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Biology SL/HL help


Mahuta ♥

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The parts in green are the parts of the syllabus concerning these points.

I went through Plant Science and photosynthesis last night and it wasn't too bad happy.gif

The ones that I find harder to understand/remember are :

-Explaining light-dependent and light-independent reactions

*Topic 8 (8.2.5)----Light Independent reaction/ Calvin's cycle*:

Calvin's Cycle:

  • Calvin Cycle is the independent reaction part of photosynthesis.
  • We start with a 5 carbon sugar called Ribulose Bisphosphate but you can call it RuBP.
  • RuBP chnages to 2 molecules of 6 carbon, so a CO2 is added.
  • The 6 carbon compound(organic acid) is called Glycerate 3-phosphate(a 6 carbon with 3 phosphates).
  • This is done by RUBISCO ENZYME.
  • Glycerate 3-phosphate is turned into a carbohydrate called triose phosphate (by reduction = addition of Hydrogen).
  • This happens by removing 2 phosphates, hence, 2ATP--->2ADP + P.
  • Also, 2 hydrogens are ADDED, so 2NADPH----> 2NADP+.
  • You have 6 molecules of triose phosphate formed. 5 of which are regenerated into RuBP. One molecule is used to form glucose phosphate to use for biomass, storage..etc..etc.

The whole purpose of the Calvin's Cycle is to convert CO2 to a carbohydrate. This how we get glucose as a product of photosynthesis. This is also why we say plants generate their own nutrition.

*Topic 8 (8.2.3)----Light dependent reaction*:

A.Photoactivation of photosystem 2:

1)Chlorophyll absorbs light exciting an electron in the molecule making it move up a higher level - Chlorophyll is photoactivated.

2)This electron will move from molecule to molecule until it reaches a receptor at the center of the P2.

(the photoactivation of photosystem II)

B. Electron transport chain of the thylakoid membrane:

1)The ETC is a chain of proteins that carry the electron from the P2 to P1.

2)Every time the electron goes from one protein to another, H+ is pumped into the thylakoid- Proton gradient formed.

3)When the electron reached ATP synthase, the protons will flow back outside through the enzyme. As the name suggests, we're going to have synthesis of ATP

(electron transport)

C. Photo-activation of Photosystem 1:

1)After the production of ATP, the electron will pass onto P1.

2)Photoactivation takes place in the same way releasing another electron.

3)The two electrons will move through another chain until they reach a carried that will pass them on to NADP+ in the stroma.

4)NADP+ will accept the 2 electrons and one of the protons:

NADP
+
+ 2e
-
+ H
+
------> NADPH

The NADPH will be used in the Calvin's cycle later on.

(photoactivation of photosystem I), (reduction of NADP+)

D. Photolysis:

1)The electrons transported through the chain must be replaced, this is where water is used.

2)Photolysis of water takes place where the H2O is split to 2H+, Oxygen ions and 2 electrons.

3)Chlorophyll is positively charged, so it will attract the electrons.

4)Oxygen is a waste product, which is why we have O2 as a product in the overall reaction.

(photo-activation of photosystem I)

E. Cyclic and non-cyclic phosphorylation:

Non cyclic is the one I described above.

Cyclic is used when there is shortage of NADP+, which means electrons have no acceptors.

The electrons will go from P1 through ETC then back to P1.

Cyclic phosphorylation will not produce O2 nor NADPH.

(cyclic and non-cyclic photophosphorylation)

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-C.4.4 Explain photophosphorylation in terms of chemiosmosis. :sweat:

*TOPIC 8 (8.2.4)---Photophosphorylation in terms of chemiosmosis*

Ok, no worries, it's easy. Just understand it:

This follows the same principal as oxidative phosphorylation in respiration.

1)When light is absorbed by the photosystem (2), electrons are excited and released into the electron carrier chain(which consists of proteins).

2) Everytime electrons move from one carrier to another, a Hydrogen ion is pumped across the thylakoid membrane into the thylakoid space.3)So, you will have a high concentration of protons(hydrogen ions), therefore, you have a concentration gradient.

4)Hydrogen ions are pumped out of the thylakoid through the ATP Synthase, causing it to spin, this spinning generates energy.

5)electrons are accepted by the NADP+.

You have to remember that the hydrogen ions come from the photolysis of water that produce protons as well as electrons(which replace the ones accepted by the NADP+).

Chemiosmosis refers to the diffusion of protons, so basically, they wanted you to explain this by mentioningand referring to chemiosmosis.

I know I just gave the whole light dependent process here, but I personally write all this to garuntee that I dont miss any marks.

If there's anything else unclear, feel free to ask. smile.gif

Also, do you happen to know a great resource for the Options part of the syllabus? My teacher said we only need to learn E-H biggrin.gif

Well I use the Allot books (OXFORD) for the whole syllabus.

Option H is awesome. biggrin.gif

Thank you for taking your time to help! happy.gif

P.S. Thanks for the studying tips—They did actually help me !

Anytime. smile.gif

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It's evolution.

I totally dont get the D.3.5 about the skulls. and D.3.8 about brain size and diet?

