Feb/March 2018

An eyepiece lens in a microscope may be fitted with an eyepiece graticule. Which of the following statements about eyepiece graticules are correct? 1. They determine the true length of cells in micrometres. 2. They allow biologists to draw cells in the correct proportions. 3. Their size changes when the objective lens is switched from $\times 10$ to $\times 40$.

The microscope in cell studies

Sugars can be represented in ring form as well as in a linear form. Which sugar molecules could this diagram’s linear structure represent?

Carbohydrates and lipids

Which of these molecules are globular proteins?

Proteins

After hydrolysis, which molecules yield products that contain a carboxyl group?

Proteins

Lysosomes contain a range of hydrolytic enzymes that can function either inside cells (intracellular enzymes) or beyond cells (extracellular enzymes). Which process has to happen for lysosomal enzymes to act outside the cell?

Movement into and out of cells

The diagram illustrates an enzyme, the substrate and an enzyme/substrate complex. Which statement explains why the substrate can enter the enzyme's active site?

Mode of action of enzymes

What measurement could be used to calculate the rate of an enzyme-catalysed reaction?

Factors that affect enzyme action

Cholesterol is an essential part of the cell surface membrane. Which one of the statements about cholesterol is correct?

Fluid mosaic membranes

What type of bond in phospholipids helps to increase the fluidity of cell surface membranes?

Fluid mosaic membranes

Which one of the following substances is able to diffuse straight through cell surface membranes without the help of a carrier protein or a channel protein?

Movement into and out of cells

Companion cells use ATP to pump hydrogen ions out of the cell, while co-transporter proteins enable hydrogen ions to return together with sucrose molecules. Which two processes are occurring in this movement?

Movement into and out of cells

A student was told to use the scale bar shown to work out the magnification of a cell in a photomicrograph. The scale bar shows $2\,\mu\text{m}$. Which method could the student use to calculate the magnification of the cell?

The microscope in cell studies

At the beginning of each of these stages of the mitotic cell cycle, how many copies of each distinct DNA molecule are present in a cell? The stages shown are $G_2$ of interphase, prophase and cytokinesis.

Replication and division of nuclei and cells

The diagram lists three chromosome parts together with their functions. Parts: P1 centromere P2 histone proteins P3 telomere Functions: F1 compacts DNA into tightly packed structures F2 joins the two chromatids together F3 stops genes from being lost Which combination is correct?

Chromosome behaviour in mitosis

The graphs indicate several distance measurements recorded from metaphase of mitosis onwards. Each graph is drawn to scale relative to the others. Which row correctly matches each graph to its distance measurement?

Chromosome behaviour in mitosis

A bacterial culture was grown so that it replicated with nucleotides containing the heavy nitrogen isotope ($^{15}\text{N}$). After a number of generations, every bacterial DNA molecule contained heavy nitrogen. A DNA sample was removed from the culture, combined with caesium chloride solution and then centrifuged at high speed. During this procedure, DNA molecules with different masses separate into bands at different places in the centrifuge tube. The greater the mass of the DNA molecules, the nearer the bottom of the centrifuge tube the band appears. The diagram shows where the DNA molecules containing heavy nitrogen are located in the centrifuge tube. The bacterial culture was then grown using nucleotides containing the light nitrogen isotope ($^{14}\text{N}$). DNA samples were collected and separated by centrifugation after the bacteria had divided once and then again after they had divided twice. At which positions would the DNA be present after one cell division and after two cell divisions?

Replication and division of nuclei and cells

The diagram shows an ATP molecule. What do the labels P, Q and R represent in ATP?

Structure of nucleic acids and replication of DNA

The table lists three anticodons for different amino acids. Which DNA triplet on the DNA template strand specifies the amino acid serine?

Proteins

The photomicrograph reveals a transport tissue in the stem of a grape vine. Which structure is labelled T?

The microscope in cell studies

The diagrams illustrate transverse sections of different parts of a plant. Transport tissues are numbered 1 to 6. Which row identifies the tissues that mainly move water and the tissues that mainly move sucrose?

Movement into and out of cells

Which of the following will raise the rate of transpiration? 1 raising the humidity 2 increasing the light intensity 3 lowering the temperature 4 reducing the wind speed

Movement into and out of cells

Which water properties are important for transport in xylem? 1 cohesion 2 adhesion 3 a high energy demand for evaporation 4 effective solvent properties

Water

Which combination of eyepiece and objective lens in a light microscope permits the largest number of cells to be seen in one field of view?

The microscope in cell studies

During the cardiac cycle, which statement about blood flow is correct?

The heart

Which of the following statements about the formation of haemoglobonic acid are correct? 1 It is dependent on the formation of carbaminohaemoglobin. 2 It removes surplus hydrogen ions, stopping the blood from becoming too acidic. 3 It is associated with the action of carbonic anhydrase.

Proteins

Which substance is able to bind to the haem group in a haemoglobin molecule?

Proteins

Which factors would assist a person in adapting from living at a low altitude to living at a high altitude?

Transport of oxygen and carbon dioxide

Chronic obstructive pulmonary disease (COPD) covers bronchitis and emphysema. Which symptom is unique to emphysema?

The gas exchange system

Which structures can be found in a bronchus?

The gas exchange system

Which of the following terms is used to describe mosquitoes’ role in spreading malaria?

