Summary Topic 1: Characteristics and Classification of living organisms
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Course
Biology Unit 1 IGCSE
Institution
GCSE
Book
Cambridge IGCSE (R) Biology Workbook
Topic 1: Characteristics and Classification of living organisms: IGCSE Biology course notes which will help you study for your papers. By studying these notes I achieved a 9 - A* on my Igcse
TOPIC 1: CHARACTERISTICS AND CLASSIFICATION OF LIVING ORGANISMS
1.1 CHARACTERISTICS
→Movement: an action by an organism or part of an organism 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 and to make appropriate responses
→Growth: a permanent increase in size and dry mass by an increase in cell number or cell size or both
→Reproduction: the processes that make more of the same kind of organism
→Excretion: the removal from organisms of toxic materials, the waste products of metabolism (chemical reactions in cells
including respiration) and substances in excess of requirements
→Nutrition: the taking in of materials for energy, growth and development; plants require light, carbon dioxide, water and ions;
animals need organic compounds, ions and usually need water
1.2 CLASSIFICATION
-Classification means to put things into groups to make it easier to study them.
→Species: a group of organisms that can reproduce to produce fertile offspring.
-Organisms share features because they originally descend from a common ancestor.
-Example: all mammals have bodies covered in hair, feed young from mammary glands and have external ears (pinnas).
Binomial System:
→Binomial System (of naming species): an internationally agreed system in which the
scientific name of an organism is made up of two parts showing the genus and
species. (Organisms were first classified by Linnaeus)
-GENUS: first name (genus the organism belongs to): capital letter.
binomial
-SPECIES: second name (species the organism belongs to): small letter.
Example: Canis lupus italics ALWAYS
Genus Species
SEQUENCE OF CLASSIFICATION (to classify several genera (plural of genus))
Classifying:
→PAST:
-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).
→PRESENT:
-DNA sequencing (bases) allowed us to classify organisms using a more scientific approach.
-The more similar the base sequences in the DNA of two species, the more closely related those two species are (and the more
recent in time their common ancestor is)
-Base sequences in a mammal’s DNA are more closely related to all other mammals than to any other vertebrate groups.
-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.
1.3 FEATURES OF ORGANISMS
All living organisms
The cells of all living organisms contain the following:
→Cytoplasm
→Cell membrane
→DNA as genetic material (either found in the nucleus or free in the
cytoplasm)
→Ribosomes for protein synthesis
→Enzymes for respiration (in many, but not all types of cells, found in
mitochondria
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