Biology SL/HL help

[Mahuta ♥]

Also, are we required to know an entire food web (for ecology) and dichotomous key (for classification) by heart?

Nope you just have to understand it so that went you're asked about it you can look at it and deduce information.

[Mahuta ♥]

*TOPIC 5 (5.5.3)---Plant Phyla and their external distinguishable features*

what are the identifying features for bryophyta, coniferophyta, filicinophyta and angiospermophyta? My book has this nowhere.

Bryophytes- Mosses:

• Roots, leaves and stems: Bryophytes are distniguished by the fact that they dont have roots but instead, have 'root-hair' like projections called rhizoids. They have simple leaves and stems.
  
• Its maximum hieght is 0.5meters.
  
• It reproduces using spores that are produced capsule which develops at the top of the stalk.
  

Filicinophytes- Ferns:

• Ferns have roots and leaves. They also have a short stem(not woody). You should be able to distinguish a fern by its leaves that are curled up in a bud. Most importantly, the leaves are made up of smaller leaflets.
  
• Its maximum height is 1.5meters
  
• It reproduces using spores as well, but in ferns, they are produced on the underside of the leaf(sporangia).
  

Coniferophytes- Conifers:

• Conifers have roots and leaves and full woody stem. It has narrow leaves with a thick waxy cuticle.
  
• Its maximum height is 100 meters.
  
• It produces by seeds that are formed from the ovules which happens on the surface of the scales of the cone(female cone).
  
• Note that male cones produce pollen.
  

Angiosperms-Flowering plants:

• Flowering plants usually have roots, leaves and stem. The stem is normally woody.
  
• It maximum height is 100 meters.
  
• Obviously, it uses seeds for reproduction. They develop from the ovules which are produced in the ovaries, which are part of the flower.
  
• Fruits produced develop from the ovaries, from which seeds are dispersed.
  

[dbkozu]

Mahuta...do you know anything about Kreb's Cycle/Calvin Cycle??

Edited April 24, 2009 by dbkozu

[Mahuta ♥]

*TOPIC 8 (8.1.4/8.2.5)---Kreb's Cycle and Calvin's cycle.*

Mahuta...do you know anything about Kreb's Cycle/Calvin Cycle??

Oh my god yes! One of my favorites.

It would help if you have the diagrams infront of you now.

Krebs Cycle:

• After the link reaction, you have acytelcoA, a 2 Carbon molecule with the coA enzyme.
  
• The Cycle starts with a 4carbon.
  
• The 2carbon is added to it so: 2+4=6 we get a 6 carbon molecule.
  
• The 6 carbon is changed into 5 carbon. Therefore, we must reduce the carbon number by removing CO₂, so CO₂ is lost. Everytime a CO₂ is lost, a H₂ is lost as well. So you have the NAD⁺ + H₂----> NADH⁺ + H⁺.
  
• The 5 carbon is changed into 4carbon by the exact same process, CO₂ and NADH⁺ + H⁺ formed.
  
• The 4 carbon formed isnt the same as the one we started with, so to get it back to the first one, we remove 2H_2. One is taken by the NAD⁺ and the other by FAD.
  
• ATP is formed as well in this process.
  
• So to sum up the krebs cylce produces the following: 1 ATP, 1 FADH₂, 3NADH⁺ + H⁺, 2CO₂
  

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.

If there's any part you want clarified dont hesitate to ask me, because I dont feel I made it that clear.

[dbkozu]

Oh thanks! That's good for now.

[Guest syrianstar]

Hey Maha

I'm doing the May 2008 paper and I came across a few multiple choice questions I didn't really understand. I'd appreciate any help with them!

First Question

What type of urine would be produced in a human whose diet contains very small quantities of protein or fluid?

Well in the markscheme the answer is 'Low Urea concentration' and 'High Salt Concentration'. The way I thought of it was that if the person doesn't take in much fluid, then the concentration of both urea and salt would be high.

Second Question

After depolarisation what happens to restore the resting potential?

