A level Bio 1.2 Carbohydrates

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Molasses is a solution obtained from sugar beet plants. The sugars present in molasses are sucrose, glucose and fructose. Give the number of different types of monosaccharides present in molasses. (1)

2 (1)

A scientist used the apparatus in below figure to investigate osmosis.

Use your understanding of osmosis to explain why the air pressure in the tube increased. (3)

Water (in beaker) has higher water potential (1)

Water moves in (across) partially/selectively permeable bladder (1)

Increased (molasses/solution) volume (1)

The scientist repeated the investigation, but made one change to the molasses.

The scientist did not change the volume of molasses at the start of the investigation.

The scientist observed that the air pressure inside the tube increased by 160 kPa compared with 800 kPa in the first investigation.

Suggest the change the scientist made to the molasses to cause this smaller increase in air pressure.

Use the air pressure figures in a calculation to support your answer (2) 

Decreased (molasses) concentration (1) 

(Reduction by) 80%/5 times (1) 

Chitin is a polysaccharide. The chitin monomer is a β-glucose molecule with one OH group replaced by an NHCOCH3 group. NHCOCH3 can be represented by N(Ac).

The figure below shows the monomer that forms chitin and the chitin polymer.

Chitin has a similar structure to cellulose. Use the figure above to describe three ways the structure of chitin is similar to the structure of cellulose.(3)

(Alternate) monomers/glucoses are flipped/upside down (1) 

(Joined by ) glycosidic bonds(1) 

(forms ) straight/unbranched (chains/molecules) (1) 

Lignin is a polymer found in the walls of xylem vessels in plants. Lignin keeps the xylem vessel open as a continuous tube.

Explain the importance of the xylem being kept open as a continuous tube.(3)

(So) no barrier to (water) movement (1) 

Cohesion from H between all water molecules (1) 

Evaporation/transpiration creates tension (in column) (1) 

Iodine solution stains fresh apple tissue black.

When iodine solution is added to apples stored for a week, the stain is less black.

The water potential of apple juice decreases when apples are stored. Suggest why the water potential of apple juice decreases when apples are stored (2)

Starch hydrolysised (1)

Maltose is soluble (1)

Describe the complete digestion of starch by a mammal (5)

Hydrolysis(1)

(Of) glycosidic bonds(1)

(Starch) to maltose by amylase(1)

(Maltose) to glucose by disaccharidase/maltase(1)

Membrane-bound (disaccharidase/maltase) (1)

A precipitate is produced in a positive result for reducing sugar in a Benedict’s test.

A precipitate is solid matter suspended in solution.

A student carried out the Benedict’s test.

Suggest a method, other than using a colorimeter , that this student could use to measure the quantity of reducing sugar in a solution (2) 

Filter and dry (the precipitate) (1) 

Find mass/weight (1) 

Use of a colorimeter in this investigation would improve the repeatability of the student’s results.

Give one reason why.(1)

Colour change is subjective (1)

Explain how you would use the graph to determine the maltose concentration with a light absorbance of 0.45 arbitrary units (2)

Line of best fit drawn(1)

Read off value at 0.45(1)