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Copyright Pearson Prentice Hall

Least complex Most Complex

AtomsMoleculesCellsTissueOrganOrgan SystemOrganismPopulationCommunityEcosystemBiosphere

Levels of Organization

7-1 Life Is Cellular

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The Discovery of the Cell


The invention of the microscope allowed us to make cells visible.


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Early Microscopes

In 1665, Robert Hooke used an early compound microscope to look at a thin slice of cork, a plant material.

In Holland around the same time, Anton van Leeuwenhoek used a microscope to observe living things.

Cells are the basic units of life.


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The Cell Theory

1838 -1855: Scientists, such as Schleiden Schwann, and Virchow as well as other biologists observed the cell, developed theories, and summarized their ideas. These discoveries led to the cell theory.


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The Cell theory states:

•All living things are composed (made up of) of cells.

•Cells are the basic units of structure and function in living things.

•New cells are produced from existing cells.


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MICROSCOPES

LIGHT MICROSCOPE (LM) LM - Works by passing visible through a specimen, such as an microorganism or a piece of plant or animal tissue

Micrograph- a photo taken through a microscope

Magnification - the increase in the actual size

Resolving power: a measure of the clarity


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Exploring the Cell

MICROSCOPES

Electron Microscopes (EM) - 2 Types

Electron microscopes reveal details 1000 times smaller than those visible in light microscopes.

Electron microscopy can be used to visualize only nonliving, preserved cells and tissues.


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Exploring the Cell

1. TRANSMISSION ELECTRON MICROSCOPES (TEMS)

• Used to study cell structures and large protein molecules

• Used to study the details of the internal cell structure


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Exploring the Cell

2. SCANNING ELECTRON MICROSCOPES (SEMS)

• Produce three-dimensional images of cells

• Specimens do not have to be cut into thin slices

• Used to study the external cell structure


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Exploring the Cell

Scanning Electron Micrograph of Neurons


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Prokaryotes and Eukaryotes

CELL TYPES

Prokaryotes and Eukaryotes

Contain small organs called organelles


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Prokaryotes & Eukaryotes

All cells, Prokaryotic & eukaryotic have three common features.

Nucleus, which contains DNA, the genetic material contained in one or more chromosomes and located in a non-membrane bound nucleoid region in prokaryotes and a membrane-bound nucleus in eukaryotes


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Three main parts

Plasma membrane, a phospholipid bilayer with proteins; separates the cell from the surrounding environment; functions as a selective barrier for the import and export of materials

Cytoplasm, the rest of the material of the cell within the plasma membrane, excluding the nucleoid region or nucleus, that consists of a fluid portion called the cytosol


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Prokaryotes

Prokaryotic cells

•Plasma membrane

•Cytoplasm

•Nucleoid region

•DNA

•Ribosomes

•Pili

•Flagellum

Smaller and simpler than eukaryotes

Bacteria are prokaryotes


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Eukaryotic Cells

Eukaryotes

Plant and Animal Cells

More complex - Many cells are highly specialized.Plants, animals, fungi, and protists are eukaryotes


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PLANT CELL

CYTOSKELEYTON: Microtubules, CYTOSKELEYTON: Microtubules, Intermediate filaments, & microfilaments

NucleusNucleus


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Plant Cells

PLANT CELLS contain chloroplasts, a cell wall, & a central vacuole, which are NOT found in animal cells.

Chloroplasts are plant cell organelles that contain chlorophyll and the enzymes required for photosynthesis.

Mitochondria - (singular = mitochondrion) All eukaryotic cells contain mitochondria, often many hundreds per cell. They harvest energy from food during cellular respiration and generate ATP (energy).


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Cytoskeleton

CYTOSKELETON: Structural Support

•Microfilaments - solid, helical rods composed of globular proteins called actin (shape & movement)

•Intermediate filaments - made of fibrous proteins, for reinforcement and anchoring

•Microtubules - straight, hollow tubes made up of globular proteins called tubulin ( tubulin pairs)

Together they maintain cell shape, anchor organelles, and cause cell movement.


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Cell Movement

Cell Movement: Cilia and Flagella

Cilia -short, numerous appendages

• On cell lining the human windpipe

Flagella - long, less numerous appendages

• sperm

Both are composed of a core of microtubules; a ring of 9 - microtubule doublets that surround a central pair of microtubules; combined called 9 + 2. The 9-doublets extend into an anchoring structure called a basal body (identical to centrioles). The basal body has 9 - microtubule triplets.

The microtubule doublets are connected by dynein arms that help them bend and move (H - page 65)


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Endomembrane system

Endomembrane system (4.14) -Transport

•Nucleus

•nuclear envelope

•endoplasmic reticulum (ER)- both

•Golgi apparatus

•Transport vesicles (develop into lysosomes and vacuoles.

•plasma membrane.


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Cell Junctions

Extracellular Matrix

1. Tight junctions: bind cells together

2. Anchoring junctions (gap): attach adjacent cells to each other

3. Communicating junctions : channels that allow water and other small molecules to flow between cells.

Anchoring junctionsAnchoring junctions

CommunicatingCommunicating

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