topic 1- introduction to cell
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Topic 1
Introduction to cell
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Biologyis the systematic study of life
The branch of science that is concerned with
the study on life and living organisms
The characteristics of life: All living organismsshare the following characteristics of life:
i) Organization: the levels of biological organization
extend as follows:
Introduction
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ii) Acquisition of materials and energy from the
environment
iii) Reproduction: they produce offspring
iv) Respond to stimuli: they react to internal and
external events
v) Internal homeostasis
vi) Growth and developmentvii) Adaptations to a changing environment
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The Diversity and Unity of Cells
Cells are the fundamental units of all living
things
Although the diversity organisms isincredible, the cells of all organism share
many similarities.
Only a few structural differences betweenmost types of cells.
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Cell Theory
All organisms are composed of one or
more cells.
Cells are the basic living unit of structureand function in organisms.
All cells come only from other cells.
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Cell Theory (cont.)
Four generalizations constitute the cell theory:
1. Every living organism consists of one ormore cells
2. A cell is the smallest unit of life, individuallyaliveeven as part of a multicelled organism
3. All living cells come from division ofpreexisting cells
4. Cells containhereditary material, which
they pass to their offspring during division
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Two main types of cells
There are 2 components to the cell theory.
i) All organisms are composed of cells.
ii)Cells come only from preexisting cells.
All cells have an outer membrane called theplasma membrane.
The plasma membrane encloses asemifluid substance called thecytoplasmand the cells genetic material.
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The word cellentered biology in the 17thcentury.
Anton van Leeuwenhoekis recognized forinventing one of the earliest microscopes and
observing a first cell.
Robert Hookeconfirmed earlier findings andcoined the term cell.
Matthias Schleidenstated that plants are
composed of cells.
Theodore Schwannstated that animals are
composed of cells.
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Size of Cell
Cell size varies, but are quite small.
A frogs egg is about 1 millimeter (1mm) in
diameter. Large enough to be seen by naked eye
Most cells are smaller than 1mm.
Some cells are as small as 1 micrometer
(1mm).
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Size of Cell (cont.)
Cells being small is an advantage formulticellular organisms:
Nutrientssuch as glucose can enter thecell.
Wastessuch as CO2 can exit cell.
Therefore surface area affects the ability toget materials in and out of a cell.
As cells increase in volume, the proportionateamount of surface area decreases.
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Size of Cell (cont.)
For a cube-shaped cell:
The volumeincreases by the cube of the
sides (height X width X depth). The surface area increases the square of
the sides and the number of sides (height
X width X 6). If a cell doubles in size, its surface area
increases fourfold, while the volume
increases eightfold.
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Surface Area / Volume Ratio
All 3 have the same volume, but the group
on the right has 4 times the surface area
One 4-cm cube Eight 2-cm cubes Sixty-four 1-cm cubes
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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How scientist study cells?
Most cells are far too small to see withthe naked eye
We use different types of microscopes
and techniques to reveal cells andtheir internal and external details
Cells under the microscope
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Cells under the microscope (cont.)
Our bodies are comprised of severalhundred different types of cells, withbillions of each cell type present.
Each type of cell is specialized in itsparticular function.
Cells are so small that a microscope isneeded to see them.
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Types of microscopes
1. Light microscopes
2. Phase-contrast
microscopes
3. Fluorescence
microscope
4. Electronmicroscopes
5. TransmissionelectronMicroscopes
6. Scanning electronmicroscopes
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Examples of microscopes
Compound light microscope Transmission electronmicroscope (TEM)
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phosphor
screen
incoming electron beam
condenser
lens
specimen
on gridobjective
lensprojectivelens
Transmission electron microscope (TEM)
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Cells under the microscope (cont.)
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Cells under the microscope (cont.)
Light microscopes can be used to view
cells but not in much detail.
Electron microscopes allow the
structure of cells to be viewed in greater
detail.
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Sizes of Living Things
10 m1 m0.1 m1 cm1 mm100 m10 m100 nm10 nm1 nm0.1 nm
mousefrog egg
human eggmost bacteria
virus
protein
atomant
electron microscope
light microscope
human eye
human
blue whale
chloroplastrose
1 km100 m1 m
amino
acids
plant and
animal
cells
ostrich
egg
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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ALight micrograph. BLight micrograph. CFluorescence
micrograph.
DA transmission
electron micrograph
reveals fantastically
detailed images of
internal structures.
E A scanning
electron micro-graph
shows surface
details. SEMs may beartificially colored to
highlight specific
details.
A reflected light
microscope captures
light reflected fromspecimens.
A phase-contrast
microscope yields high-
contrast images oftrans- parent
specimens. Dark areas
have taken up dye.
This image shows
fluorescent lightemitted by
chlorophyll
molecules in the
cells.
Different views of different microscopes, reveal
different characteristics of the same organism
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Cells under the microscope (cont.)
Cells are small because they are limited bytheir surface-area-to-volume-ratio.
The surface area of a cell is critical because
it must be large enough to allow adequatenutrients to enter the cell.
Cells can increase their surface area with
specialized projections such as microvilli.
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Traits common to all cells
Cells differ in size, shape, and function.
Although cells differ in size, shape andfunction, each starts out with a plasmamembrane, cytoplasm, and a region of
DNA (in eukaryotic cells, a nucleus)
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