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

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