Chapter 2: The Nature of Life

2.1 Characteristics of Living Things Organism: Another name for a living thing.

Living things exhibit 5 characteristics:

1. Living things are made up of cells. Cell: a structure that contains all of the materials needed for life. Organisms can be made of one cell (a unicellular organism) or of many cells (a multicellular organism).

2. Living things respond to their environment. Stimulus: A condition or event in your surroundings. Response: A change that happens in response to a stimulus.

Homeostasis: The process by which living things respond to stimuli in ways that allow them to maintain and balance internal conditions necessary for life.

3. Living things can adapt. Adaptation: Any trait that helps an organism survive in its environment.

4. Living things reproduce. Reproduction: The process by which living things make more organisms like themselves. Species: A group of organisms that has similar physical characteristics and can mate to produce offspring capable of producing their own offspring.

5. Living things grow and develop. Unicellular organisms get larger. Multicellular organisms increase the number of cells that make up the organism.

2.2 The Needs of Living Things Organisms have 5 different needs that must be met in order for them to survive:

1. Energy Energy: The ability to cause change or do work. Heterotrophs: Organisms that get matter and energy by eating plants or other organisms.

2. Water Water makes up approximately 60% of the human body! Water is involved in the chemical reactions and processes in the body. It’s a solvent (can dissolve other substances). Water also helps maintain body temperature.

3. Temperature Organisms need to live within a certain temperature range. Endotherm: An organism that produces thermal energy to maintain its temperature.

4. Air All organisms need gases (oxygen in our case) to survive.

5. Space All organisms need a place to live that provides all of the things that they need to survive , as well as protection.

2.3 The Chemistry of Living Things Matter: Anything that has mass and takes up space. Atoms: The small units that matter is made from. Each element’s atoms are different. Atoms join together to make molecules.

Organic molecules contain bonds between carbon and hydrogen atoms. The four main classes of organic molecules are: carbohydrates proteins lipids nucleic acids

Carbohydrates Found in breads, fruits, and pastas. Provide energy to the cells. Monosaccharide: Simple sugar. (glucose) Disaccharide: Two simple sugars bonded together. ( sucrose – table sugar) Polysaccharide: Chains of simple sugars bonded together. (starch, cellulose, glycogen)

Lipids Oils and fats. Main component of membranes that surround cells. Also store energy and provide insulation. Insoluble: does not dissolve in water.

Proteins Amino acid: the building blocks of proteins There are 20 amino acids that, in different combinations, make up every type of protein. Building/binding materials, enhance chemical reactions, transport materials, and allow some actions.

Nucleic Acids Genetic information. DNA: deoxyribonucleic acid. Contains the instructions for making all of a cell’s proteins. RNA: ribonucleic acid. Translates the information in DNA to make proteins.