Why are there so many insects?
Insects have the largest number of species among animals on the Earth. Out of ten different animal species, eight are of insects. They can survive in almost all types of habitats regardless of temperature. Many can survive only in specific environmental conditions, while others are found in all parts of the world. The reason for this difference within the species is not known. Insects have six legs and a body divided into three parts with a solid outer covering called the armour. Many insects are useful (bees which pollinate fruit tree flowers), while others are harmful (plant louse on indoor plants).
How do fish reproduce?
Female fish lay eggs – they spawn. The male fish eject their semen on the eggs, and thus fertilize them. Many fish like the salmon return to their place of birth for laying eggs. The salmon eggs hatch in streams and from freshwater fish turn into saltwater fish in 1 – 3 years. Then, they remain in the sea up to 4 years. When they wish to reproduce, they return to their birthplace covering a distance of as much as 6000 km. They have to swim against the current and overcome all the obstacles in their way. Once at the destination they spawn. It is a mystery how the salmons find their birthplace. Scientists assume that they are guided by the magnetic field of the Earth.
What is the difference between reptiles and amphibians?
Amphibians such as frogs and newts are more dependent on the aquatic habitat than reptiles. Their eggs are protected only by a thin membrane and are laid in water. Many of them go through several developmental stages, till they become adults. Unlike amphibians, reptiles such as tortoises, crocodiles or snakes have a scaly skin. Their eggs are covered by a hard calcite shell and are laid on land.