May/June 2013

What size ranges are visible using a light microscope?

The microscope in cell studies

One naturally occurring polysaccharide is made up of a straight, unbranched chain of acetylglucosamine molecules joined by $\beta$-$1,4$ glycosidic bonds. The $-$CH$_2$OH groups alternate from one side of the polysaccharide chain to the other. Many hydrogen bonds are formed between these straight chains. Which polysaccharide has a structure similar to the one described?

Carbohydrates and lipids

Which molecules possess properties that depend on hydrogen bonding?

Water

The characteristics of four proteins, W, X, Y and Z, are given below. W is made up of two polypeptides joined by disulfide bonds. X is made up of three polypeptides wound tightly around each other. Y is made up of four polypeptides, and each one has a prosthetic group. Z is made up of four polypeptides joined together by disulfide bonds. Which row correctly matches the named proteins?

Proteins

How are fish that live in ponds able to survive winter temperatures below $0^{\circ}\text{C}$?

Water

Four students, 1, 2, 3 and 4, counted how many oxygen bubbles were released during an investigation into the effect of catalase from plant tissue on hydrogen peroxide. Each student repeated the experiment five times and found the mean number of bubbles per minute. Which have correctly calculated the mean? (A table is shown of students, raw data in bubbles minute$^{-1}$, and calculated mean values.)

Factors that affect enzyme action

The diagram illustrates a metabolic pathway. reactant $\xrightarrow{\text{enzyme 1}}$ substance X $\xrightarrow{\text{enzyme 2}}$ substance Y $\xrightarrow{\text{enzyme 3}}$ end product What would happen if a small quantity of a non-competitive inhibitor of enzyme 2 were introduced?

Factors that affect enzyme action

Which of the following may raise the fluidity of the cell surface membrane at low temperatures?

Fluid mosaic membranes

Which process permits molecules that are too large to cross the surface membrane to move?

Movement into and out of cells

The diagram indicates the water potential of three cells. Cell X has a water potential of $-700\ \text{kPa}$. The two cells next to it have water potentials of $-800\ \text{kPa}$ and $-1000\ \text{kPa}$. In what directions will net movement of water occur by osmosis to or from cell X?

Movement into and out of cells

Which statement best describes a cell from a haploid organism that can reproduce?

Replication and division of nuclei and cells

The diagram is of a mitochondrion based on an electronmicrograph. The distance from X to Y on the mitochondrion is $3000\,\text{nm}$. What magnification has been used for the drawing of the mitochondrion?

The microscope in cell studies

Some chemicals, which are used to halt tumour growth, act by stopping the DNA double helix from uncoiling and separating. At which stage of the cell cycle do they act?

Replication and division of nuclei and cells

Nocodazole is a chemical used in the investigation of mitosis. It makes every mitotic cell arrest at metaphase. Which statements correctly show how this chemical could act?

Chromosome behaviour in mitosis

What is the greatest possible number of hydrogen bonds in a DNA strand section containing 700 base pairs?

Structure of nucleic acids and replication of DNA

Which type of molecule is always produced as the final product of transcription?

Protein synthesis

The table shows the tRNA anticodons for four amino acids. A cell produces a polypeptide with the following amino acid sequence: glutamic acid - asparagine - threonine - proline What is the sequence of bases in the DNA strand that was complementary to the mRNA used to form this polypeptide?

Proteins

The diagram illustrates a xerophytic leaf under two different conditions, P and Q. Which of the statements about the cells in layer X of the leaf in conditions P and Q are correct?

Movement into and out of cells

Several processes involved in the loading of sucrose into companion cells are listed below. Which one is an active process?

Movement into and out of cells

Which statement about transpiration is correct?

Water

Halophytes are plants able to survive in places that are often exposed to sea water. Sea water has a water potential of approximately $-2500\text{ kPa}$. Which adaptations would you expect halophytes to have?

Movement into and out of cells

Which structural features allow the aorta to withstand ventricular systole?

The circulatory system

What role do nucleoli play?

Protein synthesis

Haemoglobin is able to bind with carbon dioxide, carbon monoxide and oxygen. Which statement about the binding sites of haemoglobin is correct?

Proteins

The diagram illustrates the pressure changes in different structures on the left side of the heart during the cardiac cycle. At the end of which period, A, B, C or D, is the ventricle full of blood?

The heart

Which substances cause oxygen to be displaced from oxyhaemoglobin?

Proteins

Which statement about chronic obstructive pulmonary disease is incorrect?

The gas exchange system

Which of the following statements about coronary by-pass surgery is correct?

The microscope in cell studies

In what way does smoking raise the likelihood of developing atherosclerosis?

Carbohydrates and lipids

Which advancement in vaccine production would be the most significant in efforts to eradicate measles in developing countries?

