Plant Responses: Auxin in Phototropism and Geotropism | A-level Biology | OCR, AQA, Edexcel

[@jancuales]

There might be an error on the illustration at 10:30. should the IAA be at the shaded side?

[@ankiemightprobablybeankie2898]

roots inhibits IAA, so the side where there is no IAA grows, grows away from the sunlight

[@SalsaKingoftheApes]

I agree, a small error.

[@donmalik8888]

Auxin always moves away from a light source so your diagram at 1:47 would not be correct. The difference between auxin action in the sh0ot and roots is that in the shoots it stimulates growth and in the roots inhibits growth.

[@anastaziecupidon4363]

Hi .....may i know why auxin moves away from light? Please!

[@guilhermepaixao826]

The best biology channel. I'm a brazilian student and I'm getting ready to do one important exam called ENEM. That's the best way to get into the university in Brazil and of course all those classes are helping me a lot.

[@gingesauce]

2:10 the IAA should be on the shaded side.

[@japhethloyd516]

Thanks, your video was perfect.

[@tomasobrien8762]

How do u know weather IAA encourages or inhibits cell elongation??

[@nickcoates1767]

Interesting but there are a couple of hand-wavy bits. You say the light "causes the auxin to move to the opposite side" but there is no explanation of the mechanism of this. I have looked at a number of presentations and papers and none have explained this. I wondered if the IAA on the lit side was destroyed by the light or is there another light sensitive process which restricts its production in the tip or flow? Also although thinking of gravity as pulling the auxin down might be a good way to remember it, I am pretty sure that is not how it works. After all if the IAA is a solute in plant sap which is mostly water and solutions do not separate out under gravity. Any thoughts on this?

[@meenakshikannan5904]

Protein pumps facilitate the migration of auxin to the unlit side. Different light intensities cause auxin efflux pumps to move which sets up a concentration gradient of auxin (lower conc. on the lighter side and higher conc. on the darker side). I suggest checking out this video if you're interested kzbin.info/www/bejne/rpqcn4idmqhkb5Y - he explains it quite well. Hope this helps!

[@nickcoates1767]

@@meenakshikannan5904 Thank you very much for your reply. I am partially satisfied but I think I suffer from being primarily a physicist, wanting to understand the whole causal chain. Your reply indicates that it is not the auxin which is photosensitive, but another process which causes it to move. That begs the question, what caused the efflux pumps to activate? I am still guessing it responds to a photosensitive chemical. I know from other sites that phototrophism responds to blue light. This explains how angiosperm trees are able to grow towards a blue-sky hole in the green woodland canopy. If you have any further insight I would be most grateful.

[@meenakshikannan5904]

@@nickcoates1767 Hi again! I did a quick search online for auxin transport and found this article ( www.sciencedirect.com/science/article/pii/S0960982201004973 ). These two excerpts might help shed some light - "Light quality also has an impact on auxin transport rates. Cucumber seedlings germinated in dim-red light exhibit significantly increased auxin transport rates, indicative of a functional link between light signaling and auxin transport" and "As auxin levels are determined in part by the presence and activity of auxin efflux carriers, light might in fact change the expression and/or activity of efflux carriers in a first step towards complex light response mechanisms. In line with this model, the expression of some auxin efflux carriers is regulated by light, with both the circadian clock and the red-light receptor phytochrome A affecting transcript levels of auxin efflux carrier genes 15., 16.. If auxin efflux carriers in fact play a central role in light responses, as suggested by the model, resulting alterations in auxin homeostasis may turn on and off light-regulated target genes that are essential for the control of photomorphogenesis. According to this model, light-induced alterations of auxin efflux carrier expression and/or activity could also require DOC1/TIR3. Alterations in light regulation associated with doc1 would then be caused by changes in auxin efflux carrier expression and/or activity." Personally, I find it to be confusing but you might find it helpful!

[@nickcoates1767]

@@meenakshikannan5904 Thank you for your continued interest in my question. I hope you are enjoying the conversation. I have now spent some time 'geeking out' on this question. My interest in this is the possibility of making structures from naturally shaped wood. www.beamz.org.uk . what is yours? I have come to the conclusion that although the role of Auxin in phototropism is well known and characterised, the process which controls that is not fully understood even to this day. The paper below indicates the role of blue light sensitive photoreceptors, energy production through ATP and pumping processes. A look at Figure 2 will show that this is not a straightforward process www.sciencedirect.com/science/article/pii/S0960982215003358#bib7 Thank you again for your interest. Nick

[@nickcoates1767]

If as I had originally assumed, the control of the auxin and therefore the direction of growth was perhaps a simple single photosensitive process, it would not have the same modulation as the complex process provides. The plant responds to blue light after being exposed for about 20 mins. It does not matter how bright the light is. Now a hardwood (Angiosperm ) sapling growing in a sunlit woodland where a hole in the canopy had recently opened up, perhaps due to another tree having fallen, would receive bright green light from the illuminated leaves in the canopy, and less bright blue light from the sky. The sapling will grow as fast as possible towards the blue-sky hole to deploy its own canopy in this space. If the sapling simpluy followed the brightest light then trees here in the Northern Hemisphere would tend to lean to the South.

[@fayyazafridi1999]

perfect and easy way to understand

[@tiaaday6613]

thank you so much for the clear animation

[@AdreannaRhysand]

Perfect explanation

[@zoedavies3965]

Thank you!!!

[@kavinduharshitha4486]

really a good video...thanks a lot...!!!!!!

[@sarahmallon2426]

Is the shaded side the stem of the plant?

[@MichiKai]

Was really helpful

[@faseehmorio8592]

Thanks sir a lot u gave me best concept ... Love from Pakistan

[@thierrytrevorbusinge8186]

Top of their line stuff right here

[@abcdefgh-fb5ny]

thank you for your video, it taught me a lot. I have a question though. If auxins avoid light, can you say it's negatively phototropic? My biology homework insists that I find the benefits of negative phototropism in stem shoots but I can't find anything that says stems are negatively phototropic except that one study about arabidopsis mutants. So I assume it's the auxins but is it correct tho?

[@mukiibimarvin9817]

I think we consider the growth of plant towards light,since the plant bends towards the stimuli (light),then we consider it positive phototropism

[@mennamosaad5717]

I am using this for my igcse !! Thank you

[@mennamosaad5717]

Till the third minute lmao

[@fiddlesticks6146]

you explain so well!! ty :)

[@kajalgaur3362]

Best explaination 😍 tq so much sir.....

[@dr.rehmatullahawan4424]

perfect video.

[@phakamiledumile9611]

thank you

[@hanasalah9148]

Thank you so much

[@barigabdalla657]

Perfect

[@nadveenaliiii]

Sir I would like to ask you some questions

[@hemantmagwana2997]

I like the vdo

[@oscarvandeventer8226]

My biology teacher said you’re wrong!

[@thinginground5179]

Damn. He summarised like 25 times lol but it was helpful anyway

[@launchpadlearn]

Thanks! Glad you found the video helpful! 😊

[@thinginground5179]

@@launchpadlearn yoy!!

[@emeraldpools795]

lol i'm using this for level 3 NCEA biology