The answer is apparently that 'potassium channels open and potassium ions diffuse into the neurone'. I thought they were actively transported in, and then diffused out during an action potential? Also, there was another option about sodium diffusing out of the neurone...that seems a reasonable answer too

They seem really simple, and I've actually already revised these topics. It's just late and after so much revision my brain feels like a sponge!

Yeah, I know excuses excuses

Anyway, thanks a lot for your help in advance!

Edited May 1, 2009 by syrianstar

[Mahuta ♥]

First Question

What type of urine would be produced in a human whose diet contains very small quantities of protein or fluid?

Well in the markscheme the answer is 'Low Urea concentration' and 'High Salt Concentration'. The way I thought of it was that if the person doesn't take in much fluid, then the concentration of both urea and salt would be high

Small quantities of proteins means very dilute blood (too much water). Therefore, osmoregulation will cause water to be released from blood stream into loop of henle----> then the collecting duct so you're going to have a low urea concentration (lots of water taken from blood).

Second Question

After depolarisation what happens to restore the resting potential?

The answer is apparently that 'potassium channels open and potassium ions diffuse into the neurone'. I thought they were actively transported in, and then diffused out during an action potential? Also, there was another option about sodium diffusing out of the neurone...that seems a reasonable answer too

Check my post about nerve impulses and tell me if that makes sense.

anytime.

[Guest syrianstar]

Small quantities of proteins means very dilute blood (too much water). T

Can you expand more on that?

Sorry

And the post about the resting/action potentials was great. Thanks a lot

[Hedron123]

Syrian, I can help you with that. If you intake very small quantities of protein, there won't be much nitrogen (remember that the general structure of an aminoacid is NH2 - CHR - COOH) to excrete as urea [ CO(NH2)2]. Therefore, the concentration of urea in urine will be low.

If you consider the part of salt concentration you must remember this. If the water content in blood is too low (due to the "very small quantities of fluid ingested") ADH (anti-diuretic hormone) WILL be secreted by the pituitary gland. The hormone makes the cells of the collecting duct (of the kidney) produce membrane channels called aquaporins. These aquaporins render the collecting duct permeable to water. As a consequence, water will travel across the membranes into the hypertonic medulla (which has a high solute concentration) through osmosis. Final product: low volumes of highly concentrated urine (water has been reabsorbed by the kidney to prevent excessive water loss).

[Sandwich]

Can you expand more on that?

Sorry

And the post about the resting/action potentials was great. Thanks a lot

Not to butt in where I am unwanted

But if you imagine the blood as being a whole load of H2O with things dissolved in it, the less of the things dissolved in it you have (ie the less solute you have), the more dilute its going to be. In other words, if you have lots of protein dissolved in the water, the ratio of protein (or anything other dissolved thing) to water will be reasonably high. If you've got very little protein in the bloodstream, the proportion of water relative to the amount of stuff dissolved in it is obviously going to be waaaaay more water, because there's very little in it!

And so blood which has too high a proportion of H2O is too dilute and the body acts by a process of negative feedback, as detected by the osmoreceptors in the hypothalamus, to correct the problem by getting rid of water.

Edited May 1, 2009 by Sandwich

[Mahuta ♥]

Can you expand more on that?

Sorry

lol, ok. Think about the blood as being water and salt. If you have very little salt, you're going to have more water, so its dilute. Not concentrated because if so, then you would have more proteins than water.

Alice and Bernardo i didnt read your posts..lol so i probably have repeated the same thing. I have seen a bit of bernardo, lol, I just hope you wont confuse her by putting in formula . I like that though.

Not to butt in where I am unwanted

No one said you're unwanted . Feel free to comment.

[Guest syrianstar]

Wow, I didn't expect to get three replies to that question!

Thanks a lot guys, your explanations really helped and the formula completed things nicely

Thanks again!

[Hedron123]

No problem, my pleasure Feel free to ask anything, I'm trying to help Mahuta with the syllabus guidance.

