Practice Paper 2 (Edexcel IGCSE Biology)

The graph shows the effect of temperature on the activity of an enzyme.

Describe and explain the trend of the graph.

Explain how the evidence from the graph in part (a) indicates that the enzyme being studied is not likely to be one found in the human body.

A group of students wanted to investigate the effect that temperature has on the activity of pepsin, a protease found in the human digestive system.

They used the following method:

1. Put 4 cm³ of 1% protein solution into a boiling tube.
2. Put 4 cm³ of pepsin solution into a second boiling tube. Put both boiling tubes into a water bath at 20 °C.
3. After 4 minutes, add the pepsin solution to the protein solution together in one boiling tube, mixing together with a stirring rod.
4. After 20 seconds, add a drop of the mixture to a drop of Biuret solution in one well of a spotting tile.
5. Repeat step 5 until the Biuret solution no longer changes colour.
6. Repeat steps 1 – 6 at 10 °C (using an ice water bath), 30 °C, 40 °C and 50 °C.

Explain why the student left the protein and pepsin solutions in the water bath for 4 minutes in step 3.

The image below shows the incomplete results of the experiment carried out in part (c).

Complete the image below to show the results you would expect at 30 °C and at 40 °C

You should write a tick or a cross in each well of the spotting tile.

State where in the digestive system protease is secreted.

The diagram below shows a representation of a plant cell.

Describe the functions of structures P Q, and R.

(i) Label the diagram in part (a) with an S to indicate the location of the cell wall.

(ii) Describe the function of the cell wall.

Plants are one of the five groups of eukaryotes.

(i) Name another group of eukaryotes in which you might find structure P labelled in part (a).

(ii) State one other feature of the group named in part (i).

The cell shown below is found inside a salivary gland.

Suggest what can be concluded about the activities of the salivary gland cell from the image above.

The diagram shows apparatus a student uses to compare inhaled and exhaled air.

The student breathes into and out of the mouthpiece for one minute.

(i) Explain which flask exhaled air passes through.

(ii) Explain the changes that will happen in the limewater in flask A and in flask B.

(iii) The student uses limewater to compare the composition of exhaled and inhaled air.

Suggest an alternative substance that they could use.

Describe the role of the diaphragm and the intercostal muscles in inhalation.

Organisms must transport substances to and from the external environment.

Identify one substance which cells must transport across the cell membrane to support cell functions.

The diagram shows particles of two gases.

Complete the diagram by drawing the arrangement of the gas particles after 1 hour.

Name the process shown in part (b).

Which of the following is an example of simple diffusion?

The pancreas produces a range of enzymes involved in the digestion of food.

Explain the meaning of the term enzyme.

In which of the following locations does digestion by the enzyme amylase take place?

The diagram below shows an enzyme and an associated molecule labelled X that can bind with the enzyme at location Y.

Name molecule X and location Y.

The 'lock and key hypothesis' is often used as a model to describe the action of enzymes.

Use your knowledge of the lock and key hypothesis and the diagram in part (c) to explain how enzymes function in digestion.

In respiration energy is released from glucose.

State two uses, in an animal cell, of the energy released from glucose.

Earthworms are known as detritivores; they break down dead plant and animal material in the soil.

Which statement best describes how oxygen from the soil move into the body fluids of the earthworm to be used in respiration.

If the ground becomes waterlogged then less oxygen will be available in the soil and the earthworm will need to respire anaerobically. This process is represented by the equation below.

Glucose → Lactic Acid

State why this process is described as anaerobic.

Earthworms cannot survive for very long in heavily waterlogged soil.

Suggest why this is the case.

An oxygen debt is often associated with anaerobic respiration.

Describe the process that occurs in the human body during an oxygen debt.

The diagram shows Amoeba proteus, a type of unicellular microorganism found in fresh water.

Name the group of organisms that this species belongs to.

The *Amoeba proteus *gets its nutrition by surrounding other unicellular organisms with its pseudopodia and engulfing the prey, digesting the nutrients internally and storing the nutrients in the food vacuole.

(i) Describe the differences of this process in comparison with saprotrophic nutrition in fungi.

