Summary CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 11. Each lymph node has an outer layer called capsule, inner wall called cortex and medulla of fine network of cellular threads. An arteriole sends blood to the lymph node and venule drains blood away from it. There are one or more afferent and efferent lymphatic vessels leading into or out of each node, respectively. 12. Lymphoid tissues are found in the palate and pharyngeal tonsils, in the small intestine (Peyer patches), oesophagus, appendix and large intestine. The tissues contain a more concentrated aggregation of lymphatic vessels and lymph nodes. The tissues easily swell, especially when lymphatic vessels are blocked as a result of infection. 13. Spleen is the largest lymphoid organ found close to the stomach and destroys worn out red blood cells and platelets. The spleen is also the organ where antigens are detected in the blood and removed by white blood cells. The spleen has a thin capsule of connective tissue. It is supplied with an artery to carry oxygenated blood into it and a vein that drain deoxygenated blood. It has thin walls and network of cells filled with capillaries, follicles and blood spaces. It has two distinct components, the red pulp and white pulp. The red pulp is filled with complex system of blood capillaries to remove old or damaged red blood cells. The white pulp contains follicles filled with white blood cells (lymphocytes and macrophages). 14. Spleen can expand and contract when required. When the body temperature is lowered, the spleen expands to store up blood and vice versa, when it is hot. It is the only organ with no lymphatic capillary. 15. Thymus gland is a lymphoid gland that composes of lymphoid tissue and located anterior to the ventral part of the heart. It enlarges during childhood but after puberty, it shrinks in size but still functions throughout life. 16. The thymus gland has a capsule, more cellular cortex and less cellular inner medulla. Immature T lymphocytes enter into the cortex, divide, mature and pass out from the medulla into the blood vessels. Fluid Movement in Capillaries 1. The fluid movement at the arterial and venous ends of the capillaries is as shown in Figure 8.9. 2. Tissue fluid is formed when blood plasma passes through the capillary wall but not the blood cells, platelets and plasma proteins. 3. Water and solutes are forced out at the arteriole end of capillary. This is due to the capillary has a higher hydrostatic pressure of +5.18 and solute potential of –3.26 giving the difference of +1.92 kPa. Similarly, the tissue fluid has also a hydrostatic pressure of +0.66 and solute potential of –0.38 giving the difference of +0.28. Therefore, the difference in pressure between inside and outside the capillary is +1.64 kPa resulting an outward flow of liquid. Exam Tips 9LTLTILY[OLVYNHUPZH[PVU VM[OLS`TWOH[PJZ`Z[LT JVUZPZ[PUNVMS`TWOJLSSZ IVULTHYYV^]LZZLSZ UVKLZ[PZZ\LZZWSLLUHUK [O`T\ZNSHUK )OXLGÁRZVRXWDQGLQWR FDSLOODULHV Arteriole end 1.>H[LY^P[OU\[YPLU[ZÅV^ out 2. Hydrostatic (5.2 kPA) pressure higher than tissue Å\PKffR7H 3. Solute potential is (–3.3 kPa) lower than that of [PZZ\LÅ\PK¶flR7H 4. Net pressure is higher than [PZZ\LÅ\PK ffi¶¶ff¶fl = 1.6 kPa Venule end 1.>H[LY^P[O^HZ[LZÅV^ZPU 2. Hydrostatic pressure (3.3 kPa) is not very much OPNOLY[OHU[PZZ\LÅ\PKff kPa) 3.:VS\[LWV[LU[PHS¶ffR7H is much lower than that of [PZZ\LÅ\PK¶flR7H 4. Net pressure is lower than IVK`Å\PK ¶ff¶ff¶fl $¶ffR7H 2013/P2/Q18(b)
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants Blood Blood Venule More proteins High blood pressure + 0.28 Difference + 1.64 outward pressure Arteriole Tissue HP + 5.18 ^s – 3.26 + 1.92 O O H2O + solutes H2O HP + 0.66 ^s – 0.38 + 0.26 Difference + 0.65 inward pressure HP + 3.26 ^s – 3.65 – 0.39 HP + 0.66 1.64 – 0.65 = 1.04 ^ Lymphatic capillary s – 0.38 Low blood pressure Slightly more negative solute potential Capillary Figure 8.9 Formation of lymph 4. Water and solutes are absorbed back at the venule end of the capillary. This is due to the higher inward or suction pressure. The hydrostatic pressure inside is 3.26 and solute potential is –3.65 giving a difference of –0.39. The hydrostatic pressure in the tissue fluid is +0.66 and water potential is –0.38 giving a pressure of +0.26. Therefore, there is a suction pressure of +0.65 kPa into the capillary Exam Tips 9LTLTILYOV^S`TWOPZ formed and the calculation VMO`KYVZ[H[PJWYLZZ\YL HUKZVS\[LWV[LU[PHSPU[OL TV]LTLU[VMÅ\PKIL[^LLU ISVVKJHWPSSHY` HUK[PZZ\L Å\PK 8.2 Transport System in Vascular Plants The Uptake of Water and Ions from the Soil by Root Hairs 1. Root hairs are special adaptations of the roots to absorb water and mineral ions. These root hairs are very fine around 1.0 mm in length and 10 μm in diameter. They are found at the tips of young roots or young branches, a few mm behind the root cap and spread not more than 1 cm along the length of the root. 2. The root hairs greatly increase the surface area to volume ratio for absorption. These fine hairs can also grow into fine crevices in between the soil particles. Learning Outcomes Students should be able to: H L_WSHPU[OL\W[HRLVM ^H[LYHUKTPULYHSPVUZ from the soil by the root OHPYZPU]VS]PUN^H[LY WV[LU[PHS" I KLZJYPIL[OLHWVWSHZ[ Z`TWSHZ[HUK]HJ\VSHY WH[O^H`VM^H[LY TV]LTLU[[OYV\NO[OL root tissues; (c) describe the root WYLZZ\YLJVOLZPVU tension theory and [YHUZWPYH[PVUW\SS
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 3. The wall of the root hairs is very thin consisting of primary cell wall material of cellulose, hemicellulose and pectin. The wall is very porous to water. These root hair cells will die in a few days and be replaced by suberised cells further distance away as the root branches grow. 4. There are specific transport proteins in the plasma membrane of the root hairs where essential ions are taken in selectively by passive and active transport. Proton pumps transport hydrogen ions out and specific ions are co-transported in. For some plants, even nonessential ions are absorbed specifically by the transport protein, e.g. silicate ions. 5. Water enters the root cells by osmosis following the concentration gradient. In some halophytes, the root hairs have much lower water potential than the salt water outside so that water can still diffuse in by osmosis. 6. Water and ions can also simply imbibe into the porous cell walls and move about along the walls. The water and ions may enter the inner cells later and finally have to enter the endodermal cells. 7. Mineral ions may be taken into the root hair cells by facilitated diffusion with the help of transport proteins within the plasma membrane of the root cells. This also follows concentration gradient. 8. Most essential mineral ions are taken into the cells against their concentration gradient by active transport in which ATP is required. Such ions include nitrate, phosphate, sodium, potassium, calcium and sulphate ions. From Root Hair to Xylem 1. The pathway in which water and mineral ions move from the piliferous layer (epidermis) to the xylem in the centre of the root is as shown in Figure 8.10. PUYLSH[PVU[V^H[LY movement from the roots to leaves; K L_WSHPU[YHUZSVJH[PVU \ZPUN[OLTHZZÅV^ electro-osmosis, J`[VWSHZTPJZ[YLHTPUN HUKWLYPZ[HS[PJ^H]LZ O`WV[OLZLZ" L L_WSHPU[OLJVUJLW[ of source and sink, HUKWOSVLTSVHKPUN HUK\USVHKPUNPU [YHUZSVJH[PVUHJJVYKPUN [VWYLZZ\YLÅV^ O`WV[OLZPZ Root hair Epidermis Symplast pathway Apoplast pathway Pericycle Endodermis Xylem Vacuolar pathway Vacuole Cortex Casparian strip Figure 8.10 Water pathway entering in the root INFO ;YHUZWVY[VM>H[LY and Minerals in Plants
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 2. There are three pathways for the water to move from one cell to the another cell in the plant (Figure 8.11). To xylem Vacuolar pathway Apoplast pathway Symplast pathway Cytoplasm Cellulose cell wall Plasmodesmata Figure 8.11 Different pathways of water going through cells (a) Apoplast pathway is a way in which water and mineral ions do not enter the cells in the root but just move along the porous adjacent cellulose wall. All solutes from the soil can just diffuse and flood the porous wall and intercellular spaces of the cells in the cortex. (b) Symplast pathway is a way where water and ions enter the protoplast of the cell without going into the sap vacuole and then move into the protoplast of next cell through the cell wall and plasma membrane, and so on. Certain amount of water and ions can go through plasmodesmata to the next cell. (c) Vacuolar pathway is a way in which water and ion move into the sap vacuole and out into the vacuole of the next cell through the cell wall and plasma membranes, and so on. The water and ions must go through the tonoplast when they move in and out. Certain ions may be retained in the vacuole. Plasmodesmata are involved too when ions move from one cell to another. 4. The movement of water and ions along the cells in the cortex is mainly by diffusion until they reach the endodermis, before they enter the xylem. The xylem in the leaves has the least water and solute potentials so the water and ions are constantly being ‘pulled’ up into the leaves from the roots during the day. The water and ion potential within cell wall of the root outside the endodermis is the same as that of the soil. Inside Direction of water entry from outside Casparian strip Plasma membrane with specific transport proteins to control ions passing through Figure 8.12 Water going through the endodermis Exam Tips Exam Tips Remember the three WH[O^H`ZMVY^H[LY movement Remember you cannot use VZTV[PJWYLZZ\YL[VL_WSHPU [OLTV]LTLU[VM^H[LY0[ T\Z[ILIHZLKVU^H[LY WV[LU[PHS $SRSODVWV\PSODVWDQG YDFXRODUSDWKZD\V Apoplast 1. Along cell wall but does not cross the plasma membrane 2. Solutes do not enter cells 3. Imbibition and diffusion down water potential gradient 4. Stopped by endodermal Casparian strip Symplast 1. Cross plasma membrane/ plasmodesmata and cytoplasm but does not enter vacuole 2. Solutes enter cells 3. Diffuse down water potential gradient or actively transported against concentration gradient 4. Finally into xylem through endodermis Vacuolar 1. Through tonoplast into vacuole and out 2. Solute enter cells 3. Diffuse down water potential gradient or active transport against concentration gradient 4. Finally into cytoplasm of endodermis and xylem $SRSODVW V\PSODVW DQ Summary
CHAPTER 8 fl Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 5. Endodermis with the suberised Casparian strip regulates the intake of water and ions into the xylem. The suberised strip stops apoplast pathway. Water and ions have to go through the symplast pathway as there is no vacuole within the endodermis. 6. The plasma membrane of the endodermis thus exerts control of solutes and water into the living protoplast of the cell. Certain toxins produced by pathogenic bacteria and fungi can be excluded from the endodermis. Through the plasma membrane especially the outer tangential side of the endodermis, solutes and water are regulated to go into the xylem or stele. 7. Endodermis may actively load salts into the xylem vessels so that root pressure is exerted for the water to go up the stem in certain plants. This is the cause of guttation in certain plants where water oozes out from the tips of the leaves. 8. In older roots, the suberised Casparian strip grows to cover the whole inner tangential wall, preventing passage of substances. Only a few passage cells are left to regulate the flow of substances into the xylem. How Water Moves Up in Xylem Vessels Towards the Leaves 1. The vessels and tracheids in the xylem are the cells that are involved in the transport of water. 2. Three experimental evidences to show that the xylem is involved in the transport of water: (a) Stem that is ‘killed’ by immersing in picric acid is still able to transport coloured water up, indicating dead cells can transport water. Xylem is a dead tissue in living stem and the dye which is more often found inside the xylem provides proof of xylem involvement. (b) The xylem vessels if blocked by fat cannot transport water up the stem. This can be done by thrusting stem into fats or applying Vaseline a few times. The transport of water up the stem is blocked. (c) The most convincing proof is by radioactive tracing in which radioactive water is added in the soil. Radioactive water is found later in the xylem of the stem and moved up into the leaves. 3. Root pressure and cohesion-tension theory are involved in the movement of water from the roots to leaves. Root pressure 1. Root pressure is a force found in certain stems after being cut at the base. It causes the oozing of water out of the cut surface continuously for some time. 2. Examples of such plants belong to the Apocynaceae family that also produce latex like rubber tree. Exam Tips Remember the functions of endodermis (also in root WYLZZ\YL
