Carbohydrates Flashcards
Cow’s milk contains the sugar lactose.
Many cats are unable to digest cow’s milk because they are lactose intolerant.
Cow’s milk can be made suitable for these cats by treating it with the enzyme lactase to hydrolyse lactose.
This makes the cow’s milk lactose-free. Beads are coated with lactase and placed in a tube, as shown in the diagram below.
Cow’s milk flows over the beads and the lactose is hydrolysed.
( Diagram shows a funnel-like container containing beads coated with lactase. )
( Cow’s milk containing lactose is poured from the top of the container and comes out from the bottom as Lactose-free milk )
Attaching lactase to the beads is a more efficient use of lactase than adding the lactase directly to cow’s milk.
Suggest three reasons why it is more efficient to attach lactase to the beads.
- Beads are reusable
- No need to remove lactase from milk
- Allows for a continuous process
Monosaccharides and disaccharides taste sweet.
The lactose-free milk made after hydrolysis with lactase tastes sweeter than the cow’s milk containing lactose.
Suggest why.
- Lactose is hydrolysed to galactose and glucose
- So more sugar molecules are present
Give two ways in which the structure of starch is similar to cellulose.
- They’re both polysaccharides
- Both contain glycosidic bonds
Give two ways in which the structure of starch is different from cellulose.
- Starch contains alpha glucose molecules
- There are no hydrogen bonds between molecules in Starch
In plants, mass transport of sugars takes place through columns of sieve cells in the phloem.
Other cells, called companion cells, transport sugars into, and out of, the sieve cells.
The diagram shows the structure of phloem.
( Diagram shows a phloem labelled “ Companion cells “ on the right side and “ Sieve cells “ on the left side )
( The “ left side “ is labelled with “ cytoplasm “ and “ vacuole “ )
( It also has a layer within the sieve cells, horizontal to the phloem, which is labelled “ I “ )
( On the “ right side “, the membrane of the phloem is labelled “ J “ )
( There’s also an arrow going straight down the phloem, which is labelled “ Mass transport of sugars “ )
Structures I and J allow the transport of sugars between cells.
Using the diagram, suggest and explain one other way in which sieve cells are adapted for mass transport.
- There’re few organelles within the sieve cells
- So there’s more flow of sugars
Using the diagram, suggest and explain one other way in which companion cells are adapted for the transport of sugars between cells.
( Diagram shows a phloem labelled “ Companion cells “ on the right side and “ Sieve cells “ on the left side )
( The “ left side “ is labelled with “ cytoplasm “ and “ vacuole “ )
( It also has a layer within the sieve cells, horizontal to the phloem, which is labelled “ I “ )
( On the “ right side “, the membrane of the phloem is labelled “ J “ )
( There’s also an arrow going straight down the phloem, which is labelled “ Mass transport of sugars “ )
- Mitochondria release ATP
- For active transport
Starch and cellulose are two important plant polysaccharides.
The following diagram shows part of a starch molecule and part of a cellulose molecule.
( The diagram for Starch shows a series of alpha glucose and how they are bonded, showing the “ O “ molecules )
( The diagram for cellulose shows a series of beta glucose and how they are bonded, showing the “ O “ molecules )
( The diagram for cellulose is the inversion of the Starch diagram to where the beta glucose molecules are bonding )
Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the diagram above.
- Starch is formed from alpha glucose while cellulose is formed from beta glucose
- Position of hydrogen and hydroxyl groups on carbon atom 1 are inverted
Starch molecules and cellulose molecules have different functions in plant cells.
Each molecule is adapted for its function.
Explain one way in which starch molecules are adapted for their function in plant cells.
- Starch molecules are insoluble
- So they don’t affect water potential
Explain how cellulose molecules are adapted for their function in plant cells.
- Cellulose molecules have straight and long chains
- They are linked together by many hydrogen bonds which form micro fibrils
- These micro fibrils provide strength to the molecule
A student investigated the effect of chewing on the digestion of starch in cooked wheat.
He devised a laboratory model of starch digestion in the human gut. This is the method he used.
- Volunteers chewed cooked wheat for a set time.
