The Biology AS-level Thread

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Really ? Well, I havent really done any complete unit 2 papers yet ? But I feel unit 1 is much easier, perhaps I think that because my unit 2 teacher was not as good....

i have forgot most of bio1 .... and the amount of application of science required is unbelievable - i mean i dont mind regurgitating answers but there is so much applications .. its unreal :|

Reply 781

pinkgorilla

Original post by ryanb97

i have forgot most of bio1 .... and the amount of application of science required is unbelievable - i mean i dont mind regurgitating answers but there is so much applications .. its unreal :|

Is there not as much application in bio2 ?
And i guess one you get the hang of it, you wont find it so irritating.

Reply 782

Chloesmith9

Anyone done the Biology Reaction Time IsA
I've done the:
- Biology AS Osmosis and Glucose
- Biology A2 Populations
- Chemistry AS and Chemistry A2 ISAs too.

They've been okay, but not many people seem to have done the reaction time?

Reply 783

craiok

Can somebody please help me, on aqa and have my empa next week. How does a potometer work?

Reply 784

Sports chick

heeyy guyys, i had my AS empa task 1 today. i was just enquiring when i do my task 2 (which is next week) do i get my task one question booklet back? I missed a question off and was wondering if i could fill it in next time?

Does anybody know? if so it would be great help and much appreciated!! xx

Reply 785

J_Parker

Original post by Sports chick

No you do not unfortunately, the only paper you get back is the task two when you sit the section B paper.

Reply 786

Sports chick

Oh man that sucks :frown:

(

Reply 787

JennaK

Original post by Skz8

What happens to the reaction of enzyme when you add an inhibitor.
Help

The reaction is slowed down as the enzyme is unable to function normally, so less ESCs(Enzyme substrate complexes) are formed and so less product is formed. How this happens really depends on the type of inhibitor,
Competitive Inhibitors: Bind to active site because they have complementary shapes that are able to fit into it and so they stop substrates from binding to the active site of the enzyme.
Non-competitive Inhibitors: Bind to the enzyme AWAY from the active site and so change the shape of the active site so that the substrate is unable to bind to the active site as it is no longer complementary.

Hope that helped! I'm doing OCR btw so if you are doing AQA it may be different.

Reply 788

pinkgorilla

Can anyone help me with water transport up roots and stems - symplastic pathways, etc.
Pleasee? I find it really confusing .
Thanks

Reply 789

lolly107

Original post by Sports chick

Yes you do generally get your task 1 back :smile:

Reply 790

lolly107

Original post by J_Parker

No you do not unfortunately, the only paper you get back is the task two when you sit the section B paper.

I thought you generally do get your task 1 back when you do the task 2?

Reply 791

amyyy163

Original post by craiok

Can somebody please help me, on aqa and have my empa next week. How does a potometer work?

Hey! I have mine then as well.

As for the potometer...

It measures rate of transpiration by assuming that rate of water uptake = rate of water loss.

But it doesn't because:

Water is used for photosynthesis

Water is used by the plant for respiration.

Water is used for structural support and the building of the protoplasm.

An air bubble is placed in the capillary tube via a water reservoir. A milimetre scale runs along side the capillary tube. In a set period of time (20 mins for example), the distance the bubble moves is measured on this scale. At the end of this time, work out rate. Distance/time.

But you must ensure apparatus is airtight, there are no other air bubbles, and the leafy shoot is cut underwater.

The water is drawn up by cohesion tension and root pressure when water is lost through transpiration (loss of water from stomata on under side of leaves by evaporation).

Hope this has helped :smile:

good luck!

Reply 792

amyyy163

Original post by pinkgorilla

Can anyone help me with water transport up roots and stems - symplastic pathways, etc.
Pleasee? I find it really confusing .
Thanks

Symplast pathway (think of it as simple) - water moves through the cytoplasm of cells (the living parts). It moves between neighbouring plant cells through gaps in the cell walls called plasmodesmata (cool word right? :wink:

).

