MYTUTOR SUBJECT ANSWERS

413 views

How do auxins bring about positive phototropism in plants?

1) Phototropins are enzymes found in the plasma membrane of particular cells.  They are phosphorylated when hit by blue light.

2) This phosphorylation triggers the movement of auxin across the plant shoot by active transport as transporter proteins pump the hormone out of cells.

3) As a result, there is more auxin on the shaded side of the plant, producing a concentration gradient.

4) Auxin promotes active transport of hydrogen ions into the cell wall by ATPase action.  Where there is more auxin, more ions are brought in.

5) The hydrogen ions lower the pH of the cell wall, reaching the optimum for the enzymes that hydrolyse bonds withincellulose fibres.  The ions also disrupt hydrogen bonds between cellulose fibres.  This makes the cell wall less rigid.

6) As the cell absorbs water by osmosis, it swells and elongates.  Because of the reduced rigidity of the cell wall, the cell can stretch more than cells with lower auxin concentrations and therefore more restrictive cell walls.

7) Consequently the cells on the shaded side of the plant grow longer than those facing the light due to the difference in auxin concentration.  This causes the plant to bend towards the light.

Katherine F. A Level Chemistry tutor, A Level Biology tutor, GCSE Fre...

9 months ago

Answered by Katherine, an A Level Biology tutor with MyTutor


Still stuck? Get one-to-one help from a personally interviewed subject specialist

123 SUBJECT SPECIALISTS

£20 /hr

Rasmus K.

Degree: Medicine (Bachelors) - Nottingham University

Subjects offered: Biology, Human Biology+ 4 more

Biology
Human Biology
.UKCAT.
.BMAT (BioMedical Admissions)
-Personal Statements-
-Medical School Preparation-

“Who am I? Hi, my name is Rasmus. I'm a fourth year medical student at the University of Nottingham. For me, medicine came from an initial love of science and became a dream that I am now fulfilling. I hope to instil the same enthusias...”

£20 /hr

Charlotte G.

Degree: Medicine (Bachelors) - University College London University

Subjects offered: Biology, Maths+ 2 more

Biology
Maths
Chemistry
.BMAT (BioMedical Admissions)

“About Me: I am a medical student at University College London (UCL) who has always had a real passion for science and finding out how things work. I adore Medicine, I very much enjoyed learning about biology, maths and chemistry at s...”

£30 /hr

Subi S.

Degree: Medicine (Bachelors) - Cambridge University

Subjects offered: Biology, Chemistry+ 5 more

Biology
Chemistry
.UKCAT.
.BMAT (BioMedical Admissions)
-Personal Statements-
-Oxbridge Preparation-
-Medical School Preparation-

“I am a medical student currently studying at Cambridge University. I have always loved Biology and enjoy teaching it! I think that science should be studied in a practical way with pictures and models and experiments - textbooks too! ...”

About the author

Katherine F.

Currently unavailable: for new students

Degree: Biochemistry (Bachelors) - Oxford, Trinity College University

Subjects offered: Biology, German+ 2 more

Biology
German
French
Chemistry

“Hi!  I'm a first-year biochemist at Oxford University and I am very keen to help with biology and chemistry A levels, or with French and German at GCSE.  I love learning and want to pass on this enthusiasm, as well as helping students ...”

MyTutor guarantee

You may also like...

Posts by Katherine

What evidence is there to support the delocalised model of benzene over Kekulé's model?

How can an aldehyde be distinguished from a ketone?

How do auxins bring about positive phototropism in plants?

How do ionic charge and radius affect lattice enthalpy?

Other A Level Biology questions

What are the different types of epistasis?

How does antibiotic resistance develop in bacterial populations?

What is magnification of a microscope vs. the resolution?

Describe the events that take place in a neurone which produce an action potential

View A Level Biology tutors

Cookies:

We use cookies to improve our service. By continuing to use this website, we'll assume that you're OK with this. Dismiss

mtw:mercury1:status:ok