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

Plant cells have a cell wall in addition to a cell membrane, whereas animal cells have only a cell membrane. Plants use cell walls to provide structure to the plant. Plant cells contain organelles called chloroplasts, while animal cells do not. Chloroplasts allow plants to make the food they need to live using photosynthesis.

In this unit you will learn:

• About the turning effect of forces
• Turning effects are called moments
• Understand that regular and irregular shaped objects have a centre of gravity
• An objects centre of gravity determines if it is in a stable, neutral, or unstable equilibrium

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

Overview of animal and plant cells. Topics include cell walls, vacuoles, chloroplasts, peroxisomes, lysosomes, mitochondria, etc.