•The Origin of Life•Conditions for the Origin of Life

•Cells

TODAY’S OBJECTIVES:

ORIGIN OF LIFE

The evolution of the Earth has involved the following sequence of events

Unicellular or single celled organisms

Multi-cellular organisms Increase in cell number Cell specialization

CONDITIONS FOR THE ORIGIN OF LIFE

A sequence of chemical reactions lead to life on Earth

Sun and planets coalesced as result of a supernova

On Earth, heavier materials sank to the core while lighter substances concentrated the surface

Hydrogen, Oxygen and Carbon

CONDITIONS (CONT.)

Current Atmosphere:

78% N2

21% O2

Trace amounts of CO2,

Primordial Atmosphere:

Far more Hydrogen

Far less Oxygen

NH3, H2O, and CH4

CHON

4 common elements in living organisms

Carbone, Hydrogen, Oxygen, and Nitrogen

Some include 2 others Phosphorus and Sulfur

P is crucial in DNA/RNA ; forms core of the phosphate groups in ATP/ADP

S is used in the formation of some amino acids

CONDITIONS (CONT.)

Ocean Formation:

High temperatures of Earth’s early crust continually evaporated water that had rained

As the Earth cooled, rain water washed dissolved minerals to low areas creating lakes, seas, and oceans

Volcanic explosions on land and in our oceans were the cause for accumulation of salts in our oceans

STANLEY MILLER EXPERIMENT

Miller duplicated chemical conditions of early oceans and atmosphere and provided an energy source (electric spark)

Found that the warm water and gasses when provided an energy source would continue to spark for about a week, forming organic compounds.

Further experimentation supports Miller’s evidence by stating that amino acid that make up proteins form quite readily in this environment.

CELLS

Magnification needed to be seen

Termed by Robert Hooke in 1665

Observed cork under magnification

Cell

Functional basic unit of life

Hooke’s initial discovery led to differentiation in plant and animal cells

Plant cells have a thick cell wall

Animal cells have a thinner, more flexible plasma (cell) membrane

CELLS

Unicellular organisms

carry out all necessary functions that support life within one cell without any help from other cells

Multi-cellular organisms

An organism consisting of many cells

Cells have specific functions, and the aggregate of cells forms a complex organism

CELL THEORY

Termed by Matthias Shleiden and Theodor Schwann

Cell Theory states:

1. Cells are the fundamental units of life

2. Cells are the smallest entities that can be called living

3. All organisms are made up of one or more cells and new cells arise from pre-existing cells.

CELL STRUCTURE AND SIZE

Cells provide structure and form to the body by coming in a variety of shapes and sizes

e.g., round, concave, rectangular, elongate, tapered, spherical, etc.

Range from 5 – 50 microns Short for micrometer (10-3)

CELL STRUCTURE AND SIZE

Cell size:

Restriction by ratio of surface area to volume

Cells have a relationship with their surrounding medium and constantly absorb and release molecules.

Cell volume increases much more rapidly in perspective with the surface area and cell may become too large to maintain a stable internal environment

CYTOPLASM & NUCLEOPLASM

Cytoplasm

Everything within the plasma membrane except the nucleus

Nucleoplasm

Contents within the nuclear membrane

CELL MEMBRANE

Cell Membrane:

Membrane surrounding the cytoplasm at the surface of the cell

Contains various amounts of proteins and lipids

Provides support, shape, strength, and regulates flow of materials

Fluid-mosaic model Explains how molecules can move in and out of

cell

MOVEMENT THRU MEMBRANE

Cells use 2 methods to keep a Chemical homeostasis or maintaining a constant internal environment.

Passive transport Molecule movement occurs on its own without

any energy input

Active transport Cell expends energy to move molecules

QUESTIONS TO THINK ABOUT

1. There are 4 elements common to living things. Name them.

2. What is a cell? How do plant and animal cells differ?

3. What is the cell theory?

4. What is a plasma (cell) membrane?

EXIT TICKET

Why are most cells small?