Edexcel IGCSE Biology Biology Paper 2 June 2023 question paper 4BI1/2BR

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Tissue culture and plants

In micropropagation, plant tissues are grown in vitro on plant tissue culture media, under aseptic conditions in a controlled environment. This technique is possible because plant cells can differentiate and become specialised cells. This allows them to change their metabolism, growth and development to form a whole plant.

Plant tissue culture media contain substances to support the normal growth and development of plants. The media are mainly composed of minerals, vitamins, and plant hormones. The pH of the media is kept constant.

Plant hormones play an essential role in determining how cells and tissues develop in culture media. Plant cells can differentiate into different tissues and cell types. The concentration of hormones can determine the tissue that develops. Auxins and cytokinins are the most widely used. A balance of both auxin and cytokinin leads to the development of a mass of undifferentiated cells known as a callus.

In vitro cell culture offers an alternative method for conserving endangered species and varieties. Tissue culture can be used when the plant species produce seeds that do not germinate or have seeds that cannot be stored for a long period of time. These can be successfully preserved using in vitro techniques for the maintenance of gene banks.

Embryo culture is a type of plant tissue culture that is used to grow embryos from seeds in nutrient media. In embryo culture, the plant develops directly from the embryo or indirectly through the formation of a callus and then subsequent formation of shoots and roots. The technique has been developed to break dormancy in seeds, and to reproduce rare species and haploid plants.

Scientists are also using cell suspension culture systems from which products can be extracted. A suspension culture is developed by transferring a portion of the callus into liquid media. The media are maintained under suitable conditions of agitation, light and temperature. This system can provide a continuous, reliable source of natural products independent of climate and soil conditions. The first commercial application of large‑scale suspension cultivation of plant cells was carried out to produce shikonin. Shikonin is used in traditional Chinese medicine and is a potential anti‑cancer treatment.

State what is meant by the term in vitro. (line 1)

Explain how plant cells differ from human cells in their ability to differentiate and specialise. (lines 2 and 3)

Give the function of two named minerals included in the culture media. (line 6)

Explain why the pH of the media needs to be kept constant. (line 7)

Auxin also controls the response of plants to light.

Describe a simple experiment you could do to show the phototropic response of plant stems to light.

Explain why scientists want to conserve endangered plant species and varieties. (lines 13 and 14)

Explain why plant cell suspension culture media are maintained under suitable conditions of agitation, light and temperature. (lines 24 and 25)

The diagram shows two cells from a plant root.

Which structure is the vacuole?

Which structure is the nucleus?

The actual length of the root cell from P to Q is 80 µ m.

Determine the magnification of the diagram.

[1000 µ m = 1 mm]

magnification =_........

Root hair cells are specialised cells adapted for their functions.

Explain how root hair cells are adapted for their functions in the plant.

The picture shows two biscuits, A and B.

The table shows some nutritional information supplied by the manufacturers of the two biscuits.

Calculate the percentage of the total carbohydrate in biscuit A that is starch.

A doctor has advised a person to lose weight.

Comment on which biscuit, A or B, would be most suitable for the person to maintain a healthy diet and to lose weight.

Use the information in the table and your own knowledge in your answer.

A teacher tells some students to carry out an experiment to compare the energy values of biscuit A and biscuit B.

Describe a suitable method the students could use for their experiment.

The energy values the students determined for the biscuits were much lower than the energy values supplied by the manufacturers.

Give two reasons why this is the case.

The diagram shows the nitrogen cycle. Some of the stages have been labelled.

Which stage shows nitrogen fixation?

Which stage shows nitrification?

Which stage shows denitrification?

Farmers sometimes add chemical fertiliser to the soil.

Describe how pollution by fertiliser can affect aquatic ecosystems.

Give an alternative to chemical fertiliser that a farmer could use.

Diagram 1 shows part of a DNA molecule.

Strand 1 G G C T A G T T G

Complete Diagram 1 by writing the letters of the missing bases in the empty boxes for strand 2.

Give the maximum number of amino acids that are coded for by this DNA strand (strand 2).

The original DNA strand is used to produce mRNA.

Complete the empty boxes in Diagram 2 to show the mRNA coded for by this DNA strand.

DNA G G C T A G T T G

A length of DNA consists of 25 000 base pairs.

This makes a total of 50 000 bases.

In this length of DNA, 30% of the bases are adenine (A).

Determine the number of thymine (T) bases, cytosine (C) bases, and guanine (G) bases in this length of DNA.

Describe the differences between the process of transcription and the process of translation.

Smoking cigarettes has harmful effects on the body.

Graph 1 shows the number of hospital admissions in thousands due to conditions caused by smoking each year from 2009 to 2019.

Using information from Graph 1, calculate the percentage increase in the number of hospital admissions caused by smoking in 2019 compared with 2009.

Graph 2 shows the percentage of all hospital admissions that were due to conditions caused by smoking each year from 2009 to 2019.

Comment on the changes in the number of hospital admissions caused by smoking and the percentage of all hospital admissions that were caused by smoking.

Use data from graph 1 and graph 2 in your answer.

Smoking causes harmful effects on the lungs.

Describe the consequences of smoking cigarettes for the functioning of the lungs.