Feb/March 2021

The photomicrograph displays onion cells. The true length of the onion cell marked Y is $350\,\mu\text{m}$. What magnification does the photomicrograph have?

The microscope in cell studies

A triglyceride contains ......1...... bonds that are formed by joining fatty acids to ......2...... . Which row completes this statement correctly?

Carbohydrates and lipids

The diagram presents a phospholipid molecule split into three sections, X, Y and Z. R, in section X, stands for a variety of possible chemical groups. The three sections X, Y and Z influence the properties of cell surface membranes in different ways. Which row identifies the effect of each section on the properties of a cell surface membrane?

Fluid mosaic membranes

Which statement concerning collagen is correct?

Proteins

Catechol is a chemical present in several fruits. The enzyme catechol oxidase can oxidise catechol into a quinone. Catechol oxidase is inhibited by parahydroxybenzoic acid (PHBA), which has a structure similar to catechol. When PHBA is present, the Michaelis-Menten constant ($K_m$) of catechol oxidase increases. In what way does PHBA inhibit catechol oxidase?

Factors that affect enzyme action

Which statements concerning the fluid mosaic model of a membrane are correct?

Fluid mosaic membranes

Diagram 1 and diagram 2 illustrate how the transverse section of a leaf is altered when the leaf is transferred from solution X to solution Y. Which row gives the water potential of the leaf cells and the surrounding solutions in diagram 2 compared with diagram 1?

Movement into and out of cells

Which features have to be present for water to move between two solutions by osmosis?

Movement into and out of cells

When living pancreatic cells were put into a solution containing the red dye neutral red, the cytoplasm turned red. The cells were then taken out of the neutral red solution. The red dye in the cytoplasm then passed into vesicles, which were released from the cell, so that the cell eventually became colourless. Which transport mechanisms could account for the red dye entering and leaving the cells?

Movement into and out of cells

DNA molecules in a eukaryotic cell need to be packed tightly because their total length is far greater than the diameter of the nucleus. Which structures are needed in the process of packing DNA molecules tightly?

Chromosome behaviour in mitosis

Which of the following statements about mitosis are correct?

Chromosome behaviour in mitosis

Which row correctly indicates the presence of a cell structure in typical plant cells and in typical prokaryotic cells?

Cells as the basic units of living organisms

A human chromosome consists of different sections. In a typical human chromosome, certain sections are found in greater numbers than others. Which sections are arranged from the smallest number to the largest number in a human white blood cell?

Chromosome behaviour in mitosis

A double-stranded DNA fragment with $12 \times 10^3$ nucleotides is transcribed and then translated to form one polypeptide. What is the greatest possible number of amino acids in this polypeptide?

Proteins

Which statements about complementary base pairing are true?

Replication and division of nuclei and cells

What substances are formed when a DNA molecule replicates?

Replication and division of nuclei and cells

Which statements are true of phloem sieve tube elements and of xylem vessel elements?

Structure of transport tissues

Several root structures that take part in the movement of water in a plant are shown below. 1 Casparian strip 2 cell walls of cortex cells 3 endodermal cells 4 epidermal cells 5 xylem vessels Which sequence represents part of the route by which water can pass through a root?

Movement into and out of cells

What is one example of a mass flow system in a plant?

Movement into and out of cells

The diameter of a tree trunk usually becomes a little smaller during the day. Which day-time changes in environmental factors could make the diameter decrease by a larger amount?

Movement into and out of cells

Which statement correctly describes the function of co-transporter proteins in sucrose movement?

Movement into and out of cells

Which row gives the correct description of the heart during atrial systole?

The heart

Which letter labels the cell structures in which semi-conservative replication of DNA takes place?

Replication and division of nuclei and cells

The diagram illustrates a capillary, some tissue cells and a lymph vessel. Which row correctly names arrows 1, 2, 3 and 4?

Movement into and out of cells

The table presents the data used to construct an oxygen dissociation curve for adult haemoglobin. What is the percentage increase in the volume of oxygen per gram of haemoglobin when the partial pressure of oxygen rises from $3\,\text{kPa}$ to $5\,\text{kPa}$?

Proteins

The graph presents the oxygen dissociation curves for adult haemoglobin at two carbon dioxide concentrations. Which letters indicate measurements taken in the capillaries of the lungs and in the capillaries of active muscle?

Proteins

Which substances are able to combine with adult haemoglobin and lower the blood’s oxygen-carrying capacity?

Proteins

As it diffuses from an air space in an alveolus, through a cell in the capillary wall, and into a red blood cell, how many times does a molecule of carbon monoxide have to pass through a cell surface membrane?

Movement into and out of cells

A person's heart rate while resting was measured at intervals across two 15-minute periods. In the first five minutes of the second 15-minute period, the person smoked a cigarette. The graph displays the readings obtained over the two 15-minute periods. What conclusion can be drawn from the graph?

