OCR 2010 A2 Biology Unit 2 - Control, Genome and Environment

Hey, can someone please go through the evidence for apical dominace for me. The chronological, wordy explanation in the Hienemann book is a bit confusing.

Reply 1821

skatealexia

14

buyingtheticket

Hey, can someone please go through the evidence for apical dominace for me. The chronological, wordy explanation in the Hienemann book is a bit confusing.

I can try.

Basically, the highest concentration of auxins in found in the apical bud, this inhibits the growth of side shoots, and promotes stem elongation in the shoot tip. When the apical bud is removed, obviously the concentration of auxins drops, side shoots then grow by cell division and stem elongation ( I'd say cytokinins and gibberellins). And Im not sure how abscisic acid comes into this.

Edit; the evidence for apical dominance Im sure we just need to know how to analyse it, not what the actual evidence is... if you remove the apical bud, side shoots grow... so.

Reply 1822

buyingtheticket

13

skatealexia

I can try.

Basically, the highest concentration of auxins in found in the apical bud, this inhibits the growth of side shoots, and promotes stem elongation in the shoot tip. When the apical bud is removed, obviously the concentration of auxins drops, side shoots then grow by cell division and stem elongation ( I'd say cytokinins and gibberellins). And Im not sure how abscisic acid comes into this.

Edit; the evidence for apical dominance Im sure we just need to know how to analyse it, not what the actual evidence is... if you remove the apical bud, side shoots grow... so.

I'm pretty sure it said in the spec we had to evaluate/summarise the evidence...thanks anyway.

Reply 1823

ibysaiyan

16

Aww miss ya @ thread. Will be back soon once I get my maths and other stuff sorted. :wink:

Reply 1824

cfc18

6

buyingtheticket

Hey, can someone please go through the evidence for apical dominace for me. The chronological, wordy explanation in the Hienemann book is a bit confusing.

Ok this is the simplest way :

1) cut of the tips of two shoots , to one of the shoots apply sythetic auxin 1AA and the shoot will continue to grow with the lateral buds inhibited and apical dominance is maintained. However to the other shoot where no auxin had been aplied we see that side branches grow and later buds can grow since supply of auxin has been cut off.

2) When a plant is grown upside down apical dominance is lifted and doesnt occur , this is because auxin cannot be transported up against gravity and therefore can not reach the internodes beside the lateral buds , hence these buds can grow sideways.

And also its auxi which acts on the lateral bud , inhibits the later buds from growing , so experiments follow the method by preventing auxin being transported down the stem of a plant.
Hope that helps. :smile:

Reply 1825

Falcon91

Well for some reason im finding meiosis hard to remember so ill write it out, hopefully it does me good :biggrin:

Meiosis - produces gametes, takes place in the reproductive organs (testes and ovaries) to produce haploid cells from the original diploid cells. This ensures when fertilisation takes places that the zygote that is formed has a diploid number of chromosomes and then can divide and develop.

The chromosome number thus needs to be halved.

Meiosis has 2 stages, Meiosis 1 and 2.
Meiosis 1:
-Brief interphase where DNA and organelles replicate and then chromatin condenses to form visible X-shaped chromosomes

Prophase 1:
-homologous chromosomes come together to form a bivalent. Genes are found at the same locus on both, one is maternal and one is paternal
-non-sister chromatids in the bivalent, attach and wrap around each other at points called Chiasmata. These sections can be swapped over which produces a new combination of alleles on chromatids and thus increasing genetic variation
-Nucleolus and nuclear envelope break down
-Centrioles at poles and being to form spindle fibres (formed of microtubules)

Metaphase 1:
-The bivalents randomly arrange themselves on the spindle fibre equator (random assortment) which leads to random segregation of chromosomes which increases variation by ensuring each gamete is unique.
-The spindle fibres attach at centromeres

Anaphase 1:
-The chromosomes in the bivalent are pulled apart by the contraction of spindle fibres, one in each pair goes to opposite ends of the cell
-The centromeres do NOT divide

Telophase 1:
-In an animal cell, a nuclear envelope forms around each of the sets of chromosomes, and the cell divide by cytokinesis. There is a brief interphase and the chromosomes condense

-In plant cells they go straight into meiosis 2

Meiosis 2
Prophase 2 - Nuclear env and nucleolus breaks down if theyve formed, and chromosomes condense and spindle fibres form again

Meta 2 - Random arrangement of (non-sister)chromatids on the spindle fibre equator, non-sister due to crossing overm and this ensures random segregation. Spindle fibres attach at centromeres.

Ana 2 - Spindle fibres contract and chromosomes pulled apart at centromeres and chromatids randomly segregate.

Telo 2- animal cells form a nuclear envelope, the 2 cells then divide to form 2 cells. Plant cells form a tetrad of cells.

