mass flow hypothesis (4)
- Source sugars activity transported into phloem
- by companion cells
- lowering water potential of sieve cells, and water enters by osmosis
- increase in pressure = mass movement
High blood pressure = a lot of tissue fluid (3)
- high blood pressure = high hydrostatic pressure
- increase outward pressure from arterial end of artery
- more tissue fluid is formed
Describe movement of water through a plant
Water enters the roots via osmosis
enters the xylem
moves up the xylem
goes to the leaves where it evaporates into the air spaces in the leaf
then diffuses out through the stomata into the surrounding air
Describe and explain structure to function of arteries and veins (5)
Arteries:
- Thick elastic wall SO can stretch and recoil with changing
pressure [1]
- Smooth endothelium SO friction is reduced
- Thick muscle layer SO pressure is maintained
Veins:
- Valves SO backflow of blood is prevented
- Walls are thinner and with less muscle and elastic tissue
BECAUSE they don’t have to withstand high pressure
2 features that adapt capillaries to be efficient (4)
-The capillary wall is 1 cell thick
-Means the diffusion distance is very short
-The lumen is very narrow
-Red blood cells pressed against wall/pass through one cell
at a time ensuring diffusion has time to occur
Role of H+ in translocation (4)
- H+ actively transported out of the companion cell (into
source) - Creating a concentration gradient between source and
companion cell - This drives the co-transportation of H+ and sucrose into
the companion cell - Leading to the diffusion of sucrose into the phloem/sieve
tube element
How sucrose is transported from the sieve tubes at the source to the sink (3)
-Low water potential in sieve tube at source
-Water moves in from the xylem by osmosis/down water
potential gradient
-high hydrostatic pressure = gradient = movement away from source
Diastole
- As the atria fill, the pressure in them rises
- Atrioventricular valves open, blood flows through with the aid of gravity
- Walls are relaxed - causes them to recoil and reduces the pressure within the ventricle
- This causes pressure to be lower than the aorta and the pulmonary artery
- Semi-lunar valves in the aorta and the pulmonary artery close
- This makes the “dub” sound
Atrial Systole:
Contraction of atrial walls ( + recoil of relaxed ventricle walls) pushes blood into the ventricles
Ventricular systole:
- Short delay allow ventricles to fill with blood
- Walls contract simultaneously
- Increases blood pressure, shutting the atrioventricular valves
- Valves closing creates a “lub” sound
- Pressure rises further, blood is forced into vessels
- Ventricle has thick muscular walls that contract forcefully, creating high pressure. Left ventricle pumps to extremity of body whereas right only to lungs.
Arteries
Function
- transport blood under high pressure from heart to tissue (from heart to arterioles)
Adaptations:
- muscle layers are thick compared to veins
- smaller arteries can be constricted and dilated to control the volume of blood passing
- elastic layer = relatively thick
- for blood to reach extremities, blood pressure must stay high. To maintain high pressure + smooth pressure surges, elastic wall is stretched (systole) and springs back (diastole)
- overall thickness is great
- resists vessel bursting under pressure
- no valves
- constant high pressure due to the heart pumping blood into the arteries
Arterioles
Function
- carry blood from arteries to capillaries and control the flow of blood between them
Adaptations:
- muscle layer is relatively thicker than in arteries
- contraction allows constriction of the lumen. This restricts flow of blood so controls it’s movement into the capillaries that supply the tissues with blood
- elastic layer is relatively thinner than in arteries
- blood pressure is lower
Veins
Function:
- Veins transport blood slowly (low pressure) from the capillaries in tissues to the heart.
Adaptations:
- muscle layer is relatively thin
- veins carry blood away so constriction + dilation can’t control flow of blood
- elastic layer is relatively thin
- low pressure of blood so it won’t burst and pressure is too low to create a recoil
- overall thickness of the wall is small
- Pressure within the veins is too low to burst allowing them to be flattened easily
- valves
- prevents back flow. When body muscles contract, veins are compressed, pressuring the blood within them
Capillaries
Function:
- exchange metabolic materials between blood + cells. Flow of blood is slower allowing more time for exchange
Adaptations:
- Walls are made up of lining layer
- thin = short diffusion pathway
- numerous and highly branched
- L.S.A
- narrow diameter
- permeate tissue, no cell is too far = short diffusion pathway
- narrow lumen
- RBC are squeezed flat against the side bringing them closer to the cells
- spaces between endothelial cells
- allows WBC to escape to deal with infections
Formation of tissue fluid:
- Hydrostatic pressure = pressure created when heart pumps, found at the end of capillaries
- causes tissue fluid to move out of the blood plasma.
- outward pressure is opposed by two other forces:
- hydrostatic pressure causes tissue fluid outside resists outward movement of liquid
- lower water potential of the blood due to plasma proteins, that cause water to move back into the blood within the capillaries
- the resultant force of these two creates an overall pressure that pushes tissue fluid out of the capillaries at the arterial end, only enough to force small molecules out of these capillaries
- leaving all cells and proteins in the blood because they’re too large to cross the membrane.
- this type of filtration is under pressure is called ultrafiltration
- leaving all cells and proteins in the blood because they’re too large to cross the membrane.
Return of Tissue Fluid to the Circulatory System:
- The loss of the tissue fluid from the capillaries reduces the hydrostatic pressure inside them.
- As a result, by the time the blood has reached the venous end of the capillary network its hydrostatic pressure is usually lower than that of the tissue fluid outside it.
- Therefore tissue liquid is forced back into the capillaries by the higher hydrostatic pressure outside them.
- In addition, the plasma has lost water and still contains proteins. It therefore has a lower water potential than the tissue fluid.
- as a result, water leaves the tissue by osmosis down a water potential gradient.
Movement of water up the stem in the Xylem:
due to cohesion-tension
The movement of water up the stem occurs as follows:
- Water evaporates from mesophyll cells due to heat from the sun leading to transpiration.
- Water molecules form hydrogen bonds between one another and hence tend to stick together (cohesion).
- Water forms a continuous, unbroken column across the mesophyll cells and down the xylem.
- As water evaporates from the mesophyll cells in the leaf into the air spaces beneath the stomata, more molecules of water are drawn up behind it because of cohesion.
- A column of water is therefore pulled up the xylem as a result of transpiration (transpiration pull).
- Transpiration pull puts the xylem under tension, that is, there is a negative pressure within the xylem, hence the name cohesion-tension theory.
What are the three types of valves?
Atrioventricular, semi-lunar, pocket valves
Atrioventricular valves
- Between atrium and ventricle
- Prevents back flow of blood when contraction of the ventricles means that ventricular pressure exceeds atrial pressure.
- Closure of these valves ensures that, when the ventricles contract , blood within them moves to the aorta and pulmonary artery rather than back to the aorta
Semi-lunar valves
- In aorta and pulmonary artery.
- Prevents back flow into ventricles hen pressure in vessels exceeds that in the ventricles.
- This happens when the elastic walls of the vessels recoil, increasing the pressure within them and when the ventricle walls relax, reducing the pressure within the ventricles.
Pocket valves
- In veins
- So when veins are squeezed, blood flows back towards the heart not away
Describe how a high pressure is produced in the leaves (3)
- water potential becomes lower as sugar enters the phloem
- h20 enters phloem by osmosis
- increased vol. of water causes increase in pressure