Click 4 BIology and IB GUides dont have a D option page

Can't tell you about D.3.5 as I didn't do option D either, but I've since done some stuff on Evolution at Uni so can fill you in on some info regarding D.3.8.

Basically, brains are very energetically expensive things to run - neural tissue uses up way more energy than any other tissue in the body, and also comes with some annoying eccentricities. For instance, most other tissues can get energy from a variety of metabolic fuels - glucose, amino acids, fatty acids, glycerol etc., whereas the brain can only use glucose, more or less. This makes it even MORE energetically expensive because you not only have it being a major drain on fuels, but specifically on one fuel.

So, in order to have evolved a bigger brain, what we need is a diet which is going to give us a lot of energy. A high-energy diet which is rich in sources of glucose means we're going to be able to support a bigger brain.

Interestingly and actually quite relevant, although I'm not sure if it's on the syllabus, there's a famous hypothesis in evolution called the Gut-Brain Hypothesis which basically suggests that, in order to get bigger brains you (obviously) need to have more fuel. In order to free up more energy for the brain, you need to reduce the amount of energy you expend keeping other organs going. Stuff like the kidneys, liver, heart etc. are obviously too important to cut down on, but one thing which can be cut down on is gut size. If we change our diets to eat foods which are higher in energy and more easily absorbed, we don't need to have big long guts like cows and other animals have. We can have smaller guts that require less energy to run, and in turn we'll have more energy spare and available for a bigger brain.

Said big brain is also useful for helping us improve the quality of our diet (we can think about things and hunt more effectively etc.), so it's positive feedback, really.

It makes quite a lot of sense. All evolution is really just applying common-sense theories to evidence. I strongly suggest you get an IB textbook (e.g. the Course Companion) because that's guaranteed to have EXACTLY the information you need in it for the exam. The IB support websites are, in my honest opinion, really **** information sources. I had to give mine back or I'd be able to give a better answer!

Also re: the links above...

http://kstruct.com/ib_notes/Option_D_-_Evolution <--- that link is out of date, using an old syllabus!

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Hi :)

I've got this question concerning MEIOSIS & MITOSIS. As to mitosis, I don't understand why is the cell 4n at the beginning, not 2n. And as to meiosis I don't understand where do the homologous pairs come from.

Thanks,

Matt

For your first question, it's at 4n to begin with because during Prophase the cell has doubled up its DNA in preparation for division (so it'll have enough to make 2 x 2n cells, it needs 4n).

For your second question, homologous pairs arise because each cell starts off with 2n (i.e. is a normal cell) and so if n means you have 1 version of each of the 23 chromosomes, 2n means you have 2 versions of each chromosome. The homologous pairs are just where each chromosome lines up with the other matching chromosome that's already within the cell. You've already got two versions of each chromosome, so it's literally just them twinning up.

Hope that helps?

Meiosis and Mitosis are tricky to get your head around because for some reason textbooks never bother to explain the starting number of chromosomes!

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One more question:

The dihybrid ratio is 9:3:3:1, but that is only when the characteristics are controlled by genes on different chromosomes. Does this mean that we have two chromosomes in each parent cell and that on each of those chromosomes we have a different gene. I mean that one of the pair is responsible for long hair and the other is responsible for curly hair in the father and in the mother the same way but one is responsible for short hair and the other for straight hair. So, if the above stated is correct, then if one chromosome was responsible for both traits in the father and the same thing in the mother, the ratio of 9:3:3:1 would not work? I'm really confused with this, I hope the problem is at least clear :blink:

I guess that what I mean is - is it possible for two alleles (two genes of the same characteristic but different) to be located on the same chromosome?

Edited by Hinuku
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One more question:

The dihybrid ratio is 9:3:3:1, but that is only when the characteristics are controlled by genes on different chromosomes. Does this mean that we have two chromosomes in each parent cell and that on each of those chromosomes we have a different gene. I mean that one of the pair is responsible for long hair and the other is responsible for curly hair in the father and in the mother the same way but one is responsible for short hair and the other for straight hair. So, if the above stated is correct, then if one chromosome was responsible for both traits in the father and the same thing in the mother, the ratio of 9:3:3:1 would not work? I'm really confused with this, I hope the problem is at least clear :blink:

I guess that what I mean is - is it possible for two alleles (two genes of the same characteristic but different) to be located on the same chromosome?

No, an allele is an alternative version of the same gene, and you cannot have more than one version of the same gene on a chromosome.

The dihybrid ratio is 9:3:3:1 because it's the result of an AABB x aabb cross (which will all be AaBb), then those offspring bred again together. So you have AaBb x AaBb and you'd have these possibilities:

AABB

AABb

AaBB

AaBb

AABb

AAbb

AaBb

Aabb

AaBB

AaBb

aaBB

aaBb

AaBb

Aabb

aaBb

aabb

i.e. 9 that have a capital A and capital B, 3 that have a capital A but no capital B, 3 that have a capital B but no capital A and 1 that has neither. 9:3:3:1.

