There are 90 different elements, like the oxygen that we breathe, that can be found in nature. When two or more elements combine, they are held together by a chemical bond and form a compound. In 1869, chemist Dmitri Mendeléev organized the elements into a chart that is known as the Periodic Table of Elements.
Cells are the building blocks of life. According to Cell Theory, all living things are made of cells; cells are the basic unit of life; and all cells come from other cells. The nucleus of a cell has chromosomes made of DNA, which make each individual unique.
All plants need sun, water, air, and food to grow. Plants are anchored to the ground by their roots, which take in nutrients from the soil. Stems and stalks hold up plants and give them shape, and also hold the plumbing system of the plant. Leaves are the place where food is made for the plant. Many plants make crops for us to eat.
Plants and animals that need one another in an environment form an ecosystem. All ecosystems have energy pyramids that show the exchange of energy from one food source to another. Biomes are areas of the Earth that have their own climate and characteristics. Ecosystems all over the world are in danger due to pollution, hunting, and other factors. By conserving water, recycling, and reducing pollution, we can help protect Earth's ecosystems and biomes.
What things do all animals have in common? How do scientists classify animals? How are humans classified and what makes them different? Enter the animal kingdom with zoologists who study animals! You'll explore how scientists use a system called taxonomy to classify and organize different kinds of living things as you explore the wonderful world of animals.
To understand why humans are the way they are, look at cellsâ€”especially the material in the center, called chromosomes. People have 23 pairs of chromosomes, so each cell has 46 in all. Parents pass chromosomes to their children. DNA carries the genetic information in alleles and is the blueprint for the cells of an organism. DNA tells one's body how to put certain materials together to produce certain traits.