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B4.1 - Comm. & Homeo
Communication & Homeostasis - OCR A2 Biology
| Question | Answer |
|---|---|
| What is homeostasis? | The maintenance of a constant internal environment. |
| Why is homeostasis important? | Keeping the internal environment is important to ensure that cells function correctly, and do not get damaged (e.g. Denaturing of enzymes) |
| What is negative feedback? | It keeps things around the normal level. Receptors detect when a level is too high or low, this info is communicated via the nervous system to effectors which alter this. |
| What is positive feedback? | This amplifies a change from the normal level, further increasing it away from the normal level. (This is not homeostasis as it doesn't keep your internal environment constant) |
| What is an example of positive feedback? | A blood clot forming after an injury. |
| What is a sensory neurone? | These transmit nerve impulses from receptors to the Central Nervous System (CNS) (The brain and spinal cord) |
| What is a motor neurone? | This transmits nerve impulses from the CNS to effectors. |
| What is a relay neurone? | This transmit nerve impulses between sensory and motor neurones. |
| When a neurone is in a resting state, the outside of the cell is ........... charged compared to the inside. So the membrane is ......... there is a difference in charge. | When a neurone is in a resting state, the outside of the cell is positively charged compared to the inside. So the membrane is polarised there is a difference in charge. |
| Roughly what charge is the resting potential of a neurone? | -60mV |
| For every three sodium ions actively transported out of the neurone, how many potassium ions are moved in? | Two. |
| What does a stimulus do to a neurone? | This excites the cell, na+ channels open, allowing them to diffuse in, making the inside of the neurone less negative. |
| What is depolarisation? | If the p.d. reaches the THRESHOLD POTENTIAL (-55mV) more sodium channels open, allowing ions to diffuse in. |
| What is repolarisation? | At around (+30mV) the sodium channels close, and potassium channels open. Allowing ions to diffuse out and return the neurone to it's resting potential. |
| What is hyper-polarisation? | Potassium channel are slow to close, this means the p.d. of the membrane becomes more negative than the resting potential. |
| How does a neurone return to the resting potential after an action potential has passed through? | The sodium-potassium pumps 'reset' the membrane to it's original state. |
| How do action potentials travel along a non-myelinated neurone? | They move along the neurone as a wave of depolarisation. The wave travels as during the refractory period (repolarisation to hyper polarisation) as it cannot fire an action potential. |
| How is the size of a stimulus transmitted? | A bigger stimuli results in more frequent impulses. |
| What is a myelin sheath made up of? | Schwann cells, between these cells are tiny patches of bare membrane called 'nodes of Ranvier'. |
| How do action potentials travel along a myelinated neurone? | They 'jump' between the nodes of Ranvier. This is because depolarisation can only happen at these nodes, and the cytoplasm of the neurone conducts enough electrical charge to depolarise the next node. |
| What is the travelling of an action potential in a myelinated neurone called? And compare it's speed to non-myelinated neurones: | Saltatory conduction. The rate of conduction is faster in a myelinated neurone. |
| What is a synapse? | A junction between a neurone, and the next cell. The gap is called the synaptic cleft. |
| Why are synapses useful? | They allow many neurones to join, or one neurone to disperse. They also finely tune the nervous response. They also ensure that impulses are only transmitted in one direction. |
| What are endocrine glands? | They secrete hormones. These are chemical messengers. They are secreted when the endocrine gland is stimulated. Hormones are secreted directly into the blood. |
| What are exocrine glands? | They secrete chemicals through ducts into cavities, or onto the surface of the body (e.g. sweat glands). |
| What are the exocrine cells of the pancreas called and where are they located? | Acinar cells, they're located in clusters around the pancreatic duct. |
| What is the exocrine function of the pancreas? | The acinar cells secrete digestive enzymes into the pancreatic duct. The enzyme digest food in the duodenum (part of the small intestine) |
| What are the areas of endocrine tissue in the pancreas called and where are they located? | Islets of Langerhans, they're found in clusters around blood capillaries. |
| What are the Islets of Langerhans made up of? | Alpha cells that secrete Glucagon. And Beta cells that secrete Insulin. Both of these hormones help control the blood glucose concentration. |
| What does the cortex of adrenal glands do? | It secretes steroid hormones. |
| What does the medulla of adrenal glands do? | It secretes modified amino acids. |
| What is an ectotherm? | They cannot control their body temperature internally, they change it by altering their behaviour. Their internal temperature depends on their external temperature. They have a variable metabolic rate. |
| What is an endotherm? | They control their internal body temperature via homeostasis as well as altering their behaviour. They have a high metabolic rate. |
| What is the hypothalamus and where is it located? | It is a part of the brain that maintains body temperature in mammals. It receives information from thermoreceptors, and acts upon this information with effectors. |
| What mechanisms does the body have to REDUCE body temperature? | Sweating. Hairs lying flat. Vasodilation. |
| What mechanisms does the body have to INCREASE body temperature? | Shivering. Sweating less. Hairs stand up. Vasoconstriction. Hormones. |
| How does insulin lower the blood glucose concentration? | It increases the permeability of cell membranes so they absorb more glucose. It activates enzymes that convert glucose into glycogen, which can be stored in the cytoplasm of cells as an energy source (glycogenesis). |
| How does glucagon raise the blood glucose concentration? | It binds to specific receptors in liver cell. It activates enzymes that break down glycogen into glucose (glycogenolysis). It promotes the formation of glucose from fatty and amino acids. |
| What part of the body manufactures and releases adrenaline? | The Adrenal Medulla. It is found in the centre of the gland. |
| What is a steroid hormone? | A hormone that can pass through the membrane and enter the cell to have a direct affect on DNA. |
| What is the Adrenal cortex and what does it do? | This uses cholesterol to produce certain steroid hormones. |
| What is a protein hormone? | They're not soluble and do not enter the cell. |
| If the demand for oxygenated blood increases, what happens to the heart? | Heart rate increases, and the volume per beat increases. |
| The heart muscle is myogenic, what does this mean? | It initiates it's own contractions. |
| What part of the heart acts as the 'pacemaker'? | The Sinoatrial Node (SAN) |
| Nerves from the Medulla Oblongata go to the heart. What effect do the 'Accelerator' and 'Vagus' nerves have? | Impulses sent down the Accelerator nerve increase the heart rate, impulses sent down the Vagus nerve decrease the heart rate. |
| What happens in step 1 of an impulse travelling across a Synapse? | The action potential depolarises the synaptic knob. Calcium channels open. |
| What happens in step 2 of an impulse travelling across a Synapse? | Synaptic vesicles fuse with the pre-synaptic membrane. Neurotransmitter is released into synaptic cleft. |
| What happens in step 3 of an impulse travelling across a Synapse? | Acetylcholine binds with receptor sites on sodium channels. Sodium channels open. |
| What happens in step 4 of an impulse travelling across a Synapse? | Depolarisation in post-synaptic neurone. If threshold potential is reached, action potential is sent along axon. |
| What happens in step 5 of an impulse travelling across a Synapse? | Acetylcholinesterase breaks down acetylcholine into acetyl and choline. Sodium channels close. Two parts diffuse back across Synaptic cleft. |
| What happens in step 6 of an impulse travelling across a Synapse? | ATP released by mitochondria recombines the two parts, stored in synaptic vesicles for future use. |
| Where is a dendrite? | It carries action potentials towards the cell body. |
| Where is an axon? | It carries action potentials away from the cell body. |
| A neurone will either conduct an action potential or not, what is this called? | The all-or-nothing law. |
Created by:
Sparksy
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