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These three short online lessons discuss asteroids, comets and meteors.

Introduction to cell theory--the idea that 1) all living things are made of one or more cells, 2) cells are the basic unit of life and 3) all cells come from other cells. Explore the roles that Hooke, Leeuwenhoek and others played in developing cell theory.

Hooke and Leeuwenhoek were two of the first scientists to use microscopes to study the microscopic world of cells. Hooke coined the term "cell" after observing the tiny compartments in cork, while Leeuwenhoek discovered a variety of living creatures in pond water, blood, and other samples. They contributed to the cell theory by suggesting that cells are the fundamental units of life and structure, and that all living things consist of one or more cells that originate from other cells by division. 

All living things are made up of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular).

Video 1: What are frequency polygons?
Video 2: Examples of frequency polygons
Video 3: Further examples of frequency polygons

By the end of this unit you will be able to:

• Calculate measures of central tendency and percentiles on grouped data.
• Construct a frequency polygon.
• Construct a line graph.

This video explores how to find the mean from data in a table.

This video explores the histogram: which is one of the ways in which to present data.

Video 1: How to create a line graph based on data
Video 2: Examples of different line graphs
Video 3: Further examples of line graphs

Introduction to the cell.

Other objects in the solar system are discussed in this online textbook viz. asteroids, meteorites, comets and dwarf planets.