Chapter 4 · 2015. 11. 12. · Introduction •In 1665, Hooke examined a piece of cork under a...

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Campbell Biology: Concepts & Connections, Eighth Edition REECE • TAYLOR • SIMON • DICKEY • HOGAN

Chapter 4

Lecture by Edward J. Zalisko

A Tour of the Cell

Introduction

• Cells have a cytoskeleton that

• provides support and

• allows some cells to crawl and others to swim.

• Our understanding of nature often goes hand in

hand with the invention and refinement of

instruments that extend our senses.

Introduction

• In 1665, Hooke examined a piece of cork under a

crude microscope and identified “little rooms” as

cells.

• Leeuwenhoek, working at about the same time,

used more refined lenses to describe living cells

from blood, sperm, and pond water.

• Since the days of Hooke and Leeuwenhoek,

improved microscopes have vastly expanded our

view of the cell.

Figure 4.0-1

Figure 4.0-2

Introduction to the Cell

Chapter 4: Big Ideas

The Nucleus and

Ribosomes

The Endomembrane

System

Energy-Converting

Organelles

The Cytoskeleton and

Cell Surfaces

INTRODUCTION TO THE CELL

4.1 Microscopes reveal the world of the cell

• A variety of microscopes have been developed for

a clearer view of cells and cellular structure.

• The first microscopes were light microscopes. In a

light microscope (LM), visible light passes

through a specimen, then through glass lenses,

and finally is projected into the viewer’s eye.

• Specimens can be magnified by up to 1,000 times.

• Magnification is the increase in an object’s image

size compared with its actual size.

• Resolution is a measure of the clarity of an image.

In other words, it is the ability of an instrument to

show two nearby objects as separate.

• Microscopes have limitations.

• The human eye and the microscope have limits of

resolution—the ability to distinguish between small

structures.

• Therefore, the light microscope cannot provide the

details of a small cell’s structure.

• Using light microscopes, scientists studied

• microorganisms,

• animal and plant cells, and

• some structures within cells.

• In the 1800s, these studies led to cell theory,

which states that

• all living things are composed of cells and

• all cells come from other cells.

Figure 4.1a

Figure 4.1b

Figure 4.1c

Figure 4.1d

Figure 4.1e-0

Human height

Length of some

nerve and

muscle cells

Chicken egg

Frog egg

Paramecium

Human egg

Most plant and

animal cells

Nucleus

Most bacteria

Mitochondrion

Smallest bacteria

Viruses

Ribosome

Proteins

Lipids

molecules

100 mm

(10 cm)

(1 cm)

100 nm

0.1 nm

100 μm

10 μm

Figure 4.1e-1

Human height

Length of some

nerve and

muscle cells

Chicken egg

Frog egg

Paramecium

Human egg U

100 mm

(10 cm)

(1 cm)

100 μm

Figure 4.1e-2

Frog egg

Paramecium

Human egg

Most plant and

animal cells

Nucleus

Most bacteria

Mitochondrion

Smallest bacteria

Viruses

Ribosome

Proteins

Lipids

molecules

100 nm

0.1 nm

100 μm

10 μm

• Beginning in the 1950s, scientists started using a

very powerful microscope called the electron

microscope (EM) to view the ultrastructure of

cells.

• Instead of light, EM uses a beam of electrons.

• Electron microscopes can

• resolve biological structures as small as 2

nanometers and

• magnify up to 100,000 times.

• Scanning electron microscopes (SEMs) study

the detailed architecture of cell surfaces.

• Transmission electron microscopes (TEMs)

study the details of internal cell structure.

• Differential interference light microscopes amplify

differences in density so that structures in living

cells appear almost three-dimensional.

4.2 The small size of cells relates to the need to exchange materials across the plasma membrane

• Cell size must

• be large enough to house DNA, proteins, and

structures needed to survive and reproduce, but

• remain small enough to allow for a surface-to-

volume ratio that will allow adequate exchange with

the environment.

Figure 4.2a

Total volume

Total surface

Surface-to-

volume ratio

27 units3 27 units3

54 units2 162 units2

• The plasma membrane forms a flexible boundary

between the living cell and its surroundings.

• Phospholipids form a two-layer sheet called a

phospholipid bilayer in which

• hydrophilic heads face outward, exposed to water,

• hydrophobic tails point inward, shielded from water.

• Membrane proteins are embedded in the lipid

bilayer.

