Oct/Nov 2014

In experimental measurements, which of the following methods could be subject to parallax error? 1 employing a calibrated eyepiece graticule to measure length 2 using a measuring cylinder to determine volume 3 using a ruler to measure the length of a shoot

The microscope in cell studies

When haemoglobin is fully saturated with oxygen, how many oxygen molecules are attached to each haemoglobin molecule?

Proteins

Why do large increases in temperature or pH change enzyme activity?

Factors that affect enzyme action

Ethylene glycol is a chemical that is used to stop water from freezing. If ethylene glycol is accidentally swallowed, an enzyme in liver cells metabolises it and a toxic product is formed. Normally, this enzyme catalyses the oxidation of ethanol to a harmless product. People who have swallowed ethylene glycol are given large doses of ethanol. This stops a toxic product from being made and gives the body time to excrete the ethylene glycol. Which statement explains why this treatment is effective?

Mode of action of enzymes

Increasing what kind of bond makes the cell surface membrane more fluid?

Fluid mosaic membranes

The diagram illustrates three pathways, X, Y and Z, by which substances may move across a cell surface membrane. Which option correctly indicates the pathways for vitamin D, which is fat soluble, and vitamin C, which is water soluble?

Movement into and out of cells

In plants adapted to cold conditions, the composition of their cell surface membranes alters as the weather becomes colder, enabling the plants to carry out exocytosis. Which alteration takes place in their cell surface membranes?

Fluid mosaic membranes

Which statement does not describe a diploid cell correctly?

Replication and division of nuclei and cells

Laboratory mice in which the $p53$ genes had been turned off developed tumours. When the $p53$ genes were switched back on, the tumour cells stopped dividing and died within a few days. The healthy cells in the mice were not affected. What do these observations suggest?

Replication and division of nuclei and cells

The diagram illustrates part of a DNA molecule. Which regions include phosphate groups?

Structure of nucleic acids and replication of DNA

Some antibiotics act by attaching to ribosomes and stopping protein synthesis. Which statement explains why these antibiotics destroy bacterial cells but do not affect human cells?

Protein synthesis

Which cell structure is frequently continuous with the rough endoplasmic reticulum?

Cells as the basic units of living organisms

Which statements concerning tRNA are correct?

Proteins

What is the chief role of a companion cell in phloem tissue?

Structure of transport tissues

By which route is sucrose transported from chloroplasts into the phloem?

Movement into and out of cells

A large number of aphids were used to obtain samples of the contents of the sieve tubes in a tomato plant. Different samples of sieve tube solution were tested. Which result was correct?

Testing for biological molecules

Which row gives the correct answer for the pulmonary vein?

The circulatory system

Which statement correctly explains the Bohr effect?

Proteins

What product is formed by the action of carbonic anhydrase?

Mode of action of enzymes

In the cardiac cycle, valve movements produce sounds that may be listened to with a stethoscope. What produces the first sound after atrial systole in the cardiac cycle?

The heart

The following list shows the parts of the heart that regulate the heartbeat. 1 sinoatrial node (SAN) 2 atrioventricular node (AVN) 3 Purkyne tissue Which row correctly shows atrial contraction and ventricular contraction?

The heart

The photomicrograph displays a cross-section of a bronchus. What functions do tissues X and Y carry out?

The gas exchange system

Which structures are present in both chloroplasts and mitochondria? 1 $70\text{S}$ ribosomes 2 $80\text{S}$ ribosomes 3 circular DNA

Cells as the basic units of living organisms

Which component or components of tobacco smoke bring about higher blood pressure and greater clotting?

The circulatory system

Peak Flow is used in hospitals to diagnose some lung diseases. It measures the greatest rate at which air can be breathed out of the lungs. How will the Peak Flow for a person with emphysema differ from that for a healthy person?

The gas exchange system

The list below gives four ways in which infectious diseases can be passed on. 1 droplet 2 food 3 contact 4 vector Which row correctly matches each disease with its organism and its transmission method?

Infectious diseases

40% of the world’s population live in an area where malaria poses a threat to health. In recent years, the number of malaria cases in Africa has risen sharply. What is the social factor that is allowing the spread of malaria to get out of control?

Infectious diseases

Which illnesses are treated using antibiotics?

Antibiotics

Which of these are specific immune responses?

The immune system

Why has vaccination not succeeded in eradicating cholera?

The microscope in cell studies

A person’s blood group is decided by the antigens on the red blood cells. Even if people have never had a blood transfusion, antibodies are present in their blood plasma. These antibodies are found in the plasma of the person receiving the blood, which means that some transfusions are unsafe. The table gives the antigens and antibodies in the blood of people with different blood groups. Which blood groups can safely receive blood from a person with blood group A?

