AQA BIOL2 Biology Unit 2 Exam - 26th May 2011

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Temperature - increase in kinetic energy increases rate, water pulled up faster? Im not sure how to word this . cohesion tension theory?

Air movement - the more air movement there is, the more dispersed the humid layer gets so it lowers the water potential in the air. High water potential near stomata? mesophyl layer? Concentration gradient? ?

For temperature, we were told to write that an increase in temperature increases the kinetic energy of water molecules and so they move faster consequently increasing the rate of evaporation of water from the leaves thus increasing the rate of transpiration.. :smile:

Reply 681

liviaaa

Original post by ScienceGeek3

Cell wall provides mechanical strength to the plant and prevent the bursting of the cell due to osmotic pressure..

Chloroplasts are used in the process of photosynthesis as they contain thylakoids which contain the green photosynthetic pigment cholorophyll. They are also used for maximum light absorption!

How does the strutcture of starch differ from that of cellulose?

Starch is made from a-glucose, cellulose is b-glucose. Cellulose is always long straight unbranches molecules, where as strach can be highly branches (amylopectin.) Starch may also be in a helix shape (amylose) but not cellulose. Starch's glycosidic bonds are the same way around, however in cellulose the bonds rotate by 180 degrees.

Influence of selective breeding, on genetic diversity?

Reply 682

nasira372

Can anyone summarise all they know about oxygen dissociation curves. It covers like 1 page in my textbook but there have been Qs on it every exam paper

Reply 683

angel1992

Original post by ScienceGeek3

Oh I see, erm well yeah a gene contains the coded information for making polypeptides, so yes, I would assume different forms of a gene go on to make different of polypeptide chains :confused:

so wouldnt that mean that different alleles are different genes or maybe the differences are so small that they can be classed as the same gne

ohh so maybe its different versions of the sameish polypeptide chain???
so say if you had 200 amino acids for a chain and one amino was different the polypeptide chain type would still be the same in this case, just this slight variation give slight difference to the one characteristic?

overall techincally genes code for one polypeptide chain, but that one polypeptide chain can have many different forms which involve that change of an amino acid which makes a subtle difference on the chain but its still the same chain

analogy, think of it like a row of maltesers and then you replace it with a square malteser its still the same row just the slight difference

Reply 684

liviaaa

Original post by EffKayy

Ermm: Temperature increases the rate of transpiration, as the water molecules have more kinetic energy so move away from the leaf faster. This maintains a high concentration gradient, so the rate increases. I think. :smile:

Yeah high water potential is right with the air movement (small water potential gradient). ^

Reply 685

ksimmi25

Original post by liviaaa

Isn't this unit one? :confused:

Nope, definetly unit 2 - all to do with semi conservative replication and stuff but I just can't get my head around the drawings and particularly this type of question so really need help!!! :/

Reply 686

ScienceGeek3

Original post by liviaaa

Selective breeding reduces genetic diversity as only organisms with desirable characteristics are made to breed and therefore reduces the number of alleles present amongst the organisms.

Why is courtship behaviour necessary?

Reply 687

liviaaa

Original post by nasira372

Can anyone summarise all they know about oxygen dissociation curves. It covers like 1 page in my textbook but there have been Qs on it every exam paper

Lungs have a high partial pressure of oxygen. In the lungs haemogolbin has a high affinity for oxygen due to the high partial pressure, so the haemoglobin is saturated with oxygen.

In the respiring tissues, there's a low patial pressure of oxygen. Therefore haemoglobin has a low affinity for oxygen, and unloads the oxygen. The respiration also produces carbon dioxide, which increases the H+ content in the cells, so oxygen is more readily unloaded.

:smile:

Reply 688

emmaf

In mammals after fertilisation, cells divide by mitosis. Suggest how these cells develop into different tissues.

Reply 689

liviaaa

Original post by ScienceGeek3

For species recoginition.
To find a fertile partner.
To create a bond to raise a "baby" :tongue:

.

Definition of tissues.
Definition of an organ.

Reply 690

Aimo_1

Q4 Jun 2009,

Why is the Mass of DNA in the sperm cell a quarter of the mass of DNA in prophase?

Reply 691

ScienceGeek3

Original post by angel1992

But the only issue is that the slight difference in the polypeptide chain could for instance cause a change in shape of an enzymes active site, which would mean the substrate of complementary shape can no longer bind and therefore the enzyme would be disfunctional..

Reply 692

liviaaa

Original post by emmaf

In mammals after fertilisation, cells divide by mitosis. Suggest how these cells develop into different tissues.

By cell differentiation, so only certain genes are switched "on". Not sure how much detail we need to know about that?

Reply 693

ps3g4m3r

Expecting a HUGE 6 mark at least question on movement of water in plants...dont think its come up yet....know your apoplastic and symplastic pathways! and cohesion tension for good measure

Reply 694

ScienceGeek3

Original post by liviaaa

For species recoginition.
To find a fertile partner.
To create a bond to raise a "baby" :tongue:

.

Definition of tissues.
Definition of an organ.

A tissue is a group of similar cells working together to perform a specific function.
An organ is a combination of tissues co-ordinated to perform a variety of functions however they often have one predominant function :smile:

Explain how gas is exchanged in insects.

Reply 695

liviaaa

Original post by Aimo_1

Q4 Jun 2009,

Why is the Mass of DNA in the sperm cell a quarter of the mass of DNA in prophase?

During prophase, the DNA has just doubled. Therefore the original cell was half of this. So, a gamete sperm cell is half teh original, so a quater of the doubled DNA. Hope that makes sense. :tongue:

Reply 696

iguess

In meisosist he amount of chromosomes are halved so why is there meiosis 1 and meiosis 2?

Originally two homologous chromosomes >>> 1 chromosome in each daughter cell (Meiosis 1)

why not stop there? :confused:

Reply 697

parallal

Original post by nasira372

Can anyone summarise all they know about oxygen dissociation curves. It covers like 1 page in my textbook but there have been Qs on it every exam paper

If the curve shifts to the right, haemoglobin has a lower affinity for oxygen, it favours unloading oxygen and becomes saturated at higher partial pressures of oxygen. This shift usually happens when there is an increase in carbon dioxide concentration (during exercise) to keep up with the demands for oxygen by quickly respiring cells.

If the curve shifts to the left, heamoglobin has a higher affinity for oxygen, it favours loading oxygen and becomes saturated at lower partial pressures of oxygen. This shift usually happens in the heamoglobin of organisms at very high or very low altitudes where there isn't a lot of oxygen.

Fetal heamoglobin has a dissociation curve to the left so it has a high affinity for oxygen, favours loading and becomes saturated at lower partial pressures of oxygen. This is important because there isn't a lot of oxygen in the mother's blood (because the mother uses up most of the oxygen).

"Normal" heamoglobin loads oxygen when partial pressure is high (e.g. in the lungs) and unloads when partial pressure is low (e.g. in tissues)

(edited 12 years ago)

Reply 698

F1's Finest

Original post by liviaaa

During prophase, the DNA has just doubled. Therefore the original cell was half of this. So, a gamete sperm cell is half teh original, so a quater of the doubled DNA. Hope that makes sense. :tongue:

the actualy dna doubles at the interphase along with protein synthesis, not prophase, prophase is where the chromosomes widen and the nuclear envelope disappears , i think.

Reply 699

Aimo_1

Original post by liviaaa

During prophase, the DNA has just doubled. Therefore the original cell was half of this. So, a gamete sperm cell is half teh original, so a quater of the doubled DNA. Hope that makes sense. :tongue:

Thanks, how has it doubled btw? Just after DNA Replication?