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CellsWhat are cells?
The basic unit of structure and function in organisms
StructureThis refers to the manner of construction of something
and the arrangement of its parts in other words how
it is built.
FunctionWhat something is used for or in other words how
something works or does
We see a very high correlation between structure andfunction in almost all things, e.g A fish has fins andgills (structure) that enables it to swim and breath(functions) under water
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Prokaryotic and Eukaryotic cellsThere are two types of cells:
Prokaryotic cellsEarliest cellsLack membrane bound organellesNo nucleus
No mitochondriaHave membrane, cytoplasm & free DNAEukaryotic cellsMay have evolved from Prokaryotic
Have a nucleus that holds the DNA inside a membraneHave mitochondriaAlso have cell membrane & cytoplasm
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plant cells and animal cells
All organisms are constructed bycells
There are two main types of cells, plant cells and animalcells.
Most cells are so small that you can see them onlywith the help of a microscope.
All cells come only from other cells.
Living things is diverse but all cells share commoncharacteristics
Cells are composed of one cell unicellular or morecells multicellular.
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Using the microscopes to see cells
There are two types of microscopes, the light microscopeand the electrone microscope
Photographs of what is seen through a microscope arecalled micrographsor photomicrographs:
Light microscope
Magnifies X 1500
Light micrographsshow what can be seen with a lightmicroscope.
Electron microscopeMagnifies X 200 000
Electron micrographsshow what can be seen with anelectron microscope.
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Why not?
Cells are small so they can exchange materials withtheir surroundings.Surface area relative to the volume decreases as sizeof cell increases.
Cell size is limited because as the size of the cellincreases the less the cells ability to take in nutrientsand remove waste products .
Here is how it works!
Are there cells the size of an Elephant?
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Cell surface volume ratio
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Sizes of living things
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The general structure of a plant
Cell wall
Cell surface membrane
Cytoplasm
MitocodriaNucleus
Vacuole containing cell sap
Starch granule
Nuclear membrane
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Ultra stucture of a plant cellThis structure is what is observed at about X 200 000 under
an electron microscope cell organelles can be identified.
Cell wall
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The two pictures
(micrographs) shows howA plant cell looks likeunder a light microscope.
NoticeThe cell wallThe nucleus, one of the
dark circles near the
cell wall.The chloroplasts, the
rest of the circles.The large vacuole which
appears inside the cell.
Light micrograph of some plant cells
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The general structure of an animal cell
Cell surface membrane
Cytoplasm
Vacuole containing cell sap
Nucleus
Nuclear membraneMitocodria
Notice
How small the vacules arecompared to the plant cell.
The absence of the cell wall The irregular chape of the cell compared to the regular
plant cell.
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Ultra stucture of an animal cellThis structure is what is observed at about X 200 000 underan electron microscope, cell organelles can be identified.
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The structure of plant and animal cells
Here are the common features in all cells Cell surface membrane: a thin membrane that separates
the cell contents from the surrounding. The cytoplasm: a jelly-like liquid which contains a
mixture of proteins, and other substances. The nucleus: surrounded by a nuclear membrane and
contains genetic material. Vacuoles: structures in the cytoplasm that contain
fluid, usually larger in animal cells than in plant cells.
These are the differencesPlant cells have a cell wall that surrounds the cell chloroplasts which are responsible for producing
chlorophyll the green pigment seen in plant leaves and
stems.
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Functions and structures
1 Cell Membrane:Semi-permeable,
controls what enters and leaves the cell, outercontainment envelope.
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Cytoskeleton: A microscopic network of actin filaments
and microtubules in the cytoplasm of many living cellsthat gives the cell shape and coherence or simplygives structure to a cell.
2 Nucleus: control center for activities & reproductionof the cell, DNA & chromosomes are housed here.
Nucleolus: contains and makes RNA
Chromosome: coiled DNA: contains instructions forcharacteristics of an organism.
Chromatin: protein composing of chromosomes
Functions and structures
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Nucleus and nuclear envelop
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Functions and structures
Nuclear membrane
protects and controls whatgoes in and out of the nucleus
It is made up of two
membranes with a narrowspace between them.
