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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.

Comparison of the processes of mitosis and meiosis. Mitosis produces two diploid (2n) somatic cells that are genetically identical to each other and the original parent cell, whereas meiosis produces four haploid (n) gametes that are genetically unique from each other and the original parent (germ) cell. Mitosis involves one cell division, whereas meiosis involves two cell divisions.

Outcomes:

• Describe how the concept of density relates to an object's mass and volume.
• Explain how objects of similar mass can have differing volume, and how objects of similar volume can have differing mass.
• Explain why changing an object's mass or volume does not affect its density (ie, understand density as an intensive property).
• Measure the volume of an object by observing the amount of fluid it displaces.
• Identify an unknown material by calculating its density and comparing to a table of known densities.

Learn about DNA (deoxyribonucleic acid). Overview of DNA bases, complementary base pairing, and the structure of the double helix.

This YouTube video delves into the impact that tourism can have on a country's economy.

This YouTube video delves into the impact that tourism can have on the environment.

Enzymes as catalysts for reactions in biological systems; discussion of substrates, active sites, induced fit, and activation energy.

Clarifying some points on evolution and intelligent design.

This video explains how to calculate the gradient (slope) of a straight line.

This YouTube video explains how to calculate an irregular area on a map.