CHAPTER 8 ffi Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 3. When measured, such pressure varies between 100-200 kPa in a manometer. However, most plants do not exhibit such pressure. 4. The flow of water is stopped by treatment with respiratory poison such as cyanide, indicating the process is energy-dependent. Active transport is involved and ATP is required. 5. Further proof of this energy-dependent process can be observed by lowering the temperature or cutting off oxygen supply, in which the process stops. 6. This can be explained by active loading of salts into the xylem vessels through the endodermis. This lowers the water potential in the xylem very much and osmosis occurs, forcing the water up in it in the stem. 7. Root pressure can be used to explain guttation, a process where excess water exudes out from the tips of leaves. Guttation is observed in grass seedlings and trees in waterlogged area of tropical rain forest. 8. Since the process is only found in certain plants, it can be concluded that this is not the sole process involved in the ascent of water up the stem. Root pressure only assists it. Cohesion-tension theory 1. Cohesion-tension theory is a theory that explains the movement of water up in tiny xylem vessels of the plants assisted by tension exerted from the leaves at the top. 2. The theory involves three forces i.e. cohesion, adhesion and transpiration pull. 3. Cohesion is the force of attraction between like molecules i.e. among water molecules caused by hydrogen bondings. This force enables water in a tiny column to withstand a reasonable strength without breaking if pulled from the top. Wall of tube Cohesive force Adhesive force Water molecules Figure 8.13 Cohesive and adhesive forces 4. Adhesion is an attraction force between unlike molecules. (a) In the xylem vessels, the force is between water molecules and the strongly hydrophilic glucose residues of the cellulose found inside the wall of the vessels. (b) The adhesive and cohesive forces produce a tremendous strength especially in the tiny vessels and tracheids of the xylem. The smaller the diameter of the vessel, the higher is the strength. Root pressure 1. Root exerts pressure forcing water up 2. The pressure is caused by high concentration of salt in root xylem 3. Only occurs in some families of plants 4. Endodermal plasma membrane has carrier proteins that actively load salts into xylem 5. Water diffuses into xylem by osmosis forcing water up into stem. 6. Pressure of 200 kPa can be created in some plants 7. Adding respiratory poison stops root pressure Cohesion-tension theory 1. Transpiration pull exerts suction from leaves. 2. The pulling force is caused by transpiration of water vapour through stomata. 3. Occurs in all plants. 4. Evaporation of water from cell wall of mesophyll cells create very low water potential in leaf xylem. 5. Water diffuses up in xylem vessels in stem and root aided by cohesion and adhesion 6. Pressure of more than 100 kPa can be created in giant forest trees 7. Evidence from more leaves in shoot causes more water being sucked up Summary 2014/P2/Q3 STPM
CHAPTER 8 ffl Biology Term 2 STPM Chapter 8 Transport in Animals and Plants (c) This can be seen to support and transport of water and mineral ions up in the xylem of the tree, even if it is more than 100 meters tall. 5. Cohesion and adhesion help to keep the water in a xylem vessel moving as a continuous column. 6. The loss of water vapour from the leaves of a plant is called transpiration. Transpiration pull is the combined suction force exerted by all the leaves in a plant when transpiration occurs. (a) During transpiration, loss of water by mesophyll cells ultimately sucks water from the xylem tissue of the leaves. (b) As the xylem tissue of the leaves is connected to that of the stem and in turn to that of the root, water moves in continuous streams right from the soil to the stem and then to the leaves. (c) Evaporation of water on the surfaces of the mesophyll cells causes the pull. The pull by several leaves produced a force more than that of a vacuum pump as shown by experiment indicated in the diagram below. Leafy shoot Mercury Water Manometer More than 70 cm Figure 8.14 The force of transpiration pull 7. Beside that, anatomical adaptations of the vessels and tracheids produce an effective transport system even if bubbles are formed in the vessels. The tiny pits of the vessels and tracheids can move water sideways and air bubbles cannot go through the pits. Phloem and Translocation Evidences and structure of phloem 1. Three evidences that prove phloem are involved in translocation of organic solutes are as follows: (a) Ringing the bark of a tree always causes the tree to die. Before it dies, it can be observed that sugar and other organic compounds accumulated at the upper part of the ring. This is because the ringing process has removed the phloem and solutes cannot pass across the gap into the root. The plant dies because the root dies from starvation. Exam Tips 9LTLTILY[OL[^V[OLVYPLZ PU[OLHZJLU[VMZHWPU WSHU[Z 2010
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants Stem Ringed shoot (phloem removed) After a few days Sugar and organic compounds accumulated at the upper part of the ring Figure 8.15 Evidence of phloem involved in food translocation (b) The dye used for staining organic substances also stain the contents of the phloem. This indicates that phloem is involved in the transport of organic solutes. (c) More conclusive evidence is from radioactive tracing of radioactive carbon dioxide. The products of carbon fixation, which are radioactive are transported in the phloem. (d) A direct observation to show that sieve tube is involved is using aphid that has its mouth parts penetrated into the sieve tube. When the tube-like mouth part is cut, the chemical content inside the sieve tube and the rate of flow can be measured. Electromicrograph showing the position of the tip of the mouth part can also be prepared. 2. The structure of sieve tube and companion cell are as shown in Figure 8.16. The sieve tube has no nucleus when matured. The sieve tube has little cytoplasm at the periphery but it has sieve plates at both ends that form the tube. The sieve plate prevent bulging of the tin-walled cell and forms cellulose to seal off broken sieve tube. Companion cells has many plasmodesmata adjacent to sieve tube and many mitochondria to supply ATP for loading of sucrose into the sieve tube. Thin cellulose cell wall of companion cell Nuclear membrane Nucleus of companion cell Nucleolus Nuclear pore Plasmodesmata Ribosomes Golgi apparatus Small vacuole Mitochondrion Rough endoplasmic reticulum Middle lamella Sieve plate Companion cell Cellulose Plasma proteins passing through pore Smooth endoplasmic reticulum Phloem protein Plasma membrane Mitochondrion Thin layer of cytoplasm Plastid with starch grains Sieve pore Figure 8.16 Structure of sieve tube and companion cell
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants Concept of source and sink 1. The source refers to the site where organic substances such as sucrose are loaded into the phloem. Therefore, the source is a photosynthesising leaf. 2. The sink refers to the site where the sucrose is taken out of the phloem. Usually, the sink is the root. Sinks can be any organs like shoot apices, buds, flowers, and developing fruits in the plant of both above and below the photosynthesising leaves. Thus, phloem sap can flow upwards and downwards in phloem. This is in contrast with xylem, in which the flow is always upwards. Loading and unloading 1. In the leaf mesophyll cells, photosynthesis in chloroplasts produces triose sugars, some of which are converted into sucrose. The sucrose, in solution, then moves from the mesophyll cell, across the leaf to the phloem tissue. It may move by the symplast pathway, moving from cell to cell via plasmodesmata. Alternatively, it may move by the apoplast pathway, travelling along cell walls. 2. Sucrose is loaded into a companion cell by indirect active transport. Figure 8.17 shows how this may be done. Proton pump actively pumps hydrogen ions, H+ out of the companion cells, using ATP as an energy source. This creates a large excess of hydrogen ions outside the companion cell. The hydrogen ions can move back into the cell down their concentration gradient, through channel or carrier proteins called co-transporter. The sucrose is carried through the cotransporter molecules passively together with H+ into the companion cells. The sucrose can then diffuse down concentration gradient into sieve tube through plasmodesmata as shown in Figure 8.17. Loading 1. At source 2. Example: leaf 3. Sucrose and amino acids are transported into sieve tube 4. With the help of companion cell 5. Involves proton pump and co-transporter 6. ATP is required Unloading 1. At sink 2. Examples: root, bud, ÅV^LYMY\P[HUKZ[VYHNL organ 3. Sucrose and amino acids are transported out of sieve tube 4. With the help of companion cell 5. Just diffusion across plasmodesmata 6. ATP may not be required Sieve-tube element Companion (transfer) cell Mesophyll cell Cell walls (apoplast) Plasma membrane Plasmodesmata Mesophyll cell Bundlesheath cell Phloem parenchyma cell Low H+ concentration Sucrose Co-transporter High H+ concentration Proton pump ATP H+ H+ H+ S S Figure 8.17 A possible method by which sucrose is loaded into phloem 3. Unloading occurs into any tissue that requires sucrose. It also occurs through the companion cell in the root. Hydrogen ions are pumped into the companion cell from neighbouring cells to create a concentration gradient. Then, sucrose is carried through co-transporter together with H+ out of the companion cells into the cells which need it. Summary
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 4. A certain amount of sucrose just diffuses down concentration gradient into root cells through plasmodesmata. The sucrose is hydrolysed to glucose and fructose, and used in respiration. Hypotheses of Phloem Translocation Mass flow hypothesis 1. The mass flow or pressure flow hypothesis proposed by Munch is as shown in the Figure 8.18. sugar mass flow Water going in Concentrated sugar solution (source) Semipermeable membrane D Direction of water flow B Water going in Water going out 0XQFK·VDSSDUDWXVWRVKRZ PDVVIORZ Dilute sugar solution (sink) Semi-permeable membrane A C Sucrose is loaded into sieve tube High hydrostatic pressure here, due to dissolved sugar Source cell Water loss by evaporation Transpiration stream Xylem Water uptake in root hair Low hydrostatic pressure here because sucrose is converted to insoluble starch Sink cell Mass flow along sieve element from high to low hydrostatic pressure zone A B C D Figure 8.18 :V\YJLZZPURZHUKTHZZÅV^PUWOSVLT 2. Phloem sap moves by mass flow. Plants have to use energy to create the pressure differences needed for mass flow in phloem. So, phloem transport can therefore be considered an active process. 3. The pressure difference is produced by active loading of sucrose into the sieve elements at the place from which sucrose is to be transported. This is usually true in a photosynthesising leaf. 4. As sucrose is loaded into the sieve elements, it creates low water potential in the sieve tubes of the leaves. Therefore, water follows the sucrose into the sieve elements from the xylem by osmosis. 5. In the root or another point along the sieve tube, sucrose is unloaded into other cells. As sucrose is removed, water follows the sucrose out of sieve tube by osmosis. 6. This creates a pressure difference; hydrostatic pressure is high in the part of the sieve tube in the leaf, and lower in the part in the root. This pressure difference causes water to flow from the high pressure area to the low pressure area, taking with it any solutes.
