WJEC biology BY4 11/01/2013

So, someone asks a question, then the person who answers it asks another. Go. Define homeostasis

The manintance of internal optimal conditions for cellular reactions

PCT adaptations?

Contain large number of mitochondria for active transport.
It's long and winding nature along with a brush border of microvilli increase surface area from which selective reabsorbtion can occur.
Describe and explain photosynthesis.
Also heres a question, does cyclic take place whilst non-cyclic is going on. Is it just part of non-cyclic?

I don't cover cyclic/ non cyclic or in as much detail in human bio

Light dependent- takes place in thykaloid

light hits chlorophyll causing a photoexcitation of an electron. The electron is passed to an electron acceptor molecule. the acceptor passes it to a chain of electron carriers as with the chemiosmotic theory, as the electron is passed ATP is produced by photophosphorylation (trapping of chemical energy from sunlight)

Water is split by photolysis into oxygen (released as a waste gas) hydrogen which reduces NADP to NADPH2 and an electron which reduces the chlorophyll

Calvin cycle- takes place in the stroma:

CO2 (fixed) combines with RuBP by a catalysed reaction using the enzyme rubisco to form an unstable 6C molecule which quickly splits into 2 3C molecules of GP. ATP and NAPH2 reduce and phosphorylate it into triose phosphate, 5/6 of which is regenerated into RuBP whilst the remaining amount can be converetd into glucose, amino acids which are used in the plants metabolism

That's pretty good knowledge for not doing it in detail, there isn't a great more in our syllabus to be perfectly honest!
Another question?

why do farmers plough the soil after each harvest?

Umm anyway, back BY4, describe the population growth curve

Improve aeration of the soil, and too encourage nitrogen fixation.

For bacteria (as that's the most common)Lag phase - Adapting to environment, high metabolic rate, protein synthesis. Little or no population growth.Log phase - Rapid population growth. Birth rate > Death rate. Sufficient nutrients etcStationary phase - Stable population, no growth. Birth rate = Death rate. Population limited by nutrients etcDeath Phase - Decline in population due to death of cells. Death rate > Birth rate. Due to lack of nutrients etc.Question; Describe and explain the effect on nerve transmission of each of the following; Myelin, Axon Diameter

Hey! Quick question!

In the Nitrogen cycle is the process called "Putrefaction" or "Putrefication" simply because in the student guide they use "Putrefaction" however just looking through the mark scheme for Jan 12 and they use "Putrefication"...So not sure which one to use!

Thank you!

Myelin increased speed of impulse transmission because of salt story conduction. The impulse jumps between each node of ranvier. The larger the axon diameter the faster the impulse because of the increase in velocity?

Hey use putrefaction

I have a quick question! Ultrafiltration, driven by hydrostatic pressure - the pressure's generated by changes in diameter between afferent and efferent arterioles and then apparently due to the water potential of the blood or something - could someone explain how the water potential of the blood generates pressure? It was never explained to us and I find it so much easier to remember things if I completely understand it!

Thanks!

I've never heard that second one to be a reason. The other one I've got in my notes is that the narrowness of the capillaries forces blood through at high hydrostatic pressure.