May/June 2014

Which statement best compares an electron microscope with a light microscope?

The microscope in cell studies

The diagram illustrates the structures of four amino acids in solution. Which of these four amino acids have an overall charge?

Proteins

Which structural level of a haemoglobin molecule is encoded by a DNA molecule?

Proteins

The statements concern enzymes. Which of these statements is true for every enzyme?

Mode of action of enzymes

A tropical grass has been discovered to contain an unusual enzyme. It speeds up the hydrolysis of the fungal polysaccharide chitin into amino sugars. It also reduces the activity of an enzyme in locust guts that catalyses the digestion of amylose. Which description best fits the actions of this unusual enzyme?

Mode of action of enzymes

Several factors can alter the fluidity of the cell surface membrane. If the fluidity of cell surface membranes falls, which process would be affected the least?

Fluid mosaic membranes

Which molecules in cell surface membranes play a role in cell recognition?

Fluid mosaic membranes

Which statement is correct about facilitated diffusion and active transport?

Movement into and out of cells

Which features enhance the efficiency of ion uptake by a root hair cell?

Movement into and out of cells

During which processes does mitosis take place?

Replication and division of nuclei and cells

The diagram illustrates crosses involving wild wheat and two kinds of grass. What chromosome number does the fertile hybrid 2 have?

Chromosome behaviour in mitosis

In a cell, where are cisternae located?

Cells as the basic units of living organisms

The diagram illustrates a human cell $(2n = 46)$ at the close of prophase of mitosis (cell 1) and daughter cells immediately after telophase (cells 2 and 3). How many DNA molecules are present in the nucleus of cell 1 and cell 2?

Chromosome behaviour in mitosis

Which diagram shows a correct base pair in DNA?

Structure of nucleic acids and replication of DNA

The amino acid sequences present in normal and sickle cell haemoglobin are shown here. normal haemoglobin sequence: thr-pro-glu sickle cell haemoglobin sequence: thr-pro-val-glu The possible mRNA codons for these amino acids are listed below. glutamic acid (glu): GAA, GAG proline (pro): CCU, CCC threonine (thr): ACU, ACC valine (val): GUA, GUG Which tRNA molecule does not take part in producing this section of the sickle cell haemoglobin?

Proteins

Two batches of bacteria were cultured in different nitrogen-containing growth media. For one batch, the medium contained the ‘heavy’ isotope of nitrogen, $^{15}\text{N}$, and the bacteria were kept there until every DNA molecule became labelled. The other batch was cultured in a medium containing the ‘light’ isotope of nitrogen, $^{14}\text{N}$, until all the DNA was labelled. DNA was taken from each batch of bacteria and then centrifuged. The diagram indicates where this DNA appeared in the centrifuge tubes. Bacteria whose DNA was labelled with $^{15}\text{N}$ were moved into a medium containing $^{14}\text{N}$ and allowed to divide once. DNA was then extracted from the resulting generation of bacteria and centrifuged. Which tube shows where the DNA from this new generation of bacteria is found?

Replication and division of nuclei and cells

What processes take place in transpiration?

Movement into and out of cells

The photomicrograph depicts a vascular bundle taken from a plant stem. Which labels are correct for structures X, Y and Z?

Structure of transport tissues

The graph presents the findings from a potometer used to investigate how wind speed affects the rate of water loss in a plant. Which statement accounts for the results of the investigation?

Movement into and out of cells

Land covered by seawater flooding is not appropriate for plant growth after the salty flood water has drained away. Which water-potential values in the xylem and in the soil water help to explain why land flooded with salty water is unsuitable for plant growth?

Movement into and out of cells

During sucrose loading into a sieve tube element, what function does ATP serve in a companion cell?

Movement into and out of cells

What features enable an artery to withstand changes in the pressure of the blood flowing through it?

The circulatory system

Which adaptation would raise the active transport of carbohydrates from a plant cell?

Movement into and out of cells

Which reactions are occurring in the blood in a capillary beside an alveolus?

Movement into and out of cells

The photomicrograph shows a cross-section of two structures found in mammals, observed with a light microscope. Which row is correct?