The wheat had been cooked in boiling water. - This chewed wheat was mixed with water, hydrochloric acid and a protein-digesting enzyme and left at 37 °C for 30 minutes.
- A buffer was then added to bring the pH to 6.0 and pancreatic amylase was added.
This mixture was then left at 37 °C for 120 minutes. - Samples of the mixture were removed at 0, 10, 20, 40, 60 and 120 minutes, and the concentration of reducing sugar in each sample was measured.
- Control experiments were carried out using cooked wheat that had been chopped up in a blender, not chewed.
What reducing sugar, or sugars, would you expect to be produced during chewing?
Give a reason for your answer.
- Maltose
- Salivary amylase breaks down Starch
In this model of digestion in the human gut, what other enzyme is required for the complete digestion of starch?
( A student investigated the effect of chewing on the digestion of starch in cooked wheat.
He devised a laboratory model of starch digestion in the human gut. This is the method he used.
- Volunteers chewed cooked wheat for a set time.
The wheat had been cooked in boiling water. - This chewed wheat was mixed with water, hydrochloric acid and a protein-digesting enzyme and left at 37 °C for 30 minutes.
- A buffer was then added to bring the pH to 6.0 and pancreatic amylase was added.
This mixture was then left at 37 °C for 120 minutes. - Samples of the mixture were removed at 0, 10, 20, 40, 60 and 120 minutes, and the concentration of reducing sugar in each sample was measured.
- Control experiments were carried out using cooked wheat that had been chopped up in a blender, not chewed. )
( Maltose is produced when digested by amylase )
- Maltase
What was the purpose of step 2, in which samples were mixed with water, hydrochloric acid and pepsin?
( A student investigated the effect of chewing on the digestion of starch in cooked wheat.
He devised a laboratory model of starch digestion in the human gut. This is the method he used.
- Volunteers chewed cooked wheat for a set time.
The wheat had been cooked in boiling water. - This chewed wheat was mixed with water, hydrochloric acid and a protein-digesting enzyme and left at 37 °C for 30 minutes.
- A buffer was then added to bring the pH to 6.0 and pancreatic amylase was added.
This mixture was then left at 37 °C for 120 minutes. - Samples of the mixture were removed at 0, 10, 20, 40, 60 and 120 minutes, and the concentration of reducing sugar in each sample was measured.
- Control experiments were carried out using cooked wheat that had been chopped up in a blender, not chewed. )
- Mimics the effect of the stomach
In the control experiments, cooked wheat was chopped up to copy the effect of chewing.
Suggest a more appropriate control experiment. Explain your suggestion.
- Adding boiled saliva
- Everything else would be the same as the original experiment but denatured salivary amylase is used
The figure below shows the student’s results.
( The figure shows two graphs, one representing “ Chewed cooked wheat “ and the other “ Chopped cooked wheat “ )
( Both are line graphs and are more or less rate of reaction curves )
( The y-axis is labelled “ Mean concentration of reducing sugars in samples of cooked wheat / mg g^- 1 )
( The x-axis is labelled “ Incubation time / minutes )
( “ Chewed cooked wheat “ starts at a higher concentration of reducing sugars and has a faster rate of reaction, shown by a sharper decrease in the gradient )
( “ Chopped cooked wheat “ starts at a lower concentration of reducing sugars and has a slower rate of reaction )
( Both graphs finish at the same end point )
Explain what these results suggest about the effect of chewing on the digestion of starch in wheat.
- Some starch was already digested when chewed
- There’s a faster digestion with chewed starch
- There’s the same amount of digestion without chewing at the end
In humans, the enzyme maltase breaks down maltose to glucose.
This takes place at normal body temperature.
Explain why maltase:
• only breaks down maltose
• allows this reaction to take place at normal body temperature.
- The tertiary structure of the enzyme ( maltase )
- Has an active site that is only complementary to the substrate ( maltose )
- As maltase binds to maltose, the tertiary structure of maltase changes slightly so that maltose can bind to it
- This causes stressing on the maltose allowing it to break apart
- The enzyme is a catalyst
- By forming an enzyme-substrate complex
