Changes in Matter

Chapter Eighteen: The Chemistryof Living Systems

• 18.1 The Chemistry of Carbon

• 18.2 Protein, Fats, and Nucleic Acids

Investigation 18A

• What are some common molecules that contain carbon?

Carbon and It’s Chemistry

18.1 The chemistry of carbon• Carbon molecules come in three basic forms:

straight chains, branching chains, and rings. • All three forms are found in important biological

molecules.

18.1 Carbohydrates

• All living things contain:

– carbohydrates– proteins– fats– nucleic acids

18.1 Carbohydrates• Carbohydrates are

mainly composed of carbon, hydrogen, and oxygen in a ratio of about 1:2:1.

• Carbohydrates exist as small molecules, like glucose, and long-chain molecules, like starches.

• Table sugar is a carbohydrate called sucrose.

18.1 Proteins• Proteins are large

molecules composed of carbon, hydrogen, oxygen, nitrogen, and trace elements.

18.1 Fats

• Fats are medium-to-large nonpolar molecules that do not dissolve in water.

18.1 Nucleic Acids

• Nucleic acids such as DNA store the genetic code that allows organisms to reproduce.

18.1 Carbohydrates

• Carbohydrates are relatively small molecules used to store and transfer energy in living systems.

• Carbohydrates are classified as either sugars or starches.

18.1 Carbohydrates

• Starches are long chains of simple sugars joined together.

• Cellulose is the primary molecule in plant fibers, including wood.

18.1 Photosynthesis• Photosynthesis is the foundation of the food

chain on Earth.

• For every glucose sugar molecule produced, six molecules of carbon dioxide are removed from the air, and six molecules of oxygen are produced.

18.1 Respiration• Animals get energy and nutrients by

breaking up glucose, starch, and other organic molecules.

• Cellular respiration breaks down glucose into water and carbon dioxide again, extracting energy in the process.

• Each cell converts the energy in glucose into chemical energy stored in molecules of ATP.

18.1 The importance of water

• Liquid water is essential to life as we know it.

• The human body is typically between 60 and 65 percent water by weight.

• Most of the chemical reactions that sustain life only work in solution.

18.1 The importance of water

• There are 3 important characteristics of water that make it essential for life:

– Water is a good solvent.– Liquid water has a wide

temperature range.– Water has a high specific

heat capacity.