foreign [Music] over to Afrin okay hello everyone so today we're doing another episode of IGCSE biology and we're going to discuss chapter 14 that is coordination and response uh okay so here's the presentation so this chapter has about five parts I think so let's get into that okay so this is the syllabus and this is the first part of the syllabus and basically says it discusses about how you're supposed to know about the electrical impulses and the different parts of that our nervous system and the roles of the various parts of our nervous system and you know the different mechanisms such as the reflex arc the pupil reflex uh functions and wait you don't have pupil reflex in this part yet you have the synopsis and that's about it so if you're doing the core part of the syllabus you basically just need to know what is the syllabus however if you're going for the extended part of the syllabus the supplement part you need to know about the actual process that's happening at the synapse and then the different uh effects it has on your body and how different things can affect the functions of the synapse so for the introduction this is the very first part of your syllabus first of all you need to be able to state that electrical impulses travel along neurons so this could come as a one more question for you so you basically just have to make the statement electrical impulses travel along neurons and then you need to know the two parts of the central the nervous system that is the central nervous system and this consists of the brain and the spinal cord and these are the areas of coordination so these this is the think of it as the control center for your nervous system that's the brain and the spinal cord and then there's peripheral nervous system and this is the nerves and the neurons and this part of the nervous system coordinate and regulate bodily functions so you'll see how that that happens further along the chapter but for now you need to know the two parts of the nervous system that's the Central and the peripheral the central consists of your brain and the spinal cord the peripheral nervous system consists of nerves and neurons okay and then you need to know what are involved reactions and what are voluntary actions so voluntary actions are actions that are not under conscious control and voluntary actions are the exact opposite of that so it's like something you think you consciously decide to do and you carry them out and then you need to know what is a nerve impulse a nerve impulse is an electrical signal that passes along nerve cells called neurons so nerve cells are called neurons and electrical signals or electrical impulses like we discussed earlier passes along nerve cells these are called nerve impulses okay then you need to know about the types of neurons once again neurons are nerve cells so for adjacency biology you need to know about the three types of neurons there is the motor neuron there's the relay neuron and there's the sensory neuron so we you need to know about the structure and the basic function of it okay so there's the motor neuron and this is what it looks like it has a cell body at one end of the the cell and then the length of it is covered in it's insulated by the myelin sheath and then there's nerve endings the other end of it okay and then if you notice you'll see some gaps between the myelin sheath that is um and you oops yeah you'll notice the the length of this cell itself that is the axon or the nerve fiber however you need to learn the word axon okay and at the cell body you'll notice some fingerlings okay extending out of it those are the dendrites and these basically connect with other neurons okay and if you'll notice the direction of impulse it goes from the cell body to the other end with the nerve endings okay so this is the motor neuron and then this is the sensory neuron now the difference here is you'll notice the cell body is smaller and it's in the middle of the cell and then you have dendrites in one end and you have the axon terminal at the other end and you'll notice the axon is here too this yeah this is the sensory neuron basically and then you've got the really neuron if you'll notice it's much more branched out it's the the length of it is covered in synaptic endings and you've got the cell body at one end once again the cell body has dendrites and you notice that the axon is shorter here so you need to know the three you need to be able to visually identify and differentiate between these neurons so the relay neuron is shorter it's more branched out cell body at the end of it and then you've got the sensor in your own the cell body in the center and then you've got the motor neuron with the cell body in the center in this in the end and a myelin sheath okay so these are the features that distinguish the three types of cells all right now we look at the reflex arc okay the reflex arc is how your body automatically like okay first of all you need to default the definition The Reflex action is the means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors so what is stimuli anything in the environment a change in environment for example a change in temperature or if you uh prick your finger with a pin and then what are effectors effectors are parts of your body that react to it so if you're if it's hot your sweat glands release uh sweat so that's the effector in that case or if you touch a pin with your finger your arm contracts so the muscles in your arms are the effectors in this case right okay so remember we discussed involuntary actions so a reflex action is an invalid reaction it is quick uh it is quick to respond to a stimulus in order to order in order to protect your body from danger