HL Paper 3
The rate of transpiration can be measured using a data-logging pressure sensor connected to a plant cutting via a plastic tube. In an experiment, a control set-up was connected to the tube and placed in a well-lit room with normal humidity levels.
State the specific type of plant tissue that the plastic tube is meant to model.
Predict, with a reason, what will happen to the pressure in this tube as transpiration occurs.
Outline how this control set-up could be modified to test the effect of either humidity or temperature on the rate of transpiration.
The stomatal density is the number of stomata per area of leaf epidermis. A study was done on the stomatal density of the lower epidermis of leaves from Protium decandrum, a tree found in the Amazon forest.
The image shows the epidermis stripped from the lower surface of a leaf.
[Source: Camargo, M.A.B. and Marenco, R.A., 2011. Density, size and distribution of stomata in 35
rainforest tree species in Central Amazonia. Acta Amazonica, 41(2), pp.205–212. Image courtesy of Miguel from
Camargo & Marenco (2011).]
Calculate the magnification of the image, showing your working.
. . . . . . . . . . . . . . . . . . . . x
The mean stomatal density for the lower epidermis of P. decandrum was around 600 per mm2. Predict how the stomatal density for the upper epidermis would compare.
The micrograph shows a section through the root of a dicotyledonous plant (× 400).
Label tissues X and Y.
Calculate the actual width along line A-B of the parenchyma cell shown.
Describe the distribution of vascular tissues in the stem of dicotyledonous plants.
The drawing shows part of a Thunbergia grandiflora plant. It has been widely cultivated as an ornamental garden plant.
[Source: from Wight, R., Icones Plantarum Indiae Orientalis, vol. 3 (1846)]
The drawing shows a section through a T. grandiflora flower, which contains a honeybee (Apis mellifera).
[Source: © D G Mackean (www.biology-resources.com/drawing-plant-flower-tropical-06.html)]
Using the drawing, deduce which plant phylum T. grandiflora belongs to, giving one visible recognition feature of this phylum.
Identify the structure labelled X.
Outline the relationship the bee has with the T. grandiflora flower.
After fertilization, seeds of T. grandiflora form in a small pod. If you were provided with Petri dishes, absorbent cotton balls and seeds, suggest how one variable affecting germination of these seeds could be investigated.
The diagram shows the development of potato plants (Solanum tuberosum) over 14 weeks. New tubers start growing from week 9. These are modified underground stems serving as a starch reserve and bearing buds from which new plants arise.
Scientists planted several potato plants in a greenhouse. The sucrose and amino acids in potato plant phloem exudates were measured during several weeks.
Describe briefly how scientists obtained leaf phloem sap from the potato plants.
Suggest reasons for different amounts of sucrose in the leaf phloem sap of the potato plants.
A student designed an experiment to study the transpiration through the leaves of a tomato plant (Solanum lycopersicum). Measurements were taken in the initial conditions with five leaves on a tomato shoot and then again after each of the five leaves was removed.
[Source: R. C. Hodson and J. Acuff . 2006. Water transport in plants: anatomy and physiology in
Tested Studies for Laboratory Teaching, Volume 27 pp 163–183]
Describe the trend in the data.
Transpiration continued after the fifth leaf had been removed. Suggest what can be concluded.
State the independent variable in this investigation.
Explain how the results in the graph could have been obtained.
A leafy shoot was cut from a plant and connected to a potometer to measure the transpiration rate. The length of the air column in the glass tube was measured using the ruler.
[Source: © International Baccalaureate Organization 2019]
Red dye was added to the water in the potometer. A cross section of the stem was observed under the light microscope.
[Source: Nbnidhi, https://commons.wikimedia.org/wiki/File:Transverse_section_of_dicot_stem.jpg]
State the function of the tap and reservoir.
Describe how the apparatus could be used to demonstrate that the transpiration rate is affected by air movement.
One criticism of the experiment is that it only measured the rate of transpiration indirectly. Explain how the experiment is an indirect measurement of transpiration.
Label with an R the tissue where the red dye would appear.
Label with a C the tissue where organic compounds are transported.
Transpiration in plants can be measured using a bubble potometer or a mass potometer.
Suggest a possible research question that could be investigated using a potometer.
Evaluate the limitations of using a potometer in the investigation you suggested in (a).
The graph shows the effect of relative humidity on the transpiration rate in Chinese privet (Ligustrum sinense).
The rate of water uptake was measured using the potometer shown in the diagram. The diameter of the capillary tube is 1 mm.
Outline how the rate of water uptake is recorded in this potometer.
State a variable that needs to be controlled in this experiment.
Explain the effect of relative humidity on the rate of water uptake.