.

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An organ is a structure made up of a group of tissues, working together to perform specific functions. Examples include the HeartHeart in animals and the LeafLeaf in plants.

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An organ system is a group of organs with related functions, working together to perform body functions. Examples include the Circulatory systemCirculatory\ system and the Shoot systemShoot\ system.

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Biological drawings and micrographs require magnification calculations. Always ensure units are consistent (e.g., converting mmmm to μm\mu m using the factor 10310^3).

📐Formulae

Magnification=Image sizeActual sizeMagnification = \frac{Image\ size}{Actual\ size}

Actual size=Image sizeMagnificationActual\ size = \frac{Image\ size}{Magnification}

1 mm=1000 μm1\ mm = 1000\ \mu m

1 μm=10−3 mm1\ \mu m = 10^{-3}\ mm

💡Examples

Problem 1:

A student measures the length of a plant cell in a micrograph as 45 mm45\ mm. The actual length of the cell is 0.15 mm0.15\ mm. Calculate the magnification of the micrograph.

Solution:

Magnification=45 mm0.15 mm=×300Magnification = \frac{45\ mm}{0.15\ mm} = \times 300

Explanation:

Using the formula M=IAM = \frac{I}{A}, we divide the image size (45 mm45\ mm) by the actual size (0.15 mm0.15\ mm). Since both units are already in mmmm, no conversion is necessary.

Problem 2:

An image of a mitochondrion has a magnification of ×20,000\times 20,000. If the image length is 10 mm10\ mm, what is the actual length of the mitochondrion in micrometres (μm\mu m)?

Solution:

Actual size=10 mm20,000=0.0005 mmActual\ size = \frac{10\ mm}{20,000} = 0.0005\ mm 0.0005 mm×1000=0.5 μm0.0005\ mm \times 1000 = 0.5\ \mu m

Explanation:

First, calculate the actual size in mmmm using A=IMA = \frac{I}{M}. Then, convert the result from mmmm to μm\mu m by multiplying by 10001000 to get the final answer of 0.5 μm0.5\ \mu m.

Levels of organisation - Revision Notes & Key Diagrams | IGCSE Grade 11 Biology