May/June 2010

Which structures are quantified in these units?

The microscope in cell studies

How many fatty acid residues are typically found in one phospholipid molecule?

Carbohydrates and lipids

When a frozen lake begins to thaw after a cold winter, mineral nutrients are carried up to the surface. Which properties of water help make this happen?

Water

What characteristic sets starch apart from glycogen?

Carbohydrates and lipids

What characteristic of haemoglobin makes it a globular protein?

Proteins

An enzyme is fully denatured at $50\,^{\circ}\text{C}$. A fixed concentration of this enzyme is added to a fixed concentration of its substrate. The time needed to complete the reaction is measured at different temperatures. Which graph shows the results?

Factors that affect enzyme action

Lysozyme, which is released by tear glands, builds up as deposits on contact lenses. Which ingredient would be suitable in a cleaner for contact lenses to remove these deposits?

Mode of action of enzymes

Membranes inside cells and on the cell surface carry out different functions. The diagram makes it possible to identify the different organelles in the cell by referring to membrane structure and function. Which of the answers shown below correctly identifies the organelles that have the membrane and function given?

Fluid mosaic membranes

Which processes enable movement into and out of a cell?

Movement into and out of cells

Plant and animal cells were put into different solutions, and the outcomes are shown. Which cells were put into which solution?

Movement into and out of cells

What takes place during anaphase of mitosis?

Chromosome behaviour in mitosis

The diagram shown below is taken from an electron micrograph of an animal cell. Which option shows the same cell as it would appear under a light (optical) microscope at $400$ magnification?

The microscope in cell studies

The diagram illustrates chromosomes during metaphase in mitosis. What are the diploid and haploid numbers for this species?

Chromosome behaviour in mitosis

What outcome would be obtained by analysing a section of a DNA molecule?

Structure of nucleic acids and replication of DNA

DNA is known to copy itself in a semi-conservative manner. The results from Meselson and Stahl’s experiments provided very strong support for this theory. They worked with $E.\ coli$, which has a generation time of 50 minutes. The stages in their experiment are listed below, but the order is incorrect. 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 were grown in a $^{15}\text{N}$ medium for many generations. T Bacteria were moved to a $^{14}\text{N}$ medium and sampled every 50 minutes. Which sequence of letters shows the correct order of the steps in the experiment?

Replication and division of nuclei and cells

How many base substitutions, at minimum, are needed to convert the nucleotide sequence of the HbA (normal) allele into the HbS (sickle cell) allele?

Proteins

In a DNA molecule, the base sequence AGT specifies the amino acid serine. Which base sequence is found in the anti-codon on the tRNA that serine attaches to?

Proteins

The diagrams show transverse sections of the stem, root and leaf of a non-woody dicotyledonous plant. The arrangement of the tissues is indicated in each section. Which sequence of numbers correctly shows how xylem and phloem are distributed in the stem, root and leaf?

Structure of transport tissues

What takes place in the sieve tube elements of a photosynthesising leaf and an actively growing root?

Movement into and out of cells

Some fungi that live in the soil make crop plants wilt by multiplying inside the xylem vessels. Which process will be affected directly by these fungi?

Movement into and out of cells

The trace shows the electrical activity of the heart during a single heart beat. Which letters identify the flow of current through the atria and the recovery of the ventricle walls?

The heart

What does systolic blood pressure mean?

The heart

The diagram depicts a stage micrometer, whose divisions are spaced $0.1\text{ mm}$ apart, as seen through an eyepiece 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

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

The heart

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

The gas exchange system

Which statement is an example of epidemiological evidence that connects smoking with lung cancer?

Infectious diseases

The diagram presents a spirometer trace showing tidal volume and vital capacity. During moderate exercise, what happens to the volumes marked X and Y?

Movement into and out of cells

What pathogens cause cholera, malaria and TB?

Infectious diseases

40\% of the world’s population live in a region where malaria poses a health threat. Over recent years, Africa has seen many more cases. What social factor is allowing the spread of malaria to get beyond control?

Infectious diseases

State one difference between T-lymphocytes and B-lymphocytes in the immune system.

