Transcript H 3 - Absorption of digested foods - IBDPBiology-Dnl

Assessment Statements
 H.3.1 Draw and label a diagram showing a transverse
section of the ileum as seen under a light microscope.
 H.3.2 Explain the structural features of an epithelial
cell of a villus as seen in electron micrographs,
including microvilli, mitochondria, pinocytotic
vesicles and tight junctions.
 H.3.3 Explain the mechanisms used by the ileum to
absorb and transport food, including facilitated
diffusion, active transport and endocytosis.
 H.3.4 List the materials that are not absorbed and are
egested.
Draw a labelled diagram showing a transverse
section of the ileum as seen under a light
microscope
Villi, epithelial cells & microvilli
Structural features of an epithelial
cell of a villus
Structural features of an epithelial cell of a
villus
Can you also identify; mitochondria, pinocytotic vesicles and
tight junctions?
Structural features of an epithelial
cell of a villus
 microvilli – these tiny, finger-
like infoldings of the cell
surface facing the lumen of the
gut, greatly increase the
surface area in contact with
material to be absorbed
 mitochondria – these
organelles are present in large
numbers, suggesting a
significant demand for ATP in
these cells for active transport
 pinocytotic vesicles – these
are the site of pinocytosis by
which fluid is taken up or
released in tiny vesicles, across
the plasma membrane of a cell
 tight junctions – these bind
together the individual
epithelial cells, so that the only
way into the tissues of the
body is through the epithelium
Mechanisms used by the ileum to
absorb and transport food
 end products of digestion need
to be moved into the cells in
order to be used
 transport of digested food may
occur passively (by simple
diffusion or facilitated
diffusion)or actively (by active
transport or endocytosis)
 simple diffusion & facilitated
diffusion occur down the
concentration gradient and
does not require energy
 in simple diffusion, molecules
such as lipids move through
phospholipid bilayer
 in facilitated diffusion,
molecules such as amino acids
& glucose move through carrier
proteins
 transport of many of the
nutrients is an active process,
for which energy in form of
ATP is required to move
molecules against the
concentration gradient
 large molecules such as DNA
are transported by endocytosis
which also requires energy
Materials that are not absorbed and
are egested
 egestion;- the removal
of substances that has
not been absorbed
 egested materials
include;
 cellulose,
 lignin,
 bile pigments,
 bacteria &
 intestinal cells