A2 Biology OCR June 2015 Revision Thread

Original post by HeyThereHarry

Can anybody clarify this for me:

Why does interbreeding two organisms with different numbers of chromosomes produce infertile offspring?

I know that having an uneven number of chromosomes means homologous pairs can't form so meiosis can't occur.

As you quite rightly say, meiosis cannot occur when bivalents are unable to form. This is because some of the chromosomes will be unable to pair up and thus the separation of homologous chromosomes at Anaphase I cannot happen (as some didn't pair up in the first place).

Don't doubt yourself, you understand it! :smile:

Reply 762

Original post by TheLegalDealer

NMJ only has acetylcholine as the neurotransmitter while S has acetylcholine + many others

S is between 2 neurons while NMJ is between a neuron and muscle

S requires many action potentials to cause deporisation while the NMJ requires only one
+ S has many enzymes to breakdown the neurotransmitters

Thanks!

Although, this is where I am getting confused as at the neuromuscular junction between a sympathetic neurone and an effector the neurotransmitter is noradrenaline? So the NMJ's do use more than just acetylcholine?

Reply 763

Original post by Hilton184

At the neuromuscular junction - in other words, the synapse between the postganglionic neurone and the effector, the neurotransmitter is acetylcholine.

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But what about between the effector and the neurone when that neurone is sympathetic, is the neurotransmitter not then noradrenaline?

Reply 764

Does anyone know what the hydrogen acceptors are in anaerobic respiration?
My textbook is once again confusing me, whilst it says that in mammals pyruvate is the hydrogen acceptor, it says for yeast that ethanol is?

Does anyone know whether it should be pyruvate and ethanal, or lactate and ethanol?

Reply 765

a123a

14

Original post by Glh96

Does anyone know what the hydrogen acceptors are in anaerobic respiration?
My textbook is once again confusing me, whilst it says that in mammals pyruvate is the hydrogen acceptor, it says for yeast that ethanol is?

Does anyone know whether it should be pyruvate and ethanal, or lactate and ethanol?

The hydrogen acceptor is pyruvate for lactate fermentation and ethanal for alcoholic fermentation. I remember an exam question on this and ethanal was the right answer.

Reply 766

Beni24

2

Guys I know we've still got a few weeks to go but does anyone have any predictions for F214 or F215? :smile:

Reply 767

Original post by a123a

The hydrogen acceptor is pyruvate for lactate fermentation and ethanal for alcoholic fermentation. I remember an exam question on this and ethanal was the right answer.

Thanks, it says ethanol in the back but I guess that's just another OCR textbook error!

Reply 768

charlottealevel

could someone explain this for me please :smile:

- 'describe how artificial selection has been used to produce bread wheat (Triticum aestivum)'

Reply 769

Original post by Glh96

Thanks!

Although, this is where I am getting confused as at the neuromuscular junction between a sympathetic neurone and an effector the neurotransmitter is noradrenaline? So the NMJ's do use more than just acetylcholine?

No, it's ACh only.

Reply 770

Original post by AnnekaChan173

No, it's ACh only.

.?

Reply 771

Original post by Glh96

.?

at a synapse? Synapses are neurone to neurone. Not at the NMJ, the NMJ is always ACh only.

Reply 772

bakedbeans247

20

Anyone have any predictions of topics for this years A2 exams? :smile:

Reply 773

Original post by bakedbeans247

Anyone have any predictions of topics for this years A2 exams? :smile:

Galapagos. I'm so worried.

Reply 774

Hilton184

9

Original post by Glh96

But what about between the effector and the neurone when that neurone is sympathetic, is the neurotransmitter not then noradrenaline?

You are confusing two different things here.

Neuromuscular junction I believe is the synapse between a somatic motor neurone and a sarcomere/muscle fibre. This is voluntary controlled. We voluntarily move our arms.

Sympathetic neurones are part of the autonomic nervous system - involuntary controlled - increase heart rate for example. Noradrenaline released here is not at a neuromuscular junction.

Neuromuscular junction is between somatic motor neurone and a skeletal muscle.

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(edited 8 years ago)

Reply 775

bbadonde2

4

Original post by AnnekaChan173

Galapagos. I'm so worried.

Just remember habitat destruction, overeploitation of species and introduction of new species, then fill in the rest with facts! E,g. Red quinine tree out competes scalesia tree!

Reply 776

Original post by bbadonde2

Just remember habitat destruction, overeploitation of species and introduction of new species, then fill in the rest with facts! E,g. Red quinine tree out competes scalesia tree!

How do you remember the tree names? So much to revise, so little time :frown:

Reply 777

bbadonde2

4

Yeah a neuromuscular junction is from neurone to muscle.

There are also ganglionic synapses at the effectors in the autonomic nervous system. The sympathetic uses noradrenaline as a neurotransmitter at these synopses and the parasympathetic uses acetylcholine

Original post by Hilton184

You are confusing two different things here.

Neuromuscular junction I believe is the synapse between a somatic motor neurone and a sarcomere/muscle fibre. This is voluntary controlled. We voluntarily move our arms.

Sympathetic neurones are part of the autonomic nervous system - part of the autonomic nervous system. Noradrenaline released here is not at a neuromuscular junction.

Posted from TSR Mobile

Reply 778

bbadonde2

4

Original post by AnnekaChan173

How do you remember the tree names? So much to revise, so little time :frown:

I base my revision on key points and then fill in with facts. I don't know it just stays in!

Reply 779