HSC Biology Marathon 2017 (1 Viewer)

[ShootingDuck]

How does that work? How come if the walls of the Xylem are thinner, they collapse? Also, the transpiration cohesion adhesion theory is when water molecules from the leaves evaporate in which the cohesion force between the molecules will act like a train, dragging the liquid water molecule up from the plants body to the leaves to replace the evaporated water molecule. The adhesion force between the molecule and the wall (i guess) will just allow the water to stay in place without it falling back down to the roots or whatever.

I think its the fact that if they're thinner, it wouldn't be able to support it's own weight, causing the xylem tube to "collapse." Also if the xylem tubes "collapse," it could block itself off. Therefore no or limited amount of water can go through its own xylem tubes, causing the plant to effectively wilt rather than only affecting the adhesion forces between the water molecules and the wall.

 

[pikachu975]

Quarantine measures exist to prevent the spread of disease into Australia

Justify TWO measures that you would expect AQIS (the Australian Quarantine and Inspection Service) to take in response to the recent swine flu outbreak in Mexico and North America (4 marks)

- The AQIS could isolate individuals from Mexico and North America coming into the country for a certain incubation period to ensure they are free from swine flu. This would prevent its spread into Australia as it would be a good precautionary measure for any Mexican or North American, where the outbreak came from.
- The AQIS could also check organic material, animals, and plants to check if the swine flu has transmitted to other things besides humans. If found to be infected, they would be isolated through quarantine at the borders until the disease has subsided, thereby preventing its spread.

 

[budgetjackiechan]

Analyse the effect of high mutation rates of viruses on human health as well as the survival of the virus. 7 marks

 

[LADislav]

Analyse the effect of high mutation rates of viruses on human health as well as the survival of the virus. 7 marks

This question is basically 2005 HSC Q27 slightly re-worded and without the background information given about the influenza virus. Anyway, I'll take a shot at answering the HSC question:

27. The influenza virus has a high rate of mutation which can lead to changes of the viral
surface antigens that contain protein. Analyse the impact of high mutation rates for this virus and the implications for
human health (8 marks).
- A viral pathogen such as the influenza virus is engulfed by a macrophage and it’s surface antigen is transported to a lymph node to be presented to a helper T cell. Here, the helper T cell ‘sensitises’ B cells to the pathogen. The B cells then clone and differentiate into plasma B cells and memory B cells. The plasma B cells manufacture antibodies which are specific to the virus, which then bind to the viral antigens and neutralise them, allowing cytotoxic T cells to directly destroy them. The role of the memory B cells is to respond rapidly in the event of a second infection by the same virus.
- If this happens, they clone rapidly to make plasma B cells and the immune response (secondary response) is faster and of greater magnitude than the primary (first) response. This will generally prevent the host from suffering from the disease a second time.
- However, with rapidly mutating viruses such as the influenza virus, the viral surface antigens would have changed to the point where the memory B cells don’t recognise it and don’t trigger the secondary immune response. Therefore the host experiences the virus’s symptoms once again while the mutated viral pathogen survives until the host's immune system initiates another primary response against it.
- In today’s society most countries have a seasonal-flu vaccine, however since the influenza virus constantly mutates a new version has to be developed each year or so, an expensive process which can takes months. This time lag could be potentially deadly to overall human health if there were ever to be a severe influenza pandemic in which the virus spread rapidly around the world, since humans have little to no immune protection against new flu strains.