Feb/March 2019

The diagram below was produced from an electron micrograph of an animal cell. Which diagram would show the same cell as it would appear under a simple light microscope, with daylight as the only illumination source?

The microscope in cell studies

A student made four claims about what occurs during the hydrolysis of a carbohydrate. Which claims are correct?

Carbohydrates and lipids

The table compares three molecules, X, Y and Z, each of which contains only carbon, hydrogen and oxygen. The percentage of carbon, hydrogen and oxygen atoms in every molecule is given. Which row gives the correct identification of molecules X, Y and Z?

Carbohydrates and lipids

Which statements describing the differences between phospholipids and triglycerides are correct?

Carbohydrates and lipids

An investigation was done to find out how different treatments affect the permeability of the cell surface membranes and tonoplasts in beetroot cells. The vacuoles of beetroot cells contain a red pigment. This pigment cannot leave the cells because it is unable to diffuse through the tonoplasts or the cell surface membranes. $1\text{ cm}^3$ cubes were taken from beetroot tissue and rinsed under running water for 20 minutes to remove any pigment released from damaged cells. The cubes were then put into test-tubes containing different contents and left for five minutes before being observed. Which row gives a correct explanation for the observation recorded for one of the treatments?

Movement into and out of cells

Which protein-structure levels can determine an enzyme’s specificity?

Mode of action of enzymes

The graph illustrates how substrate concentration affects the initial rate of an enzyme-catalysed reaction. The enzyme concentration remains constant. Which statement about the graph is accurate?

Factors that affect enzyme action

The diagram shows the reversible binding between the active site of an enzyme and the inhibitors X and Y. Which row correctly names the type of inhibition shown by inhibitor X and inhibitor Y?

Mode of action of enzymes

Which statements concerning the movement of water into and out of cells are correct?

Movement into and out of cells

The diagram illustrates part of a cell surface membrane. Which row correctly identifies the functions of two of the numbered molecules?

Fluid mosaic membranes

In animal cells undergoing mitosis, which process takes place after prophase?

Chromosome behaviour in mitosis

In a diagram, the diameter of a red blood cell was measured to be $2.5\ \text{cm}$. Its true diameter was $7\ \mu\text{m}$. Which calculation would produce the correct magnification of the red blood cell shown in the diagram?

The microscope in cell studies

Embryonic stem cells can keep dividing without limit. During their repeated mitotic cell cycles, what happens to the telomeres?

Chromosome behaviour in mitosis

A DNA fragment was analysed and sequenced. $24\%$ of its nitrogenous bases were adenine. What percentage of the bases is cytosine?

Proteins

Rifampicin is an antibiotic that is used to treat tuberculosis (TB). It acts by blocking RNA polymerase in bacteria. Which processes are directly blocked by this antibiotic?

Factors that affect enzyme action

Which terms are used to describe the way water is transported in xylem vessel elements?

Transport mechanisms

Which combination of features is typical of a phloem sieve tube element while it is being loaded from a source?

Movement into and out of cells

The diagrams illustrate cross-sections of parts of a plant, with some transport tissues labelled from 1 to 6. Which row identifies the tissues that mainly carry water and the tissues that mainly carry sucrose?

Movement into and out of cells

Which features of lignin are important for the role of xylem vessels in the stem of a tall plant, such as a tree?

Structure of transport tissues

A heating sleeve was fitted around the trunk of a small tree at a height of $1\,\text{m}$ above the ground. This made it possible to warm a narrow section of the trunk to $60\,^{\circ}\text{C}$. How would heating this section to $60\,^{\circ}\text{C}$ affect the movement of phloem sap and xylem sap between the roots and leaves?

Factors that affect enzyme action

The photomicrograph shows a section through a structure found in mammals when viewed under a light microscope. What are the principal components of layer W?

The microscope in cell studies

Which row correctly shows the places where a type of molecule or cell may be found?

The immune system

The diagram depicts a fin whale drawn to scale. A student wrote three statements about the diagram. Which of the statements are correct?

The microscope in cell studies

Which statements about how haemoglobinic acid is formed are correct?

Proteins

The graph illustrates the oxygen dissociation curves of haemoglobin in eight species of mammal. Which conclusion agrees with the data in the graph?

Proteins

The statements below list some events in the cardiac cycle. They are not arranged in the correct sequence. Which statement describes the second event to happen in the cardiac cycle?

The microscope in cell studies

Which statement concerning typical bronchioles is correct?

The gas exchange system

Tobacco smoke contains substances that influence the functioning of the human body. Which option correctly matches the substances with their effects?

Transport of oxygen and carbon dioxide

Which two diseases are spread through airborne droplets?

Infectious diseases

What characteristics are shared by the causative agents of measles, malaria and tuberculosis (TB)?

Infectious diseases

Why are most viruses that cause disease in humans not affected by antibiotics?

Antibiotics

What causes the white blood cell count to rise in people with leukaemia?

Replication and division of nuclei and cells

In what location are antibodies present during an immune response?

Proteins

Which structures occur in both chloroplasts and mitochondria?

Cells as the basic units of living organisms

The graph illustrates how the concentration of antibodies in a baby's blood changes before birth and throughout the first few months after birth. Which statement correctly describes the changes in immunity during the first few months after birth?

Proteins

Radioactively tagged amino acids are added to a cell that is actively secreting an enzyme. In which cell structure would the radioactivity first accumulate?

Protein synthesis

Ribosomes are made up of distinct subunits that come together during protein synthesis. What do these subunits consist of?

