IGCSE BIOLOGY------>TRANSPORT IN PLANTS

[twilight]

i'll try cooking grass after my examz ..

ppl u really make me laugh .. the exams are getting everyone totally insane 

[SGVaibhav]

alright, then we can remove our taste buds.
whats the prob then?

if we got more better doctors,
then we can design another mouth for grass, which goes in 2nd stomach which might be called grass stomach.

lol


becoming serious, these jokes actually make learning fun, and help in revising stuff.

[saifalan]

And where do u put that other mouth ?? I realy cant find a opening in the human body that we dont need. Or r u an alien ??

[emi]

hey saif , whos the guy in ur dp ?  when ever i scroll some page my eyes fall on that icon

[saifalan]

If u r reffering to my profile pic, thats not me. Its a hollywood star named Bruce Campbell. He starred in Evil Dead.

[emi]

i see 

[astarmathsandphysics]

This new breed of cows cum humans, being able to more efficiently convert grass into poo than the grass-cow-human-poo cycle we have now, will be better able to exploit the earths resources. The new cow-cum-human super race, able to run faster, jump higher, eat more, will out compete both humans and cows until they are no more. And because their stomachs are hidden in their bums, everyone will think they are just very fast, very fat people.

[SGVaibhav]

i thought that was u saifalan

[K_M]

Hey i have a doubt.

Active Uptake is the movement of molecule of a substance against their concentration gradient (from lower concentration to high concentration). But how it is applicable to the absorption of mineral ions from the soil by the roots. Because obviously the soil has more mineral ions than the root.

Please explain this to me asap. I think ive misunderstood the concept.

[ambitious94]

Whoever asked the xylem thingi question im gonna xplain in my own words
Imagine sipping juice through a straw. The straw is really thin so the water rises through it easily-imagine sippin the juice through a pipe. Its hard ryt? So that’s pretty much capillary action, which is weak - u see xylem vessels r thin so water rises up against gravity easily.
Now in the root cells, thers pressure due 2 accumulation of water. This forces water out of one cell and into the other so they reach the xylem vessels. That’s root pressure or turger pressure but its also a weak pressure. Now @ th top, in the leaves, water is being lost due 2 transpiration. They are fewer water particles up here and more down the xylem vessels so as u no in osmosis water particles move from a region of high water potential to lower water potential n the water potential gradient is created due 2 all these thingis.Voila!water moves up :p
Hope u understand
n By the way i dunno tht hydrogen ions thingi cn u xplain more pls?

Ur explanation is rlly good, except for the part where water moves up by osmosis. That's an incorrect statement, because osmosis is the movement of water particles from a region of higher concentration to a region of lower concentration through a partially permeable membrane there fore, the transpiration stream is not caused by osmosis, but due to the fact that water molecules are attracted to each other, so when they escape by transpiration, water is pulled up the xylem vessels. This was in my study guide.

[SGVaibhav]

oh wow, i remember this topic so well.......
memories

 active uptake is the movement of molecule of a substance against their concentration gradient (from lower concentration to high concentration)... but for absorption of mineral ions, i guess osmosis or diffusion is involved.

[SGVaibhav]

PEOPLE, CHECK PREVIOUS POSTS OF THIS TOPIC....
BEST MEMORIES EVER..
check from PAGE 4 ONWARDS

Well lets see Mr sgvaibhav's hard questions.
Plants again? Oh God! I hate plants. Okay.
Wait....

What did you mean by (water in the cell moves from cell to cell
and from cell wall to cell wall)? I didnot get it at all. Please tell me what you mean so I can help with that..

For germenation..Germenation? Auxins and those things are not about germenation ?! Its about sensetivity and movement in plants.
Listen, plants respond to a certain stimuli..What we are concerned about are light( photo-stimulus) and gravity( geo-stimulus) A growth response carried out by a plant in response to the direction of a stimulus is called a tropism..Easy for now?
A +ve response is a growth movement towards the stimulus and a negative response is a growth movement away from the stimulus. For example:
-a stem growing towards light is a +ve phototropism
-a stem growing upwards (away from gravity) is a -ve geotropism.
-a root growing downwards(away from light but towards gravity) is a +ve geotropism but a -ve phototropism
*Roots are positively geotropic:
-they grow into the soil which provides a source of water and mineral ions
-they provide an extensive system of support and anchorage for the plant
*Shoots are positively phototropic:
-leaves are in the optimum position to absor light energy for photosynthesis
-flowers are lifted into the position where they are most likely to recieve pollen. They will be held out into the wind or may be more visible to pollinating insects

NOW..! Auxins!
Phototropism is controlled by auxin..Auxin is simply a "growth substance"..
Here are some simple observations about it:
-if the tip of the shoot is cut off the shoot can no longer respond to stumuli.This suggests that the tip produces the auxin
-a shoot responding to a stimulus always bends just behind the tip. The auxin appears to travel from the tip(where it is made) to a region behind the tip(where it has its action)
-auxin can diffuse back from the tip and can be collected in blocks of agar jelly(allows the diffusion of auxin).These blocks can then allow the tip to resond to the light
-when shoot tips are exposed to light from one side auxing accumelates on the "dark" side of the shoot.The auxin is somehow affecting the growth of the dar side of the shoot.

Imagine now the sun light is distrbuted from all directions..the auxin will be prodeuced at the tip and diffuses slowly down the plant.Cells on both sides are affected equally and the shoot grows straight upwards.Got it?
But when the light comes from one of the sides only..the light reduces the concentration of auxin on the "light" side.The cells absorb less water and so swell less than normal.The light side therefore grows less quickly and the shoot bends towards the light.While the cells on the dark side recieve more auxin . they absorb more water and so increase the size more that normal. The dark side therefore grows more quickly and the shoot bends away from the dark i.e towards the light.

