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Summary IGCSE Biology Topic 1 (Characteristics & Classification of Living Organisms)
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A summary note of IGCSE Biology Topic 1 (Characteristics & Classification of Living Organisms).
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Characteristics and ClassificationMonday, 6 September, 2021 12:40 PM
Characteristics of Living Organisms
- Movement: An action by an organisms causing a change of position or place
- Respiration: The chemical reactions that break down nutrient molecules in living cells to release energy for metabolism
- Sensitivity: The ability to detect or sense stimuli in the internal or external environment & to make appropriate responses
- Growth: A permanent increase in size & dry mass by an increase in cell number or cell size or both
- Reproduction: The processes that make more of the same kind of organisms
- Excretion: The removal from organisms of toxic materials, the waste products of metabolism (chemical reactions in cells
including respiration) & substances in excess of requirements
- Nutrition: The taking in of materials for energy, growth & development
MRS.GREN
Concept and uses of Classification Systems
• Definition of Species: A group of organisms that can reproduce to produce fertile offspring
• These species can be classified into groups by the features that they share.
• Binomial System: The Genus (always capital letter) & followed by the species (starting with small letter).
• The sequence of classification: Kingdom, Phylum, Class, Order, Family, Genus, Species
King Philip Came Over For Gran's Spaghetti
• Organisms share features because they originally descend from a common ancestor
• Originally, organisms were classified using morphology (the overall form and shape of the organism, e.g. whether it had wings
or legs) and anatomy (the detailed body structure as determined by dissection).
• Studies of DNA sequences of different species show that the more similar the base sequence in the DNA of two species, the
more closely related those two species are (and the more recent in time their common ancestor is).
• As DNA base sequences are used to code for amino acid sequences in proteins, the similarities in amino acid sequences can
also be used to determine how closely related organisms are.
Features of Organisms
The cells of all living organisms contain the following:
• Cytoplasm
• Cell Membrane
• DNA as genetic material
• Ribosomes for protein synthesis
• Enzymes for respiration
Animals Plants Fungi Protoctists Prokaryotes
Multicellular Multicellular Multicellular Most are unicellular but Unicellular
some
are multicellular
Contain a nucleus but no Contain a nucleus, Have nuclei & cell Have a nucleus, some may Have cell walls (not made
cell walls or chloroplasts chloroplasts & walls not made from have cells walls & of cellulose) & cytoplasm
cellulose cell walls cellulose chloroplasts but no nucleus or
mitochondria
Feed on organic Feed by Don't Some photosynthesise &
substances made by other photosynthesis photosynthesize by some feed on organic
living thing feed by saprohytic or substances made by other
parasitic nutrition living things
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