Digestion And Absorption Flashcards
The action of carrier protein X in figure 1 (where sodium and potassium is) is linked to a membrane bound ATP hydrolase enzyme
Explain the function of this ATP hydrolysase
2 marks
- (ATP to ADP + Pi) Releases energy;
- (energy) allows ions to be moved against a concentration gradient
OR
(energy) allows active transport of ions;
For ions’ accept Na* or K*.
The movement of Na+ out of cell allows absorption of glucose into the cell lining of the ileum
Explain how
Two marks
- (Maintains/generates) a concentration/diffusion gradient for Na (from ileum into cell);
Accept (Maintains/generates) a lower concentration of Na inside the cell compared with outside the cell’.
- Na moving (in) by facilitated diffusion, brings glucose with it
OR
Na moving (in) by co-transport, brings glucose with it;
Accept ‘co-transporter’ for ‘co-transport.
The material from which Visking tubing is made is partially permeable.
After 15 minutes, the student removed samples from the liquid in the beaker and from the liquid inside the Visking tubing. She carried out biochemical tests on these samples. She drew the table below to record her results.
Why does buriet test show protein would be still in visking tubing?
Why does iodine test for starch show it is either inside tubing or not in any
Why does Bendicts test for sugar show it is in both viscous tubing and in the liquid of beaker
3 marks
- Biuret: protein molecules too large to pass through tubing;
Neutral: enzyme molecules - lodine in potassium iodide solution: starch molecules too large to pass through tubing;
If no tick in 04.2, allow no starch hydrolysed - Benedict’s: starch hydrolysed to maltose, which is able to pass through tubing.
Reject: glucose
Suggest and explain why the combined actions of endopeptidases and exopeptidases are more efficient than exopeptidases on their own.
2 marks
Endopeptidase hydrolyse the peptide bonds in the middle of the protein.
Exopeptidase hydrolyse the peptide bonds at the end of the protein.
A combination is more efficient because their are more ends which increases the surface area for the exopeptidase to hydrolyse.
Scientists investigated how the diet of rabbits affected their digestion and absorption of protein. The scientists fed rabbits an identical mass of food but varied the percentage of protein in the food.
The scientists measured the mean mass of protein fed to the rabbits that was absorbed, which they then expressed as a percentage value.
The scientists’ results are shown in Figure 1.
The error bars show + 2 standard deviations.
+ 2 standard deviations cover 95% of the data.
What can you conclude about the absorption of the products of protein digestion as the percentage of protein increased in the rabbits food?
3 marks
Graph shows standard deviation overlapping
- No significant difference (in protein absorption);
- (because ‡ 2) SDs overlap;
Accept error bar for SD - (So mean) percentage absorbed not affected by percentage in diet;
- Amount of protein (in diet) is not a limiting fact
Or
Something else is limiting factor eg amount of protease; - (But) small range of protein in diet (Should) Investigate wider range;
The food eaten by a rabbit is digested mainly by microorganisms in its caecum. The caecum is a section of intestine attached between the ileum and the large intestine. The resulting semi-digested material leaves the anus of a rabbit as soft, caecal droppings. The rabbit then eats these caecal droppings.
Use this information and Figure 2 to suggest how eating its own caeçal droppings helps a rabbit’s digestion and absorption of dietary protein
3 marks
- More/remaining/undigested (protein) broken down;
Accept all (protein) broken down - (So more) amino acids absorbed;
- (Because) protein/food passes again through stomach/ileum;
Describe the role of micelles in the absorption of fats into the cells lining the ileum.
3 marks
- Micelles include bile salts and fatty acids;
Ignore other correct components of micelles. - Make the fatty acids (more) soluble in water;
For ‘fatty acids’ accept fats / lipids. - Bring/release/carry fatty acids to cell/lining (of the ileum);
For ‘fatty acids’ accept fats/lipids. - Maintain high(er) concentration of fatty acids to cell/lining (of the ileum);
- Fatty acids (absorbed) by diffusion;
Reject if absorbed by facilitated diffusion
Ignore if micelles themselves are being absorbed.
Ignore references to monoglycerides.
What is the advantage of micelles
Micelles carry FA’s and glycerol to the epithelial cells
In mammals, in the early stages of pregnancy, a developing embryo exchanges substances with its mother via cells in the lining of the uterus. At this stage, there is a high concentration of glycogen in cells lining the uterus.
Suggest and explain 2 way the cell surf mb of cell lining the uterus may be adapted to allow rapid transport of nutrients
2 marks
- Membrane folded so increased / large surface area;
Or
Membrane has increased / large surface area for (fast) diffusion / facilitated diffusion / active transport / co-transport; - Large number of protein channels / carriers (in membrane) for facilitated diffusion;
- Large number of protein carriers (in membrane) for active transport;
- Large number of protein (channels / carriers in membrane) for co-transport;
1: Accept microi villi to increase surface area
Note feature and function required for each marking point and reference to large / many / more.
List rule applies.
Explain the advantages of lipid droplet and micelle formation
3 marks
- Droplets increase surface areas (for lipase / enzyme action);
- (So) faster hydrolysis / digestion (of triglycerides / lipids);
- Micelles carry fatty acids and glycerol / monoglycerides to / through membrane / to (intestinal epithelial) cell;
