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WJEC BY4 January 25 Unofficial Mark scheme

I thought it'd be useful to provide an unofficial mark scheme. Most of these will initially be off my memory so I don't remember the question numbers, sorry.

First question: (Labelling of the neurone)
From top to bottom:

i)Dendrite
Axon
Node of Ranvier
Synaptic Bulb

ii) Two types of effectors
Muscle
Gland

iii) Where would region X be found in a spinal cord?
Ganglion

iv) Which root would Y be found?
Ventral(As it's a motor neurone)

Kidney micrograph question:
There was definately a glomerulus and bowman's capsule present, not sure about the third one.

When asked which section of the kidney it is from, it's the cortex.

In micrograph B, those seen are loop of henle (ascending and descending) and collecting duct

Nitrogen cycle "filling in the gaps"

Pseudomonas decomposes the nitrates from plants into ammonia
Nitrosomonas convert ammonia into nitrites
Nitrobacter decompose the waste products of this bacteria to nitrates
Rhizobium found in root nodules
Azotobacter found free living in soil

Bacteria graph:
Why is the population growth less in lactate than in glucose?
Possibly because an enzyme is required to split lactate into its' monosaccharides
Possibly because it has less Carbons

Describe the graph of Q
Possible answers:
General increase, from 0-30 minutes it enters lag phase, synthesising of enzymes
30-210 enters log phase where it generally increases(population)
The dip could be due to intraspecific competition, or where nutrients ran out and were re-added
Enters stationary phase after 210 minutes, death rate = birth rate

Labelling of ATP:
What is the name of the reaction produces ATP?
Phosphorylation

What is the name of the pentose sugar?
Ribose

What is the name of the base?
Adenine

Describe how energy is released from ATP

High energy phosphate bonds hydrolyses. Catalysed by the enzyme ATPase. Releases 30 kJmol-1 of energy

Photosynthetic alga question:
Describe and explain the distribution of bacteria

The bacteria are found mainly in blue and red wavelength sections. Photosynthesis releases oxygen and takes place best with red and blue wavelengths of light. In these sections more oxygen will be present and so the oxygen seeking bacteria will be most likely to stay near these areas.

What would happen if the prism was removed?
The bacteria would align in the centre point (Where the light would shine)

Describe the process by which oxygen is released by the alga?
Non cyclic photophosphorylation. PSI loses 2 electrons which are replaced by 2 electrons from PSII. Water undergoes photolysis which products are oxygen, electrons and hydrogen. The electrons and hydrogen are used to reduce NADP and the oxygen is evolved - thus producing oxygen. (Worth 6 marks so more points would be needed)

Essay questions:

a) (I didn't do this so don't remember it)

b) i) Describe the important of the cell membrane in nerve transmission:
Explain about there being pumps and channels in the membrane and when an impulse arrives the Na+ channels open and the Na+ ions rush in by diffusion, depolarising the membrane. Then K+ channels open and this causes repolarisation. There is a refactory period where the channels and pumps can not work which ensures unidirectionality. (Requires more points as it was 7 marks)

ii) And in nerve transmission across a synapse:

Describe how the impulse causes Ca2+ to move into the synaptic bulb and this causes the synaptic vesicles to fuse with the presynaptic membrane, secreting their neurotransmitter by exocytosis. This diffuses across the synaptic cleft and the protein receptors in the post synaptic membrane detect them, which causes the Na+ channels in the post synaptic neurone to open, and Na+ diffuses in, causing depolarisation.

If you know any more questions/want to know answers let me know and I'll try and remember what I put. :smile:

P.S. These are what I wrote and asked my teacher and so they may or may not be correct

(edited 12 years ago)

Scroll to see replies

Reply 1

Rhodz999

Nitrogen cycle "filling in the gaps"

Pseudomonas decomposes the nitrates from plants into ammonia

Pseudomonas are denitrifying bacteria and so convert ammonia/ammonium ions + nitrates back to nitrogen
the opposite reaction of nitrification.

Reply 2

WelshLewis!

Original post by Rhodz999

yeah you're right. for that blank i put 'decomposing bacteria and fungi' because we aren't actually given a name in the guide or anywhere else.

Reply 3

AlexBamsey

Original post by WelshLewis!

yeah you're right. for that blank i put 'decomposing bacteria and fungi' because we aren't actually given a name in the guide or anywhere else.

Ah right. In my WJEC guide (The black/green one) it had psuedomonas in it :tongue:

Reply 4

AlexBamsey

Ah my bad guys I see what you mean now! I said putrefying bacteria I think.

Reply 5

SophieArmstrong

For question one, wouldn't structure X be found in the grey matter, as it was a motor neurone, and it's the cell bodies of sensory neurones that are found in the dorsal root ganglia?

Reply 6

lee_vassallo

The bit labelled X was grey matter and motor neurones are found in the ventral root

Reply 7

Kharman11

Original post by WelshLewis!

yeah you're right. for that blank i put 'decomposing bacteria and fungi' because we aren't actually given a name in the guide or anywhere else.

I pit putrefaction bacteria, how do you know?

Reply 8

Kharman11

Original post by lee_vassallo

The bit labelled X was grey matter and motor neurones are found in the ventral root

Are you certain?

Reply 9

WelshLewis!

Original post by Kharman11

I pit putrefaction bacteria, how do you know?

How do I know what? Putrefaction is also correct.

Reply 10

WelshLewis!

Original post by AlexBamsey

Ah my bad guys I see what you mean now! I said putrefying bacteria I think.

Do you know when we normally get these results? I didn't sit any in January last year.

Reply 11

XO*

Synaptic bulb? Surely it was axon terminals.

Reply 12

Fatcho10

Original post by XO*

Synaptic bulb? Surely it was axon terminals.

This is what I was told too.

Reply 13

XO*

It was putrefaction not dentrification. So the answer was saprobiotic bacteria.

Pretty sure it was dorsal root.

(edited 12 years ago)

Reply 14

XO*

Original post by AlexBamsey

I thought it'd be useful to provide an unofficial mark scheme. Most of these will initially be off my memory so I don't remember the question numbers, sorry.

P.S. These are what I wrote and asked my teacher and so they may or may not be correct

In that case why title this as a mark scheme?

Reply 15

WelshLewis!

Axon terminal/ Synaptic Knob/ Synaptic Terminal are normally all acceptable. Never heard of Synaptic Bulb though.
And my teacher said it was the ventral root.

Reply 16

Kharman11

Original post by XO*

Synaptic bulb? Surely it was axon terminals.

This is what I put also

Reply 17

LGrosvenor101

Original post by XO*

It was putrefaction not dentrification. So the answer was saprobiotic bacteria.

Pretty sure it was dorsal root.

I'm guessing decomposers would be alright as well? Had to decide between putrefaction and decomposers, so put the substance that does it as the rest of the passage was mostly talking about the substances/enzymes. I am guessing they would accept but putrefaction and decomposers though, as it was not made clear whether to put the name of the process, or what actually does it? :smile:

Reply 18

supersajjad

It is putrefaction, denitrification is wrong because it's a different process, and it was grey matter, not ganglian, i think x on the kidney picture was an efferent arteriole