Transcript Chemistry+Cells

The Plant Cell
EARLY STUDIES OF CELLS
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English scientist Robert Hooke was the first person to
describe cells in 1665.
Hooke examined the microscopic structure of cork
and found that it was organized into small units which
resembled the cubicles in monasteries where monks
slept. These rooms were called "cells."
He gave that name to the little compartments in cork
and the term was eventually applied to mean the
basic unit of life.
Although the cork cells were not living, Hooke later
looked at living plants and described cells there also.
Cell Theory
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In the mid-nineteenth century, scientists
firmly established the Cell Theory
which is one of the major principles in
biology. Cell Theory recognizes
 The
cell as the basic unit of life.
 All organisms are composed of cells and
 All cells arise from pre-existing cells.
THE PLANT CELL
All plants are composed of cells.
 Angiosperms are complex multicellular
organisms composed of many different
types of cells.
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Cell Wall
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Found surrounding plants cells not animal
cells
Surrounds all the other parts of the cell
(other parts called the protoplast)
Plant cell walls may consist of one or two
layers called primary and secondary wall
Middle Lamella is a layer of sticky material
between walls of adjacent cells
Primary Wall
The first wall layer is the primary wall
 It is formed early in the life of a plant cell
 Composed of cellulose and other
polysaccharides
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Wall Strucuture
The cellulose is in the form of fibrils,
extremely fine fibers, which can only be
seen with an electron microscope.
 The fibrils are embedded in a matrix of
other polysaccharides.
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Secondary Wall
The secondary wall develops internal to
the primary wall in some cells.
 Only cells that are specialized for
support, protection, or water conduction
have secondary walls.
 Lignin is a major component of the
secondary wall in addition to the
cellulose and other polysaccharides.
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Lignin
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Complex organic molecule that is very
difficult to break down
Provides support to plant cells and gives
wood its characteristic strength
Provides protection against attack by
pathogens and consumption by herbivores.
Only one group of wood rotting fungi are
able to decompose lignin
Cell Wall Components
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Important
component of
worldwide biomass
Because of all the
plant material in the
world
 Cellulose
is the most
abundant organic
compound on Earth
 Lignin is a close
second
Wooden artifacts from ancient
Egypt
•Throne from tomb of Tutankamen
~ 3300 yrs old
•Funeary barge for Khufu at Giza
~ 4600 yrs old
Wall Openings
Cell wall is not a solid structure.
 Minute pores exist called pits
 Some pits are large enough to be seen
with the light microscope.
 Pits allow for the transfer of materials
from cell to cell through cytoplasmic
connections called plasmodesmata.
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The Protoplast
All of the plant cell enclosed by the cell
wall.
 It consists of the nucleus plus the
cytoplasm
 Cytoplasm contains a variety of
organelles - each with a specific
function
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The Plant Cell
Ribosomes
Cell Wall
Nucleolus
Cell Structures and Functions
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Cell Wall -- Support and protection
Plasma Membrane -- Regulates passage of
materials into and out of cell
Nucleus -- Control center of cell, directs
protein synthesis and cell reproduction
Nucleolus -- Ribosome formation
Ribosomes -- Protein synthesis
Endoplasmic Reticulum -- Transport and
protein synthesis (rough ER)
Cell Structures and Functions
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Golgi apparatus -- Processing and packaging of
proteins, secretion
Mitochondrion -- Cellular respiration
Chloroplast -- Photosynthesis
Leucoplast -- Storage, especially starch
Chromoplast -- Imparts color
Central Vacuole -- Storage of various
substances
Cytoskeleton -- Cell support and shape
Plasmadesma -- Movement of materials
between cells
Plasma membrane
The outermost layer of the protoplast
 Composed of lipids (phospholipids) and
proteins.
 Acts as a permeability barrier allowing
some molecules to pass but not others
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Fluid Mosaic Model
Lipid bilayer
Proteins
Diffusion and Osmosis
How things move in and out of cells
Cells constantly exchange materials
with their environment. One way this
occurs is by diffusion.
 Diffusion is the movement of particles or
molecules from areas of higher
concentration to lower concentration.
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Diffusion
Diffusion also occurs within living
organisms, but the membranes present
barriers to this movement of molecules.
 Membranes are differentially
permeable. They permit the diffusion of
some molecules, but present a barrier to
the passage of other molecules.
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Osmosis
The diffusion of water across cell
membranes is called osmosis.
 Water can move freely through
membranes.
 The direction the water molecules move
is dependent upon the relative
concentrations of substances on either
side of the membrane, moving from high
concentration to low
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Osmosis
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If you place a cell in a
highly concentrated
solution of salt or
sugar, water will leave
the cell.