Infectious diseases

Bacteria causing skin wounds may develop resistance to the antibiotic usually used to kill them. Which statement explains how these bacteria could develop resistance to the antibiotic?

Antibiotics

Some children are born with severe combined immunodeficiency (SCID). Because of this inherited disease, these children usually lack T-lymphocytes and experience many infectious diseases. How can SCID be cured in these children?

The immune system

The hybridoma method is used to produce monoclonal antibodies. Which two cell types are involved in this method?

Proteins

Which row correctly pairs each cell structure with its function?

Cells as the basic units of living organisms

A vaccine is given to produce artificial active immunity. Once a person has received a vaccine, there is a time interval before long-term immunity to the disease develops. Which statement about this time interval accounts for this delay?

Proteins

Which animal cells would contain the most extensive Golgi bodies?

Cells as the basic units of living organisms

Which of the following processes needs ATP? 1. movement of water in the xylem 2. semi-conservative replication of DNA 3. facilitated diffusion of amino acids into the cell

Movement into and out of cells

Which concentrations could be obtained by carrying out a serial dilution of an $8.00\%$ glucose solution?

Carbohydrates and lipids

A student recorded the following claims about polysaccharides. 1. Amylose is produced by condensation reactions involving $\beta$-glucose monomers. 2. Branches in amylopectin molecules are formed between carbon atoms $1$ and $4$ on $\alpha$-glucose molecules. 3. In unbranched $\beta$-glucose chains, each monomer is rotated $180^{\circ}$ relative to the monomer next to it. Which statements are correct?

Carbohydrates and lipids

Which diagram correctly illustrates the formation of a peptide bond between two amino acids?

Proteins

Fig. 1.1 shows an electron micrograph of part of a eukaryotic cell.

Protein synthesis

Mycobacterium tuberculosis is the principal bacterium responsible for tuberculosis (TB) in humans. In most instances, the illness affects the lungs. This bacterium is able to enter cells and stay inactive in a latent (dormant) condition. It can later become active and cause the symptoms of the disease. In a person with active TB, the pathogen may be found in airborne droplets that are breathed out. Usually, when a healthy person inhales these droplets, the gas exchange system has effective defence mechanisms that stop infection.

The immune system

The unicellular fungus Kluyveromyces lactis is present in dairy products. It is a safe microorganism to culture for obtaining the enzyme lactase. Lactase catalyses the breakdown of lactose, a sugar present in milk. The reaction catalysed by lactase is shown in Fig. 3.1.

Protein synthesis

Fig. 4.1 shows a diagram of a cross-section through part of a young root.

Transport mechanisms

Outline the roles of the sinoatrial node (SAN) and the atrioventricular node (AVN) in starting and regulating heart action.

The heart

In a cell that is dividing, DNA replication takes place before mitosis.

Structure of nucleic acids and replication of DNA

The aye-aye, Daubentonia madagascariensis, is a primate that lives in Madagascar. Aye-ayes are nocturnal, meaning they are active during the night, and they build nests high in trees. Their diet includes insect larvae living inside tree trunks. Fig. 1.1 is an image of an aye-aye. The International Union for Conservation of Nature (IUCN) is the world’s largest international environmental organisation. The IUCN Red List of Threatened Species™ assesses the conservation status of plant and animal species. The aye-aye is listed as endangered on the IUCN Red List, so it is at a very high risk of becoming extinct in the wild.

Evolution

Section B. Select one question and answer it.

Control and coordination in plants

Motor neurones are cells in the nervous system.

Control and coordination in mammals

The $b2$-globin gene specifies the $b2$-globin polypeptide found in haemoglobin. It exists in two allelic forms, $Hb^{A}$ (normal) and $Hb^{S}$ (sickle cell). The sickle cell allele differs from the normal one because of a base substitution mutation, and that mutation causes one amino acid in the $b2$-globin polypeptide to change. A man and woman who both carry sickle cell trait may decide to have children through IVF. This makes it possible to determine the genotype of embryos by gene testing before implantation. Embryos with the normal genotype can then be chosen and placed into the mother. One method that can be used to gene test an embryo for the $Hb^{S}$ allele is restriction fragment length polymorphism (RFLP) analysis.

Principles of genetic technology

Ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) is a key enzyme in the light independent stage (Calvin cycle) of photosynthesis. It carries out carbon fixation by joining carbon dioxide with RuBP. In some cases, a sugar phosphate occupies rubisco's active site, which leaves the enzyme inactive. Rubisco can be reactivated when another enzyme, rubisco activase, is present.

Photosynthesis as an energy transfer process

The sliding filament model explains the contraction of striated muscle.

Fluid mosaic membranes

Cells known as melanocytes produce the black pigment melanin, which affects hair, skin and eye colour.

The roles of genes in determining the phenotype

Fig. 7.1 shows a red deer, Cervus elaphus. Red deer are herbivores that eat many different kinds of plants. Table 7.1 shows that the number of red deer in the UK rose between 1960 and 2010.

Natural and artificial selection

For respiration, the relevant structures and compounds are listed below: 1 coenzyme A, 2 cytoplasm, 3 pyruvate, 4 NAD, 5 outer mitochondrial membrane, 6 carrier protein, 7 inner mitochondrial membrane, 8 intermembrane space of mitochondrion, 9 ADP, 10 acetyl group.

Respiration

Section B. Answer a single question.

Photosynthesis as an energy transfer process