The microscope in cell studies

Which cells or tissues have been matched incorrectly with their function?

Cells as the basic units of living organisms

Which factor could result in chronic bronchitis?

The gas exchange system

What is the smallest number of cell membranes through which a molecule of carbon dioxide and a molecule of oxygen pass during gas exchange between alveoli and the capillaries?

Movement into and out of cells

The statements concern the disease tuberculosis (TB). Which factor explains why antibiotic treatment for TB takes such a long time?

Replication and division of nuclei and cells

The first column of the table lists statements about disease. The columns labelled 1-4 stand for four different diseases that are named. Which set of column headings correctly matches the diseases in the table?

The microscope in cell studies

The events below happen as a phagocyte reacts to the presence of a pathogen. 1. endocytosis 2. enzymic digestion 3. exocytosis 4. phagocytosis 5. vacuole formation What is the correct order of these events?

Movement into and out of cells

Which kind of immunity develops when an infant receives antibodies by drinking its mother’s milk?

Antibodies and vaccination

An insect dwells within the tissue of oak tree leaves and feeds on it, then birds eat the insect. Which ecological terms are being described in this information about the insect?

Infectious diseases

In what order of size are cell structures arranged?

Cells as the basic units of living organisms

A farmer plants a different crop in the same field in each of three years. In the fourth year, the farmer sows a leguminous crop and then ploughs it into the soil. The following year, the rotation begins once more. By the time the rotation begins again, which microorganisms will have increased in number? 1. denitrifying bacteria 2. nitrifying bacteria 3. nitrogen-fixing bacteria 4. decomposing bacteria

The microscope in cell studies

The diagram shows several similarities among chloroplasts, mitochondria and prokaryotes. Which row is correct?

Cells as the basic units of living organisms

A student performed four tests for biological molecules on a solution. The outcomes are given in the table. Which three molecules could be present in this solution?

Testing for biological molecules

The molecule illustrated is a polymer made from reducing sugars. Which procedures could be carried out to test for the presence of the reducing sugars in this molecule?

Testing for biological molecules

Which molecules represent the structures of $\alpha$-glucose and $\beta$-glucose?

Carbohydrates and lipids

In unsaturated lipid molecules, where are the double bonds found?

Carbohydrates and lipids

At about what magnification does light microscopy become unsuitable because the resolution is too low?

The microscope in cell studies

The structures of phospholipids and triglycerides are shown below. Which features of these structures allow a lipid bilayer to form in cell surface membranes?

Fluid mosaic membranes

Which molecule has a glycosidic bond?

Carbohydrates and lipids

The diagrams display the structures of two amino acids, and each contains two carboxylic acid (-COOH) groups. A peptide bond is made between the two amino acids. Which groups make the peptide bond?

Proteins

The drug ritonavir is sometimes used to treat HIV/AIDS. Ritonavir is made up of three amino acids and acts as a competitive inhibitor of HIV protease. Which of the following statements about ritonavir are correct?

Mode of action of enzymes

The diagram illustrates the fluid mosaic model of part of a cell surface membrane. What functions does each of the components labelled 1 to 3 have?

Fluid mosaic membranes

Proteins in the cell surface membranes of human cells and mouse cells were marked with red and green fluorescent dyes, respectively. After a human cell was fused with a mouse cell, the dyes were first found in separate areas, but later they became evenly spread throughout. What explains this observation?

Fluid mosaic membranes

The diagram depicts a plant cell. This plant cell is placed in a solution whose water potential is less negative than the cell contents. What change will be seen in the cell’s appearance?

Movement into and out of cells

The cell cycle contains mitosis. Which characteristics describe nuclear division?

Chromosome behaviour in mitosis

Which statement about cell and nuclear division is correct?

Replication and division of nuclei and cells

Diploid ($2n$) organisms that reproduce sexually form haploid ($n$) gametes. However, some plants, including wheat, are able to make diploid or haploid gametes. These gametes may then fertilise diploid or haploid gametes from another plant. Which of the following statements are correct for plants of this type? 1. Diploid gametes may arise from an error during reduction division (meiosis). 2. The offspring will always have a higher chromosome number. 3. The offspring could be either $2n$, $3n$ or $4n$. 4. In theory, the chromosome number could rise in every generation.

