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Chapter 3 Cell Structure.

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Presentation on theme: "Chapter 3 Cell Structure."— Presentation transcript:

1 Chapter 3 Cell Structure

2 Section 3-1 Looking at Cells

3 Microscopes Reveal Cell Structure
Cells are too small to see with the naked eye Robert Hooke used a crude microscope to observe a thin slice of cork in 1665, he saw “a lot of little boxes”

4 Characteristics of Microscopes
Two common kinds of microscopes In a light microscope, light passes through one or more lenses to produce an enlarged image An electron microscope forms an image of a specimen using a beam of electrons rather than light

5 Microscopes cont… An image produced by a microscope is a micrograph
Magnification is the ability to make an image appear larger Resolution is a measure of the clarity of an image You need both high magnification and a good resolution to be able to view the details

6 Compound Light Microscope
Light microscopes that have two lenses are called compound light microscopes Both lenses magnify the image Objective lens is closest to the specimen, and the ocular lens is closest to your eye 40x objective lens and a 10x ocular lens produces a 400x magnification Most powerful magnification is 2,000x

7 Electron Microscopes Magnification as high as 200,000 X
The electron beam and the specimen must be placed in a vacuum chamber so the electron beam does not bounce off gas molecules Living cells cannot survive in a vacuum

8 Transmission Electron Microscope
The electron beam is directed at a thin specimen stained with metal ions The heavily stained specimen absorbs electrons and forms a fluorescent image on a screen

9 Scanning Electron Microscope
The electron beam is focused on a specimen coated with a thin layer of metal The electrons that bounce off the specimen form a 3-D image

10 Section 3-2 Cell Features

11 Cell Theory The cell theory has 3 parts:
All living things are made of one or more cells Cells are the basic units of structure and function in organisms All cells arise from existing cells

12 Cells must be small Small cells function more efficiently than large cells Small cells can exchange substances more rapidly than large cells because small objects have a higher surface area to volume ratio so substances do not need to travel as far to reach the center a small cell

13 Prokaryotes Prokaryotes are the smallest and simplest cells
They are single-celled organism that lacks a nucleus and other internal compartments The genetic material in a prokaryote is a single, circular molecule of DNA

14 Bacteria Modern prokaryotes are informally called bacteria
Many bacteria grow and divide very quickly Some need oxygen to survive, others do not Some bacteria can even make their own food

15 Bacteria cont… The cytoplasm, or interior, of a bacterial cell includes everything inside the cell membrane There are no interior structures dividing the cell so enzymes and other structures move freely DNA is circular and near the center of cell

16 Bacteria cont… Bacteria have strong cells walls for structure and support Some bacteria have capsules which allow bacteria to cling to almost anything.. Food, teeth, skin Many bacteria have flagella, or long threadlike structures that propel movement


18 Eukaryotic Cells The first cells with internal compartments developed 1.5 billion years ago A eukaryote is an organism whose cells have a nucleus The nucleus is an internal compartment that houses DNA

19 Eukaryotic Cells cont…
Other internal compartments or organelles allow eukaryotes to function in ways different from bacteria Organelles are structures that carry out specific activities in the cell Many eukaryotes have cilia or short hair like structures to propel them

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