notes on cell wall, PEROXISOMES and vacuole

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VACUOLE
A vacuole is a membrane-enclosed fluid filled sac found in the cells of plants
including,fungi.
Vacuoles can be large organelles occupying between 30% and 90% of a cell by
volume.
Vacuoles appear to have three main functions,
They:
 Contribute to the rigidity of the plant using water to develop hydrostatic
pressure
 Store nutrient and non-nutrient chemicals
 Break down complex molecules.
Vacuoles are membrane-bound organelles that can be found in both animals
and plants. In a way, they're specialized lysosomes.
That is to say that their function is really to handle waste products, and by
handle, mean take in waste products and also get rid of waste products.
Sometimes the waste product is water, and therefore a vacuole would have as
its function to maintain the balance of water inside and outside a cell.
Sometimes a vacuole's function is to get rid of harmful toxins or to clear the
extracellular space of those harmful toxins by bringing them into the cell for
conversion; for chemical conversion into more safe compounds. The vacuoles
are quite common in plants and animals, and humans have some of those
vacuoles as well. But vacuole also has a more generic term, meaning a
membrane-bound organelle that's lysosome-like.
CELL WALL
Not all living things have cell walls, most notably animals and many of the
more animal-like protistans. Bacteria have cell walls containing the chemical
peptidoglycan.
Plant cells, have a variety of chemicals incorporated in their cell walls.

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Cellulose, a nondigestible (to humans anyway) polysaccharide is the most
common chemical in the plant primary cell wall. Some plant cells also
have lignin and other chemicals embedded in their secondary walls.
The cell wall is located outside the plasma membrane.
Plasmodesmata are connections through which cells communicate chemically
with each other through their thick walls.
Fungi and many protists have cell walls although they do not contain
cellulose, rather a variety of chemicals (chitin for fungi).
Animal cells, lack a cell wall, and must instead rely on their cell membrane to
maintain the integrity of the cell.
Many protistans also lack cell walls, using variously modified cell membranes
o act as a boundary to the inside of the cell.
A cell wall is a rigid, semi-permeable protective layer in some cell types. This
outer covering is positioned next to the cell membrane (plasma membrane)
in most plant cells, fungi, bacteria, algae, and some archaea. Animal
cells however, do not have a cell wall. The cell wall has many important
functions in a cell including protection, structure, and support.
Cell wall composition varies depending on the organism. In plants, the cell
wall is composed mainly of strong fibers of
the carbohydrate polymer cellulose. Cellulose is the major component of
cotton fiber and wood, and it is used in paper production. Bacterial cell walls
are composed of a sugar and amino acid polymer called peptidoglycan. The
main components of fungal cell walls are chitin, glucans, and proteins.

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The plant cell wall is multi-layered and consists of up to three sections. From
the outermost layer of the cell wall, these layers are identified as the middle
lamella, primary cell wall, and secondary cell wall. While all plant cells have a
middle lamella and primary cell wall, not all have a secondary cell wall.
 Middle lamella: This outer cell wall layer contains polysaccharides called
pectins. Pectins aid in cell adhesion by helping the cell walls of adjacent
cells to bind to one another.
 Primary cell wall: This layer is formed between the middle lamella
and plasma membrane in growing plant cells. It is primarily composed of
cellulose microfibrils contained within a gel-like matrix of hemicellulose
fibers and pectin polysaccharides. The primary cell wall provides the
strength and flexibility needed to allow for cell growth.
 Secondary cell wall: This layer is formed between the primary cell wall
and plasma membrane in some plant cells. Once the primary cell wall
has stopped dividing and growing, it may thicken to form a secondary
cell wall. This rigid layer strengthens and supports the cell. In addition to
cellulose and hemicellulose, some secondary cell walls contain lignin.
Lignin strengthens the cell wall and aids in water conductivity in plant
vascular tissue cells.

