VIEWS: 25 PAGES: 17 POSTED ON: 4/5/2010
B3 Life on Earth Revision How did life on Earth begin and evolve? Or did they Life on Earth come from began about elsewhere in 3500 million the solar years ago. system? The molecules Simple organisms could have been developed from produced by molecules that environmental could copy conditions on themselves Earth at that time Evolution What is Evolution? happens by natural Individuals of a species selection are not identical –their characteristics vary. The environment changes Resources become scarce Competition! Individuals with certain characteristics have a better chance of surviving Next Generation More individuals have these useful characteristics Next Generation Even more individuals have these useful characteristics Variation Variation is a name given to differences in a species, e.g. dogs: Variation is due to each animal having different GENETIC INFORMATION in their cells. Variation within a species is due to the ENVIRONMENT and GENES. Cells mutate when: • Mistakes are made when copying chromosomes • Ionizing radiation changes the DNA • Some chemicals can change DNA What if sex cells mutate? • The mutation may have no effect • The fertilized egg may not develop • The offspring may have a better chance of surviving and reproducing. Then the mutated gene passes on to the next generation and becomes more common. • Over many years and generations, new species have evolved. • This is the result of the effects of mutations, environmental change, and natural selection. How did humans evolve? Many different Those with hominid species bigger brains and evolved from a who walked upright common ancestor had a better chance of surviving Gradually all hominid species except Homo sapiens became extinct How are human communication systems organised? • Multicellular organisms evolved 2 communication systems: Nervous Systems Hormones QUESTIONS • B3 Life on Earth 1. What makes organisms members of the same species? 2. What are the two different causes of variation in living things? 3. What is the evidence for evolution? 4. Describe selective breeding and give an example? 5. Briefly describe Natural selection 6. Sum up the main ideas of Lamark and Darwin. 7. What are the body’s two main communication systems? The Nervous System • Uses electrical impulses to transmit messages and respond quickly • Is made of neurones • Is controlled by the brain and spine (CNS) Hormones • Are chemicals that travel in the blood • Carry information all over the body • Bring about long lasting effects • Eg testosterone insulin Homeostasis • Homeostasis is keeping a constant internal environment. • If you are too hot the brain detects that the blood temperature is too high. • An electrical impulse makes your sweat glands work. Food webs Food webs contain many interlinking food chains… because all living organisms depend on other species and the environment for their needs. Breaking the links Q. What would happen if an animal or organism was “taken out”? e.g take out the crab: 1) What would happen to the population of flat winkles? They would probably ______ because… 2) What would happen to the population of herring gulls? They would probably ______ because … Why do some species become extinct? Sudden changes in environmental Other species in the conditions food web become extinct New species arriving that compete with, eat, X or cause disease of the species Why is biodiversity important? • We may develop different medicines from species that we do not yet use. • For new food sources : breeding cultivated rice with wild species may produce rice that is resistant to disease. • This allows sustainable development : using the environment to meet the needs of people today without damaging Earth for the people of the future.
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