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.