The microscope in cell studies

What might lead to a malaria outbreak in a country where it had previously been eliminated?

Infectious diseases

Termites are insects that construct large nests containing millions of termites of the same species. These nests are common in tropical savanna, which usually has grasses and widely spaced trees. In this habitat, the termites feed on wood and other dead plant material. Which statement is correct?

The microscope in cell studies

In the nitrogen cycle, microorganisms take part in nitrogen fixation, nitrification and denitrification. Which soil conditions are suitable for each process?

Cells as the basic units of living organisms

The diagram shows a stage micrometer whose divisions are $0.1\,\text{mm}$ apart, as seen through a microscope fitted with a graticule. What is the area of the microscope’s field of view at this magnification? $(\pi = 3.14)$

The microscope in cell studies

Which processes are needed to make nitrogen in dead plant material available to growing plants?

Mode of action of enzymes

Which organelles are needed to make the hydrolytic enzymes present in lysosomes?

Protein synthesis

The diagram has been obtained from an electronmicrograph of a cell that secretes enzymes. In which part are these enzymes synthesized?

Protein synthesis

X and Y represent the structures of two hexose sugars. Which statement is correct?

Carbohydrates and lipids

The structural formula for a carbohydrate molecule may be represented as: (a Fischer projection with an aldehyde group $\text{C}=\text{O}$ at the top, a carbon chain with alternating $\text{H}$ and $\text{OH}$ side groups, and a terminal $\text{CH}_2\text{OH}$ group.) Which of the molecules could be shown by this formula?

Carbohydrates and lipids

What happens when sucrose is hydrolysed into monosaccharides?

Carbohydrates and lipids

A light microscope is being used to view two membranes separated by $200\,\text{nm}$. When the objective lens is switched from low power to high power $(\times 400)$, what is the distance between the membranes?

The microscope in cell studies

The diagram shows part of a glycogen molecule. In what way is this molecule different from an amylose molecule?

Carbohydrates and lipids

Which of these molecules contains a carboxyl group?

Proteins

The table lists the diameters of some atoms when they make bonds. Using the values in the table, the approximate length of the amino acid shown below was estimated as $0.7\,\text{nm}$. What is the approximate length of a dipeptide made from this amino acid?

Proteins

Which property of water is least likely to influence the survival of an animal in a tropical rain forest?

Water

Two pairs of students each recorded how many oxygen bubbles were released in 1 minute while investigating the effect of catalase from plant tissue on hydrogen peroxide. Each pair carried out the experiment five times and then worked out the mean number of bubbles per minute. Which pair has correctly worked out the mean?

Mode of action of enzymes

When examining the rate of reaction of the enzyme lipase in the hydrolysis of triglycerides, pH must be kept at an optimum to stop the lipase denaturing. What is the reason for this?

Factors that affect enzyme action

Which of the following is able to raise the fluidity of the cell surface membrane?

Fluid mosaic membranes

The diagram illustrates a cell that makes protease enzymes. Which row is right?

Protein synthesis

The diagram illustrates two identical plant cells. One of the plant cells is placed in a solution whose water potential is less negative than that of the cell contents. The other is placed in a solution whose water potential is more negative than that of the cell contents. What changes will be seen in the appearance of each cell?

Movement into and out of cells

Chromosome telomeres are necessary for DNA replication, and they are not entirely copied during mitosis. A substance X is known to replace telomeres completely during mitosis. What effect would be seen when cells are grown with substance X and when they are grown without substance X?

Chromosome behaviour in mitosis

The electron micrograph shows a chloroplast. The length of the chloroplast on the line indicated is $80\,\text{mm}$. The actual length of the chloroplast is $10\,\mu\text{m}$. Calculate the magnification of the chloroplast.

The microscope in cell studies

The diagram shows a cell nucleus in prophase of mitosis. Which statement gives the description of the chromosomes in each daughter nucleus immediately after this cell has divided by mitosis?

Chromosome behaviour in mitosis

Which aspects of mitosis ensure that the cell’s genetic constitution is preserved?

Chromosome behaviour in mitosis

What is the greatest number of hydrogen bonds possible in a length of DNA containing 700 nucleotides?

Structure of nucleic acids and replication of DNA

What kind of molecule is produced at the end of translation?

Proteins

A polypeptide molecule has the amino acid order: glycine - leucine - lysine - valine. The table lists the DNA codes for these amino acids. glycine: CCC; leucine: GAA; lysine: TTT; valine: CAA. Which tRNA anticodons are required to make this polypeptide?

Proteins

Which plant cells lack a nucleus? 1. Companion cells 2. Sieve tube elements 3. Xylem vessel elements

Structure of transport tissues

The diagram depicts three xerophytic leaves of the same kind in three separate conditions, P, R and S. Layer X is labelled. Which statement about the water potential of the cells in layer X is correct?

