Testing for biological molecules

A milk sample is heated with Benedict’s solution. Once boiling has occurred, a yellow colour is seen. Which conclusion is correct?

Feb/March 2017

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?

Feb/March 2019

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?

Feb/March 2021

A student used Benedict’s solution to test a sample that is known to contain carbohydrate. When the test was finished, the solution remained blue. Which carbohydrate might be present in the sample?

Feb/March 2022

To determine the glucose concentration in an unknown solution, equal amounts of several glucose solutions with known concentrations were each combined with the same excess volume of Benedict’s solution. Once mixed, the samples were kept in a thermostatically controlled water-bath at $90\,^{\circ}\text{C}$ for three minutes. The unknown solution was then handled in the same way, and the colours of the known and unknown solutions were compared. What is the independent variable in this procedure?

Feb/March 2023

Many flowers make a sugary fluid known as nectar. Bees given nectar use enzyme Q to convert the nectar into honey. When a nectar sample was checked for reducing sugar with standard laboratory reagents, it was blue. When a honey sample was checked in the same way, it was orange. Which conclusion about the reaction catalysed by enzyme Q is consistent with these results?

Feb/March 2024

Which flow chart that describes the test for non-reducing sugars is correct?

Feb/March 2024

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?

May/June 2010

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?

May/June 2010

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.

May/June 2010

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.

May/June 2010

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.

May/June 2010

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

May/June 2010

Four distinct fruit juices, A, B, C and D, were examined using Benedict’s solution. A second portion of each juice was hydrolysed and then tested with Benedict’s solution. The table shows the masses of precipitates produced. Which juice has the largest mass of non-reducing sugar?

May/June 2011

Benedict’s solution was used to test four different fruit juices, A, B, C and D. A separate sample from each juice was then hydrolysed and tested again with Benedict’s solution. Which juice has the largest mass of non-reducing sugar?

May/June 2011

A group of students carried out an ecological investigation of a defined stretch of seashore (A) in Brittany, France. One team chose to examine a rockpool (B) and recorded data such as the oxygen concentration and temperature of the seawater (C). After examining all the different living organisms (D) found in the rockpool, the students chose to study the limpets, Patella vulgata (E), in more detail. They gathered information on the role of the limpets in the rockpool, including interactions with other organisms (F). For instance, limpets grazed on green seaweeds, while the shore crab, Carcinus maenas, fed on small limpets.

May/June 2011

Fig. 5.1 shows a triglyceride molecule. Name components A and C, and state the name of bond B. Write your responses on the dotted lines in Fig. 5.1.

May/June 2011

Within anaerobic soil, bacteria such as $\textit{Pseudomonas stutzeri}$ are able to use nitrate ions $(\text{NO}_3^-)$ as an oxygen supply for respiration. The word equation shown below represents this process: glucose + nitrate $\rightarrow$ water + carbon dioxide + nitrogen

May/June 2011

Samples taken from a combination of biological molecules were tested. After iodine in potassium iodide solution had been added to one sample, the mixture changed to black. The biuret test was then done on a different sample, and the mixture became purple. Which biological molecules were present in the mixture?

May/June 2012

Which carbohydrate produces a brick-red colour when heated with Benedict’s solution?

May/June 2012

A student performed a set of tests on an extract from a plant. The table displays the results of these tests. Which row indicates the molecules present in the plant extract?

May/June 2012

Samples taken from a combination of biological molecules were tested. After iodine in potassium iodide solution was added to one sample, the mixture became black. A different sample was then tested using the biuret test, and the mixture turned purple. Which biological molecules were present in the mixture?

May/June 2012

Name the structure in each statement as precisely as you can.

May/June 2012

The slime mould, Dictyostelium discoideum, belongs to the eukaryotes and acts as a decomposer of protein-rich material. Fig. 5.1 illustrates the life cycle of D. discoideum.

May/June 2012

Study the passage below. Catfish are an economically significant freshwater fish species that are used as food by humans. In the wild, catfish occur in a wide range of large freshwater environments, including rivers, lakes and reservoirs. In North America, they are commonly kept in catfish ponds, which are man-made environments. Each pond acts as a self-supporting ecosystem with its own collection of organisms. Catfish eat live and dead fish, amphibians, insects and even dead mammals that are found on the pond bottom. Several species of phytoplankton are always present in these ponds. These are tiny organisms suspended in the water, and they are vital for the growth of all the other pond organisms.

May/June 2012

Which statement describes the emulsion test for detecting lipids?

May/June 2013

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?

May/June 2013

The cells in Fig. 1.1 come from one organism and have the same appearance. The cells in Fig. 1.1(a) were formed by mitosis, while the cells in Fig. 1.1(b) were formed by meiosis.

