Biology…What is it?

Biology is the study of life.

SO….What does it mean to be living?

Characteristics of Life

To be considered living, an organism must…..

1. Be based on a universal genetic code.

– DNA

2. Grow and develop

Characteristics of Life

4. Use materials and energy -Metabolism

3. Be able to Reproduce

-Asexually

-Sexually

Characteristics of Life

5. Be able to respond to their environment-stimulusresponseHumans:

Plants:

Characteristics of Life

6. Maintain stable internal environment-Homeostasis

Characteristics of Life

7. Change over time, as a group.-Evolution

8. Made of units called Cells-Unicellular-Multicellular

Cell Theory

Matthias Schleiden

concluded that all plants are made of

cells (1838)

Theodore Schwann

concluded that all animals are made

of cells (1839)

Rudolf Virchowconcluded that all cells came from pre-existing cells

(1855)

Cell Theory

• all living things are made up of cells• cells are the basic units of structure and function in

an organism• new cells are produced from existing cells

Levels of OrganizationLevel Function Example

Organism Single living thing

Organ System Different organs function together

Organ Different tissues function together

Tissues Similar cells function together

Cells Smallest unit of life

Molecules Smallest unit of a substance with the same properties

Atom Smallest unit of matter

NervousSystem

Brain

Nervous Tissue

Nerve Cell

Protein

Carbon

Human

Viruses…Living or not?

Now that we know what makes something living, let’s look at a virus.

Viruses come in many different shapes and they cause many different diseases but, they all have something in common….

Viruses and Living Cells

Characteristic Virus Cell

Structure Genetic material surrounded by a protein capsid

Cell membrane, cytoplasm; genetic material, ribosomes

Reproduction Only within a host cell Yes, sexually and asexually

Genetic Code DNA or RNA DNA

Growth and Development

No Yes

Obtain and Use Energy

No Yes

Response to Environment

No Yes

Evolve Yes Yes

Homeostasis No Yes

Verdict? No, Viruses are not considered a

living thing because they do not meet all of the living characteristics.