A level Biology: Post your doubts here!

[Saad (سعد)]

Thanx people bt the pro is check out mj/11 p21 the ms says that CO2 combines with Hb and carboxyhaemoglobin is formed! Please check it out and explain...thanx soo much and God bless you all!

Error in the Mark Scheme. They meant to write 'carbamino-haemoglobin'.

We should sue those Examiners... they deduct our marks when we get it wrong, but when they get it wrong, they're totally silent about it.

 

[Soldier313]

Error in the Mark Scheme. They meant to write 'carbamino-haemoglobin'.

We should sue those Examiners... they deduct our marks when we get it wrong, but when they get it wrong, they're totally silent about it.

Bro, are u a 100% sure it's an error in the ms????? I mean mayb just maybe there is some reason to them writing that, thanx fr ur help guys!

 

[Saad (سعد)]

Bro, are u a 100% sure it's an error in the ms????? I mean mayb just maybe there is some reason to them writing that, thanx fr ur help guys!

There's no other reason. 100%.

The only time carbon dioxide combines with haemoglobin to stimulate the haemoglobin to release oxygen is when it forms carbaminohaemoglobin, or the hydrogen atoms add to the haemoglobin to form haemoglobinic acid. Carboxyhaemglobin has no role here.

Don't worry, its an error. The Mark Scheme makers have been doing that a lot lately.

 

[Soldier313]

There's no other reason. 100%.

The only time carbon dioxide combines with haemoglobin to stimulate the haemoglobin to release oxygen is when it forms carbaminohaemoglobin, or the hydrogen atoms add to the haemoglobin to form haemoglobinic acid. Carboxyhaemglobin has no role here.

Don't worry, its an error. The Mark Scheme makers have been doing that a lot lately.

Owhkay tx a lot!) and yea so when exactly would the carboxyhaemoglobin play a role?

 

[user]

AsSalamoAlaikum Wr Wb!

Can someone give me the definition for ecosystem.
Here are the ms points.

community (of organisms) ;​

physical / abiotic, factors / environment ;​

ref to interaction between organisms ;​

ref to interaction between organisms and physical environment ;​

ref to ‘self-contained’ / delimited by some physical feature ;​

use of named example to illustrate one above point ;​

​

It’s Q:6 of Nov:2007 P2
9700_w07_qp_2.pdf

 

[Paparazzi478]

can anyone answer this question
Explain how sucrose in the phloem sap is moved from sieve tube elements in leaves to
cells in a sink, such as a root.
9700_w11_qp_21
oct/nov 11 question 5(c)

 

[Saad (سعد)]

Owhkay tx a lot!) and yea so when exactly would the carboxyhaemoglobin play a role?

Carboxyhaemoglobin is a damaging molecule. It is formed when we inhale carbon monoxide (usually in cigarette smoke). Carbon monoxide combines irreversibly with haemoglobin to form carboxyhaemoglobin; which reduces oxygen-carrying capacity of the blood, as haemoglobin's affinity for CO is 250 times more than that for O2. This means that inhaling even a 0.1% of CO could be potentially fatal if not immediately treated. CO can cause hypoxia due to limiting the supply of oxygen to respiring tissues.

AsSalamoAlaikum Wr Wb!

Can someone give me the definition for ecosystem.
Here are the ms points.

community (of organisms) ;​

physical / abiotic, factors / environment ;​

ref to interaction between organisms ;​

ref to interaction between organisms and physical environment ;​

ref to ‘self-contained’ / delimited by some physical feature ;​

use of named example to illustrate one above point ;​

​

It’s Q:6 of Nov:2007 P2
9700_w07_qp_2.pdf

An ecosystem consists of all the living organisms of all species (the community), and their non-living components such as their environment, that are found together in a defined, self-contained area and that interact with one another.

can anyone answer this question
Explain how sucrose in the phloem sap is moved from sieve tube elements in leaves to
cells in a sink, such as a root.
9700_w11_qp_21
oct/nov 11 question 5(c)

In the phloem sap, in the sieve-tube elements in the leaves, there's a less negative water potential due to the presence of assimilates. Water enters via osmosis from surrounding tissue, which results in an increase in the hydrostatic pressure. At the sink, sucrose is unloaded, hence water potential of surrounding tissue is lowered. Water moves out, resulting in a decrease in the hydrostatic pressure. The pressure gradient results in a mass flow of sucrose and other substances towards the sink.

