Section 3 - organisms Exchange substances with their environment

Question 1

Define digestion

Answer 1

The hydrolysis of large insoluble molecules into smaller molecules taht can be absorbed across cell membranes.

Question 2

Which enzymes are involved in acrogydrate digestion and where are they found?

Answer 2

• salaivary amylase in mouth. pancreatic amylase in pancreas.
• Maltase, sucrase, lactase in membrane of small intestine as memebrane bound enzymes.

Question 3

What are the substrates and products of the carbohydrate digestive enzymes?

Answer 3

Amylase -> starch into smaller polysaccarides such as maltose.
Maltase -> maltose into 2 x Alpha glucose.
Sucrase -> scucrose into glucose and fructose.
Lactase -> lactose into glucose and galactose.

Question 4

Where are lipids digested / hydrolysed?

Answer 4

The small intestine (ileum)

Question 5

What needs to happen before lipids can be digested/ hydrolysed?

Answer 5

They must be emulsified by bile salts produced by the liver. this breaks down large fat molecules into smaller soluble droplets surrounded by bile salts to form micelles. this increases surface area. for lipase to work on.

Question 6

Which enzymes are involved in protein digestion? What are their roles?

Answer 6

-Endopeptidases = breaks bonds between amino acids in the middle of a polypepetide.
-Exopeptidases = break bonds between amino acids at the end of a polypepetide
-Dipeptidases (membrane bound) break dipeptides into amino acids.

Question 7

What is co-transport?

Answer 7

• The coupled movement of substances across a cell membrane via a carrier protein Despite a negative concentration gradient
• This involves a combanation of facilitated diffusion and active transport.

Question 8

Which molecules require co -transport in the ileum and how does this happen?

Answer 8

• sodium and glucose and amino acids.
• The active transport of sodium ions from the epithelial cell into the blood via the sodium potassium pumplowers the concentration inside the cell and generates a sodium ion concentration gradient between the ileum and the epithelial cell
• sodium ions move into the cell from the ileum via faccilated diffusion carrying glucose molecules with them via a cotransport protein
• the glucose concentration inside the epithelial cell increases and glucose molecules eneter the blood via facillitated diffusion

Question 9

Why do fatty acids and monoglycerides not require co transport?

Answer 9

the molecules are non-polar, meaning they can easily diffusr across the membrane of the epithelial cells