Organisms Exchange Substances with their Environment: Digestion & Absorption - Absorption

Question 1

What are bile salts?

Answer 1

• A type of salt produced by the liver and stored in gall bladder, to aid digestion of lipids

Question 2

Describe how bile salts emulsify lipids

Answer 2

• They emulsify lipids - cause lipids to form small droplets
• These small droplets have a bigger SA
• This speeds up hydrolysis of lipids

Question 3

What do bile salts do once lipids are hydrolysed?

Answer 3

• Once lipid is hydrolysed, the monoglycerides and fatty acids stick with bile salts to form micelles
• Micelles help products of lipid digestion be absorbed

Question 4

How is glucose absorbed across the ileum epithelium into the bloodstream?

Answer 4

• Glucose is absorbed into epithelial cell from ileum via co-transport
• Sodium ions are actively transported out of epithelial cells into the ileum
• Sodium ions diffuse back into cells through sodium-dependent co-transporter proteins, carrying glucose molecules with them
• Glucose diffuses into bloodstream by facilitated diffusion via a carrier protein

Question 5

How is galactose absorbed across the ileum epithelium into the bloodstream?

Answer 5

• Absorbed in same way as glucose using the same co-transporter protein

Question 6

How is fructose absorbed across the ileum epithelium into the bloodstream?

Answer 6

• Fructose is absorbed via facilitated diffusion through a different transporter protein

Question 7

How are monoglycerides and fatty acids absorbed across the ileum epithelium into the bloodstream?

Answer 7

• Entering epithelial cells
- Micelles help move monoglycerides and fatty acids towards the epithelium

• Reassembling

• Lipid-soluble so can enter cell membrane
• Once inside the epithelium, they are reassembled within the SER into triglycerides

• Chylomicrons

• The triglycerides are packaged with cholesterol and phospholipids to form chylomicrons
• Chylomicrons are then transferred to lacteal (type of lymphatic vessel) by exocytosis

Question 8

How are amino acids absorbed across the ileum epithelium into the bloodstream?

Answer 8

• Amino acids are absorbed into epithelial cell via co-transport
• Sodium ions are actively transported out of epithelial cells into the ileum
• Sodium ions diffuse back into cells through sodium-dependent co-transporter proteins, carrying the amino acids with them
• Amino acids transported to bloodstream by facilitated diffusion via a carrier protein