The immune system

In a study of the immune response, a volunteer was given two different antigens, X and Y. The level of antibody in the blood was recorded at regular intervals over 60 days. The graph indicates the time at which the volunteer was exposed to each antigen and shows antibody concentration against time for antigens X and Y. What is the explanation for the results shown on the graph?

Proteins

The diagram represents a tropical ocean food chain, and the efficiency of energy transfer between trophic levels is 10\%. phytoplankton → herbivorous zooplankton → carnivorous zooplankton → small fish → tuna. The net primary production of phytoplankton is $1300\,\text{g m}^{-3}\,\text{yr}^{-1}$. What is the net primary production each year for the carnivorous zooplankton and the tuna?

The microscope in cell studies

The diagram illustrates part of the nitrogen cycle. Which number sequence correctly indicates the roles played by different kinds of microorganism in the nitrogen cycle?

Cells as the basic units of living organisms

Which structures occur in both animal cells and plant cells?

Cells as the basic units of living organisms

Two animal species live in the same forest-and-grassland region. During spring and summer, both feed on the same plant material. In autumn and winter, however, one species feeds on nuts in the forest while the other feeds on roots in the grassland. The same predator eats both species. The number of root-eating animals is lowered the most by this predator, but they bounce back more quickly because they breed faster. What conclusion can be drawn about these two animal species?

Infectious diseases

Which features would indicate that a cell is eukaryotic?

Cells as the basic units of living organisms

In experiments, which measuring methods are affected by parallax error?

The microscope in cell studies

A student carried out tests on four food samples, A, B, C and D, to check for lipids, protein, reducing sugars and starch. One of the food samples, milk, was shown to contain lipid, protein and reducing sugar. From the results given below, which food sample is milk?

Testing for biological molecules

Which statement explains how the molecular structure of starch is adapted to its function?

Carbohydrates and lipids

Which diagram shows part of the ring structure of a molecule of $\beta$-glucose?

Carbohydrates and lipids

The enzyme lysozyme released by tear glands builds up on contact lenses. Which ingredient would be effective in a contact lens cleaner for removing these deposits?

Mode of action of enzymes

The diagram below has been taken from an electron micrograph of an animal cell. Which option shows that same cell as it would appear under a light (optical) microscope at $\times 400$ magnification?

The microscope in cell studies

Which observations indicate that a cell is eukaryotic?

Cells as the basic units of living organisms

Which structures occur in both animal cells and plant cells? 1. centriole 2. lysosome 3. nucleolus 4. vacuole

Cells as the basic units of living organisms

Which structures are being measured by these units?

The microscope in cell studies

The diagram presents a spirometer trace showing tidal volume and vital capacity. What changes occur to the volumes labelled X and Y during moderate exercise?

The microscope in cell studies

Aortic stenosis is a disorder of a heart valve where the opening of the aortic semi-lunar valve is reduced in size. What effect could aortic stenosis have on the heart’s structure and function?

The heart

What does systolic blood pressure mean?

The circulatory system

The trace shows the electrical activity of the heart during one heart beat. Which letters show the movement of current through the atria and the recovery of the ventricle walls?

The heart

A student examined four food samples, A, B, C and D, to test whether they contained lipids, protein, reducing sugars and starch. One of the food samples, milk, was shown to have lipid, protein and reducing sugar. From the results below, which of the food samples is milk?

Testing for biological molecules

Which statement explains how the molecular structure of starch is adapted to its function?

Carbohydrates and lipids

An enzyme becomes fully denatured at $50\,^{\circ}\text{C}$. A constant concentration of this enzyme is mixed with a constant concentration of its substrate. The time for the reaction to reach completion is recorded at different temperatures. Which graph shows these results?

Factors that affect enzyme action

A phospholipid molecule normally contains how many fatty acid residues?

Carbohydrates and lipids

In an investigation of the immune response, a volunteer was exposed to two different antigens, X and Y. The concentration of antibodies in the blood, relative to each other, was recorded at regular intervals throughout 60 days. The graph indicates the time at which the volunteer was exposed to each antigen and plots antibody concentration against time for antigens X and Y. What explains the results shown on the graph?

The immune system

What distinguishes T-lymphocytes from B-lymphocytes in the immune system?

