The Biology AS-level Thread

Oh yh there is only one EMPA exam... but what about the Task 1 and Task 2 Questions ?
He said it might be on either enzymes or something.. hasn't confirmed it..

the questions are all based on the empa exams!

Has anyone actually done the AQA EMPA tasks yet?

How's it going guys?

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Yes, I am.

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Always remember the side with greater pressure is what is pushing the valve. (In most cases to open)


. During Diastole as the blood enters the atria from the pulmonary vein and vena cava pressure builds up in the atria as it fills which pushes open the atrioventricular valves.


. The semi lunar valves are shut at this time as the muscles in the ventricles are relaxed which helps in reducing the pressure in the ventricles causing the pressure to be lower here than in the aorta and pulmonary artery. The semi lunar valve is thus shut which causes the first dub sound of the heart.

This is what I do not get. Thanks so much for the diagram and explanation it makes sense. BUT not with what the text book says. It says: Valves are made up of a number of flaps of tough but flexible fibrous tissue which are cusp shaped. It then says when pressure is greater on the CONVEX side it causes the cusps to move apart and blood to flow though them. And then when pressure is greater on the CONCAVE side it causes blood to fill up in the bowl of the cusps pusshing them together preventing backflow of blood.

Do you get where I'm confused?

This is what I do not get. Thanks so much for the diagram and explanation it makes sense. BUT not with what the text book says. It says: Valves are made up of a number of flaps of tough but flexible fibrous tissue which are cusp shaped. It then says when pressure is greater on the CONVEX side it causes the cusps to move apart and blood to flow though them. And then when pressure is greater on the CONCAVE side it causes blood to fill up in the bowl of the cusps pusshing them together preventing backflow of blood.

Do you get where I'm confused?

Could you say what exactly the textbook says (not with your own words)

Well if you look at the diagram above the side labelled convex has the cusps concave and the concave side has the cusps convex

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Yes if you could write the exact words of the book, it will help me understand the description of the book better. Also what book is this?



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Ive finally go it...well I think I now understand it....we were taught Meiosis the other day in college but not to much detail and I didnt understand it. Just read the book. Im going to try and explain what I think it is, if I make any mistakes I would appreciate if someone points it out.


Meiosis occurs in order to divide a diploid cell to form 4 haploid cells.In interphase the DNA is being replicated to make an exact copy of the DNA. The chromosomes can not be seen at this stage. After this stage is Prophase I where the DNA & the replicated DNA join up and are in conjunction with proteins to form chromosomes. Homologous pairs of chromosomes then partner up and 2 things happen which are important to how each haploid cell differs. Crossing and homologous recombination. The homologous chromosomes interlink and wind certain sections of the chromosomes creating tension. This tension causes a parts of the chromosomes to come off which is attached unto the other same section of the partnered homologous chromosome. The next step is metaphase I where the centresome and microtubicles in the cell help to align the homologous pair of chromosome in a line in the middle of the cell and then Anaphase I occurs where a chromosome is pulled from each pair of chromosomes. Then in telephase I the nuclear membrane reforms and nucleoli within them as the chromosomes frail back into chromatids. The increased froce between the 2 new cells called cleavage separates the nuclei and forms 2 cells in a process called cytokineses.


Prophase II occurs where the DNA join back together to form chromosomes and these chromosomes. Then it is metaphase II where the chromosomes are moved and arranged in a line by structures called the microtubicles and centresomes. Anaphase II then occurs as the chromosome is split into 2 chromatids which in are separated. The nuclear membrane then reforms in Telephase II and 2 nuclei are formed due to the increasing force causing a cleavage. The 2 cells are then formed through a process called cytokineses.

Hahaa yes my own words are confusing . Okay straight from the text book:

" The design of all the valves is basically the same. They are made up of a number of flaps of tough, but flexible fibrous tissue, which are cusp shaped. When pressure is greater on the convex side of these cusps rather than the concave side they move apart to let blood pass between these cusps. However, when pressure is greater on the concave side, than on the convex side, blood collects within the bowls of the cusps. This pushes them together to form a tight fit that prevents the passage of blood."

And that's word to word from the text book.

Hahaa yes my own words are confusing . Okay straight from the text book:

" The design of all the valves is basically the same. They are made up of a number of flaps of tough, but flexible fibrous tissue, which are cusp shaped. When pressure is greater on the convex side of these cusps rather than the concave side they move apart to let blood pass between these cusps. However, when pressure is greater on the concave side, than on the convex side, blood collects within the bowls of the cusps. This pushes them together to form a tight fit that prevents the passage of blood."

And that's word to word from the text book.

I wrote the words of the text book in my post above and its the Nelson Thornes AQA text book. Thanks for the meiosis thingy by the way but I finally got my head around that haaha!