,
, CAMBRIDGE OL BIOLOGY To be a star
Chapter 1: Characteristics and Classification of Living Organisms
1. The Characteristics of Living Organisms
All living organisms share seven characteristics (often remembered by the acronym MRS GREN).
• Movement: An action by an organism or part of an organism causing a change of position or place.
• Respiration: The chemical reactions in cells that break down nutrient molecules and release energy for metabolism.
• Sensitivity: The ability to detect or sense changes in the internal or external environment (stimuli) 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 the waste products of metabolism (chemical reactions in cells including
respiration), toxic materials, and substances in excess of requirements.
• Nutrition: 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.
Extra Note: Dry Mass
• Dry mass is the mass of an organism after the removal of all its water content.
• How to prepare a dry mass: Heat the organism gently in an oven or incubator at a low temperature (about 80 C).
This increases the rate of evaporation without burning the organic matter. Weigh it repeatedly until the mass becomes
constant (which means all water has evaporated).
2. Classification and the Binomial System
Classification is sorting organisms into groups based on the features they share.
• Species: A group of organisms that can reproduce to produce fertile offspring.
• The Binomial System: An internationally agreed system in which the scientific name of an organism is made up of
two parts showing the genus and species.
• Rules of Binomial Naming: 1. The first name is the Genus (starts with a capital letter). 2. The second name is the
species (starts with a small letter). 3. Example: Homo sapiens.
• Methods of Classification:
• Traditional Method: Based on studies of morphology (outer shape) and anatomy (internal structure).
• Modern / More Accurate Method: Based on comparing DNA base sequences and the sequences of amino acids in
proteins. Organisms that share a more recent ancestor (closer relatives) have base sequences in DNA that are more
similar than those that share only a distant ancestor.
3. The Five Kingdoms of Living Organisms
1. Animal Kingdom:
• Multicellular organisms.
• Cells contain a nucleus, but have no cell walls and no chloroplasts.
• Feed on organic substances made by other living organisms (Heterotrophic nutrition).
By Dr Bassel Yassen +201008884502 1
, CAMBRIDGE OL BIOLOGY To be a star
2. Plant Kingdom:
• Multicellular organisms.
• Cells contain a nucleus, chloroplasts, and a cell wall made of cellulose.
• Feed by photosynthesis (Autotrophic nutrition).
3. Fungus Kingdom:
• Usually multicellular (like mushrooms), but some are unicellular (like yeast).
• Cells have nuclei and cell walls (made of chitin, not cellulose).
• They do not have chloroplasts (they cannot photosynthesize).
• Feed by saprotrophic or parasitic nutrition (feeding on dead or living organic matter).
• Reproduce mainly by producing spores.
4. Protoctist Kingdom:
• Usually unicellular, but some are multicellular (like seaweeds).
• Cells contain a nucleus.
• Some have chloroplasts and photosynthesize, while others do not.
5. Prokaryote Kingdom (Bacteria):
• Always unicellular.
• They have no true nucleus (their genetic material is a circular strand of DNA loose in the cytoplasm).
• Have cell walls (made of peptidoglycan, not cellulose).
• Contain small circular loops of DNA called plasmids.
• They do not have mitochondria or chloroplasts.
4. Viruses (Not a Kingdom)
• Viruses are not classified in any of the five kingdoms because they do not show the typical characteristics of living
organisms (they do not respire, feed, excrete, etc.).
• They can only reproduce when they are inside a living host cell.
• Structure: They do not have cells. They only consist of genetic material (DNA or RNA) surrounded by a protein
coat.
By Dr Bassel Yassen +201008884502 2
, CAMBRIDGE OL BIOLOGY To be a star
Chapter 1: Characteristics and Classification of Living Organisms
1. The Characteristics of Living Organisms
All living organisms share seven characteristics (often remembered by the acronym MRS GREN).
• Movement: An action by an organism or part of an organism causing a change of position or place.
• Respiration: The chemical reactions in cells that break down nutrient molecules and release energy for metabolism.
• Sensitivity: The ability to detect or sense changes in the internal or external environment (stimuli) 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 the waste products of metabolism (chemical reactions in cells including
respiration), toxic materials, and substances in excess of requirements.
• Nutrition: 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.
Extra Note: Dry Mass
• Dry mass is the mass of an organism after the removal of all its water content.
• How to prepare a dry mass: Heat the organism gently in an oven or incubator at a low temperature (about 80 C).
This increases the rate of evaporation without burning the organic matter. Weigh it repeatedly until the mass becomes
constant (which means all water has evaporated).
2. Classification and the Binomial System
Classification is sorting organisms into groups based on the features they share.
• Species: A group of organisms that can reproduce to produce fertile offspring.
• The Binomial System: An internationally agreed system in which the scientific name of an organism is made up of
two parts showing the genus and species.
• Rules of Binomial Naming: 1. The first name is the Genus (starts with a capital letter). 2. The second name is the
species (starts with a small letter). 3. Example: Homo sapiens.
• Methods of Classification:
• Traditional Method: Based on studies of morphology (outer shape) and anatomy (internal structure).
• Modern / More Accurate Method: Based on comparing DNA base sequences and the sequences of amino acids in
proteins. Organisms that share a more recent ancestor (closer relatives) have base sequences in DNA that are more
similar than those that share only a distant ancestor.
3. The Five Kingdoms of Living Organisms
1. Animal Kingdom:
• Multicellular organisms.
• Cells contain a nucleus, but have no cell walls and no chloroplasts.
• Feed on organic substances made by other living organisms (Heterotrophic nutrition).
By Dr Bassel Yassen +201008884502 1
, CAMBRIDGE OL BIOLOGY To be a star
2. Plant Kingdom:
• Multicellular organisms.
• Cells contain a nucleus, chloroplasts, and a cell wall made of cellulose.
• Feed by photosynthesis (Autotrophic nutrition).
3. Fungus Kingdom:
• Usually multicellular (like mushrooms), but some are unicellular (like yeast).
• Cells have nuclei and cell walls (made of chitin, not cellulose).
• They do not have chloroplasts (they cannot photosynthesize).
• Feed by saprotrophic or parasitic nutrition (feeding on dead or living organic matter).
• Reproduce mainly by producing spores.
4. Protoctist Kingdom:
• Usually unicellular, but some are multicellular (like seaweeds).
• Cells contain a nucleus.
• Some have chloroplasts and photosynthesize, while others do not.
5. Prokaryote Kingdom (Bacteria):
• Always unicellular.
• They have no true nucleus (their genetic material is a circular strand of DNA loose in the cytoplasm).
• Have cell walls (made of peptidoglycan, not cellulose).
• Contain small circular loops of DNA called plasmids.
• They do not have mitochondria or chloroplasts.
4. Viruses (Not a Kingdom)
• Viruses are not classified in any of the five kingdoms because they do not show the typical characteristics of living
organisms (they do not respire, feed, excrete, etc.).
• They can only reproduce when they are inside a living host cell.
• Structure: They do not have cells. They only consist of genetic material (DNA or RNA) surrounded by a protein
coat.
By Dr Bassel Yassen +201008884502 2
