HSC Biology Marathon 2015 (2 Viewers)

[Flop21]

Kidney disease is the 8th leading cause of death in the United States. An estimated 31 million people in the United States (10% of the population) have chronic kidney disease (CKD). CKD is more common among women, but men with CKD are 50% more likely than women to progress to kidney failure (also called end-stage renal disease or ESRD).

Renal dialysis or kidney transplants can be used to treat CKD. Discuss issues associated with both treatments. (5 marks)

Renal dialysis involves cleaning the blood by passing it through a semi-permeable tube, surrounded by dialysis solution, so wastes diffuse out. This process needs to be done 3 times a week, 4-5 hours at a time. It can be dangerous due to the anti-clotting agent added to the clean blood, risk of infection and damage to blood cells passing through the tubing. Also, nutrients cannot be selectively reabsorbed, but are lost, as well as water.

A kidney transplant also has possible issues. When an organ transplant occurs, the body recognises the tissue as foreign and thus attacks the organ. Immunosupressive drugs are therefore needed to suppress the immune system, however this makes the patient more vulnerable to complications from pathogens, such as the common cold. Even so, the body still may reject the organ and destroy it; a deadly complication. The organ therefore needs to be closely matched as possible to the receiver's MHCI molecules(is this correct? otherwise what would I say here). Additionally, there may not be a kidney available and long waiting lists, especially due to the necessity for a close matched organ. The risks of surgery are also a possible issue, such as infection, complications, and blood loss.

 

[Loudvicuna]

Explain why DNA replication needs to be exact. 3 MARKS

DNA replication occurs in both the processes of mitosis and meiosis. DNA replication must be exact to prevent mutations which have the potential to change cell activity and be potentially harmful to the individual. DNA replication is subject to addition, deletion and subtraction whereby the genetic nucleotides can be incorrectly placed. This results in the formation of a new amino acid sequence, thus polypeptides and proteins which are responsible for the expression of traits and essential for correct body functioning. DNA replication errors that occur in meiosis are cause unexpected traits in the offspring.

 

[rand_althor]

Explain why DNA replication needs to be exact. 3 MARKS

For optimal cell functioning. If there is an incorrect order of bases: different mRNA strand produced in transcription -> different amino acids and polypeptides produced in translation -> potentially impaired cell activity.

Not sure if that is what the question was asking for.

 

[Loudvicuna]

Contrast the movement of materials in the phloem tissue of plants with the movement of blood in the vascular system of mammals. (4 marks)

Phloem tubes are responsible for the movement of sugar around the plant and can be explained through the source to sink theory. The sugars are produced in the source companion cell and diffuse into the lower gradient phloem tubule. The water in the xylem that runs alongside the phloem diffuses across through osmosis and causes a pressure build-up that caused the sugar to move toward the sink. The nutrients are actively transported into the sink where they are stored or used and the water returns back to the xylem through osmosis. Similarly, the movement of blood in mammals utilises pressure. The heart pumps blood into the aorta which is carried around the body into thin capillaries which transport blood to individual cells around the body whereby nutrients diffuse across to sustain cellular processes. The capillaries reconnect with veins that carry the blood back to the heart to be re-pumped.

 

[rand_althor]

Describe the method employed and results obtained for an investigation you conducted that demonstrated the effect of the environment on the phenotype of an organism (5)

1. 20 cuttings of length 10cm were made from a Germanium plant.
2. Each cutting was embedded into a pot with standard potting mix one third of the way deep.
3. The cuttings were randomly allocated into two groups of 10.
4. The first group received water everyday, while the second group received no water.
5. After 3 weeks, the height of each cutting was measured and recorded.

On average, the plants which were watered everyday had a greater height than those that were not. This difference can be attributed to the varying levels of water the plants received.

 

[Loudvicuna]

Renal dialysis involves cleaning the blood by passing it through a semi-permeable tube, surrounded by dialysis solution, so wastes diffuse out. This process needs to be done 3 times a week, 4-5 hours at a time. It can be dangerous due to the anti-clotting agent added to the clean blood, risk of infection and damage to blood cells passing through the tubing. Also, nutrients cannot be selectively reabsorbed, but are lost, as well as water.

A kidney transplant also has possible issues. When an organ transplant occurs, the body recognises the tissue as foreign and thus attacks the organ. Immunosupressive drugs are therefore needed to suppress the immune system, however this makes the patient more vulnerable to complications from pathogens, such as the common cold. Even so, the body still may reject the organ and destroy it; a deadly complication. The organ therefore needs to be closely matched as possible to the receiver's MHCI molecules(is this correct? otherwise what would I say here). Additionally, there may not be a kidney available and long waiting lists, especially due to the necessity for a close matched organ. The risks of surgery are also a possible issue, such as infection, complications, and blood loss.

Pretty sure thats right but self-antigens can be used

 

[Flop21]

Contrast the movement of materials in the phloem tissue of plants with the movement of blood in the vascular system of mammals. (4 marks)

The movement of materials in the phloem tissue of plants is described by the pressure-flow theory. The products of photosynthesis (glucose) are actively transported from the source into the phloem. Water also moves into the phloem tissue osmotically creating pressure at the source, thus pushing the glucose towards the sink, where it is then actively removed from the phloem and unloaded into the sink.

