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x-Sophie-x
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#3021
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#3021
Can someone please explain why a tree trunk changes size in relation to root pressure and cohesion tension?

Also, why is root pressure negative?



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pnaidu
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#3022
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#3022
(Original post by LiamDaly)
If anybody knows the possible 6 mark questions for the plant?

How water enters root hair?
The apoplastic and symplastic pathway?
How water travels up the xylem?

Please?


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do you mean type out model answers?
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iamNatasha
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#3023
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#3023
(Original post by Rebeelouise)
For all you last minuters ;D
I can't see the attachments and boy do i need to see them as i am a very last minuter!!
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LiamDaly
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#3024
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#3024
(Original post by pnaidu)
do you mean type out model answers?
I mean model answers would be amazing but the different possible questions would be useful and what you'd include in each one would be amazing.

Thanks


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BingTaoBing
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#3025
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#3025
(Original post by Thebest786)
Once it stops, does it go through the xylem after? And the symplast goes straight to the xylem?

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Both the water from the symplast and the apoplast end up in the final endothelial cell. Then all the water crosses the endothelial membrane into the xylem. The endothelial membrane is like a customs office in an airport. All the water has to pass through it and be checked before going into the xylem.
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oak12
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#3026
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#3026
(Original post by x-Sophie-x)
Can someone please explain why a tree trunk changes size in relation to root pressure and cohesion tension?

Also, why is root pressure negative?



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as the column water is pulled up the xylem, the walls of the xylem are pulled inwards due to adhesion, this is called tension, and causes the diameter of the tree trunk to reduce. it is also negative pressure.

root pressure pushes on column of water - it would normally produce positive pressure (pushes wall of xylem outwards)
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oak12
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#3027
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#3027
anyone need any help?
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Thebest786
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#3028
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#3028
(Original post by BingTaoBing)
Both the water from the symplast and the apoplast end up in the final endothelial cell. Then all the water crosses the endothelial membrane into the xylem. The endothelial membrane is like a customs office in an airport. All the water has to pass through it and be checked before going into the xylem.
Good explanation, thanks. Good luck with the exam tomorrow. :sexface:

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pnaidu
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#3029
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I THINK for the tree trunk changing diameter - diameters always the lowest or narrowest at the point of maximum photosynthesis, as its going through transpiration( the side effect of photosynthesis), and the enactment of the cohesion-tension theory (with the increased flow of water molecules being pulled up) pulls in the xylem walls.

hope that helped a teeny bit
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Linked
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#3030
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#3030
what are stop and start codons ?
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senz72
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#3031
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#3031
(Original post by iamNatasha)
Whoa! I would never be able to do that... I feel for ya brah. Good luck!
I've given up to be fair.
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Hi, How are you ?
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#3032
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#3032
(Original post by Linked)
what are stop and start codons ?
Any of three codons in a molecule of messenger RNA that do not code for an amino acid and thereby signal the termination of the synthesis of a protein. The three stop codons are UAA, UAG, and UGA, where U is uracil, A is adenine, and G is guanine. Also called termination codon .

Surces, http://dictionary.reference.com/browse/stop+codon

Hoped I helped?
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oak12
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#3033
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#3033
(Original post by Linked)
what are stop and start codons ?
start codons are the triplet code that always appears at the start of the amino acid sequence, it is always methionine

stop codons do not code for an amino acid, so they end the chain
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JM17
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#3034
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#3034
Some possible essay questions.

Meiosis

DNA unravels and replicates so there are two copies of each chromosome, called chromatids.

The DNA condenses to form, double armed, chromosomes made from two sister chromatids.

The chromosomes arrange themselves into homologous pairs.

Meiosis I: the homologous pairs are separated, halving the chromosome number.

Meiosis II: The pairs of sister chromatids that make up each chromosome are separated.

Four haploid (gametes) that are genetically different from each other are produced.

DNA Replication

The enzyme DNA helicase breaks the hydrogen bonds between two polynucleotide DNA strands.

Each original strand acts as a template for a new strand. Free floating nucleotides join to the template by specific base pairing.

DNA Polymerase enzyme joins the nucleotides together. Hydrogen bonds form between the bases on the original and new strand.

Each new DNA molecule contains one original strand and one new strand. This is SEMI CONSERVATIVE.

Mitosis

In Mitosis a parent cell divides to produce two genetically identical daughter cells.

Interphase: The cell carries out normal functions but also prepares to divide. The DNA is unraveled and replicated to double the DNA content.

Prophase: Proteins called centriole move to opposite ends of the cell. Forming a spindle. The nuclear envelope breaks down and the chromosomes are free in the cytoplasm.

Metaphase: Chromosomes each with two chromatids line up along the middle of the cell, and are attached to the spindle by their centromere.

Anaphase: The spindle fibre pulls chromatids apart. The chromatids are pulled to opposite ends of the cell, centromere first.

Telophase: Chromatids uncoil and become long and thin, they are again called chromosomes. A nuclear envelope forms around each group of chromosomes. The cytoplasm divides and there are now two daughter cells that are genetically identical.

Potometers



Assemble the potometer.

Cut a shoot underwater.

Remove the apparatus from the water but keep the end of the capillary tube submerged in a beaker of water.

Check that the apparatus is watertight and airtight.

Dry the leaves, allow time for the shoot to acclimatise and then shut the tap.

Remove the end of the capillary tube from the beaker of water until one air bubble has formed, then resubmerge tube.

Record starting position of the air bubble, then record the distance moved by the bubble per unit time.
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moa7
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#3035
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#3035
(Original post by Linked)
what are stop and start codons ?
They mark the start and end of the polypeptide chain.
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oak12
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#3036
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#3036
anyone need any help?

questions or topics?
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MrPolish
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#3037
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#3037
do you have to know all of the main arteries and veins, i.e. Hepatic artery, renal artery etc..?
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2013leaver
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#3038
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#3038
Is it apoplastic and symplastic, or apoplast and symplast? which is the right one?
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Thebest786
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#3039
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#3039
Does anyone have the slightest idea of what type of question is likely to come up on mitosis, meiosis

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2013leaver
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#3040
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#3040
Yes, it says in the spec, although it has never been tested.
Knowing my luck, it will come up.
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