Classification Chapter Notes | IGCSE Cambridge Science for Year 6 - Class 6 PDF Download

Classifying Animals

Variation of Characteristics

• Scientists group organisms based on similarities and differences - a process called classification.
• Every organism has distinct features or characteristics that may vary between different organisms.
• Variation in characteristics helps recognize and differentiate between organisms.

Kingdoms

• Kingdoms are the largest groups of organisms (e.g., plant kingdom, animal kingdom).
• Characteristics used to classify plants and animals include cellular features visible under a microscope.
• Other kingdoms include the fungus kingdom (mushrooms, yeasts) and the prokaryote kingdom (bacteria).

Vertebrates and Invertebrates 

• The animal kingdom is divided into vertebrates (with a backbone) and invertebrates (without a backbone).
• Vertebrates are further classified into five groups: mammals, reptiles, fish, amphibians, and birds, based on specific characteristics.

Vertebrates

Carl Linnaeus 

• Swedish scientist Carl Linnaeus developed a system to classify living things into smaller groups based on variations in characteristics.
• The smallest group in this system is called a species, identified by a two-word Latin name.

Species

• Organisms of the same species share very similar characteristics but exhibit variation.
• Members of the same species can reproduce and produce fertile offspring.
• Offspring produced by members of different species are called hybrids and are usually infertile.

 Viruses

• Viruses are not considered living organisms as they lack the seven life processes (movement, reproduction, sensitivity, growth, respiration, excretion, nutrition).
• Viruses can only replicate inside a host cell by taking over its genetic machinery.
• Viruses cannot move any part of themselves and so require other things to move them. 
• We do not know if viruses can detect changes around them. They are very simple structures, so it is unlikely. 
• Viruses do not grow bigger and they require respiration by the host cell to supply the energy for replication. 
• Viruses do not excrete waste and they rely on the food substances inside a host cell to build the new virus particles.
• Some scientists consider the combination of a virus and its host cell as a living entity.

Biological keys

Dichotomous Keys

• Dichotomous keys are tools used by scientists to identify organisms based on a series of questions with two possible answers, dividing them into smaller groups.
• The process involves answering each question sequentially to narrow down the identification.

Dichotomous Keys

Using Keys to Classify Plants

• Within the plant kingdom, major groups include flowering plants, conifers, ferns, and mosses, classified based on characteristics like seed production, roots, and leaf structures.
• Leaf characteristics (edges, shape, arrangement) are often useful for identifying specific trees or plants.