HOMEOSTASIS & RESPONSE - GCSE Biology (AQA Topic B5)

homeostasis is the term given to an organism's ability to regulate internal conditions even when external conditions change this is important so that crucial chemical reactions involving enzymes can happen at an Optimum rate amongst other things our bodies work hard to regulate blood glucose concentration temperature and water levels for example one way that our body achieves this is with our nervous system it consists of the CNS that's central nervous system that's the brain and spinal cord and the pns peripheral nervous system the nerves that go through the rest of the body a receptor for example skin

detects a change due to a stimulus like a hot hob an electrical signal travels to the spine through sensory and relay neurons nerve cells the signal travels across the gap between these neurons called the sinaps by a neurotransmitter chemical once at the spine the signal can go to the brain where you can make the conscious decision to act the signal then goes back to an affector like the muscle in your arm via relay and motor neurons so that you move your arm a reflex is when the signal bypasses the brain and goes straight through the

spine to the affector this is a reflex arc this of course is much faster than a conscious decision glands can also be affectors which produce specific chemicals your body needs depending on the situation for example your salivary glands in your mouth making saliva when you eat food you can investigate into reaction Times by holding the bottom of a ruler between a person's finger and thumb and drop it without warning then you measure the distance it falls before they catch it do this multiple times and and taking mean average not tooo many times though as their

nervous systems will start to get a bit better at reacting to this you can introduce an independent variable like a stimulant for example coffee or a sugary drink or a depressant which will have the opposite effect although I can't think of any ones that are legal for you at the minute to see how they decrease or increase Reaction Time respectively you could calculate the reaction time from the distance using suat S equals half 80 squar but you'll never be expected to do that in this paper but it's something you could mention if you were asked

to marker on this quite a bit that's just for triple biology now that's the brain eye and Thermo regulation skip to hormones if you're doing combined Trilogy that is double science there are three parts of the brain you need to know the cerebral cortex is responsible for higher level functions like memory speech and problem solving the cerebellum is responsible for your motor skills movement balance and coordination the medulla onbling controls unconscious actions your body takes you don't think about them like your heart and breathing rates it's also what controls the release of adrenaline MRI scans

magnetic resonance imaging are a way of seeing the activity in your brain safely if something goes wrong with your brain though it can be very difficult or impossible to treat without damaging important parts of it your eyes are the most mind-bogglingly designed cameras ever conceived of accommodation is the ey's ability to change the shape of the lens in order to focus light that come from objects that are different distances away on the retina to focus light that comes from objects that are far away the ciliary muscles relax and the suspensory ligament tighten they're both connected

to the lens this results in the lens becoming thin and that means that light is only refracted a little bit and that focuses the light on the retina to focus on near objects the opposite is true the sary muscles contract the suspensory ligaments slacken and the lens becomes fatter or thicker and so that means that it becomes more powerful actually so light is refracted more which means that the light coming from the object still converges meets focuses on the retina so you can see a clear image the pupil the hole in the iris can change

size depending on the light intensity hitting the eye the cornea is the transparent outer layer where light enters the eye it has a slight lensing effect itself while the White surface that covers the rest is called the Scara the light is focused then on the retina at the back of the eye which consists of Rod and Cone cells which respond to light rods can only detect light intensity so no color while there are three different types of cones which detect green blue or red wavelengths of light a mix of which will produce the colors we

then perceive when the signal reaches our brain via the optic nerve myopia is the medical term for shortsightedness you can't focus on Far objects hyperopia is long-sightedness glasses or contact lenses are usually used to mitigate this by slightly converging or diverging the light before it enters the eye laser eye surgery aims to change the shape of the cornea to achieve the same effect Thermo regulation is your body controlling its internal temperature by the brain sensing blood temperature then sending nervous and hormonal signals to various effectors around your body in order that your body loses heat

to its surroundings more slowly or quickly for example if you're too hot sweat glands in your skin cause water to cover the surface this evaporates taking heat away from your body quickly blood vessels also dilate widen we call this Vaso dilation to increase blood flow to the skin to increase the rate of heat loss too cold we have Vaso constriction instead hence why you go pale you also shiver which causes your muscles to produce more heat okay back to double science goodness which is for everyone the endocrine system is a system of glands that produce

or secrete hormones that travel to affectors Via the blood this is of course slower than any signal carried by the nervous system the pituitary gland in your brain can be considered the main or Master gland as it produces hormones in response to stimuli that travel to other glands in your body in order that they start then producing certain chemicals the examples are the pancreas which produces insulin we'll talk more about that in a bit the thyro oid controls all sorts of things like growth heart muscle and digestive function and more the adrenal glands produce adrenaline

