Summary
Summary Xylem structure and function A level Biology
- Institution
- AQA
Year 1 Biology AQA A level notes. Achieved an A* in my final exam using these notes. They are based on the mark scheme requirements.
[Show more]
Seller
Follow
Content preview
Xylem structureand function
summary notes
09 May 2023 17:45
- Water absorbed by roots by osmosis through root hair cells
- Transported through hollow, thick walled tubes- xylem vessels- transpiration is the ma
pulls water through
- Cell wall made of spirals of lignin- stronger
Movement of water out through stomata
- Water potential gradient from the air spaces through the stomata to the air- humidity
atmosphere usually less than that of air spaces next to stomata
- Water vapour diffuses out from the air spaces into surrounding air
- Water lost by diffusion from air spaces is replaced by water evaporating from cell wall
surrounding mesophyll cells
- Can control rate of transpiration by changing size of stomatal pores
Movement of water across cells of a leaf
- Water lost from mesophyll cells by evaporation from their cell walls to the air spaces o
- This is replaced by water reaching the mesophyll cells from the xylem by the cell walls
cytoplasm
For the cytoplasmic route:
- Mesophyll cells lose water to air spaces by evaporation due to heat from sun
- These cells have a lower water potential and so water enters by osmosis from neighbo
- Loss of water from these neighbouring cells lowers their water potential
- They then take in water from their neighbours by osmosis
Movement of water up the stem in the xylem - Cohesion tension theory
- Water evaporates from mesophyll cells due to heat from sun- leads to transpiration
- Water molecules form hydrogen bonds between one another- stick together- cohesion
- Water forms a continuous, unbroken column across mesophyll cells and down the xyle
- As water evaporates from mesophyll cells in the leaf into the air spaces beneath the st
more water molecules drawn up behind - due to cohesion
- Hydrogen bonds form between the polar water molecule and the lignin in the cell wall
xylem vessels by adhesion
- Column of water pulled up xylem- transpiration pull
- Transpiration pull puts xylem under tension- this stretches the water column- decrease
of the xylem vessels slightly- decreases pressure that the water column applies to xyle
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller arabellasherratt. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £4.49. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
52928 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy revision notes and other study material for 14 years now