• Some proteins form channels (tunnels) that shield

ions and other hydrophilic molecules as they pass

through the hydrophobic center of the membrane.

• Other proteins serve as pumps, using energy to

actively transport molecules into or out of the cell.

Figure 4.2b

Outside cell

Inside cell

Hydrophilic

Hydrophobic

Phospholipid

Channel

protein

Hydrophilic

regions of

a protein

Hydrophobic

regions of

a protein

Figure 4.UN01

4.3 Prokaryotic cells are structurally simpler than eukaryotic cells

• Bacteria and archaea are prokaryotic cells.

• All other forms of life are composed of eukaryotic

cells.

• Eukaryotic cells are distinguished by having

• a membrane-enclosed nucleus and

• many membrane-enclosed organelles that perform

specific functions.

• Prokaryotic cells are smaller and simpler in

structure.

• Prokaryotic and eukaryotic cells have

• a plasma membrane,

• an interior filled with a thick, jellylike fluid called the

cytosol,

• one or more chromosomes, which carry genes

made of DNA, and

• ribosomes, tiny structures that make proteins

according to instructions from the genes.

• The inside of both types of cells is called the

cytoplasm.

• However, in eukaryotic cells, this term refers only

to the region between the nucleus and the plasma

membrane.

• In a prokaryotic cell,

• the DNA is coiled into a region called the nucleoid

(nucleus-like) and

• no membrane surrounds the DNA.

• Outside the plasma membrane of most prokaryotes

is a fairly rigid, chemically complex cell wall, which

• protects the cell and

• helps maintain its shape.

• Some prokaryotes have surface projections.

• Short projections help attach prokaryotes to each

other or their substrate.

• Longer projections called flagella (singular,

flagellum) propel a prokaryotic cell through its liquid

environment.

Figure 4.3-0

Fimbriae

Ribosomes

Nucleoid

Plasma

membrane

Cell wall

Capsule Bacterial

chromosome

A typical rod-shaped

bacterium

A colorized TEM of the

bacterium Escherichia coli

Flagella

Figure 4.3-1 Fimbriae

Ribosomes

Nucleoid

Plasma

membrane

Cell wall

Capsule Bacterial

chromosome

A typical rod-shaped

bacterium Flagella

Figure 4.3-2

A colorized TEM of the

bacterium Escherichia coli

4.4 Eukaryotic cells are partitioned into functional compartments

• A eukaryotic cell contains

• a membrane-enclosed nucleus and

• various other organelles (“little organs”), which

perform specific functions in the cell.

• The structures and organelles of eukaryotic cells

perform four basic functions.

1. The nucleus and ribosomes are involved in the

genetic control of the cell.

2. The endoplasmic reticulum, Golgi apparatus,

lysosomes, vacuoles, and peroxisomes are

involved in the manufacture, distribution, and

breakdown of molecules.

3. Mitochondria in all cells and chloroplasts in plant

cells are involved in energy processing.

4. Structural support, movement, and

communication between cells are functions of

the cytoskeleton, plasma membrane, and cell

• The internal membranes of eukaryotic cells

partition it into compartments.

• Cellular metabolism, the many chemical activities

of cells, occurs within organelles.

• Almost all of the organelles and other structures of

animals cells are present in plant cells.

• A few exceptions exist.

• Lysosomes and centrosomes containing centrioles

are not found in plant cells.

• Only the sperm cells of a few plant species have

flagella.

• Plant but not animal cells have

• a rigid cell wall that contains cellulose,

• plasmodesmata, cytoplasmic channels through cell

walls that connect adjacent cells,

• chloroplasts, where photosynthesis occurs, and

• a central vacuole, a compartment that stores water

and a variety of chemicals.

Figure 4.4a

endoplasmic

reticulum

Smooth

endoplasmic

reticulum

Golgi apparatus

Lysosome

Mitochondrion

Centrosome

with pair of

centrioles

Plasma

membrane

Peroxisome

Intermediate

filament

Microfilament

Microtubule

CYTOSKELETON

NUCLEUS Nuclear envelope

Nucleolus Chromatin

Ribosomes

Figure 4.4b

endoplasmic

reticulum

Smooth

endoplasmic

reticulum

NUCLEUS Nuclear envelope Nucleolus Chromatin

Ribosomes

Plasma

membrane

Peroxisome

Mitochondrion

Microfilament Microtubule

CYTOSKELETON

Cell wall of

adjacent cell Golgi

apparatus

Plasmodesma

Cell wall

Chloroplast

Central

vacuole

THE NUCLEUS AND RIBOSOMES

4.5 The nucleus contains the cell’s genetic instructions

• The nucleus

• contains most of the cell’s DNA and

• controls the cell’s activities by directing protein

synthesis by making messenger RNA (mRNA).