so okay your boiling something and you touch the pot on accident before you realize you've you've touched something really really hard your fingers already moved away from it you've jerked away from it okay and then you realize oh okay that's what's happening that's what's happening so what's happening here is before you can even think about it the signal doesn't really reach your brain it the response is immediate so that's what the reflex arc is so yeah that's the example they gave here you're moving your hand from a really hot metal surface and this action involves the three types of neurons the sensory neuron the real neuron and the motor neuron you need to know is of that of the synapse the gap between neurons is called the synapse so not all neurons are actually touching okay there are neurotransmitters that transmit the messages so this gap between the neurons are called the synapse okay now we look at the simple reflex art so this is something you need to memorize because this could they could ask you in detail as a four Mark or so question or they could give you like a table as in a flow chart with boxes and some of the boxes would be filled with some of the information and the other boxes you'll have to fill so it really depends how your exam is but yeah so this is something you need to know from top to bottom so it starts with the stimulus affecting a receptor what is a receptor a receptor is a cell or an organ that converts a stimulus into an electrical impulse Okay so it's safer if you learn the definition of receptors and then the next step is that the sensory neuron carries impulse from the receptor to the CNS that is the central nervous system okay then there are really neurons at the CNS that carries the impulse slowly because it has no myelin sheath so that's the function of the myelin shade it basically speeds up the rate of impulse uh the impulse transferred however since the really neuron has no impulse it's uh it moves a bit slowly across the spinal cord and then from the really neuronic those impulse moves to the motor neuron and it that carries the impulse from the central nervous system to the effector affect her once again is the organ that's reacting to the stimulus all right so effector either a muscle or gland carries out the response so um we will look at some of the examples of the of a simple reflex R coming up and we'll also look at examples of effectors and how they work like how your body reacts will change in temperature or change in blood glucose concentrations so this is a diagram to explain what I just said so if you look at the right top right of the image you'll see the stimulus affecting the stimulating the receptor and then the impulse is carried by the sensory neurons through the central nervous system where it is carried by the impulses carried by this really neurons to the motor neurons which then triggers the effectors to react or to respond to the stimulus okay and then okay this is about synopsis again this is a bit this is the supplement part of it so once again this is a better different definition here a synapse is the junction between two neurons consisting of a gap across the impulse across which impulses passed by diffusion of neurotransmitters the synaptic cleft is the small gap between each pair of neurons and this is okay yeah so inside the neurons axon that's the end of it you remember the thing that the wire that we were talking about across the length of the neuron there are hundreds of tiny vacuoles the these are vesicles that contain a chemical called neurotransmitters and the function of the synapse is that it ensures the impulses travel only in One Direction so when so that there's no backflow it's not the correct word but that's how you can understand it this is the back flow of the trial impulses the impulse keeps moving in the in One Direction and it completes the entire cycle that it needs to all right and then this is the events that are synapse so over here you look at what the neurotransmitter is and what the vesicles are so when an Impulse arrives at a neuron the vesicles move to the cell membrane and emptied their content into a synaptic lift vesicles are basically tiny sacs containing uh chemicals that's what they mean by the content part so these vesicles move the cell membrane and empty their content into the synaptic lift once again that's the Gap that Junction between two neurons the neurotransmitter is what's carried by the vesicles the neurotransmitter quickly diffuse across the synapse and attaches to the receptor molecule in the next neuron so in this case it's the relay neuron and this can happen because the Shears of the neurotransmitter molecules is complementary the shape of the receptor molecule so I want to do things back to enzymes and how substrate on the active side of the enzymes work this is some this is a similar mechanism to that okay now what you need to know is you need to know that you need to be able to discuss this you need to be able to discuss describe this process it could come for three or four marks in the exam and you it's a paper four question and if you're lucky if this comes because this is actually very easy marks this is something you memorize and you dump on your paper yeah and then you uh you need to know how drugs can affect the function of the synapse basically drugs act upon synapses by uh preventing these neurotransmitters from diffusing across the synapse and so it can make you feel less pain so the the main function of these neurotransmitters is for you to feel pain that's so that you can detect any change in environment so these some drugs like heroin can prevent that from happening okay and that's about that we have coordination