El Niño

A periodic climate pattern that occurs across the tropical Pacific Ocean every five years.

Underground waters

Groundwater and aquifers are types of underground waters.


Regular dice can be used for solving statistical and probability exercises.

Volume of a tetrahedron

To calculate the volume of a tetrahedron we start by calculating the volume of a prism.

Dividing Space into Regions by 3 Planes

Division of space by three intersecting planes in several different arrangements.

String quartet

A string quartet consists of four string players, it appeared in the late 18th century.


The bell is a percussion instrument and an idiophone. Many types of bells exist.


Ports must provide necessary infrastructure and services for industry and marine transportation.

Types of surface epithelium

Surface epithelia cover the external and internal surfaces of the body

Male reproductive system

The reproductive system consists of organs which work together for the purpose of reproduction.


This animation demonstrates the anatomy of birds through the example of mallards.

Types of synovial joints

Synovial joints can be categorised by the direction of movement they allow.

Patellar reflex

The reflex triggered by the stretching of the thigh extensor muscle is the patellar reflex.

Endocrine system

Glands of the endocrine system secrete hormones into the blood.


The zygote is the initial cell formed when two gamete cells are joined by means of sexual reproduction.

Common carp

Freshwater fish used as food in many parts of the world.

Grass snake

A type of snake with a characteristic spot on its neck.

Cockchafer (Maybug)

The cockchafer (or maybug) is a widespread bug in Europe. Its larvae, known as chafer grubs are considered a pest.

European mole

Moles are small subterranean mammals with modified, spade-like forelegs.

Freshwater pearl mussel

A species of mollusk widespread in freshwaters.

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