May/June 2013

Polysaccharides are produced through condensation reactions between monosaccharide subunits (monomers).

May/June 2013

Fig. 3.1 depicts part of the nitrogen cycle.

May/June 2013

A student performed four tests for biological molecules on a solution. The outcomes are given in the table. Which three molecules could be present in this solution?

May/June 2014

The molecule illustrated is a polymer made from reducing sugars. Which procedures could be carried out to test for the presence of the reducing sugars in this molecule?

May/June 2014

Four sugar solutions were examined using Benedict’s solution. The table shows the colours of the solutions after the test. What is the most appropriate interpretation of the results?

May/June 2014

A student completed four tests for biological molecules on a solution. The findings are shown in the table. iodine solution – orange biuret – blue Benedict’s – orange emulsion – clear Which molecules are present in this solution?

May/June 2014

Azolla filiculoides is a floating aquatic fern that rests on the surface of lakes. The nitrogen-fixing microorganism Anabaena azollae lives inside the fern leaves. The beetle Stenopelmus rufinasus feeds on A. filiculoides.

May/June 2014

Starch consists of two polysaccharides, amylose and amylopectin. Fig. 3.1 illustrates a molecule of α-glucose before it joins the end of an amylose molecule.

May/June 2014

Fig. 1.1 summarises the movement of energy through a forest ecosystem. The thickness of the arrows is proportional to the amount of energy transferred between each part of the ecosystem.

May/June 2014

A student performed four tests for biological molecules on a solution. The results are given in the table. iodine solution: orange biuret: purple Benedict’s: orange emulsion: cloudy Which molecules could be present in this solution?

May/June 2015

Biological molecule solutions are checked for sugars. The table shows the colours of the solutions after the test. Which one may contain non-reducing sugars?

May/June 2015

Which row is the correct one?

May/June 2015

A student performed four tests to identify biological molecules. The results are listed below. Tests and observations: - iodine: orange - biuret: purple - Benedict’s: orange - emulsion: clear Which molecules are present in the solution?

May/June 2015

Sentences (i) and (ii) have been taken from longer definitions of ecological terms. In each sentence, two or more words are missing. Complete (i) and (ii) by choosing the correct terms from the list provided.

May/June 2015

In oceans, the nitrogen cycle includes some bacteria that are different from those on land. One ocean bacterium is Nitrococcus mobilis, and it carries out this step in the nitrogen cycle: $\text{NO}_2^- \rightarrow \text{NO}_3^-$.

May/June 2015

Two solutions, 1 and 2, were examined using a range of reagents to establish their identities, with one solution containing starch and sucrose and the other containing glucose and protein. The table presents the conclusions drawn from the results obtained for the different tests. Which row correctly matches the two solutions?

May/June 2016

Benedict’s solution was used to test a milk sample, and a yellow colour was seen. Which conclusion is correct?

May/June 2016

Table 1.1 sets out the characteristics of three infectious diseases: malaria, tuberculosis (TB) and cholera.

May/June 2016

Fig. 5.1 depicts plant cells at different stages of mitosis.

May/June 2016

The diagram presents the outcomes of tests on four solutions that contain biological molecules. Which one shows the solution containing only starch and protein?

May/June 2017

Steps 1-4 are carried out to test for a non-reducing sugar. 1 Place $5\,\text{cm}^3$ of solution in a test-tube. 2 Add several drops of acid. 3 Neutralise using alkali. 4 Add $6\,\text{cm}^3$ of Benedict’s solution. At what point is the solution boiled?

May/June 2017

Meristematic tissue occurs in plant growth regions, such as root tips.

May/June 2017

A student needed to estimate the concentration of glucose in a solution by carrying out the Benedict’s test. The student was given a $1.0\,\text{mol dm}^{-3}$ glucose solution and instructed to prepare a $0.6\,\text{mol dm}^{-3}$ solution through proportional dilution. Which row gives the correct volumes of the $1.0\,\text{mol dm}^{-3}$ glucose solution and distilled water required to prepare the $0.6\,\text{mol dm}^{-3}$ solution?

May/June 2018

Three biological molecule solutions are examined for sugars. The table gives the colours of the solutions after the test. Which solutions had glucose present before the test?

May/June 2018

Fig. 1.1 shows a drawing based on a photomicrograph of a spongy mesophyll cell taken from a leaf.

May/June 2018

Fig. 1.1 shows a photomicrograph of a root tip meristem. Cells can be seen in different parts of the cell cycle. Some cells are at the same point in the cell cycle, and some are at the same point in mitosis.