The membranes have smallopenings called nuclear pores.
(notice the nuclear pores inthis picture of a nucleus)
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3 Ribosomes: Ribosomes are composed of a large
subunit and a small subunit which are small beads ofRNA (ribonucleic acid).
Site of Protein Synthesis on the E.R. Ribosomes are made in the nucleolus of the nucleus They move from the nucleus to the cytoplasm They then attach to the surface of the endoplasmic
reticulum Once attached they make proteins, both for the cell
itself and for export to other cells.
The ribosomes are therefore found on theendoplasmic reticulum were they perform their
functions in protein synthesis.
Functions and structures
F ti d t t
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4 Endoplasmic reticulum (ER) is a system of membranouschannels which run from the nuclear envelope to the cellsurface membrane.
The are two types of endoplasmic reticulum ER
Rough ER is studded with ribosomes and is the site of proteinsynthesis and processing.
Smooth ER lacks ribosomes and is the site of synthesis ofphospholipids and the packaging of proteins into vesicles,among other functions.
The functions of the endoplasmic reticulum are to Transport RNA from the nucleus to the ribosomes
Provide a very large surface area for attachment ofribosomes
Provide trans ort for roteins that the ribosomes roduce
Functions and structures
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Proteins made by the ribosomes are:
Pushed through the ER membrane into the tunnels ofthe ER
Enclosed in bits of the smooth ER membranes whichthen get pinched off to form small transport vesicles
Then carried by these transport vesicles through thecytoplasm to the golgi bodies.
The Golgi apparatus specializes in the production &transport of lipids and membrane proteins
Rough ER has ribosomes
Smooth ER lacks ribosomes
Functions and structures
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Functions and structures
5 The Golgi bodies
The Golgi apparatus consists of a stack of curvedchannels.
The Golgi bodies perform the following functions
Receives protein and also lipid-filled vesicles fromthe ER,
packages, processes, and distributes them within
the cell. This organelle may also be involved in secretion by
producing lysosomes by sealing off digestiveenzymes in packets of membrane.
F ti d t t
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Functions and structures
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Functions and structures
6 Lysosomes are vesicles produced by the Golgi
apparatus.Lysosomes have the following functions
Contain hydrolytic enzymes
Are involved in intracellular digestion.
7 Vacuoles (large) and vesicles (small) are membranoussacs in the cell that store substances.
Store water, sager and other substances in the cellsap
To help keep the cell firm (turgid)
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8 Chloroplasts
These are bound by two membranes enclosing a fluid-filledstroma that contains enzymes.
Membranes inside the stroma are organized into
thylakoidsthat house chlorophyll.
Chlorophyll absorbs solar energy and carbohydrates aremade in the stroma.
the main function of chloroplasts is to make food duringphotosynthesis.
Functions and structures
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F ti d t t
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Functions and structures9Thetonoplast is the membrane separating the cell
vacuole from the cytoplasm. It controls what moves in
and out of the vacuole
10 The mitochondriaTheseare found in plant and animal cells.
Mitochondria are bounded by a double membranesurrounding fluid-filled matrix.
The inner membranes of mitochondria are cristae.
The matrix contains enzymes that break downcarbohydrates and the cristae house proteincomplexes that produce ATP.
F ti d t t
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Functions and structures
10 The mitochondria
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Plant cells
Plant cells have different structures than animalcells
Plant cells have something called a CELL WALL whileanimals do not.
Plant cells have an organelle called a CHLOROPLASTthat takes energy from the sun and converts it intosugars.
Does your body make sugar from the sun or do youget it from food?
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Animal cells organize the body. You have brain cells,stomach cells, bone cells, and many other types ofcells. Each is different from the others.
Nerve cells conduct electrical impulses through thebody. There are cells in your intestine that absorbnutrients from the food you eat. Stomach cellssecrete an acid to digest your food
Do you think that your skin cells can absorb thenutrients from your lunch? Why not?
Animal cells