Edexcel GCE Biology Unit 5 6BI05 June 2013

Can someone please tell me about dark and light adaptation? I just don't understand it no matter how many sources I've read

do you mean the rods or the plants and phytochromes?

Reply 581

joan2468

1

Original post by Zahra333

Hi guys,

Someone please explain to me about phytocromes please :frown:

despite reading over the textbook and revision guide again and again I'm extremely confused.

I know that
PR is red light (non active)
and PFR is far red light ( biologically active )
PR converts to make PFR which is the cause of flowering and biological processes right?
and PFR converts to PR which is useless.
but at night time it is important that PFR converts to PR? WHYYY?

The phytochrome that stimulates flowering actually depends on the type of plant, although the textbook does sometimes make it sound like it's always PFR.

For short-day plants, lack of PFR actually stimulates flowering (since they're adapted to shorter periods of exposure to sunlight, which as you know has more red light than far red light so converts PR to PFR).

For long-day plants, build-up of PFR stimulates flowering. Long-day plants are adapted to longer exposure to sunlight so more PR is converted to PFR. Not all the PFR can be converted back to PR during the short nights so PFR builds up, stimulating the plant to flower.

Hope this helps (:

Reply 582

SKK94

1

Original post by Mallika

Can someone please tell me about dark and light adaptation? I just don't understand it no matter how many sources I've read

Light adaptation:
- all rhodopsin in rod cells have been broken down (bleached)
- so rod cells cannot respond to dim light anymore
- example:when you switch off the lights in a bright room, you initially cannot see anything for a few seconds (because rhodopsin has already broken down, and has to be remade). Rod cells cannot respond to low light levels.

Dark adaptation:
- all rhodopsin has been reformed (with use of ATP)
- so rod cells can respond to dim light
- example: after some time being in a dark room, you can start to identify objects/shadows faintly, this is because rhodopsin has been re-synthesised and so your rod cells can respond to low light levels.

(edited 10 years ago)

Reply 583

Nilie

Original post by Zahra333

Hi guys,

Someone please explain to me about phytocromes please :frown:

despite reading over the textbook and revision guide again and again I'm extremely confused.

I know that
PR is red light (non active)
and PFR is far red light ( biologically active )
PR converts to make PFR which is the cause of flowering and biological processes right?
and PFR converts to PR which is useless.
but at night time it is important that PFR converts to PR? WHYYY?

yes
Pr and Pfr are isomers and are intercovertable.
When red light hits Pr it starts to convert into Pfr; when far-red light hits Pfr it starts converting to Pr; Pfr also converts to Pr in the darkness.

In short night plants (those, that need maximum 12 hrs of uninterrupted darknes) Pfr triggers flowering; in long night plants (those, that need minimum 12 hrs of uninterrupted darknes) Pfr inhibits flowering. They need Pr to germinate and flower.

(edited 10 years ago)

Reply 584

Nilie

To avoid confusion (based on the answer by joan2568),

long night plants are short day plants,
short night plants are long day plants =)

Reply 585

hussaincute

am i the only one who found june 2012 paper weird or is there any one else?

Reply 586

iwantopas19

whats the reason behind mole rats being bald and wrinkly ?

Reply 587

Zahra333

Ok I'm completely new to student room so I dont know how to reply to you individually but thank you so much Joan2568 and Nilie. I've finally understood it now.

Thats basically what you need to know for the phytocromes right? and the two experiments ( the shining the light on the seeds and observing growth and the grafting experiment )

:smile:

Reply 588

Nilie

Original post by Zahra333

Ok I'm completely new to student room so I dont know how to reply to you individually but thank you so much Joan2568 and Nilie. I've finally understood it now.

Thats basically what you need to know for the phytocromes right? and the two experiments ( the shining the light on the seeds and observing growth and the grafting experiment )

:smile:

you're welcome! and welcome to the forum =)

yes, that's it)

ps to answer press "quote" at the bottom of each post))

xx

Reply 589

iwantopas19

Original post by Zahra333

Hi guys,

Someone please explain to me about phytocromes please :frown:

despite reading over the textbook and revision guide again and again I'm extremely confused.

I know that
PR is red light (non active)
and PFR is far red light ( biologically active )
PR converts to make PFR which is the cause of flowering and biological processes right?
and PFR converts to PR which is useless.
but at night time it is important that PFR converts to PR? WHYYY?

https://www.google.mv/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&ved=0CC8QFjAB&url=http%3A%2F%2Fwww.thestudentroom.co.uk%2Fattachment.php%3Fattachmentid%3D136066%26d%3D1331490609&ei=bnq8UcSkHMzyrQfI6YCACg&usg=AFQjCNGvZK80Rx49JXV8qzzqw_VFAgJtwQ

have a look

Reply 590

hussaincute

can somebody help me with june 2012 paper? how did every1 else find it?

Reply 591

SKK94

1

Original post by iwantopas19

whats the reason behind mole rats being bald and wrinkly ?

They're bald because they live in hot conditions, so they don't need fur to keep them warm.

I'm not sure but wrinkles could make their skin more tough and resistant to damage as they dig tunnels and encounter rocks etc.
:smile:

Reply 592

rudizzy123

5

What time is the exam, AM or PM? My friends in my class are NOT responding

Reply 593

iwantopas19

Original post by SKK94

They're bald because they live in hot conditions, so they don't need fur to keep them warm.

I'm not sure but wrinkles could make their skin more tough and resistant to damage as they dig tunnels and encounter rocks etc.
:smile:

hehe...thanks... :smile:

Reply 594

iwantopas19

Original post by rudizzy123

What time is the exam, AM or PM? My friends in my class are NOT responding

dont u have a time table?
its pm :biggrin:

Reply 595

iwantopas19

Original post by SKK94

They're bald because they live in hot conditions, so they don't need fur to keep them warm.

I'm not sure but wrinkles could make their skin more tough and resistant to damage as they dig tunnels and encounter rocks etc.
:smile:

btw, thats anatomial adaptations, isnt it?

Reply 596

rudizzy123

5

Original post by iwantopas19

dont u have a time table?
its pm :biggrin:

Thanks, it's my last exam, and I knew when it was so foolishly threw it away.

I am currently resitting this unit, I have been getting a* in all the past papers (as i did last year) but last year, June 2012 was absoloutley ridiculous and featured next to NO biology in it, I was crushed and got a D, an anomoly for me, hopefully, as long this paper is a normal biology paper, I should be fine :smile:

Reply 597

iwantopas19

Original post by rudizzy123

Thanks, it's my last exam, and I knew when it was so foolishly threw it away.

I am currently resitting this unit, I have been getting a* in all the past papers (as i did last year) but last year, June 2012 was absoloutley ridiculous and featured next to NO biology in it, I was crushed and got a D, an anomoly for me, hopefully, as long this paper is a normal biology paper, I should be fine :smile:

I really hope so, but all papers are really weird and sick this time. but wish u all the best :smile:

Reply 598

SKK94

1

Original post by iwantopas19

btw, thats anatomial adaptations, isnt it?

Yeah.

Reply 599

bubblegummer

Can someone pls explain why after a few hours in darkness, Pfr will convert slowly back to Pr... also, is Pr formed through enzymes thus cause flowering in plants? i thought flowering only happens when there is Pfr. correct me if i am wrong. thanks

Edexcel GCE Biology Unit 5 6BI05 June 2013

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you