The immune system

Which organisms cause cholera, malaria and TB?

Infectious diseases

40 % of the world’s population lives in a region where malaria poses a health risk. Over the last few years, the number of cases in Africa has risen greatly. Which social factor is causing the spread of malaria to become uncontrolled?

Infectious diseases

DNA is described as replicating in a semi-conservative manner. Meselson and Stahl’s experimental results provided very strong evidence for this theory. They worked with E. coli, which has a generation time of 50 minutes. The steps in their experiment are listed below, but they are not in the right order. P: Every bacterium contains $^{15}\text{N}$ DNA. Q: Every bacterium contains hybrid DNA ($^{15}\text{N}$ DNA and $^{14}\text{N}$ DNA). R: Bacteria contain either only $^{14}\text{N}$ DNA or hybrid DNA. S: Bacteria were grown in a $^{15}\text{N}$ medium for many generations. T: Bacteria were moved to a $^{14}\text{N}$ medium and taken as samples every 50 minutes. Which sequence of letters gives the correct order of the experimental steps?

Replication and division of nuclei and cells

What happens during anaphase of mitosis?

Chromosome behaviour in mitosis

The diagram illustrates chromosomes during metaphase of mitosis. What are the diploid and haploid numbers for this species?

Chromosome behaviour in mitosis

The diagram illustrates a section of the nitrogen cycle. Which sequence of numbers correctly indicates the roles of the different kinds of microorganism in the nitrogen cycle?

Cells as the basic units of living organisms

The diagram illustrates a tropical ocean food chain with $10\%$ efficiency of energy transfer between trophic levels. Net primary production of phytoplankton is $1300\,\text{g m}^{-3}\,\text{yr}^{-1}$. What is the annual net primary production for the carnivorous zooplankton and the tuna?

Carbohydrates and lipids

What feature sets starch apart from glycogen?

Carbohydrates and lipids

Two animal species occur in the same forest-and-grassland region. During spring and summer, both feed on the same plant material. Yet in autumn and winter, one eats nuts in the forest while the other feeds on roots in the grassland. The same predator hunts both species. The numbers of the root-eating animals are decreased the most by this, but they bounce back more quickly because they reproduce at a faster rate. What conclusion can be made about these two animal species?

Cells as the basic units of living organisms

The diagram shows a cross-section of a type of epithelium. In the respiratory system, where is this type of epithelium found?

The gas exchange system

Which statement provides an example of epidemiological evidence that connects smoking with lung cancer?

Infectious diseases

Which processes make it possible for materials to move into and out of a cell?

Movement into and out of cells

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

The microscope in cell studies

In experiments, which measurement methods are affected by parallax errors?

The microscope in cell studies

Membranes located inside cells and on the cell surface carry out different functions. The diagram makes it possible to identify the different organelles in the cell by referring to their membrane structure and function. Which of the outcomes shown below correctly identifies the organelles that have the membrane and function described?

Fluid mosaic membranes

As a frozen lake begins to warm following a cold winter, mineral nutrients are carried up to the surface. Which properties of water help bring about this process?

Water

Which characteristic of haemoglobin means that it is a globular protein?

Proteins

What is the smallest number of base substitutions needed to alter the nucleotide sequence of the HbA (normal) allele into the HbS (sickle cell) allele?

Proteins

Which diagram shows part of the ring structure of a $\beta$-glucose molecule?

Carbohydrates and lipids

Within a DNA molecule, the base sequence AGT specifies the amino acid serine. What base sequence is found in the anti-codon on the tRNA that serine attaches to?

Proteins

What would analysing a segment of a DNA molecule show?

Structure of nucleic acids and replication of DNA

Some plant and animal cells were put into different solutions, and the results are shown. Which cells were placed in each solution?

Movement into and out of cells

The diagrams show transverse sections of the stem, root and leaf of a non-woody dicotyledonous plant. In each section, the arrangement of the tissues is illustrated. Which sequence of numbers correctly shows the arrangement of xylem and phloem in the stem, root and leaf?

Structure of transport tissues

Some fungi that live in soil cause crop plants to wilt because they grow inside the xylem vessels. Which process will be directly affected by these fungi?

