MBBS Biology

Chemical Basis of Life

  • Matter consists of elements and compounds. A compound forms when elements combine in fixed proportions and undergo a chemical reaction. A mixture forms when substances combine in any proportions without a chemical reaction.
  • Energy is a property of matter. It cannot be created or destroyed. Organisms obtain light energy from sunlight or chemical energy from food and change the energy into different forms, including heat energy.
  • Matter can exist in one of several differen tstates, including a gas, liquid, or solid state. States of matter differ in the amount of energy their molecules have. When matter recycles, it changes state by gaining or losing energy.
  • Carbon’s exceptional ability to form bonds with other elements and with itself allows it to form a huge number of large, complex molecules called organic molecules. These molecules make up organisms and carry out life processes.
  • Carbohydrates are organic molecules that consist of carbon, hydrogen, and oxygen. They are made up of repeating units called saccharides. They provide cells with energy, store energy, and form structural tissues.
  • Lipids are organic compounds that consist of carbon, hydrogen, and oxygen. They are made up of fatty acids and other compounds. They provide cells with energy, store energy, and help form cell membranes.
  • Proteins are organic compounds that consist of carbon, hydrogen, oxygen, nitrogen, and, in some cases, sulfur. They are made up of repeating units called amino acids. They provide cells with energy, form tissues, speed up chemical reactions throughout the body, and perform many other cellular functions.
  • Nucleic acids are organic compounds that consist of carbon, hydrogen, oxygen, nitrogen, and phosphorus. They are made up of repeating units called nucleotides. They contain genetic instructions for proteins, help synthesize proteins, and pass genetic instructions on to daughter cells and offspring.
  • A chemical reaction is a process that changes some chemical substances into others. It involves breaking and forming chemical bonds. Types of chemical reactions include synthesis reactions and decomposition reactions.
  • Some chemical reactions are exothermic, which means they release energy. Other chemical reactions are endothermic, which means they consume energy. All chemical reactions require activation energy, which is the energy needed to get a reaction started.
  • Rates of chemical reactions depend on factors such as the concentration of reactants and the temperature at which reactions occur. Both factors affect the ability of reactant molecules to react.
  • Enzymes are needed to speed up chemical reactions in organisms. They work by lowering the activation energy of reactions.
  • Most of Earth’s water is salt water located on the planet’s surface. Water is constantly recycled through the water cycle.
  • Water molecules are polar, so they form hydrogen bonds. This gives water unique properties, such as a relatively high boiling point.
  • A solution is a homogeneous mixture in which a solute dissolves in a solvent. Water is a very common solvent, especially in organisms,
  • The ion concentration of neutral,pure water gives water a pH of 7 and sets the standard for defining acids and bases. Acids have a pH lower than7,and bases have a pH higher than 7.
  • Water is essential for most life processes, including photosynthesis, cellular respiration, and other important chemical reactions that occur in organisms.
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