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Characteristics & Classification of living organisms biology IGCSE
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detailed notes of biology IGCSE topic 1: characteristics and Classification of Living Organisms
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IGCSE Biology Topic 1 (Characteristics & Classification of Living Organisms)
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Cambridge IGCSE/GCSE : Biology 0610Topic 1: Characteristics and Classification of Living organisms.
Properties of Living Organisms
All living organisms share a certain number of properties, which can be simplified
into the words “MRS GREN” as follows:
● Movement: The ability to change positions from one place to another.
● Respiration: A chemical reaction that occurs in the cells, by breaking down
nutrient molecules to release energy.
○ note: energy is released, and NEVER produced.
● Sensitivity: The ability to detect and respond to stimuli.
○ Stimuli: changes in the environment.
● Growth: A permanent increase in dry mass.
○ DRY mass like bone mass, muscle mass or fat mass, however drinking
water and adding it to the body’s mass is not growth as it is not
permanent.
● Reproduction: The ability to reproduce to produce fertile offspring.
○ In order to produce fertile offspring, the two mates should be of the
same species.
● Excretion: The organism getting rid of metabolic wastes, substances in
excess of requirements, and toxins.
○ For example: exhaling carbon dioxide, urination excess water and
salts, or the organism getting rid of toxins (ex: the liver in animals
filters out toxins)
● Nutrition: Obtaining nutrient molecules.
Classification of Living Organisms
Living organisms can be classified according to their:
Kingdom > Phylum > Class > Order > Family > Genus > Species
● Species: a group of living organisms that have the same external
features, and can breed together to produce fertile offspring.
● Genus: a group of living organisms that have the same external
features.
The Binomial System is an internationally agreed system of naming living
organisms according to their Genus (initial letter is uppercase, word is in italic)
and species (first letter is lowercase, word is in italic) , and both of them
should be latin names.
ex: Homo sapiens (humans)
, Reflecting Evolutionary Relationships
According to classification, it means that when organisms share many
features, they are said to be closely related.
Using DNA to classify Living organisms
● Because comparing the physical features to find out if organisms are
closely related or not is inaccurate, scientists have decided to compare
the organisms’ DNA sequences to find out their relativity to each other.
● They identify the species from the DNA by comparing the base
sequences, which means that the more similar the base sequences
are, the more likely the organisms are to be related. (accurate method)
The Kingdoms of Living Organisms
Animal Kingdom
- They are multicellular organisms (consist of more than one cell)
- They are heterotrophs; which means they cannot make their own food,
and have to rely on other organisms to obtain their energy from
nutrients.
- Their cells don’t contain a Cell wall, Large Permanent Vacuoles (they
still have tiny temporary vacuoles though)
- Their Classes include: Mammals, Amphibians, Fish, Reptiles, and
Birds.
Kingdom Prokaryotes
Commonly known as bacteria, prokaryotes contain no nucleus (as their
name suggests, Pro: before, karyota: nucleus), unlike eukaryotes.
- They are Unicellular Organisms.
- They have a cell wall made of Murein/peptidoglycan
- Have smaller Ribosomes than other living organisms (ribosomes:
for protein synthesis)
- Some have flagella: for mobility/movement
- They reproduce Asexually, during a process known as ‘Simple
Binary Fission’
- Have an outer ‘capsule’ for resistance against antibiotics.
Virus(not in a kingdom)
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