Protein synthesis

Four solutions were examined using Benedict’s solution. The table gives the colours of the solutions after the test. Which row represents solutions that could have produced these results?

Testing for biological molecules

The diagram depicts a molecule made up of three hexose sugars labelled 1, 2 and 3. Which row correctly identifies examples of carbohydrates in which these three hexose sugars are found?

Carbohydrates and lipids

What feature of glycogen sets glycogen apart from starch?

Carbohydrates and lipids

Fig. 1.1 and Fig. 1.2 show photomicrographs of cross-sections through the leaves of two different plants. Fig. 1.1 is a photomicrograph of a section through a leaf of Cornish heath, Erica vagans. Fig. 1.2 is a photomicrograph of a section through a leaf of Himalayan cedar, Cedrus deodara. Fig. 1.1 and Fig. 1.2 are not shown at the same magnification.

Transport mechanisms

In mammalian red blood cells, carbonic anhydrase plays a significant part in transporting carbon dioxide. Carbonic anhydrase is an enzyme.

Protein synthesis

In 2015, the World Health Organization (WHO) issued the Global Technical Strategy for Malaria 2016-2030. This worldwide strategy, building on the 2008 Global Malaria Action Plan (GMAP), is intended to advance the control and elimination of malaria. Both the global strategy and GMAP are designed to lower: • the case incidence (the number of new cases each year) of malaria • the mortality rate (the number of deaths each year) from malaria.

Infectious diseases

In a double circulatory system, blood moves through the heart twice during one full journey around the body. That full journey includes pulmonary circulation and systemic circulation.

The heart

Human prolactin (hPRL) is a globular protein made up of one polypeptide chain containing 199 amino acids. It moves in the bloodstream and affects only cells whose cell surface membrane protein is called PRLR. One function of hPRL is to stimulate mammary gland cells to produce breast milk. Cells that have been stimulated by hPRL need a larger supply of glucose, so passive glucose uptake rises.

Transport mechanisms

Mitosis in plant and animal cells produces two genetically identical daughter cells from one parent cell.

Structure of nucleic acids and replication of DNA

The influence of light intensity on the rate of photosynthesis may be studied using a cut shoot of a pond plant. Fig. 1.1 shows the apparatus used in the investigation. Light intensity can be altered by moving the lamp to different distances from the pond plant.

Investigation of limiting factors

State the general theory of evolution and explain how natural selection works in evolution.

Evolution

Glucagon is one hormone that acts as a cell signalling molecule. Table 2.1 sets out the main events that happen when the blood glucose concentration drops below the set point. The events are not arranged in the correct sequence.

Homeostasis in mammals

In an immune response, only B-lymphocytes whose receptors match the antigens present become activated. This activation happens when an antigen attaches to a receptor on a B-lymphocyte. The activated B-lymphocytes enlarge and then undergo mitosis. Numerous further mitotic divisions then take place, which increases the number of B-lymphocytes carrying receptors specific to the antigen. In time, cells formed in this sequence will differentiate into either plasma cells that secrete antibodies or memory B-cells. Fig. 3.1 gives a summary of B-lymphocyte activation and the events that follow. The formation of plasma cells and memory B-cells in this sequence depends on transcription factors.

Gene control

Mexican spadefoot toads, Spea multiplicata, spend most of their lives on land, but they go back to ponds to reproduce. Eggs are deposited in water and hatch into tadpoles, which feed in ponds before becoming adults. The tadpoles can be grouped into two broad types: omnivore-type tadpoles and carnivore-type tadpoles. The phenotype differences between these two tadpole types are linked to their different feeding habits. Omnivore-type tadpoles consume tiny fragments of detritus (dead material from plants and animals) and algae (microscopic photosynthetic organisms) at the bottom of ponds. These tadpoles grow slowly. Carnivore-type tadpoles eat small animals in the water, such as fairy shrimp and small omnivore tadpoles. These tadpoles grow rapidly. Fig. 4.1 shows two tadpoles of the same age, one of each type. A fairy shrimp is also shown. All three organisms are the same distance from the camera. Between these two main types of tadpole there is a continuous range of tadpoles with intermediate body phenotypes and feeding habits. For any individual tadpole, regardless of age, a phenotype score can be calculated from the tadpole's features. A tadpole with a phenotype score close to 3 is a typical omnivore type, whereas a tadpole with a phenotype score close to 7 is a typical carnivore type. Phenotype scores were measured for a large number of tadpoles sampled from two ponds. In one pond, detritus and algae were abundant, whereas in the other pond they were scarce. All other conditions in the two ponds were similar. For both ponds, phenotype scores were measured soon after the tadpoles had hatched from eggs and again ten days later.

Natural and artificial selection

Fig. 5.1 presents the area of land used to grow genetically modified (GM) crops in the USA, Brazil, India and China between 2004 and 2015.

Genetically modified organisms in agriculture

MELAS syndrome is an inherited disorder caused by a mutation in a gene within mitochondrial DNA (mtDNA). Every mtDNA molecule is inherited from the mother. Fig. 6.1 depicts four generations of a family in which several members have MELAS syndrome.

Passage of information from parents to offspring

(a) Isolated mitochondria were used to examine respiration. • Mitochondria were taken from respiring mammalian cells and placed in a buffer solution. • Pyruvate and inorganic phosphate (Pi) were added at time zero. • ADP was added one minute later. • The oxygen concentration of the buffer solution containing mitochondria was monitored for the whole investigation. The results of the investigation are shown in Fig. 7.1.

Homeostasis in plants

Explain what the term biodiversity means.

Biodiversity

Section B. Answer just one question.

Control and coordination in mammals