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Ck 12: Life Science: Prokaryotic and Eukaryotic Cells
[Free Registration/Login may be required to access all resource tools.] There are two basic types of cells, prokaryotic cells and eukaryotic cells. The main difference between eukaryotic and prokaryotic cells is that eukaryotic cells...
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Ck 12: Life Science: Producers
[Free Registration/Login may be required to access all resource tools.] Energy is the ability to do work. In organisms, this can be physical work, like walking or jumping, or it can be the work used to carry out the chemical processes in...
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Ck 12: Life Science: Plant Reproduction and Life Cycle
[Free Registration/Login may be required to access all resource tools.] The life cycle of a plant is very different from the life cycle of an animal. Humans are made entirely of diploid cells (cells with two sets of chromosomes). Our...
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Ck 12: Life Science: Plant Cell Structures
[Free Registration/Login may be required to access all resource tools.] Even though plants and animals are both eukaryotes, plant cells differ in some ways from animal cells. Plant cells have a large central vacuole, are surrounded by a...
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Ck 12: Life Science: Photosynthesis
[Free Registration/Login may be required to access all resource tools.] Plants are producers, which means they are able to make their own food, as well as "food" for other organisms. Plants are also autotrophs - they collect energy from...
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Ck 12: Life Science: Peripheral Nervous System
[Free Registration/Login may be required to access all resource tools.] The peripheral nervous system (PNS) contains all the nerves in the body that are found outside of the central nervous system. They include nerves of the hands, arms,...
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Ck 12: Life Science: Natural Selection
[Free Registration/Login may be required to access all resource tools.] The theory of evolution by natural selection means that the inherited traits of a population change over time. Inherited traits are features that are passed from one...
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Ck 12: Life Science: Microscopes
[Free Registration/Login may be required to access all resource tools.] A microscope is a tool used to make things that are too small to be seen by the human eye look bigger. Before microscopes were invented in 1595, the smallest things...
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Ck 12: Life Science: Lymphatic System
[Free Registration/Login may be required to access all resource tools.] If pathogens get through the body's first two lines of defense, a third line of defense takes over. This third line of defense involves the immune system. The immune...
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Ck 12: Life Science: Population Growth Patterns
[Free Registration/Login may be required to access all resource tools.] What does population growth mean? You can probably guess that it means the number of individuals in a population is increasing. The population growth rate tells you...
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Ck 12: Life Science: Importance of Biodiversity
[Free Registration/Login may be required to access all resource tools.] Biodiversity is a measurement of the amount of variation of the species in a given area. More specifically, biodiversity can be defined as the variety of life and...
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Ck 12: Life Science: Limiting Factors to Population Growth
[Free Registration/Login may be required to access all resource tools.] For a population to be healthy, factors such as food, nutrients, water and space, must be available. Limiting factors are resources or other factors in the...
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Ck 12: Life Science: Digestive System Organs
[Free Registration/Login may be required to access all resource tools.] The mouth and stomach are just two of the organs of the digestive system. Other digestive system organs are the esophagus, small intestine, and large intestine....
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Ck 12: Life Science: Nonrenewable Resources
[Free Registration/Login may be required to access all resource tools.] A nonrenewable resource is a natural resource that is consumed or used up faster than it can be made by nature. Two main types of nonrenewable resources are fossil...
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Ck 12: Life Science: Vitamins and Minerals
[Free Registration/Login may be required to access all resource tools.] Vitamins and minerals are also nutrients. They do not provide energy, but they are needed for good health. Learn more about vitamins and minerals in this learning...
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Ck 12: Life Science: Reproductive Behavior of Animals
[Free Registration/Login may be required to access all resource tools.] Some of the most important animal behaviors involve mating. Mating is the pairing of an adult male and female to produce young. Adults that are most successful at...
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Ck 12: Life Science: Theory of Evolution by Natural Selection
[Free Registration/Login may be required to access all resource tools.] Do you ever wonder why some birds are big like ostriches and some birds are small like robins? Or why a lion has a mane while a leopard has spots? In the 19th...
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Ck 12: Life Science: Structural Evidence for Evolution
[Free Registration/Login may be required to access all resource tools.] Even though two different species may not look similar, they may have similar internal structures that suggest they have a common ancestor. That means both evolved...
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Ck 12: Life Science: Fossils
[Free Registration/Login may be required to access all resource tools.] Fossils are the preserved remains of animals, plants, and other organisms from the distant past. By studying fossils, evidence for evolution is revealed....
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Ck 12: Life Science: Human Population
[Free Registration/Login may be required to access all resource tools.] How quickly is the human population growing? If we look at worldwide human population growth from 10,000 BCE through to today, our growth looks like exponential...
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Ck 12: Life Science: Taste and Smell
[Free Registration/Login may be required to access all resource tools.] Imagine you open a gallon of milk, and you suddenly smell a foul odor. Your sense of smell has informed you that the milk has spoiled. So you pour the spoiled milk...
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Ck 12: Life Science: Mass Extinctions
[Free Registration/Login may be required to access all resource tools.] An organism goes extinct when all of the members of a species die out and no more members remain. Extinctions are part of natural selection. Species often go extinct...
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Ck 12: Life Science: Innate Behavior of Animals
[Free Registration/Login may be required to access all resource tools.] Many animal behaviors are ways that animals act naturally. They are not learned behaviors. Cats are natural-born hunters. They don't need to learn how to hunt....
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Ck 12: Life Science: Cyclic Behavior of Animals
[Free Registration/Login may be required to access all resource tools.] Many animal behaviors change in a regular way. They go through cycles. Some cycles of behavior repeat each year. Other cycles of behavior repeat every day. Learn...