• DNA is associated with many proteins and is

organized into structures called chromosomes.

• When a cell is not dividing, this complex of proteins

and DNA, called chromatin, appears as a diffuse

mass within the nucleus.

• The double membrane nuclear envelope has

pores that

• regulate the entry and exit of large molecules and

• connect with the cell’s network of membranes

called the endoplasmic reticulum.

• The nucleolus is

• a prominent structure in the nucleus and

• the site of ribosomal RNA (rRNA) synthesis.

Figure 4.5

Nucleolus Nuclear

envelope

Endoplasmic

reticulum

Ribosome

Pore Chromatin

4.6 Ribosomes make proteins for use in the cell and export

• Ribosomes are involved in the cell’s protein

synthesis.

• Ribosomes are the cellular components that use

instructions from the nucleus, written in mRNA, to

build proteins.

• Cells that make a lot of proteins have a large

number of ribosomes.

4.6 Ribosomes make proteins for use in the cell and export

• Some ribosomes are free ribosomes; others are

bound.

• Free ribosomes are suspended in the cytosol.

• Bound ribosomes are attached to the outside of the

endoplasmic reticulum or nuclear envelope.

Figure 4.6

Rough ER

Bound ribosome

Endoplasmic

reticulum

Protein

Ribosome

Free ribosome

THE ENDOMEMBRANE SYSTEM

4.7 Many organelles are connected in the endomembrane system

• Many of the membranes within a eukaryotic cell

are part of the endomembrane system.

• Some of these membranes are physically

connected, and others are linked when tiny

vesicles (sacs made of membrane) transfer

membrane segments between them.

• Many of these organelles interact in the

• synthesis,

• distribution,

• storage, and

• export of molecules.

• The endomembrane system includes the

• nuclear envelope,

• endoplasmic reticulum (ER),

• Golgi apparatus,

• lysosomes,

• vacuoles, and

• plasma membrane.

• The largest component of the endomembrane

system is the endoplasmic reticulum (ER), an

extensive network of flattened sacs and tubules.

4.8 The endoplasmic reticulum is a biosynthetic workshop

• There are two kinds of endoplasmic reticulum,

which differ in structure and function.

1. Smooth ER lacks attached ribosomes.

2. Rough ER has bound ribosomes that stud the

outer surface of the membrane.

Figure 4.8a

Rough ER

Smooth ER

Ribosomes

Rough ER

Smooth ER

Figure 4.8b

Bound ribosome

Transport vesicle

buds off

Secretory

protein

inside trans-

port vesicle

Rough ER

Glycoprotein

Growing

polypeptide

• Smooth ER is involved in a variety of metabolic

processes, including

• the production of enzymes important in the

synthesis of lipids, oils, phospholipids, and steroids,

• the production of enzymes that help process drugs,

alcohol, and other potentially harmful substances,

• the storage of calcium ions.

• Rough ER makes

• additional membrane for itself and

• secretory proteins.

4.9 The Golgi apparatus modifies, sorts, and ships cell products

• The Golgi apparatus serves as a molecular

warehouse and processing station for products

manufactured by the ER.

• Products travel in transport vesicles from the ER to

the Golgi apparatus.

• One side of the Golgi stack serves as a receiving

dock for transport vesicles produced by the ER.

4.9 The Golgi apparatus modifies, sorts, and ships cell products

• Products of the ER are modified as a Golgi sac

progresses through the stack.

• The “shipping” side of the Golgi functions as a

depot, where products in vesicles bud off and travel

to other sites.

