Biology
Species
A species is a group of organisms that can naturally interbreed and produce fertile offspring. Members of a species have similar genetic and physical characteristics.
Characteristics of a Species
Similar body structure and characteristics.
Similar genetic makeup.
Can reproduce among themselves.
Produce fertile offspring.
Chromosomes
Chromosomes are thread-like structures in the nucleus of cells that contain DNA and genes.
Functions:
Store hereditary information.
Determine inherited traits.
Transfer genetic information from parents to offspring.
Humans have 46 chromosomes arranged in 23 pairs.
Evolution of Species
Species change over time through evolution.
Causes of evolution:
Mutations in DNA
Natural selection
Environmental changes
Isolation of populations
Over many generations, these changes can lead to the formation of new species.
Speciation
Speciation is the process by which new species are formed.
It occurs when populations become separated and gradually accumulate differences until they can no longer interbreed successfully.
Classification of Living Organisms
Living organisms are arranged into groups based on similarities and differences. Classification helps scientists identify organisms and understand their evolutionary relationships.
Hierarchy of Classification
Kingdom → Phylum → Class → Order → Family → Genus → Species
As we move downward:
The number of organisms decreases.
Similarities between organisms increase.
Organisms become more closely related.
The Five Kingdoms
1. Kingdom Animalia
Multicellular organisms
Cannot make their own food
Usually capable of movement
Have no cell walls
2. Kingdom Plantae
Multicellular organisms
Make their own food by photosynthesis
Have chlorophyll and cell walls
3. Kingdom Fungi
Mostly multicellular
Cannot make their own food
Absorb nutrients from dead or living matter
Have cell walls made of chitin
4. Kingdom Protista
Mostly single-celled organisms
Some make their own food and some do not
Show characteristics of both plants and animals
5. Kingdom Monera
Single-celled organisms
Lack a true nucleus
Includes bacteria and similar microorganisms
Viruses and Classification
Viruses are not placed in any kingdom because they:
Are not made of cells
Cannot carry out life processes independently
Reproduce only inside living cells
However, they are still classified into species because they possess genetic material and undergo evolution.
Quick Revision
Species: Organisms that can interbreed and produce fertile offspring.
Chromosomes: Structures containing DNA and genes.
Evolution: Gradual change in species over time.
Speciation: Formation of new species.
Classification hierarchy: Kingdom → Phylum → Class → Order → Family → Genus → Species.
Five kingdoms: Animalia, Plantae, Fungi, Protista and Monera.