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Characteristics and Classification of Living Organisms - Features of organisms

Grade 11IGCSEBiology

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

🔑Concepts

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Characteristics of Living Organisms: Defined by the mnemonic MRSMRS GRENGREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition.

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Respiration: The chemical reactions in cells that break down nutrient molecules to release energy for metabolism. Aerobic respiration requires glucose (C6H12O6C_6H_{12}O_6) and oxygen (O2O_2).

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

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The Binomial System: A naming system where each species is given a two-part scientific name consisting of the GenusGenus (capitalized) and the speciesspecies (lowercase), e.g., HomoHomo sapienssapiens.

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Classification: Organisms are grouped based on shared features. Modern classification uses DNADNA base sequences (AA, TT, CC, GG) and protein structure (amino acid sequences) to determine evolutionary relationships.

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Five Kingdoms: 1. AnimaliaAnimalia (multicellular, no cell walls); 2. PlantaePlantae (cellulose cell walls, chlorophyll); 3. FungiFungi (chitin cell walls, saprophytic); 4. ProtoctistaProtoctista (unicellular/multicellular with nucleus); 5. ProkaryotaProkaryota (no nucleus, e.g., bacteria).

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Arthropod Groups: Classified by number of legs and antennae: Insects (66 legs), Arachnids (88 legs), Crustaceans (1010-1414 legs), and Myriapods (manymany legs).

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Dichotomous Keys: Used to identify organisms based on a series of paired statements (couplets) regarding visible features.

📐Formulae

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

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

6CO2+6H2O→light + chlorophyllC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{\text{light + chlorophyll}} C_6H_{12}O_6 + 6O_2

💡Examples

Problem 1:

A biological specimen has an actual length of 0.05 mm0.05\text{ mm}. In a textbook diagram, the same specimen is drawn with a length of 10 mm10\text{ mm}. Calculate the magnification of the drawing.

Solution:

Magnification=10 mm0.05 mm=×200\text{Magnification} = \frac{10\text{ mm}}{0.05\text{ mm}} = \times 200

Explanation:

Magnification is calculated by dividing the measured size of the image by the actual size of the object. Ensure both units are identical (mmmm) before dividing.

Problem 2:

Two species of birds have very similar plumage. Species A has a DNADNA base sequence of A−T−T−G−C−CA-T-T-G-C-C for a specific gene, while Species B has A−T−T−G−C−GA-T-T-G-C-G. A third species, C, has A−C−G−G−C−GA-C-G-G-C-G. Which two species are most closely related?

Solution:

Species AA and Species BB.

Explanation:

Species AA and BB share 55 out of 66 bases in the sequence, whereas Species CC shares significantly fewer. Organisms with more similar DNADNA base sequences are more closely related evolutionarily.

Features of organisms - Revision Notes & Key Diagrams | IGCSE Grade 11 Biology