• We need your support!

    We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
    Click here to Donate Now (View Announcement)

A level Biology: Post your doubts here!

Messages
185
Reaction score
37
Points
38
Describe the structure of a myelinated sensory neurone. [7]
(b) Explain how an action potential is transmitted along a sensory neurone. [8]
[Total18

1 nucleus in cell body ;
2 (long) dendron ; R plural
3 (shorter) axon ;
4 many mitochondria (in cell body) ;
5 many RER/nissl’s granules, (in cell body) ;
6 synaptic knobs ;
7 detail of synaptic knob ;
8 (terminal) dendrites ;
9 Schwann cells ;
10 detail of myelin sheath ;
11 nodes of Ranvier ;
accept points on labelled diagram [7 max]
(b) 12 Na+ channels open ; A sodium channels
13 Na+ enter cell ; R enter membrane
14 inside becomes, less negative/positive/+40mV or membrane depolarised ;
15 Na+ channels close ; A sodium channels
16 K+ channels open ; A potassium channels
17 K+ move out (of cell) ; R of membrane
18 inside becomes negative or membrane repolarised ; A negative figure
max 5
19 local circuits/description ;
20 (myelin sheath/Schwann cells) insulate axon/does not allow movement of ions ;
21 action potential/depolarisation, only at nodes (of Ranvier)/gaps ;
22 saltatory conduction/AW ;
23 one-way transmission ;
24 AVP ; e.g. hyperpolarisation/refractory period

can anyone help me to integrate those marking points to make a proper answer
 
Messages
4,988
Reaction score
23,955
Points
523
Describe the structure of a myelinated sensory neurone. [7]
(b) Explain how an action potential is transmitted along a sensory neurone. [8]
[Total18

1 nucleus in cell body ;
2 (long) dendron ; R plural
3 (shorter) axon ;
4 many mitochondria (in cell body) ;
5 many RER/nissl’s granules, (in cell body) ;
6 synaptic knobs ;
7 detail of synaptic knob ;
8 (terminal) dendrites ;
9 Schwann cells ;
10 detail of myelin sheath ;
11 nodes of Ranvier ;
accept points on labelled diagram [7 max]
(b) 12 Na+ channels open ; A sodium channels
13 Na+ enter cell ; R enter membrane
14 inside becomes, less negative/positive/+40mV or membrane depolarised ;
15 Na+ channels close ; A sodium channels
16 K+ channels open ; A potassium channels
17 K+ move out (of cell) ; R of membrane
18 inside becomes negative or membrane repolarised ; A negative figure
max 5
19 local circuits/description ;
20 (myelin sheath/Schwann cells) insulate axon/does not allow movement of ions ;
21 action potential/depolarisation, only at nodes (of Ranvier)/gaps ;
22 saltatory conduction/AW ;
23 one-way transmission ;
24 AVP ; e.g. hyperpolarisation/refractory period

can anyone help me to integrate those marking points to make a proper answer
I remember sharing P4 solved thread's link here.
I'm just gonna copy paste the thing since I actually found it helpful.I know the answer may seem so huge.But it's good incase you can't recall some points.
I hope this helps.

PART A

A sensory neuron has a long dendron and an axon which is often shorter than the dendron. Within the cytoplasm of an axon, all of the usual organelles such as endoplasmic reticulum, Golgi apparatus and mitochondria, are present. Large numbers of mitochondria are found at the tips of the terminal branches of the axon, together with many vesicles containing chemicals called transmitter substances.
The axon and dendron is insulated by the myelin sheath. The myelin sheath is made largely of lipid, together with some proteins, and is formed by a Schwann cell wrapping around the axon many times. This forms many layers of cell membrane surrounding the axon.
At intervals, there are gaps in the sheath between each Schwann cell, called nodes of Ranvier.

PART B

An action potential is generated in the sensory neuron, where an impulse reaches the neuron, leading to the opening of Na+ channels. This causes Na+ ions to move down their concentration gradient and into the neuron, increasing the potential difference of the cell from -70 mV to +40 mV. This is known as depolarization. Once the potential difference reaches +40 mV, an action potential is generated. The Na+ channels then close and the K+ channels open causing K+ ions to move out of the cell. This decreases the potential difference of the neuron (repolarisation) and continues even after the potential difference drops below -70 mV due to the opening of large number of K+ channels. This is known as hyperpolarisation. However, the cell regains its resting potential of -70 mV as the K+ channels close.
The action potential jumps from one node of Ranvier to the next. This is because this is the only place where the sodium ions can pass across the membrane, as the myelin sheath insulates the axon and hence prevents the movement of ions across it. This is called saltatory conduction. The period between one action potential and another, is known as refractory period.
 
