AQA BIOL2~3rd June 2013~AS Biology (Now Closed) Watch
THICKER MUSCLE LAYER THAN ARTERIES: So when they contract, they can control and restrict the blood flow into the capillaries.
THINNER ELASTIC LAYER THAN THE ARTERIES: Because blood pressure is lower.
Tissue fluid is liquid that contains glucose, amino acids, fatty acids, salts and oxygen.
At the arteriole end, blood pumps into the arterioles then capillaries, this creates Hydrostatic pressure which forces Tissue Fluid out of the capillary and into the cells. Only small molecules are forced out so leaves large proteins in the capillary, this lowers the water potential in the capillary.
Once the blood has reached the venule end, the hydrostatic pressure in the cells is higher than the hydrostatic pressure in the capillaries thus it forces the tissue fluid back into the capillary. Also, the lower water potential created by the proteins create a water potential gradient so since, there's higher water potential in the cells, water moves by osmosis into the capillary.
Any excess returns via the lymphatic system.
Hope this helps! Good luck
Apoplastic pathway is the movement of water through the cell walls of the root cells, crossing the cortex, until it reaches the casparian strip. The casparian strip is impermeable and made from Suberin, giving the plant more control over what enters it or not. It then merges with the symplastic pathway.
The symplastic pathway is the movement of water when it moves by osmosis into the cells by osmosis until it reaches the xylem, moving through the plasmodesmata. In both cases water moves from a high to low water potential. The concentration gradient is maintained by pumping minerals into the xylem.
I think it's worth a share
The lumen of the artery is surrounded by a layer of cells known as the endothelium. The endothelium is a thin layer and it simply reduces the friction of blood flow!
It's definitely smooth and not folded!
I don't think we'll ever be asked about how it can be smooth but also stretch, because I hope they're not expecting us to be cardiovascular surgeons :P
Basically water wants to get from the soil into the xylem vessels. It can do this by 2 methods or 'pathways' called the SYMPLAST PATHWAY or APOPLAST PATHWAY. (Might be useful if you get a labelled diagram showing xylem/root hair cell etc whilst reading this).
In the Symplast pathway, water moves through the CYTOPLASMS of the cells.
Water diffuses along a water potential gradient through PORES between the cells of the Cortex called plasmodesmata. The Cortex is simply all the cells between the Root hair cell and the Xylem vessel.
In the Apoplast pathway, water moves through the CELL WALLS of the cells.
Water stops at the ENDODERMIS as there is a CASPARIAN STRIP which prevents the water from passing further, making the water pass through a membrane by osmosis down a water potential gradient INTO THE SYMPLAST PATHWAY, which is useful as it prevents harmful substances such as toxins or viruses from entering the xylem vessels as the membrane would not let them past.
- Water potential in the root hair cell is lowered by the active transport of mineral ions from the soil, hence water can move from the soil into them down a water potential gradient.
Watch this, if you need more help:
- Heart = pulmonary artery/vein, Liver = hepatic artery/vein, Kidney = renal artery/vein
- Arteries have thick muscular tissue that can stretch and recoil to cope with increased pressure. They transport blood away from the heart (except the pulmonary artery)
- Veins have valves to prevent backflow of blood, and are surrounded by body muscles which contract to control blood flow. They transport blood to the heart (except the pulmonary vein)
- Arterioles are small vessels. Blood is directed to different areas of demand by muscles contracting to restrict blood flow, and relaxing to allow it.
- Substances are exchanged at the capillaries:
---- Short diffusion pathway achieved by the capillary being near the tissue and being only one cell thick.
---- Large surface area has lots of them form a network.
- Tissue fluid is made of substances that leave the blood at the venal end of the capillary due to hydrostatic pressure.
- Cells take in nutrients from it, and release metabolic waste into it.
- Water from tissue fluid moves back into the blood down a water potential gradient at the arterial end by osmosis
- Excess tissue fluid is drained by the lymph, and is transported and released back into the circulatory system
THIS WASN'T POSTED BY ME. So no credit.It seems like a good answer.