The Circulation of Blood
The circulation of blood is the continuous movement of blood around the body, pumped by the heart through a network of vessels. This understanding,…
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Mendelian Inheritance
Mendelian inheritance is the set of principles describing how traits are passed from parents to offspring through discrete units we now call genes.…
The Human Skeleton
The human skeleton is the internal framework of bones that supports the body, protects its organs, and allows it to move. An adult skeleton has 206…
Cell Theory
Cell theory is one of the foundational ideas of biology. It holds that all living things are made of cells, that the cell is the basic unit of life,…
The Human Eye
The human eye is the organ of sight, a remarkable structure that turns light into the images we see. Roughly the size of a ping pong ball, it…
Photosynthesis
Photosynthesis is the process by which plants, algae, and some bacteria convert light energy (typically sunlight) into chemical energy stored in…
Octopus
The octopus is a soft-bodied marine animal with eight arms, a bulbous head, and a level of intelligence unmatched among invertebrates. A member of…
Polar Bear
The polar bear is the largest land carnivore on Earth and the undisputed master of the Arctic. Superbly adapted to one of the planet's harshest…
Panspermia
Panspermia is the hypothesis that life exists throughout the universe and is spread between worlds by space dust, meteoroids, asteroids, and comets.…
The Gaia Hypothesis
The Gaia hypothesis proposes that life and its physical environment on Earth form a single, self regulating system that keeps the planet suitable for…
The Human Brain
The human brain is the command centre of the body and the most complex object known in the universe. Weighing only about 1.4 kilograms, it contains…
Bald Eagle
The bald eagle is a large bird of prey native to North America and the national bird and emblem of the United States. With its white head and tail,…
Blue Whale
The blue whale is the largest animal ever known to have lived, bigger even than any dinosaur. Reaching up to about 30 metres long and weighing as…
Lion
The lion (Panthera leo) is a large cat of the genus Panthera, the second-largest living cat after the tiger. Once spread across Africa, southern…
The Rare Earth Hypothesis
The Rare Earth hypothesis proposes that complex, multicellular life, of the kind found on Earth, is extremely rare in the universe, because it…
Honey Bee
The honey bee is a flying insect famous for two things: producing honey, and pollinating a vast share of the plants that humans and ecosystems depend…
Germ Theory of Disease
The germ theory of disease is the scientific theory that many illnesses are caused by microorganisms, living agents too small to see, that invade the…
Water (H₂O)
Water is a chemical compound with the formula H₂O, consisting of two hydrogen atoms covalently bonded to one oxygen atom. Its bent molecular geometry…
The Human Heart
The human heart is a muscular pump, roughly the size of a clenched fist, that drives blood through the body every moment of life. Beating around…
Nature versus Nurture
The nature versus nurture debate asks how much of who we are, our intelligence, personality, talents, and behavior, comes from our genes, and how…