and response that's this is the second part where we discuss about the sense organs so over here we Define sense organs we identify parts of the eye the eye is a very big part here and then over here we have the pupil reflex and we talk about accommodation accommodation is a process that's happening in your eye and we look at some of the functions of the parts of the eye okay so first of all you need to know that scent organs are groups of receptor cells that respond to specific stimuli water stimuli and its change in environment like light sound touch temperature and chemicals okay so your body is equipped with like a lots of mechanisms lots of organs that are responsible for responding to these changes in environment and that's what some of we're going to look at some of these here so this is the eye a side cross section of the eye you need to be able to identify these parts so what we are looking at are these specific parts so you need to know about the cornea the iris the lens retina and on the optic nerve so the coronary reflects refracts light okay so if you you need to be very careful when you're saying reflect and when you're saying refract in igcc biology I think pretty sure that's the same case in igc physics so make sure you're not confusing those two words the cornea refract slide so this the cornea is the top clear layer the first layer in your eye and not sure if you can make it out over here but this is the first layer and it's clear you can see it so you need to be able to identify this on the diagrams and then there's the iris iris is is the part of the eye that controls how much light enters the pupil so that is basically the colored part of your eye if you can see it here surrounding the lens okay on the top of the lens and how there's a gap between the two parts of the iris that's that Gap is the the pupil okay so the pupil is the part of the eye from which the light enters okay and there is the lens the lens can become thicker or thinner depending on how the lightest focused is supposed to be focused onto the retina and then the retina is the part of the eye that contains light receptors like rods and cones and they are sensitive to light and different colors so this is these the rods and cones that you have in the retina is why you're able to identify and detect the different colors that you see okay so the retina is at the back of the eye the other parts that we've looked at like the cornea Iris and lens are in the big in the front you don't know you don't need to know much about the other parts of the eye you need to know about suspensory ligaments and and the ciliary muscles however you won't be required to identify them in diagrams you need to know about their phobia phobia is where most of the light receptors are concentrated but and then you need to know about the optic nerve optic nerve you'll see is the part that's extending out of the eye and that is the part that carries impulses to the brain and you know carries information of what you're seeing to the brain so you're able to see what you're seeing okay now we have the pupil reflex so if you'll notice how when you shine bright you're in a bright room or if you're shining light into your eyes your pupils get smaller or when you're in a dark room your pupils get bigger so that more light is entering your eye and more you're able to see things in the dark so this process that's action that your eyes have your pupils is called the pupil reflex and the function of the pupil reflects is to adjust your eyes for high or low light intensity okay excuse me so when the light intensity is low your radial muscles so these are the circle parts sorry the the straight lines that those lines those are the muscles that contract to become shorter so they're basically pulling the pupil to become bigger and so it's the diameter increases and the pupil becomes wider so that more light enters and a clear image is spawned so once again when it's low light intensity the radial muscles that is the straight lines they contract and the circular muscles relax radial muscles contract and circular muscles relax this could easily be a two to four mark question in paper four so this is something you need to know when light intensity is low radial muscles and in this diagram for your ease they've differentiated this radial and the circular muscles based on the circles and the straight lines so the radial muscles are the straight lines those muscles contract so the diameter of the pupil increases and more light can enter so you can form a clear image on the retina when the light intensity is high however the circular muscles contract that's the circles on that pupil you see those circular muscles contract and become shorter to reduce the size of a pupil to protect the retina from bleaching so I don't know if you've noticed but when you look at something really really bright for really really long you'll notice white spots in the eye so that's basically what's happening there okay so when light intensity is high circular muscles contract radial muscles relax when light intensity is low radial muscles contract and circular muscles relax so these are just the two things you need to know for this part of the syllabus and then you need to know about the antagonistic muscles so this is when a muscle opposes the action of another muscles so for example when you're flexing your biceps your uh biceps and triceps are antagonistic so your biceps are Contracting and your triceps are relaxing however when your arms are straight your triceps are Contracting and your biceps are relaxing uh so that's one example of that and the other example is the radial and circular muscles in the eye so once one Contracting the other