Movement into and out of cells

What takes place in the sieve tube elements of a photosynthesising leaf and an actively growing root?

Movement into and out of cells

Fig. 1.1 illustrates how a sucrose molecule is broken down.

Protein synthesis

Fig. 2.1 shows part of an alveolus together with the tissue around it. The magnification is $\times 3500$.

The gas exchange system

Fig. 3.1 presents a cross-section through the heart at valve level.

The heart

Malaria and tuberculosis (TB) are among the most significant infectious diseases.

Infectious diseases

Name the phase of the mitotic cell cycle in which DNA replication happens.

Structure of nucleic acids and replication of DNA

Many legume species live in nitrate-poor tropical soils. Some are large trees, for example the flamboyant tree, Delonix regia. Bacteria in the genus Rhizobium inhabit swollen sections on legume roots. These swellings are called root nodules. A student traced nitrogen cycling in an area containing many flamboyant trees. Fig. 6.1 shows an overview of the nitrogen flow in the area.

Testing for biological molecules

Fig. 1.1 shows a diagram based on an electron micrograph of a plant cell. Fig. 1.2 shows a diagram based on an electron micrograph of an animal cell. Neither diagram is complete.

Testing for biological molecules

Fig. 2.1 shows a vertical section through a healthy mammalian heart.

The heart

The HIV/AIDS pandemic has had a major effect on life expectancy in many African countries. Table 3.1 presents estimated figures for seven African countries for the average life expectancy of someone born in 2002, the percentage of the population who tested positive for HIV in 2002, and the average life expectancy of someone born in 2002 if the HIV/AIDS pandemic had not occurred.

Infectious diseases

Fig. 4.1 depicts the primary structure of a lysozyme molecule, an enzyme present in tears, saliva and lysosomes.

Protein synthesis

Fig. 5.1 shows part of the human gas exchange system.

The gas exchange system

In ecosystem studies, food chains and food webs are drawn. Read the passage below about trophic relationships on one of the Galapagos Islands. Marine iguanas eat kelp, which grows attached to rocks in shallow waters. Kelp is a photosynthetic organism. Farther inland, xerophytes are grazed by land iguanas. Many herbivorous insects, including numerous species of short-horned grasshoppers, feed on the xerophytes. An examination of the gut contents of lava lizards shows that these insects are prey for the lizards. The lizards are then preyed upon by Galapagos snakes. The snakes also hunt grasshoppers and newly hatched iguanas. The Galapagos hawk has a varied diet and captures animals such as Galapagos snakes, short-horned grasshoppers, small lava lizards and newly hatched iguanas.

Testing for biological molecules

Fig. 1.1 displays part of an animal cell as seen with an electron microscope.

Protein synthesis

Fig. 2.1 presents a diagram of a cross-section through a human heart.

The heart

Fig. 3.1 shows the amino acid sequence for the protein hormone insulin.

Protein synthesis

Reducing malaria is one of the World Health Organization (WHO)'s highest priorities. At present, no effective vaccine exists for this disease, so other preventive measures have to be used to limit the spread of malaria.

Infectious diseases

Bacteria such as Rhizobium perform nitrogen fixation, a vital stage in the nitrogen cycle.

Testing for biological molecules

Different parts of the human gas exchange system are modified in different ways so that each can carry out its own role.

The gas exchange system

The flatback turtle, *Natator depressus*, is an endangered species that nests on beaches in northern Australia. Fig. 1.1 shows a flatback turtle. Each female lays about 50 eggs in a nest, which is fewer than in any other marine turtle species. The eggs are buried in sand and, when the hatchlings emerge, each has a mass of about 43 g. In contrast to most marine turtles, flatback turtles spend most of their time in coastal waters, where they feed and mate. Fig. 1.2 shows the number of female flatback turtles nesting on a beach in northern Australia from 1993 to 2002.

Conservation

Describe how a kidney nephron and its associated blood vessels are structured.

Homeostasis in mammals

CD28 and CD40 glycoproteins are present on the surface of T-lymphocytes (T-cells). They act as binding sites for cell-signalling molecules and are needed to trigger T-cell cloning during an immune response. A monoclonal antibody (mAb), which could inhibit the CD40 signalling pathway, was made from hamsters by the hybridoma method. Outline the procedure, beginning with a hamster, for producing mAbs that are suitable for use in another mammal, for example a mouse.