Replication and division of nuclei and cells

The diagram displays a stage micrometer alongside an eyepiece graticule scale, with a magnification of $\times 400$. At the same magnification, a chloroplast is measured and is found to be 4 eyepiece graticule divisions in length. How long is the chloroplast?

The microscope in cell studies

Which nucleic acid bases are classed as pyrimidines?

Structure of nucleic acids and replication of DNA

What is the correct order of the processes that take place when an enzyme is formed in a cell?

Proteins

A DNA fragment that was 15 base pairs long was examined in order to determine how many nucleotides were present in each polynucleotide strand. Some of the findings are shown below. How many nucleotides containing adenine (A) were in strand 2?

Structure of nucleic acids and replication of DNA

Which property of xylem vessel elements supports adhesion during transpiration?

Water

The diagram shows a section of the phloem pathway, including neighbouring cells, extending from leaf to root. Which process is taking place between 1 to 2 and what effect does it have on the water potential at 2?

Movement into and out of cells

Which xerophytic adaptations decrease the water potential gradient? 1. rolled leaves 2. hairy leaves 3. sunken stomata 4. fewer stomata 5. fleshy leaves

Movement into and out of cells

Which of the following is not a factor that affects blood pressure?

The circulatory system

Which of the following occur in blood, lymph and tissue fluid? 1. carbon dioxide 2. fatty acids 3. white blood cells 4. proteins

Movement into and out of cells

The graph compares the percentage saturation of haemoglobin with oxygen at different partial pressures of oxygen and at two different concentrations of carbon dioxide. How does increasing the concentration of carbon dioxide affect this?

Proteins

A hole may be present between the right atrium and the left atrium in some babies. These babies have a higher count of red blood cells. What explains this rise?

Replication and division of nuclei and cells

Which organelle lacks a partially permeable membrane?

Fluid mosaic membranes

Within the lungs, oxygen and carbon dioxide move through cell membranes by diffusion. Which row is the correct one?

Movement into and out of cells

Which statement explains how substances in cigarette smoke raise the chance of atherosclerosis developing?

Carbohydrates and lipids

Which flow diagram correctly shows what happens when tar enters the lungs?

The gas exchange system

What could directly lower the surface area available for gas exchange in human lungs?

Movement into and out of cells

The malarial parasite, Plasmodium, enters red blood cells and degrades haemoglobin. Unbound haem groups are poisonous to Plasmodium, so the parasite changes them into non-toxic, crystalline haemozoin by means of an enzyme, HDP, that occurs in every species of Plasmodium. What would be the long term effect of treating patients with malaria with a drug that inhibits HDP?

Factors that affect enzyme action

In a primary immune response, the following stages take place. 1 Certain B-lymphocytes differentiate into plasma cells. 2 B-lymphocytes with the matching cell surface receptors undergo repeated mitotic division. 3 A specific antibody is synthesised. 4 T-helper cells release cytokines. 5 T-helper cells recognise a particular antigen. In what order do these stages happen?

Replication and division of nuclei and cells

Which statement about the body's defence against infectious disease is incorrect?

The immune system

An antiserum for a snake toxin may be produced by injecting the toxin into a horse. A few weeks later, blood plasma is collected from the horse and used to prepare the antiserum. This antiserum is then given to a person who has been bitten by the same species of snake. Which type of immunity is produced by the use of this antiserum?

Proteins

The diagram illustrates how nutrients move through an ecosystem. Which letter indicates decomposers?

Transport mechanisms

An insect feeds solely on the leaves of grass. Carnivorous beetles eat this insect. Which ecological terms are being described by this information about the insect?

Infectious diseases

An electron micrograph of a plant cell is shown in the diagram. What substances are present in structures X, Y and Z?