Figure 4.9

Golgi apparatus

“Receiving” side of Golgi apparatus

Transport vesicle

from the ER

Transport

vesicle from

the Golgi

“Shipping” side of

Golgi apparatus

4.10 Lysosomes are digestive compartments within a cell

• A lysosome is a membrane-enclosed sac of

digestive enzymes

• made by rough ER and

• processed in the Golgi apparatus

4.10 Lysosomes are digestive compartments within a cell

• Lysosomes

• fuse with food vacuoles and digest food,

• destroy bacteria engulfed by white blood cells, or

• fuse with other vesicles containing damaged

organelles or other materials to be recycled within a

Animation: Lysosome Formation

Figure 4.10a-1

Digestive

enzymes

Lysosome

Plasma membrane

Figure 4.10a-2

Digestive

enzymes

Lysosome

Food vacuole

Plasma membrane

Figure 4.10a-3

Digestive

enzymes

Lysosome

Food vacuole

Plasma membrane

Figure 4.10a-4

Digestive

enzymes

Lysosome

Food vacuole

Plasma membrane

Digestion

Figure 4.10b-1

Lysosome

Vesicle containing

damaged mitochondrion

Figure 4.10b-2

Lysosome

Vesicle containing

Figure 4.10b-3

Lysosome

Digestion Vesicle containing

4.11 Vacuoles function in the general maintenance of the cell

• Vacuoles are large vesicles that have a variety of

functions.

• Some protists have contractile vacuoles, which help

to eliminate water from the protist.

• In plants, vacuoles may

• have digestive functions,

• contain pigments, or

• contain poisons that protect the plant.

Video: Paramecium Vacuole

Figure 4.11a

Contractile

vacuoles

Nucleus

Figure 4.11b

Central vacuole

Chloroplast

Nucleus

4.12 A review of the structures involved in manufacturing and breakdown

• The following figure summarizes the relationships

among the major organelles of the endomembrane

system.

Figure 4.12

Nucleus

Smooth ER

Rough ER

Transport vesicle

Lysosome

Nuclear envelope

Golgi apparatus

Plasma

membrane

Transport

vesicle

4.12 A review of the structures involved in manufacturing and breakdown

• Peroxisomes are metabolic compartments that do

not originate from the endomembrane system.

• How they are related to other organelles is still

unknown.

• Some peroxisomes break down fatty acids to be

used as cellular fuel.

ENERGY-CONVERTING

ORGANELLES

4.13 Mitochondria harvest chemical energy from food

• Mitochondria are organelles that carry out cellular

respiration in nearly all eukaryotic cells.

• Cellular respiration converts the chemical energy

in foods to chemical energy in ATP (adenosine

triphosphate).

• Mitochondria have two internal compartments.

1. The intermembrane space is the narrow region

between the inner and outer membranes.

2. The mitochondrial matrix contains

• the mitochondrial DNA,

• ribosomes, and

• many enzymes that catalyze some of the reactions

of cellular respiration.

• Folds of the inner mitochondrial membrane, called

cristae, increase the membrane’s surface area,

enhancing the mitochondrion’s ability to produce

Figure 4.13

Mitochondrion

Intermembrane

membrane

Crista

Matrix

4.14 Chloroplasts convert solar energy to chemical energy

• Photosynthesis is the conversion of light energy

from the sun to the chemical energy of sugar

molecules.

• Chloroplasts are the photosynthesizing

organelles of plants and algae.

4.14 Chloroplasts convert solar energy to chemical energy

• Chloroplasts are partitioned into compartments.

• Between the outer and inner membrane is a thin

intermembrane space.

• Inside the inner membrane is a thick fluid called

stroma, which contains the chloroplast DNA,

ribosomes, many enzymes, and a network of

interconnected sacs called thylakoids, where green

chlorophyll molecules trap solar energy.

• In some regions, thylakoids are stacked like poker

chips. Each stack is called a granum.

Figure 4.14

Chloroplast

Granum

Stroma

Inner and

outer membranes

Thylakoid

4.15 EVOLUTION CONNECTION: Mitochondria and chloroplasts evolved by endosymbiosis

• Mitochondria and chloroplasts contain

• DNA and

• ribosomes.

• The structure of this DNA and these ribosomes is

very similar to that found in prokaryotic cells.

4.15 EVOLUTION CONNECTION: Mitochondria and chloroplasts evolved by endosymbiosis

• The endosymbiont theory states that

• mitochondria and chloroplasts were formerly small

prokaryotes and

• they began living within larger cells.

