Absorption Of Biological Molecules

Question 1

Describe the absorption of glucose.

Answer 1

1. • Sodium ions are actively transported through the sodium/potassium pump.
     - This requires energy which is produced from ATP hydrolysis.
     - Against the concentration gradient.
     - From the epithelial cells in the ileum into the bloodstream.
     - This now creates a concentration gradient between the epithelial cells and the ileum.
2. • Sodium ions diffuse through sodium/glucose co-transport proteins.
     - This doesn’t require energy.
     - Down the sodium ion concentration gradient.
     - From the lumen of the ileum, into the epithelial cells.
     - This causes an increase in glucose concentration inside of the cell.
3. • Glucose diffuses through a channel protein via facilitated diffusion.
     - This doesn’t require energy.
     - Down the glucose concentration gradient.
     - From the epithelial cells, into the bloodstream.

Question 2

Describe the absorption of amino acids.

Answer 2

1. • Sodium ions are actively transported through the sodium/potassium pump.
     - This requires energy which is produced from ATP hydrolysis.
     - Against the concentration gradient.
     - From the epithelial cells in the ileum into the bloodstream.
     - This now creates a concentration gradient between the epithelial cells and the ileum.
2. • Sodium ions diffuse through sodium/amino acid co-transport proteins.
     - This doesn’t require energy.
     - Down the sodium ion concentration gradient.
     - From the lumen of the ileum, into the epithelial cells.
     - This causes an increase in amino acid concentration inside of the cell.
3. • Amino acids diffuses through a channel protein via facilitated diffusion.
     - This doesn’t require energy.
     - Down the amino acid concentration gradient.
     - From the epithelial cells, into the bloodstream.

Question 3

Describe the absorption of lipids.

Answer 3

1. • Glycerol and fatty acids are lipid soluble so are diffused into the epithelial cell by simple diffusion, through the phospholipid bilayer.
     - This doesn’t require energy.
     - Down the concentration gradient.
     - From the lumen into the epithelial cells.
2. • In the smooth endoplasmic reticulum, the fatty acids and glycerol are rejoined by condensation reactions, forming triglycerides.
     - The Golgi body processes the fats and joins them with proteins, forming chylomicrons.
     - These chylomicrons are then packaged into vesicles which then move and fuse with the cell membrane.
     - The chylomicrons are then released from the vesicles.
3. • The chylomicrons/ fats diffuse into the lacteals (lymph vessels).
     - The fluid in the lacteals later drains out into the bloodstream.

Question 4

What are the structural adaptations of the ileum?

Answer 4

• Large surface area due to its long length, presence of villi and microvilli (on the epithelial cells)
• Higher number of transport proteins available, so an increased rate of active transport and facilitated diffusion.
• Single layer of epithelial cells as the wall of the villi, so a short diffusion pathway
• Many small branching capillaries in the villi which increase surface area
• Continual blood flow which maintains a high diffusion gradient
• Lacteals absorb lipids, maintaining a high diffusion gradient
• Many mitochondria present which supply ATP for active transport.