Messages
4,988
Reaction score
23,955
Points
523
Describe the structure of a myelinated sensory neurone. [7]
(b) Explain how an action potential is transmitted along a sensory neurone. [8]
[Total18

1 nucleus in cell body ;
2 (long) dendron ; R plural
3 (shorter) axon ;
4 many mitochondria (in cell body) ;
5 many RER/nissl’s granules, (in cell body) ;
6 synaptic knobs ;
7 detail of synaptic knob ;
8 (terminal) dendrites ;
9 Schwann cells ;
10 detail of myelin sheath ;
11 nodes of Ranvier ;
accept points on labelled diagram [7 max]
(b) 12 Na+ channels open ; A sodium channels
13 Na+ enter cell ; R enter membrane
14 inside becomes, less negative/positive/+40mV or membrane depolarised ;
15 Na+ channels close ; A sodium channels
16 K+ channels open ; A potassium channels
17 K+ move out (of cell) ; R of membrane
18 inside becomes negative or membrane repolarised ; A negative figure
max 5
19 local circuits/description ;
20 (myelin sheath/Schwann cells) insulate axon/does not allow movement of ions ;
21 action potential/depolarisation, only at nodes (of Ranvier)/gaps ;
22 saltatory conduction/AW ;
23 one-way transmission ;
24 AVP ; e.g. hyperpolarisation/refractory period

can anyone help me to integrate those marking points to make a proper answer

Na⁺ ion channels open, Na⁺ ions enter the cell, the inside becomes positive in other words depolarised. Na⁺ channels then close, K⁺ channels open, and K⁺ move out of the cell, the inside becomes negative or repolarised. Local circuits are built up. The myelin sheat insulates the axon so an action potential occurs only at the nodes of Ranvier. The action potential jumps from node to node, this is known as saltatory conduction. There is one-way transmission as the node behind the action potential is still in the refractory period.

This is a simpler and shorter version for part b.
 
Messages
185
Reaction score
37
Points
38
I remember sharing P4 solved thread's link here.
I'm just gonna copy paste the thing since I actually found it helpful.I know the answer may seem so huge.But it's good incase you can't recall some points.
I hope this helps.

PART A

A sensory neuron has a long dendron and an axon which is often shorter than the dendron. Within the cytoplasm of an axon, all of the usual organelles such as endoplasmic reticulum, Golgi apparatus and mitochondria, are present. Large numbers of mitochondria are found at the tips of the terminal branches of the axon, together with many vesicles containing chemicals called transmitter substances.
The axon and dendron is insulated by the myelin sheath. The myelin sheath is made largely of lipid, together with some proteins, and is formed by a Schwann cell wrapping around the axon many times. This forms many layers of cell membrane surrounding the axon.
At intervals, there are gaps in the sheath between each Schwann cell, called nodes of Ranvier.

PART B

An action potential is generated in the sensory neuron, where an impulse reaches the neuron, leading to the opening of Na+ channels. This causes Na+ ions to move down their concentration gradient and into the neuron, increasing the potential difference of the cell from -70 mV to +40 mV. This is known as depolarization. Once the potential difference reaches +40 mV, an action potential is generated. The Na+ channels then close and the K+ channels open causing K+ ions to move out of the cell. This decreases the potential difference of the neuron (repolarisation) and continues even after the potential difference drops below -70 mV due to the opening of large number of K+ channels. This is known as hyperpolarisation. However, the cell regains its resting potential of -70 mV as the K+ channels close.
The action potential jumps from one node of Ranvier to the next. This is because this is the only place where the sodium ions can pass across the membrane, as the myelin sheath insulates the axon and hence prevents the movement of ions across it. This is called saltatory conduction. The period between one action potential and another, is known as refractory period.
i didnt understand in terminal branches there are synapse
 
Messages
185
Reaction score
37
Points
38
I remember sharing P4 solved thread's link here.
I'm just gonna copy paste the thing since I actually found it helpful.I know the answer may seem so huge.But it's good incase you can't recall some points.
I hope this helps.

PART A

A sensory neuron has a long dendron and an axon which is often shorter than the dendron. Within the cytoplasm of an axon, all of the usual organelles such as endoplasmic reticulum, Golgi apparatus and mitochondria, are present. Large numbers of mitochondria are found at the tips of the terminal branches of the axon, together with many vesicles containing chemicals called transmitter substances.
The axon and dendron is insulated by the myelin sheath. The myelin sheath is made largely of lipid, together with some proteins, and is formed by a Schwann cell wrapping around the axon many times. This forms many layers of cell membrane surrounding the axon.
At intervals, there are gaps in the sheath between each Schwann cell, called nodes of Ranvier.