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Functions of the cell wall:
 Support: The cell wall provides mechanical strength and support. It also
controls the direction of cell growth.
 Withstand turgor pressure: Turgor pressure is the force exerted against
the cell wall as the contents of the cell push the plasma membrane
against the cell wall. This pressure helps a plant to remain rigid and
erect, but can also cause a cell to rupture.
 Regulate growth: The cell wall sends signals for the cell to enter the cell
cycle in order to divide and grow.
 Regulate diffusion: The cell wall is porous allowing some substances,
including proteins, to pass into the cell while keeping other substances
out.
 Communication: Cells communicate with one another via
plasmodesmata (pores or channels between plant cell walls that allow
molecules and communication signals to pass between individual plant
cells).
 Protection: The cell wall provides a barrier to protect against plant
viruses and other pathogens. It also helps to prevent water loss.
 Storage: The cell wall stores carbohydrates for use in plant growth,
especially in seeds.
NUCLEUS
A nucleus is a membrane-bound organelle that contains the cell's
chromosomes. Pores in the nuclear membrane allow for the passage of
molecules in and out of the nucleus.
The nucleus is one of the most obvious parts of the cell when you look at a
picture of the cell. It's in the middle of the cell, and the nucleus contains all of
the cell's chromosomes, which encode the genetic material.
So this is really an important part of the cell to protect.
The nucleus has a membrane around it that keeps all the chromosomes inside
and makes the distinction between the chromosomes being inside the nucleus
and the other organelles and components of the cell staying outside.

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Sometimes things like RNA need to traffic between the nucleus and the
cytoplasm, and so there are pores in this nuclear membrane that allow
molecules to go in and out of the nucleus. It used to be thought that the
nuclear membrane only allowed molecules to go out, but now it's realized that
there is an active process also for bringing molecules into the nucleus.
Peroxisomes
 They are membrane-bound spherical bodies of 0.2 to 1.5 μm in diameter
found in all eukaryotic organisms including both plants and animal cells.
 They are found floating freely in the cytoplasm in close association of ER,
mitochondria or chloroplast within the cell.
 They are among the simplest of eukaryotic organelles.
 They exist either in the form of a network of interconnected tubules called
peroxisome reticulum or as individual micro peroxisomes.
 They are variable in size and shape according to the cell and usually
circular in cross-section.
 They range from 0.2 -1.5 μm in diameter.
 It consists of a single limiting membrane of lipid and protein molecules
enclosing the granular matrix.
 The matrix consists of fibrils or a crystalloid structure containing enzymes.

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CYTOSOL
 The cytosol is the liquid medium contained within a cell.
 The cytosol is a component of the cytoplasm. The cytoplasm includes
the cytosol, all the organelles, and the liquid contents inside the
organelles. The cytoplasm does not include the nucleus.
 The main component of cytosol is water. It also contains dissolved ions,
small molecules, and proteins.
 The cytosol is not uniform throughout the cell. Protein complexes and
the cytoskeleton give it structure.
 The cytosol serves several functions. It is the site of most metabolic
processes, transports metabolites, and is involved in signal transduction
within the cell.
Difference between Cytosol and Cytoplasm
Cytosol and cytoplasm are related, but the two terms are not usually
interchangeable. The cytosol is a component of cytoplasm.
The cytoplasm encompasses all of the material in the cell membrane,
including the organelles, but excluding the nucleus. So, the liquid within
mitochondria, chloroplasts, and vacuoles is part of the cytoplasm, but is not a
component of the cytosol. In prokaryotic cells, the cytoplasm and the cytosol
are the same.
Cytosol Composition
The cytosol consists of a variety of ions, small molecules,
and macromolecules in water, however, this fluid is not a homogeneous
solution. About 70% of the cytosol is water. In humans, its pH ranges between
7.0 and 7.4. The pH is higher when the cell is growing. Ions dissolved in the
cytosol include K+, Na+, Cl-, Mg2+, Ca2+, and bicarbonate. It also contains amino
acids, proteins, and molecules that regulate osmolarity, such as protein
kinase C and calmodulin.
Cytosol Functions
The cytosol serves several functions within a cell.

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It is involved in signal transduction between the cell membrane and the
nucleus and organelles.
It transports metabolites from their production site to other parts of the cell.
It is important for cytokinesis, when the cell divides in mitosis.
The cytosol plays a role in eukaryote metabolism. In animals, this includes
glycolysis, gluconeogenesis, protein biosynthesis, and the pentose phosphate
pathway.
However, in plants, fatty acid synthesis occurs within chloroplasts, which are
not part of the cytoplasm. Nearly all of a prokaryote's metabolism occurs in
the cytosol.
Refrence
 Urry, L. A., Cain, M. L. 1., Wasserman, S. A., Minorsky, P. V.,
Reece, J. B., & Campbell, N. A. (2017). Campbell
biology. Eleventh edition. New York, NY, Pearson Education,
Inc.
 www.nptel.com
 www.khanacademy.com