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Edexcel IAL Biology Topic 2 Membranes, Proteins, DNA and Gene Expression

Identify the molecular structure or process being tested, annotate the evidence precisely and link each bond, gradient or sequence change to its biological outcome.

Syllabus
First assessment 2019
Course
Biology YBI11
Level
AS

Exam points

  • Interpret membrane and gas-exchange diagrams through structure, gradients and transport.
  • Explain protein and enzyme behaviour through bonds, shape and molecular interactions.
  • Apply DNA and gene-expression mechanisms to sequences, data and experimental evidence.

Covered syllabus points

2.1—Gas exchange surfaces and Fick's Law2.2—Cell membrane structure and models2.3—Core Practical 3 - membrane permeability2.4—Osmosis and water potential gradients2.5—Membrane transport mechanisms2.6—Amino acids, proteins and protein structure2.7—Enzyme action and specificity2.8—Core Practical 4 - enzyme-catalysed reaction rate2.9—Nucleotides, DNA, RNA and base pairing2.10—DNA replication and Meselson-Stahl evidence2.11—Genetic code2.12—Gene as a DNA base sequence2.13—Protein synthesis2.14—DNA replication errors and mutations2.15—Inheritance terminology and monohybrid inheritance2.16—Cystic fibrosis gene mutation effects2.17—Genetic screening uses and implications2.18—Ethical and social issues in genetic screening

Topic 2 - Membranes, Proteins, DNA and Gene Expression question 1

[Maximum number: 3]

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

Figure for Question Topic 2 - Membranes, Proteins, DNA and Gene Expression question 1 — 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.

Topic 2 - Membranes, Proteins, DNA and Gene Expression question 2

[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

Topic 2 - Membranes, Proteins, DNA and Gene Expression question 3

[Maximum number: 9]

Beetroot cells contain a red pigment called betalain. This pigment does not leak out of the cells, unless their membranes are damaged.

A student investigated the effect of detergent on beetroot cell membranes.
Discs of tissue were cut from a beetroot. Any betalain on the outside of the discs was removed.
One disc was placed into each of five test tubes, containing 0.2% detergent solution.
The five tubes were left for 30 minutes at 20∘C20^{\circ} \mathrm{C}.
The discs were then removed carefully.
Betalain had leaked from the discs and formed a red solution in each test tube.
Light was shone through this solution. The percentage of the light transmitted through the solution was recorded.

The same procedure was repeated using detergent concentrations of 0.0%,0.5%, 1.0% and 2.0%.

Question (a)

(a)

The table shows the results of this investigation.

Table for Question (a) — Edexcel A-Level Biology AS
[ 9 ]

Question (i)

(i)

Detergent permanently damages beetroot cell membranes.

Explain what will happen to the rate of loss of betalain if these discs are then transferred to test tubes of distilled water.

[ 3 ]

Question (ii)

(ii)

In a second investigation, the effect of temperature on beetroot cell membrane permeability was studied.

The graph shows the results of the second investigation.

Compare and contrast the effects of detergent concentration and temperature on the leakage of betalain from beetroot cells.

Figure for Question (ii) — Edexcel A-Level Biology AS
[ 3 ]

Question (iii)

(iii)

Estimate the percentage of light transmitted at 80^ C.

Use the information in the graph and your own knowledge to support your answer.

[ 3 ]
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