Air moves into the lungs when the air pressure in the lungs is lower than the air pressure outside of the lungs. This occurs when the muscels of the diaphragm contract.
You can see this by breathing in and out deeply. When you breath in you can feel your chest being pushed up and out by your diaphragm. The reason the pressure in the chest is lower is that when you breathe in you are increasing the volume of your chest. As there is the same amount of air in your chest the pressure decreases.
Answer:
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms' activities. This chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water, "light", and sunthesis, "putting together". In most cases, oxygen is also released as a waste product. Most plants, most algae, and cyanobacteria perform photosynthesis; such organisms are called photoautotrophs. Photosynthesis is largely responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and supplies most of the energy necessary for life on Earth.
Although photosynthesis is performed differently by different species, the process always begins when energy from light is absorbed by proteins called reaction centres that contain green chlorophyll pigments. In plants, these proteins are held inside organelles called chloroplasts, which are most abundant in leaf cells, while in bacteria they are embedded in the plasma membrane. In these light-dependent reactions, some energy is used to strip electrons from suitable substances, such as water, producing oxygen gas. The hydrogen freed by the splitting of water is used in the creation of two further compounds that serve as short-term stores of energy, enabling its transfer to drive other reactions: these compounds are reduced nicotinamide adenine dinucleotide phosphate (NADPH) and adenosine triphosphate (ATP).
The endosymbiosis explains how eukaryotic cells may have evolved from prokaryotic cells.