Fluid mosaic membranes

The diagram illustrates the transfer of energy among organisms in an ecosystem. Which option correctly names each organism in the ecosystem?

Transport mechanisms

In a freshwater food chain, which stage has the least efficient transfer of energy?

Transport mechanisms

Tay-Sachs disease develops when cells cannot make an enzyme, so particular lipids accumulate inside cells. Which cell structure would fail to work properly, causing the disease?

Cells as the basic units of living organisms

Which statement about processes occurring in the nitrogen cycle is not correct?

Transport mechanisms

Which structures occur in a Plasmodium cell?

Cells as the basic units of living organisms

The diagram represents a triglyceride molecule that has undergone partial hydrolysis. What are the products of the complete hydrolysis of the molecule shown?

Carbohydrates and lipids

Which of the following represents $\alpha$-glucose?

Carbohydrates and lipids

Which option correctly pairs the functional and structural characteristics of cellulose, collagen, glycogen or triglyceride?

Carbohydrates and lipids

The diagram illustrates how the levels of protein structure are related to bonds. Which row is the correct one?

Proteins

Which lens combination in a light microscope produces the highest magnification?

The microscope in cell studies

Which bond involved in stabilising the tertiary structure of a protein would be the least likely to break if the temperature rises above the protein’s optimum?

Proteins

The diagram displays the structures of four amino acids in solution. Which amino acids carry no overall charge?

Proteins

The statements concern the properties of water. Which property is important in transpiring plants for preventing enzymes in leaves from being denatured?

Water

Which terms in the table correctly finish the paragraph about enzymes? When the pH of a surrounding environment falls below an enzyme’s optimum pH, ……… between neighbouring ……… groups, which maintain the ……… structure, are broken.

Factors that affect enzyme action

Lipase is a digestive enzyme made by the pancreas that catalyses the hydrolysis of dietary lipids. The graph indicates how the pH of a liquid food with a large lipid content falls over time. Which statements could explain the experimental results between 50 and 60 minutes?

Factors that affect enzyme action

The AIDS virus synthesises a long polypeptide, which is then hydrolysed by a protease enzyme into a number of shorter peptides. This viral protease is the target of anti-AIDS drugs. Which feature is vital for these drugs to work successfully?

Mode of action of enzymes

How wide is the cell surface membrane?

Fluid mosaic membranes

Some functions of molecules present in cell surface membranes are shown below. Which of these are functions of cholesterol?

Fluid mosaic membranes

Lactase is an enzyme located in the membranes of epithelial cells that line the small intestine. This enzyme consists of a single polypeptide that folds into three regions. What type of amino acid would be present in each of these three regions?

Proteins

A student observed the cells in the growing region (meristem) of an onion root and recorded the data shown below. What percentage of cells contain chromosomes that appear as two chromatids?

Chromosome behaviour in mitosis

What sequence of steps is required to determine the actual width of a xylem vessel seen in transverse section with a $\times 10$ objective lens?

The microscope in cell studies

Which statements correctly define diploid and haploid in typical eukaryotic cells?

Replication and division of nuclei and cells

What type of sugar and which types of bonds are present in a DNA molecule?

Structure of nucleic acids and replication of DNA

Which nucleic acid bases are classified as purines?

The microscope in cell studies

A DNA fragment 15 base pairs in length was examined in order to determine how many nucleotides were on each polynucleotide strand. Some of the findings are shown below. The table gives the numbers of nucleotide bases A, C, G and T for strand 1 and strand 2. Strand 1 contains 6 cytosine bases and 3 thymine bases. Strand 2 contains 4 thymine bases. How many nucleotides containing guanine were present in strand 1?

Structure of nucleic acids and replication of DNA

The diagram illustrates a transverse section through a stem. Which region is the phloem?

Structure of transport tissues

A leafy shoot was connected to a potometer and placed under several different conditions. For each condition, the time required for the meniscus to travel $50\,\text{mm}$ along the capillary tubing was measured. Which option indicates the lowest and highest rates of water uptake?

Movement into and out of cells

The diagram illustrates four plant cells. In which direction might there be a net movement of water by osmosis?

Movement into and out of cells

In what way will waterlogged soil affect the root pressure in a plant?

Movement into and out of cells

The diagram illustrates how phloem sieve tube elements, xylem vessel elements and companion cells are related. Which statement is correct?

Structure of transport tissues

Small arteries (arterioles) lie close to the tissues. One role of an arteriole is to raise or lower the amount of blood flowing to the tissues. Which tissues would be found in the wall of an arteriole to enable this role? 1 collagen 2 elastic 3 muscle

The microscope in cell studies

The statements all describe cell structures. Which row identifies the type of cell where each of these cell structures is usually found?

