The cardiac cycle
DEOXYGENATED BLOOD ---> vena cava ---> right atria ---> right atrioventricular valve ---> right ventricle ---> pulmonary semilunar valve ---> lungs ---> oxygenated.
Leaves organs via VEINS:
Intestines and stomach: Hepatic portal vein then hepatic vein
Liver: Hepatic vein
Kidneys: Renal vein
OXYGENATED BLOOD ---> pulmonary veins ---> left atria ---> left atrioventricular valve ---> left ventricle ---> aortic semilunar valve ---> aorta ---> arterioles ---> capillaries ---> oxygen changed for carbon dioxide ---> body
Enters organs via ARTERIES:
Intestines and stomach: Intestinal artery
Liver: Hepatic artery
Kidneys: Renal artery
Arteries: carry blood away from the heart (to the organs)
>> Thick muscular layer - to control flow of blood
>> Thick elastic layer - to smooth surges from the heart
Veins: carry blood to the heart (away from organs)
>> Thin muscle and elastic layer
>> Has valves
Arterioles: control blood flow from arteries to capillaries
>> Thicker muscular layer than arteries - to control blood flow
>> Thinner elastic layer
Capillaries: link arterioles to veins
>> Thin layer of cells for short diffusion distance
>> Highly branced for large surface area
>> Narrow diameter to keep cells close
>> Narrow lumen to keep red blood cells close
>> Spaces between cells to allow white blood cells to escape
Tissue fluid: watery liquid that contrains glucose, amino acids, fatty acids, salts and oxygen.
Heart passes blood along the arteries, then arterioles and then narrow capillaries = thus creates hydrostatic pressure at the end of the capillaries (due to the vessels getting narrower).
>> Hydrostatic pressure forces tissue fluid out of the blood plasma and prevents outward movement
>> Creates low water potential in the blood so water is pulled back into blood within the capillaries.
Results in ultrafiltration
Return of tissue fluid (to the blood plasma via capillaries):
>> Loss of tissue fluid in capillaries leads to reduced hydrostatic pressure inside
>> Hydrostatic pressure is now less than the pressure of tissue fluid on outside
>> Tissue fluid is forced back into capillaries by higher hydrostatic pressure outside capillaries
>> Osmotic forces pull water back into capillaries
Water movement from soil in a plant root hair cell
PROCESS OF OSMOSIS
Root hair cell: Lower water potential due to dissolved sugars, mineral ions and amino acids.
Soil: Higher water potential (although contains minerals, the soil is mostly water)
Water moves from the SOIL which has a HIGHER water potential to an area of LOWER water potential = ROOT HAIR CELL -- moves down a water potential gradient.
ROOT HAIR CELLS:
>> Large surface area: large extensions, many of them
>> Thin surface layer: (cell surface membrance and cellulose cell wall) = materials can move easily
^^ make water movement more effective ^^
Water movement from root hair cell through the cor
APOPLASTIC PATHWAY: Water moving through the cell wall.
Water --> endothermal cells --> more water dragged due to cohesive properties of water molecules.
A tension is created that pulls water along cells walls of root cortex.
SYMPLASTIC PATHWAY: Water moving across the cytoplasm of the cells of the cortex as a result of osmosis. Moves through openings called plasmodesma which are filled with a single strand of cytoplasm expanding from the root of the hair cell into the xylem.
1) Water enters by osmosis - increases water pot of root hair cell.
2) Root hair cell = higher water pot than first cell of cortex.
3) Water moves from root hair cell down a water pot grad into first cell of cortex.
4) First cell = higher water pot than its neighbour (second cell) inside the stem
5) Water moves from first cell down a water pot grad into neighbouring cell in stem.
6) Second cell = higher water pot than its neighbour (third cell)
7) Water moves from second cell down a water pot grad into third cell.
8) At same time, loss of water from first cortical cell lowers wat pot = more water enters by osmosis into root hair cell.
9) Water pot hrad is set up acorss all cells in the cortex
The apoplastic pathway has the most water travel through as there is more space, and a mesh like structure.
Passage of water into the xylem
PROCESS = ACTIVE TRANSPORT of mineral ions and salts into the xylem by endodermal cells - creates a low water potential. The process needs energy of which exists within living tissue. Takes place along carrier proteins in the cell surface membrane.
Because there is now a low water potential, water enters by OSMOSIS. This creates a force that helps to move water up the plant = ROOT PRESSURE.
1) Water reaches endodermis by apoplastic pathway
2) Waterproof band in Casparian strip in endodermal cells prevents it progressing further along cell wall
3) Water is forced into protoplast of cell.
