Gas exchange is the process by which oxygen is taken in from the environment and carbon dioxide is released. This mainly happens in the lungs where oxygen is diffused into the bloodstream and carbon dioxide is diffused back into the lungs to be exhaled.
Digestion is the process by which food is broken down into smaller molecules that can be absorbed into the bloodstream. This process starts in the mouth, continues in the stomach, and finishes in the small intestine.
Respiration
Respiration is the process by which cells convert glucose and oxygen into energy, releasing carbon dioxide and water as byproducts. There are two types of respiration: aerobic (with oxygen) and anaerobic (without oxygen).
Anaerobic respiration: Glucose → Lactic acid + Energy (in animals) or Glucose → Ethanol + Carbon Dioxide + Energy (in yeast and plants)
Photosynthesis
Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy. Plants use chlorophyll to capture sunlight, which is then used to convert carbon dioxide and water into glucose and oxygen.
Exothermic reactions release energy into the surroundings, usually in the form of heat. This causes the temperature of the surroundings to increase. (e.g., combustion)
Endothermic reactions absorb energy from the surroundings, usually in the form of heat. This causes the temperature of the surroundings to decrease. (e.g., thermal decomposition)
Combustion and Thermal Decomposition
Combustion is a rapid chemical process that involves the reaction between a substance with an oxidant, usually oxygen, to produce heat and light. It is an exothermic reaction.
Thermal decomposition is the breakdown of a chemical substance by heat. It is an endothermic reaction.
The Periodic Table, Elements, and Compounds
The periodic table is a tabular arrangement of chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties. Elements are substances that cannot be broken down into simpler substances by chemical means. Compounds are substances consisting of two or more different elements chemically bonded together.
Forces, Pressure and Hooke's Law
Force is any interaction that, when unopposed, will change the motion of an object. Pressure is the force applied perpendicular to the surface of an object per unit area. (P = \frac{F}{A}), where P is pressure, F is force, and A is area.
Hooke's Law states that the force needed to extend or compress a spring by some distance is proportional to that distance. (F = -kx), where F is the force, k is the spring constant, and x is the displacement.
Natural Selection and Evolution
Natural selection is the process by which organisms better adapted to their environment tend to survive and reproduce more than those less adapted