 

[Soldier313]

Carboxyhaemoglobin is a damaging molecule. It is formed when we inhale carbon monoxide (usually in cigarette smoke). Carbon monoxide combines irreversibly with haemoglobin to form carboxyhaemoglobin; which reduces oxygen-carrying capacity of the blood, as haemoglobin's affinity for CO is 250 times more than that for O2. This means that inhaling even a 0.1% of CO could be potentially fatal if not immediately treated. CO can cause hypoxia due to limiting the supply of oxygen to respiring tissues.



An ecosystem consists of all the living organisms of all species (the community), and their non-living components such as their environment, that are found together in a defined, self-contained area and that interact with one another.



In the phloem sap, in the sieve-tube elements in the leaves, there's a less negative water potential due to the presence of assimilates. Water enters via osmosis from surrounding tissue, which results in an increase in the hydrostatic pressure. At the sink, sucrose is unloaded, hence water potential of surrounding tissue is lowered. Water moves out, resulting in a decrease in the hydrostatic pressure. The pressure gradient results in a mass flow of sucrose and other substances towards the sink.

tx a lot

 

[Soldier313]

Are the B and T lymphocytes always activated together....or is there a particular time/situation when only either the B cells or the T cells are activated?????

 

[geek101]

Are the B and T lymphocytes always activated together....or is there a particular time/situation when only either the B cells or the T cells are activated?????

According to what i understand the T cells release cytokines which activate B cells. so T cells are activated first when the phagocyte displays the non self antigens.

 

[Paparazzi478]

how to calculate tidal volume?

 

[Soldier313]

According to what i understand the T cells release cytokines which activate B cells. so T cells are activated first when the phagocyte displays the non self antigens.

owhkay but mj/11 qn 6a it says B or T cells activated! i mean i thought that it's always the case that the T cells must be there for B cells to function so how can they say 'or'??
http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_s11_qp_21.pdf
http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_s11_ms_21.pdf

???

 

[Soldier313]

http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_s11_qp_22.pdf
qn 1 can someone please identify a cell undergoing telophase? tx

 

[Soldier313]

http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_s11_qp_22.pdf
qn 1 can someone please identify a cell undergoing telophase? tx

 

[geek101]

owhkay but mj/11 qn 6a it says B or T cells activated! i mean i thought that it's always the case that the T cells must be there for B cells to function so how can they say 'or'??
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_qp_21.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_ms_21.pdf

???

in this question you are not going into the deep details of the immune response, its outlining the method, so we know that both B and T cells are activated...you can mention the B cells here since they are the ones which divide to produce the antibodies, so it will be understood that they were first activated by T cells, you dont need to, altough you may...mention the exact detailed steps, its 3 marks....so just outline the process. hope this helps. good luck for tomorrow!

 

[user]

AsSalamoAlaikum wr wb!

What is antigenic concealment?

 

[Soldier313]

in this question you are not going into the deep details of the immune response, its outlining the method, so we know that both B and T cells are activated...you can mention the B cells here since they are the ones which divide to produce the antibodies, so it will be understood that they were first activated by T cells, you dont need to, altough you may...mention the exact detailed steps, its 3 marks....so just outline the process. hope this helps. good luck for tomorrow!

tx a lot....g'luck to u too

 

[Soldier313]

AsSalamoAlaikum wr wb!

What is antigenic concealment?

i think this is the ability of the antigens to hide themselves/conceal themselves from the body's immune system....for eg the vibrio cholerae which is the bacteria causing cholera, survives in the small intestine, a place where it is kind of hard for the immune system to access, hence allowing it to thrive better.
Hope this helps!

 

[Soldier313]

can someone please provide a detailed explanation which we can write for: Describe the pathway taken by water as it passes from the root hair cells into the cells which are specialized for transport of water and mineral ions(xylem vessels) and then from the xylem vessels out of the plant (by transpiration). Btw these are two qns combined. The marking scheme gives very short points...so please elaborate....tx a lot! and please answer asap as my xam is just in a few hours....tx agan.....God bless.

 

[eyamwir]

can anyone explain to me in a simplified version the action of B and T lymphocyte thank you. please do hurry