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A level Biology: Post your doubts here!

Farhad221

Farhad221

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qwertypoiu said:
We want chromosomes that appear as two chromatids:
Interphase - nope, DNA appears as loose chromatin form, not chromosomes nor chromatids
Prophase - yes! The DNA material has condensed to appear as two chromatids on every chromosome
Metaphase - yes! At Metaphase the chromosomes just moved towards the equator of the cell, but they all still appear with two chromatids
Anaphase - nope. The chromosomes have been split by centrioles through their microtubule spindle fibers. They do not appear with two chromatids, rather each chromosome has one chromatid only.
Telophase - nope. They have reached the ends and nuclear envelope is forming, but each chromosome has still one chromatid.

Figure the math part out yourself if you can't I'll do it insha Allah :)
Click to expand...
Got it thanks
 
Farhad221

Farhad221

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Tasneem_m98 said:
http://onlineexamhelp.com/wp-content/uploads/2013/10/9700_s13_qp_11.pdf number 39
isnt nitrogen fixation an anaerobic process??
Click to expand...
As you can see it is aerobic and anaerobic depending on the bacterium used, however as you see the question says soil conditions so we consider Free living bacteria in soils not the symbiotic ones hence it is an aerobic process.
All the nitrogen-fixing organisms are prokaryotes (bacteria). Some of them live independently of other organisms - the so-called free-living nitrogen-fixing bacteria. Others live in intimate symbiotic associations with plants or with other organisms (e.g. protozoa). Examples are shown in the table below.

Examples of nitrogen-fixing bacteria (* denotes a photosynthetic bacterium)

Free living

Symbiotic with plants

Aerobic

Anaerobic (see Winogradsky column for details)

Legumes

Other plants

Azotobacter
Beijerinckia
Klebsiella (some)Cyanobacteria (some)*

Clostridium (some)
Desulfovibrio
Purple sulphur bacteria*
Purple non-sulphur bacteria*
Green sulphur bacteria*

Rhizobium

Frankia
Azospirillum
 
qwertypoiu

qwertypoiu

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Farhad221 said:
As you can see it is aerobic and anaerobic depending on the bacterium used, however as you see the question says soil conditions so we consider Free living bacteria in soils not the symbiotic ones hence it is an aerobic process.
All the nitrogen-fixing organisms are prokaryotes (bacteria). Some of them live independently of other organisms - the so-called free-living nitrogen-fixing bacteria. Others live in intimate symbiotic associations with plants or with other organisms (e.g. protozoa). Examples are shown in the table below.

Examples of nitrogen-fixing bacteria (* denotes a photosynthetic bacterium)

Free living

Symbiotic with plants

Aerobic

Anaerobic (see Winogradsky column for details)

Legumes

Other plants

Azotobacter
Beijerinckia
Klebsiella (some)Cyanobacteria (some)*

Clostridium (some)
Desulfovibrio
Purple sulphur bacteria*
Purple non-sulphur bacteria*
Green sulphur bacteria*

Rhizobium

Frankia
Azospirillum
Click to expand...

I don't get the table part... It's not clear. If you got this from the internet can you please tell me the link so I can see the table?
Thanks.
 
T

Tasneem_m98

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Farhad221 said:
As you can see it is aerobic and anaerobic depending on the bacterium used, however as you see the question says soil conditions so we consider Free living bacteria in soils not the symbiotic ones hence it is an aerobic process.
All the nitrogen-fixing organisms are prokaryotes (bacteria). Some of them live independently of other organisms - the so-called free-living nitrogen-fixing bacteria. Others live in intimate symbiotic associations with plants or with other organisms (e.g. protozoa). Examples are shown in the table below.

Examples of nitrogen-fixing bacteria (* denotes a photosynthetic bacterium)

Free living

Symbiotic with plants

Aerobic

Anaerobic (see Winogradsky column for details)

Legumes

Other plants

Azotobacter
Beijerinckia
Klebsiella (some)Cyanobacteria (some)*

Clostridium (some)
Desulfovibrio
Purple sulphur bacteria*
Purple non-sulphur bacteria*
Green sulphur bacteria*

Rhizobium

Frankia
Azospirillum
Click to expand...


alright thank you so much!
 
T

Tasneem_m98

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A molecule can enter a cell by two different passive processes. Which process would increase the rate at which this molecule enters the cells?
A. diffusion
B endocytosis
C facilitated diffusion
D osmosis


the answer is C but I dont understand why isnt it A??
this is O/N 2012 paper 11 question number 17
 
Farhad221

Farhad221

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Carrier proteins increase the rate of diffusion by allowing more solute to enter the cell. Hence it is C.
Tasneem_m98 said:
A molecule can enter a cell by two different passive processes. Which process would increase the rate at which this molecule enters the cells?
A. diffusion
B endocytosis
C facilitated diffusion
D osmosis


the answer is C but I dont understand why isnt it A??
this is O/N 2012 paper 11 question number 17
Click to expand...
 
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