Figure 4.15 Endoplasmic

reticulum Nucleus

Ancestor of

eukaryotic cells (host cell)

Mitochondrion

Engulfing of

photosynthetic

prokaryote

Mitochondrion

Photosynthetic eukaryote

Chloroplast

Nonphotosynthetic

eukaryote

At least

one cell

Engulfing of oxygen-

using prokaryote

Figure 4.15-1 Endoplasmic

reticulum Nucleus

Ancestor of

reticulum Nucleus

Ancestor of

Mitochondrion

Nonphotosynthetic

eukaryote

using prokaryote

reticulum Nucleus

Ancestor of

Mitochondrion

Engulfing of

photosynthetic

prokaryote

Mitochondrion

Photosynthetic eukaryote

Chloroplast

Nonphotosynthetic

eukaryote

At least

one cell

using prokaryote

THE CYTOSKELETON AND

CELL SURFACES

4.16 The cell’s internal skeleton helps organize its structure and activities

• Cells contain a network of protein fibers, called the

cytoskeleton, which organize the structures and

activities of the cell.

Video: Cytoplasmic Streaming

• Microtubules (made of tubulin)

• shape and support the cell and

• act as tracks along which organelles equipped with

motor proteins move.

• In animal cells, microtubules grow out from a

region near the nucleus called the centrosome,

which contains a pair of centrioles, each composed

of a ring of microtubules.

• Intermediate filaments

• are found in the cells of most animals,

• reinforce cell shape and anchor some organelles,

• are often more permanent fixtures in the cell.

• Microfilaments (actin filaments)

• support the cell’s shape and

• are involved in motility.

Figure 4.16-0

Nucleus

Microtubule

25 nm Intermediate filament

Microfilament

Figure 4.16-1

Nucleus

Microtubule

Figure 4.16-2

Nucleus

Intermediate filament

Figure 4.16-3

Microfilament

Figure 4.16-4

Nucleus

Figure 4.16-5

Nucleus

Figure 4.16-6

4.17 SCIENTIFIC THINKING: Scientists discovered the cytoskeleton using the tools of biochemistry and microscopy

• In the 1940s, biochemists first isolated and

identified the proteins actin and myosin from

muscle cells.

• In 1954, scientists, using newly developed

techniques of microscopy, established how

filaments of actin and myosin interact in muscle

contraction.

• In the next decade, researchers identified actin

filaments in all types of cells.

4.17 SCIENTIFIC THINKING: Scientists discovered the cytoskeleton using the tools of biochemistry and microscopy

• In the 1970s, scientists were able to visualize actin

filaments using fluorescent tags and in living cells.

• In the 1980s, biologists were able to record the

changing architecture of the cytoskeleton.

Figure 4.17

4.18 Cilia and flagella move when microtubules bend

• The short, numerous appendages that propel

protists such as Paramecium are called cilia

(singular, cilium).

• Other protists may move using flagella, which are

longer than cilia and usually limited to one or a few

per cell.

• Some cells of multicellular organisms also have

cilia or flagella.

Video: Paramecium Cilia

Video: Chlamydomonas

Figure 4.18a

Figure 4.18b

Flagellum

• A flagellum, longer than cilia, propels a cell by an

undulating, whiplike motion.

• Cilia work more like the oars of a boat.

• Although differences exist, flagella and cilia have a

common structure and mechanism of movement.

• Both flagella and cilia are composed of

microtubules wrapped in an extension of the

plasma membrane.

• In nearly all eukaryotic cilia and flagella, a ring of

nine microtubule doublets surrounds a central pair

of microtubules.

• This arrangement is called the 9 2 pattern.

• The microtubule assembly is anchored in a basal

body with nine microtubule triplets arranged in a

Animation: Cilia and Flagella

Figure 4.18c-0

microtubule

doublet

Central

microtubules

Cross-linking

proteins

Motor proteins

(dyneins)

Plasma membrane

Figure 4.18c-1

microtubule

doublet

Central

microtubules

Cross-linking

proteins

Motor proteins

(dyneins)

Figure 4.18c-2

microtubule

doublet

Central

microtubules

Cross-linking

proteins

Motor proteins

(dyneins)

Plasma

membrane

• Cilia and flagella move by bending motor proteins

called dynein feet.

• These feet attach to and exert a sliding force on an

adjacent doublet.

• This “walking” causes the microtubules to bend.

4.19 The extracellular matrix of animal cells functions in support and regulation

• Animal cells synthesize and secrete an elaborate

extracellular matrix (ECM), which

• helps hold cells together in tissues and

• protects and supports the plasma membrane.

4.19 The extracellular matrix of animal cells functions in support and regulation

• The ECM may attach to the cell through other

glycoproteins that then bind to membrane proteins

called integrins.