May/June 2018

Adipose tissue is made up of cells called adipocytes, stores large amounts of triglycerides, and acts as a tissue for energy storage. Fig. 2.1 shows a photomicrograph of adipose tissue.

May/June 2018

A student performed Benedict’s test on a range of known concentrations of $\alpha$-glucose. Which graph shows the results accurately?

May/June 2019

When a milk sample is heated with Benedict’s solution, a yellow colour is seen. Which statement about the milk sample is correct?

May/June 2019

Cells are made up of carbohydrates, proteins, lipids and nucleic acids.

May/June 2019

The flow chart indicates the outcomes of several tests carried out on a solution containing biochemicals. Benedict’s test: blue; non-reducing sugar test: yellow; iodine test: blue-black; biuret test: purple. Which substances are present in the solution?

May/June 2020

A student performed Benedict’s test on a sample and obtained a negative result. What should the student do to confirm that there are no sugars in the sample?

May/June 2020

A positive Benedict’s test produces this colour because copper oxide is formed. The mass of copper oxide is directly proportional to the amount of reducing sugar present. Fruit juice samples were tested with the Benedict’s test to check for reducing sugars and non-reducing sugars. The table gives the mass of copper oxide obtained after boiling with Benedict’s solution and after acid hydrolysis followed by boiling with Benedict’s solution. Which sample had the greatest amount of non-reducing sugar?

May/June 2020

Saccharomyces cerevisiae is a single-celled fungus of major importance in brewing and baking. Fig. 4.1 shows a diagram based on a transmission electron micrograph of S. cerevisiae.

May/June 2020

A food sample was warmed with Benedict’s solution, and the colour altered to green. A second portion of the same food was heated with dilute hydrochloric acid, then made neutral with sodium hydrogencarbonate. After that, it was warmed with Benedict’s solution, and the colour changed to red. What do these results indicate?

May/June 2021

Which pair of molecules contains only macromolecules present in animal cells?

May/June 2021

A student performs a semi-quantitative test using Benedict's solution. Which statement concerning this procedure is correct?

May/June 2021

Samples of glucose, sucrose, and a mixture of glucose and sucrose were split into two portions, M and N. M was then tested using Benedict’s solution. N was heated with dilute hydrochloric acid, neutralised, and then tested using Benedict’s solution. The colour of the solution was compared with colour standards. Which table shows the correct colour changes for these samples?

May/June 2022

Four extracts were prepared from different plant materials and then tested using Benedict’s solution. Each extract was boiled with Benedict’s solution for $240$ seconds, after which the final colour was noted: extract 1: red; extract 2: yellow; extract 3: blue; extract 4: green. Which sequence of plant extracts shows an increasing amount of reducing sugar?

May/June 2022

The concentration of reducing sugar in a solution can be determined by comparing an observational measurement with a standard. Which observational measurement could be used to estimate the concentration of reducing sugar in an unknown solution? 1 the colour of the solution after 20 minutes 2 the time taken for the first colour change to happen 3 the rate at which solid particles form

May/June 2022

Trehalose is a sugar that gives a negative result in a test with Benedict’s solution. If a molecule of trehalose is hydrolysed, it produces two $\alpha$-glucose molecules. Which row is the correct one?

May/June 2022

In mammals, adipocytes are cells located in adipose tissue. They take up glycerol and fatty acids and combine them to form triglycerides for long-term storage. Fig. 4.1a shows one glycerol molecule together with three fatty acids. Fig. 4.1b shows the triglyceride molecule produced from these parts.

May/June 2022

Hummingbirds are the tiniest birds and occur in the Americas. Several species travel hundreds of kilometres between warmer overwintering regions and the summer breeding grounds. As with mammals, birds keep a constant body temperature. Because hummingbirds have a very high metabolic rate, they need a large supply of sugars. Fig. 3.1 shows a hummingbird taking nectar, which is one of its chief food sources.

May/June 2022

The table lists a number of steps that may be used when doing Benedict’s test. Which combination of steps is needed to carry out a semi-quantitative test on a reducing sugar solution?

May/June 2023

Which sequence of steps is the most suitable way to carry out the emulsion test for lipids?

May/June 2023

A student was given a carbohydrate solution. Two portions were taken from it and tests were carried out on each portion, as shown. Which statement accounts for the results?

May/June 2023

Which polymers are found in every virus, every prokaryote and every eukaryote?

May/June 2023

Stages 1, 2, 3 and 4 are carried out to test for a non-reducing sugar. 1. Place $5\,\text{cm}^3$ of solution in a test-tube. 2. Add a few drops of acid. 3. Neutralise using alkali. 4. Add $6\,\text{cm}^3$ of Benedict’s solution. At what point is the solution heated or boiled?

