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Biology - Characteristics and classification of living organisms

Grade 9IGCSE

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

🔑Concepts

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Characteristics of Living Organisms (MRS GREN): Movement, Respiration (the chemical reactions in cells that break down nutrient molecules to release energy, e.g., C6H12O6+6O2→6CO2+6H2OC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O), Sensitivity, Growth, Reproduction, Excretion (removal of toxic materials and substances in excess of requirements like CO2CO_2 and urea), and Nutrition.

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

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The Binomial System: An internationally agreed system in which the scientific name of an organism is made up of two parts: the Genus (capitalized) and the species (lower case), e.g., PantheraPanthera leoleo.

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Classification Hierarchy: Organisms are classified into groups based on shared features. The sequence is: Kingdom, Phylum, Class, Order, Family, Genus, Species.

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DNA and Classification: Modern classification uses the sequence of bases in DNA and the sequence of amino acids in proteins to determine how closely related organisms are. More similar sequences indicate a more recent common ancestor.

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The Five Kingdoms: 1. Animalia (multicellular, no cell walls), 2. Plantae (multicellular, cellulose cell walls, contains chlorophyll), 3. Fungi (multicellular/unicellular, chitin cell walls), 4. Protoctista (unicellular/multicellular with nucleus), 5. Prokaryota (unicellular, no nucleus, circular DNA).

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Main Groups of Arthropods: Myriapods (many segments), Insects (3 body parts, 3 pairs of legs), Arachnids (2 body parts, 4 pairs of legs), and Crustaceans (calcified exoskeleton, more than 4 pairs of legs).

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Dichotomous Keys: A tool used to identify organisms by asking a series of paired questions based on observable physical features.

📐Formulae

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

Actual Size=Image SizeMagnification\text{Actual Size} = \frac{\text{Image Size}}{\text{Magnification}}

Aerobic Respiration:C6H12O6+6O2→6CO2+6H2O\text{Aerobic Respiration}: C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O

💡Examples

Problem 1:

A biological drawing of a bacterial cell is 50 mm50\text{ mm} long. The actual length of the bacterium is 2 \mum2\text{ \mu m}. Calculate the magnification of the drawing.

Solution:

Magnification=50×103 \mum2 \mum=×25,000\text{Magnification} = \frac{50 \times 10^3\text{ \mu m}}{2\text{ \mu m}} = \times 25,000

Explanation:

To calculate magnification, units must be the same. Convert 50 mm50\text{ mm} to micrometers (1 mm=1000 \mum1\text{ mm} = 1000\text{ \mu m}) resulting in 50,000 \mum50,000\text{ \mu m}, then divide by the actual size.

Problem 2:

Identify the kingdom of an organism that is multicellular, has a cell wall made of chitin, and does not perform photosynthesis.

Solution:

Kingdom Fungi

Explanation:

Kingdom Plantae has cellulose walls and performs photosynthesis. Kingdom Animalia lacks cell walls. Kingdom Fungi is characterized by chitinous cell walls and saprophytic or parasitic nutrition (no chlorophyll).

Problem 3:

Two different organisms belong to the same 'Family'. What other classification ranks must they also share?

Solution:

Kingdom, Phylum, Class, and Order.

Explanation:

In the hierarchy of classification, if two organisms share a lower rank (like Family), they must also share all the higher ranks above it. They do not necessarily share the Genus or Species.