Circulatory Systems :) Flashcards
What is positive pressure?
The act of pushing contents forward due to pressure from behind.
What is negative pressure?
The act of drawing contents in via a vacuum or loss of a substance
What are some of the issues with positive pressure?
- Providing sufficient force for movement
- Allowing for stress points
- Avoiding blockages
- Moving against gravity
How are some of the issues with positive pressure overcome?
- Bulk flow
- Physical properties of channels
- Pumps
- Differing between closed and open systems.
What are some of the challenges associated with negative pressure?
- Providing sufficient suction
- Not allowing embolisms
- Countering elasticity (Avoiding collapse)
- Gravity
How do we overcome some of the issues with negative pressure?
- Physical properties of vessels – capillary action
- Solid walls for vessels – no elasticity
- Closed vs open systems
- Valves
What are some problems with transport faced by plants?
- No pump – must use physics to move things
- Need to transport water and sugars in two different directions
- Height – how to defy gravity
- How to load the transport system
- How to regulate flow rate
- In addition to bulk flow of metabolites, the transport system must also provide physical support
In what direction does the phloem carry minerals?
Shoots to roots
In what direction does the xylem carry minerals?
Roots to shoots.
Name to two types of cell present in the phloem and what connects them.
Sieve elements and companion cells, linked by plasmodesmata.
Name some features of Sieve elements
- Living cells
- No nucleus
- Few Organelles
- Clear to enable fast flow through cells.
How does bulk flow in the phloem occur?
- Sucrose is actively transported into companion cells at source
- Water potential decreases in companion cell
- Water moves into companion cell by osmosis
- Increases pressure potential at source end of phloem
- Forces sap down sieve-tube elements to sink
How is the Xylem formed?
- Elongation stops
- Secondary walls continue to thicken
- Areas of primary wall left without secondary thickening ( pits)
- Cell dies, leaving hollow tube
- Pits enable water to flow between tubes
What is the main difference between Tracheids and Vessel elements?
In Tracheids, water moves only through pits, hence is slow.
In Vessel elements water moves through pits and end wall perforations, which is much faster.
How is negative pressure formed in the Xylem?
Transpiration of water out of the leaf - Cohesion of water molecules translates this pull throughout the xylem - Adhesion of water molecules to the xylem walls allows them to counteract against gravity.