Cells as the basic units of living organisms

A gardener has a waterlogged garden where plants are growing badly. He decides to drain it in order to try to reduce the numbers of certain harmful bacteria. Which type of bacteria is he trying to reduce in number?

Infectious diseases

An amino acid enters a cell and is then used to make an enzyme that is secreted by the cell. In what order do the cell structures take part in the synthesis of the enzyme?

Protein synthesis

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

Cells as the basic units of living organisms

Which option identifies the basic unit of glycogen?

Carbohydrates and lipids

Four sugar solutions were examined using Benedict’s solution. The table shows the colours of the solutions after the test. What is the most appropriate interpretation of the results?

Testing for biological molecules

What features make a cellulose molecule suitable for its function?

Carbohydrates and lipids

A microscope’s eyepiece lens is fitted with an eyepiece graticule. Which of the following statements about the graticule are correct?

The microscope in cell studies

In triglyceride molecules, at which positions are double bonds found?

Carbohydrates and lipids

The diagram shows an amino acid. R denotes a variable side chain. Which one is not a possible side chain?

Proteins

Which statements show some functions of enzymes? 1 speed up the breakdown of larger molecules into smaller ones 2 reduce the activation energy needed to begin a reaction 3 raise the number of collisions between molecules 4 provide the activation energy needed to begin a reaction

Mode of action of enzymes

The graph plots the rate of activity of the enzyme sucrase against sucrose concentration. What is the reason that the rate of enzyme activity stays unchanged between $80$-$90\ \text{g dm}^{-3}$?

Factors that affect enzyme action

Which graph illustrates the effect of a non-competitive inhibitor?

Factors that affect enzyme action

The diagram illustrates a section of the cell surface membrane. Which molecules contain both hydrophobic and hydrophilic regions?

Fluid mosaic membranes

A particular type of antigen is produced by a reaction between two different molecules. Other than oxygen, which elements are present in this antigen?

Proteins

What are the characteristics of facilitated diffusion? 1 Protein channels in the membrane are used, and it is powered by energy from ATP. 2 Molecules move from areas of higher concentration to areas of lower concentration, and the process is driven by the kinetic energy of the diffusing molecules. 3 Protein channels in the membrane are used, and the maximum rate of diffusion depends on how many of these channels are present.

Movement into and out of cells

Single-celled animals living in fresh water contain a vacuole that repeatedly contracts to expel surplus water. Single-celled plants living in fresh water do not possess an equivalent vacuole. Which statement gives the reason these animals require this vacuole but plants do not?

Movement into and out of cells

In which process does mitosis alone take place?

Replication and division of nuclei and cells

The diameters of living cells show a wide range. A typical eukaryotic cell has a diameter of $1.5 \times 10^{1}\,\mu\text{m}$. A typical prokaryotic cell has a diameter of $7.5 \times 10^{2}\,\text{nm}$. From these values, determine the greatest number of each cell type that could be arranged in a straight line $1\,\text{cm}$ long?

Cells as the basic units of living organisms

The photomicrograph displays cells at various stages of mitosis. In what sequence do these stages happen?

Chromosome behaviour in mitosis

The information given concerns genes and proteins that play a role in breast cancer. • The protein encoded by the $\text{BRAC1}$ gene slows the growth of breast cancer cells. • The protein encoded by the $\text{RAD51}$ gene is needed to repair damaged DNA. Which pair of genes is most likely to lead to breast cancer?

Replication and division of nuclei and cells

The diagram illustrates some links among different nucleic acid bases. Which row is the correct one?

Replication and division of nuclei and cells

The diagram illustrates the structures of several drugs that are similar in structure to nucleotides. The presence of these drugs lowers nucleic acid synthesis. Which statement explains how the drugs reduce nucleic acid synthesis?

Replication and division of nuclei and cells

What causes the formation of a polypeptide chain to stop during protein synthesis in cells?

Proteins

Under which combination of environmental conditions are the stomata in a plant most likely to close?

Movement into and out of cells

The diagrams illustrate some tissue types in plant organs. Which row identifies the tissue types?

Structure of transport tissues

Which characteristics are shared by sieve tube elements and xylem vessel elements?