Blood is moved throughout the vascular system of mammals by the heart which pumps the blood. The heart creates pressure on the blood, forcing it at high pressures through the arteries oxygenated. The pressure is lower, the further the blood has to travel and thus the veins which carry deoxygenated blood have one-way valves to prevent blood flowing in the wrong direction. Materials and nutrients in the blood are mostly dissolved in the plasma.

 

[rand_althor]

Phloem tubes are responsible for the movement of sugar around the plant and can be explained through the source to sink theory. The sugars are produced in the source companion cell and diffuse into the lower gradient phloem tubule. The water in the xylem that runs alongside the phloem diffuses across through osmosis and causes a pressure build-up that caused the sugar to move toward the sink. The nutrients diffuse into the sink where they are stored or used and the water returns back to the xylem through osmosis. Similarly, the movement of blood in mammals utilises pressure. The heart pumps blood into the aorta which is carried around the body into thin capillaries which transport blood to individual cells around the body whereby nutrients diffuse across to sustain cellular processes. The capillaries reconnect with veins that carry the blood back to the heart to be re-pumped.

Not enough differences. You could also mention:
- Blood flows in one direction in arteries, capillaries and veins, whereas phloem sap direction can vary
- Blood moves in different vessels (arteries, capillaries, veins) whereas phloem moves in sieve tubes
- Phloem carries products of photosynthesis whereas blood moves many substances such as carbon dioxide, oxygen etc.

 

[Flop21]

Phloem tubes are responsible for the movement of sugar around the plant and can be explained through the source to sink theory. The sugars are produced in the source companion cell and diffuse into the lower gradient phloem tubule. The water in the xylem that runs alongside the phloem diffuses across through osmosis and causes a pressure build-up that caused the sugar to move toward the sink. The nutrients diffuse into the sink where they are stored or used and the water returns back to the xylem through osmosis. Similarly, the movement of blood in mammals utilises pressure. The heart pumps blood into the aorta which is carried around the body into thin capillaries which transport blood to individual cells around the body whereby nutrients diffuse across to sustain cellular processes. The capillaries reconnect with veins that carry the blood back to the heart to be re-pumped.

I was going to say 'similarly' as well. But the question said "contrast". So wouldn't we have to show the differences between these two things, rather than the similarities?

 

[Flop21]

Not enough differences. You could also mention:
- Blood flows in one direction in arteries, capillaries and veins, whereas phloem sap direction can vary
- Blood moves in different vessels (arteries, capillaries, veins) whereas phloem moves in sieve tubes
- Phloem carries products of photosynthesis whereas blood moves many substances such as carbon dioxide, oxygen etc.

Ahhh right. Good question

 

[Flop21]

Describe what each of these technologies measure (2 marks):

- pulse oximeter

- blood gas analyser

 

[Loudvicuna]

I was going to say 'similarly' as well. But the question said "contrast". So wouldn't we have to show the differences between these two things, rather than the similarities?

Yeah you're right, I thought the definition was something like compare

 

[rand_althor]

I was going to say 'similarly' as well. But the question said "contrast". So wouldn't we have to show the differences between these two things, rather than the similarities?

Yep that's correct. The sample answers had: "Movement of bloods relies on the pumping of the heart, while movement of phloem sap relies on differences in osmotic pressure".

 

[tfw english]

Describe what each of these technologies measure (2 marks):

- pulse oximeter

- blood gas analyser

The pulse oximeter uses two wavelengths of light, passed through a finger, to measure the absorption on one side. This can determine the saturation levels of haemoglobin and hence the oxygen levels

The Blood gas analyser needs only a sample of blood from an artery and can help with distinguishing between conditions with similar symptoms
It can determine the concentration of oxygen and carbon dioxide and the ph level in the blood

 

[Flop21]

btw add a question after you answer one


Identify the current theories of the transportation of materials in the xylem and phloem.

 

[tfw english]

With reference to a named example that you have studied, assess the benefits to society of hybridisation within a species. (4)

 

[rand_althor]

btw add a question after you answer one


Identify the current theories of the transportation of materials in the xylem and phloem.

Phloem - Source-path-sink theory
Xylem - Transpiration stream theory

 

[tfw english]

Pectinase is an enzyme which is used commercially in the production of fruit juice. It catalyses the breakdown of the cell walls of the fruit to both turn fruit pulp into juice and to make cloudy juice clear.

Outline a procedure you could follow to investigate the effect of pH on the activity
of pectinase. (6)

In your answer make sure you include:
 a hypothesis
 a list of equipment needed
 a step by step method
 one safety procedure
 the measures you should take to ensure that your results are valid and reliable

 

[Mr_Kap]

Help someone. Why is the answer C not A.

 

[tfw english]

Help someone. Why is the answer C not A.

Because ADH does not control the levels of salt in the blood. It only controls the concentration of salt through water retention. (Usually because of dehydration)
It makes collecting ducts more permeable so that water can be reabsorbed back into the blood and body tissues.

And when aldosterone is released, there is more sodium absorbed which leads to more water returning to the blood (in order to complement the salt and retain normal levels)

They work off each other