CellsHow their

discovery led to the Cell

Theory

CellsHow their

discovery led to the Cell

Theory

HistoryCells were unknown until the discovery of microscopes in the 1650’s

two scientists working independently built the first microscopes

Anton von Leeuwenhoek in Holland

Robert Hooke in England

Leeuwenhoek

Studied pond water, sour milk, and semen

named moving organisms “animalcules”

scared people and caused a sensation

Leeuwenhoek’s drawings of “animalcules” set off a flurry of amateur and sometimes ridiculous claims, such as:

- pond water animalcules causing madness!

and...

Human sperm cells contain tiny human beings!

Today we can look back and think “crazy,” but at the time people took these ideas very seriously.

Hooke

Studied cork - a kind of tree bark

named the structures he saw “cells” because they reminded him of the small rooms monks slept in.

Definition of Cell

• A cell is the smallest unit that is capable of performing life functions.

• A cell is the basic unit of life.

Examples of CellsAmoeba Proteus Plant

Stem

Red Blood CellNerve

Cell

Bacteria

The Cell TheoryThe cell theory has three parts:

All living things contain at least one cell

Cells are the smallest working units of all living things.

Cells can only come from pre-existing cells through cell division (meiosis)

The cell theory-a closer look

All living things contain at least one cell

Many scientists working after Hooke and Leeuwenhoek observed different plants and animals

Each of them noted that no matter what they observed, if it was alive it had cells.

Cells are the smallest working units of all living things.

Scientists (Theodor Schawnn &Matthias Schleiden) quickly realized that when cells were dissected or broken open they died

This meant that whatever “life” is, it is something that happens inside cells

Cells can only come from pre-existing cells through cell division

does not answer the question of where the first cell came from or how it came to be.

has not been disproved yet- no scientist has ever built a living cell from nonliving organic molecules

Spontaneous Generation

From pre-historic times to about 1850, most people believed that under the right conditions, living things could spontaneously appear from non-living material.

People throughout the Middle Ages

believed that mice could be “created” spontaneously by putting grain in dark, quiet place

and leaving it for a few weeks.

The discovery of cells only confused people more- If cells are alive, then where do they come from?

Can these almost invisible things appear spontaneously from the air?

Francesco RediBorn 1626 in Italy

First to challenge the idea of spontaneous generation

Did not accept the common belief that flies magically appeared from rotting meat

Redi’s Experiment

IV=cover

DV=presence of flies

Hypothesis: If a jar containing rotting meat is covered, then it will produce no flies

Redi’s Conclusions

Flies lay eggs, which grow into maggots, which metamorphose into flies

If flies can’t lay eggs, then no new flies can grow

Fly eggs

Objections to RediMany people rejected Redi’s claim that flies do not spontaneously generate

Their reasoning:

“sealing the jar closed prevented a magical essence from entering the rotting meat and brining it to life”

“Scientists seek only to challenge belief systems and stir things up”

1729. Italian

Believed microbes that spoil food come from the air and can be killed by boiling

IV= air, DV=food spoilage

Hypothesis: If air is allowed to reach food, then microbes will get in and cause it to spoil

Lazzaro Spallanzani

Spallanzani’s Experiment

Flask 1: boiled broth, open

Flask 2: boiled broth, sealed shut

Results

Flask 1 spoiled

Flask 2 did not spoil

Objections to Spallanzani

Sealing the flask shut blocked the entrance of a magical life force in the air from getting to the broth.

Since few people had seen these microbes, few people believed him.

Louis Pasteur1822. France

Supported that spontaneous generation is a myth

Invented pasteurization (sterilization by heat)

Pasteur’s Experiment

An improvement on Spallanzani’s work

Used special “swan-neck flasks” that allowed air in but kept bacteria out

IV= bacteria, DV=spoiling broth

Hypothesis; If boiled broth is kept free of bacteria, then it will not spoil even if air can reach it.

The curved neck allows air in but traps bacteria-carrying dust and dirt

particles

Spontaneous generation is dead!

Redi didn’t believe in it, and did an experiment using flies

Spallanzani didn’t believe in it, and experimented with broth

Pasteur disproved it conclusively with his open-air yet spoilage free flasks.

Pasteur is the father of modern microbiologysupported the last part of the cell theory: cells only come from pre-existing cells

identified yeasts as the microbes that change grape juice into wine

showed that heat can be used to sterilize foods and preserve them in sealed glass containers, and later cans.

The cell theory is one of the most important theories in biology.

All living things contain at least one cell

Cells are the smallest living units of matter

Cells can only come from pre-existing cells

Cell Structure & Function

http://koning.ecsu.ctstateu.edu/cell/cell.html

Examples of Cells

Amoeba Proteus Plant

Stem

Red Blood CellNerve

Cell

Bacteria

Two Types of Cells

• Prokaryotic

• Eukaryotic

ProkaryoticDo not have structures surrounded by membranes

Few internal structures

One-celled organisms, Bacteria

http://library.thinkquest.org/C004535/prokaryotic_cells.html

EukaryoticContain organelles surrounded by membranes

Most living organisms

PlantAnimal

“Typical” Animal Cell

“Typical” Plant Cell

Cell Parts

Organelles

Surrounding the Cell

Cell Membrane

Outer membrane of cell that controls movement in and out of the cell

Double layer

http://library.thinkquest.org/12413/structures.html

Cell Wall

Most commonly found in plant cells & bacteria

Supports & protects cells

Inside the Cell

Nucleus

Directs cell activities

Separated from cytoplasm by nuclear membrane

Contains genetic material - DNA

Nuclear Membrane

Surrounds nucleus

Made of two layers

Openings allow material to enter and leave nucleus

Chromosomes

In nucleus

Made of DNA

Contain instructions for traits & characteristics

Nucleolus

Inside nucleus

Contains RNA to build proteins

Cytoplasm

Gel-like mixture

Surrounded by cell membrane

Contains hereditary material

Endoplasmic Reticulum

Moves materials around in cell

Smooth type: lacks ribosomes

Rough type (pictured): ribosomes embedded in surface

Ribosomes

Each cell contains thousands

Make proteins

Found on ribosomes & floating throughout the cell

MitochondriaProduces energy through chemical reactions – breaking down fats & carbohydrates

Controls level of water and other materials in cell

Recycles and decomposes proteins, fats, and carbohydrates

Chemical diagram of an ATP molecule.

Golgi Bodies

Protein 'packaging plant'

Move materials within the cell

Move materials out of the cell

LysosomeDigestive 'plant' for proteins, fats, and carbohydrates

Transports undigested material to cell membrane for removal

Cell breaks down if lysosome explodes

VacuolesMembrane-bound sacs for storage, digestion, and waste removal

Contains water solution

Help plants maintain shape

Chloroplast

Usually found in plant cells

Contains green chlorophyll

Where photosynthesis takes place