• Integrins

• span the membrane and

• attach on the other side to proteins connected to

microfilaments of the cytoskeleton.

Figure 4.19

Collagen fiber

EXTRACELLULAR FLUID

CYTOPLASM

Glycoprotein

complex with long

polysaccharide

Connecting

glycoprotein

Integrin

Plasma

membrane

Microfilaments

of cytoskeleton

4.20 Three types of cell junctions are found in animal tissues

• Adjacent cells adhere, interact, and communicate

through specialized junctions between them.

• Tight junctions prevent leakage of fluid across a

layer of epithelial cells.

• Anchoring junctions fasten cells together into

sheets.

• Gap junctions are channels that allow small

molecules to flow through protein-lined pores

between cells.

Animation: Desmosomes

Animation: Gap Junctions

Animation: Tight Junctions

Figure 4.20

Tight junction

Anchoring

junction

Gap junction

Plasma membranes

of adjacent cells

Ions or small molecules Extracellular matrix

Tight junctions

prevent fluid from

moving across a

layer of cells

4.21 Cell walls enclose and support plant cells

• A plant cell, but not an animal cell, has a rigid cell

wall that

• protects and provides skeletal support that helps

keep the plant upright and

• is primarily composed of cellulose.

• Plant cells have cell junctions called

plasmodesmata that allow plants tissues to share

• water,

• nourishment, and

• chemical messages.

Figure 4.21

Vacuole

Plant cell

Plasmodesmata

Primary cell wall

Secondary cell wall

Plasma membrane

Cytosol

4.22 Review: Eukaryotic cell structures can be grouped on the basis of four main functions

• Eukaryotic cell structures can be grouped on the

basis of four functions:

1. genetic control,

2. manufacturing, distribution, and breakdown of

materials,

3. energy processing, and

4. structural support, movement, and intercellular

communication.

Table 4-22-0

Table 4-22-1

Table 4-22-2

You should now be able to

1. Describe the importance of microscopes in

understanding cell structure and function.

2. Describe the two parts of cell theory.

3. Distinguish between the structures of prokaryotic

and eukaryotic cells.

4. Explain how cell size is limited.

5. Describe the structure and functions of cell

membranes.

6. Explain why compartmentalization is important in

eukaryotic cells.

7. Compare the structures of plant and animal cells.

Note the function of each cell part.

8. Compare the structures and functions of

chloroplasts and mitochondria.

9. Describe the evidence that suggests that

mitochondria and chloroplasts evolved by

endosymbiosis.

10. Compare the structures and functions of

microfilaments, intermediate filaments, and

microtubules.

11. Relate the structure of cilia and flagella to their

functions.

12. Relate the structure of the extracellular matrix to

its functions.

13. Compare the structures and functions of tight

junctions, anchoring junctions, and gap

junctions.

14. Relate the structures of plant cell walls and

plasmodesmata to their functions.

15. Describe the four functional categories of

organelles in eukaryotic cells.

Table 4-1

Figure 4.UN02

Figure 4.UN03

a. b. c.

Figure 4.UN04-0

Poles of dividing cell

Figure 4.UN04-1

Poles of dividing cell

Figure 4.UN04-2

Chapter 4 · 2015. 11. 12. · Introduction •In 1665, Hooke examined a piece of cork under a...

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Cell: the smallest unit of life Discovery of Cells 1665- Robert Hooke was the first to identify and name cells. 1674- Anton van Leeuwenhoek made better.

MICROBIOLOGÍA: HISTORIA ETAPA DESCRIPTIVA: S. XVII-XIX HOOKE:1665 Micrographia-Microscopios LEEUWENHOEK: 1679 BACTERIAS Y MICROSCOPIOS SEMMELWEIS: 1850:

TEORÍA CROMOSÓMICA TEORÍA CELULAR ROBERT HOOKE 1665 MICROSCOPIO PRIMITIVO CELDAS = CÉLULA ANTON VAN LEEUWENHOEK 1673 OBSERVA MICROORGANISMOS DE CHARCAS,

Cells. Discovery of Cells 1665: Robert Hooke looking at cork under crude microscope.

El microscopio de roberth hooke en 1665

A Tour of the Cell. Discovery of cells needed microscopes 1665 – Robert Hooke observes “boxes” in cork bark; he calls them cells. 1674 – Anton van Leeuwenhoek.