Edexcel IAL Biology Unit 1 Questions

[Maximum number: 12]

The structure and properties of the cell membrane are important in controlling which molecules can enter and leave a cell.

(a)

The photograph shows part of a cell membrane, as seen using an electron microscope.

Figure for Question (a) — Edexcel A-Level Biology AS

The width of this cell membrane is 5.00 nm .
A phosphate head of a phospholipid is between 0.8 and 0.9 nm in diameter and the fatty acid tails are between 1.25 and 1.75 nm long.

Explain how this electron micrograph provides evidence for the structure of the cell membrane.

Use the information given to support your answer.

[ 3 ]

An explanation that includes the following points:

- because it shows that it is \{made of two layers of phospholipid / a bilayer\} (1)

- the size of a phospholipid is in the range 2.05 nm to 2.65 nm (1)

- therefore the width of the membrane $(5 \mathrm{~nm})$ is within a bilayer range (of 4.1 nm to 5.3 nm ) (1)

Accept it shows two layers of
phosphate heads separated by a
band of lipids

(3)

(b)

Cell membranes contain cholesterol.

The molecular formula of cholesterol is $\mathrm{C}_{27} \mathrm{H}_{46} \mathrm{O}$ .
The diagram shows a cholesterol molecule.

Figure for Question (b) — Edexcel A-Level Biology AS

Explain the location of cholesterol in cell membranes.
Use the information in the diagram to support your answer.

[ 3 ]

(c)

The diagram shows the permeability of cell membranes to some chemicals.
sodium and chloride ions

Figure for Question (c) — Edexcel A-Level Biology AS

The sodium and chloride ions, glucose and water are polar chemicals.
A steroid is a non-polar chemical.

[ 6 ]

(i)

Describe the dipolar nature of water.

[ 2 ]

(ii)

Explain the permeability of cell membranes to each chemical shown in the diagram.

[ 4 ]

[Maximum number: 3]

Hydra are small animals that live in water.
They have a cylindrical body.
The drawing shows a hydra.

Figure for Question Unit 1: Molecules, Diet, Transport and Health question 2 — Edexcel A-Level Biology AS

A hydra has a hollow body that is made up of two layers of cells.

Explain how a hydra is adapted for gas exchange.

[Maximum number: 11]

The structures of polysaccharides, disaccharides and monosaccharides relate to their roles in living organisms. They are all types of carbohydrate.

(a)

The table shows the main type of carbohydrate present in some foods.

Table for Question (a) — Edexcel A-Level Biology AS

[ 5 ]

(i)

Which row of the table shows an example of a polysaccharide, a disaccharide and a monosaccharide? □ A □ B □ C □ D

Table for Question (i) — Edexcel A-Level Biology AS

[ 1 ]

(ii)

Lactose is a disaccharide composed of galactose and glucose. Complete the diagram to show a molecule of lactose.

Figure for Question (ii) — Edexcel A-Level Biology AS

[ 2 ]

(iii)

Glycogen is another carbohydrate.

Describe the structure of glycogen.

[ 2 ]

A description that makes reference to the following points:

- \{polymer of / polysaccharide of / made of many\} ( $\alpha$ ) glucose (1)

- branched with (1-4 and 1-6 / together with 1-4) glycosidic bonds (joining glucoses) / has 1-4 and 1-6 glycosidic bonds (1)

DO NOT ACCEPT made of amylose
and amylopectin

(b)

*(c) Carbohydrate metabolism includes the group of chemical reactions that break down carbohydrates. Some of these reactions convert one type of carbohydrate into another type. The flowchart shows what happens to some of the carbohydrates that we eat.

Explain how carbohydrates are metabolised, transported and used in the cells of the body and stored in liver cells. Use the information in the question and your own knowledge of the structures, roles and properties of carbohydrates and transport mechanisms.

[ 6 ]

*6(c)

1. Carbohydrate metabolism:

- carbohydrates broken down by hydrolysis

- by enzymes

- to speed up rate of reaction / to lower activation energy (E)

- starch to maltose / glucose, lactose to glucose and galactose, maltose to glucose, sucrose to glucose and fructose

- because starch is insoluble (so cannot move into blood) (E)

- so that sugars are soluble (and can be moved into the blood stream) (E)

2. Carbohydrate transport:

- monomers / named monomer pass into blood by facilitated diffusion / channel proteins / carrier proteins

- because it is a large / polar molecule (E)

- as there is more glucose in digestive system than in blood (E)

- transported in blood by mass transport

- to overcome the limitations of diffusion (E)

- because dissolves in blood plasma (E)

- because they are polar molecules (E)

3. Carbohydrate usage in cells:

- glucose passes into cells by facilitated diffusion / channel proteins / carrier proteins

- because more glucose in blood than cells (E)

- used as a respiratory substrate / respiration

- respiration to release energy (for cells) (E)

- used to form glycoproteins

- glycoproteins for cell membranes (E)

4. Carbohydrate storage in liver:

- liver stores carbohydrate as glycogen

- to lower blood sugar levels / glucose is in excess (E)

- glucoses joined by condensation reactions

- glycogen is insoluble (so can be stored) (E)

- glycogen does not have osmotic effect (E)

- glycogen broken down to re-enter blood stream

- as glycogen too large / insoluble to pass out of cells (E)

- when blood sugar levels are too low (E)

Additional guidance

Level 0

0

No awardable content

Level 1

1-2

An explanation may be attempted but with limited interpretation or analysis of the scientific information and with a focus on mainly just one piece of scientific information. The explanation will contain basic
information, with some attempt made to link knowledge and understanding to the given context.

Simple descriptions of data with no real attempt of an explanation

1 mark = one description made

2 marks = three descriptions made

Level 2

3-4

An explanation will be given, with occasional evidence of analysis,
interpretation and/or evaluation of both pieces of scientific information.
The explanation shows some linkages and lines of scientific reasoning, with some structure.

Some explanation given (E)

3 marks = explanation for one aspect of question

4 marks = explanation for two aspects of question

Level 3

5-6

An explanation is made that is supported throughout by sustained application of relevant evidence of analysis, interpretation and/or evaluation of both pieces of scientific information. The explanation shows a well-developed and sustained line of scientific reasoning, which
is clear and logically structured.

Extended explanation given (E)

5 marks = explanation for three aspects of question

6 marks = explanation for four aspects of question

[Maximum number: 1]

All organisms contain one or more cells.

In which of the following is a cell membrane present?

A

animal cells only

B

animal and plant cells only

C

plant and prokaryotic cells only

D

animal, plant and prokaryotic cells

Edexcel IAL Biology Unit 1 Molecules, Diet, Transport and Health

Covered syllabus points

Covered syllabus points

Unit 1: Molecules, Diet, Transport and Health question 1

Question (a)

Question (b)

Question (c)

Question (i)

Question (ii)

Unit 1: Molecules, Diet, Transport and Health question 2

Unit 1: Molecules, Diet, Transport and Health question 3

Question (a)

Question (i)

Question (ii)

Question (iii)

Question (b)

Unit 1: Molecules, Diet, Transport and Health question 4