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Ck 12: Life Science: Nerve Cells and Nerve Impulses
[Free Registration/Login may be required to access all resource tools.] The nervous system is made up of nerves. A nerve is a bundle of nerve cells. A nerve cell that carries messages is called a neuron. The messages carried by neurons...
CK-12 Foundation
Ck 12: Life Science: Nails and Hair
[Free Registration/Login may be required to access all resource tools.] Along with the skin, the integumentary system includes the nails and hair. Both the skin and hair contain the tough protein, keratin. The keratin makes your nails...
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Ck 12: Life Science: Plant Hormones
[Free Registration/Login may be required to access all resource tools.] Plants may not move, but that does not mean they don't respond to their environment. Plants can sense gravity, light, touch, and seasonal changes. Learn more about...
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Ck 12: Life Science: Preserving Water Sources
[Free Registration/Login may be required to access all resource tools.] It might seem like there is plenty of water on Earth, but that's not really the case. Water is a limited resource. That means that it is used faster than it is...
CK-12 Foundation
Ck 12: Life Science: Seeds and Seed Dispersal
[Free Registration/Login may be required to access all resource tools.] Plants seem to grow wherever they can. How? Plants can't move on their own. So how does a plant start growing in a new area? Learn more about seeds and seed...
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Ck 12: Life Science: Tracing Evolution
[Free Registration/Login may be required to access all resource tools.] How fast is evolution? Can you actually see evolution happening within your lifetime? Usually evolution takes a long time. So how can we visualize how it has...
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Ck 12: Life Science: Choosing Healthy Foods
[Free Registration/Login may be required to access all resource tools.] Foods such as whole grain breads, fresh fruits, and fish provide nutrients you need for good health. But different foods give you different types of nutrients. You...
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Ck 12: Life Science: Frogs and Toads
[Free Registration/Login may be required to access all resource tools.] Frogs and toads are amphibians in the order Anura. In terms of classification, there is actually not a big difference between frogs and toads. Learn more about frogs...
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Ck 12: Life Science: Human Skeletal System
[Free Registration/Login may be required to access all resource tools.] How important is your skeleton? Can you imagine your body without it? You would be a wobbly pile of muscle and internal organs, and you would not be able to move....
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Ck 12: Life Science: Menstrual Cycle
[Free Registration/Login may be required to access all resource tools.] The menstrual cycle is a series of changes in the reproductive system of mature females that repeats every month. Learn more about the menstrual cycle in this...
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Ck 12: Life Science: Segmented Worms
[Free Registration/Login may be required to access all resource tools.] When you think of worms, you probably picture earthworms. There are actually many types of worms, including flatworms, roundworms, and segmented worms. Earthworms...
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Ck 12: Life Science: Circulation and the Lymphatic System
[Free Registration/Login may be required to access all resource tools.] The lymphatic system is a network of vessels and tissues that carry a clear fluid called lymph. The lymphatic system works with the cardiovascular system to return...
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Ck 12: Life Science: Excretion
[Free Registration/Login may be required to access all resource tools.] You might have noticed that sometimes your urine is darker than usual. This can happens when your body is low on water and trying to reduce the amount of water lost...
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Ck 12: Life Science: Human Digestive System
[Free Registration/Login may be required to access all resource tools.] Nutrients in the foods you eat are needed by the cells of your body. How do the nutrients in foods get to your body cells? What organs and processes break down the...
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Ck 12: Life Science: Mammal Characteristics
[Free Registration/Login may be required to access all resource tools.] What is a mammal? They walk, run, swim, and fly. They live in the ocean, fly in the sky, walk on the prairies, and run in the savanna. There is a tremendous amount...
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Ck 12: Life Science: Types of Archaea
[Free Registration/Login may be required to access all resource tools.] The first archaea described could survive in extremely harsh environments in which no other organisms could survive. As a result, archaea are often distinguished by...
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Ck 12: Life Science: Chromosomal Disorders
[Free Registration/Login may be required to access all resource tools.] Some children are born with genetic defects that are not carried by a single gene. Instead, an error in a larger part of the chromosome or even in an entire...
CK-12 Foundation
Ck 12: Life Science: Types of Mollusks
[Free Registration/Login may be required to access all resource tools.] There are approximately 160,000 living species and probably 70,000 extinct species of mollusks. They are typically divided into ten classes, of which two are...
CK-12 Foundation
Ck 12: Life Science: Vision Correction
[Free Registration/Login may be required to access all resource tools.] You probably know people who need eyeglasses or contact lenses to see clearly. Maybe you need them yourself. Lenses are used to correct vision problems. Two of the...
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Ck 12: Life Science: Bacteria Nutrition
[Free Registration/Login may be required to access all resource tools.] Like all organisms, bacteria need energy, and they can acquire this energy through a number of different ways. Learn more about bacteria nutrition in this learning...
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Ck 12: Life Science: Food and Nutrients
[Free Registration/Login may be required to access all resource tools.] Refusing one meal won't stunt your growth. But lack of proper food over a period of time can lead to malnutrition. That means the body is not getting enough...
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Ck 12: Life Science: Fungi Reproduction
[Free Registration/Login may be required to access all resource tools.] Different fungi reproduce in different ways. Many fungi reproduce both sexually and asexually. However, some reproduce only sexually and some only asexually. Asexual...
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Ck 12: Life Science: Importance of Reptiles
[Free Registration/Login may be required to access all resource tools.] Reptiles play an important role in the life of humans. In addition to playing an important role in many food chains, which keep the populations of small animals...
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Ck 12: Life Science: Lizards and Snakes
[Free Registration/Login may be required to access all resource tools.] Lizards and snakes belong to the largest order of reptiles, Squamata. Lizards are a large group of reptiles, with nearly 5,000 species, living on every continent...