Movement into and out of cells

The diagram illustrates the loading of sucrose into a sieve tube element. What form of transport is involved in moving the substances in steps 1, 2 and 3?

Movement into and out of cells

Halophytes are plants able to survive in areas that are repeatedly exposed to sea water. Sea water has a water potential of approximately $-2500\,\text{kPa}$. Which adaptation would you expect halophytes to have?

Movement into and out of cells

Several different tissues are present in the walls of major blood vessels. Which row correctly names the main tissues found in the three layers of an artery wall?

The circulatory system

The diagram below comes from an electron micrograph of an animal cell. Which one shows that same cell, as it would be observed with a light microscope at $\times 400$ magnification?

The microscope in cell studies

The diagram illustrates how pressure varies in the different structures on the right side of the heart during the cardiac cycle. Which structures are shown by X, Y and Z?

The microscope in cell studies

Which statement accurately describes the Bohr effect?

Proteins

Aortic stenosis is a heart valve disorder where the opening of the aortic semi-lunar valve is narrowed. Which effect might aortic stenosis have on the structure and function of the heart?

The heart

What may be seen in some of the tissues in a transverse section of a trachea?

The gas exchange system

There is extensive epidemiological evidence that connects smoking with illness and premature death. Which option best describes the term ‘epidemiological’?

The microscope in cell studies

Which row indicates the effects of chronic bronchitis?

The gas exchange system

A country had below $2.5$ deaths per $100\,000$ people from TB in one year, and in the following year this increased to $25$ deaths per $100\,000$. What could have led to this change? 1. reduced contact tracing 2. more refugee camps 3. sewage-contaminated water supply

Infectious diseases

A tissue graft, for example skin, taken from another person is normally rejected by the body. Which statement regarding graft rejection is correct?

Fluid mosaic membranes

The diagram illustrates a simplified nitrogen cycle. Which row gives the correct labels for P, Q, R and S?

The microscope in cell studies

Which of the following statements about energy flow in ecosystems are correct?

Cells as the basic units of living organisms

What characteristics allow an organism to be recognised as a prokaryote?

Cells as the basic units of living organisms

In many freshwater ecosystems, the amount of inorganic nitrogen compounds available acts as a limiting factor for growth. In other words, producers are unable to grow as rapidly as they otherwise could, even when no other factor is limiting. Which statements about these ecosystems are correct?

Movement into and out of cells

The diagram depicts an electronmicrograph of a typical animal cell. What is the function of the membrane system marked X?

Cells as the basic units of living organisms

An animal cell and a plant cell are put into distilled water. The animal cell takes in water, becomes larger and then bursts, whereas the plant cell also takes in water and expands but does not burst. What explains this difference?

Movement into and out of cells

Amino acid R groups (side chains) may be hydrophobic, hydrophilic, acidic, or basic. The diagram presents four different amino acid R groups. Ala: $\text{CH}_3$ Asp: $\text{COOH}$ attached to $\text{CH}_2$ Lys: $\text{NH}_2$ attached to $(\text{CH}_2)_4$ Ser: $\text{OH}$ attached to $\text{CH}_2$ Which row is correct for these amino acid R groups?

Proteins

Which statement describes the emulsion test for detecting lipids?

Testing for biological molecules

A carbohydrate molecule can be represented by a structural formula. Which one of the following molecules could this formula represent?

Carbohydrates and lipids

An electron microscope has greater resolution than a light microscope. What is one consequence of this higher resolution?

The microscope in cell studies

A polysaccharide that occurs naturally is a branched chain made of $\alpha$-glucose. Its unbranched sections are joined by $\alpha$-1,6 glycosidic bonds, and it has a small number of branches that are connected by either an $\alpha$-1,3 glycosidic bond or an $\alpha$-1,4 glycosidic bond. Which polysaccharide has a structure most like the one described?

Carbohydrates and lipids

Which molecule has characteristics that are not influenced by hydrogen bonds?

Water

What happens to proteins during denaturation caused by extremes of pH?

Proteins

As the ice covering the top of a pond melts, which changes are advantageous to the pond ecosystem?

Water

In the presence of a competitive inhibitor, how does a rise in substrate concentration influence the rate of an enzyme-catalysed reaction?

Factors that affect enzyme action

The effect of catalase on hydrogen peroxide was investigated by four students. At the start of the experiment, each student began a digital timer and then stopped it once 25 bubbles had been counted. The reading shown by the digital timer is given below. hours: 00, minutes: 01, seconds: 33, hundredths: 54 Which student obtained results with the greatest precision for the apparatus used?

Factors that affect enzyme action

Which of the following could reduce the fluidity of the cell surface membrane?