Cells as the basic units of living organisms

The graph shows a dissociation curve for haemoglobin. Which axis labels would be appropriate for the x-axis and y-axis?

Proteins

One congenital heart defect is known as atrial septal defect (ASD), in which the left and right atria are not fully separated. ASD typically causes blood to flow from the left atrium to the right atrium. As a result, blood pressure in the right atrium rises and blood pressure in the left atrium falls. Which row shows the other effects of ASD on blood pressure and oxygenation?

The heart

What effects does carbon monoxide in tobacco smoke have on the body?

Proteins

The graph illustrates the amount of air expelled rapidly and forcefully after a deep inhalation for three different people, X, Y and Z. What is one possible reason for the differences in the amounts of air expelled by these people that are shown?

The gas exchange system

Which flow diagram correctly shows the effect when tar enters the lungs?

The gas exchange system

Which statements concerning people infected with HIV/AIDS are correct?

The microscope in cell studies

The statements concern polio and tuberculosis (TB). Which statement explains why the polio vaccine can be given by mouth whereas the TB vaccine must be injected?

Factors that affect enzyme action

Which reason explains why sickle cell anaemia has not been eradicated?

Proteins

Which method of acquiring immunity can be described as natural active immunity?

The immune system

At which stage of energy transfer is the efficiency the lowest?

The microscope in cell studies

Which structures occur in both typical eukaryotic cells and typical prokaryotic cells?

Cells as the basic units of living organisms

The diagram illustrates a simplified nitrogen cycle. In which stage does decomposition occur?

Infectious diseases

Which sequence illustrates some of the stages involved in the manufacture and secretion of an enzyme?

Proteins

Which plan diagram of a transverse section through a dicotyledonous leaf shows the xylem and phloem in the correct positions when the palisade mesophyll layer is twice as thick as the spongy mesophyll layer?

Structure of transport tissues

Proteases are a class of enzymes that break down proteins. Which statement about proteases is correct?

Mode of action of enzymes

Two disaccharides are maltose and sucrose. Maltose is made from two molecules, whereas sucrose is made from fructose and glucose. Which row gives the molecular formulae of these two disaccharides?

Carbohydrates and lipids

The diagram illustrates a carbohydrate molecule. Which polymers could this molecule be part of?

Carbohydrates and lipids

An eyepiece graticule is inserted into the eyepiece of a microscope, and a stage micrometer is mounted on the microscope. Which of the following statements about the stage micrometer scale are correct?

The microscope in cell studies

Which term from the following list could be used to describe the secondary structure of a protein?

Proteins

Why is haemoglobin described as having a quaternary structure?

Proteins

A sample of an enzyme was mixed with a sample of its substrate. The graphs illustrate how the concentrations of the enzyme, the substrate, the enzyme-substrate complex and the product vary with time. Which graph shows the change in concentration of the enzyme-substrate complex?

Mode of action of enzymes

Which statement is correct about a competitive inhibitor of an enzyme?

Mode of action of enzymes

Which two substances help keep cell membranes fluid?

Fluid mosaic membranes

Membrane proteins are termed ‘peripheral’ when they are attached to the membrane only temporarily, and ‘integral’ when they remain attached permanently. Integral proteins are called ‘intrinsic’ if they pass through the entire bilayer, whereas they are ‘extrinsic’ if they occur on just one side of the bilayer. How would you describe a channel protein?

Fluid mosaic membranes

The diagram shows an apparatus arranged to examine how altering the concentration of glucose in the surrounding solution affects the movement of molecules across a selectively permeable membrane (Visking tubing) over 15 minutes. As the concentration of glucose solution in the surrounding solution rises, which statements are correct?

Movement into and out of cells

Which statement is always correct for cytokinesis?

Replication and division of nuclei and cells

The statements concern genes and proteins associated with breast cancer. • The protein produced by the $\text{BRAC1}$ gene prevents the division of breast cancer cells. • The protein produced by the $\text{p53}$ gene inhibits tumours. Which pairing of genes is most likely to lead to breast cancer?

Replication and division of nuclei and cells

Which structural characteristic of the DNA molecule differs?

Proteins

Density gradient centrifuges are used to separate cell structures according to their relative density. Cell structures with a larger density move further down the centrifuge tube. What is the correct sequence of the cell structures, beginning at the top of the centrifuge tube?

