The features that suit it for its
function include:
♦ Long, thin cells that form a
continuous layer to absorb sunlight.
♦ Lots of chloroplasts arranged
to best collect sunlight.
♦ A large vacuole that pushes
the cytoplasm and chloroplasts
to the edge of the cell.
Cell Wall
The cell wall consists of microfibrils of the
polysaccharide cellulose embedded in a matrix.
Cell walls have the
following features:
♦ A number of polysaccharides,
such as cellulose.
♦ The 'middle lamella', a thin layer
between adjacent cell walls which
cements them together.
Functions of the cell wall are:
♦ To prevent the cell bursting
under the pressure created by
the osmotic entry of water.
♦ To give mechanical strength
to the plant.
♦ Allow water to pass along it.
Cellulose
microfibrils are
very strong.
Chloroplasts
Disc-shaped, 2-10μ long and 1μm in
diameter. Their main features are:
♦ The Chloroplast Envelope - a double
plasma membrane. It selects what comes
in and out of the chloroplast.
♦ The Grana - are stacks of up to 100
thylakoids, which contain chlorophyll. 1st
stage of photosynthesis takes place here.
♦ The Stroma - a fluid-filled matrix.
Contains starch grains. 2nd stage of
photosynthesis takes place here.
Chloroplasts are adapted to their function of
carrying out photosynthesis in the following
ways:
♦ The granal membranes provide a large
surface area for the attachment of chlorophyll,
electron carriers and enzymes that carry out
the 1st stage of photosynthesis.
♦ The fluid of the stroma has all the enzymes
needed for the 2nd stage.
♦ Chloroplasts contain DNA and ribosomes so
they can quickly and easily manufacture some
of the proteins needed for photosynthesis.
Differences Between Plant and Animal Cells:
Plant Cells
Cellulose cell wall &
cell-surface membrane.
Vast amounts of chloroplasts.
Have a large, single, central
vacuole filled with cell sap.
Starch grains are used for storage.
Animal Cells
Only cell-surface membrane.
No chloroplasts.
If vacuoles are present they
are small and scattered around.