B3: Life on Earth

• Life on Earth began about 3500 million years ago
• A species is a group of organisms which can freely breed with each other to produce fertile offspring.
• The very first living things on Earth developed from simple molecules that could copy or replicate themselves (natural cloning)
• Evolution occurs due to natural selection
  
• There is variation between individuals of the same species.
• Individuals with certain characteristics have a better chance of surviving, and reproducing, if the environment changes or vital resources become scarce. (survival of the fittest)
• There will be more individuals with these characteristics in the next generation as the characteristics are passed onto offspring.

• There is competition for food and mates within each species.
• Selective breeding involves making deliberate selections based on desireable characteristics.
• New species have elvolved over long periods of time.
• Genes can be changed by mutation which can cause cancer cells.
• Mutated genes in sex cells can be passed onto offspring and produce new characteristics.
• A large change in the environment may cause an entire species to become extinct.
• A new species can be produced by the combined effects of mutations, environmental changes and natural selection.

• There is evidence to suggest that all exisiting organisms share certain traits, including celluar and genetic code, therefore sharing a common ancestor.
• There are 2 sources of evidence to support the hypothesis:
• The fossil record
  Fossils are remains of plants/animals from many years ago found in rock. Fossils indicate the history of species and can show the evolutionary changes in organisms over millions of years.
  
• DNA evidence
  Comparing the gene sequence of organisms revels that some organisms have a high degree of similarity in the DNA. eg. chimpanzee and human.

• Hominids are animals that are more like humans than apes. They lived in Africa between 1.5 and 4 million years ago. During evolution, the hominid family diverged (branched) amd several Homo (meaning person) species developed. eg. homo-sapiens (humans)
• The theory that hominids had big brains before they started to walk upright was proved wrong because in 1924 a skull was discovered which was a hominid. The skull had a small brain and a hole at the of bottom which shows that the animal stood on 2 legs.
• A larger brain increases the chance of survival and allowed the development of new skills eg. make and use tools, hunt and make fire.

• Jean-Baptiste Lamark
  Explanation: Organisms developed new features as a result of an "inner urge" for improvement.
  
• Georges Curvier
  Explanation: No connection between the species in 1 layer of rock and those in another. Organisms were wiped out by a series of catastrophes. eg. Noah's flood. God then created new improved versions.
  
• Charles Darwin
  Explanation: Living things evolved. Evolution happened by natural selection or survival of the fittest.
  
• The theory that becomes generally excepted at any particular time is the one that:
  - best fits the data
  - is not successfully challenged at the time
  - explains new data

What can cause extinction?

• A new species moves in:
  -Could be predators to other species
  - Could cause disease
  - Competition eg. 2 different species that need exactly the smae things cannot live together (in perfect harmony)
• Another species becomes extinct eg. caterpillars become extinct = no food for birds
• Change in the environment
  - eg. global warming: temperature, water, light, natural disasters.
  
  
  

  Any species of plants or animals that are at risk of extinction are endangered.

• A food web can show which organisms eat other organisms in a particular habitat.
  
• Different species in a particular habitat often compete for the same space or food source.
  
• A change which affects one species in a food web also affects other species in the same food web.
  
• Ecosystems can often adjust to changes but large disruptions may change an ecosystem permanently.
  

• Humans can cause extinction of other species directly by hunting and indirectly by taking away their habitat or bringing other species into their habitat.
  
• The variety of life in and between species on Earth is called biodiversity.
  
• Sustainability means meeting the needs of people today without damaging Earth for future generations.
  
•  Using the Earth sustainably means balancing:
  - environmental factors
  - economic factors
  - social factors

• The Central Nervous System (CNS) enables us to react to our surroundings. It consisits mainly of the brain, the spinal cord, nerve cells (Neurones) and receptors.
• Types of receptor:
  - Light receptors in the eyes
  - Sound receptors in the ears
  - Taste receptors on the tongue
  - Smell receptors in the nose
  - Touch, pressure and temperature receptors on skin.
• Hormones are chemical substances, produces by glands, which are transported around the body by the bloodstream. Hormones give slower, longer lasting responses and regulate the functions of many organs and cells.
  
• The human body uses both nervous and hormonal signals to ensure the body systems are stable.
• Homeostasis: the maintenance of a constant internal body environment.