when similar cells are connected we call this a tissue say heart tissue tissues form organs for example your heart and organs work together in an organ system like your circulatory system your digestive system breaks down food you eat into useful nutrients for your body to use acid in your stomach breaks it down bile and enzymes work together in your small intestine to break it down further bile is made in the liver and stored in the gallbladder before being used what it does is neutralize the acid from the stomach and also emulsifies fats to form droplex that increases their surface area exposed to the enzyme so they're broken down faster enzymes are biological catalysts some of which break down larger molecules into smaller ones that can then be absorbed by the Villi in your small intestine into the bloodstream to be transported to every part of your body for example amalay is the enzyme that breaks down starch into glucose it's found in your small intestine and saliva enzymes are specific that is they only break down certain molecules for example carbohydrases break down carbohydrates into simple sugars Amal is one of these proteases break down proteins into amino acids and lipases break down lipids that's fats into glycerol and fatty acids they're specific because they work on a lock and key principle the substrate for example the starch binds to the enzyme's active site with then call this a complex however this can only happen if the substrate is the right shape in order to fit the active site in reality they are incredibly complex shapes no pun intended these shapes here are just to represent them much like a lock and key it only works if they're the right shape for each other the rate of enzyme activity increases with temperature due to the molecules having more energy that is until the active site changes shape and so the substrate no longer binds we say the enzyme has denatured this maximum rate occurs at the optimum temperature Optimum meaning best this is similar for pH as well except it can denature a too high or too low PH the Practical on this involves mixing amas with starch at different temperatures or with different pH buffer Solutions once mixed we start timing then every 10 seconds we remove a couple of drops and put in a spot in tile dimple with iodine in to begin with the iodine will turn black due to the still being starch present but eventually it will stay orange showing that all of the starch has been broken down calculate the time taken to do that then plot these times against pH or temperature draw a curved line of best fit and the lowest point is where the starch would have taken the shortest time to be broken down that's the optimum temperature or pH however in true biology fashion we're technically not allowed to interpolate between points for some reason so we must only say that the optimum pH or temperature is between the two lowest points shrug food test allow us to identify what nutrients are in our grub iodine turns from to Black in the presence of starch like we just saw Benedict solution turns from Blue to Orange in the presence of sugars bir's reagent turns from Blue to purple with proteins cold ethanol will go cloudy with lipids that is fats respiratory system next all to do with breathing and gas exchange breathing isn't respiration but it does provide the necessary oxygen for respiration to happen in our cells the air moves down the trachea into the bronchite then the bronchioles and ends up in the Alvi the air saxs where it diffuses into the blood vessels around it like we said earlier alveol are lumpy to have a large surface area so this happens at a fast rate the oxygen then binds to the hemoglobin in your red blood cells they then transport it to every cell in your body to be used for respiration carbon dioxide made from respiration is dissolved into the plasma of the blood which diffuses into the lungs and is exhaled some water is also excreted this way too as you know when you breathe on a cold mirror the heart is at the center of the circulatory or circulatory system the transport system of your body we call it a double circulatory system blood enters the heart twice every time it's pumped around the body deoxygenated blood from the body enters in the right side of your heart by the way you always look at the heart as if it's yours and it enters through the venina Cava the main vein into the right atrium of the heart the valve between the right tumor of the right ventricle stops back flow just like all valves to stop deoxygenated blood from going back into the body the heart muscles contract and it goes through the pulmonary artery to the lungs to be oxygenated it then comes back to the heart through the pulmonary vein into the left atrium then it goes into the left ventricle then out to the body through the aorta the left side of the heart has thicker walls as the left ventricle has to pump blood to the whole body while the right ventricle only pumps to the lungs a group of cells near the right atrium create a electrical pulses that cause the heart muscles to contract the heart to beat if these aren't working properly you can be given an artificial pacemaker to do the same job blood vessels that go away from the heart are always arteries veins towards that means that arteries carry oxygenated blood apart from the pulmonary artery and vice versa for veins arteries have thicker walls to withstand the higher pressure so they have a thinner Lumen that's the hole in the middle veins have thinner walls due to the lower blood pressure but have valves to stop back float like we said archeries split and get smaller and smaller until they end up as Tiny capillaries with one cell thick walls to allow the fast diffusion of molecules in and out of cells the heart is a muscle so it needs its own supply of oxygen and therefore blood to keep the muscle pumping this is delivered by the coronary artery if these are blocked by the buildup of fatty deposits a heart attack can occur this is CHD coronary heart disease stents are little tubes that are inserted into blood vessels to keep them open so blood can flow in this case statins are drugs that reduce cholesterol which in turn reduces the fatty deposits faulty heart valves result in backflow occuring these can be replaced with artificial ones along with plasma and red blood cells Blood also carries white blood cells which combat infections more on this later and platelets which Clump together to clot wounds and stop bleeding cvd cardiovascular disease is an example of a non-communicable disease as the cause of it comes from inside your body other examples of such diseases include autoimmune conditions like allergic reactions and cancer a communicable disease must be caused by a pathogen that enters your body that will cause a viral bacterial or fungal infection again more on these in a bit back to non-communicable diseases obesity and too much sugar can cause type 2 diabetes a bad diet smoking and lack of exercise can affect the risk of heart disease alcohol can cause liver diseases smoking lung disease or cancer a carcinogen is the name given to anything that increases the risk of cancer for example ionizing radiation cancer is a result of damaged cells dividing uncontrollably leading to tumors benign cancers don't spread through the body and they're relatively easy to treat however malignant cancers are when these cancerous cells spread through your body much worse plants also have organs leaves are where photosynthesis takes place producing food for the plant water also leaves the plant through them allowing transpiration to take place the diffusing of water into roots up the xylm roots are where water and mineral irons enter the plant the merry stem is where new cells are made like we saw earlier xylm are the long continuous tubes which water rises up we say it's unidirectional only goes in One Direction that's transporation like we said while flm are the conveyor belts of cells that transport sugars food and sap up and down the Plant we call this translocation that's bidirectional the rate of transpiration can be increased by the following increasing the temperature decreasing the humidity and increasing the air movement all of these result in water evaporating from the leaves at a faster rate just for triple real quick the lack of nitrate ions means the plant can't synthesize proteins effectively and that stunts growth chlorosis is the scientific term for the yellowing of leaves this can be due to magnesium deficiency as it's needed to make chlorophyll the cross-section of a leaf looks like this every layer has its own specific function at the top we have the waterproof waxy cuticle not to stop water from entering the leaf but to stop it from evaporating from the top and causing the leaf to dry out the upper epidermis epidermis just means outer layer consists of transparent cells that allow light to pass through to the palisade mesophyll layer mesophyll just means a layer in the middle these are chalk full of chloroplasts so this is where the majority of photosynthesis takes place under that is the spongy mesophyll layer that has lots of gaps around the cells to increase the surface area through which gas exchange can occur carbon dioxide diffuses into the cells while oxygen and water diffuse out we also have the vascular bundle that includes the xylm and flm the lower epidermis is the bottommost layer of the leaf and it has holes in it called stomata which is how gases enter and exit the leaf the size of a sto is controlled by the guard cells that flank the hole they change size to control the rate at which gases enter and leave for example they close the stomat at night to reduce the rate of water loss as less water is needed for photosynthesis so I hope you found that helpful leave a like if you did and pop any questions or comments below I'll see you in the next video