The microscope in cell studies

DNA is described as replicating by a semi-conservative mechanism. The findings from Meselson and Stahl’s experiments provided strong evidence in favour of this idea. They worked with $E.\,coli$, and its generation time is 50 minutes. The following stages took place in their experiment, but they are listed in the incorrect order. $^{14}\text{N}$ DNA refers to DNA with the ‘light’ nitrogen isotope. $^{15}\text{N}$ DNA refers to DNA with the ‘heavy’ nitrogen isotope. P All bacteria contain $^{15}\text{N}$ DNA. Q All bacteria contain hybrid DNA ($^{15}\text{N}$ DNA and $^{14}\text{N}$ DNA). R Bacteria contain either all $^{14}\text{N}$ DNA or hybrid DNA. S Bacteria grown in a $^{15}\text{N}$ medium for many generations. T Bacteria transferred to a $^{14}\text{N}$ medium and sampled every 50 minutes. Which sequence of letters gives the correct order of the stages in the experiment?

Replication and division of nuclei and cells

Which molecules take part in transcription, and which molecules take part in translation?

Proteins

What processes take place in the vascular tissue of leaves and roots?

Movement into and out of cells

The diagram illustrates the water potential ($\Psi$) for some plant cells and for the surrounding environment. cell 1 $\Psi = -7\,\text{kPa}$ cell 2 $\Psi = -5\,\text{kPa}$ cell 3 $\Psi = -4\,\text{kPa}$ environment $\Psi = -5\,\text{kPa}$ Which statements are correct?

Movement into and out of cells

A part of a plant that contains vascular tissue is exposed to a metabolic poison. How will this treatment influence transport between roots and leaves through xylem and phloem?

Movement into and out of cells

A group of students were given the photomicrograph of a cross-section of an unfamiliar material and were asked to make observations. They described X as 1 round 2 a hollow tube 3 a spherical structure Which description(s) are correct?

The microscope in cell studies

Which statement is correct about tissue fluid?

Movement into and out of cells

The graph illustrates the dissociation curves for adult haemoglobin at two different (unidentified) concentrations of carbon dioxide. Which point indicates the oxygen concentration in red blood cells as they leave a resting muscle?

Proteins

The diagram illustrates the pressure changes in several structures on the left side during the cardiac cycle. Which letter indicates when the ventricle contains no blood?

The heart

Which statement about events that take place in the heart is correct?

The heart

Red blood cells have a diameter of $7000\,\text{nm}$. Pancreatic cells have a diameter of $35\,\mu\text{m}$. Which statement about the relative sizes of these cells is correct?

Cells as the basic units of living organisms

Which row correctly identifies the regions of the gas exchange system that contain cartilage, ciliated epithelium, goblet cells and smooth muscle?

The gas exchange system

What observation would suggest a difference in the structure of the gas exchange system of a cigarette smoker and a non-smoker?

The gas exchange system

Asthma is a lung condition brought on when an allergen, for example pollen or dust, is breathed in. The allergen causes the bronchii and bronchioles to become swollen and narrowed, and the goblet cells in the walls of these airways to release too much mucus. What effects would these changes have on the gaseous exchange system of a person with asthma?

Movement into and out of cells

After coming back home from a trip to another country, a person begins to experience fevers at set intervals. Blood tests carried out both between the fevers and while the fevers are happening reveal a fall in the red blood cell count (anaemia). Which disease does this person have?

Infectious diseases

What factors make cholera infection more likely among people living in refugee camps?

Infectious diseases

Which statements help to explain why cholera has not been eliminated by vaccination?

Antibodies and vaccination

Cells that divide and produce macrophages are known as stem cells. In which part of the body do these stem cells divide?

Replication and division of nuclei and cells

What type of immunity is acquired after a pathogen infects the body?

The immune system

The diagram illustrates a section of the nitrogen cycle. Which process is performed by denitrifying bacteria?

Cells as the basic units of living organisms

The graph illustrates the yearly variation of the following factors in a lake: • daily light intensity • producer numbers • primary consumer numbers • nutrient quantity Which curve shows the primary consumer numbers?

The microscope in cell studies

Which cell structure visible in the electron micrograph is the place where protein modification and packaging occur?

Cells as the basic units of living organisms

Within a food chain, which stage has the least efficient transfer of energy?

Carbohydrates and lipids

The diagram illustrates several similarities among typical prokaryotes, chloroplasts and mitochondria. Which statement is correct?

Cells as the basic units of living organisms

A sample mixture of biological molecules was examined using Benedict’s solution and ethanol. Once the tests were completed, the solutions were blue with Benedict’s reagent, biuret and cloudy with ethanol. Which molecules might be present in the mixture?

Testing for biological molecules

The diagram represents part of a polysaccharide. In which polysaccharide(s) might this section occur?

Carbohydrates and lipids

Chromatography is a method used to separate molecules according to their solubility. The diagram shows one piece of apparatus used for this method. Chromatography was performed on four different carbohydrates: sucrose, cellulose, the products of hydrolysis of sucrose and the products of hydrolysis of cellulose. Which diagram shows the presence of the products of sucrose digestion?

Testing for biological molecules

In lipid molecules, at what positions are double bonds found?

Carbohydrates and lipids