What is Biology?

Biology: the scientific study of living things

• Life can be defined as an organized genetic unit capable of metabolism, homeostasis, reproduction, and evolution.

• Life is incredibly diverse and complex, and not all organisms display all these characteristics of life all the time.

Living things: all the organisms descended from a single-celled ancestor.

• All are composed of cells.

• A cell is the basic fundamental unit of life.

What is Biology?

Characteristics of living organisms:

• Consist of one or more cells

• Contain genetic information that allows them to reproduce themselves

• Grow, develop and have a limited life span

• Are genetically related and have evolved

• Have the ability to adapt

What is Biology?

Characteristics of living organisms:

• Can obtain and use materials and energy.

(nutrients converted into ATP)

• Exchange gases such as oxygen and carbon dioxide

• Respond to their environment

• Can regulate their internal environment – maintain homeostasis

What is Biology?

Evolution: a central theme

Living systems evolve through differential survival and reproduction.

The Many Faces of Life (Part 1)

The Many Faces of Life (Part 2)

What is Biology?

Unicellular organisms: a single cell carries out all the functions of life

Multicellular organisms: made of many cells that are specialized for different functions

All Life Consists of Cells

The study of cells was made possible by the invention of the microscope.

• Discovery of cells was made possible by the invention of the microscope in the 1590s by Dutch spectacle makers Zaccharias and Hans Janssen.

• The first biologists to improve and apply this technology to living organisms were Antony van Leeuwenhoek and Robert Hooke in the late 1600s.

• Hooke coined the term cells to describe the repeated structures he saw in cork tissue.

What is Biology?

Cell Theory:

• Cells are the basic structural and physiological units of all living organisms.

• Cells are both distinct entities and building blocks of more complex organisms.

(Schleiden and Schwann 1838)

What is Biology?

Cell Theory:

• All cells come from preexisting cells.

• All cells are similar in chemical composition.

• Most of the chemical reactions of life occur within cells.

• Complete sets of genetic information are replicated and passed on during cell division.

What is Biology?

Charles Darwin proposed that all living organisms are descended from common ancestors.

Evolution by natural selection

What is Biology?

Species: a group of organisms that look alike and can breed successfully with one another.

What is Biology?

Humans select for desired traits when breeding animals.

Darwin postulated that natural selection could occur through differential survival and reproductive success.

What is Biology?

Traits that increase the probability that the organism will survive and reproduce will become more common in the population.

Natural selection leads to adaptation.

Adaptations to the Environment

What is Biology?

DNA: the information that is passed from parent to daughter cells

Genome: sum total of all the DNA in the cell

All cells in a multicellular organism have the same genome.

What is Biology?

DNA: repeating subunits—nucleotides

Gene: a specific segment of DNA molecule—contains information for making proteins

Mutations are alterations in the nucleotide sequence.

The Genetic Code Is Life’s Blueprint

What is Biology?

Cells acquire nutrients from their environment.

Nutrients supply energy and materials for building biological structures (synthesis).

Nutrient molecules contain energy in the chemical bonds.

Energy from Nutrients Can Be Stored or Used Immediately

What is Biology?

Living organisms control their internal environment.

Multicellular organisms have an internal environment that is not cellular.

Cells are specialized, and organized into tissues, tissues are organized into organs.

Biology Is Studied at Many Levels of Organization

What is Biology?

Living organisms interact:

They may be territorial or they may cooperate.

Figure 1.7 Conflict and Cooperation

What is Biology?

Individuals are part of populations.

Interacting populations of many different species form a community.

Interacting communities in a given area form ecosystems.

How is All Life on Earth Related?

Life arose by chemical evolution.

Molecules that could reproduce themselves were critical.

Biological molecules were then enclosed in membranes.

Life’s Calendar

How is All Life on Earth Related?

For 2 billion years, life consisted of single cells—prokaryotes.

These cells were in the oceans, protected from UV radiation.

How is All Life on Earth Related?

Metabolism: the sum of all chemical reactions that occur in cells.

Photosynthesis evolved about 2.5 billion years ago.

Photosynthetic Organisms Changed Earth’s Atmosphere

The first photosynthetic cells were similar to cyanobacteria.

How is All Life on Earth Related?

Consequences of photosynthesis:

• O2 accumulated in the atmosphere

• Aerobic metabolism began

• Ozone layer formed—allowed organisms to live on land

How is All Life on Earth Related?

Eukaryotic cells evolved from prokaryotes.

Organelles—membrane bound compartments with specialized functions:

• Nucleus

• Chloroplast