Habitats
Habitat is a place where a community of organisms live together. The organisms - plants and animals - in a habitat need each other to survive, and different habitats support different plants and animals. Woodland is an example of terrestrial habitat whereas a pond is an aquatic habitat.
The conditions in a habitat make up the organisms' enviroment. Plants and animals develop features and become adapted to their environments over millions of years. For example, tigers developed camouflage stripes to adapt to their grassland environment.
Fossils
Fossils are traces of organisms preserved in rocks. Most fossils were formed when the remains of plants and animals were buried by sediment and they give a record of organisms that lived a long time ago. They also provide evidence that animals and plants can change over long periods of time. If a species cannot adapt when the environment changes it may become extinct. This is Darwin’s theory of evolution through natural selection.
Fossil remains have been found in rocks of all ages. Fossils of the simplest organisms are found in the oldest rocks, and fossils of more complex organisms in the newest rocks. This supports the theory of evolution, which states that simple life forms gradually evolved into more complex ones.
Simple life forms first developed more than three billion years ago - the Earth is about 4.5 billion years old. The timeline below shows some of the key events in the evolution of life forms on Earth, from the first bacteria to the first modern humans:
- 3.5 billion years ago (Archaeozoic era) - first bacteria (prokaryotes)
- 2.0 billion years ago (Archaeozoic era) - first cells with organelles (eukaryotes)
- 1.0 billion years ago (Proterozoic era) - first multicellular oragnisms: algae, seaweeds, sponges, jellyfish, worms
- 500 million years ago (Proterozoic era) - first fish
- 450 million years ago (Paleozoic era) - first land plants and fungi
- 390 million years ago (Paleozoic era) - first amphibians, insects and repitiles. Much of land surface covered in fern forests which will eventually become coal
- 250 million years ago (Mesozoic era) - first mass extinction of life forms (the Permian-Triassic Extinction)
- 220 million years ago (Mesozoic era) - dinosaurs evolve
- 200 million years ago (Mesozoic era) - first mammals and birds
- 130 million years ago (Mesozoic era) - first flowering plants
- 65 million years ago (Cenozoic era) - second mass extinction (Cretaceous - Tertiary Extinction). Dinosaurs die out
- 45 million years ago (Cenozoic era) - first modern mammals
- 35 million years ago (Cenozoic era) - first grasses
- 3 million years (Cenozoic era) - first hominids (Australopithecus)
- 200 thousand years ago (Cenozoic era) - first Homo sapiens evolve, first Neanderthals evolve
- 100 thousands years ago (Cenozoic era) - Humans colonise all habitable land masses
- 20 thousand years ago (Cenozoic era) Neanderthals die out, leaving Homo sapiens as only species of human
- 15 thousand years ago (Cenozoic era) - agriculture begins
Adaption
Individuals that are poorly adapted to their environment are less likely to survive and reproduce. This means that their genes are less likely to be passed to the next generation. Given enough time, a species will gradually evolve or become extinct.
Food Chains and Food Webs
The plants and animals in a food chain belong to the same ecosystem. All the living things in one habitat are in the same community, and a community and its environment are known as an ecosystem.
Food chains show what is eaten by what, the arrows show the 'food for' and also the 'energy flow'. Food webs contain many interlinked food chains.
Producer - all plants are producers, they use the Sun's energy to produce food energy
Consumer - all animals are consumers
Primary consumer - an animal which eats producers (plants)
Secondary consumer - an animal which eats primary consumers
Tertiary consumer - animal which eats secondary consumers
Herbivore - animals which only eat plants (e.g. tadpoles, rabbits, caterpillars)
Carnivore - eats only animals, never plants
Omnivore - eats both plants and animals
Top carnivore - is not eaten by anything else
Green plants are the world's food factories. Using energy from the Sun, plants make food in the form of glucose, a form of sugar. The glucose is made from carbon dioxide and water. Once glucose is made, it can be converted into other carbohydrates such as starch. Starch is the form in which plants store food. Potatoes store starch in tubers; cabbages store startch in their leaves and celery store theirs in their stems. Primary consumers get their energy from the carbohydrates stored in plants. Omnivores get theirs from plants and animals whereas carnivores get their energy from eating other animals.
The food chain shows how energy passes from the producer to the consumers. The number of organisms decreases going from one level to the next. This is becuase the energy is 'lost' from the food chain but has been used to keep everything alive. This is also shown by the number pyramids representing the size of the populations where the first level (the producer level) is the most populated and the population size decreases from one level to the next.
Whereas energy is lost in a food chain, poisons build up as they are passed along a food chain - they get more concentrated going up through the chains with increasing harmful effects.
Survival and Population
Pressure is the effect of a force