General certificate of education june 2002 advanced subsidiary examination biology/human biology (specification a) bya1 unit 1 molecules, cells and systems

General Certificate of EducationJune 2002Advanced Subsidiary Examination BIOLOGY/HUMAN BIOLOGY (SPECIFICATION A)
Unit 1 Molecules, Cells and Systems
No additional materials are required.
• Use blue or black ink or ball-point pen.
• Fill in the boxes at the top of this page.
• Answer all the questions in the spaces provided. All working must be
• Do all rough work in this book. Cross through any work you do not Information
• The maximum mark for this paper is 75.
• Mark allocations are shown in brackets.
• You will be assessed on your ability to use an appropriate form and style of writing, to organise relevant information clearly and coherently,and to use specialist vocabulary, where appropriate.
• The degree of legibility of your handwriting and the level of accuracy of your spelling, punctuation and grammar will also be taken intoaccount.
Answer all questions in the spaces provided.
Complete the following table. Use a tick if the feature is present or a cross if it is absent.
Plasma membrane
Cell wall
Cells were scraped from the cut surface of a potato tuber. They were stained with iodinesolution and examined with an optical microscope. The drawing shows one of these cells.
Blue-black staining featuresin cytoplasm of cell Name two polysaccharides found in this cell which would not be found in a red
blood cell.
The diameter of this cell, measured from A to B, is 40 µm.
Calculate the magnification of the drawing. Show your working.
The focusing knob of the microscope was adjusted slightly. The drawing belowshows how the cell then looked.
Explain the difference in appearance of the cell contents.
Turn over
A protein is formed from 300 amino acids. The diagrams show the primary, secondaryand tertiary structures of this protein.
Explain what causes the secondary structure to differ in length from the primarystructure.
Explain what is meant by the tertiary structure of a protein.
Heating may affect the tertiary structure of a protein. Explain how.
The first step in investigating the primary structure of a protein is to break it into shorterlengths with enzymes. The table shows some of the enzymes used and the position of thepeptide bonds they break.
Position of peptide bond that enzyme breaks
First amino acid
Second amino acid
The diagram shows a polypeptide chain. The sequence of amino acids should be readfrom left to right.
How many amino acid fragments will be produced from this polypeptide if it isincubated with a mixture of trypsin and V8 protease? Explain why trypsin and chymotrypsin break peptide bonds between differentamino acids.
Turn over
Describe how phospholipid molecules are arranged in a plasma membrane.
Cholesterol is a substance needed in human cells. It is carried in the blood in a particle calleda low-density lipoprotein (LDL). The diagram shows how an LDL is taken into a cell and howthe cholesterol it contains is released in the cytoplasm.
LDL in blood plasma
Plasma membrane of cell
Plasmamembranepinches offto form avesicle Organelle A
released in
of cell

Organelle A
Suggest why an LDL will only attach to certain areas on the plasma membrane of a cell.
Name the process by which the LDL enters the cell.
Name organelle A.
Explain how this organelle is involved in the release of cholesterol from thevesicle.
Turn over
Fick’s law shows how some factors affect the rate of diffusion.
Rate of diffusion is proportional to surface area × difference in concentration Describe one adaptation of the alveolar epithelium which allows efficient diffusion.
Emphysema is a condition in which the walls between the alveoli break down andenlarge the air spaces. The blood of a person with emphysema contains a higherconcentration of carbon dioxide than the blood of a healthy person. Use Fick’s law toexplain why.
The table shows some measurements made on people living at two different altitudes.
Concentration of oxygen
Number of red
in blood in arteries/
blood cells in
cm3 per 100 cm3
1 mm3 of blood
The concentration of oxygen in the blood in the arteries of people living at 3700 mis higher than in the arteries of people living at 150 m. Use the information in thetable to explain why.
People who move from low to high altitude are often breathless at first.
Suggest why this breathlessness disappears after living at high altitude for severalweeks.
Turn over
When heated, hydrogen peroxide breaks down to water and oxygen.
The graph shows the energy changes which take place during this reaction.
What is represented by the part of the curve labelled X?
This reaction also takes place in many living cells. Here it is catalysed by theenzyme catalase. Sketch a curve on the graph to show the energy changes whichtake place when the enzyme is present.
When the reaction with catalase is carried out in a test-tube, the test-tube feelswarm at the end of the reaction. Use the graph to explain why.
The turnover number of an enzyme is the number of substrate molecules converted toproduct per second. The maximum turnover number of catalase is 200 000 molecules persecond. Explain why the turnover number falls as the temperature gets lower.
Turn over
An athlete ran at different speeds on a treadmill. The graph shows some of the changes whichoccurred as running speed increased.
Amount of oxygenin veins comingfrom muscles Give suitable units for the rate of blood flow in the pulmonary artery.
Explain why the rate of blood flow in the pulmonary artery changes when theheart rate changes.
Describe how nerves going to the heart can increase heart rate.
During exercise, red blood cells give up more of the oxygen they are transporting.
Give one piece of evidence from the graph which supports this statement.
Suggest how an increase in the rate of blood flow in the pulmonary artery helps tosupply more oxygen to muscles.
Turn over
If you read a sports magazine, it will not be long before you come across an advert for a sportsdrink. These adverts often claim that performance can be improved by consuming such drinks.
Is this just a sales gimmick or is there a scientific basis for these claims? Most sports drinks have a similar composition. Apart from water, the main ingredient is carbohydrate. This is usually a mixture of different sugars – sucrose and the two monomersfrom which it is formed by condensation – glucose and fructose. This combination improvestaste and ensures efficient water absorption from the intestine. Most commercially availabledrinks are advertised as isotonic. They have the same water potential as the body fluids. Whensugars are transported into the cells lining the intestine, water will also be absorbed.
10 Recently there has been an interest in the addition of particular amino acids to these drinks.
Glutamine has been added because it is supposed to help protect the body from minor illnessand infection. As well as glutamine, amino acids with a branched R-group may be added.
These appear to be linked with the delay of biochemical processes in the body which causefatigue.
Use the information from the passage and your own knowledge to answer the questions.
Glucose and fructose both have the same molecular formula, C6H12O6.
Suggest how two molecules can have the same formula but a different structure.
What is the molecular formula of a molecule of sucrose? The uptake of sugars from the intestine involves facilitated diffusion and activetransport.
Give two ways in which facilitated diffusion differs from active
Explain how transport of sugars into cells lining the intestine (lines 8-9) leads towater being absorbed.
Give two ways in which the structure of a glutamine molecule (line11) is identical to the
structure of an amino acid with a branched R-group (line 12).
Describe how you would use chromatography to separate and identify the differentsugars in a sports drink.
Turn over
During the cardiac cycle the heart fills with blood and then the ventricles contract. Thetable gives the filling time and the contraction time at different heart rates.
Heart rate/beats
Filling time/seconds
per minute
Give two conclusions that can be drawn from the figures in the table.
Explain how you would use the figures in the table to calculate the contractiontime at a heart rate of 60 beats per minute.
What additional information would you need in order to find the cardiac output ata particular heart rate? The diagram shows variations in blood pressure in different parts of the circulatorysystem.
Left ventricle
Complete the table with ticks to show whether each of the valves is open or closed
at the point indicated with the letter A on the diagram.
Valve located between
A pulse can be felt when the fingers are placed over an artery that is close to thesurface. Explain why a pulse cannot be felt when the fingers are placed over a veinwhich is close to the surface.
Turn over
What causes the blood pressure to increase at the point indicated with a letter B
on the diagram?
Explain how tissue fluid is formed and returned to the circulatory system.


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