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Characteristics and Classification of Living Organisms - Concept and use of a classification system

Grade 12IGCSEBiology

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

🔑Concepts

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Characteristics of Living Organisms (MRS GREN): Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition.

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Concept of Species: A group of organisms that can reproduce to produce fertile offspring.

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Binomial System: A globally recognized system of naming organisms using two parts: the Genus (capitalized) and the species (lower case), e.g., HomoHomo sapienssapiens. Names are usually written in italics or underlined.

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Hierarchy of Classification: Organisms are classified into groups of increasing specificity: Kingdom, Phylum, Class, Order, Family, Genus, and Species.

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Modern Classification Tools: Traditional classification used morphology and anatomy; modern classification uses DNA base sequences (sequences of AA, TT, CC, and GG) and the sequence of amino acids in proteins to determine evolutionary relationships.

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Dichotomous Keys: Used to identify organisms based on a series of paired, contrasting statements based on observable features.

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Respiration: The chemical reactions in cells that break down nutrient molecules to release energy. Aerobic respiration involves C6H12O6C_6H_{12}O_6 and O2O_2.

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Excretion: Removal from organisms of the waste products of metabolism, toxic materials, and substances in excess of requirements (e.g., CO2CO_2 and urea).

📐Formulae

C6H12O6+6O2→6CO2+6H2O+EnergyC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy}

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

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

💡Examples

Problem 1:

An organism is identified with the scientific name PantheraPanthera tigristigris. Identify its Genus and explain the rules for writing this name.

Solution:

Genus: PantheraPanthera. species: tigristigris.

Explanation:

In the binomial system, the first name is the Genus (starts with a capital letter) and the second is the species (starts with a lowercase letter). Both should be italicized or underlined separately if handwritten.

Problem 2:

Two different organisms share the same sequence of DNA bases for a specific protein, while a third organism has a slightly different sequence. Which two are more closely related?

Solution:

The first two organisms.

Explanation:

Organisms with more similar DNA base sequences share a more recent common ancestor. Therefore, the two organisms with identical sequences for the protein are more closely related to each other than to the third organism.

Problem 3:

A biological drawing of a cell shows a nucleus that measures 15 mm15\text{ mm} in diameter. If the actual diameter of the nucleus is 0.005 mm0.005\text{ mm}, calculate the magnification.

Solution:

Magnification=15 mm0.005 mm=3000×Magnification = \frac{15\text{ mm}}{0.005\text{ mm}} = 3000\times

Explanation:

Using the formula M=IAM = \frac{I}{A}, divide the image size (15 mm15\text{ mm}) by the actual size (0.005 mm0.005\text{ mm}) ensuring units are consistent.

Concept and use of a classification system Revision - Grade 12 Biology IGCSE