Principles of genetic technology

Fig. 3.1 illustrates the arrangement of a section of a seminiferous tubule in the human testis.

Passage of information from parents to offspring

Fig. 4.1 shows a photomicrograph of a transverse section of a C4 plant leaf.

Photosynthesis as an energy transfer process

Anole lizards occur across the Caribbean and the nearby mainland, and the genus includes many species. With the exception of Anolis carolinensis, which is present in mainland Florida, each species is restricted to a single island or to a small cluster of islands. Fig. 5.1 illustrates where four species of anole lizards are found. A study was then carried out on the relationships among these four species by means of DNA analysis. The base sequences of a section of mitochondrial DNA from the four species were compared, and the findings are given in Table 5.1. A smaller number indicates a smaller difference between the base sequences of the two species.

Evolution

Explain what the term gene mutation means.

Passage of information from parents to offspring

In the early stages of respiration, 1 molecule of glucose is converted into 2 molecules of a 3C compound.

Respiration

Cystic fibrosis (CF) is an inherited condition.

Genetic technology applied to medicine

Section B. Attempt one question.

Photosynthesis as an energy transfer process

The American crocodile, Crocodylus acutus, was listed as an endangered species by the USA in 1975. It occurs in estuarine areas of southern Florida. Fig. 1.1 shows an American crocodile. Water salinity was considered to affect the distribution of the American crocodile.

Conservation

Describe the arrangement of a myelinated sensory neurone.

Control and coordination in mammals

Follicle stimulating hormone (FSH) and luteinising hormone (LH) each have two polypeptide chains, the $\alpha$ and $\beta$ chains. • The $\alpha$ chains in FSH and LH are identical. • FSH has a $\beta$ chain of 111 amino acids, whereas LH has a $\beta$ chain of 121 amino acids. • FSH and LH attach to different receptors in the cell surface membranes of their target cells. • This attachment causes steroid synthesis in the target cells.

Control and coordination in mammals

The disc diffusion method can be used to assess how sensitive bacteria are to antibiotics. First, an inoculum of the bacteria is spread over agar culture plates, and then filter paper discs soaked with antibiotic are placed on the agar surface. After incubation, the bacteria form a continuous ‘lawn’ over the agar, but a circular clear region, called the zone of inhibition, is seen around any disc where bacterial growth has been prevented. Two bacterial species, A and B, were cultured on separate plates with three different filter paper discs: 1 - no antibiotic (control) 2 - penicillin V, a natural penicillin 3 - carboxypenicillin, a synthetic penicillin. The incubated plates are shown in Fig. 3.1.

Genetic technology applied to medicine

Cereal crops, for example sorghum and rice, supply a large share of nutrients worldwide.

Respiration

Drosophila, the fruitfly, includes many species. Three of them, Drosophila pseudoobscura, D. persimilis and D. miranda, are believed to be closely related. Samples of these three species were gathered from the western United States of America. Fig. 5.1 shows the places where these species naturally occur.

Evolution

In humans, a rare recessive allele that is sex-linked causes the iris in the eye to change shape. This disorder is called cleft iris (CI).

Passage of information from parents to offspring

Fig. 7.1 is a simplified sketch of the Krebs cycle. A two carbon acetyl group enters the cycle by joining with a molecule of oxaloacetate. This produces a molecule of citrate, which is then decarboxylated and dehydrogenated to regenerate the oxaloacetate. The letters $P$ to $V$ indicate steps in the cycle.

Respiration

Gene technology has a wide range of applications, including making substances such as insulin.

Genetically modified organisms in agriculture

Answer just one question.

Photosynthesis as an energy transfer process

The American crocodile, Crocodylus acutus, was listed as an endangered species in the USA in 1975. It occurs in estuarine areas of southern Florida. Fig. 1.1 shows an American crocodile. The salinity of the water was believed to influence the distribution of the American crocodile.

Conservation

Describe the structure of a myelinated sensory neurone.

Control and coordination in mammals