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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).

Meiosis is a process where germ cells divide to produce gametes, such as sperm and egg cells. In prophase I of meiosis, chromosomes condense and homologous recombination takes place, leading to genetic variation through chromosomal crossover. This forms a tetrad, which is made up of four chromatids (two sister chromatids per chromosome).

Outcomes:

• Determine what color the person sees for various combinations of red, green, and blue light.
• Describe the color of light that is able to pass through different colored filters.

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.

This online resource discusses the distribution of earth's water.

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

This online tutorial will explain the earth's shape and its hemispheres.

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