Now auxin thing in geotropism..you just have to know that when the pull of gravity occur..more growth substances"auxin"reaches the lower side..and stops it extending as much as the top side...
Take as a note that auxin inhibits(slows down) the cell growth in roots but stimulates(speeds up) cell growth in shoots.

NOW ANOTHER EXPLANATION IF YOU WISH:
Auxin is produced by cells at the tips of stems and roots. It speeds up growth ain stems.It slows down growth in roots.
Phototropism and auxin:
*When light comes from above auxin spreads evenly down the stem.The stem grows straight.
*When light comes from one side auxin spreads down the shaded side of the stem.
*Auxin makes stem cells grow faster.this causes the stem to bend towards the light.
Geotropism and auxin:
*If a plant is laid on its side auxin gathers in the lower half of the stem and root.
*Auxin at the root slows down the growth of root cells.The root curves downwards.
*Auxin at the shoot speeds up growth of stem cells.The stem curves upwards

Pay attention that both explanations should be taken into consideration, as both are so important. If you like print what I wrote and study it because its very useful.

About your last question about the experiment, from your understanding and knowledge of the above thing, you should be able to answer it. The rolling jar means that auxin will be spread on the whole of the plant equally and it will grow in a straight way. Study the notes above and still if you have any question please ask.

I hope you'll understand.
sweetsh

Sorry but I was studying chemistry....

OKay now...
My book is Complete Biology for IGCSE by Ron Pickering...
http://www.worldcat.org/oclc/162144426

About the transpiration thing...let me explain it in simple words...
First thing...you have to know how the uptake of water and minerals occur in roots...They enter root hair cells by osmosis...As the water in the soil has a high water potential gradient than the cytoplasm of the root hair cell...Thats how the water enters...  Then,,,water crosses the living cells of the cortex by osmosis...It crosses the cell wall and cytoplasm of the endodermis...The cell wall of the endodermis contains a waxy material which makes them impermiable to water...So the membranes of endodermis cells select what sybstances can enter the xylem and to be distributed through the body of the plant...

Now part(2)...Transport in plants  You know that inside the plants there xylem tissue and phloem tissue...
Xylem tissue contains xylem vessels...to transport water and dissolved mineral ions...
Its walls are thickened by LIGNIN...its waterproof and prevent the cells collapsing inwards...
There is no cytoplasm or organelles inside..(which is a kind of adaptation) so there will be no obstruction to the flow of water and mineral ions...
NOW...the end walls are removed...cells join to form long hollow tunes calles xylem vessels...
**They have small holes in their sides called pits..When the water from the root hair cell arrive in the center of the root it goes into the xylem vessels through there pits...

Well the picture in mybook is very useful and I cant find a good picture to make you understand!!

Third thing...Phloem tissue...it contains sieve tubes and companion cells...Its adapted for transport of the organic products of photosynthesis(sugars as sucrose) and amino acids...This is called Translocation
Translocation is the movement of sugars and amino acids from source(where they were made)to the sink(where they are stored or used)
They have think cytoplasm-cell must remain alive or sugar transport stops..
There is no nucleus or organelles..so sugar flow is not impeded...
Pores in sieve plates allows sugars to pass from one cell to the next...
Companion cells doesnt transport sugars but carries out some life processes of the sieve tubes..... !!!

Now a little bit explanation about transpiration because im sure you got bored or maybe slept on the keyboard!!!
Transpiration stream is the flow of water through the plant to replace the losses by evaporation from the leaf...
As the water loss occur from the leaves...this reduces the pressure at the tops of the xylem vessels by transpiration.It becomes less than the pressure of the base,thats why water moves upwards..
1)Water uptake occur by osmosis(as I mentioned above)
2)water moves  up the stem in the xylem due to the tension caused by water loss from the leaves.
3)water moves from xylem to enter the leaf tissue down the water potential in the leaf tissues///
4)water evaporates into internal air spaces from the surfaces of leaf cells
5)water diffuses through stomata dow water potential gradient....

You may also know the leaf structure and how its adapted to reduce transpiration...

And the atmospheric conditions that affect transpiration...I think those are included in your textbooks and can be easily understood...

Dont forget how some plants are adapted to reduce water loss in diff. environments...(such as cacti,aquatic plants, and maram grass)

I hope I benefited you from this huge article!!! But I really wish you understand!!
Note: I attached a silly photo which shows transpiration very simply just to help you in studying...

Good Luck for you and Me...
sweetsh

Oh if ur reading this, than thanks again sweetsh =).....
i got A+ in BIO !~!

[ambitious94]

Hey i have a doubt.

Active Uptake is the movement of molecule of a substance against their concentration gradient (from lower concentration to high concentration). But how it is applicable to the absorption of mineral ions from the soil by the roots. Because obviously the soil has more mineral ions than the root.

Please explain this to me asap. I think ive misunderstood the concept.

As the plant is absorbing mineral ions by diffusion, there is a build-up of these ions in the root hair cells, which causes the concentration of the mineral ions to increase within the root, above that in the soil. And as the root abosrbs more and more of these ions, their concentration in the soil drops. So obviously now the plant can't lose these ions by diffusion, so it continues uptake by active transport.
That's the concept I was taught. Hope you find it useful!

[SGVaibhav]

i want all mods and admins to read posts from page 4 onwards.....
its sick funny

[K_M]

As the plant is absorbing mineral ions by diffusion, there is a build-up of these ions in the root hair cells, which causes the concentration of the mineral ions to increase within the root, above that in the soil. And as the root abosrbs more and more of these ions, their concentration in the soil drops. So obviously now the plant can't lose these ions by diffusion, so it continues uptake by active transport.
That's the concept I was taught. Hope you find it useful!

Thankyouu it actually makes sense now!