one's relaxing and vice versa so yeah that's that's basically it okay um that's the antagonistic muscles now you have accommodation accommodation is the function in your eye where it adjusts first thing near and distant objects so when you're looking at a near object the ciliary muscles contract so I'm not sure if you've noticed the scenery muscles however it is bordering the lens at the top at the bottom so the celery muscles they contract when you're looking at an ear object and the ligaments relax that's the suspensary ligaments and your lengths becomes shorter and fatter okay so it becomes more rounded like this okay so if you've forgotten this in the exam this is a tip I've learned from my teacher you should what you should do is put your hand in your eye and try to focus on that and you'll feel this strain in your eye so that should remind you about how the CDV muscles are Contracting all right so in your object the when you're looking at something that's near your lengths are becoming shorter and fatter however when you're looking at a distant object the CVV muscles relax and the ligaments the suspensory ligaments tighten or contract okay and then the lens becomes thinner and longer so you can the diagram here shows how the diff how differently the light reflect refracts when the lenses battle and when the lens is thinner so that is basically how um your light accommodates itself in order to refract the light so that you can see this say an object from a particular distance okay now you have the rods and cones these are the light receptor cells so first like I said you need to know about the fovea which is the part of the retina where the receptor cells are pushed more closely together so they are concentrated there and you need to know about the functions of the rods and the cones so the rods provide low detailed black and white images and they are most useful for seeing things in low intense low light intensity so that is that night and that is what helps you see it in the dark you know and the rods are packed more slightly around the edge of the retina when so you can see the things most clearly when not looking directly at them okay so over here what you need to know most importantly is that rods are useful for seeing things in low light intensity and they provide low detailed black and white images the cones on the other hand provide detailed colorful images and they work in highlight intensity so the cones are part are the light receptors that are that enable you to distinguish colors and their most tightly packed at the center of the retina so they so that the objects are seen most clearly when they're being directly looked at okay uh not sure why this one's here again okay so once again this is a look take a look at the eye you need to know about the iris the cornea the lens and the pupil and the ceiling suspensory ligaments however you won't be able to you won't be required to identify the sea level in suspensary ligaments in diagrams and then you also need to know where the retina and the fovea are and the optic nerve up but the objective shouldn't be a hurdle to look for in the diagram because because how obviously it's protruding out of the structure okay and then we've come at the third part of the chapter that's the hormones so over here you need to know you need to Define hormone you need to know about the different places where the hormonal glands secrete hormones you need to know about the functions of some of the hormones that we have and yeah that's that's basically it okay so first of all first things first you need to know the definition of hormones so a hormone is a chemical substance produced by a gland and carried by the blood so if you remember broad blood is the transport um fluid in our body the main transfer fluid in our body and this is where the hormone travels and hormones are produced in the gland travel by the carried in the blood which Alters the effect activity of one or more specific Target organs this is something you need to know word for word because this could come as a come for a two-mark definition question and then you need to know where the hormones are secreted where they're formed and where what's their functions so we'll start with adrenaline I'm sure you've heard of this one the adrenaline adrenaline is produced in the adrenal gland which is right above your kidneys and the function of this hormone is to prepare your body for vigorous action or just when you're in an exciting situation when you need to be in a fighter flights it when you're in a fight-or-flight situation so for example when you're going on a roller coaster you'll feel your height pounding you feel a bit light-headed so these are all effects of the adrenaline and you know it's preparing your body for vigorous action so that it gets your heart pumping so that there's more blood flow all over your body we look at this more into detail when we're in the coming slides because the syllabus requires you to know more about adrenaline and then you need to know about insulin this is also we look into more detail in the coming slides the insulin is produced in the pancreas and it reduces the concentration of glucose in the blood and then you need to know about the testosterone and the estrogen testosterone is produced in the testis and it causes the development of male sexual characteristics so these are hormones that kick in when males are undergoing puberty and then you've got the estrogen which is produced in the ovaries and this causes development of female sexual characteristics and these hormones kick in when females are going through puberty so this is about adrenaline it is a hormone secreted by the adrenal gland it increases the pulse