[sweetnsimple786]

I'm having a hard time understanding how antibodies are produced. Once my teacher said only plasma cells can make them, but then he has also said that B cells can make them as well. Can you tell me where I'm going wrong with my logic:

B cells "eat" antigens and directly produce antibodies.

or

T cells activate B cells that undergo mitosis and become plasma and memory cells. The plasma cells produce antibodies.

[Sandwich]

*TOPIC 11 (11.1.4) -Production of antibodies

For the IB all you need to know is that

1. Phagocytes come across pathogens, ingest them by phagocytosis and break them down into their constituent parts ('antigens') and then display these antigens using MHC (major histocompatibility complex) proteins on their membranes.

2. A T-Helper Cell which binds that specific antigen comes across and binds to the antigen being displayed by the phagocyte on its MHC (one example of a phagocyte is a Macrophage, if you need to name a specific cell type, but there are many different types). Binding of the T-Cell Receptor to its antigen presented by the phagocyte serves to activate the T-Cell via intracellular signals.

3. The activated T-Helper Cell can then activate a B-Cell that is specific for the same antigen as the T-Helper cell (i.e. the B Cell which produces the correct antibody for that antigen).

4. The B Cell rapidly divides by mitosis to form B Memory Cells (later used as part of long-term immunity) and also B Plasma Cells which have lots and lots of rough endoplasmic reticulum to synthesise antibodies and act as antibody factories.

5. These antibodies attach to the antigen, and thereby disable viruses/pathogens/anything evil. Two of the ways they do this (although there are many others) is by binding to and thereby preventing viruses/bacteria from docking to new cells and also by causing agglutination, so viruses/bacteria stick together in a lump and can't do anything useful.

That's more or less all you need to know. Check it against a textbook, but I reckon that's the whole thing. In other words, your second statement is correct, I just reckon it's easier to remember these things in the context of the whole (which is after all how you write about them!).

Edited March 30, 2012 by Sandwich

[Mahuta ♥]

I am moving this to the Biology help thread.

[HJ:)]

MAHA~~~ i need help.

I forgot how to answer these questions

I'm studying for my finals and revising but this question.......is #$@#%@$^$@^$@^@$

In a species of plant, tall is dominant to short and the production of round seeds is dominant

to that of wrinkled seeds. The alleles are unlinked.

A plant heterozygous for both characteristics is crossed with a plant homozygous for tall

with wrinkled seeds.

Use the letters:

T – allele for tall

t – allele for short

R – allele for round seed

r – allele for wrinkled seed.

Determine the phenotypes and genotypes of the offspring of this cross.

can you tell me steps of how to solve this???

[HJ:)]

can you explain the answer for this question?

Explain how the properties of phospholipids help to maintain the structure of cell membranes.

Thanks again

[Mahuta ♥]

MAHA~~~ i need help.

I forgot how to answer these questions

I'm studying for my finals and revising but this question.......is #$@#%@$^$@^$@^@$

In a species of plant, tall is dominant to short and the production of round seeds is dominant

to that of wrinkled seeds. The alleles are unlinked.

A plant heterozygous for both characteristics is crossed with a plant homozygous for tall

with wrinkled seeds.

Use the letters:

T – allele for tall

t – allele for short

R – allele for round seed

r – allele for wrinkled seed.

Determine the phenotypes and genotypes of the offspring of this cross.

can you tell me steps of how to solve this???

Ok HJ, They told you that its unlinked so basically its an absolutely normal dihybrid cross.

ALWAYS..Determine the parents genotype and then the possible gametes.

SO:

1)

Parents Phenotype: (Heterozygous for both characteristics) (Homozygous for tall and wrinkled)

Parents Genotype: TtRr TTrr

2)

Possible Gametes: TR, Tr, tR, tr Tr

and then do the cross of the following table.

[Mahuta ♥]

The bilayer membrane has a hydrophobic and hydrophilic sides. The hydrophobic tails from both layers are strongly attracted to each other and are keeping themselves away from the water. The hydrophilic heads are attracted to water, so they will leave themselves facing the water. This question isnt normally more than 3 marks, so just tell them these ideas.

Sorry for the late reply, I wasnt home. If you need anything else tell me, whens your exam?