IGCSE Biology MCQ Revision – Plant Nutrition

IGCSE Biology MCQ Revision - Plant Nutrition

hey guys thank you for joining me in another IGCSE biology revision video today I just want to go through a couple of mcq questions regarding the topic of plant nutrition so what I'll do is I'll flick through the questions quickly and as I do so I want you to pause the video arrive at your answer and I'll go through the answers individually so here we've got so the first question the second question the third the fourth the first and lastly the sixth question I can enlarge that for you as well so hopefully you have arrived at your answer so let's just go through this first question which is to do with the limiting factors of photosynthesis and the answer here was C the reason why the answer we'll see is because when you get any of these graphs initially you'll find that the graph sort of rises and elevates and so at least in the first regions of these graphs here you can see that the rate of photosynthesis increases with light intensity that suggests that the rate of photosynthesis is dependent or rely on light intensity but at some stage a sort of plateau is out or the graph sort of flattens which the point P is placed around that region and when the graph flattens that suggests that even though light intensity is increasing it's not actually affecting the rate of photosynthesis that means that something else is now sort of limiting the rate of photosynthesis and light intensity has no bearing on that so whenever you get this sort of graph here the initial stages will always suggest that that particular variable is the variable or the limiting factor of rate of photosynthesis whereas when it flattens then something else must be the case and here is that scenario we've got P which is on the flattened part of the graph and that suggests that it's not light intensity as the other factors such as temperature and carbon dioxide concentrations so the answer here was see this question here is a the second question regarding the your knowledge about photosynthesis and carbon the story and respiration respiration obviously produces carbon dioxide as a by-product and uses up oxygen whereas photosynthesis produces oxygen and uses of carbon dioxide the here was see the answer we'll see because the first two test tubes have no light that's getting through so photosynthesis can't happen with these inside these water plants so respiration is happening at least an egg with the snail producing carbon dioxide and even the water plant producing carbon dioxide but nothing is actually being absorbed back because photosynthesis is not happening so therefore carbon dioxide is not used and we're expected to elevate rather than decrease or a and B would not have been correct if you can consider the scenario D here you've got a snail inside which is obviously gonna respire and produce carbon dioxide that it's gonna dissolve into the liquid here but there's no plant or anything like that and the photosynthesis is obviously not gonna happen here and so therefore carbon dioxide it's just gonna start to increase as well see you've got this plot which is expected to respire but it is also going to photosynthesize because it has access to light and when that happens carbon dioxide is still gonna be you know moderately used up and you could expect the rate of photosynthesis to be higher than the rate of respiration simply because plants don't really need to respire a lot at least compared to animals and so therefore C would have been the most likely answer with karma dogs are being used up from the photosynthesis that's happening and not much carbon dioxide being produced this question here is a very very basic question regarding your knowledge about the formula of photosynthesis and here the answer was B hopefully there's not much explanation to you know do here we've got the the photosynthesis equation going you know carbon dioxide and water being produced or sort of basically producing glucose and oxygen and the procedure and so obviously there are that would have been B so we've got the diagram that shows the sections through the leaf and all you needed to do was sort of label what each of these things were and so the answer here was B and this really just tests your structural understanding of a leaf and we've got some a quick diagram here just to recap we've got the cuticle on the very top surface of the leaf and then comes the upper epidermis below that you've got the palisade layer which is of course compact and it has a lot of chloroplasts and the main function of the palisade mesophyll layer is for photosynthesis if you've got the spongy mesophyll layer that has a lot of air spaces and the main purpose here with the air spaces is for the diffusion and exchange of gases and you've got the lower epidermis and sometimes you've got another cuticle layer and you've got got guard cells that basically form the little hole called the stomata where gases go in and out of the leaf so if you take a look at this diagram here we should consider the fact that we've got P being the cuticle and so really the only answer here would have been B to start off with so the other the only thing that could have confused people would be Q here which is you know pointing towards some part of the vascular bundle but if you think about the xylem being generally at the top part rather than the bottom half of the vascular bundle then that would have given you the answer there as well but overall a pretty easy question and so this question fifth question here the answer was a and the answer was a because this really is again testing your knowledge about the leaf structure and sort of the the fundamental functions of each of the layers of the leaf and we touched on this right before with the diagram I showed you here and so the palisade mesophyll layer is the main site of photosynthesis so it's got the moist chloroplasts and hopefully you are aware of that now the second most layer that has the second most chloroplast within the leaf is the spongy mesophyll where photosynthesis can still happen it's not the main function because it's got a lot of air spaces that is used for gas exchange mainly so this question here is just really testing your knowledge about chloroplast distributions throughout the leaf so without even looking at the questions or the answers here we can see that two must be the palisade mesophyll and three must be the spongy mesophyll and one whatever is remaining so that really just gives us the answer of a via I've got the guard cell we're having lowest amount of chloroplasts because of per se meets level having the most and the spongy mesophyll having the second most and this last question here the answer here was C and the reason that we'll see is because this question is really just testing your understanding of how to set of experiments in terms of you know rate of photosynthesis and all that and one of the reasons or one of the one of the methods and measuring the rate of photosynthesis is measuring how much bubbles are formed per minute because the bubbles signify oxygen production and we know that oxygen production is a result of photosynthesis and so the investigation was repeated several times and the average amount of gas collected was calculated which two factors was kept constant during this investigation so during any sort of investigation regarding rates of photosynthesis or respiration or any sort of cellular in a metabolism we need to keep every other thing that can potentially affect the rate of that particular metabolism exactly the same throughout the experiment and so here if you think about the rate of photosynthesis what makes more sense is that we keep the size of the aquatic plant constant because if you have a larger mass of the plant then you'd expect that would produce more oxygen and the rate of you know photosynthesis may turn out to be higher because simply just because it has more cells in them the other thing is the duration of light obviously light is an important part of photosynthesis you need light for that to happen so again if you put one in dim conditions and one lit conditions the one in lit conditions will mostly produce higher rates of photosynthesis and that wouldn't really give you an accurate measurement or a test so the variables that you need to keep constant are obviously the the aquatic plant size and the duration of exposure of light so the answer there was C so I hope that helped you guys out please check out my patreon if you want to access to all these mcq questions I have a lot more if you if you subscribe to that but otherwise I will see you in the next video please like share and subscribe Cheers

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