knowledge-11 Mt

• mass transport moves substances efficiently over large distances between cells and exchange surfaces. This is important for large organisms that cannot rely on simple diffusion.
• Red blood cells contain haemoglobin to transport oxygen from the lungs to the cells.
• The protein haemoglobin has a quaternary structure , and it is made of four polypeptide chains with haem groups.
• Oxygen loading: at the alveoli , when the first oxygen molecules bind to the first haem group, the haemoglobin changes shape. This makes it easier to bind a further three oxygen molecules.
• Oxygen unloading: at tissues, oxygen dissociates from the haemoglobin due to low partial pressure of oxygen in the tissues. In high carbon dioxide concentrations , such as at the tissues , haemoglobin releases oxygen.
• Bohr effect:

  • haemoglobin's oxygen binding affinity is inversely related to the concentration of carbon dioxide in the blood.
• Bohr effect:

  on the graph , the lower part of the High PCO occurs in the active tissues . the top part of the low PCO occurs at the lung capillaries.

  
• Bohr effect:

  the dissociation of oxyhaemoglobin is therefore higher at the tissues ,where partial pressure of carbon dioxide is higher. This is known as the Bohr effect.
• Humans have a double circulatory system that circulates blood between the heart and the lungs, and from the heart to the body.
• The heart itself is supplied with blood from the coronary arteries.
• The hear has two main arteries: pulmonary artery ( taking deoxygenated blood to the lungs) and the aorta (sending oxygenated blood to the body).
• The heart has two main veins: the pulmonary vein ( receiving oxygenated blood from the lungs) and the vena cava (receiving deoxygenated blood from the body).
• The kidneys are supplied with blood via the renal artery and blood is taken away by the renal vein.
• Arteries- have thick walls containing elastic tissue and smooth muscle tissue to maintain high pressures.
• Arterioles- are much smaller arteries that deliver blood to the capillaries. Arterioles have thinner walls than arteries and less elastic tissue.
• Veins have thin walls, containing much less elastic and muscle tissue , and a larger lumen compared to arteries . Most contain valves.
• Capillaries are very small blood vessels , 4-10 um.
• capillaries only allow one blood cell through at a time. they have very low blood pressure.
• capillaries are made up of a single layer of endothelial cells.
• Water and solutes can pass through capillary walls to and from the tissues. Tissue fluid forms around the body cells , bathing them in solutes. tissue fluid drains into lymphatic vessels.
• The human heart has four chambers of cardiac muscle- two atria and two ventricles.
• Each atrium and ventricle is separated by valves to keep a unidirectional flow of blood.
• oxygenated blood is collected in the left atrium, pushed into the left ventricle (has a thicker muscular wall) and then pumped through the aorta to the whole body.
• At the same time as oxygenated blood collection, deoxygenated blood returns from the body into the right atrium and is pushed into the right ventricle , which pumps the blood to the lungs via the pulmonary artery.
• Aortic pressure rises when muscle in the wall of the ventricles contracts as blood is forced into the aorta. It gradually falls, but never below around 12 kPa, because of the elasticity of its wall, which creates recoil action. The recoil produces a temporary rise in pressure at the start of the relaxation phase.
• Plants transport sugar , water and mineral ions using two vessels: phloem and xylem.
• Water and dissolved mineral salts are transported in the xylem. This happens in one direction only -from roots to the top of the plant.
• phloem actively transports organic molecules such as sucrose from photosynthesis.
• The cambium are cells that sit between the xylem and the phloem , and can differentiate into either xylem or phloem cells.
• The xylem , phloem and cambium cells form the vascular bundle.
• Active transport can occur in two directions and uses energy in the form of ATP.
• Xylem transports water up the plants thanks to the transpiration stream, as well as dissolved minerals to the tissues that need them. It is made from dead cells that from dead cells that form continuous tubes.
• Xylem:

  Water moves from the soil into the root hair cell by osmosis from a higher to lower water potential, moving through root tissue to the xylem vessel.
• Xylem:

  Water evaporates from the leaves causing tension, which pulls water molecules up the stem. This creates a continuous transpiration stream.
• phloem is made up of living cells that have sieve plates between them and the companion cells beside them ,which provide metabolic support.
• Translocation:

  Plants transport sucrose and other substances from sources to sinks (cells that use or store substances).

  higher hydrostatic pressure is created at the source and lower hydrostatic pressure at the sink.

  the pressure gradient moves the phloem sap from the source to sink. It is known as the mass flow hypothesis.