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Faculty of Science, School of
Sciences, Lautoka Campus
BIO509 Botany
Lecture 4: Cells and cell components
The Three Domain System is based on molecular studies
Prokaryote
Eukaryote
Before we learn more about the three
domain system
lets divert a little bit and lets first look
at what are cells?
Cells
• Cells are the basic functional units of life.
• Cells make up the entire structure for an organism, some
organisms, such as bacteria, are unicellular while other
organisms are multicellular.
• Cells can take in nutrients, convert those nutrients into
energy, and carry out specialized functions.
• Cells also contain the organisms hereditary material and
can make copies of themselves.
Onion cells
Common cell components
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Plasma membrane
Cytoplasm
Nucleus
Nuclear Membrane
Endoplasmic Reticulum
Ribosomes
Golgi Bodies
Mitochondria
Lysosomes
Vacuoles
Some organelles are found only in Plant cells. These organelles
are:
• Cell Wall
• Chloroplasts
Plasma membrane
• Composed of two layers of phospholipids.
• The two layers of phospholipids are arranged with the “heads”
on the outside and the “tails” on the inside.
(Attracts water)
(Repels water)
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Plasma membrane continued …
• Proteins molecules are interspread, some going all
the way to both sides, some not.
• Proteins passing all the way through aid in passage of
certain ions.
• Molecules of cholesterol are also found imbedded in
it.
Functions of a plasma membrane
• Serves as an envelope enclosing the cytoplasm.
• Controls passage of molecules into and out of the
cell, preventing some and promoting others.
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Nucleus
• Contains the genetic material
and is the control center of
the cell and sends coded
messages via DNA.
• Stores the cell’s hereditary
information and controls all
cell activities.
• Bounded by a double
membrane (=nuclear
envelope) which is
sometimes continuous with
endoplasmic reticulatum.
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• Inside the nucleus there is one or more
nucleoli, roughly spherical shape.
• Made of protein and ribosomal DNA.
• Serve in the production and assembly of
ribosomes components.
• The rest of the nucleus comprises the
granular nucleoplasm packed with
chromatin, the resting-cell form of DNA.
• Chromatin forms chromosomes when cell
is dividing.
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Endoplasmic reticulum (ER)
• Three dimensional membrane system
within the cell.
• Network of flattened sacs and tubes that
form channels, creating
subcompartments.
• Two kinds of ER
• Rough ER is covered with ribosomes
- Functions in synthesis, secretion, and
storage of proteins
- Predominates in cells storing proteins
• Smooth ER is mostly without ribosomes
- Functions in making lipids
- Predominates in cells that secrete lipids
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Ribosomes
• Small ellipsoidal particles 17—23 nm in
diameter.
• About 60% of mass is RNA, the rest mostly
protein.
• Considered an organelle, but not membrane
bounded.
• Located floating in the cytoplasm, on the rough
ER, in other organelles, and on the nuclear
membrane.
• Comprise two subunits made of RNA and
proteins.
• The two parts function in assembling proteins
by reading (transcribing) messenger RNA and
putting the amino acids in the correct order
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Lysosomes
• Functions in digesting
food or cellular
invaders.
• Recycling cellular
components
• (The lysosome is not
found in plant cells)
Golgi apparatus
• Golgi apparatus collective term for golgi
bodies, roundish flattened sacs
scattered in cytoplasm.
• Polarized membrane system with one
side facing the nucleus (cis) & the other
(trans) the plasma membrane.
• Often 5 to 8 in a stack, but 30+ in
simpler organisms.
• Produce and secrete non-cellulose
polysaccharides sent to the cell wall.
• Involved in the transport of lipids
around the cell, as well as creating
lysosomes
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Mitochondria
• Double membrane organelle,
that is involved in cells energy
generation.
• Inner membrane forms cristae
(partitions). These increase
surface area for enzymes to
work.
• Matrix also contains DNA, RNA,
ribosomes, proteins, and
dissolved substances.
• Energy released in cellular
respiration inside them
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Chloroplast in plant cells
• They are organelles bound by a double
membrane.
• Several kinds concerned with storage and
photosynthesis.
• Usually 75 to 125 per cell is common, more
than that in algae, and up to several
hundred in some plants.
• Usually 4–6 (2–10 ) microns in diameter.
• Function to capture light energy in
photosynthesis and convert it to energy
used in cell—virtually all of world’s food.
Vacuoles in plant cells
• Makes up to 90% of cell contents.
• Bounded by vacuolar membranes
(tonoplast) single, and similar to
cell membrane.
• Filled with cell sap, slightly to
moderately acidic, contains
inorganic ions, sugars, acids, and
amino acids.
• Functions mainly to maintain
turgor pressure.
flaccid
turgid
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A typical bacterial cell
A typical animal cell
A typical plant cell
Animal vs Plant cell
Study of cells
• The invention of the microscope made it
possible for people to discover and learn about
cells.
• Cell structure and function can be studied
provided by preparing tissues of study in
different ways.
Modern microscopes
Light microscopes
• Provide basic information about cell structure and
some organelles within the cells.
• Form an image when light passes through one or more
lenses to produce an enlarged image of a specimen
• Two basic types
- compound microscopes (a)
- stereo or dissecting microscopes (b)
a
b
Electron microscopes
• Reveal detailed images of tiny structures within the
cells.
• Form an image of a specimen using a beam of
electrons rather than light.
• Two types
– Transmission electron microscope (a)
– Scanning electron microscope (b)
a
b
Readings
• Chapter 3, Stern’s Introductory Plant Biology.
Questions are welcome???