krit.club logo

Biology - Classification and Variation

Grade 7IGCSE

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

🔑Concepts

•

Classification is the process of grouping organisms based on shared characteristics. The standard hierarchy is: Kingdom, Phylum, Class, Order, Family, Genus, and Species.

•

The Binomial System, developed by Carl Linnaeus, uses a two-part Latin name for every species: the GenusGenus (capitalized) and the speciesspecies (lowercase), for example PantheraPanthera leoleo (lion).

•

Organisms are divided into Five Kingdoms: ProkaryotaeProkaryotae (no nucleus, e.g., bacteria), ProtoctistaProtoctista (mostly unicellular with a nucleus), FungiFungi (cell walls made of chitin, saprophytic), PlantaePlantae (cellulose cell walls, produce C6H12O6C_6H_{12}O_6 via photosynthesis), and AnimaliaAnimalia (multicellular heterotrophs).

•

Plants are classified into groups like BryophytesBryophytes (mosses), FilicinophytesFilicinophytes (ferns), ConiferophytesConiferophytes (conifers), and AngiospermophytesAngiospermophytes (flowering plants).

•

Variation refers to the differences between individuals of the same species. It can be continuous (a range of values, e.g., height) or discontinuous (distinct categories, e.g., blood groups AA, BB, ABAB, or OO).

•

Variation is caused by genetic factors (DNA inherited from parents) and environmental factors (surroundings/lifestyle).

•

Dichotomous keys are tools used to identify unknown organisms through a series of paired 'yes/no' questions based on observable physical features.

📐Formulae

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

6CO2+6H2O→lightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{\text{light}} C_6H_{12}O_6 + 6O_2

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

💡Examples

Problem 1:

A biological drawing of a leaf is 150150 mmmm long. If the actual leaf is 3030 mmmm long, calculate the magnification of the drawing.

Solution:

Magnification=150 mm30 mm=5×Magnification = \frac{150 \text{ mm}}{30 \text{ mm}} = 5\times

Explanation:

Magnification is a ratio of the image size to the actual size. Since both measurements are in the same unit (mmmm), we divide 150150 by 3030 to get a magnification of 55 times.

Problem 2:

Identify whether the following human characteristics are continuous or discontinuous variation: 1. Blood Group, 2. Body Mass, 3. Fingerprint pattern.

Solution:

  1. Discontinuous, 2. Continuous, 3. Discontinuous.

Explanation:

Blood groups and fingerprint patterns fall into specific, non-overlapping categories (discontinuous). Body mass can take any value within a range and is influenced by both genetics and environment (continuous).

Problem 3:

A student observes a unicellular organism under a microscope that has a cell wall but no visible nucleus. To which Kingdom does this organism likely belong?

Solution:

Kingdom ProkaryotaeProkaryotae (also known as MoneraMonera or Bacteria).

Explanation:

The defining characteristic of ProkaryotaeProkaryotae is the absence of a nucleus (prokaryotic cell structure). All other four kingdoms (PlantaePlantae, AnimaliaAnimalia, FungiFungi, ProtoctistaProtoctista) possess a nucleus (eukaryotic).

Classification and Variation - Revision Notes & Key Formulas | IGCSE Grade 7 Science