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