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CELL THEORY - cells
are the basic units of an organism
- an
organism is a collection of independent though co-operating cells
ORGANISMS - an organism consists
of interdependent cells whose functions are dictated by the needs of the whole
organism
- the whole organism
is the basic entity, the cells are merely sub-units
ANIMAL
& PLANT CELLS - differences are related to the different
tasks that each cell type has to perform
- animal
& plant cells have many structures in common
- plasma/cell
membrane
- cytoplasm
- nucleus
- light
microscopes are unable to allow us to view the detailed structure of cells
- cell membrane as a thin line
- granules in the cytoplasm
- chromosomes
in the nucleus
CELL
STRUCTURES CELL MEMBRANE - outer
boundary of all living cells
- contains protoplasm - cytoplasm
& nucleus
- selectively semi-permeable - allows some
substances to pass through (e.g. water, oxygen, carbon dioxide)
- flexible,
elastic, capable of being altered by external pressure
- also
capable of changing shape and movement in some organisms
- substances
move into and out of cells by:
- diffusion
- active transport
- endocytosis
- phagocytosis & pinocytosis
- exocytosis
CYTOPLASM
- appears to be uniformly homogeneous
- use
of stains reveals numerous granules and inclusions
- stores
carbohydrate
- site of a cell's many complex chemical reactions
- once
thought to be fluid, but contains an elaborate network of protein filaments called
microtrabeculae
- microtrabeculae
- connect organelles (e.g. mitochondria) with ER
- hold organelles
in place
- only able to be seen under very powerful magnification
NUCLEUS
- bound by nuclear membrane
- contains:
- nucleoplasm
- nucleolus
- chromatin - condenses into
chromosomes during cell division
- chromosomes
carry hereditary material in the form of DNA (deoxyribonucleic acid)
NUCLEOLUS
- site for manufacture of main components of ribosomes
MITOCHONDRIA
- number in cells varies
- typical cell
contains about 1000
- cells that expend large amounts of
energy contain high numbers of mitochondria often packed together in the part
of the cell that requires the energy
- spermatozoa - at the base of the
motile tail
- muscle - beside the contractile fibrils
- at the surface
of cells in which active transport occurs e.g. liver cells
- shape & size varies
- generally
"sausage-shaped" with an inner diameter of approx. 1µm and a length
of 2.5µm
- wall consists of two thin membranes separated by a narrow fluid-filled
space
- the inner membrane is highly folded into a series of partitions
(cristae)
- "powerhouses"
of cells
- site of cellular respiration in eukaryotes
(prokaryotes - cytoplasm)
- energy in the form of ATP (Adenosine
Tri-Phosphate) is made available for the needs of the cells
ENDOPLASMIC
RETICULUM - network of membranes continuous with the
nuclear membrane
- site for many of the cell's biochemical
activities
- system of channels for moving materials through
the cell
- matrix containing a system of parallel flattened
interconnected cavities lined with a thin membrane (approx. 4nm thick)
- 2
types - smooth & rough ER
(a)
Smooth ER - without ribosomes
- forms
the tubules that transport substances around the cell and to the surface for export
- particularly
found in cells of the gut, liver, and certain glands
- concerned
with the synthesis and transport of lipids and steroids
(b)
Rough ER - with ribosomes
- ribosomes
- are attached to the matrix side of the membranes
- are
rich in RNA (ribonucleic acid)
- produce proteins including enzymes and
hormones
GOLGI BODIES - involved
in the export of the cell's products
- each
- consists of a little groups of flattened sacs composed of membranes
stacked on one another
- is surrounded by tubules and vesicles (very small
vacuoles
- serve as "packing centres"
especially for substances produced in the ER
- sites for
the assembly of complex molecules found on the surface of cell membranes
- animal
cells contain 10 to 20
- plant cells may contain several
several hundred
- also form small vesicles called lysosomes
LYSOSOMES
- "bags" of specialised enzymes
(hydrolytic enzymes)
- enzymes
used to break down/digest all components of a living cell including
- old cell fragments
- foreign organisms
- if
the lysosomes break open, the cell would be completely destroyed
- white
blood cells phagocytose bacteria and fuse with vacuoles containing lysosomes that
digest the bacteria
CELL WALL - primary
& secondary walls of cellulose
- middle
lamella - mainly pectin
- tough, slightly elastic
- with
sap vacuole, helps maintain the cell's shape
- more
complex in higher-order plants
- may be large
- particularly
rigid secondary cell walls impregnated with lignin to give wood, or with suberin
to give cork
PLASMODESMATA - narrow
pores in cell walls
- carry fine strands of cytoplasm
(ER)
- connect adjoining cells
- facilitate
movement of substances between cells
- ER - continuous between
cells
PLASTIDS - hollow ovoid
or spherical bodies
- appear as granules in the cytoplasm
- 2
main types
- chloroplasts - with pigments
- leucoplasts - without
pigments
(a)
Chloroplasts - contain green
pigment/s - chlorophylls
- site of photosynthesis
(b)
Leucoplasts - Starch Grains (Amyloplasts) - colourless
- contain
starch
- found widely in plant cells
- major
form of carbohydrate store for plants (equivalent to glycogen in animal cells)
CELL PROCESSES PROTEIN
SYNTHESIS - takes place in the Ribosomes
- DNA
(in nucleus) "unzips", makes mRNA - transcription
- mRNA
attaches to ribosome on ER
- tRNA a specific amino acid and
positions it in it's complementary position on the mRNA - translation
- when
the polypeptide is complete it detached from the ribosome and moves away from
the ER
- some move to a Golgi body to complete the formation
of the protein
CELLULAR
RESPIRATION - aerobic respiration takes place in
the Mitochondria
- glucose + oxygen + water -> carbon
dioxide + water
- glycolysis occurs in the cytoplasm (anaerobic)
- Krebs
cycle takes place in the matrix (ribosomes, circular DNA molecules & enzymes)
- electron
transfer reactions take place on (or in) the inner membrane and cristae
PHOTOSYNTHESIS
- takes place in the Chloroplasts
CELL
REPRODUCTION | |
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