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.
Achieving successful rooting of cuttings is difficult in some shrub species. An experiment was undertaken to determine whether juvenile shoots (J) of shrubs root more successfully than mature shoots (M).
Distinguish between the rooting success of the juvenile shoots and the mature shoots.
Suggest one reason for the difference in the rooting success in the juvenile shoots and the mature shoots.
Outline one variable that would need to be controlled in this experiment.
Auxin is a hormone that can be applied to improve the percentage success of rooting in those study plants with poor rooting success. Explain the effects of auxin on plant cells.
The image shows a severed aphid stylet embedded in plant tissue.
Identify the tissue labelled II.
Outline one piece of evidence that the tissue labelled I is phloem tissue.
Explain how aphid stylets can be used to study the movement of solutes in plant tissues.
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.
The larval stage of the fly Eurosta solidaginis develops in the plant Solidago altissima. The larva secretes a chemical which causes plant tissue to grow around it forming a swelling called a gall. The gall provides the developing insect with protection from predators.
The E. solidaginis fly is preyed upon by the parasitic wasp Eurytoma gigantea. The graph shows the relationship between gall diameter and the percentage of flies that avoid predation by E. gigantea.
In order to form galls, the insects choose a location where cell division occurs at a high rate. State the term for a region of rapid cell division within a plant.
Describe the relationship between gall diameter and percentage survival of E. solidaginis.
Explain the concept of directional selection with respect to this example.