The heart

Emphysema is a form of chronic obstructive pulmonary disease (COPD). A person who has emphysema finds breathing out difficult. Why does emphysema make breathing out difficult?

The gas exchange system

Which factors lead to measles outbreaks following natural disasters?

Infectious diseases

Antibiotics fall into two main categories: broad spectrum and narrow spectrum. Broad spectrum antibiotics act on a broad range of bacteria, whereas narrow spectrum antibiotics act on particular kinds of bacteria. Which uses of antibiotics could lead to antibiotic-resistant bacteria?

Mode of action of enzymes

People who have the autoimmune disease myasthenia gravis can receive treatment to reduce the symptoms. In this treatment, one component of their blood is taken out. Which blood component is taken out?

Proteins

In which parts of a cell are ribosomes found? 1 chloroplast 2 mitochondrion 3 Golgi body 4 cytoplasm

Cells as the basic units of living organisms

For what reason are spleen cells fused with myeloma cells in monoclonal antibody production?

Replication and division of nuclei and cells

What diameter range is usually found in prokaryotic cells?

Cells as the basic units of living organisms

Which row presents a set of molecules that might be present together in one isolated virus?

Infectious diseases

A student performed four biochemical tests on a food sample. emulsion: cloudy Benedict’s: yellow biuret: purple iodine: yellow Which conclusion is supported by these results?

Testing for biological molecules

Which diagram shows a molecule of $\alpha$-glucose?

Carbohydrates and lipids

Which of the following statements about glycosidic bonds are correct?

Carbohydrates and lipids

Fig. 1.1 shows a transverse section image of the trachea in the gas exchange system.

The gas exchange system

Starch is the principal storage substance in many cereal grains, including barley grains.

Protein synthesis

T-helper lymphocytes and Leydig cells are both mammalian cell types. Their principal function is to make and release cell-signalling molecules. T-helper lymphocytes make proteins called cytokines. Leydig cells make the steroid (lipid) hormone testosterone from cholesterol. Leydig cells also make cholesterol.

The immune system

At $\times 400$ magnification with a light microscope, the various blood cell types can be recognised on prepared slides of mammalian blood. Fig. 4.1 provides a guide for identifying the different blood cell types on prepared slides of mammalian blood. In Fig. 4.1, letters C, D, E and F denote four separate blood cell types.

The immune system

Every meristem cell in a leaf bud can enlarge and divide by mitosis to form two daughter cells that are genetically identical to one another and to the cell that divided originally. Fig. 5.1 shows the stages in the mitotic cell cycle of a meristem cell.

Structure of transport tissues

In March 2019, a tropical cyclone in the south-west Indian Ocean led to extensive flooding across several countries. Because the cyclone flooded areas and caused damage, many people faced a very high risk of cholera. Once the natural disaster had happened, cholera outbreaks were reported in many different places. Soon afterwards the disease had spread broadly and affected large numbers of people.

Antibiotics

The European eel, Anguilla anguilla, is a fish species. Although eels produce huge numbers of young, the size of eel populations usually stays fairly steady.

Evolution

Explain what is meant by bioinformatics and outline the role of bioinformatics after the sequencing of the genomes of humans and parasites.

Principles of genetic technology

The grey wolf, Canis lupus, is a large predator. In south-west Europe during the 20th century, hunting drove the grey wolf to the brink of extinction.

Conservation

Vitamin A deficiency is a major public health issue that affects many people. One dietary source of vitamin A is carotene. In the body, carotene can be changed into vitamin A. White rice grains cannot provide vitamin A in the diet because they contain no carotene. Scientists have genetically modified a rice variety to improve the diets of people who lack vitamin A. The grains of this genetically modified rice contain carotene.

Genetically modified organisms in agriculture

Red algae consist of multicellular protoctists that carry out photosynthesis and contain phycoerythrin. Phycoerythrin is a photosynthetic pigment.

Photosynthesis as an energy transfer process

Many processes and activities in plants and animals arise from ions moving. Table 5.1 shows several ions, the direction each ion moves in and the effect produced by that movement. Complete Table 5.1 by filling in the missing details.

Control and coordination in plants

Dogs possess an exceptionally acute sense of smell. They are able to detect molecules in the air at a concentration of one part per trillion ($10^{12}$).

Control and coordination in mammals

Fig. 7.1 illustrates two chromosomes at one phase of meiosis. The letters G to M indicate the dominant alleles of seven genes, while g to m indicate the recessive alleles of those same seven genes.

Passage of information from parents to offspring

Fig. 8.1 is a transmission electron micrograph showing a mitochondrion.

Respiration

Section B: Answer just one question.

Fluid mosaic membranes