Classification
Cambridge Definition:
Classification is the process of grouping organisms according to the features that they share.
Key Points:
- Organisms with similar characteristics are placed into the same groups.
- Classification makes identification and study of organisms easier.
- Scientists use physical features and DNA evidence for classification.
Species
Cambridge Definition:
A species is a group of organisms that can reproduce to produce fertile offspring.
Key Points:
Members of the same species:
- Can reproduce with each other.
- Produce fertile offspring.
Fertile offspring:
- Can reproduce themselves.
Binomial Naming System
Cambridge Definition:
The binomial system of naming species is an internationally agreed system in which the scientific name of an organism is made up of two parts showing the genus and species.
Structure:
Scientific name:
Genus + species
Example:
Homo sapiens
- Homo = genus.
- sapiens = species.
Advantages:
- Used worldwide.
- Avoids confusion caused by different common names.
- Gives every organism a unique scientific name.
Dichotomous Keys
Definition:
A dichotomous key is a tool used to identify organisms by using a series of choices based on observable features.
How to Use a Dichotomous Key:
- Start at the first pair of statements.
- Choose the statement that matches the organism.
- Follow the instructions to the next step.
- Continue until the organism is identified.
Example:
1a. Has wings → go to step 2
1b. No wings → go to step 3
Classification and Evolutionary Relationships (Supplement)
Classification systems aim to show how organisms are related through evolution.
Common Ancestors:
- Organisms that share a recent common ancestor are more closely related.
- Organisms that share a distant ancestor are less closely related.
DNA and Classification
DNA base sequences are used to classify organisms.
Key Points:
- DNA contains genetic information.
- Scientists compare DNA base sequences between organisms.
- Similar DNA sequences indicate closer relationships.
Relationship:
More similar DNA → more closely related.
Less similar DNA → more distantly related.
Examiner Tips – 1.2 Classification Systems
- Remember species are defined by producing fertile offspring.
- Binomial names always contain genus followed by species.
- The more similar the DNA base sequences, the closer the evolutionary relationship.
- Practise reading dichotomous keys carefully; one incorrect choice leads to the wrong identification.