4) Joins water which has arrived by the symplastic pathway.
EVIDENCE FOR ROOT PRESSURE:
>> Pressure increases with a rise in temperature and decreases at lower temperatures.
>> Metabolic inhibitors prevent energy release by respiration and causes a build up of pressure.
>> Decrease in availability of oxygen or respiratory substrates causes a reduction in root pressure.
Rate of transpiration (factors affecting)
TRANSPIRATION: water evaporating from the air spaces in a plant.
Stomatal pore size:
>> Light intensity
>> Concentration of carbon dioxide
>> Surface area of leaf
>> Number of leaves
Rate of evaporation:
>> Atmospheric temperature
>> Surface area of leaf
>> Number of leaves
Movement of water up stems
MOVEMENT OF WATER OUT THROUGH STOMATA:
If stomata are open (they close when water loss is excessive), water vapour molecules diffuse out of the air spaces and into the surrounding air. Water lost is replaced by water evaporating from the cell walls of surrounding mesophyll cells.
MOVEMENT OF WATER ACROSS THE CELLS OF A LEAF: water is lost through mesophyll cells by evaporation from their surfaces to the air spaces of the leaf. This is replaced by water reaching the mesophyll cells from the xylem by either the apoplastic or symplastic pathway:
1) Mesophyll cells lost water to air spaces
2) Mesophyll cells = lower water pot - water reenters by osmosis from neighbouring cells
3) Loss of water from neighbouring cells lowers their water pot
4) Take water from neighbouring cells
~~ water pot grad is created - pulls water from xylem across mesophyll and out into atmosphere.
Movement of water up stems
MOVEMENT OF WATER UP THE STEM IN THE XYLEM
COHESION TENSION THEORY:
1) Water evaporates from leaves as a result of transpiration
2) Water molecules from hydrogen bonds between one another causing them to stick together = cohesion.
3) Water forms a continuous, unbroken pathway across the mesophyll cells and down the xylem.
4) 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 as a result of this cohesion.
5) Water is hence pulled up the xylem as a result of transpiration. This is called transpiration pull.
EVIDENCE TO SUPPORT THEORY:
>> CHANGE IN DIAMETER:
day = greatest transpiration - more tension - diameter shrinks
night = lowest transpiration - less tension - diameter increases
>> If a xylem vessl is broken and air enters the tree can no longer draw up water as molecules can't stick together --> air being drawn in shows there is tension.
Daughter cells: The cells produced as a result of the mitosis or meosis of a parent cell.
Mitosis: Cell division in which all daughter cells produced are genetically identical (same DNA) to the parent cell.
For growth and tissue repair.
Chromosomes become visible, spindle apparatus forms, nucleolus disappears and nuclear envelope breaks down.
Chromosomes arrange themselves on the equator of the spindle, attached by their centromeres
The spindle fibres contract, causing the two chromatids of each chromosome to separate and move to opposite poles of the cell
The chromosomes reach the poles and a new nuclear envelope forms around each set; the chromosomes uncoil, once more becoming visible
Biology behind heart disease
Atheroma: fatty deposit in the endothelium that can build up (grow bigger) due to platelets clotting blood and as a result, break through to the lumen. Begins as fat accumulated of white blood cells, have taken up LDLs.
Thrombosis: a blood clot formed when the endothelium cracks is called a thrumbus and the condition is thrombosis. This thrombus may block the blood vessel preventing blood supply of oxygen and glucose to the heart muscle, tissues and cells.
Aneurysm: when the thrombus weakens the artery walls which swells like a balloon, blood filled structure called a aneurysm. This will eventually burst leading to haemorrhage.
Myocardial infarction: heart attack.
Biology behind heart disease: Risk factors
(casual link - haemoglobin
correlation - the more cigarettes smoked per day the higher the chance of heart disease):
Carbon monoxide: combines with haemoglobin = carboxyhaemoglobin = reduces the oxygen carrying capacity of blood so heart must work faster to get oxygen and glucose to tissues and cells.
Can cause high blood pressure - increases risk of heart disease and strokes.
May be insufficient to supply heart muscle during exercise.
Nicotine: stimulates production of adrenaline = increase blood pressure and heart rate = greater risk of heart disease and/or strokes.
Nicotine also makes platelets more 'sticky' = higher risk of thrombosis.
HIGH BLOOD PRESSURE = artiers thicken and don't recoil as well - heart works faster.
(causal link - build up of LDLs --> atheroma --> thrombosis --> myocardial infarction)
High in saturated fats and salts = high blood cholesterol = increase in LDLs
More exercise = less change of heart disease due to heart muscle growing stronger = negative correlation