rate and makes glycogen in muscle converted to glucose you have so that there's more glucose various cells to break down and release energy and then you're breathing more deeper and more rapidly and your Airways become wider and your skin becomes pale as the blood is diverted away into it into more into areas more likely to be used such as your muscles and then that's yeah that's basically it for this hormone you need to know the effects of it when it's in your bloodstream so yeah you need to know about how your pulse rate increases how the glycogen in your muscles is converted to glucose how you breathe more rapidly how blood is diverted from some areas to other areas so that you're more useful for example if you need to be in combat or if you need to you know if you need to have if you have any physical activities to do so adrenaline is secreted for example while bungee jumping or riding a roller coaster like I said okay and then you've got the nervous and the hormonal systems so a lot of people confuse these two they are not the same you need to know about the difference between the two for this of course okay so we have a few factors of comparison we've got the speed of action the nature of messages the duration of response the area of response and yeah that's basically it then we look at some examples so for the speed of action in nervous system it's very very quick much much quicker than it's so quick you cannot even process it by the time it's done okay but the endocrine system that is the hormonal system this is a name you need to know by the way the endocrine system speed of action is quite slow it could take minutes to days okay depending on what exactly is happening all right and then the nature of message in the nervous system is electrical impulses which travel along nerves however in the endocrine system it's a chemical messenger hormones are chemical Messengers that travel in the bloodstream and then the duration of the response in the nervous system the speed of action is passed however the deviation is also much much faster than it is in the endocrine system in the endocrine system the duration of the effects of the hormones can last for years for example in puberty and then the area of response in the nervous system it's a localized area okay it's just the area that the target area however in the endocrine system it is a widespread response if it like the effect of the hormone can be felt in many different organs so an example of the nervous system in action is the reflexes that is blinking so if you if someone's putting their finger too close to your eye you're going to Blink immediately that is the effect of the nervous system however in the endocrine system an example is they develop enough the reproductive system okay so in this part we're looking at homeostasis so we've covered three parts and I think there's about two more left so right now we're looking at homeostasis we're going to look at what exactly is homeostasis we're going to look at the uh we've discussed how adrenaline works but we haven't discussed how insulin works that's something we're going to look at in this part of it and we're going to look at how your body adapts to the the temperature fluctuations in the environment and how a constant environment is maintained inside your body okay so first things first homemade faces the maintenance of constant internal environment home and Insulin decreases blood glucose concentration this is something we already discussed and in this chapter in this part of the chapter we're also going to look at glucagon so this is a hormone that is also produced in the pancreas and let's get into it so we'll start with the negative feedback feedback controls the production of hormones the hormones regulate their own production so how this works is when the concentration of one of the hormones increases it causes one of them to decrease or vice versa so that's basically what they mean in this line okay and then a negative feedback control is when the change in hormone level acts as a signal to cancel out that change so like I just said when one of them increases the other one decreases or when one of them reaches a certain level it indicates another hormone to be in to be secreted that causes the initial hormone levels to fall okay so it's kind of like a balance here okay and the hormone themselves control their own production regulate their own production how much in what concentrations they should be found in our bloodstream okay so that is the negative feedback we will look at um an example of it here in gluco regulation so blood glucose levels is something that's very important and a vital factor in how healthy we are so blood glucose levels are monitored and controlled by the pancreas that's why we have insulin and glucagon produced in the pancreas the pancreas produces and releases different hormones depending on the blood glucose level insulin is released when blood glucose levels are high so when your blood glucose levels are too high a hormone called insulin is produced what insulin does is it stores excess glucose as glycogen in your cells in the liver okay the glucagon however has the exact opposite effect so when your blood glucose levels are too low the liver the cells in the liver can convert stored glucagon glycogen my bad into glucose and releases it into the releases it into the blood so don't make the mistake I just made made a lot of people they confused glucagon and glycogen glycogen so you need to take extra extra care while you're writing answers from this part of the topic because it's extremely easy to confuse the two and sometimes you won't even realize what you've done until after you've received the paper and