1. Describe the difference between pluripotent and unipotent cells.
Answer
Pluripotent cells are found in embryos and can divide an unlimited number of times, and specialise into any type of cell. Unipotent cells are found in mature mammals and can divide only to form cells of the same type.
2. What proteins are involved in regulating transcription ?
Answer
Transcription factors.
3. What is meant by "epigenetics" ?
Answer
Heritable changes in gene function without changes to the DNA base sequence.
4. Crop yield in many parts of the world is damaged by pests. One major pest is a type of nematode (roundworm) that lives in the soil and feeds on the roots of crop plants. It also causes the plants to become infected with bacterial and fungal diseases. Suggest how nematode damage to plant roots could cause the plants to become infected by bacteria and fungi.
Answer
Nematode damage to plant roots can break down cell walls, membranes, or the protective waxy covering, making it easier for bacteria and fungi to enter and infect the tissues.
5. Scientists have been investigating control of nematodes using RNA interference (RNAi). They hope to use RNAi to control gene expression in the nematodes in order to kill them. Scientists investigated how plants could be stimulated to produce small interfering RNA (siRNA), and therefore the resistance to nematodes, using organic compounds introduced to the soil; these are called biostimulants. Once the plant cell is stimulated, double stranded RNA (dsRNA) was expressed within the cell. One of the strands of dsRNA is then removed using an enzyme called a dicer. Once single stranded, it is referred to as small interfering RNA (siRNA). siRNA is then associated with a series of proteins to form an RNA-induced silencing complex. This process is shown in the figure below. Explain how siRNA is able to silence a gene.
Answer
siRNA is single stranded and complementary to the target mRNA. It forms hydrogen bonds with the mRNA through complementary base pairing. The enzymes associated with siRNA then hydrolyse the mRNA backbone. As a result, the fragments of mRNA can no longer be translated, and the gene is silenced.
6. The nematodes feed on the plant root cells. In doing so, the nematode consumes the dsRNA, which enters the nematode gut, triggering RNAi against their own genes, thus reducing their ability to feed, grow and ultimately survive. An investigation was carried out to see how different biostimulants affect a plant's ability to be resistant to nematodes by the production of different siRNA. Explain why a control was used in this investigation.
Answer
A control was used to allow for comparison. It shows the specific effect that the biostimulants had on the plants' ability to resist nematodes through siRNA production.
7. Using information from the table below describe the effect biostimulants have on plant survival and growth.
Answer
All the biostimulants reduce nematode invasion, increasing plants' ability to survive and grow. Biostimulants 2 and 4 have the greatest effect, while biostimulants 1 and 3 have less effect.
8. The figure below compares siRNA synthesis in the presence of different biostimulants as a ratio with the control.
The figure below shows the silencing efficiency of each biostimulant when this was introduced to the seed, or the medium in which the plant was grown.
Although the reduction of nematode infection was similar for biostimulants 1 and 3, the silencing efficiency of these two was very different. Suggest why.
Answer
Biostimulant 3 may cause a different type of siRNA to form. The siRNA induced by biostimulant 3 may target the mRNA of a gene that plays a more vital role in nematode growth, resulting in a stronger silencing effect.
9. One student looking at the results concluded that using biostimulant 3 was the most effective in reducing the effect nematodes have on plant growth. Evaluate this claim.
Answer
When introducing the biostimulant 3 to the seeds, yes it has the greatest efficacy at silencing the genes. However when looking at biostimulants introduced to the soil, it had the least effect on silencing. So only valid when introduced to seed.
10. One way to control these nematodes is to use pesticides. However, the use of pesticides can have negative effects on the ecosystem. Suggest some possible negative effects.
Answer
The use of pesticides can kill non‑target species, including useful organisms. They may also cause bioaccumulation or leave harmful residues in crops. In addition, nematodes can develop resistance to pesticides over time.