PART B

An action potential is generated in the sensory neuron, where an impulse reaches the neuron, leading to the opening of Na+ channels. This causes Na+ ions to move down their concentration gradient and into the neuron, increasing the potential difference of the cell from -70 mV to +40 mV. This is known as depolarization. Once the potential difference reaches +40 mV, an action potential is generated. The Na+ channels then close and the K+ channels open causing K+ ions to move out of the cell. This decreases the potential difference of the neuron (repolarisation) and continues even after the potential difference drops below -70 mV due to the opening of large number of K+ channels. This is known as hyperpolarisation. However, the cell regains its resting potential of -70 mV as the K+ channels close.
The action potential jumps from one node of Ranvier to the next. This is because this is the only place where the sodium ions can pass across the membrane, as the myelin sheath insulates the axon and hence prevents the movement of ions across it. This is called saltatory conduction. The period between one action potential and another, is known as refractory period.
u mentioned nothing about local circuits in part b
 
Messages
185
Reaction score
37
Points
38
I remember sharing P4 solved thread's link here.
I'm just gonna copy paste the thing since I actually found it helpful.I know the answer may seem so huge.But it's good incase you can't recall some points.
I hope this helps.

PART A

A sensory neuron has a long dendron and an axon which is often shorter than the dendron. Within the cytoplasm of an axon, all of the usual organelles such as endoplasmic reticulum, Golgi apparatus and mitochondria, are present. Large numbers of mitochondria are found at the tips of the terminal branches of the axon, together with many vesicles containing chemicals called transmitter substances.
The axon and dendron is insulated by the myelin sheath. The myelin sheath is made largely of lipid, together with some proteins, and is formed by a Schwann cell wrapping around the axon many times. This forms many layers of cell membrane surrounding the axon.
At intervals, there are gaps in the sheath between each Schwann cell, called nodes of Ranvier.

PART B

An action potential is generated in the sensory neuron, where an impulse reaches the neuron, leading to the opening of Na+ channels. This causes Na+ ions to move down their concentration gradient and into the neuron, increasing the potential difference of the cell from -70 mV to +40 mV. This is known as depolarization. Once the potential difference reaches +40 mV, an action potential is generated. The Na+ channels then close and the K+ channels open causing K+ ions to move out of the cell. This decreases the potential difference of the neuron (repolarisation) and continues even after the potential difference drops below -70 mV due to the opening of large number of K+ channels. This is known as hyperpolarisation. However, the cell regains its resting potential of -70 mV as the K+ channels close.
The action potential jumps from one node of Ranvier to the next. This is because this is the only place where the sodium ions can pass across the membrane, as the myelin sheath insulates the axon and hence prevents the movement of ions across it. This is called saltatory conduction. The period between one action potential and another, is known as refractory period.
u wrote that Na ion move down concentration gradient into sensory neuron
how synapse usually separate receptor from sensory neuron
i think we should say that receptor activates sensory neuron
 
Messages
397
Reaction score
2,898
Points
253
Can anyone see my answer for this question and tell me how many marks I should earn please?( it holds 4 marks)1221.png
My answer: amylose is formed by joining multiple glucose units unto unbranched 1,4 glycosidic bonds.amylopectin is formed from joining multiple glucose units into 1,4 glycosidic bonds branching from 1,6 glycosidic bond.
 
Messages
4,988
Reaction score
23,955
Points
523
Can anyone see my answer for this question and tell me how many marks I should earn please?( it holds 4 marks)View attachment 59707
My answer: amylose is formed by joining multiple glucose units unto unbranched 1,4 glycosidic bonds.amylopectin is formed from joining multiple glucose units into 1,4 glycosidic bonds branching from 1,6 glycosidic bond.
3 I think. :p
Do mention condensation or alpha helix or branches.
Hey guys, can anybody help me with this question? i wrote my answer but i am not sure if it should fulfil the markscheme or not,so here is the question:
View attachment 59554 View attachment 59555
My answer:
a-glucose molecules are bonder together as monomers from carbon 1 to carbon 4 to form unbranched chain known as amylose. a-glucose molecules are bonded together by both c1 to c4 and c1 to c6 to from a polysacharride with a branched chain known as amylopectin.

so, how many points should i earn for my answer?

thanks in advance. :)
I think you would get 3 or full marks. You should've also mentioned about condensation.

This is what I wrote...maybe it can help.
View attachment 59556
 
Top