A2 Biology Discussion and Help

MUSCLE CONTRACTION HELP!

How do you know the difference between A band, I band, Z line etc What do they mean????

A sarcomere is the area between the two Z lines.
The I band is the area with only the actin filaments.
The H band is the area with only the myosin filaments.
The A band is the area where you have both the myosin and actin filaments.

When the muscle contracts, the whole length of the sarcomere decreases, as the actin filaments slide over the myosin filaments. The length of the I band and the H band decrease. The size of the A band however stays the same, as the length of the myosin filaments doesn't change.

Thank you so much! You managed to make that 1000x easier than anyone else has ever made it out to be aha

No problem good luck! Which exam board are you doing? I think with most of them that amount of detail is ok

OCR

can anyone please solve these 2 with full working out its from aqa biology unit 4 june 2014

What does it mean to say an ecosystem is dynamic?

Guyssss helppppp. Basically with the resting potential it is said that most of the ion channels - both sodium and potassium ion channels are closed but I don't understand it when it says that the membrane is more permeable to potassium ions doesn't that mean that the potassium ions channels are open - it did mention that some channels can be open or closed but I saw this question and it wanted to know whether the potassium / sodium ions channels are open or closed during resting potential and the mark scheme said potassium ion channels are closed. Will we only refer to the opening of potassium ions channels when it is trying to establish a resting potential so repolarization but on the whole when it is at resting potential then both sodium and potassium channels are closed? Btw I'm AQA

During resting potential the aim is to get a negative charge inside of the neurone so
- Na+ ion channels are closed - so we say the membrane is less permeable to Na+
- The Na+ K+ pump uses ATP to actively pump 3Na+ out of the neurone and pumps 2K+ into the neurone
- BUT it wants a negative charge inside the cell so we need to get rid of those positive K+: so we have K+ channels open so the K+ diffuse out

Omg thank you so much! But on the whole you would say that at a resting potential stage majority of the channels are closed hence the question I mentioned before right?