[4.5] co-transport & absorption of glucose in ileum

Question 1

describe the co-transport of glucose from the small intestine to the blood [7]

Answer 1

1. sodium-potassium pump proteins in the cell membrane of the epithelial cells actively transport potassium ions from the blood into the cells and sodium ions from the cells into the blood. this requires energy from ATP hydrolysis
2. this establishes a lower concentration of sodium ions in the epithelial cells than in the lumen of the intestine
3. therefore, sodium ions will move from the intestine into the epithelial cells by facilitated diffusion
4. they will move through a co-transport protein, also bringing glucose molecules with them
5. this establishes a higher concentration of glucose in the cells than in the blood stream
6. therefore, the glucose will move from the cells to be blood by facilitated diffusion
7. the movement of new digested food material in the intestine and the circulation of blood in the blood vessels will both ensure that the relative concentration gradients are maintained

Question 2

what adaptions can you see/would you expect to see?

Answer 2

• microvilli which increases SA for rapid rate of diffusion

~ mitochondria to provide energy for active transport
~ ribosomes, endoplasmic reticulum and golgi apparatus to form proteins

Question 3

what is cytosis?

Answer 3

when vesicles carry large molecules across the membrane, which requires energy from ATP hydrolysis

Question 4

what is endocytosis?

Answer 4

entry into the cell

Question 5

describe the process of endocytosis (3)

Answer 5

1. cell membrane binds to a large molecule
2. vesicle is formed
3. vesicle containing large molecule enters into cell

Question 6

what are the two major types of endocytosis?

Answer 6

phagocytosis and pinocytosis

Question 7

what is the difference between phagocytosis and pinocytosis?

Answer 7

• phagocytosis is endocytosis which allows for the uptake of solids
• pinocytosis is endocytosis which allows for the uptake of fluids

Question 8

what is exocytosis?

Answer 8

secretion from the cell

Question 9

what is the process of exocytosis? (3)

Answer 9

1. substances to be released (eg. enzymes) are packaged into secretory vesicles formed at golgi body
2. vesicles travel to and fuse with cell surface membrane
3. vesicles release contents outside of cell