HL Paper 2
Boreal forests stretch across Canada, Russia and Scandinavia. This northern ecosystem accounts for 29 % of the world’s forest areas. The long, cold winters favour tall evergreen trees with either needles or scale-like leaves. These trees are wind-pollinated and their seeds are not enclosed in a fruit. The photograph shows a typical boreal forest in winter.
Identify the dominant plant phylum in the boreal forest.
In some areas there are gaps in the boreal forest where trees fail to grow and peat tends to accumulate. Suggest reasons for this.
An increase in global temperatures poses a critical threat to boreal forests. Explain the consequences of climate change to this northern ecosystem.
Suggest one advantage for the evergreen trees of the boreal forest being pollinated by wind.
Discuss the advantages of the production of seeds enclosed in fruit.
The boreal forests are situated close to the north pole and even in summer the intensity of sunlight is lower than at the equator. Sketch a graph showing the effect of light on the rate of photosynthesis, labelling the axes.
In some boreal species, Rubisco is down-regulated during the winter months. Describe the role of Rubisco in photosynthesis.
Arabidopsis is a small flowering plant in the mustard family (Brassicaceae) that is widely used in basic research. It has a short life cycle, flowers quickly producing a large number of seeds and is easy to cultivate. It forms a circle of leaves known as a rosette that lies close to the soil. Flowers form at the end of short stems.
A study was carried out of differences in development between Arabidopsis plants grown in long days (16 hours light, 8 hours dark) or short days (8 hours light, 16 hours dark). The sixth leaf (L6) to emerge in the rosette of each plant was used in all investigations.
New leaves are initiated by the meristem and go through four stages as they develop.
• Stage 1 (S1) – rapid cell division
• Stage 2 (S2) – cell division has ceased, cell expansion continues
• Stage 3 (S3) – decreasing cell expansion rate
• Stage 4 (S4) – leaf growth complete
The start of each stage of leaf development for plants grown in long days and short days is shown above the first graph.
Leaves were removed from Arabidopsis plants that had been grown in long day and short day conditions and the concentration of starch within them was measured. This was done both at the end of the day (D) and at the end of the night (N) in each of the four stages of development (S1, S2, S3, S4).
To account for the observed phenotypic and metabolic differences, researchers analysed mRNA transcript data. They found certain transcripts over-represented in Arabidopsis plants grown in long days (dark grey) compared with the amount expected due to chance.
Other types of transcripts were over-represented in Arabidopsis plants grown in short days (light grey).
Calculate the difference (in mm2) in the mean leaf area of L6 at the start of stage 4 between the leaves of plants grown in long days and short days.
Distinguish between plants grown in long days and short days in the timing of the four stages of leaf development.
Distinguish between plants grown in long days and short days in the mean number of leaves per rosette during the experimental period.
Discuss the evidence provided in the bar chart for the hypothesis that plant leaves use up starch reserves for cell respiration during the night.
For each of the stages, identify whether the starch concentration at the end of the day is higher in the leaves grown in long day or short day conditions.
Suggest reasons for the difference in end of day starch concentrations in stage 2 (S2) for the plants grown in long days and short days.
Using the data in the bar chart, discuss the evidence for Arabidopsis plants adapting to different daylight regimes by changing the pattern of gene expression.
Using all relevant data in this question, deduce with reasons whether Arabidopsis is a long day plant or a short day plant in terms of flowering.
Outline how greenhouse gases interact with radiation and contribute to global warming.
Outline how plants make use of the different wavelengths of light.
Explain how organic compounds are transported within plants.
A broad bean is the seed of a species, Vicia faba, in the Fabaceae, a family of flowering plants. This family contains many species that are used as sources of food.
On the diagram, label the testa and the radicle.
An experiment was done to test the hypothesis that temperature affects the rate of germination of the broad bean. Outline two factors apart from temperature that should be controlled in this experiment.
State the genus of the broad bean.
Broad beans are rich in starch and cellulose. Compare and contrast the structure of starch and cellulose.
