B3 – Life On Earth
Food Webs / Competition• Living organisms are dependent on the
environment and other species for their survival• Competition for resources between different
species that are part of the same food web
Rapid Change may cause Extinction• Environmental Change• New species introduced (competitor,
predator, disease organism)• A species in the food web becomes extinct
Extinction due to Human Activity• Hunting• Deforestation• Poaching
• Grey Wolf – 1740 – Great Britain
– Deforestation and hunting• Martinique Amazon Parrot
– 1722 – America – Habitat cleared for
agriculture• Bali Tiger
– 1937 - Indonesia– Habitat loss and hunting
• Caribbean Monk Seal– 1952 – Mexico– Hunted for meat and oil
Biodiversity• Biodiversity provides high variety of crops,
livestock, forestry, and fish, which are important sources of food and medicine for humans.
• Important for sustainable development
Evolution• All species that have
ever lived evolved from very simple living things.
• Life on Earth began about 3500 million years ago
• If conditions on Earth at any stage were different, natural selection could have produced different results
Evidence for Evolution• Fossils• Similarities and Difference in DNA
The Begining of Life• The first living things
developed from molecules that could copy themselves.
• These molecules were produced by conditions on Earth or have come from elsewhere (asteroid)
Natural Selection• How evolution happens.• The natural genetic variation within a population of
organisms means that some individuals will survive and reproduce more successfully than others in their current environment.
• This means that more of this organisms genes will be passed on to the next generation
Environmental and Genetic Variation• Variation is cause by both of these, but only
genetic variation can be passed on to offspring.
Selective Breeding• Selective breeding is the process of breeding
plants and animals for particular genetic traits.
Mutations• Mutations are changes in
DNA caused by radiation, viruses or other factors.
• Mutations that occur in sex cells (sperm or egg cells) can be passed onto offspring and may produce new characteristics (eg: 4 wings instead of 2, red eyes, etc)
Creating a New Species• The combined effects of:
– Environmental Changes– Mutations– Natural Selection
• Can product a new species over time
Evolution of Multi-cellular Organisms• Led to nervous and hormonal communication
systems
Receptor and Effector Cells
• Neurones (Nerve Cells) link receptor cells to effector cells
Central Nervous System• In vertebrates, the nervous system is
coordinated by the CNS
• The Nervous System uses electrical impulses for fast, short-lived responses. It doesn’t make permanent, long lasting changes
Hormones• Chemicals which travel in the blood and bring
about slower, longer-lasting responses.
Examples
• Nervous Communication– Blinking– Muscle Control– Heart Beat
• Hormonal Communication– Puberty (Testosterone, Oestrogen)– Mood, appetite, sleep (Serotonin)– Increase heart rate and blood pressure (Dopamine)
Homeostasis• Nervous and Hormonal systems are involved in
maintaining a constant internal environment
Larger Brain• Evolution of larger
brain gave early humans a better chance of survival– Smarter– Quicker– More social– More artistic– Language
Human Evolution
• Common Ancestor
• Divergence (Separation) of Hominid Species
• Extinction of all but one of these species