Structure of transport tissues

How do the water potential and the volume of liquid in the phloem change when carbohydrate is transferred into a sink?

Movement into and out of cells

Certain plant species are able to absorb heavy metal contaminants that are dissolved in soil water and then move them through the plant. In plant cells, these heavy metals build up in the vacuole. Which of the following suggestions about the transport and accumulation of heavy metals are valid? 1 After first entering the root, some of the heavy metals may cross the tonoplast and be kept in the vacuole of cortical cells. 2 The heavy metals follow an apoplastic route in the xylem, but at the endodermis they have to use a symplastic route. 3 The rate at which heavy metals accumulate in leaf cells will be greater at night, when photosynthesis is not taking place, than in the daytime. 4 The presence of the heavy metal will interfere with active transport, so the transpiration stream will slow and the transpiration rate will be reduced.

Movement into and out of cells

To complete the sentence below, which process and cell structure are correct? Cells with a high rate of ……1…… tend to contain many ……2…… .

Cells as the basic units of living organisms

Which process can take place in a mature red blood cell?

Transport of oxygen and carbon dioxide

Which statement about phagocytes is not correct?

Movement into and out of cells

Which of the following are present in blood, lymph and tissue fluid? 1 carbon dioxide 2 glucose 3 white blood cells 4 fatty acids

Movement into and out of cells

The diagram shows a cross-section of a type of epithelium. In which part of the respiratory system is this type of epithelium located?

The gas exchange system

The diagram presents an enlarged view of part of the lungs that contains specialised tissues. In which location would a high proportion of carbonic anhydrase, $\text{HCO}_3^-$ ions and lysosomes be present?

Transport of oxygen and carbon dioxide

Which row correctly shows the effects of carbon monoxide, nicotine and tar?

Transport of oxygen and carbon dioxide

Which factors could raise the risk of cholera in refugee camps? 1 food not being refrigerated 2 rise in the number of people 3 absence of hand washing facilities

Infectious diseases

What does the term antigens refer to?

Proteins

In an ecosystem, the producers have a total of $3 \times 10^6\ \text{kJ m}^{-2}\ \text{yr}^{-1}$ available to them. In theory, what amount of this energy would be passed on to tertiary consumers?

Transport mechanisms

In a food chain, which link is associated with the least efficient transfer of energy?

Transport mechanisms

A cell that secretes glycoproteins is given radioactively-labelled glucose, and this is detected in the cytoplasm first. In which organelle would radioactively-labelled glucose be detected next?

Cells as the basic units of living organisms

The growth of crop plants is frequently restricted by how much nitrogen is present in the soil. The graph presents the findings of an investigation into the yield of a crop plant as the amount of nitrogen supplied is increased. Which of the following gives the best explanation for the form of this curve?

Proteins

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

Cells as the basic units of living organisms

A student completed four tests for biological molecules on a solution. The findings are shown in the table. iodine solution – orange biuret – blue Benedict’s – orange emulsion – clear Which molecules are present in this solution?

Testing for biological molecules

During the hydrolysis of an amylose molecule, which bonds are broken? 1 $\alpha(1,4)$ 2 $\beta(1,4)$ 3 $\alpha(1,6)$ 4 $\beta(1,6)$

Carbohydrates and lipids

Which statement explains how starch’s molecular structure is adapted to its function?

Carbohydrates and lipids

Which statements comparing biological molecules are correct? 1 A collagen molecule is a fibrous protein made up of many amino acids with hydrophobic R-groups, whereas a haemoglobin molecule is a globular protein with no amino acids with hydrophobic R-groups. 2 Breaking down sucrose by hydrolysis causes glycosidic bond breakage and yields equal amounts of fructose and $\alpha$-glucose molecules, whereas hydrolysis of cellulose gives only $\beta$-glucose molecules. 3 The glycosidic bonds in glycogen are formed between two $\alpha$-glucose molecules, whereas in amylopectin the bonds are formed between an $\alpha$-glucose molecule and a $\beta$-glucose molecule.

Carbohydrates and lipids