Hi guys I have some questions

1) If stomata are closed on hot dry days where does the CO2 come from for C3 or C4 plants?

2) why does photorespiration exist at all? I understand what occurs, it releases CO2 in the plant but why? what good does that do? (did I just answer question number 1? lol, but if its a hot dry day, there wouldn't be much H20 to turn into O2 in photorespiration anyway right?)

3)C3 plants are more ancient, a hundred million years ago there was more CO2 in the atmosphere, so why have a O2 fixing pathway at all? I would think that as O2 levels rise over millions of years photorespiration might increase, but instead C4 plants have the advantage because they figured a way to use PEP & PEP carboxylaze to only fix CO2 but on a hot day when stomata are closed, and what little H2O is being converted to O2 in the light reactions, wouldn't it be advantageous for C4 plants to use the O2 from the water to make CO2 for the calvin benson cycle? even when stomata are open, the air around a leaf only has .036% CO2 why hasn't photorespiration increased to provide more CO2 for the CB cycle? and if it isn't useful the way I mentioned then why does it exist at all?

4)at the end of meiosis I (telophase I) the division is still referred to as cytokinesis? I ask because my book has a picture and a slide photo but describes the end as "the cell divides" when the picture and photo are depicting the chromosomes on opposite poles with a line down the middle of the old cell but STILL fused, even in the picture of interkineses they are not fully seperated, was this type of drawing shown to save space? or was it worded wrong? I know that Mitosis and cytokineses are considered seperate events at the end of the M phase of the cell cycle but that wasn't made clear about meiosis.

5) so yellow round pea X green wrinkled pea = yellow wrinkled pea is an example of recombinant phenotypes, could you also say that having your moms eyes and having your dads hair color is an example of recombinant phenotype? if not how can you use people for this example?

6)Law of Independent Assortment is true for alleles of different genes FAR apart right? if they are close they are linked and assort together right (I might be waaaay off)?

7)my book says with 23 chromosome pairs that 2^23 possible combinations can be produced so all the chromosomes are homologous? (I wouldn't think so) if not why 2^23 different combination's?

8)my book says a linkage group is the full set of loci on a given chromosome, the number of linkage groups in a species equals the number of homologous chromosome pairs, that doesn't make sense does it? if there are 23 pairs shouldn't there be 46 linkage groups?

Hi guys I have some questions

1) If stomata are closed on hot dry days where does the CO2 come from for C3 or C4 plants?

2) why does photorespiration exist at all? I understand what occurs, it releases CO2 in the plant but why? what good does that do? (did I just answer question number 1? lol, but if its a hot dry day, there wouldn't be much H20 to turn into O2 in photorespiration anyway right?)

3)C3 plants are more ancient, a hundred million years ago there was more CO2 in the atmosphere, so why have a O2 fixing pathway at all? I would think that as O2 levels rise over millions of years photorespiration might increase, but instead C4 plants have the advantage because they figured a way to use PEP & PEP carboxylaze to only fix CO2 but on a hot day when stomata are closed, and what little H2O is being converted to O2 in the light reactions, wouldn't it be advantageous for C4 plants to use the O2 from the water to make CO2 for the calvin benson cycle? even when stomata are open, the air around a leaf only has .036% CO2 why hasn't photorespiration increased to provide more CO2 for the CB cycle? and if it isn't useful the way I mentioned then why does it exist at all?

4)at the end of meiosis I (telophase I) the division is still referred to as cytokinesis? I ask because my book has a picture and a slide photo but describes the end as "the cell divides" when the picture and photo are depicting the chromosomes on opposite poles with a line down the middle of the old cell but STILL fused, even in the picture of interkineses they are not fully seperated, was this type of drawing shown to save space? or was it worded wrong? I know that Mitosis and cytokineses are considered seperate events at the end of the M phase of the cell cycle but that wasn't made clear about meiosis.

5) so yellow round pea X green wrinkled pea = yellow wrinkled pea is an example of recombinant phenotypes, could you also say that having your moms eyes and having your dads hair color is an example of recombinant phenotype? if not how can you use people for this example?

6)Law of Independent Assortment is true for alleles of different genes FAR apart right? if they are close they are linked and assort together right (I might be waaaay off)?

7)my book says with 23 chromosome pairs that 2^23 possible combinations can be produced so all the chromosomes are homologous? (I wouldn't think so) if not why 2^23 different combination's?

8)my book says a linkage group is the full set of loci on a given chromosome, the number of linkage groups in a species equals the number of homologous chromosome pairs, that doesn't make sense does it? if there are 23 pairs shouldn't there be 46 linkage groups?

1-the calvin cycle is just haulted when stomata are closed (during high heat/wind/arid). light rxn are taking place producing ATP and NADPH (C4 plants still take up CO2, they just do it night)

2-rubisco, remember can act as a carboxilase and an oxygenase. when high levels or O2 are present (from the light rxn's - when stomata typicaly are closed) then it will take the oxygen and form intermediates that can be used during respiration. now when CO2 levels are higher than that of O2 (when stomata are open usually) rubisco will remove CO2 and start the calvin cycle.

3-see response to #2 ; Re: bold part above - the relative concentrations of O2 and CO2 are much closer in dissolved fluids inside the mesophyll where photorespiration is actually taking place

4-telophase of mitosis or meiosis I/II and cytokinesis typically overlap. there is complete cell division between MI and MII (as with everything in biology, there are exceptions, but dont worry about those :) )

5- technically - yes. eye color is however controlled by regulation of about 3 different genes - but since you're asking about phenotypes, i would have to say yes to your question

6-law of ind assort just says that when a cell (somatic cell Aa) undergoes meiosis, the different alleles for said gene (A and a) will be separated into individual gametes (gamete A and gamete a). linked genes makes reference to multiple alleles of different genes. Law of Ind assort is referring to only 1 gene and its respected alleles

7- when asked about how many combinations of gametes one can produce via meiosis (without crossing over!!!) just use 2^n. the "n" represents the haploid number (for us human folk, we have 46 chromosomes so our haploid # is 23). just memorize that (to avoid getting into the math associated with it)

8- "a full set of loci" meaning the ones on homologous chromosome from mom + homologous chromosome from dad. so for us, that comes to 23 :)


i hope this helps ya man:cool:

thanks man, helped a lot.

Hi guys I have some questions

1) If stomata are closed on hot dry days where does the CO2 come from for C3 or C4 plants?
C3 and C4 both have their stomata open in the morning only; however, they close them in hot dry days. C4 plants have already fixed Co2 in the form of oxaloacetate; therefore, they can breakdown oxaloacetate into PEP and CO2 to continue photosynthesis even when their stomata are closed. C3 plants simply decrease their photosynthesis rate due to lack of CO2 caused by closed stomata.


2) why does photorespiration exist at all? I understand what occurs, it releases CO2 in the plant but why? what good does that do? (did I just answer question number 1? lol, but if its a hot dry day, there wouldn't be much H20 to turn into O2 in photorespiration anyway right?)
It's has various roles in plant metabolism, and not all of them are pretty well understood (check wikipedia if you are interested). I remember being so curious about it when I used to study the plant metabolism.


3)C3 plants are more ancient, a hundred million years ago there was more CO2 in the atmosphere, so why have a O2 fixing pathway at all? I would think that as O2 levels rise over millions of years photorespiration might increase, but instead C4 plants have the advantage because they figured a way to use PEP & PEP carboxylaze to only fix CO2 but on a hot day when stomata are closed, and what little H2O is being converted to O2 in the light reactions, wouldn't it be advantageous for C4 plants to use the O2 from the water to make CO2 for the calvin benson cycle? even when stomata are open, the air around a leaf only has .036% CO2 why hasn't photorespiration increased to provide more CO2 for the CB cycle? and if it isn't useful the way I mentioned then why does it exist at all?
Look at it this way: The photorespiration is itself disturbing the photosynthesis reaction since it is stealing the ribulose bisphosphate source of the Calvin cycle by reacting it with O2. It makes some small amount of CO2 at the end, but then that amount of CO2 is very small compared to the CO2 in atmorsphere, and does not hinder photorespiration from occuring. Therefore, ribulose bisphosphate continues to react with O2, same story.

4)at the end of meiosis I (telophase I) the division is still referred to as cytokinesis? I ask because my book has a picture and a slide photo but describes the end as "the cell divides" when the picture and photo are depicting the chromosomes on opposite poles with a line down the middle of the old cell but STILL fused, even in the picture of interkineses they are not fully seperated, was this type of drawing shown to save space? or was it worded wrong? I know that Mitosis and cytokineses are considered seperate events at the end of the M phase of the cell cycle but that wasn't made clear about meiosis.
cytokinesis is the division of the cytoplasm. I guess you are fine. Don't make a big deal out of this

5) so yellow round pea X green wrinkled pea = yellow wrinkled pea is an example of recombinant phenotypes, could you also say that having your moms eyes and having your dads hair color is an example of recombinant phenotype? if not how can you use people for this example?
?

6)Law of Independent Assortment is true for alleles of different genes FAR apart right? if they are close they are linked and assort together right (I might be waaaay off)?
It's for alleles of genes that are on separate chromosomes (or FAR apart). You are right.

7)my book says with 23 chromosome pairs that 2^23 possible combinations can be produced so all the chromosomes are homologous? (I wouldn't think so) if not why 2^23 different combination's?
There are 23 pairs of homologous chromosomes that have the same size, shape and genes, but most probably have different alleles for at least one of their thousand genes. therefore, there is two ways for separating each pair, and you have 23 pairs, so you get 2^23 types of gametes or combinations.

8)my book says a linkage group is the full set of loci on a given chromosome, the number of linkage groups in a species equals the number of homologous chromosome pairs, that doesn't make sense does it? if there are 23 pairs shouldn't there be 46 linkage groups?
since the homologous chromosomes have the same genes at same loci (places on chromosomes), the linkage group for a pair of homologs is the same. So you end up with 23 pair of linkage groups.