Reply 1826

radical07

Hey guys, hope everyone is doing ok. I was just wondering - you see how neuromuscular junctions use acetylcholine only - how is this so when the sympathetic motor neurones release noradrenaline and parasympathetic release acetylcholine?

Maybe the sympathetic motor neurones switch suddenly at the motor end plate?

Reply 1827

afhussain

Hi guys its been a while but ive done a powerpoint on cellular control-it does not contain stuff on genetic diagrams or variation/natural selection or homeobox genes but outlines the rest of stuff (meiosis, lac operon, protein syntheis, definitions how variation comes about, mutations etc)

Hope its of help.

Also a mod said they would organise all the notes for this unit a few months ago? Whats going on?! lol

Cellular Control..pptx

Reply 1828

HELPME-ology

Hi people..
if anyone knows please quote and reply back:

1) Discuss the possible effects of a high blood cholesterol level on the heart and circulatory system with reference to HDL's and LDL's.

Reply 1829

HELPME-ology

Hi people...
if anyone knows, please quote and reply back:

2) Describe how the use of chemicals, including fertilisers, pesticides[for plants] and antibiotics[for animals] can boost food production.

Reply 1830

HELPME-ology

3) What are the short-term and long-term effects of smoking?

Reply 1831

HELPME-ology

4) Describe the effect of Nicotine and Carbon Monoxide on the cardiovascular system with reference to Thrombosis?

Reply 1832

lexafish

10

HELPME-ology

4) Describe the effect of Nicotine and Carbon Monoxide on the cardiovascular system with reference to Thrombosis?

That's all module two stuff, which is in this thread. I posted some revision notes in there, which may help you :-)

Reply 1833

Falcon91

HELPME-ology

Hi people...
if anyone knows, please quote and reply back:

2) Describe how the use of chemicals, including fertilisers, pesticides[for plants] and antibiotics[for animals] can boost food production.

These should be around correct...hopefully...

The use of chemicals -
-Can add inorganic minerals such as K+, NO3- and PO4 3- into the soil which improves soil and allows more minerals for the plants

-Pesticides...pests eat plants which removes biomass (which is energy used for growth), thus applying pesticides means that the pests are eliminated and so more energy is kept for biomass and thus increasing yield.

-Fungicides can damage the xylem vessels, phloem, foliage and roots. The plant has to fight the infection and of course this will use energy, applying fungicides mean that less energy is needed to fight infections and so more can be stored as biomass (i.e. growth) and increase yield.

-For animals, antibiotics has the same principle, animals have to use energy in order to fight off infections as the body has to produce a lot more antibodies and things such as the maintenance of internal temperature will require more energy. Using a human example, energy for excess mucus production to try and trap and kill bacteria/the infection (i.e. when you get a 'cold'). Using antibiotics means less energy is needed to fight the infection (as the antiobiotics are doing part of it) and so more can be used for growth.

;-; i need to get revising synoptics >.> Has anyone else done lots for synoptics yet?

Reply 1834

HELPME-ology

Falcon91

These should be around correct...hopefully...

The use of chemicals -
-Can add inorganic minerals such as K+, NO3- and PO4 3- into the soil which improves soil and allows more minerals for the plants

-Pesticides...pests eat plants which removes biomass (which is energy used for growth), thus applying pesticides means that the pests are eliminated and so more energy is kept for biomass and thus increasing yield.

-Fungicides can damage the xylem vessels, phloem, foliage and roots. The plant has to fight the infection and of course this will use energy, applying fungicides mean that less energy is needed to fight infections and so more can be stored as biomass (i.e. growth) and increase yield.

-For animals, antibiotics has the same principle, animals have to use energy in order to fight off infections as the body has to produce a lot more antibodies and things such as the maintenance of internal temperature will require more energy. Using a human example, energy for excess mucus production to try and trap and kill bacteria/the infection (i.e. when you get a 'cold'). Using antibiotics means less energy is needed to fight the infection (as the antiobiotics are doing part of it) and so more can be used for growth.

;-; i need to get revising synoptics >.> Has anyone else done lots for synoptics yet?

Thankyouu!! I dont know how you all manage to know this in such good detail by memory?!
but yeh.. its cos i am retaking my AS unit 2 .. but yeh its a good idea to link in with synopitic stuff..

Reply 1835

uer23

15

HELPME-ology

4) Describe the effect of Nicotine and Carbon Monoxide on the cardiovascular system with reference to Thrombosis?

Hey can you please post all this stuff in the Unit 2 thread, this thread is massive as it is.

Reply 1836

HELPME-ology

uer23

Hey can you please post all this stuff in the Unit 2 thread, this thread is massive as it is.

Yeh sorry about that... i am following this thread for the A2 exam..
but yeh lexafish just sent me a link to the unit 2 thread..

Reply 1837

Falcon91

Im completely stressed. I believe im getting nowhere and i keep forgetting small things, its really irking me and i feel like im wasting my time.
Maybe i should take a break from this...