May/June 2023

Glycogen and cellulose are polymers. Fig. 2.1 illustrates small, representative sections of a glycogen molecule and a cellulose molecule.

May/June 2023

Tests for biological molecules were performed on three solutions, with each solution containing just one kind of biological molecule. The results were recorded as follows. Solution 1: Benedict’s test - blue to orange Solution 2: Benedict’s test after acid hydrolysis - blue to red Solution 3: biuret test - blue to purple Which solutions would contain either sucrose or amylase?

May/June 2024

Cyclin-dependent kinases (CDKs) are enzymes that control the cell cycle.

May/June 2024

The iodine test and Benedict’s test were performed on samples of a starch solution. Amylase was added to another sample of the starch solution, which was then incubated for $10$ minutes. After this, the Benedict’s test was done on this sample. What were the outcomes of the tests?

May/June 2025

One portion of a sucrose solution is tested for reducing sugars and stays blue, but when a separate portion of the same solution is tested for non-reducing sugars the solution turns red. What accounts for these observations?

May/June 2025

Amylose and the triglyceride stearin are macromolecules. Explain why amylose and stearin count as macromolecules, but only amylose counts as a polymer.

May/June 2025

Carrots are the storage roots of the carrot plant. The carrot plant is a major food crop cultivated across the world. Their flavour is sweet because sugars make up part of the total carbohydrate content. Plant breeding has created many carrot varieties with different degrees of sweetness.

May/June 2025

A liquid is tested and the following observations are recorded. Benedict’s test: red Biuret test: lilac Iodine in potassium iodide solution: orange Which substances are present in the liquid?

Oct/Nov 2010

A liquid is tested and the following outcomes are obtained. Benedict’s test: red Biuret test: lilac iodine in potassium iodide solution: orange Which substances are contained in the liquid?

Oct/Nov 2010

Complete the passage with the term that best fits. In any ecosystem, there is a ................................ of organisms that influence one another and also interact with the surroundings. Every species has a specific ................................ in that ecosystem. Feeding links in food webs show the interactions species have with one another. In old-field ecosystems in North America, producers such as blue grass supply energy to grazing animals. These animals make up the ................................ ................................ ................................ in the food chain.

Oct/Nov 2010

State the term that matches each description in (a) to (e).

Oct/Nov 2010

Fig. 6.1 illustrates the directions in which nutrients move through a soil food web.

Oct/Nov 2010

Solutions containing biological molecules are tested for sugars. The table gives the colours observed in the solutions after the test. Which could contain reducing sugars?

Oct/Nov 2011

Solutions of biological molecules are examined for sugars. The table shows the colours of the solutions after the test. Which could contain non-reducing sugars?

Oct/Nov 2011

Which row is the correct one?

Oct/Nov 2011

Samples of biological molecules are examined for sugars. The table gives the conditions used and the outcomes after each test. Solution 1: heated with Benedict’s solution → blue; boiled with hydrochloric acid, neutralised, then heated with Benedict’s solution → yellow. Solution 2: heated with Benedict’s solution → green; boiled with hydrochloric acid, neutralised, then heated with Benedict’s solution → orange. Solution 3: heated with Benedict’s solution → orange; boiled with hydrochloric acid, neutralised, then heated with Benedict’s solution → red. Which may contain reducing sugars?

Oct/Nov 2011

Fig. 5.1 illustrates a segment of a DNA molecule.

Oct/Nov 2011

Mangroves are trees that grow along tropical coastlines in salt water. Fig. 6.1 shows part of a food chain from a mangrove habitat.

Oct/Nov 2011

Four students, 1, 2, 3 and 4, each performed the reducing sugar test and the non-reducing sugar test on a sucrose solution. Which observations show that they had carried out the correct tests?

Oct/Nov 2012

Which row is correct for every one of the molecules?

Oct/Nov 2012

Which solution, when heated, breaks glycosidic bonds?

Oct/Nov 2012

Five biochemical tests were performed on four unidentified substances, A, B, C and D. After the tests, it became possible to establish whether each biochemical was present or absent in each substance. Which substance contains glucose, fat and protein?

Oct/Nov 2012

Fig. 1.1 shows a drawing produced from an electron micrograph of a mammalian liver cell.

Oct/Nov 2012

Lancaster Sound in the Canadian Arctic is a highly productive marine habitat that sustains abundant sea birds and marine mammals. Research in this region has highlighted the role of Arctic cod, Boreogadus saida, in transferring energy to marine birds such as guillemots and fulmars, and to marine mammals such as narwhals and belugas. For many of these animals, Arctic cod is the chief food source, or even the only one. The movement of energy through the food web in Lancaster Sound is shown in Fig. 4.1.

Oct/Nov 2012