Importance of Water Flashcards
(9 cards)
what are the 4 topics for the importance of water in organisms?
Mass transport in plants
Photosynthesis
Digestion and abosrption
Mass transport in animals
what is the AO1 for water in the mass transport of plants?
- water is a polar molecule made up of 2 hydrogen atoms covalently bonded to 1 oxygen. The slightly larger oxygen molecule has a slight negative charge as electrons are attracted to it and the hydrogen atoms have a slight positive charge.
- this slight uneven distribution of charge allows for weak hydrogen bonds to form between water molecules causing them to stick together in cohesion
- explain cohesion tension theory
- allows water to be pulled up in a continuous column in the xylem in the transpiration stream of a plant
what is the AO2 for the importance of continuous column in cohesion tension theory?
water can then be used by the plant
eg
- to keep plant cells turgid by moving down a concentration gradient by osmosis into the plant cell, pushing the cytoplasm agaisnt the cell wall
- water moving through the plant contains dissolved ions such as nitrates that have been absorbed from the root hair cells, providing the plants with nutrients the plant needs.
what is the AO1 for water in photosynthesis?
- the photolysis of water in the LDR
- water is split using light energy into two protons, two electrons and half an oxygen.
- The electrons replaced the electrons lost from photosystem II in the excitation of electrons
- electrons pass through ETC and reduce NADP into NADPH
- the hydrogen ions move from low concentrations in the thylakoid space to a high concentration in the stroma - this sets up an electrochemical gradient
- the protons move down electrochemical gradient through ATP synthase, providing energy for ADP + Pi to synthesise into ATP
- this is known as the chemiosmosis theory
what is the AO2 for importance of water in photosynthesis?
- water allowed the production of ATP and NADPH in the LDR, which are important for LIR
- in the Calvin cycle, carbon dioxide reacts with RuBP to form GP (catalysed by RUBISCO enzyme)
- GP reduced by the NADPH made in LDR into triose phosphate
- ATP is hydrolysed to release energy for this reaction
- 1/6th of triose phosphate is used to produce organic compounds, such as glucose, cellulose and lipids in the plant.
- without water, electrochemical gradient not produced, ATP not synthesised, therefore GP cannot be reduced to form triose phosphate which cannot produce glucose which is an essential respiratory substrate for the plant to produce ATP for all its metabolic processes
what is the AO1 for water in digestion
- define hydrolysis = breaking bonds using water to split apart molecules
- describe digestion of carbohydrates making sure emphasis on hydrolysis reactions which require water
- eg salivary amylose and pancreatic amylose hydrolyses starch into maltose.
- membrane bound disaccharides (maltase, lactase, sucrase) hydrolyse glycosidic bonds in hydrolysis reactions using water to form glucose, fructose and galactose
what is the AO2 for importance of water in digestion?
- the digestion of carbohydrates is important as now glucose is small enough to be absorbed by co-transport into epithelial cells and the blood stream
- can be used in respiration to produce ATP or can be converted into glygogen in glygogenesis
- without water, hydrolysis not possible, so starch couldnt be broken down and therefore would be excreted/wasted
what is the AO1 for the role of water in mass transport of animals?
- water is an essential component of tissue fluid
- at the arteriold end of the capillary, there is a high hydrstatic pressure due to contraction of the left ventricle, forcing water out of tiny gaps (fenestrations) in the endothelial wall.
- the water, containing products from digestion and respiratory gases, forms the tissue fluid
- tissues/cells are bathed with useful molecules that are forced out such as glucose, oxygen and water
- at the venous end there is a lower water potential in the capillary due to the retention of plasma proteins and a higher water potential in tissue fluid so water moves down water potential gradient by osmosis back into capillary along with dissolved waste products such as carbon dioxide and urea
what is the AO2 for importance of water in tissue fluid?
- without water, tissue fluid cannot be formed and therefore respiring cells do not recieve oxygen and glucose for aerobic respiration
- no oxygen to act as the final electron acceptor in oxidative phosphorylation and less glucose is made into pyruvate in glycolysis, so less ATP prodcued for growth and reproduction of organism
- without water forming the tissue fluid, carbon dioxide and urea cannot move back into blood to be removed