and the ovaries intestines release eggs or produce sperm depending on which you have speaking of the pancreas then it's involved in making sure that your blood glucose levels aren't too high or too low too high and the pancreas secretes insulin which causes glucose to move from the blood into your cells to be used for respiration any excess glucose can be converted into glycogen to store energy and that's done by the liver too low on the other hand and the pancreas produces another hormone called glucagon which causes the liver and muscles to turn glycogen back into

glucose ready to be used type one diabetes is what you have when your pancreas can't produce enough insulin and you have to take insulin injections to do the job instead type two is when your cells no longer absorb the glucose as they should so you have to be careful with your diet and if you're overweight or obese you have a much higher risk of developing this water and nitrogen balance are triple only so skip to the next topic reproduction if you're just double your body loses water when you exhale sweat or urinate if your body

has too much water let's say for example you drink too much your kidneys remove it from your blood at a faster rate where it's mixed with Ura to become urine Ura is made from ammonia which is produced from excess proteins broken down into amino acids by the liver if that wasn't the case too much water builds up in your body and too much water would go into your cells by osmosis and then they'd become turgid and burst too little water however and they become flaccid and stop working kidneys do a good job of keeping the

water balance just right kidneys also filter your blood to absorb useful substances like glucose and some ions bit more detail about how the kidneys work then antidiuretic hormone or ADH is produced in the pituitary gland which travel to the kidneys and it causes the tubules in the kidney to reabsorb more water into the bloodstream so less then go to the bladder the water level is too high less ADH is produced so the kidneys cause more water to be lost in urine in both cases the the water level returns to normal we call this negative feedback

the term negative feedback might sound like it's bad but all it means is that the body responds in such a way as to return things to normal if your kidneys aren't working properly dialysis is required essentially your blood is sent through a machine that does the same job as your kidneys if this doesn't happen the buildup of Ura will poison you okay reproduction is for everybody well you know what I mean menstruation occurs in females after puberty eggs start to mature first FSH that's icle stimulating hormone made by the pituitary gland causes an egg to

mature in the ovary this also causes the ovaries to produce estrogen which causes the uterus lining to thicken it also inhibits or stops the production of FSH so that no more eggs mature in that cycle very clever it also causes the pituitary gland to produce LH lutenizing hormone which causes the egg to be released and it starts to travel towards the uterus via the UCT over several days finally progesterone is also produced Us by the ovaries which maintains the uterus lining this is great news if you're looking to get pregnant if not you need to

find some way of stopping a sperm cell meeing an egg cell contraception options include pills that inhibit FSH production so no eggs mature progesterone injections that stop any eggs being released you can also have an implant that slowly releases this over months or years if needed condoms for men and diaphragms for women are simple barriers to stop sperm from reaching an egg an IUD or intrauterine device like a copper coil prevents a fertilized egg from implanting in the lining you could quite simply just avoid sex for some time after the egg has been released as

that's when it travels slowly down the UCT where a sperm can meet it clamping the UCT sometimes refer to having your tubes tide or cutting the sperm ducts either of these will obviously stop the cells meeting some couples however would love to have children but can't due to infertility sometimes it's something fairly simple like not enough FSH or LH produced which injections can fix the most expensive solution to bigger issues is IVF in vitro fertilization eggs are harvested from the woman after inducing their release and will then fertilize in the lab with the prospective father's

sperm any embryos that develop are inserted back into the uterus where they will hopefully embed in the lining and grow normally the success rate however is very low but there is also the risk that they could be more than one baby born which might not be desirable we' already mentioned it adrenaline is the hormone that increas inrees heart and breathing rate in stressful situations to prepare the body for fight or flight thyroxin is another hormone that's secreted by the thyroid and it controls metabolic rate if thyroxin levels are too low the hypothalamus in your brain

releases a hormone called TR you don't need to know the full name and that causes the pituitary gland to produce another hormone called TSH so the thyroid releases more thyroxin this again is an example of negative feedback the last triple content in B5 plants also have their own hormones which we can utilize when growing plants gibberellins cause seed germination to occur which we can add to seeds to give them a wakeup core it also promotes flowering and increases the size of fruits Ethan induces ripening of fruits so we can add them to bananas for example

when they're in transit orins control Chute and root growth it's destroyed by sunlight so it gathers on the Shaded side of a chute causing more growth and elongation of cells on the Shaded side so the Chute bends toward the Sun or or light source this is what we called phototropism in Roots however orins inhibit growth the hormone gathers on the bottom of a root and so that means the top side grows more quickly causing the root to grow downwards this is called geotropism we can also use orins as weed killers rooting powders and for promoting

growth in tissue cultures we can do a mini investigation we can put some seeds on damp cotton wool in a Petri dish for example stand the petri dish on its side leave for a few days then turn 90° and you should see that the roots have bent in that time proving that geotropism is true for roots 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