A Watery Medium Flashcards
What is the process of respiration?
Glucose + oxygen Right arrow carbon dioxide + water + energy (in the form of ATP)
What is xylem?
Xylem: The transpiration-cohesion-tension mechanism is currently the theory that accounts for the ascent of xylem sap. This sap is mainly pulled by transpiration rather than pushed by root pressure. Cohesion is the “sticking” together of water molecules so that they form a continuous stream of molecules extending from the leaves down to the roots. Water molecules also adhere to the cellulose molecules in the walls of the xylem. As water molecules are removed by transpiration in the leaf, the next molecule moves upwards to take its place, pulling the stream of molecules continuously along. This is passive transport.
What is Phloem?
Phloem: The pressure-flow mechanism (or Source to Sink) is a model for phloem transport now widely accepted.
The model has the following steps.
Step 1: Sugar is loaded into the phloem tube from the sugar source, e.g. the leaf (active transport)
Step 2: Water enters by osmosis due to a high solute concentration in the phloem tube. Water pressure is now raised at this end of the tube.
Step 3: At the sugar sink, where sugar is taken to be used or stored, it leaves the phloem tube. Water follows the sugar, leaving by osmosis and thus the water pressure in the tube drops.
The building up of pressure at the source end, and the reduction of pressure at the sink end, causes water to flow from source to sink. As sugar is dissolved in the water, it flows at the same rate as the water. Sieve tubes between phloem cells allow the movement of the phloem sap to continue relatively unimpeded.
Outline the need for oxygen in living cells and explain why removal of carbon dioxide from cells is essential
Carbon dioxide is a waste product and must be removed to maintain the normal pH balance of the blood. By removing excess carbon dioxide, it prevents a build up of carbonic acid, which causes the lowering of the pH, and therefore increasing breathing rate and depth. Carbonic acid forms when carbon dioxide dissolves in water. At normal levels, (after excess removal of carbon dioxide) the carbon dioxide - bicarbonate ion (HCO3-) equilibrium is an important mechanism for buffering the blood to maintain a constant pH.