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 7. At the root, it acts as a sink where the sucrose is unloaded or taken out and used in respiration. Cytoplasmic streaming hypothesis 1. Cytoplasm streaming is the movement of cytoplasm around within a cell and into another cell. Organells are observed to circulate and move across sieve pores. 2. Solutes can be carried from one sieve tube cell to another by streaming across the pores of sieve plates. Energy in the form of ATP and kinetic energy is required for solutes to cross the sieve pores. Two ways rapid streaming were also observed in phloem of other stems. 3. Cytoplasmic streaming carries proteins, amino acids, sugars and mineral ions together at the same speed. 4. Thaine observed tubules across the pores in cucumber stem under electron microscope. He proposed that solutes are transported inside or outside the tubules. 5. This can explain the flow of substances in both directions up and down that can occur at the same time. This observation by Thaine is not observed by other scientists. Field (1972) observed cytoplasmic streaming in young wheat stem carrying plastids across sieve pores. Molecules move at a fast speed Molecules move at a slower speed Molecules forced out of the circle Molecules join the next circle Sucrose Water molecule Electro-osmosis hypothesis 1. Electro-osmosis is the movement of ions in an electrical field through a fixed, porous surface which is electrically charged, carrying with them water and any dissolved solute. 2. The sieve plates and phloem normally negatively charged, thus forming a fixed, porous surface with an electrical charge. 0DVVñRZK\SRWKHVLV 1. Water, solutes and organelles circulate in sieve tubes 2. Can cross pores at sieve plates 3. In both directions 4. Helped by protein tubules 5. Slow and depends on energy in the form of ATP 6. Kinetic energy help in the process 7. Transport sucrose and amino acids 0 ñ K KL Summary
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants Exam Tips Remember the most HJJLW[LKO`WV[OLZPZPZ[OL THZZÅV^O`WV[OLZPZ;OL V[OLYZHYLUV[^LSSHJJLW[LK but remember all four O`WV[OLZLZ (OHFWURRVPRVLVK\SRWKHVLV 1. Potential difference develops across sieve plate 2. Caused by potassium pump with K+ ions above 3. Negative charge at the pores or below 4. Negative ions accumulate above 5. Together with water & dissolved sucrose 6. When negative ions accumulated to critical level, H+ pumped in 7. Causes sucrose to move across sieve pores 8. H+ are pumped out to repeat 3. As mass flow occurs through the negatively charged sieve plates, negative ions will be repelled but positive ions will be able to pass through. The repulsed negative ions will accumulate above the sieve plate so that cell above the sieve plate will become negative. This may also due to potassium ions being actively pumped to one side of the sieve plate. 4. When the concentrations of the negative ions reach a certain critical value, hydrogen ions surge from the wall into the cytoplasm, lowering the pH and making the cytoplasm above the sieve plate positively charged. Phloem sap K+ Sucrose Water molecule Active transport + + + + + – – – – 5. This results in the movement of negative ions across the sieve plate into the cell below. Other positive charged ions including potassium ions and hydrated positive charged sucrose and amino acids are repelled and crossed the plate. This is followed by water. 6. Then, the hydrogen ions are transported back into the neighbouring cells by active transport and the process is repeated. Energy is provided by ATP from mitochondria in the companion cell. 7. This explains the role of companion cell and sieve plate. This boosts the mass flow across the sieve plates at intervals especially for tall trees. Peristaltic wave hypothesis 1. According to this hypothesis, proteins microtubules are found within the cytoplasm of sieve tubes especially the young ones. 2. The microtubules span across the pores of the sieve plates and continuous along the sieve tube. (O W L K WK Summary
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants Quick Check 2 1. Explain why transport in the xylem is passive whereas translocation in the phloem is active. 2. Can pressure flow hypothesis explain the movement of solutes in different directions at different times of the day? Objective Questions 1. Which vessel supplies nutrient directly to the myocardium? A Aorta B Coronary artery C Pulmonary artery D Pulmonary vein 2. The graph below shows different blood pressure in blood vessels, W, X, Y and Z. W X Y Z Type of blood vessels Pressure / mm Hg 120 100 80 60 40 20 0 Which of the followings explain the blood pressure that drops steeply in Y? 3. These microtubules containing sap with sucrose can constrict and relax individually in alternative pattern. This results in peristaltic waves. 4. These waves help to push substances inside and move solutes along in the sieve tubes. Each microtubule can move in different speeds and directions. 5. Energy in the form of ATP is required. The process may not occur all the time and is highly speculative. Sucrose Water molecule 1st point of constriction 2nd point of constriction 3rd point of constriction Cytoplasmic filament Phloem sap Cell wall 3HULVWDOWLFZDYHK\SRWKHVLV 1. :PL]L[\ILZHYLÄSSLK^P[O microtubules 2. Continuous from sieve tubes to the next 3. Through pores of sieve plates 4. Contain water and sucrose 5. Constrict & relax alternatively to produce peristaltic waves 6. Pushing sap from one sieve tube to the next 7. Can be at different speed & in opposite direction 8. Depends on energy in the form of ATP 3HULVWDOWLF ZDY 3 L W OWL H K\SRWK Summary STPM PRACTICE 8
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants I Valves in Y lower the resistance in it. II Y reduces risk of damage to Z and itself III Y slows the blood flow to allow the exchange of substances in Z. IV Y is elastic and has a small number of smooth muscles as in Z. A I and II C II and III B I and IV D III and IV 3. Which is the correct sequence of a cardiac cycle? A Atrial diastole, atrial systole, ventricular systole, ventricular diastole B Artrial diastole, ventricular systole, atrial systole, ventricular diastole C Atrial diastole, ventricular diastole, atrial systole, ventricular systole D Atrial diastole, ventricular diastole, ventricular systole, atrial systole 4. What is the reason for the nerve impulse delayed 0.1 second at the atrioventricular node before spreading to the walls of the ventricles? A To ensure the atria have completed the transfer of blood into the ventricles before ventricular systole begins B To prevent an over stimulation of ventricles so that ventricular systole could occur more effectively C To ensure ventricles are completely empty before blood is pumped into the ventricles from the atria D To allow the atria to rest before ventricular systole begins 5. Which of the following events occur during ventricular systole? Tricuspid valves Bicuspid valves Semilunar valves A Open Open Close B Close Close Open C Open Close Close D Close Open Open 6. Which blood vessel is dependent on skeletal muscle contraction to assist blood flow through it? A Vein C Arteriole B Artery D Capillary 7. Which structures play roles in translocation of sucrose in plants? I Stomata III Mitochondria II Sieve plates IV Casparian strips A I and III C II and III B I and IV D II and IV 8. Which event occurs during ventricular systole? I The semilunar valves open II The semilunar valves close III The atrioventricular valves open IV The atrioventricular valves close A I and III C II and III B I and IV D II and IV 9. The diagram below shows the change in blood pressure during cardiac cycle. Blood pressure / kPa 18 14 12 10 8 6 2 0 –2 Aorta Ventricle Atrium –Z Time / second 0.75 In what states are the atrium and semilunar valve at Z? Atrium Semilunar valve A Systole Open B Systole Close C Diastole Open D Diastole Close 10. Which statements regarding the artioventicular node are correct? I It transmits impulse to the Purkinje fibres. II It acts as a primary pacemaker. III It speeds up the transmission of impulse. IV It is located between the two atria. A I and III C II and III B I and IV D III and IV
CHAPTER 8 fl Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 11. Which statement is false of hypertension? I It causes gout II It is caused by arteriosclerosis III Diet high in fats and cholesterol causes it IV Smoking decreases the risk of getting it A I and III C II and III B I and IV D III and IV 12. The diagram below shows a cross section of a monocot vascular bundle. Z Y X Which statement about the water potential in the above cells is correct? A It is less negative in X than in Z and Y. B It is less negative in Y than in Z and X. C It is more negative in Z than in Y and X. D It is more negative in Y and X than in Z. 13. Which pathway is true of the passage of water in the root? I By apoplast pathway II By symplast pathway III By vacuolar pathway IV By mass flow V By cytoplasmic streaming A I and II B I, II and III C II, III and IV D III, IV and V 14. X is a compound in the walls of root endodermal cells. X What is the advantage of structure X? A Enable the mineral ions to enter xylem passively B To prevent the damage of cell wall due to high hydrostatic pressure C Able to control the movement of water and mineral ions into the xylem D Able to draw up large amount of water and mineral ions from the roots to the leaves 15. Which statement of the formation of root pressure is true? I Ions in the cytoplasm are freely transported into the stele through plasmodesmata II Movement of molecules occurs through the mechanism of mass flow and transpiration pull III Ions are transferred through the membrane of root cell into cytoplasm by active transport IV Water together with ions flow into the endodermis A II and III C I, II and III B II and IV D I, III and IV 16. Which statement about transpiration pull is correct? A Its mechanism depends on the negative pressure generated in the leaf B It is not affected by the morphology of the leaf C It causes the girth of the tree trunk to expand D It is an active process 17. The translocation of organic substances in flowering plants involves certain cells. Which cell is involved? I Companion cell II Sieve tube III Xylem IV Collenchyma V Sclerenchyma A I and II B I and III C II and III D IV and V
CHAPTER 8 ffi Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 18. Which of the followings is correct about Casparian strip in plant roots? A It is situated at the walls between endodermal and cortex cells B It increases the surface area for absorption of minerals C It provides energy for active transport of minerals into the stele from the cortex D It ensures that water and dissolved susbstances pass through cells before entering the stele 19. Which of the following statements about the control of heartbeat is true? A The secretion of adrenaline increases the rate of heartbeat. B The decrease in blood pH inhibits neurones in the chemoreceptors at the aorta and carotid artery. C The propagation of impulse through the sympathetic nerve towards the sinoatrial and atrioventricular nodes decreases the rate of heartbeat. D The propagation of impulse through the parasympathetic nerve towards the sinoatrial and atrioventricular nodes increases the rate of heartbeat. 20. Which of the following is true of atrioventricular node? A It acts as a pacemaker. B It initiates atrial systole. C It initiates ventricular systole. D It is controlled by the cardiovascular centre. 21. Which of the following is the role of the Casparian strip in the endodermis cell of the root? A To carry out active transport B To strengthen the root structure C To ensure that the water loss through transpiration can be replaced D To ensure that water and minerals enter the vascular tissue via the symplastic route Structured Questions 1. The diagram below pressure changes in the left side of the heart during the cardiac cycle in a person. 2014 14 12 10 8 4 2 0 2 6 0 0.1 0.2 0.3 A B C 0.4 Time/ s Blood pressure/ kPa 0.5 0.6 0.7 0.8 (a) (i) What occurs at points A and C? [2] (ii) What is the significance of the event at point A? [1] (b) What does graph B represent? [1] (c) Describe how the ventricular systole occurs. [3]
