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Biology A Level!

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(OCR) Plants - Part I. (OCR) Plants - Part II. (OCR) Cell Membranes. (OCR) 5 Unexpected Diseases of Smoking. (OCR) Triglycerides, Phospholipids and Cholesterol. (OCR) Enzymes - Part I. (SNAB Edexcel) The Different Parts Of The Brain. (SNAB Edexcel) Topic 8 - All You Need To Know - Part I. An axon's inside has a voltage of -70 millivolts (mV). Because the outside of an axon's membrane is not charged and the inside is at -70mV, the membrane of an axon has a potential difference across it. The membrane of an axon is therefore said to be polarised. There is an uneven distribution of ions across the cell membrane of an axon than would be expected from just diffusion occurring. This means that the axon is controlling what concentration of ions it keeps inside of itself. It does this via sodium - potassium pumps in its cell surface membrane. Sodium - potassium pumps pump sodium out of the cell and potassium into it.

These pumps work against the concentration gradient found in the axon cell surface membrane, having more potassium in the cell than out of it, but still pumping more in (working against diffusion). Since potassium ions are positive, the axon becomes more negative due to its loss of potassium. (SNAB Edexcel) Atherosclerosis. (SNAB Edexcel) Blood Clotting.