4.2 Resources from Plants

Mustard cress (Sinapis alba) seeds can be used to demonstrate the effect of mineral deficiencies on plant growth. 

These seeds can be grown on damp cotton wool in petri dishes, as shown below.

The cotton wool can be soaked with various mineral-deficient solutions and the effect on the growing plants observed. Sterile solutions containing all the necessary mineral ions for growth can be purchased. Also available are versions of the solutions that are each lacking in one particular mineral ion.

Five petri dishes were prepared with cotton wool and around 30 mustard cress seeds each. Each dish was illuminated with the same light intensity and wavelength, and kept in the same temperature-controlled room for 5 days. After that time, the growth of the germinating cress plants was observed.

Predict the observations for dishes 3, 4 and 5.

The observations of dishes 1 and 2 have been completed for you. 

Explain your prediction in each case. 

The potassium-deficient seedlings in Dish 2 of the experiment in part (a) showed yellow leaves after 5 days of germination and growth.

However, the earliest leaves that appeared in germination were not yellow, they were a normal green colour.

Explain why.

For the experiment described in part (a), describe and explain a possible control set-up that would be required to help validate the experimental conclusions.

The diagram below shows a section of a cellulose molecule.

Name parts J and K.

State the role of cellulose in plant cell walls and explain how its structure is related to this role.

Explain how the structure of amylopectin allows it to be hydrolysed quickly to supply cells with glucose for respiration.

Describe two similarities and two differences between the structures of cellulose and starch.

A student wanted to compare the tensile strengths of the following plants' fibres, with the aim of advising which would make a good sustainable substitute for plastic-based rope. 

• Jute (Corchorus olitorius)
• Flax (Linum usitatissimum)
• Hemp (Cannabis sativa L. variety) 

Devise and set out the steps the student should take in an experiment to test the tensile strength of the various plant fibres.

You may assume that the samples of fibre have already been extracted from the respective plants and supplied to the student fully prepared for the experiment. 

Your experimental design should make use of all of the following pieces of equipment. 

The units of measure at this stage should be kg. 

Before starting the investigation, the student drew out a blank results table, shown below. 

The student wished to be able to use the data in the table to calculate each fibre's tensile strength in the unit kg mm^-2.

Deduce the calculation that the student would have to do to find the cross-sectional area of a piece of the various fibres. You may assume that all the fibres are circular in cross-section.

(1)

Explain the reason for performing three repeats for each type of fibre. 

(2)

After the experiment, the student's partially completed results table looked like this:

(1)

Identify the plant tissues from the list I. - IV. that contribute significantly to the tensile strength of fibres such as those in the experiment in part (a).

1. sclerenchyma
2. phloem
3. xylem
4. cambium

Severe headaches are a symptom of migraine.

Sumatriptan is a drug that can reduce the symptoms of migraine.

Adults with migraine took part in a double blind trial to investigate the effects of sumatriptan.

Describe how the double blind trial for this drug could have been carried out.

Patients with a migraine attack were given either 10mg sumatriptan, 20mg sumatriptan or a placebo to treat the pain.

Patients recorded how long it took for them to be free of pain.

The results of this drug trial are shown in the graph below. 

(1)

After 90 minutes, the difference in the percentage of patients free of pain between those taking a placebo and those taking 20 mg sumatriptan is...

Using the information in the graph in part (b), describe the effects of sumatriptan on the treatment of the symptoms of migraine.

Using the information in the graph, deduce what conclusions can be drawn from this drug trial.