Fluid mosaic membranes

Which process would make it possible for large protein molecules to move out of the cell?

Movement into and out of cells

Pieces of potato tissue were placed in distilled water or in sucrose solutions of varying concentrations. The graph shows the percentage change in length of the potato tissue. Which row correctly indicates how the water potentials of the distilled water and sucrose solutions compare with the initial water potential of the potato tissue?

Movement into and out of cells

When cancer cells divide without control, tumours are produced. Which statement explains how a cancer cell differs from a normal cell?

Replication and division of nuclei and cells

The diagram is of a chloroplast based on an electronmicrograph. The distance of the chloroplast from X to Y is $5000\ \text{nm}$. What is the magnification of the chloroplast drawing?

The microscope in cell studies

The diagram shows a cell nucleus during prophase of mitosis. Which statement describes the chromosomes present in each daughter nucleus immediately after this cell divides by mitosis?

Chromosome behaviour in mitosis

Mutations in either the $\text{BRCA1}$ gene or the $\text{BRCA2}$ gene account for most inherited breast cancer in humans. The proteins made by these two genes move into the nucleus, where they interact with other proteins, including those encoded by the tumour suppressor gene, $\text{p53}$, and the DNA repair gene, $\text{RAD51}$. Which pattern of gene activity is most likely to lead to breast cancer?

Replication and division of nuclei and cells

Which molecule is specified by the code in one gene?

Proteins

A polypeptide contains the amino acid sequence glycine - arginine - lysine - serine. The table shows the possible tRNA anticodons for each amino acid. Which sequence of bases on DNA would code for this polypeptide?

Proteins

What is the smallest number of hydrogen bonds in a length of DNA containing 700 nucleotides?

Proteins

The diagram illustrates part of a transverse section of a leaf. Where does evaporation of water take place during transpiration?

Movement into and out of cells

The diagram depicts a xerophytic leaf under two different conditions, P and Q. Which statements describe how the cells in layer X differ between conditions P and Q?

Movement into and out of cells

A potometer may be used to measure the rate of transpiration in a plant. Why is the plant stem cut beneath water before it is attached to the potometer?

Movement into and out of cells

Three solutions, each with a different water potential $\psi$, are shown below. 1 cortex cell solution 2 endodermal cell solution 3 root hair cell solution Which row places the solutions in order from the least negative $\psi$ to the most negative $\psi$?

Movement into and out of cells

The diagram illustrates how pressure varies in different parts of the right side of the heart during the cardiac cycle. Which structure is shown by letter X?

The heart

Eyepiece graticules and stage micrometers are used to measure cells. Which is the correct reason for calibrating an eyepiece graticule?

The microscope in cell studies

The trace shows the heart’s electrical activity during one heart beat. Which letters show the current passing through the atria and the recovery of the ventricular walls?

The heart

Which row gives the changes in haemoglobin properties caused by the Bohr effect?

Proteins

Humans have a double circulation system. What is meant by the term ‘double circulation’?

The microscope in cell studies

The photomicrograph shows a cross-section of a section of the bronchus wall. What function does the tissue labelled X perform?

The gas exchange system

Why does the inner lining of the bronchiole have folds?

Movement into and out of cells

How do carbon monoxide and nicotine affect the cardiovascular system?

The circulatory system

Some antibiotics are mixed into animal feed to lower disease. What is the reason that these antibiotics should not be used to treat disease in humans?

Antibiotics

Which statement is correct about both B-lymphocytes and T-lymphocytes?

The immune system

Which organism uses energy to manufacture its own food supply from inorganic compounds?

Cells as the basic units of living organisms

Two ecosystems, X and Y, were investigated and compared. They are the same age, and each has an identical climate. The comparison results are given in the table. From the information in the table, which statements are reasonable suggestions about X and Y?

The microscope in cell studies

The electron micrograph displays part of two cells. Which labelled structures allow these cells to be recognised as eukaryotic?

Cells as the basic units of living organisms

The diagram illustrates the transfer of energy in a food web. Which option represents the decomposers?

Cells as the basic units of living organisms

When mucus is released from a goblet cell in the trachea, the following events occur. In what order do these events happen?

Movement into and out of cells

What is one function of the smooth endoplasmic reticulum?

Cells as the basic units of living organisms

Two solutions, 1 and 2, were examined with several reagents to verify their identities; one solution contained starch and sucrose, while the other contained protein. The table gives the conclusions drawn from the observations for the different tests. Which row correctly identifies the two solutions?

Testing for biological molecules

A carbohydrate molecule’s structural formula can be displayed. Which of these molecules could be represented by this formula?

Carbohydrates and lipids

The diagram displays a section of a carbohydrate molecule made from glucose. What is the name of this molecule?

Carbohydrates and lipids