Apoplast pathway - water moves through the cell walls of the plant cells (the dead bits) until it reaches the Casparian strip.

The Casparian strip - a waxy strip in the cell walls of endodermis cells. Stops water moving through the apoplast pathway and forces it into the symplast pathway. This is a benefit as water now has to pass through a plasma membrane (which controls what substances in the water pass through).

Hope this has helped. If you need to ask me anything else I'm happy to go through it with you :smile:

Reply 793

katt123

Original post by pinkgorilla

Can anyone help me with water transport up roots and stems - symplastic pathways, etc.
Pleasee? I find it really confusing .
Thanks

Write so these are basically mark scheme answers -

Water moves up the stem in the xylem:
-Water evaporates from the leaf as a result of transpiration
-Water molecules form hydrogen bonds between one another - cohesion
-Water forms a continuous, unbroken pathway across mesophyll cells and down the xylem
-As water evaporates from mesophlyll cells more water is drawn up - therefore more water is pulled us as a result of transpiration - transpiration pull
-This puts the xylem under tension - cohesion tension

Apoplastic pathway:
-Water is taken up by the root hair cells by osmosis
-Active transport of mineral ions leads to lower water potential inside root hair cells
-Water then crosses the root cortex and cohesion of water causes tension
-Water moves within cell walls with little resistance
-Water enters the endodermal cells and meets the casparian strip in t he endodermis(which is a water proof layer) so no apoplastic movement
-This causes the water to move into the cytoplasm so the uptake of water by osmosis is now regulated by the active transport of ions into the xylem
This causes root pressure

Symplastic pathway:
-Water entering by osmosis increases water potential of the root hair cell
-Water therefore moves from root hair cell into the first cell by osmosis - down the concentration gradient
-The first cell now has a higher water potential than its neighbour inside the stem - so water moves into neighbouring cells by osmosis
-In this way a water potential gradient is set up across all cells of the cortex which carries water along the cytoplasm from the root hair cell to the endodermis

Do ask if you don't understand :smile:

Reply 794

qazwsxplmty

Is there a simplified way of understanding cohesion tension theory in Biol2? And root pressure?

The way my teacher taught is way too complicated and long, I was wondering if there a shorter way of learning it but is like markscheme answers for the exam?

I do AQA :smile:

Reply 795

amyyy163

Original post by qazwsxplmty

Cohesion tension

Water evaporates from stomata

Water pulled across leaf to replace it

As water leaves, there's tension in the xylem

Water pulled up xylem as continuous column

Column maintained by cohesion (water molecules attracted to each other via Hydrogen bonds) and adhesion (water sticks to sides of xylem).

Water is pulled across root.

Root Pressure.

Endodermis cells actively transport ions into the xylem.

Lowering the water potential of the xylem.

Water moves from high water potential in endodermis into lower water potential in xylem.

As water enters xylem, it creates a hydrostatic pressure.

Hydrostatic pressure moves water up xylem along a pressure gradient (high--> low pressure) and moves water already in the xylem further up.

Reply 796

qazwsxplmty

Original post by amyyy163

Cohesion tension

Water evaporates from stomata

Water pulled across leaf to replace it

As water leaves, there's tension in the xylem

Water pulled up xylem as continuous column

Column maintained by cohesion (water molecules attracted to each other via Hydrogen bonds) and adhesion (water sticks to sides of xylem).

Water is pulled across root.

Root Pressure.

Endodermis cells actively transport ions into the xylem.

Lowering the water potential of the xylem.

Water moves from high water potential in endodermis into lower water potential in xylem.

As water enters xylem, it creates a hydrostatic pressure.

Hydrostatic pressure moves water up xylem along a pressure gradient (high--> low pressure) and moves water already in the xylem further up.

Thank you so much! If i wrote it like this with a bit more detail in the exam would it get me full marks for the question? Is it like it said on the markscheme? :smile:

Reply 797

amyyy163

Original post by qazwsxplmty

Thank you so much! If i wrote it like this with a bit more detail in the exam would it get me full marks for the question? Is it like it said on the markscheme? :smile: