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AQA BIOL2~3rd June 2013~AS Biology (Now Closed)

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Reply 2560

FatHeadedKing

Q: What is the fastest way to determine the sex of a chromosome?

A: Pull down its genes.

Reply 2561

Emily5678

I think this may already be on the thread somewhere but I cant find it anywhere, I don't really understand the apoplastic and symplastic pathway, if anyone could help me that would be great.

Reply 2562

VigneshSB

Original post by FatHeadedKing

Because when the homologous pairs line up, it's 2x diploid.

What the hell are you talking about? When they line up, its DIPLOID(Even though there are 92 CHROMATIDS, there are still only 46 CHROMOSOMES). After they divide, they become HAPLOID(Even though they then have 46 CHROMATIDS, the daughter cells have 23 CHROMOSOMES)

Reply 2563

chelley2

Original post by Rebeelouise

For all you last minuters ;D

:'( can't view them ,stupid laptop :angry:

.You think this is the right time to act funny :frown:

Posted from TSR Mobile

Reply 2564

Paulineuh

Original post by FatHeadedKing

Q: What is the fastest way to determine the sex of a chromosome?

A: Pull down its genes.

Original post by Nav_Mallhi

And its by osmosis?

Yes!

Original post by Emily5678

I think this may already be on the thread somewhere but I cant find it anywhere, I don't really understand the apoplastic and symplastic pathway, if anyone could help me that would be great.

Someone posted this earlier:

Basically water wants to get from thesoil into the xylem vessels. It can do this by 2 methods or'pathways' called the SYMPLAST PATHWAY or APOPLAST PATHWAY.

Symplast Pathway

In the Symplast pathway, water movesthrough the CYTOPLASMS of the cells.
Water diffuses along a water potentialgradient through PORES between the cells of the Cortex calledplasmodesmata. The Cortex is simply all the cells between theRoot hair cell and the Xylem vessel.

Apoplast Pathway

In the Apoplast pathway, water movesthrough the CELL WALLS of the cells.
Water stops at the ENDODERMIS asthere is a CASPARIAN STRIP which prevents the water from passingfurther, making the water pass through a membrane by osmosis down awater potential gradient INTO THE SYMPLAST PATHWAY, which is usefulas it prevents harmful substances such as toxins or viruses fromentering the xylem vessels as the membrane would not let them past.

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EXTRA

•

Water potential in the root hair cell is lowered by the active transport of mineral ions from the soil, hence water can move from the soil into them down a water potential gradient

•

Watch this, if you need more help:

http://www.youtube.com/watch?v=TWNtXw-MWtE

(edited 10 years ago)

Reply 2565

FatHeadedKing

What does DNA stand for?National Dyslexia Association.

Reply 2566

lorobolorolo

Original post by FatHeadedKing

Growth of tumour / number of days = growth of tumour per day

Control = 372/50 = 7.44 mm^3 per day
Taxol = 87/50 = 1.74 mm^3 per day

Thanks u make it seem so simple now :colondollar:

Reply 2567

VigneshSB

Original post by LiamDaly

Can someone post 6 marker on Meiosis as if it comes up I'm so screwed. Like describe the features of meiosis [6]

Posted from TSR Mobilehh

They won't ask you that amigo. All you need to know is that the chromosomes line up at the equator in homologous pairs. At this point, crossing over(rare) and independent segregation occur that increase variation. You don't need to really explain the stages of meiosis

Reply 2568

lorobolorolo

Original post by FatHeadedKing

What does DNA stand for?National Dyslexia Association.

deoxyribonucleic acid :wink:

Reply 2569

FatHeadedKing

Original post by lorobolorolo

Thanks u make it seem so simple now :colondollar:

D'aaawww. Nice to be appreciated :rolleyes:

Reply 2570

MintCrepz

Original post by VigneshSB

So this is correct?

cause I thought it was like this:

cell starts with two homologous chromosomes

( X X ) chromosome number 2 - diploid

meiosis 1

( X ) ( X) chromosome number 1? - haploid ?

meiosis 2

(\) (/) (\) (/) Chromosome number 1 - still haploid?

Reply 2571

Liam2404

Could someone just clarify if this is right about water transport in plants:
1) The Root:
- Ions are actively transported into the xylem
- This reduces water potential in the xylem
- Water moves down a water potential gradient from the soil to the root hair cells by osmosis
- This creates root pressure
2) The Routes:
- The symplast pathway involves travelling through living parts of the cell - the cytoplasm
- Cells are connected by plasmodesmata
- The apoplast pathway involves travelling through the non-living parts of the cell - the cell wall.
- Once endodermis cells are reached, a waxy casparian strip prevents the water from moving through the cell wall, so its forced to travel through the cell membrane (which allows for more control over water movement)
- Water molecules then reach the xylem
3) The Xylem:
- Water evaporates at the leaf of the plant
- This creates tension (suction) which forces more water molecules into the leaf
- Water molecules are cohesive due to hydrogen bonding, so when one is sucked up, a whole column follows
- As water enters via the roots, it pushes water already in the xylem further upwards (root pressure)

Much appreciated, need to get this!