Once the germinated bean grows above the ground, state the process used by the bean in the production of starch.
Plants have developed efficient methods for transport and for synthesis of foods.
Outline how the properties of water make it an ideal transport medium in plants.
Distinguish between the xylem and phloem of plants.
Explain how the light-independent reactions of photosynthesis rely on the light-dependent reactions.
Most of the surface of the Earth is covered with a wide diversity of ecosystems. Outline two general characteristics of all ecosystems.
Vascular plants can be found in a wide variety of ecosystems.
Outline active transport in phloem tissue.
Vascular plants can be found in a wide variety of ecosystems.
Explain how a plant replaces the water it loses in transpiration.
Compare and contrast the mode of nutrition of detritivores and saprotrophs.
Explain how some plant species are able to respond to changes in their abiotic environment and flower at a precise time of the year.
Outline the extension of the stem in plants.
Every cell is surrounded by a cell surface membrane which regulates the movement of materials into and out of the cell.
Discuss alternative models of membrane structure including evidence for or against each model.
Outline the process used to load organic compounds into phloem sieve tubes.
Extensive areas of the rainforest in Cambodia are being cleared for large-scale rubber plantations. Distinguish between the sustainability of natural ecosystems such as rainforests and the sustainability of areas used for agriculture.
Describe the roles of the shoot apex in the growth of plants.
Research suggests that many living plant species are polyploid. Explain how polyploidy occurs and, using a named example, how polyploidy can lead to speciation.
Auxin can be used to promote the development of roots from stem and leafy cuttings in some plants. In a study into the distribution of auxin in the development of these roots, scientists measured the amount of auxin in different leaves of a shoot tip of Petunia hybrida.
The figure indicates the numbering of leaves on the shoot, from L1 as the youngest and smallest to L6 as the largest and oldest leaf. The developmental stage of L5 and L6 was very similar, so L5 was not analysed. The stem base is the lowest part of the cutting where roots may form.
The graph shows the auxin concentration in the different leaves.
N-1-naphthylphthalamic acid (NPA) is an inhibitor used to block auxin transport. NPA was sprayed onto the leaves of a set of cuttings for 14 days. Development of the roots in control (non-treated) and NPA-treated cuttings was measured 14 days after taking the cuttings.
The table shows the influence of NPA on rooting.
The scientists also measured the changes in auxin concentration in L6 and the stem base during the early period of root formation. They recorded the concentration in the control and NPA-treated cuttings for 24 hours after taking the cuttings.
The scientists wanted to know whether the accumulation of auxin over time in the stem base of the controls affected expression of the GH3 gene, known to have a role in growth regulation in different plants. The technique that was used to quantify the level of transcription of the GH3 gene was Northern blotting. In this procedure the darkness
and thickness of the band is an indicator of the level of transcription of a particular gene. The image shows the result of the Northern blot from 2 hours to 24 hours after cutting.
Calculate the difference in the concentration of auxin found in L1 and L6.
. . . . . . . . . . . . . . . . . . pmol g–1
Identify the relationship between the concentration of auxin and the age of the different leaves.
Analyse the effect of NPA on the formation of roots.
Compare and contrast the changes in auxin concentration in the stem base over time for the control and NPA-treated cuttings.
Deduce the effect of NPA on auxin transport between L6 and the stem base.
Based on all the data presented and your knowledge of auxin, discuss the pattern of auxin production and distribution in the leaves and the possible relationship to root formation in leafy cuttings of Petunia hybrida.
State the name of the molecule which is produced by transcription.
Compare the pattern of GH3 transcription with the pattern of auxin concentration in the stem base control cuttings. You may use the table provided to help you to record the patterns before you compare them. (Please note: a simple
comparison in the table will not gain marks)
The scientists concluded that auxin activates the transcription of the GH3 gene. Using the information on the auxin concentration in the stem base in the graph and the Northern blot, evaluate whether this conclusion is supported.