you're like what did I do you know so glucagon is the hormone and sorry yeah glucophone is the hormone and glycogen is the sugar all right so glycogen is the polysaccharide well that is once glucose is converted to glycogen to be stored in the liver okay so when there's too much uh glucose in your blood insulin is released to convert glucose into the glycogen and sorin in your blood and when there's too little glucose in your blood the exact opposite happens glucagon is released to convert glycogen into glucose and release it back into the blood for you know being streamed around the body so this is a diagram uh diagrammatic um representation of what I just said so you started normal blood glucose levels and when it's too high there's the insulin released and the conversion of glucose into glycogen and all that yada yada yada then you've got when the blood glucose levels are too low and then you've got the secretion of glucagon and the conversion of glycogen into glucose all right so this diagram is actually quite useful this is something I would take a second look at um and yeah feel free to take a screenshot or whatever because sometimes if you are not able to describe your own certain words diagrams like these actually do help okay because you what at the end of the day what you want is to get the message across to the examiner I know what I'm writing and this is what I'm writing no so this process okay is gluco regulation and when gluco regulation doesn't work in a person that person is said to have diabetes so if for this syllabus for the foreign you need to know about type 1 diabetes and type 1 diabetes is caused by the death of cells that secrete insulin and the symptoms of this is hyperglycemia that is feeling unwell having constantly constantly having dry mouth blurred vision feeling thirsting or hypoglycemia that is when you're tired you're showing confusion and irrational Behavior and the treatment for this is eating litten and often so so you know when normally people have three big meals throughout the day but when you're diabetic it's better to have little little meals often throughout the day you know so you need to avoid large amounts of carbohydrates at one go and these patients often need to inject insulin into their bloodstream so they're able to produce their own to reduce the blood glucose concentrations okay and then after gluco regulation we have thermoregulation this is when this is when the your body is responding to the changing temperatures okay so there's first of all for this part of the chopper you need for this part of the chapter yeah you need to know about the different parts of the the different layers in the skin and different things you can find here so the first layer is the epidermis then you've got the papillary dermist and you've got radicular dermis this is not something you need to know in detail what you do need to know into detail is about the oil glands the nerve the nerves the blood vessels that the capillaries so you know when you're feeling hot your cheeks get bread that's the capillaries increasing the blood for nutrients that's something we look at later and then the hair follicles and then the sweat glands and the muscles obviously on your skin that's you know controlling like when you're frowning when you're smiling the muscles here so let's get right into it you have insulation provided by the fatty-ish tissues that retain heat and you also have hairs on your skin that become erect to trap warm Hair by Contracting the erector muscles and vice versa so if you'll notice right under the hair follicle or the erector muscles this is not something that's specified by the diagram but you should notice that and you also have sweating that is a mechanism in your body where the water evaporates giving a cooling effect so when there's when there's sweat on your body they what they are evaporating and in order to evaporate they absorb heat energy from the neighboring skin in order to in order for it to evaporate you know and then there's receptors in your skin that sense Heat and the oops okay and okay and then you've got skin receptors that sense Heat and the sensory neurons and impulses to the hypothalamus that's the part of the brain that's you know responding um sensing and responding to the changes in temperature and you've got shivering this is when your skeletal muscles are you're shivering so you're generating action so that the muscular activity generates heat in your body you know and then you've got the other part of thermody Regulation this is the vasodilation and the vasoconstriction so like I said remember when I said your cheeks get hot when it's hot or your cheeks get red when it's hot so that is because of vasodilation when it is hot the arterials that is the capillaries that Supply blood to the skin surface capillaries uh yeah and these arterials they dilate so that means they become wider to allow more blood near the skin surface to increase heat loss and that's why your skin your face gets better and vasoconstriction is when it is hot when it is cold the exact opposite happens so the arterials which is supplying blood to the skin surface capillaries they constrict that means the diameter decreases to allow less blood near to the skin surface to decrease heat loss so if you remember from the transported mammals chapter your blood is also carrying heat energy with them right so when it's hot you want them near the surface so that the heat energy is escaping okay so you have heat loss however when it's cold you don't want that so there's the that's why though um blood supply near to the surface skin surface decreases and this is also a diagrams like the one we saw in gluco regulation this this is