It's basically the case that you have two parents, each with 2 alleles each (1 allele on each chromosome), and so each parent has two alleles of A (one on each chromosome) and two alleles of B. The offspring is going to inherit 1 version of A from its mother and 1 version of A from its father, so that it will also have 2 versions of A. The same for B.

So the offspring will end up with 2 versions of A and 2 versions of B, like its parents. However, it's random as to which of the 2 A alleles its mother passes down, which of 2 A Alleles the father passes down etc., so what the Dihybrid Ratio is is working out the probability of each combination if you have gone from:

Generation 1 AABB x aabb

Generation 2 AaBb (they'll all be AaBb)

Generation 3 = AaBb x AaBb (...the incest generation...)

Generation 4 = 9:3:3:1 Phenotypically AB, Ab, aB, ab.

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Would anyone be able to help me with Transcription and Translation (3.5)? I was sick when our class did the unit and my teacher's explanation and notes didn't make sense to me at all!

Many thanks you guys! This forum is fast becoming a life saver!

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Would anyone be able to help me with Transcription and Translation (3.5)? I was sick when our class did the unit and my teacher's explanation and notes didn't make sense to me at all!

Many thanks you guys! This forum is fast becoming a life saver!

Okay, genes need to be expressed, this process is do by what is called translation process (Genes expression). Genes expresses themselves by making protein.

Translation process is the process of making protein, but to reach this transcription of RNA should take place. m-RNA is transcribed to hold the message of a certain gene in DNA.

For this lesson you need to compare RNA and DNA:

a) RNA is made up of one strand but DNA is made up of two wounded strand to form a double helix shape.

b) RNA consist Uracil instead of Thymine in DNA.

c) RNA consist ribose sugar instead of deoxyribose.

You also need to outline DNA transcription:

It is the process of making RNA by copying a part of nucleotide sequence of DNA into a complementary bases of RNA.

The steps:

-The double helix of DNA unzip and separate (how will it separate) at specific region.

-One of the strand serve as a template for the RNA.

- A enzyme called RNA polymerase matches RNA nucleotide with the complementary bases of DNA

messenger RNA hold the message of a particular gene in DNA, this message is made up of letters each one of those letters is made up of three bases called (Codon) and they are specified for a specific amino acid.

After m-RNA is transcribed it goes out the nucleus and the process of translation starts:

Translation is the second process of protein synthesis , It is decoding of the m-RNA message to make protein.

Steps:

-In the cytoplasm there is t-RNA and amino acid.

-Each amino acid will bond with a specific t-RNA

-Each base arrangement in the t-RNA is specific complementary to m-RNA base, each 3 bases of m-RNA is called codon and each three bases of t-RNA is called anti codon.

-The small subunit of the ribosome will attach to the

start codon of the m-RNA.

-Specific t-RNA carries amino acid has anticodon which fit to the codon on m-RNA.

- Large ribosome subunit will attached to the small subunit at m-RNA.

- Another t-RNA will attach to codon.

-The bond will disconnected between t-RNA and amino acid and join between the two amino acid it is called a peptide bond.

- The t-RNA will de-attached (what t-RNA will do after de-attaching).

-The ribosome will move to the next codon.

-This process will continue until reaching stop codon .

The last thing that you need to know is relationship between one gene and one polypeptide:

Scientists had believed that every gene will produce one enzyme, then they found that it is all proteins not only enzymes. and then they discovered that there is some protein that are made up of different polypeptides. For many years students learn that one gene is for one polypeptide but they recently found that m-RNA message is usually modified. So the gene message is also modified and depend on this modification one gene could result on more than one polypeptide.

I attach a presentation that i did in Grade 9, it may be helpful and it contains much important material for you. I know that this explanation may seem not in details but i need to know which point you have difficulty on so i can further explain it .

Protein Synthesis.ppt

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...

Wow, that was really helpful! My main issue was in the actual process of transcription and translation. I understood the main concept of amino acids and the actual RNA structure, but the actual process was just really confusing. So thank you very much!

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Ummm? I don't know what you're really asking for...

When picking one of the 4 I'd mentally add up the points you think you will get. If you can get the 4 and 6 mark question but fail the 8 mark one then you only get, at max, 10/18, but if you fail the 4 point and get the 6 and 8 you can get 14/18. See what I mean? Pick the question that gives you the best marks.

As for actually answering it will depend on the question, some are draw and label, or draw and annotate, some are explain questions (8 point one likely) where you will need to explain the whole concept from start to finish...

Always remember to have some sort of order though, you don't start protein synthesis with translation for example :D Start with the replication and move forward. There's always those marks that seem random too, following the protein synthesis example there could possibly be a mark for mentioning the golgi body and what it does after the protein is made (brief)...

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For the 4 mark section of one of the questions from section B they can ask you to draw and label something.

And you can always use little diagrams or little graphs to help explain your point. The Bohr shift for example (cardiovascular) would be easier to explain if you just had a rough (but explicitly labeled) graph off to the side. It doesn't need to be super detailed, but it needs to include the stuff required to answer the question. This doesn't mean you can just draw a graph and be done though :P

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