biology4alevel600

The mammalian circulatory system is a closed   double  circulation, consisting of a  heart ,  blood vessels  and  blood . The heart produces high pressure --> blood moves through the vessels by mass flow. The mammalian circulatory system is   closed:  blood travels inside vessels   double circulatory :                                         pulmonary  system:  heart -->       lungs                       --> heart                                   systemic  system     : heart --> around the rest of body --> heart Blood vessels Arteries Carry blood away from the heart. Blood that flows through arteries is pulsing and at a high pressure .  Have thick , elastic walls which can expand and recoil as the blood pulses through. The artery wall contains variable amounts of smooth muscle. This muscle does not help to push the blood through them. Arterioles  Arteries branch into smaller vessels called  arterioles.  They contain smooth muscle in their walls, which can contract and

8.1    The circulatory system 8.2    The heart As animals  become larger, more  complex and more  active,  transport systems become essential to supply nutrients to, and remove waste from, individual cells. Mammals are far more  active than  plants  and  require  much  greater supplies of oxygen.  This is transported by haemoglobin inside red blood cells. Candidates will be expected to use  the knowledge gained  in this section to solve problems in familiar and  unfamiliar contexts. Learning outcomes Candidates should  be able to: 8.1    The circulatory system The mammalian circulatory system consists of a pump, many  blood vessels and blood, which is a suspension of red blood cells and white  blood cells in plasma. a)   state that  the mammalian circulatory system is a closed double circulation consisting of a heart,  blood vessels and blood b)   observe and make  plan diagrams of the structure of arteries, veins and capillaries using prepared slides  and be able to recognise these ve

• The need for, and functioning of, a transport system in mammals • Structure and functioning of the mammalian heart Learning Outcomes Candidates should be able to: (m) [PA] describe the structures of arteries, veins and capillaries and be able to recognise these vessels  using the light microscope; (n) explain the relationship between the structure and function of arteries, veins and capillaries; (o) [PA] describe the structure of red blood cells, phagocytes (macrophages and neutrophils) and lymphocytes; (p) state and explain the differences between blood, tissue fluid and lymph; (q) describe the role of haemoglobin in carrying oxygen and carbon dioxide (including the role of carbonic  anhydrase, the formation of haemoglobinic acid and carbaminohaemoglobin); (r) describe and explain the significance of the oxygen dissociation curves of adult oxyhaemoglobin at  different carbon dioxide concentrations (the Bohr effect); (s) describe and explain the significance of the increase in the re

1. Multicellular organisms with small surface area to volume ratios need transport systems. 2. Water and mineral salts are transported through a plant in xylem vessels. Movement of water is a  passive process in which the water moves down a water potential gradient from soil to air.  3. The energy for this process comes from the Sun, which causes evaporation of water from the wet walls of mesophyll cells in leaves. Water vapour in the air spaces of the leaf diff uses out of the leaf through stomata, in a process called transpiration. This loss of water sets up a water potential gradient throughout the plant.  4. Transpiration is an inevitable consequence of gaseous exchange in plants. Plants need stomata so that carbon dioxide and oxygen can be exchanged with the environment.  5. The rate of transpiration is affected by several environmental factors, particularly temperature, light intensity, wind speed and humidity. It is difficult to measure rate of transpiration directly, but water

The movement of substances in phloem tissue is called translocation . The main substances that are moved are sucrose and amino acids , which are in solution in water. These substances have been made by the plant and are called assimilates . Phloem tissue Phloem tissue contains cells called sieve tube elements . Unlike xylem vessel elements, these are living cells and contain cytoplasm and a few organelles but no nucleus. Their walls are made of cellulose. A companion cell is associated with each sieve tube element. Sources and sinks  Vascular plants produce nutrients such as sucrose in their leaves. These nutrients must then be transported to the rest of the shoot or to the root tips, where growth occurs. The leaves are referred to as the source, and the shoot and root tips - sink. A source is an organ that produces more sugar than it requires. That's where assimilates enter the phloem.  A sink is an organ that consumes sugar for its own growth and storage. That's where assim

Most plants secure the water and minerals they need from their roots. The path taken is: soil -> roots -> stems -> leaves. The minerals (e.g., K+, Ca2+) travel dissolved in the water. Water and minerals enter the root by separate paths which eventually converge in the stele. Transpiration Transpiration is the loss of water from the plant through evaporation at the leaf surface. It is the main driver of water movement in the xylem. Transpiration is caused by the evaporation of water at the leaf, or atmosphere interface; it creates negative pressure (tension) equivalent to –2 MPa at the leaf surface.  Water from the roots is pulled up by this tension. At night, when stomata close and transpiration stops, the water is held in the stem and leaf by the cohesion of water molecules to each other as well as the adhesion of water to the cell walls of the xylem vessels and tracheids. This is called the  cohesion–tension  theory of sap ascent. How water moves from soil to air Water m