CH. 1.1 LIVING ORGANISMS
Tuesday, August 26, 2025 9:03 AM
Biology - Scientific study of living things or organisms
The distinction between living and non-living is not always clear, especially in the case of viruses but most biologists
consider them to be part of life.
The characteristics shared by all organisms logically lead to the conclusion that all living things are descended from a
single common ancestor.
All living organisms:
• Are composed of a common set of chemical components and similar structures
• Depend on interactions among structurally complex parts to maintain the living state
• Have genetic information that uses a nearly universal code
• Convert molecules obtained from their environment into new biological molecules
• Extract energy from the environment and use it for life functions
• Replicate their genetic information in the same manner when reproducing
• Have a fundamental set of genes that share structural similarities
• Evolve through gradual changes in genetic information
Earth formed between 4.6 and 4.5 billions years ago
• The earliest life evolved about 600 million years later
Complex biological molecules possibly arose from random associations of chemicals in the early environment.
Critical step for evolution of life:
• Formation of nucleic acids that reproduce themselves and contain the information to produce proteins.
Next Step:
• Biological molecules were enclosed in a membrane, to form a cell
• Fatty acids formed membranes that separated cells from the surrounding environment
• A cell interior, separate from the external environment, allowed reactants and products of chemical reactions to
be concentrated opening up the possibility that those reactions could be integrated and controlled.
For 2 billion years, organisms were unicellular prokaryotes.
Early prokaryotes were confined to oceans, where they were protected from UV light.
There was little to no O2 in the atmosphere, and hence no protective ozone (O3) layer.
The word prokaryote comes from the Greek πρό (pro, 'before') and κάρυον (karyon, 'nut' or 'kernel’)
Prokaryotes: Unicellular organisms that do not have nuclei. Not a monophyletic group; as commonly used, includes the
bacteria and prokaryotic archaeans. A term of convenience encompassing all cellular organisms that are not eukaryotes.
(Contrast with eukaryotes.)
Photosynthesis evolved about 2.7 billion years ago.
The energy of sunlight is transformed into the chemical-bond energy of biological molecules.
Earliest photosynthetic cells were probably similar to cyanobacteria
O2 was a byproduct of photosynthesis and it began to accumulate in the atmosphere.
Photosynthesis: [literally, “synthesis from light”] Metabolic processes carried out by green plants and cyanobacteria, by
which visible light is trapped and the energy used to convert CO2 into organic compounds.
O2 was poisonous to many early prokaryotes.
Organisms that could tolerate O2 evolved aerobic metabolism (energy production using O2), which is more efficient
Tuesday, August 26, 2025 9:03 AM
Biology - Scientific study of living things or organisms
The distinction between living and non-living is not always clear, especially in the case of viruses but most biologists
consider them to be part of life.
The characteristics shared by all organisms logically lead to the conclusion that all living things are descended from a
single common ancestor.
All living organisms:
• Are composed of a common set of chemical components and similar structures
• Depend on interactions among structurally complex parts to maintain the living state
• Have genetic information that uses a nearly universal code
• Convert molecules obtained from their environment into new biological molecules
• Extract energy from the environment and use it for life functions
• Replicate their genetic information in the same manner when reproducing
• Have a fundamental set of genes that share structural similarities
• Evolve through gradual changes in genetic information
Earth formed between 4.6 and 4.5 billions years ago
• The earliest life evolved about 600 million years later
Complex biological molecules possibly arose from random associations of chemicals in the early environment.
Critical step for evolution of life:
• Formation of nucleic acids that reproduce themselves and contain the information to produce proteins.
Next Step:
• Biological molecules were enclosed in a membrane, to form a cell
• Fatty acids formed membranes that separated cells from the surrounding environment
• A cell interior, separate from the external environment, allowed reactants and products of chemical reactions to
be concentrated opening up the possibility that those reactions could be integrated and controlled.
For 2 billion years, organisms were unicellular prokaryotes.
Early prokaryotes were confined to oceans, where they were protected from UV light.
There was little to no O2 in the atmosphere, and hence no protective ozone (O3) layer.
The word prokaryote comes from the Greek πρό (pro, 'before') and κάρυον (karyon, 'nut' or 'kernel’)
Prokaryotes: Unicellular organisms that do not have nuclei. Not a monophyletic group; as commonly used, includes the
bacteria and prokaryotic archaeans. A term of convenience encompassing all cellular organisms that are not eukaryotes.
(Contrast with eukaryotes.)
Photosynthesis evolved about 2.7 billion years ago.
The energy of sunlight is transformed into the chemical-bond energy of biological molecules.
Earliest photosynthetic cells were probably similar to cyanobacteria
O2 was a byproduct of photosynthesis and it began to accumulate in the atmosphere.
Photosynthesis: [literally, “synthesis from light”] Metabolic processes carried out by green plants and cyanobacteria, by
which visible light is trapped and the energy used to convert CO2 into organic compounds.
O2 was poisonous to many early prokaryotes.
Organisms that could tolerate O2 evolved aerobic metabolism (energy production using O2), which is more efficient