something once again I'll take a second look at and maybe take a screenshot of that refer to it before your exams because it really gives a summarized version of everything I just said okay and now we have Tropic responses and I think after that we're done with this chapter so in this part of the chapter we have you know different uh responses and plans so there's gravitropism phototropism and we need to talk about how they work and how plant hormones can be used how plant hormones are used in plant growth and as weed killers okay so we start with gravity tropism gravitropism is a response in which parts of a plant grows towards or away from Gravity so positive what this means is that gravity gravitopism is the response that's uh in relation to the gravity basically so a positive gravitropism is when growth is downwards so think of it as towards the gravity to work like in accordance to the direction of gravity and negative gravity tourism would be upwards that is opposite to the direction of the graph in which the gravity is working you know so auxins they tend to settle auxins or hot plant hormones and they tend to settle at the bottom end of the root however this does not make the cell tip of the plant root grow longer auxins prevent cells at the bottom tip of root from growing making cells at top of the root grow fast faster so when the cells at the top of the root grow faster they push the root deeper into the soil and the root gets longer so that it's you know reaching the water bodies and maybe more nutritional area or just you know having better support so that when it's a bigger plant it's not easy to topple over so the last line says the root grows in direction of the gravitational pull so that's basically what I meant by positive gravitropism so plant roots show positive gravitropism just because they grow in the direction of the gravitational pull okay and negative gravitopism would be in the plant shoots that's the Leaf part of the plant you know they're going they're growing away from the direction of the gravitational pull so that is what we look at in phototropism phototropism is a response in which parts of a plant grow to words or away from the direction of the light source so if Sunshine Shines on the right side of a plant shoot the auxins will accumulate on the dark opposite left side so that when the plants when the auctions accumulating in one side it's the cell it's causing cell elongation in the right side of the food okay so the oxygen accumulating mix cells on the left side grow faster than on than on the right side and this causes the left side of the food growing faster than the right side and then because of that accumulation of oxygen and because the left hand is growing faster the plant grows in the direction of The Upside so when it grows the shoot starts to bend towards the right towards the sunlight okay so in this case positive phototropism would be when the plant grows towards the sunlight and negative phototropism would be when the plant grows away from the sunlight so in if you want to connect this one on the previous part the gravitrobism it's the part of the plant which shows positive phototropism shows negative gravitotism and the part of the plant which shows positive gravity tropism shows negative phototropism and okay like we said we're discussing weed killers here so hormones can be used as weed killers spraying plants with high concentrationless hormones and in this specification you need to talk about the two for the hormone the weed killer it upserts normal growth patterns it affects different species differently so it might only kill one species and not the other so we take advantage of this fact and we use it to kill only or only the weeds and not the actual plants we want you know and how these weed killers work how these hormones work as weak Killers is they accelerate the growth process so much that the plants grow at a rate in which it cannot sustain so it does not have enough nutrition sunlight or water to sustain the rate of its growth so it ends up these plants end up dying afterwards um and I yeah that that's it so we have a few questions uh this is May June 2012 paper one they're into question 25. the diagram shows the bones in the muscles of the upper arm what must happen for the bones in the lower arm to move in the direction of the arrow so you've got a Muscle X control oops what's going on here okay uh the what must happen for the bones in the lower arm to move in the direction of the arrow so you've got X that's the biceps and Y that's the triceps and you want the lower arm to move upwards okay so your once again flexing your arms so option A is Muscle X contracts and muscle y contracts that's not possible because if you remember biceps and triceps are antagonistic muscles so when one contracts the other has to relax so a is not an option muscle option b Muscle X contracts and muscle y relaxes okay you've got the antagonistic action going on here Muscle X contracts and muscle y relaxes that does sound about right I think is the correct answer but let's look at the other options because that's what you should always do option C Muscle X relaxes and muscle y contracts uh that is not true and muscle D once again it does not show more antagonistic action both of them have the same action relaxing relaxing that's simply not possible so in this case the correct answer is B okay the next question May June 2012 question 24 the diagram shows a section through the human eye which labeled part of the eye prevents the internal reflection of light in the eye so that would be option A the lens and okay that's that's about it that is chapter 14. so thank you for watching and I hope the video was helpful