The water is actually
diffusing from an area
of high concentration
to an area of lower
concentration.
Hypertonic solution
Osmosis
If a cell is left in a hypertonic solution, for
any length of time, so much water will leave
that the protoplast actually shrinks away
from the cell wall.
 When this happens the cell is said to be
plasmolyzed. In a wilted leaf many of the
cells would be plasmolyzed.
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Osmosis
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On the other hand, if
you place a cell in
distilled water, water
will enter the cell.
Again the water is
moving from higher
(outside the cell) to
lower concentration
Hypotonic Solution
Osmosis
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When a plant cell is in a hypotonic,
solution, water will enter until the vacuole is
fully extended pushing the cytoplasm up
against the cell wall. Such cells look plump,
or turgid; this is the normal appearance of
cells in a well-watered plant.
Osmosis
When the cell is
placed in a solution
of the same
concentration,
isotonic, there is no
net movement of
water and the cell is
not turgid.
Membrane Transport
Diffusion take place when molecules
move along a concentration gradient.
 Cells can also move substances against
a concentration gradient
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 Called
active transport
 Requires energy by the cell
 Membrane proteins transport these
substances across the membrane
Summary I - Cells
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All living organisms are composed of cells
- cells are the basic unit of life.
Plant cells are eukaryotic having an
organized nucleus and membrane bound
organelles.
Substances can move in and out of cells
by diffusion and osmosis or be carried in
or out by active transport.
CELL DIVISION
The Cell Cycle
The life of an actively
dividing cell can be
described in terms
of a cycle which is
the time from the
beginning of one
division to the
beginning of the
next
Cell Division
Interphase
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The time between successive divisions is known
as interphase and consists of 3 phases:
• The G1 Phase or first gap phase. The cell is
actively growing
• The S or synthesis phase when DNA is
duplicated; other chromosomal components are
also synthesized
• The G2 or second gap phase where the final
preparations for cell division take place
Appearance of an
Interphase Nucleus
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Chromatin consists of
DNA and protein,
Prominent in the
nucleus of interphase
cell
Chromatin appears
thread-like
Duplicated during the
S phase prior to
mitosis.
Chromatin
Nucleolus
Cell Division
Mitosis - two exact copies of the
nucleus result from a process known as
mitosis.
 Cytokinesis, the division of the
cytoplasm, usually occurs during the
later stages of mitosis.
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Mitosis Consists of
Four Intergrading stages
Prophase
 Metaphase
 Anaphase
 Telophase
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Prophase
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Nucleus changes dramatically.
Chromatin begins to condense and thicken, coiling up
into bodies referred to as chromosomes.
Each chromosome is composed of two chromatids.
By the end of prophase the chromosomes are fully
formed.
Nuclear membrane and the nucleoli disperse into the
cytoplasm and are no longer visible.
This leaves the chromosomes free in the cytoplasm.
Mid to Late Prophase
Chromosomes
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Each chromosome
is composed of two
identical chromatids.
The chromatids are
joined at the
centromere
Chromatids
Metaphase
The chromosomes arrange themselves
across the center of the cell
 The spindle, composed of microtubles is
completed
 Spindle fibers stretch from each pole of the
cell to the centromeres of the chromosomes
 Other spindle fibers stretch from pole-topole
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Late Metaphase to
Early Anaphase
Anaphase
Chromatids of each chromosome separate,
pulled by the spindle fibers to opposite ends
of the cell.
 This divides the genetic material into two
identical sets each with the same number of
chromosomes.
 At the end of anaphase the spindle is no
longer visible.
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Telophase
During telophase the chromatin reappears
as the chromosomes, at each end of the cell,
begin to unwind and lengthen.
 At each pole a nuclear membrane reappears
around the chromatin.
 Two distinct nuclei become evident.
 Within each nucleus, nucleoli become
visible.
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Early Telophase
Cytokinesis
The division of the cytoplasm separates the
two identical nuclei into two cells.
 Cytokinesis begins during the latter part of
anaphase and is completed by the end of
telophase.
 The cell plate forms and becomes the cell
walls separating the newly formed daughter
cells
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Summary
Cell Division and
Asexual Reproduction
The production of new cells through cell
division enables plants to grow, repair
wounds, and regenerate lost cells.
 Cell division can lead to the production
of new genetically identical individuals
or clones. This type of reproduction is
known as asexual reproduction.
 Many crops are propagated asexually
and are gentically identical
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Summary II - Mitosis
Mitosis followed by cytokinesis, results
in two genetically identical daughter
cells
 Growth, replacement of cells, and
asexual reproduction all depend on the
process of cell division
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