(ii) As well as nutrition, name other life process is being demonstrated during this process.

The Amoeba is found in fresh water and must control its internal conditions by balancing the amount of water that moves in and out of the cell across the cell membrane. The Amobea contains a structure called a contractile vacuole, which expels excess water from the cell. As well as excess water, they also remove waste materials from the cell.

Name the life processes that the contractile vacuole carries out.

The table shows a list of positive and negative results for some tests that can be used to detect the presence of food substances.

Complete the table to identify the test reagent and substance being tested.

A balanced diet should contain a variety of different biological molecules, each of which is digested by a specific set of enzymes.

Draw lines to match up the molecule to the specific enzyme involved in its digestion.

The graph below shows the effect of temperature on an enzyme controlled reaction.

Explain the rate of reaction at 41 °C.

Enzymes are examples of proteins.

Which of the following combinations of chemical elements shows the correct four elements found in proteins?

The diagram below shows three different cells.

Calculate the size ratio of the bacterial cell compared to the liver cell and mesophyll cell.

The electron microscope image below shows a section from the inside of a liver cell...

Bochimoto H, Matsuno N, Ishihara Y, Shonaka T, Koga D, Hira Y, et al., CC BY 4.0 https://creativecommons.org/licenses/by/4.0, via Wikimedia Commons

(i) Name the organelles indicated by X.

(ii) Use information in the image to suggest the possible cell activities that take place inside a liver cell.

Separate: Biology Only

The liver is known to have a strong regenerative ability, meaning that when the liver is damaged it can regenerate itself within days. This regenerative ability is thought to be due to several types of adult stem cells present within and around the liver.

Describe the differences between adult stem cells and stem cells taken from an embryo.

Separate: Biology Only

Scientists researching the regenerative capacity of the liver have identified a chemical signalling pathway inside liver cells that prevents the liver from growing too large when it regenerates. This chemical signalling pathway has been named 'Hippo'.

A recent discovery has shown that switching off the Hippo signalling pathway reverses the differentiation process, resulting in de-differentiated liver cells.

Suggest what this discovery could mean for the development of stem cell therapies.

The diagram below shows an alveolus (plural alveoli).

Explain one feature seen in the alveolus in the diagram which allows efficient gas exchange.

Label the diagram in part (a), using an 'X', indicate where the oxygen content of the blood is the highest.

The estimated surface area of the lung system of a new-born baby is 4.2 m²; this is around one twentieth of the overall surface area of a typical adult's lungs.

Calculate the overall surface area of a typical adult's lungs.

The following list contains structures found within the breathing system.

Complete the table by numbering the structures to show the sequence in which air passes through them during an exhalation. The first structure has been numbered for you.

Describe the actions of the intercostal muscle and diaphragm during inhalation.

Separate: Biology Only

Patients with organ failure currently rely on temporary treatments and the use of donor organs for transplant, but scientists believe that it could be possible to improve the treatment for organ failure by growing entire new organs in the lab.

Scientists researching methods that could be used to grow a new heart have been investigating the use of a scaffold developed from the heart of a human or animal donor. A proposed method for this is shown in the image below.

(i) Explain why stem cells are used in this process.

(ii)Suggest why a scaffold is needed for the growth of a new organ in the lab.

(iii) Suggest the practical and ethical considerations that should be taken into account when developing scaffolds from human or animal donors.

Separate: Biology Only

While growing new hearts for transplant is still some years away, growing skin for transplant from stem cells is currently possible.

A study investigated the effect of stem cells on the rate of healing of skin wounds. Stem cells taken from human skin, known as mesenchymal stem cells (MSC), were administered to skin wounds in immune-deficient mice, and the wounds of the MSC-treated mice were monitored alongside identical wounds in a group of control mice.

The results after 12 days of monitoring are shown below.

(i) Suggest why immune-deficient mice were used in the study.

(ii) Explain the purpose of the control group of mice.

(iii) Calculate the percentage difference in wound healing time between the control group of mice and the MSC-treated mice.

A student read the results of the study described in part (b) and concluded that MSCs could be used to grow new skin to treat burn patients.

Evaluate the student's conclusion.