Revision PPT Notes Flashcards
What is a Mutation?
Change in the sequence of DNA bases
Name the two types of Mutations and give definition
Substitution: One base replaced with another
Deletion: One base removed from the sequence
Can Mutations be beneficial?
Yes because randomly-occurring mutations sometimes result in a new allele being formed
Some can be beneficial as it could enable an or be better adapted than before.
How does Natural Selection work?
- Organism with an advantageous allele have higher survival chance
- They survive and reproduce, passing advantageous allele to offspring
- Next Generation have higher proportion of advantageous allele
- Next generation have higher survival chances, reproduce and pass on advantageous allele
- Frequency of advantageous allele increases from generation to generation
- Over time (through generations) this leads to evolution
Explain Negative Feedback Loop
Optimum Conditions
Change from optimum
Receptor detects change
Communication system tells effector
Effector reacts to reverse change
Return to Optimum conditions
What happens when Blood Glucose Level Rises?
Beta cells in Pancreas detect rise in Blood Glucose Level
They respond by producing Insulin directly into Blood Plasma
This is done by:
- Insulin binding to glycoprotein receptors on cell body surface membrane, stimulate cells to take in more glucose
- Insulin bind to glycoprotein receptors on Liver cells, stimulate liver to release enzymes that catalyse the conversion of glucose to glycogen
What happens when Blood Glucose Level Decreases?
Alpha cells in Pancreas detect decrease in Blood Glucose level
They respond by producing Glucagon into blood plasma
Only Liver responds as only they have cells that have receptors binding to glucagon
Liver cells activate enzyme that converts glycogen to glucose. They also increase gluconeogenesis - conversion of amino acids and glycerol into glucose
Definition of Nervous System
Made up of complex network of cells called neurones
What is a Neurone?
Specialised cell adapted to carrying electrochemical changes called nerve impulses from one part of the body to another
What is a Nerve impulse?
Temporary reversal of the electrical potential across the axon membrane
Reversal is between two states called resting potential and action potential
This is achieved by movement of sodium and potassium ions across membrane
Describe Resting Potential
Inside of Axon negatively charged compared to outside
Resting Potential usually at -70mV
Membrane is polarised
Difference in charge between the inside and outside is achieved by several mechanisms
Describe the Sodium Potassium Pump
Sodium potassium pump actively transports 3 Na+ ions OUT of Axon
For every 3 Na+ transported out, 2K+ pumped INTO the Axon
Describe Action Potential
Inside of Axon is now positively charged compared to outside
Action potential usually around +40mV
Membrane is Depolarised
Reversal of charges caused by energy from a stimulus
Describe stages of an Action Potenial
- Resting Potential - Na+/K+ Pump
- Depolarisation - Voltage-gated Na+ Channel
- Repolarisation - Voltage-gated K+ Channel
- Resting Potential - Na+/K+ Pump
How does an Action Potential occur?
Voltage-dependent Na+ channels open. Na+ flow into the axon, depolarising the membrane
Voltage-dependent Na+ channels close. Voltage-dependent K+ channels open. K+ leave the axon, repolarising the membrane
The membrane is hyperpolarised. Voltage-dependent K+ channels close. K+ diffuse back into the axon to recreate the resting potential