CHAPTER 8 ffl Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 2. The Munch model which explains the mechanism of photosynthetic product translocation in plants is shown in the diagram below. Semipermeable membrane Container Water F sink E source (a) Name the hypothesis which is related to the model. [1] (b) Match E and F in the model to the organs which exist in a sprouting potato. [2] (c) Describe the process which occurs at the source of a plant undergoing photosynthesis. [4] (d) Why does the translocation of photosynthetic product occur only in phloem but not in xylem? [3] Essay Questions 1. (a) Describe how a diet which is high in cholesterol increases the risk of cardiovascular diseases. [9] (b) List the consequences of human internal transport if the lymphatic system is impaired. [11] 2. (a) Describe the apoplast, symplast and vacuolar pathways in the transport of water, together with mineral ions from soil, into the roots. [4] (b) Describe the mechanisms of mass-flow, cytoplasmic and electro-osmosis hypotheses in the translocation of sugar in the sieve tubes. [7] CHAPTER 8
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants Quick Check 1 1. The atrial walls are thinner as the atria pump blood only down into the ventricles. The right ventricular wall is thinner than that of left ventricle because it only pumps blood into the lungs whereas the left ventricle pumps blood to the whole body. 2. Foetal heart need not have to pump blood into the lungs, as they are not usable. There is a pore called foramen ovale in the septum separating the atria so that blood can flow across from right atrium to left atrium. Besides that, there is a by-pass called ductus arteriosus where blood from the pulmonary artery is shunt to the aorta. 3. As people become more affluent they eat ‘better’ food with more meat containing more cholesterol. They are leading a more sedentary life style, with less exercise. Besides that, mutations cause defective genes, especially those related with getting rid of cholesterol, as the environment is getting more contaminated with mutagens. Quick Check 2 1. The cohesion-tension theory explains the uptake of water in the xylem. The process is passive, as it involves transpiration pull, cohesion of water that prevent the column of water from breaking and adhesion with the water binding to the cell wall molecules for support. The mass flow hypothesis of Munch involves active transport of sucrose into the sieve tubes before physical forces help to move it to the region of low concentration gradient. 2. Yes. During the day, the higher atmospheric temperature encourages active cell division and metabolism in the shoot apex. Sucrose flows from leaves up into the shoots. During the day or night, the root cells respire, requiring sucrose to be sent from the leaves down the phloem. STPM Practice 8 Objective Questions 1. B 2. D 3. C 4. A 5. B 6. A 7. C 8. B 9. D 10. B 11. B 12. D 13. B 14. C 15. A 16. D 17. A 18. D 19. A 20. C 21. D Structured Questions 1. t 4VDI EJFU DBVTFT IJHI CMPPE DPODFOUSBUJPO PG cholesterol. t )JHI CMPPE DPODFOUSBUJPOT PG DIPMFTUFSPM DBVTF higher risks of cholesterol deposition in the arterial walls t ćJTDBVTFT UIFBSUFSJBMXBMMT UP CFOPU TPĘFYJCMF and arteriosclerosis. t ćJTJOUVSOTDBVTFTIJHICMPPEQSFTTVSF t )JHICMPPEQSFTTVSFJODSFBTFTUIFSJTLTPGJOKVSJFT to the endothelial layer of arteries. t ćJTFODPVSBHFTUIFFOUSZPGMJQJETBOEDBMDJVNJPOT into the arterial wall to form plaques. t ćFDPOUJOVBMIJHICMPPEDIPMFTUFSPMDPODFOUSBUJPOT encourage more deposition. t 'JOBMMZ UIFTFDBVTFUIFOBSSPXJOHPGUIFMVNFOPG arteries. t *G CMPDLBHFT PDDVSJO UIF DPSPOBSZ BSUFSJFT UIFTF will cause myocardial infarction. t *GCMPDLBHFTPDDVSJOUIFDBSPUJEBSUFSJFT UIFTFXJMM cause ischemic stroke. 2. (a) Pressure flow hypothesis (b) E: Leaf; F: Root (c) t 1SPUPO QVNQ BDUJWFMZ USBOTQPSUT IZESPHFO ions out through plasma membrane from companion cell. t Hydrogen ion concentration is created across the membrane and sucrose molecule is cotransported into the companion cell together with the hydrogen ion. t Sucrose diffuses into sieve tube through plasmodesmata from companion cell. t Water diffuses by osmosis into sieve tube creating hydrostatic pressure forcing sucrose down into root. (d) t 4VDSPTF DBOOPU CF USBOTQPSUFE BDSPTT YZMFN wall that is impregnated with lignin. t Xylem cells are dead cells with no membrane to keep photosynthetic products like sucrose. t Xylem transports water from root into leaf where water is diffusing out. Essay Questions 1. B t *OJUJBM EBNBHF UP FOEPUIFMJVN PG DPSPOBSZ artery. t ćJTJTVTVBMMZDBVTFECZIJHICMPPEQSFTTVSF t 4BUVSBUFE GBUT BOE DIPMFTUFSPM EJČVTF JOUP stratum intima between endothelium and stratum media. t ćF DFMMT JO UIF TUSBUVN JOUJNB EJWJEF stimulated by fats. t ćF BSUFSJBM XBMM CFDPNFT UIJDLFOFE BOE inelastic resulting in arteriosclerosis. t .PSF MJQJET BDDVNVMBUF BU DFSUBJO TQPU resulting in artherosclerosis. ANSWERS
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants t ćF MVNFO PG UIF DPSPOBSZ BSUFSZ CFDPNFT smaller. t $BMDJVNJPOTEJČVTFEJO UPGPSNBIBSEFOFE artheroma. t ćFMVNFODBOCFDPNQMFUFMZCMPDLFESFTVMUJOH in myocardial infarction. t 1BSUPSNBKPSBSFBPGIFBSUNVTDMFEJFTEVFUP lack of oxygen. (b) t )ZESPTUBUJD QSFTTVSF JOTJEF BSUFSJBM FOE PG capillary networks forces water and solutes out. t #MPPE DFMMT QMBUFMFUT BOE MBSHFS QSPUFJO molecules cannot move out. t ćFĘVJENPWFTPVUUISPVHIUIFQPSFTJOUIF endothelium and its basement membrane. t ćF ĘVJE JT GPSDFE PVU EVF UP IJHIFS OFU filtration pressure. t ćJTJTDBMMFEVMUSBĕMUSBUJPO t "U UIF WFOVMF FOE PG UIF DBQJMMBSZ OFUXPSLT negative filtration or suction pressure develops. t 8BUFSJTBCTPSCFECBDLJOUPUIFDBQJMMBSZEVF to lower water potential in the blood. t 1BSU PG UIF JOUFSTUJUJBM ĘVJE ĘPXT JOUP UIF lymphatics and empties into the vena cavae. 2. B t ćF BQPQMBTU QBUIXBZ JOWPMWFT USBOQPSU PG water together with mineral ions simply by imbibition of water into the porous cell walls of the root cells from the soil. t ćF XBUFS BOE JPOT KVTU NPWF BMPOH UIF cell walls and inter-cellular spaces without entering the cells. t ćJT JT DBVTFE CZ UIF DPODFOUSBUJPO HSBEJFOU between the central vascular tissues and the outer layers of the root cells created by transpiration pull from the leaves. t ćF TZNQMBTU USBOTQPSU QBUIXBZ JOWPMWFT active transport of mineral ions into the root cells and water is absorbed by osmosis. t 8BUFS UIFO EJČVTFTGSPN UIF FQJEFSNBM DFMMT into the inner cells by osmosis because of the concentration gradient. t 4PNF XBUFS BOE NJOFSBM JPOT NBZ KVTU ĘPX from cell to cell through the plasmodesmata. t ćFWBDVPMBSQBUIXBZBMTPJOWPMWFTPTNPTJTPG water, not only through the cell membrane but also through the tonoplast. t ćFSFGPSF TPNFXBUFSBOENJOFSBMJPOTNBZ be temporary stored in the sap vocuole of the root cells. t )PXFWFS UIFFOEPEFSNJTXJUIUIF$BTQBSJBO strip and no sap vacuole will stop the apoplast pathway of water and its ions and only allow the symplast pathway into xylem. (b) t "DDPSEJOHUPUIFNBTTĘPXIZQPUIFTJT TVHBS is actively loaded into the sieve tubes indirectly by a proton pump mechanism in the leaves. t "T UIF TVHBS JT MPBEFE JU DSFBUFT MPX XBUFS potential in the sieve tubes of the leaves and water enters through osmosis. t )ZESPTUBUJDQSFTTVSFJTHFOFSBUFEJOUIFTJFWF tubes and forces the sugar out of the leaves into those of the stem and roots as they are connected. t "U UIF SPPU JUBDUTBTB TJOLXIFSF UIF TVHBS is unloaded because of passive transport and used in respiration. t "DDPSEJOH UP UIF DZUPQMBTNJD TUSFBNJOH hypothesis, cytoplasm is observed to stream within one cell and from one sieve tube to the other on the upper or lower ends through the sieve plates. t ćJT DBO CF EVF UP EJČVTJPO UVSHPS DIBOHFT and active transport from neighbouring cells. t $ZUPQMBTNJDTUSFBNJOHDBSSJFTQSPUFJOT BNJOP acids, sugars and mineral ions together at the same speed. t "DDPSEJOH UP FMFDUSPPTNPTJT IZQPUIFTJT protein below the sieve plate is always found to be negative inside the sieve tubes. t 1PTJUJWFJPOTFBTJMZQBTTGSPNUIFVQQFSDFMMUP the lower one through the sieve plate. t )PXFWFS OFHBUJWFJPOTUFOEUPBDDVNVMBUFBU the upper side of the sieve plates. t 8IFOUIFDPODFOUSBUJPOTPGUIFOFHBUJWFJPOT reach a certain critical value, potassium ions are transported actively from neighbouring cells into the sieve tube. t ćJTSFTVMUTJOUIFNPWFNFOUPGOFHBUJWFJPOT across the sieve plate into the cell below. t ćFO UIFQPUBTTJVNJPOTBSFUSBOTQPSUFECBDL into the neighbouring cells and the process is repeated.
CHAPTER CONTROL AND REGULATION Concept Map 9 Bilingual Keywords Nervous system – Sistem saraf Brain – Otak Transmission – Penghantaran Spinal cord – Saraf tunjang Coordination – Koordinasi Hormone – Hormon Synapse – Sinaps Phytochrome – Fitokrom Control and Regulation Nervous system Hormone Sympathetic Parasympathetic The organisation of the nervous system in humans The formation of resting and action potentials The characteristics of nerve impulse The structure of synapse The mechanisms of impulse transmission along the axon and across the synapse The structure of neuromuscular junction and sarcomere The role of neurotransmitters Mechanisms of action The roles of plant hormones in growth and development The mechanism of phytochrome action The application of plant growth regulators Steroid hormone Non-steroid hormone
Learning Outcomes CHAPTER 9 63 Biology Term 2 STPM Chapter 9 Control and Regulation Students should be able to: (a) describe the organisation of the nervous system in humans; (b) explain the formation of resting and action potentials; (c) describe the characteristics of nerve impulse; (d) describe the structure of synapse, and explain the role of neurotransmitters (acetylcholine and norepinephrine); (e) explain and compare the mechanisms of impulse transmission along the axon and across the synapse; (f) describe the structure of neuromuscular junction and sarcomere; (g) explain the role of sarcoplasmic reticulum, JHSJP\TPVUZT`VÄIYPS and T tubules in muscle contraction; (h) explain the mechanism of muscle contraction according to the sliding ÄSHTLU[O`WV[OLZPZ" (i) compare the sympathetic and parasympathetic nervous systems; (j) explain the mechanisms of drug action on nervous system and neuromuscular junction (cocaine and curare). 9.1 Nervous System 9.1 Nervous System Organisation of Nervous System in Humans 1. The human nervous system consists of the central nervous system (CNS) and peripheral nervous system. (a) Central nervous system (CNS) is made up of the brain and spinal cord. (b) Peripheral nervous system is made up of two systems. The first is the somatic nervous system that consists of both spinal and cranial nerves. The somatic system is under voluntary control from the brain. The other is called autonomic (involuntary or visceral) nervous system, which is divided into (i) sympathetic nervous system that consists of only spinal nerves. It has mainly excitory effect on the body or prepares the body for stress. (ii) parasympathetic nervous system that consists of both spinal and cranial nerves. It acts antagonistically (opposite) to the sympathetic nervous system and has mainly calming influence or restores the body back to normal. 2. The whole system is summarised as shown in Figure 9.1. Human Nervous System Central Nervous System (CNS) ( YHPUHUKZWPUHSJVYK ) J[HZPU[LNYH[P]LHUKJVU[YVS centres Peripheral Nervous System (PNS) * YHUPHSULY]LZHUKZWPUHSULY]LZ ) J[ZHZJVTT\UPJH[PVUSPULZ between the CNS and the rest of the body Autonomic Nervous System 0U]VS\U[HY` 0UW\[MYVTPU[LYUHSYLJLW[VYZ 6\[W\[[VZTVV[OT\ZJSLZHUKNSHUKZ Parasympathetic Motor System 9LSH_PUNYLZWVUZLZ 5L\YV[YHUZTP[[LYHJL[`SJOVSPUL º*OVSPULYNPJZ`Z[LT» Sympathetic Motor System º-PNO[VYÅPNO[»YLZWVUZLZ 5L\YV[YHUZTP[[LYUVYHKYLUHSPUL º(KYLULYNPJZ`Z[LT» Somatic Nervous System = VS\U[HY` 0UW\[MYVTZLUZLVYNHUZ 6\[W\[[VZRLSL[HST\ZJSLZ Divided into Figure 9.1 Summary of organisation of human nervous system Exam Tips 9LTLTILY[OLV\[SPUL and describe in words the organisation of mammalian nervous system.
