Edexcel GCE Biology Unit 4 6BI04 June 2013

Could someone talk me through the core practical for hatching brine shrimps? I have no recollection of doing it at college whatsoever.

The actual experiment:
you get an equal number of brine shrimp eggs and put into water baths of different temperatures. You have to keep other variables constant such as oxygen volume of water etc. Then leave for a couple of hours and then record the number of brine shrimp that have hatched. You can calculate the rate they have hatched by using the formula...number of hatched shrimp divded by the number of hours you left them.

The reason for doing the experiment:
This experiment shows how an increase in temperature due to global warming can effect animals such as brine shrimp.
Bear in mind that after a certain temperature the brine shrimp will not hatch because the enzymes substrate complex will be damaged and they will denature. But in general they follow a classic enzyme graph.

You may have done a similar experiment on seedling growth rate..this is virtually the same but you grow seeds in different temperatures and measure the change in height

do we need to know about the different types of reproductive barriers.. I have loads of notes on it but its no where in the syllabus that we need to know the different types

Thank you! What's the optimum temperature they hatch at?

Wha are the argumens against global warming? In terms of why CO2 and Methane dont contribute?

Also what is a classic answer for speciation have to include?
I always write geographical isolation, leads to different environmental conditions thus there are increased selective pressures which leads to mutations so that you can adapt and breed therefore survive. If mutation is beneficial it is passed onto the offspring, Which leads to a change in allele frequencies in the different gene pools. This means there is reproductive isolation and a restricted gene flow therefor speciation.

I think its 30 degrees but dont quote me..but i dont think you need to know it

Yep, yours is correct, I write this:
Speciation:
· Geographical isolation happens when a physical barrier divides a population of a species – floods, volcanic eruptions, and earthquakes can all cause barriers that isolate some individuals from the main population
· Conditions on either side of the barrier will be slightly different. For example, there may be different climate on each side. This will lead to selection pressures.
· Since the environment is different on each side, different characteristics (phenotypes) will become more common due to natural selection:
Ø Because different characteristics will be advantageous on each side, the allele frequencies will each change in each population, eg: if one allele is more advantageous on one side of the barrier, the frequency of that allele on that side will increase
Ø Mutations will take place independently in each population, also changing the allele frequencies
Ø The change in allele frequencies will lead to changes in phenotype frequencies, eg – the advantageous characteristics (phenotypes) will become more common on that side
· Eventually individuals from different populations will have changed so much that they won’t be able to breed with one another to produce fertile offspring (definition of species) – they’ll have become reproductively isolated
· The two groups will have become separate species

Could someone talk me through the core practical for hatching brine shrimps? I have no recollection of doing it at college whatsoever.

Basically, it is about finding the effect of temperature on the hatch rate of brine shrimp eggs.
Independent variable: Temperature
Dependent variable: Hatch rate

Procedure:
1. Take 5 beakers and fill them with equal volumes of salt solution. Label each beaker with temperature ( 5oC, 20oC, 30oC, 35oC, 40oC)
2. Place a pinch of brine shrimp eggs on a white card
3. Wet some graph paper and place it over the eggs. Use a magnifying glass to count 40 eggs (cut off some of it so that 40 eggs are present)
4. Place the graph paper on the solution for 5oC (egg-side facing into the solution) Leave for 3 mins. and remove the paper.
5. Place the beaker in a thermostatically controlled water bath (set at 5oC) for 24 hrs.
6. After 24 hrs, place a lamp near the beaker and count the number of eggs hatched.
7. Calculate hatch rate (no. of eggs hatched/no. of hours)
8. Carry out experiment for all temperatures. Repeat twice for each temperature and calculate average hatch rate.

Controlled variables:
- Concentration of salt solution
- No. of eggs used
- same batch of brine shrimp eggs
- time kept in water bath

Hope this helped

Basically, it is about finding the effect of temperature on the hatch rate of brine shrimp eggs.
Independent variable: Temperature
Dependent variable: Hatch rate

Procedure:
1. Take 5 beakers and fill them with equal volumes of salt solution. Label each beaker with temperature ( 5oC, 20oC, 30oC, 35oC, 40oC)
2. Place a pinch of brine shrimp eggs on a white card
3. Wet some graph paper and place it over the eggs. Use a magnifying glass to count 40 eggs (cut off some of it so that 40 eggs are present)
4. Place the graph paper on the solution for 5oC (egg-side facing into the solution) Leave for 3 mins. and remove the paper.
5. Place the beaker in a thermostatically controlled water bath (set at 5oC) for 24 hrs.
6. After 24 hrs, place a lamp near the beaker and count the number of eggs hatched.
7. Calculate hatch rate (no. of eggs hatched/no. of hours)
8. Carry out experiment for all temperatures. Repeat twice for each temperature and calculate average hatch rate.

Controlled variables:
- Concentration of salt solution
- No. of eggs used
- same batch of brine shrimp eggs
- time kept in water bath

Hope this helped

A species are a group of individuals that have similar similar characteristics and can breed to produce fertile offspring.

Reproductive isolation is when individuals of a species cannot breed with each other.
This may be due to a change in structure of reproductive organs, not allowing for sexuag,l reproduction.
It could also be because individuals in a population were geographically separated, and with time, developed different reproductive cycles or courtship behaviours that do not let them to breed with each other.
Reproductive isolation is a way that different species are formed.

Could someone explain DNA transcription/ translation..including what happens with the exons and the introns..and what is post transcriptional change?

Wha are the argumens against global warming? In terms of why CO2 and Methane dont contribute?

Eeeep, I could go through DNA transcription/translation but I'm still clueless about the other bit! I'll read through the official textbook and then let you know?

Heres translation and transcription for now:
Transcription:
· Transcription starts when RNA polymerase attaches to the DNA double-helix at the beginning of a gene
· The hydrogen bonds between the two strands in the gene break, separating the strands, the DNA molecule uncoils at the point
· One of the strands is then used as a template to make an mRNA copy, the DNA strand is called the antisense strand
· The RNA polymerase lines up free RNA nucleotides alongside the template strand. Complementary base pairing means that the mRNA strand ends up being a reverse copy of the DNA template strand
· Once the RNA nucleotides have paired up with their complementary bases on the DNA strand they’re joined together, forming an mRNA molecule
· The RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand
· The hydrogen bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and strands coil back into the double-helix
· When RNA polymerase reaches a stop codon, it stops making the mRNA and detaches from the DNA
· The mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where translation can take place.

Translation:
· The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to the ribosome
· A tRNA molecule, with an anticodon that’s complementary to the first codon on the mRNA, attaches itself to the mRNA by complementary base pairing
· A second tRNA molecule attaches itself to the next codon on the mRNA in the same way
· The two amino acids attached to the tRNA molecules are joined by a peptide bond.
· The first tRNA molecule moves away, leaving its amino acid behind
· A third tRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first two and second tRNA molecule moves away
· This process continues, producing a chain of linked amino acids (a polypeptide chain), until theres a stop codon on the mRNA molecule
· The polypeptide chain (protein) moves away from the ribosome

It depends on the context of the question, but mainly it will have something to do with the data records not going back far enough, how the ways of measuring climate change/CO2 concentrations are not reliable, extrapolating data is not always reliable, or possibly about how some scientists are biased for whatever reason.