EduNinja

[Maximum number: 4]

Saccharomyces cerevisiae is a unicellular fungus that is important in the brewing and baking industries.

Fig. 4.1 is a diagram of a transmission electron micrograph of S. cerevisiae.

Fig. 4.1

(a)

One function of the lipid droplets shown in Fig. 4.1 is to store triglycerides.

The triglycerides in a lipid droplet are surrounded by a single layer (monolayer) of phospholipids.

Suggest and explain why phospholipids, rather than triglycerides, are used for the outer monolayer of the lipid droplet.

[ 2 ]

(b)

A disaccharide, trehalose, is a reserve store of energy for S. cerevisiae when glycogen stores decrease. The monomer of glycogen and trehalose is $\alpha$ -glucose.

[ 2 ]

(i)

Complete Fig. 4.2 to show the ring structure of one $\alpha$ -glucose molecule.

Fig. 4.2

[ 2 ]

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Starch molecules are the main storage molecules in many types of cereal grain, such as the grain of the barley plant.

(a)

When the seed inside a barley grain germinates, genes coding for digestive enzymes are switched on. The enzymes that are synthesised catalyse the hydrolysis of storage molecules such as proteins and starch.

[ 1 ]

(i)

Starch is a mixture of two different molecules.

Name these two molecules.

Two of the enzymes synthesised by the barley seed are $\alpha$ -amylase and maltase. These are involved in the hydrolysis of the stored starch during seedling formation.

In the food industry, the starch extracted from barley seeds (barley starch) is used in the production of sugar syrups. Fig. 2.2 summarises the reactions catalysed by $\alpha$ -amylase in the production of maltose syrup and by maltase in the production of glucose syrup.

Fig. 2.2

[ 1 ]

(b)

Some of the substances shown in Fig. 2.2 are listed in Table 2.1.

Complete Table 2.1 to identify which of the terms polysaccharide, monosaccharide and macromolecule apply to each of the substances listed.

Use a tick $(\checkmark)$ if the term applies and a cross (x) if the term does not apply.
Put a tick $(\checkmark)$ or a cross (X) in every box.

Table 2.1

When producing sugar syrups, there are advantages in using enzymes extracted from microorganisms.

For example, some enzymes extracted from microorganisms are heat stable. Heat-stable enzymes are used to increase productivity because the reactions can be carried out at higher temperatures.

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One type of covalent bond between two monomers is shown.

Figure for Question 3 — CAIE A-Level Biology AS

Which molecules contain this type of covalent bond?

A

amylopectin, amylase, glycogen and starch

B

amylopectin, amylase and glycogen only

C

amylopectin, glycogen and starch only

D

amylase, glycogen and starch only

CAIE A-Level Biology AS 2.2 Carbohydrates and Lipids Topic Practice

Question 1

Question (a)

Question (b)

Question (i)

Question 2

Question (a)

Question (i)

Question (b)

Question 3