CHAPTER 9 64 Biology Term 2 STPM Chapter 9 Control and Regulation 3. The brain is the coordination centre of almost all activities. It is divided into forebrain, midbrain and hindbrain. (a) The forebrain receives and integrates sensory information from the nose, eyes and ears. In the human brain, the cerebral cortex interacts with the limbic system, which controls emotion and contributes to memory. (b) The midbrain coordinates reflex responses to sight and sound. (c) The hindbrain controls reflexes of respiration, blood circulation and movement. In humans, it coordinates sensory input, motor dexterity and possibly mental dexterity. Lateral sulcus Auditory area Interpretation of sensory experiences, memory of visual and auditory patterns Temporal lobe Cerebellum Combining visual images, visual recognition of objects Occipital lobe General interpretative area (Wernicke's area) Parietal lobe Sensory areas involved with cutaneous and other senses Central sulcus Motor areas involved with the control of voluntary muscles Frontal lobe Motor speech area (Broca's area) Figure 9.2 The lobes of the cerebrum Spinal cord Medula oblongata Pons Hindbrain Cerebellum Midbrain Pineal body Frontal lobe Cerebrum of celebral cortex Thalamus Hypothalamus Optic chiasma Pituitary gland Figure 9.3 Human brain
CHAPTER 9 65 Biology Term 2 STPM Chapter 9 Control and Regulation 4. The spinal cord is the vital expressway for signals between the brain and peripheral nerves. It has interneurones that can exert direct control over certain reflex pathways. Dorsal root of spinal nerve Spinal canal containing cerebrospinal fluid White matter Grey matter Ventral median fissure Ventral root of spinal nerve Motor neurone Cell body of motor neurone Interneurone Dorsal root ganglion of spinal nerve Cell body of sensory neurone Sensory neurone The motor neurone synapses with muscle fibres Biceps muscle Pain receptor Figure 9.4 :WPUHSJVYKHUKYLÅL_HJ[PVUZ 5. Peripheral nervous system in humans consists of 31 pairs of spinal nerves that originates from the spinal cord and 12 pairs of cranial nerves which originates from the brain. The spinal and cranial nerves are further divided into somatic and autonomic systems. The somatic system consists of nerves serving the receptors and skeletal muscles of the limbs, trunk and head. The autonomic system consists of nerves serving the receptors, smooth muscles and glands of the internal organs. The inner parts of the brain and the outer parts of the spinal JVYKTHRL\W[OL^OP[LTH[[LY The white matter contains tracts, communication lines (not nerves), and consists of myelinated axons specialised for rapid signal transmission. The outer part of the brain and the inner part of the spinal JVYKTHRL\WVMgrey matter. The grey matter contains unmyelinated axons, dendrites, cell bodies of neurones and neuroglia. Neuroglia are nonconducting nerve cells that protect, support neurones structurally and functionally. They appear to provide nutritional support too. Info Bio Info Bio Cervical nerves Cerebrum Cerebellum Spinal cord Thoracic nerves Lumber nerves Femoral nerve Sciatic nerve Tibial nerve Sensory nerves Axons of motor nerves Spinal cord Brain CENTRAL NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM Parasympathetic system Sympathetic system Somatic subdivision (motor functions) These nerves carry signals to and from receptor skeletal muscles, and gland subsystem. Autonomic subdivision (visceral functions) These nerves carry signals to and from internal organs (gut, heart, glands, etc.) Impulse Subsystem Human nervous system Functional divisions Figure 9.5 Summary on functional divisions of human nervous system
CHAPTER 9 66 Biology Term 2 STPM Chapter 9 Control and Regulation Formation of Resting and Action Potentials 1. Nervous system is composed of cells called neurones. Neurones are cells which involve the transmission of electrical signals or impulses from one part of the body to another. 2. In some neurones, cells called Schwann cells wrap themselves around the axon all along its length. The Schwann cell spirals around, enclosing the axon in many layers of its plasma membrane. This enclosing sheath is called the myelin sheath. Not all axons have myelin sheaths. Some invertebrate animals, such as earthworms, have no myelin sheath around their neurones. In humans, about one third of our motor and sensory neurones are myelinated. The sheath speeds up the conduction of the nerve impulse. 3. Figure 9.6 shows a motor neurone with myelin sheaths and another one without myelin sheaths. Axon Direction of impuls Cell body Dendrites Myelin sheath Axon Direction of impuls Dendrites Terminal branches Cell body (a) With myelin sheaths (b) Without myelin sheaths Figure 9.6 Motor neurones with or without myelin sheaths 4. Impulse is a nervous transmission i.e. an electrochemical message that is transmitted along nerve cell, particularly the axon. It is an electrochemical signal, not a current that consists of a flow of electrons. The signal is a fleeting changes in potential difference across the cell surface membrane of the neurone that sweeps along the neurone from one end to the other. 5. When a neurone is not transmitting an impulse, the membrane of the neurone, including that of axon, has a potential (voltage) difference called resting potential. 6. Resting potential is a potential difference (voltage) between the inside and the outside of the axon membrane. The inside is negative whereas the outside is positive. The potential difference is approximate –70 millivolts (mV). The membrane is polarised.
CHAPTER 9 67 Biology Term 2 STPM Chapter 9 Control and Regulation Non-myelinated axon Impulse (d) Phospholipid layer acts as a barrier (f) Little Na+ "leaks" in More K+ "leaks" out Sodium-potassium pump = Na+ out, K+ in (e) Cell body Neurone (g) Gated Na+ channel closes Gated K+ channel closes (a) Positive outside More Na+ ions outside (c) 2K+ ATP ADP + Pi 3 Na+ Na+ Na+ + + + Na+ Na+ + + + – – – – – – K+ Less negative Potential difference 70mV Na+ K+ Na+ K+ Less K+ ions inside (b) Negative inside (c) More anions inside K+ More negative – – – Figure 9.7 Formation of resting potential 7. The formation of resting potential is as shown in Figure 9.7 and involves the following: (a) The formation is a polarisation process which occurs in the membrane of neurone (including that of the muscle) in which the inside is negative and outside is positive. (b) This is caused by more potassium and negative ions (including chloride ions, organic acids and proteins) inside the neurone and more sodium ions on the outside. (c) The larger organic acids like nucleic acids, proteins and negatively charged organic ions are not able to diffuse out. These are fixed anions that keep the inside negatively charged. The ionic concentration of extracellular and intracellular fluids in resting axon is as shown in Table 9.1. (d) The phospholipid bilayer acts as a barrier for the passage of the ions and polar molecules across it. The phosphoslipid bilayer is hydrophobic in nature whereas the ions are hydrophilic and cannot diffuse across the lipid layer. (e) Sodium-potassium pump maintains the potential difference. It is an active transport system that requires energy in the form of ATP to transport sodium ions outside and potassium ions inside. It requires carrier proteins, which specifically bind to sodium ions on the inner side to transport them out. Two potassium ions bind to the outer side and are transported in. Three sodium ions are pumped out for every two potassium ions pumped in, resulting in a slightly higher positive charge outside the membrane than inside. A concentration gradient for these two ions is also created. Table 9.1 Ions mmol / dm3 Outside Inside K+ 20 400 Na+ 460 50 Cl– 560 100 6YNHUPJ anions 0 370
CHAPTER 9 68 Biology Term 2 STPM Chapter 9 Control and Regulation (f) Certain amount of ions “leak” in or out passively (facilitated diffusion) through channel proteins in the plasma membrane. There are two such types of channel proteins, one for sodium and the other for potassium ions. However, more potassium ions leak out and very little sodium ions leak in. This also contributes to the outside of the cell containing more positive ions than the cytoplasm. (g) There are gated channel proteins in the plasma membrane for sodium and potassium ions to cross the membrane. They do not interfere with the formation of the resting potential as they are closed under the resting condition. Therefore, the sum total of the resting potential difference formed is –70 mV due to the sum total of the above effects. 8. The formation of action potential involves the following: (a) The formation is a depolarisation process that occurs when sodium ions enter and reverse the potential difference within the neurone. (b) Depending on the neurones, it happens when the membrane is suitably stimulated, such as by an electric current. This can also happen in a sensory neurone directly or through a receptor cell, such as when we step on a grain of sand with our bare foot. (c) The stimulation causes the sodium-gated channel proteins to open first and later potassium gates will open. The sodium gates are more sensitive to changes of charges around them. (d) The strength of the stimulation determines the number of sodium gates that open to allow certain amount of sodium ions to rush into the neurone. If the grain of sand is too small, the stimulation is too weak. Then, not enough sodium gates are opened and no action potential is formed. (e) The strength must be more than a threshold level, i.e. enough sodium gates must be opened so that a certain amount of change in the voltage (potential) difference between the inside and the outside of the membrane to produce an action potential. The threshold value is about –40 mV. (f) If the resulted change is higher than –40 mV, a chain reaction is started. More sodium ions enter, thus more sodium gates are opened. This results in a positive feedback and the formation of action potential. (g) This can be seen in the formation of a ‘spike’ in the wave formed in an oscilloscope screen as shown in Figure 9.8 Exam Tips 9LTLTILYOV^[VL_WSHPU the shape of the graph.
CHAPTER 9 69 Biology Term 2 STPM Chapter 9 Control and Regulation Na+ gate 1. Resting potential Na+ 2. Stimulated K+ gate Open Na+ 3. Depolarised Open –80 mV –70 mV –60 mV –50 mV –40 mV –30 mV –20 mV –10 mV 0 mV 10 mV 20 mV 30 mV 40 mV Na+ Close 4. Action potential 5. Repolarised Open K+ K+ 6. Resting potential Resting potential Resting Threshold Hyperpolarisation Membrane potential Na+ flows in K+ flows out Repolarisation Depolarisation 1 6 5 3 2 4 + + Resting potential Resting potential Direction of impulse Active sodium pump Active sodium pump Na+ K+ + + – + Action potential – ––– ++ + + –– – – ++++ –––– ++++ –––– ++++ –––– + ++ – – – –– Figure 9.8 Graph showing action potential (h) Action potential is the potential difference generated when the sodium ions rush in followed by potassium ions rush out. The inside of the neurone becomes positive and the outside of it is negative. The potential difference is about 30 mV. After a few milliseconds the membrane becomes polarised again. This is known as repolarisation. 9. Repolarisation is a process that occurs immediately after action potential is generated. The sodium gates close after about a millisecond and shut off the inflow of the ions. The potassium gates open to allow potassium ions to exit. As shown in the graph, more potassium ions tend to move out, causing a momentary hyperpolarisation. Then, the sodium-potassium pumps start to work again to restore the resting potential. 10. Mechanism of transmission and spread of impulse along the axon are as follows: (a) When one part of the axon is stimulated, a certain patch of membrane is affected with the sodium gates open. This causes depolarisation when the potential difference is more than the threshold level to produce an action potential. Exam Tips 9LTLTILY[OLMVYTH[PVU of resting and action potentials. STPM 2013/P2/Q16, 2014/P2/Q8
CHAPTER 9 70 Biology Term 2 STPM Chapter 9 Control and Regulation (b) Within a millisecond, the sodium gates close and the potassium gates open. Potassium ions diffuses out to repolarise the patch of plasma membrane. (c) However, the sodium ions that have entered trigger chain reactions, causing positive feedback. It means that as more sodium ions enter, the inside becomes more positive as more sodium gates open along the axon. (d) The action potential is self-propagating. After one patch is polarised, it spreads to the adjacent patch. The previous patch becomes repolarised. The repolarised patch is not immediately depolarised again as the sodium gates are still closed. So, the process spreads away from the starting point as shown in Figure 9.9. + (a) Electric stimulation (b) Na+ gate opens (c) K+ gate opens, the process is reversed (d) Na+ – K+ pump restores the resting potential fully + ++ + +++ – – – – – – Sodium-potassium pump Na+ gate closes but adjacent one open and it moves on Na+ gate K+ gate + + + + + ++ + ++++ – – –– + – + + + + –––– + + ++ + + ++++ + ++ + – – – –– + + – – – –– – – – – + K+ K+ K+ K+ K+ Na+ Na+ Na+ Na+ Na+ Figure 9.9 *OHUNLZPUH_VUK\YPUN[YHUZTPZZPVUVMPTW\SZL (e) The membrane thus undergoes first depolarisation, followed by repolarisation. The process spreads from one end to the other end of the axon. The transmission of impulse is a fleeting change of depolarisation followed by repolarisation. (f) Local circuits are formed on the surface of the axon. The transmission of the impulse along the membrane is in one direction as shown in Figure 9.10. Exam Tips 9LTLTILY[OLWYVWHNH[PVU or spread of impulse.
CHAPTER 9 71 Biology Term 2 STPM Chapter 9 Control and Regulation Stimulus An action potential is generated as sodium ions flow inward across the membrane at one patch. Na+ Axon First action potential + + – – – – – – + + + + – – + + + + + + – – – – The depolarisation of the first action potential has spread to the neighboring patch of the membrane, depolarising it and generating a second action potential. At the first patch, the membrane is repolarising as K+ flows outward. K+ K+ – – + + – – + + – – + + + + – – + + – – + + – – Na+ Second action potential A third action potential follows in sequence, with repolarisation and chain reactions. In this way, local currents of ions across the plasma membrane give rise to a nerve impulse that is propagated along the axon. K+ K+ – – – – + + + + + + – – + + + + – – – – – – + + Na+ Third action potential Figure 9.10 Propagation or spread of impulse The Characteristics of Nerve Impulse 1. Impulse can be generated by suitable stimuli, including electrical, mechanical, water potential, chemical, heat and light on specific receptor cells or directly on suitable neurone. Electric current can cause impulse to be produced in any nerve axon. 2. Impulse follows the ‘all-or-nothing law’ i.e. if the stimulus is less than a critical value, no impulse is produced. There is a threshold value for a stimulus acting on a particular receptor cell or neurone. Sufficient sodium gates must open to produce a positive potential difference within so that depolarisation moves to the end of the axon. 3. There is a refractory period for an impulse. The refractory period is the time taken to complete one nervous transmission. The refractory period for most neurone is 4 milliseconds. If an axon is stimulated for Exam Tips 9LTLTILYHSS[OL characteristics of impulse transmission.
