krit.club logo

Organisation of the Organism - Levels of organisation

Grade 12IGCSEBiology

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

🔑Concepts

•

Levels of Organization: The biological hierarchy progresses from organelles to cells, tissues, organs, organ systems, and finally the multicellular organism.

•

Cell: The basic functional and structural unit of all living organisms. Examples include ciliated cellsciliated \ cells and red blood cellsred \ blood \ cells.

•

Tissue: A group of cells with similar structures working together to perform a shared function. Examples: xylemxylem in plants and muscle tissue in animals.

•

Organ: A structure made up of a group of related tissues, working together to perform specific functions. Example: The leaf is an organ containing epidermisepidermis, mesophyllmesophyll, and vascularvascular tissues.

•

Organ System: A group of organs with related functions, working together to perform body functions. Example: The digestive system or the circulatory systemcirculatory \ system.

•

Size and Scale: Biological structures vary greatly in size, usually measured in millimeters (mmmm), micrometers (μm\mu m), or nanometers (nmnm).

•

Standard Unit Conversion: 1 mm=103 μm1 \ mm = 10^3 \ \mu m and 1 μm=103 nm1 \ \mu m = 10^3 \ nm.

•

Magnification: The ratio of an object's image size to its real (actual) size, represented as M=IAM = \frac{I}{A}.

📐Formulae

Magnification=size of imageactual size of objectMagnification = \frac{\text{size of image}}{\text{actual size of object}}

Actual size (A)=Image size (I)Magnification (M)\text{Actual size (A)} = \frac{\text{Image size (I)}}{\text{Magnification (M)}}

Total Magnification=eyepiece lens magnification×objective lens magnification\text{Total Magnification} = \text{eyepiece lens magnification} \times \text{objective lens magnification}

1 mm=1000 μm1 \ mm = 1000 \ \mu m

1 μm=10−3 mm=10−6 m1 \ \mu m = 10^{-3} \ mm = 10^{-6} \ m

💡Examples

Problem 1:

A micrograph of a plant cell shows a chloroplast that measures 15 mm15 \ mm in length. If the actual size of the chloroplast is 5 μm5 \ \mu m, calculate the magnification used.

Solution:

M=IA=15 mm5 μm=15000 μm5 μm=3000M = \frac{I}{A} = \frac{15 \ mm}{5 \ \mu m} = \frac{15000 \ \mu m}{5 \ \mu m} = 3000

Explanation:

First, convert all units to be the same. 15 mm15 \ mm is converted to 15000 μm15000 \ \mu m (15×10315 \times 10^3). Then divide the image size by the actual size to find the magnification of ×3000\times 3000.

Problem 2:

An image of a bacterial cell is 40 mm40 \ mm long and the magnification is ×20,000\times 20,000. What is the actual length of the cell in μm\mu m?

Solution:

A=IM=40 mm20,000=0.002 mm=2 μmA = \frac{I}{M} = \frac{40 \ mm}{20,000} = 0.002 \ mm = 2 \ \mu m

Explanation:

Using the formula A=IMA = \frac{I}{M}, divide the image size (40 mm40 \ mm) by the magnification (20,00020,000). The result is 0.002 mm0.002 \ mm. To convert to micrometers, multiply by 10310^3, giving 2 μm2 \ \mu m.

Levels of organisation - Revision Notes & Key Diagrams | IGCSE Grade 12 Biology