Download Enveroment dep 1 st Lec 1 The plant cell The cell is basic unit of life

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The plant cell
The cell is basic unit of life , all cells surrounded by
aflexible ,protective layer called plasma membrane or
cell membrane also , known as the plasma lemma .
It controls the movement of water , gases and molecules
into and out of the cell.
Plant cell component
all most of the organelles in atypical plant cell are also
found in the cells of other eukaryotes .the exceptions
are chloroplasts and alarge central vacuole ,which are
not typically found in other photosynthetic organisms
,fungi , or animals
the interior of plant cell that is ,everything except the
cell wall is called the protoplast ,it consist of the nucleus
and the cytoplasm
1- The nucleus : it has surrounding membranes ,
known together as the nuclear envelope , poresin
the nuclear envelope control movement of
substances into and out of the nucleus ., it also
contains nucleoli , which appear as round structure
associated with chromosomes , the typical nucleus
has one or two nucleoli , which synthesize sub units
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that then come together in the cytoplasm to form
ribosomes. In plant cell the DNA in the nucleus is
organized into complex thread like structures called
chromosomes , each it consists of many genes
2- Ribosomes bulid proteins : ribosomes are
organelles that are formed in the cytoplasm and
direct the synthesis of proteins , using genetic
instruction in the form of messenger RNA ,
eukaryotic ribosomes are distinctly different form
prokaryotic ribosomes , being generally layer and
having different types of RNA
3- Endo plasmic reticulum (ER) :a network of
connected membranes is continuous with the outer
nuclear envelope serves as asynthesis and
assembly site for making proteins , lipids ,the ER
has two parts ,the smooth , which is tubular in
shape makes lipids and modifies the structure of
some carbohydrates , and the rough ER is dotled
with protein synthesizing ribosomes , it as exterior ,
which typically consist of flattend , interconnected
sacs called cisternae , the space within the
cisternae and tubules of the ER is known as the
lumen
4- Golgi apparatus :consist of anumber of seprate
stacks of cisternae , known as golgi stacks , which
originate from membranes produced in the ER , in
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plant cell golgi stacks are dictyosomes it completes
and ships cell products
5- Chloroplasts : are the site of photosynthesis in
plant cell s which contain green chlorophyll
pigment they are found in the cells of green parts
plant , such as green stems and leaves ,
chloroplasts are about 5 m in diameter can be
spherical or quite elongated which have two outer
membrane and small circular chromosomes
6- Mitochondria (power house ) is smaller than
achloroplast , measuring about 1-5 m in length
and about 0.5 to 1 m in diameter . it contain their
own ribosomes , the portion of mitochondrions
inner membrane called crista ,that contain
respiratory enzyme , the inner membrane and the
liquid part inside it called the matrix , the function
of mitochondira break down sugar to store its
chemical energy in ATP
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7- Microbodies : are small sepherical organelles about
1 m in diameter that contain enzymes , at first
their function was unknown , later discovered that
microbodies generate and then break down
hydrogen peroxide formed by adding hydrogen to
water these microbodies were named peroxisome
, anther type of it called glyoxysome contains
enzyme that assist in converting stored fats into
sugar
8- Vacuoles : in many plant cells up to 90 % of volume
is occupied by alarge central vacuole , it is filled
with water and and waste products and plays
avariety of important roles , some relating to cell
metabolism ,for instance , it removes salt the
cytoplasm and controls the water balance of the
cell , the vacuole may also store toxic ions and ions
needed at chemical reaction . and it helps maintain
cell shape by pressing the rest of the cytoplasm
contents . the membrane surrounding the vacule of
plant cell is called the tonoplast
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9- Cytoskeleton :one major structure of the cell , helps
maintain the dynamic activites and shape of the
cell it composed of microtubules , microfilaments
and intermediate filament .
Microtubules are long , hollow tubes , each thread is
made of spherical proteins called alpha and beta
tubulin.
Microfilaments :are made of the globular protein
actin organized into two helical chains twisted around
each other
Inter mediate filaments the third component of
cytoskeleton , are so named because they are thicker
than microfilaments but thiner than microtubules
10-cell wall it surrounds the plasma membrane
preventing excessive water from entering the cell
.plant cell produce aprimary cell wall that is thicker
than plasma membrane and lies just outside it and in
many mature plant cell , in woody plant produce
thicker secondary cell wall
11-plasmadesmata :numerous channels maintain
direct contact between cell each plasmaesmata is
surrounded by aplasma membrane and contains
aconnection called adesmotuble between cell ,it allow
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small molecules and even macromolecules to pass
between cells