CHAPTER 9 72 Biology Term 2 STPM Chapter 9 Control and Regulation the second time in less than 4 milliseconds after the first stimulation, no impulse can be produced. This is the time taken for the closed sodium gates to be able to reopen allowing the smooth working of the sodium-potassium pump and the balancing of various ions. This is the time during which the membrane is unable to form another action potential. 4. The rate of transmission is faster in mammals than in invertebrates. In most neurones of mammals, the rate is about 100 m per second. The rate of transmission in invertebrates is less than 20 m per second. 5. Axon with a bigger diameter has less resistance and can transmit impulse faster than a smaller one. This is because larger surface area permits faster flow of ions in and out of the membrane. That is why earthworm and other invertebrates have giant axons for faster transmission. 6. Myelinated axon transmits impulse faster than an unmyelinated one. Myelinated axon is an axon with myelin sheath, which is formed by Schwann cells wrapped around it, along the whole length, as shown in Figure 9.11. This is because ions cannot pass through membrane that is insulated by the myelinated sheath. Depolarisation and repolarisation only happen in the nodes of Ranvier enabling transmission of impulse to ‘jump’ from one node to another, thus speeding the process. This is also known as saltatory or ‘jumping’ conduction. Localised circuit Na+ Na+ + – + – – + – + + – + – K+ Axon Myelin sheath Direction of impulse Node of K Ranvier + Na+ Na+ Figure 9.11 Saltatory transmission The Structure of Synapse and Role of Neutrotransmitters 1. Synapse is the part of the axon ending in which one neurone connects to another neurone, muscle or gland. A motor neurone in the spinal cord is connected by thousands of synapses from other neurones. 2. There are many types of synapses depending on their anatomy, function and position. The synapses can be attached to the cell body, dendrites, ends of dendrites or to the axons. They are usually chemical types but some are electrical with no chemical. They can be inside the central nervous system or outside of it. Dendrites Impulse from other neurons Axon Myelin sheath Figure 9.12 Multiple synapses on a single neuron 2011 STPM
CHAPTER 9 73 Biology Term 2 STPM Chapter 9 Control and Regulation 3. Each synapse has a synaptic cleft, which is a thin space of 20 nm between membranes of a neurone and a postsynaptic cell. Thus, the presynaptic membrane does not touch the postsynaptic membrane. 4. The structure of the synapse usually refers to the synaptic knob, a bulbous structure at the end of axon is as shown in Figure 9.13. (a) There are many organelles within the knob. Mitochondria are in abundance to supply ATP. (b) Golgi bodies package neurotransmitter chemical in the form of vesicles. So, there are many vesicles present. (c) There are microfilaments present. The microfilaments guide the vesicles to move towards the presynaptic membrane. Info Bio Postsynaptic neurone Receptor for neurotransmitter Postsynaptic membrane Presynaptic membrane Microfilaments Synaptic knob Presynaptic neurone Myelin sheath Impulse Golgi apparatus Axon of presynaptic nerve Mitochondrion Vesicles containing neurotransmitter, e.g. acetylcholine Synaptic cleft Figure 9.13 Vertical section of synaptic knob 5. The presynaptic membrane and postsynaptic membrane are different. The presynaptic membrane has calcium gated channels and these channels are not found in postsynaptic membrane. The postsynaptic membrane has receptor proteins that also function as gated channel to allow sodium ions to diffuse across when the channel is open after bound with neurotransmitter. 6. A neurotransmitter is usually used to transmit impulse across the synapse. The chemical is usually acetycholine found in almost all synapses. However, in the sympathetic nervous system, norepinephrine or noradrenaline is used. In the brain, there are more than 50 types of neurotransmitters that include amino acids glutamate and glycine, endorphins, dopamine and serotonin. Synapse ensures impulses are transmitted only in one direction. This is because receptors of transmitter are only found in the postsynaptic membrane i.e. an impulse can only be transmitted from presynaptic membrane to postsynaptic membrane.
CHAPTER 9 74 Biology Term 2 STPM Chapter 9 Control and Regulation 7. When an impulse arrives at the synaptic knob (Figure 9.14), the depolarisation process causes the calcium gates to open at the presynaptic membrane. Calcium ions diffuse inside from the synaptic cleft. 8. The calcium ions cause some of the vesicles to move towards the presynaptic membrane. The vesicles fuse with the presynaptic membrane and the acetylcholine within the membrane is exocytocised into the synaptic cleft. Exam Tips 9LTLTILY^OH[PZH synapse inclusive of its structure in diagrammatic form. Receptor molecule Some vesicles move to presynaptic membrane Synaptic knob of presynaptic neurone Postsynaptic neurone Synaptic cleft Localised circuit + –– + +– –+ – + + – –+ +– + – – + Ca2+ Ca2+ 1. Arrival of impulse 2. Vesicles move down Acetylcholine molecule Exocytosis of the vesicles Acetylcholine bind to receptor 3. Exocytosis of transmitter 4. Attachment of receptors Na+ Impulse Mitochondrion Cholinesterase hydrolyses the acetylcholine Ion channels closed ATP ATP 5. Na+ ion rush in 6. Depolarisation occurs Figure 9.14 Transmission of impulse across the synapse
CHAPTER 9 75 Biology Term 2 STPM Chapter 9 Control and Regulation 9. The acetylcholine molecules diffuse across the cleft and bind to the receptor molecules of the postsynaptic membrane. This causes the sodium gated channels in the postsynaptic membrane to open. 10. When the sodium ion channels open, sodium ions rush in from the synaptic cleft across the postsynaptic membrane into the postsynaptic neurone. 11. If enough sodium ions get into the postsynaptic neurone, depolarisation takes place. The action potential generated is called excitatory postsynaptic potential. 12. As soon as the impulse crosses the synapse, the acetylcholine is hydrolysed by cholinesterase present in the synaptic cleft. This is to prepare for another coming impulse. Exam Tips 9LTLTILY[OLZ`UHW[PJ transmission, inclusive of the diagrams showing the process. Comparison between Mechanism of Impulse Transmission across Synapse and along an Axon The comparison is summarised in Table 9.2. Table 9.2 Transmission across synapse Transmission along axon 1. An arrival of impulse to synapse causes Ca2+ to diffuse into the synaptic knob. An arrival of impulse to the axon does not cause Ca2+ to enter but cause Na+ channels to open. 2. Synaptic vesicles move towards the presynaptic membrane. No such movement takes place but ions move across membrane. 3. Neurotransmitter such as acetylcholine or norepinephrine is exocytosised into the synaptic cleft. No organic chemical or exocytosis is involved; involves only inorganic ions during transmission. 4. Transmission involves movement of organic chemical across synaptic cleft. No such movement of organic chemical occurs, but movement of action potential. 5. The role of neurotransmitter is to bind to specific receptor sites on the postsynaptic membrane. No such binding of organic chemical occurs, Na+ entry makes the inside positive and K+ leaving makes the inside negative. 6. The sodium channels at postsynaptic membrane open to allow sodium ions to pass through as a result of chemical stimulation. The sodium channels along the axon open as a result of electric stimulation or from impulse generated elsewhere. 7. After depolarisation, the neurotransmitter is removed by hydrolase. No enzyme is produced to hydrolyse any neurotransmitter.
CHAPTER 9 76 Biology Term 2 STPM Chapter 9 Control and Regulation Structure of Neuromuscular Junction and Sarcomere Structure of Neuromuscular Junction 1. Neuromuscular junction is a synapse between motor neurone and muscle and is also known as end plate. Each junction arises from a branched axon terminal that branches into finer endings. The endings are enclosed in an oval groove formed by the sarcolemma of a muscle fibre. 2. The structure of a neuromuscular junction is as shown in Figure 9.15. Nerve Motor neurone cell body Motor neurone axon Muscle Bone Muscle fibres Synaptic terminals at neuromuscular junction Sensory neurone Figure 9.15(a) 5L\YVT\ZJ\SHYQ\UJ[PVUH[LHJOT\ZJSLÄIYL Motor neurone axon Axon terminal Neuromuscular junction Mitochondrion Myofibril Sarcoplasm Nucleus T tubule Sarcolemma Sarcoplasmic reticulum Figure 9.15(b) :[Y\J[\YLVMUL\YVT\ZJ\SHYQ\UJ[PVUVU[OLT\ZJSLÄIYL
CHAPTER 9 77 Biology Term 2 STPM Chapter 9 Control and Regulation Language Check Calcium ions Sarcoplasm Sarcoplasmic reticulum (SR) Sarcolemma T tubule Axon terminal Synaptic vesicles Presynaptic membrane Postsynaptic membrane Acetylcholine receptors Myofibril Acetylcholine Synaptic cleft Figure 9.15(c) :[Y\J[\YLVMUL\YVT\ZJ\SHYQ\UJ[PVUVU[OLT\ZJSLÄIYL 3. The endings of the axon terminal have many mitochondria and Golgi apparatus. The Golgi apparatus packages acetylcholine into vesicles. So, there are many vesicles there. 4. There is a synaptic cleft of 20 nm between the presynaptic and postsynaptic membranes. The cleft is filled with tissue fluid with a variety of ions including calcium, sodium and potassium ions. 5. The presynaptic membrane has calcium channels to allow calcium ions to diffuse in. It also allows vesicles to fuse with it and thus, exocytosis of acetylcholine can occur. 6. The postsynaptic membrane is folded to increase the surface area for more receptors. This is the sarcolemma that surrounds a muscle fibre. It has receptors for acetylcholine and gated sodium channels. 7. Acetylcholine is released at the presynaptic membrane and diffuses across the cleft to bind with receptors at the sarcolemma. The binding will cause gated sodium channels to open to allow sodium ions to diffuse in. Structure of sarcomere 1. A sarcomere is a basic unit of a myofibril within muscle fibres. A muscle is composed of muscle fibres surrounded by membrane with two ends attached to bones by tendon. Each fibre bundle is multinucleated, with many nuclei beneath the membrane called sarcolemma and many myofibrils within. Each myofibril is composed of repeating sections of sarcomeres, which appear under the microscope as dark and light bands as in Figure 9.16. ZHYJVTLYL.YLLRZmY_ $¸ÅLZO¹TtYVZ$¸WHY[¹ $¸ÅLZO¹TtYVZ$¸WHY[
CHAPTER 9 78 Biology Term 2 STPM Chapter 9 Control and Regulation One sarcomere Z membranes I band A band One myofibril with four sarcomeres M membrane Dark band (A) Light band (I) M membrane Z membrane Thick filament (myosin) Thin filament (actin) One sarcomere Figure 9.16 Structure of a sarcomere 2. The dark band or A band consists of thick filaments supported at the centre by M membrane or line. 3. The light band or I band consists of thin filaments supported at the centre by Z membrane or line. 4. Thick filament is made up of bundle of protein called myosin that has a long, fibrous tail and a globular head, which binds to actin (Figure 9.17). The myosin head also binds to ATP, which is the store of energy for muscle movement. It can only bind to actin when the binding sites on actin are exposed. Structure of the thick filament Figure 9.17 ;OPJRÄSHTLU[ 5. Thin filament is made up of four strands of protein, two inner strands of actin, two outer strands of tropomyosin with troponin in between the two strands at regular distance along them. The four strands are twisted like string as shown in Figure 9.18. (T\ZJSLJLSSMYVTHIPJLWZ may contain 100, 000 ZHYJVTLYLZ;OLT`VÄIYPSZVM smooth muscle cells are not arranged into sarcomeres. Info Bio 2014/P2/Q5 STPM INFO Structure of Sarcomere
CHAPTER 9 79 Biology Term 2 STPM Chapter 9 Control and Regulation Myosin Troponin Actin binding site Thin filament Tropomyosin Figure 9.18 :[Y\J[\YLVM[OPUÄSHTLU[[VNL[OLY^P[O[OPJRÄSHTLU[ 6. There are binding sites located along the whole length of the actin strands for the myosin heads to bind to. When the muscle is at rest, the sites are covered by the two outer tropomyosin strands as shown in Figure 9.18. The Mechanism of Muscle Contraction According to the Sliding Filament Hypothesis 1. When an impulse reaches the neuromuscular junction, vesicles move to the presynaptic membrane. 2. Acetylcholine is released from the vesicles by exocytosis into the synaptic cleft. It diffuses across the cleft, binds to receptors on postsynatic membrane and causes the gated sodium channels to open. 3. Then, it causes action potential to develop in the postsynaptic membrane i.e. the sarcolemma of the muscle fibres if more than the threshold potential is formed. 4. Calcium ions are stimulated to be released from the sarcoplasmic reticula beneath the sarcolemma and diffuse into the myofibrils as shown in Figure 9.19. Synaptic terminal of motor neuron 1 Acetylcholine is released 2 Depolarises muscle cell 3 Action potential generated is propagated into T tubules p pg 4 Depolarisation of transverse tubule triggers calcium ions (Ca2+) release from sarcoplasmic reticulum into myofibrils Figure 9.19 Depolarisation causes release of calcium ions 5. Calcium ions then bind to the troponin molecules. When troponin is bound by calcium ion, it causes realignment of the four strands of protein in the actin strand and the binding sites along the actin strands are exposed (Figure 9.20). Exam Tips 9LTLTILY[OLZ[Y\J[\YLVM sarcomere is inclusive of the [OPJRHUK[OPUÄSHTLU[Z
