OCR Biology F211 Exam - Tues 11'th January 2011

Evidence for the use of the phloem

- If a plant is supplied with radioactively labelled carbon dioxide, the carbon soon appears in the phloem

- ringing a tree to remove the phloem causes sugars to collect above the ring

_ An aphid feeding on the plant stem leaves mouthparts showing it is taking food from the phloem.

My textbook says that an aphid feeds from the phloem, which is located on the plant stem...how sure are you about this leaf thing?

My textbook says that an aphid feeds from the phloem, which is located on the plant stem...how sure are you about this leaf thing?

My textbook says that an aphid feeds from the phloem, which is located on the plant stem...how sure are you about this leaf thing?

Carriage of CO2

CO2 transported in blood in 3 main ways:
1) 85% in the form of Hydrogen carbonate ions
2) 5% dissolves directly in plasma
3) 10% combines with haemoglobin to form carbaminohaemoglobin

When there is a HIGH PARTIAL PRESSURE OF C02 so basically lots of C02 for eg. during exercise (cells respiring more), C02 will combine with water to form carbonic acid. Enzyme called CARBONIC ANHYDRASE catalyses this.

Carbonic acid dissociates forming HCO3- and H+.
HCO3- diffuses out red blood cells. Chloride ions enter to maintain charge. This is called CHLORIDE SHIFT. To stop the red blood cell becoming too acidic, haemoglobin accepts the H+ forming HAEMOGLOBINIC ACID.

Now this does 2 things:
1) Acts as a buffer so maintains PH cos remember H+ makes environment acidic.
2) H+ COMPETE with OXYGEN for a place in the haemolgobin molecule. So Haemoglobinic acid causes OXYHAEMOGLOBIN to dissociate more releasing more oxygen.

This is really useful when your doing lots of exercise so in muscle cells. More exercise so more CO2 (increased respiration) so more H2CO3 (carbonic acid) so more H+ so more HAEMGLOBINIC ACID so more oxygen to muscle cells.

Thats CO2 carriage

Hey, any chance i could have this 50m slide powerpoint?
would be much appreciated

http://www.thestudentroom.co.uk/showthread.php?p=29211537#post29211537

for the translocation notes

cheers, much, much appreciated.

anyone think there'll be a question on the cytoskeleton?

can anyone explain what it is please?

Can anyone list the adaptations of neutrophils, epithelial cells, palisade cells, and guard cells

Thanks

One last question from me!

Can someone please list xylem and phloems structure, and how it is related to it's function?

The cytoskeleton refers to the network fibres found within cells that gives structure and shape to cells holding them in place.

It allows organelles to be moved inside the cell, i.e. moves chromosomes during nuclear division

Xylem - transport of water and dissolved minerals UP the plant
- no end walls
- no cell contents
- lignified walls - waterproofs cell and provides support (in a spiral shape to allow flexibility of xylem)
- also has some parenchyma cells.
- bordered pits to allow water to enter adjacent vessels to reach different parts of the plant, or enter living parts of the plant.

Phloem - transport of sucrose up and down the plant.
- sieve tube elements - have sieve plates
- Companion cells - linked to sieve tube elements by thin layer of dense cytoplasm to allow transfer of sucrose
companion cells actively transport H+ ions out of cell against concentration gradient, which then diffuse back into the cell through contransporter proteins which allows sucrose to enter the cell, which can then pass into the sieve tube elements by Diffusion.