CHAPTER 9 80 Biology Term 2 STPM Chapter 9 Control and Regulation Actin Ca2+ binding sites Tropomyosin Troponin complex Ca2+ bound Ca2+ Myosin binding site exposed (a) Myosin binding sites blocked; muscle cannot contract (b) Myosin binding sites exposed; muscle can contract Figure 9.20 7YLZLUJLVMJHSJP\TPVUZJH\ZLZIPUKPUNZP[LZ[VILL_WVZLK 6. This realignment enables the myosin heads to bind to the sites on the actin filament and starts the ‘ratchet’ mechanism. Thin filament Thick filament Myosin cross bridge attaches to the actin filament Myosin head ADP+Pi ADP Pi Working stroke - the myosin head pivots and bends as it pulls on the acting filament, sliding it towards the M line ATP As new ATP attaches to the myosin head, the cross bridge detaches ADP+Pi As ATP is split into ADP and P, cocking of the myosin head occurs ATP ATP hydrolysis Figure 9.21 ‘Ratchet’ mechanism 7. In the ‘ratchet’ mechanism (Figure 9.21), ATP is required by the myosin heads to detach from the actin filament. 8. The myosin heads change their conformation, releasing ADP and phosphate and pulling the thin filament. 9. Then, the myosin heads are released and when another ATP binds to each of the myosin head, the process is repeated, with the myosin heads binding to more distal sites, pulling the thin filaments towards the thick filaments. 10. This sliding causes the sarcomere to shorten and in turn all the myofibrils to shorten and thus, the muscle contracts. The shortening is shown in Figure 9.22. This is called sliding filament hypothesis. The myosin head can bind, pull and release. The process is repeated about 50 times per second. Info Bio Exam Tips 9LTLTILY[OLZSPKPUN ÄSHTLU[O`WV[OLZPZMVY muscle contraction (2010 STPM essay question)
CHAPTER 9 81 Biology Term 2 STPM Chapter 9 Control and Regulation Thin filaments (actin) Thick filament (myosin) Z line Z line (a) (b) Figure 9.22 Shortening of the sarcomere 11. When the muscle relaxes, calcium ions re-enter the sarcoplasmic reticula and the tropomyosin strands once again cover the sites along the actin strands. 12. ADP is reconverted back to ATP when reacts with creatine phosphate or from oxidative phosphorylation. Sliding Filament Hypothesis 2010, 2011 1. This hypothesis explains that the contraction of the muscle fibre is due to the sliding of the thick and thin filaments into each other, causing the myofibril to shorten. 2. When the muscle is relaxed, electromicrograph shows that the filaments are as shown in Figure 9.23(a). Both sarcomeres and light bands have long lengths. Dark band (A) Light band (I) M membrane Z membrane Thick filament (myosin) Thin filament (actin) One sarcomere Dark band Light band Z membrane Thick filament (myosin) Thin filament (actin) One sarcomere H :HYJVTLYLYLSH_ I :HYJVTLYLJVU[YHJ[LK Figure 9.23 3. After the muscle is contracted, the thin filaments slide into the thick filaments as in Figure 9.22. The sarcomere becomes shorter. This is because the dark bands do not change their length, whereas light bands shorten. 4. This sliding is caused by the ‘ratchet’ mechanism of the myosin heads pulling their filaments towards each other. 9L[PJ\S\T¶ZPUN\SHY 9L[PJ\SH¶WS\YHS 9L[PJ\S\T¶ZPUN\SHY 9 P S S S Language Check 9L[PJ\SH¶WS\YHS
CHAPTER 9 82 Biology Term 2 STPM Chapter 9 Control and Regulation The Role of Sarcoplasmic Reticula, Calcium Ions, Myofibrils and T Tubules in Muscle Contraction Sarcoplasmic Reticulum 1. It receives calcium ions from the outside of the muscle fibres to transport and store them within the complex. 2. It releases and distributes the calcium ions rapidly when the sarcolemma is depolarised. 3. It enables the calcium to enter deep into the thin filaments of the myofibril to bring about contraction of the muscle. 4. It reabsorbs the calcium ions and stores them after the muscle contraction for contractions that are going to follow. Calcium Ions 1. They bind to troponin, the protein found regularly spaced along the tropomyosin strands of the thin filament inside the myofibril. 2. The calcium ions, after binding with the troponin, form complexes that cause realignment of the two outer tropomyosin strands and the two inner actin strands exposing the actin sites along the whole length of the actin strands for the myosin heads of cross bridges to bind. 3. Calcium ions are thus, required to start the process of filament sliding thus causing the muscle to contract. 4. Calcium ions are also required at the synaptic cleft of the neuromuscular junctions for them to diffuse through the calcium channels at the presynaptic membrane into the junctions. This would cause the vesicles to move to the presynaptic membrane and exocytosise the acetylcholine into the cleft and cause the depolarisation of sarcolemma. Myofibril 1. It can contract thus, causing the muscle fibre to contract and the muscle as a whole to contract. This is due to each muscle consists of a bundle of fibres and each contain many myofibrils. 2. Each myofibril shortens during muscular contraction. Each myofibril is made up of alternating dark bands of thick filaments and light bands of thin filaments. The thick and thin filaments can slide into one another making the myofibril to shorten. 3. The myosin heads of the thick filaments within each myofibril work in a very fast pace to bind on to the actin binding sites of the thin filaments and pull them towards the thick filaments. Role of Sarcoplasmic Reticulum 1. Transports calcium ions 2. Releases and distributes the calcium ions 3. Enables calcium to enter deep into the thin ÄSHTLU[ZVM[OLT`VÄIYPS 4. Reabsorbs the calcium ions and store them after the muscle contraction Calcium Ions 1. They bind to troponin 2. Causes realignment L_WVZPUN[OLHJ[PUZP[LZ 3. Start the process of ÄSHTLU[ZSPKPUN 4. Causes the vesicles to move to the presynaptic membrane 4`VÄIYPS 1. Can contract 2.:OVY[LUT\ZJSLÄIYL 3. Sliding of thick and thin ÄSHTLU[Z 4. Myosin heads carry out ‘ratchet’ mechanism ;[\I\SLZ 1. Increase the surface area of the sarcolemma 2. Increase the number of gated sodium channels 3. Faster generating of L_JP[H[VY`WVZ[Z`UHW[PJ potential 4. Increase the rate of [YHUZWVY[VMV_`NLUHUK nutrients 5. Increase the rate of transport of carbon KPV_PKLHUK^HZ[LZ Summary
CHAPTER 9 83 Biology Term 2 STPM Chapter 9 Control and Regulation Language Check 4. Therefore, the ‘ratchet’ mechanism within the myofibril with the expenditure of energy in the form of ATP causes the myosin to shorten and contract. The ‘ratchet’ mechanism of each myosin head binds to binding sites along the thin filament, release and bind to a more distal site each time to cause the thick and thin filament to slide into each other. T tubules 1. T tubules increase the surface area of the sarcolemma. The sarcolemma is the postsynaptic membrane. The T tubules are the folding of the sarcolemma at regular intervals along the whole membrane of each muscle fibre. 2. T tubules would increase the number of gated sodium channels across the membrane. These channels would allow more sodium ions to cross into muscle fibre in the shortest possible time. This would enable a faster generating of excitatory postsynaptic potential and also the ability to amplify the effect of weak impulse arriving at the neuromuscular junction. 3. T tubules would increase the rate of transport of oxygen and nutrients into the muscle fibre. The muscle fibres require nutrients like glucose, amino acids, phosphates and calcium ions. 4. T tubules would also increase the rate of transport of carbon dioxide and wastes out of the muscle fibre. The wastes include lactic acid and creatinine. Quick Check 1 1. Why can’t normal cells like epidermal cells transmit impulse? 2. How are synapses involved in the memory process? 3. How do smooth muscles contract? Comparison between Sympathetic and Parasympathetic Nervous System 1. The autonomic nervous system is the part of the nervous system that controls unconscious or visceral activities such as beating of the heart, peristalsis in the gut and sweating. 2. It is divided into two subsystems, which work antagonistically. Their components are as shown in Figure 9.24. . HUNSPVU¶ZPUN\SHY Ganglia – plural
CHAPTER 9 84 Biology Term 2 STPM Chapter 9 Control and Regulation Table 9.3 +PɈLYLUJLZIL[^LLUZ`TWH[OL[PJHUKWHYHZ`TWH[OL[PJZ`Z[LTZ Aspect Sympathetic system Parasympathetic system 1. Organisation It composes of only spinal nerves. It composes of branches of cranial nerves number 3, 7, 9, 10 and branches of sciatic spinal nerve. 2. Ganglion locations Its ganglia are located near the spinal cord, away from effectors. Its ganglia are far away from the spinal cord, nearer to effectors. 3. Length of nerves Preganglionic nerves are short and postganglionic nerves are long. Preganglionic nerves are long and postganglionic nerves are short. 4. Ganglion connections Ganglia connect with larger ganglia called plexus. Ganglia do not connect to form larger ganglia. 5. Number of nerves from each ganglion There are more postganglionic nerves. There are less postganglionic nerves. 6. Nerve distribution from each ganglion Preganglionic nerves serve larger areas from both sides of spinal cord. Preganglionic nerves serve smaller areas closer to the organs involved. 7. Areas affected Its effect is more distributed along both sides of spinal cord. Its effect is more localised in viseral organs. Parasympathetic system Sympathetic system Cranium nerves iii Iris Tear gland Salivary gland Heart Lung Stomach Small intestine Pancreas Adrenal gland Large intestine Urinary bladder Sex organ Short post ganglionic nerves vii ix x parasympathetic ganglion Iris Tear gland Salivary gland Heart Lung Stomach Small intestine Pancreas Adrenal gland < Large intestine < < < < < < < < < < < < < < < < < < < < < < < < < < < < < Urinary bladder Sex organ < < < < Inferior mesentric plexus Superior mesentric plexus Seliac plexus Spinal nerve Vagus nerve Long post ganglionic nerves Mesenteric ganglionic chain Figure 9.24 Components of autonomic system 2013/P2/Q5 STPM 3. The differences between the two systems are as shown in Table 9.3.
CHAPTER 9 85 Biology Term 2 STPM Chapter 9 Control and Regulation Aspect Sympathetic system Parasympathetic system 8. Neurotransmitter Norepinephrine is used in the postganglionic nerves. Acetylcholine is used in the postganglionic nerves. 9. Effects to (a) Iris (b) Tear glands (c) Salivary glands (d) Heartbeat (e) Bronchioles (f) Breathing (g) Peristalsis (h) Digestive juices (i) Anal sphincter (j) Visceral arterioles (k) Blood to brain and muscles It dilates pupils to let in more light. It has no effect on the glands. It inhibits secretion of saliva. It increases the rate and strength of heartbeat. It dilates bronchioles to let in more oxygen. It increases its rate. It decreases peristalsis. It inhibits secretion. It contracts the muscle. It constricts them, less blood is brought in. It increases blood flow to brain and skeletal muscles. It constricts pupils to see sharper images. It stimulates tear secretion. It stimulates secretion of saliva. It decreases the rate of heartbeat. It constricts bronchioles. It decreases its rate. It increases peristalsis. It stimulates secretion and more digestion. It inhibits its contraction. It dilates them to let in more blood. It decreases blood flow to brain and skeletal muscles. (l) Blood pressure (m) Spleen (n) Hair angles (o) Skin arterioles (p) Sweat glands (q) Kidney (r) Bladder (s) Penis (t) Adrenal glands It increases blood pressure. It contracts the spleen, so it has less blood It increases hair angles. It constricts skin arterioles. It increases sweating to lower body temperature. It decreases urine production It contracts its sphincter muscle. It stimulates ejaculation. It stimulates release of adrenaline. It decreases the pressure. It has no effect on the spleen. It has no such effect. It dilates arterioles to face. It has no such effect. It has no effect, so normal kidney function normally. It inhibits its contraction. It stimulates erection. It has no such effect. 10. Summary To prepare the body for stress and exercise To restore the body from stress and exercise
CHAPTER 9 86 Biology Term 2 STPM Chapter 9 Control and Regulation Quick Check 2 1. Why is there a need for autonomic system? 2. Give two examples of reflex actions occurring in the head. Mechanisms of Drug Action on Nervous System and Neuromuscular Junction Mechanism of action of cocaine on the nervous system 1. Cocaine acts as a stimulant to give euphoria and state of arousal to the person taking it. 2. It acts in synapses of the brain and the sympathetic system of the peripheral nervous system. 3. It causes a large amount of neurotransmitters, including dopamine and norepinephrine, to remain in the synaptic clefts. 4. In the brain, it affects synapses of the limbic system, the pathway that produces pleasure with dopamine as the neurotransmitter. 5. Cocaine binds tightly to transporter proteins in the synaptic cleft, leaving the dopamine and norepienephrine to accumulate. The transporter proteins would transport the neurotransmitters back into the synaptic knob for reuse if there is no cocaine. 6. The dopamine binds to receptors in the postsynaptic membrane to produce pleasure. Under normal circumstances, certain stimuli e.g. reading a book would stimulate this pleasure pathway. 7. The accumulation of dopamine produces heightened pleasure and the effect is addictive as more new signals arrive in such synapses. 8. In the sympathetic nervous system, cocaine blocks the uptake of norepinephrine in the synaptic clefts. This occurs in the brain as well as in the postganglionic nerves. 9. Cocaine causes accumulation of norepinephrine, so it heightens activities of the sympathetic system. The whole body is in a state of arousal. 10. Therefore, heartbeat, blood pressure and sexual appetite increase and the user feels more confident. 11. When all the dopamine and norepinephrine diffuse away, the neurones cannot produce such concentrations of neurotransmitters. Pleasure is replaced by depression. 12. Besides that, the body responses to the drug by producing less receptors for it in the postsynaptic membrane. More cocaine has to be taken to produce the same amount of pleasure. The user becomes addicted.
CHAPTER 9 87 Biology Term 2 STPM Chapter 9 Control and Regulation Transmitting neurone Cocaine Receiving neurone Intensity of effect Dopamine transporter blocked by cocaine Dopamine Dopamine receptor Intensity of effect Dopamine ceptor Do rec Figure 9.25 Mechanism of action of cocaine in synaptic cleft 13. Physiological changes also take place in the user’s liver to produce more enzymes to get rid of the drug at a faster rate. 14. The body is dependent on the high drug concentration to work well. Without the drug, withdrawal symptoms develop. The addict becomes sleepy, nauseated, feverish and shivers. 15. After prolonged and heavy use of cocaine, ‘pleasure’ is no longer possible. The addict loses weight, cannot sleep well, immune system is weakened and heart abnormalities begin to develop. Overdose upsets the brain functions and produces acute psychosis, cardiac arrest and death. 16. Cocaine can be used medically as local anaesthesia for operations in the eye, nose, throat and mouth, especially during dental surgery. Mechanism of action of curare on neuromuscular junctions 1. Curare is a poison used by the South American natives on the arrowheads to hunt wild animals. 2. Curare causes the hunted animal, especially monkeys, to drop as it tries to jump away after being hit by the drugged arrow. Monkeys hit by the bullet die immediately and may get lodged high up in the branches of the tree. 2010 2015
CHAPTER 9 88 Biology Term 2 STPM Chapter 9 Control and Regulation 3. Curare acts on synapses where acetylcholine is used as neurotransmitter. Curare binds to receptor that the neurotransmitter is supposed to bind to transmit impulse through the synapse. So, curare blocks acetylcholine from binding to the receptor. These receptors are also known as nicotinic receptors. Exam Tips 9LTLTILYOV^J\YHYL HɈLJ[Z[OLUL\YVT\ZJ\SHY junction (2010 STPM essay question). Acetylcholine has bound Curare is blocking acetylcholine Ca2+, Na+ K+ Acetylcholine Binding site about to bind Receptor and sodium channel Channel closes Channel open Figure 9.26 Curare binds to receptor, sodium gate does not open 4. The effects of curare are particularly noticeable in neuromuscular junctions. The molecule binds to the receptor of the acetylcholine preventing the synapse from transmitting impulse to the skeletal muscles causing paralysis. 5. A high concentration of curare can cause death. This is because curare prevents impulses from being sent to all muscles and causes paralysis, including those involved in the breathing processes. So, no oxygen is being absorbed when breathing stops. 6. Victims of curare poisoning can be saved by continual artificial respiration, until the effects of the drug wear off. 7. Curare in low concentration causes relaxation of muscles so the muscles cannot contract. It is used in surgery for easier cutting and minimise damage to muscles. Breathing has to be maintained artificially. Quick Check 3 1. Why do drugs usually affect the synapses or neuromuscular junctions?
CHAPTER 9 89 Biology Term 2 STPM Chapter 9 Control and Regulation Students should be able to: (a) explain the mechanisms of action of steroid hormone and nonsteroid hormones; (b) explain the roles of plant hormones in growth and development; (c) explain the mechanism fo phytochrome action and their roles in photoperiodism and ÅV^LYPUN" (d) outline the application of plant growth regulators (synthetic auxin, synthetic gibberellins, and synthetic ethylene) in agriculture. 9.2 Hormones 9.2 Hormones 1. Hormone is a biochemical messenger, which is synthesised in small quantity and released by a specific group of cells from one part of the organism, transported to another part where it acts on cells with specific receptors for it. 2. There are hormones in both animals and plants, though they are called growth substances in plants. This is because plant hormones promote or inhibit growth. 3. Animal hormones are produced by specific endocrine gland whereas those of plants are not produced by special glands but just a group of young cells. 4. Animal hormones are transported by blood whereas those of plants are seldom transported by xylem or phloem, but usually by diffusion. 5. Chemical coordination makes use of chemicals, usually hormones, to streamline or signal processes in response to stimuli from the environment. 6. There are two main types of hormone based on its mechanisms of actions (Table 9.4). Learning Outcomes 2013/P2/Q6 Table 9.4 Types Examples (a) Steroid and steroid-like hormones Oestrogen, progesterone, testosterone, cortisol, aldosterone and adrenal corticoids. Thyroxine acts like steroid hormones (b) Non-steroid or Peptide hormones Peptides Proteins Glycoproteins Amino acid derivatives Glucagon, ADH, oxytocin and thyrotrophic-releasing hormone Insulin, somatotropin and prolactin FSH, LH and thyrotrophic hormone Epinephrine (adrenaline) 7. The physical properties of hormones are as follows: (a) Human hormones are produced by endocrine glands, which are ductless. (b) Very little is produced but the effects can be great. (c) The hormone is released directly into the blood capillaries and circulated throughout the body. 8. The chemical properties of hormones are as follows: (a) The hormones may be steroids, act like steroid or amino acid derivatives or peptides. (b) They may act on target organs or cells in general. The cells must have specific receptors for the hormone. INFO Hormones
CHAPTER 9 90 Biology Term 2 STPM Chapter 9 Control and Regulation (c) Steroid hormones, including thyroxine which is a steroid-like hormone, enter the cell easily and interact with the DNA of the cell to induce protein synthesis. (d) Peptide hormones interact with enzyme of the membrane to bring about a certain effect. 9. The physiological roles of hormones are to coordinate metabolic, growth and reproductive activities, and to complement the nervous functions. Mechanism of Action of Steroid and Non-steroid Hormones 1. Steroid hormones eg. testosterone have the mechanism of action via activation of genes. 2. The mechanism of action for steroid hormones is as follows (Figure 9.27): Capillary Steroid hormone Cell membrane Enter cytoplasm Protein receptor Hormone-receptor complex Enter the nucleus Binds with gene Transcription mRNA is produced mRNA leaves nucleus mRNA translated to protein Protein is synthesised Figure 9.27 Mechanism of action of steroid hormone (a) The hormone molecule diffuses through the plasma membrane of target cells, such as sarcolemma of striated muscles. Steroid molecules are lipid soluble and can easily diffuse through phospholipid membranes. (b) The hormone then binds to specific protein receptors that are found in the cytoplasm. It may go through the nuclear envelope to bind to the receptors found in the nucleoplasm. (c) The hormone-receptor complex formed in the cytoplasm enters the nucleus. The complex then binds with specific genes in the DNA. Mechanisms of action of Steroid hormone Enters cell A binds to receptor AJVTWSL_ enters nucleus A binds to ZWLJPÄJNLULA stimulates transcription A translation produces protein A muscle proteins by testosterone Non-steroid hormone Binds to receptor at plasma membrane A activates adenyl cyclase A produces cAMP A activates kinase AJHZJHKLLɈLJ[ZA activates phosphorylase & phosphatase A produces glucose from glycogen in liver A increases blood glucose by insulin Summary 2014/P2/Q6 STPM
CHAPTER 9 91 Biology Term 2 STPM Chapter 9 Control and Regulation (d) The complex stimulates transcription of specific genes and mRNA is produced. (e) The mRNA leaves the nucleus and moves to the cytoplasm where it is translated to form proteins. (f) The proteins formed in this case may include myosin, actin and proteins that are required to form muscles. (g) This brings about growth of the muscles, such as the effect of testosterone, especially on puberty males. Thus, protein synthesis takes place in cells that have receptors for the hormones. 3. Non-steroid hormones eg. adrenaline, insulin and glucagon have mechanism of action via activation of cAMP. 4. The mechanism of action for non-steroid hormones is as follows (Figure 9.28): G protein Protein kinase A (inactive) Phosphorylase kinase (inactive) Glycogen phosphorylase (inactive) Glycogen Cytoplasmic Glucose Glucose-1-phosphate Glycogen phosphorylase (active) Phosphorylase kinase (active) Protein kinase A(active) cAMP Extracellular Activated adenylate cyclase Activate G protein Adrenaline receptor Adrenaline GTP _ _ a a ` ` GTP GDP ATP P Figure 9.28 Detailed mechanism of action of non-steroid hormones (a) The hormone molecule, such as adrenaline, binds to specific protein receptor at the plasma membrane of target cells such as liver cells. Such protein spans the plasma membrane and extends into the cytoplasm. (b) The hormone-receptor complex formed stimulates an enzyme adenylate cyclase, which is also found in the membrane. The enzyme breaks down ATP to form a second messenger i.e. cAMP. 2011 VIDEO J(47:LJVUK Messenger
CHAPTER 9 92 Biology Term 2 STPM Chapter 9 Control and Regulation (c) This formation triggers the start of a cascade effect of reactions. This means that small amount of hormones, the first messenger cause the formation of a lot more cAMP, the second messenger and so on. (d) These cAMP molecules in turn activate a lot of enzyme kinase A from its inactive form. (e) This kinase A activates a lot of enzyme phosphorylase, which converts glycogen to glucose phosphate and another enzyme phosphatase, finally converts glucose phosphate to glucose. A lot of glucose is thus formed in a short period of time. (f) The glucose in the liver cells is released into the blood, thus raising the blood glucose level almost instantly, which is one of the effects of adrenaline. 5. Cascade effect is a chain reaction in which the first messenger, the hormone such as adrenaline, causes the increase in the production of the second messenger, the cyclic AMP. The effect is amplified until numerous last product is formed. In this case, a lot of glucose is formed from glycogen in the liver. (a) Cascade effect is very important to bring about a fast achievement of result. Thus, adrenaline brings about an almost instant rise in blood glucose level. (b) Another example of cascade effect is seen in the case of production of glycogen from glucose by adrenocorticotrophin-releasing factor as shown in Figure 9.29. Exam Tips 9LTLTILY[OLKPɈLYLUJLZ between the two mechanisms including examples. The detailed mechanism of steroid is based on easy crossing of lipoprotein membrane (STPM 2010 essay question) whereas non-steroid hormone bind to receptors on the surface of membrane (characteristics of hormones, STPM 2010 essay question). Hypothalamus Anterior pituitary gland Adrenocorticotrophin releasing factor [0.1 μg] Adrenotrophin [1.0 μg] Adrenal cortex Liver Cortisol [50 μg] Glucose Glycogen [5,000 μg] Total amplification is 50,000 times Figure 9.29 *HZJHKLLɈLJ[VMOVYTVULZ Differences in the mechanism of action between steroid and non-steroid hormones Table 9.5 +PɈLYLUJLZPU[OLTLJOHUPZTVMHJ[PVUIL[^LLUZ[LYVPKHUKUVUZ[LYVPKOVYTVULZ Steroid hormone Non-steroid hormone 1. It can easily pass through the lipoprotein membrane of target cells. It cannot pass through the lipoprotein membrane structure. 2. It binds to the receptor in the cytoplasm or nucleoplasm. It binds to the receptor at the surface of plasma membrane. 3. The complex formed does not activate adenyl cyclase. The complex formed activates adenyl cyclase.