- Skeletal muscles is made up long muscle fibres, the cell membrane of which is called the sarcolemma. Bits of this fold inwards and stick to the sarcoplasm and help to spread electrical impulses to the muscle fibres. They are called transverse tublues and have lots of ATP.
- Myofibrils contain thick myofilaments called myosin, and thin myofilaments called actin. Myosin and actin slide over one another to make sarcomeres contract, the silmultaneous contraction of sarcomeres mean that muscle fibres contract. This is called the sliding filament theory.
- Myosin filaments have globular heads and binding sites. Tropomyosin and troponin are found between actin filaments which help the myofilaments to move over one another. Binding sites in resting muscles are blocked by tropomyosin, but when an action potential triggers an influx of calcium ions, it depolarioses the sarcomere and the calcium ions bind to troponin, making it change shape and expose the binding site and an actin-myosin cross bridge is formed.
- ATP provides the energy needed to moved th myosin head, as calcium ions also activate ATPase, and it also provides energy to break the cross bridge.
- Slow twitch muscle fibres contract slowly, are used for posture and endurance, release energy through aerobis repiration and meed lots of mitochondria.
- Fast twitch muscle fibres contract quickly, are used for fast movement and short bursts of power, release energy via anaerobic respiration using glycogen and use few mitochondria.
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The Heart and Lungs
- An electrical impulse starts in the Synoactrial Node (SAN), which is in the wall of the right atrium, causing both the left and the right atria to contract at the same time. The impulse is then sent to the Atrioventricular Node (AVN), where there is a short delay to allow the atria to fully contract before it is sent down the Bundles of His to the Purkyne Fibres, where they spread over the ventricular walls, making the ventricles contract.
- Cardiac output = Ventricular voulme x Heart rate.
- Breathing rate is controlled by the Medulla. The inspiritory centre in the Medulla sends signals to the intercostal and the diaphragm to make them contract, increasing volume and decreasing lung presure. Air enters the lungs due to the pressure difference. As they inflate streatch receptors are stimulated, sending impulses back to the Medulla to inhubit the respiratory centre. The lungs then deflate.
- An increase in PH causes an increase in oxygen levels in the lungs.
- An increase in PH or blood pressure causes a decrease in heart rate.
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- Glycolysis make pyruvate from glucose. This happens in the cytoplasm of cells and is the first stage of anaerobic and aerobic respiration, however it is anaerobic itself. There are two stages of glycolysis: Phosphorylation: glucose is phosphorylated by adding 2 phosphates from ATP. This creates 2 molecules of TP and ADP. Oxidation: TP is oxidised forming 2 molecules of pyruvate. NAD collectes the H ions lost during oxidisation and forms 2x Reduced NAD. 4xATP are produced, with a net gain of 3.
- Links reactions convert pyruvate to Actyl Coenzyme A by decarboxylation. NAD is reduced, changing pyruvate into acetate, which combines tiwth coenzyme A to form Acetyl Coenzyme A.
- Krebs Cycle produces reduced coenzymes and ATP. Acteyl Coenzyme A combines with oxaloacetate to form citrate (6C), which is converted into a 5C molecule by decarboxylation and dehydrogenation producing rediced NAD. The 5C molecule is then converted into a 4C molecule by decarboxylation and dehydrogenation, producing 1x Reduced FAD and 3x Reduced NAD. ATP is also produced.
- The electron transport chain produces lots of ATP. H atoms are released from reduced NAD and reduced FAD, they then split into protons and electrons. The electrons move along the electron transport chain, losing energy at each carrier. This energy is used to pump protons from the inner mitochondrial matrix into the intermembrane space. An electrochemical gardient is formed, protons move down it through ATPase generating ATP. This is called chemiosmosis. The protons, electrons and O2 from blood combine to make water.
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- Anaerobic respiration does not use oxygen and doesnt involve the link reaction, krebs cycle or oxidative phosphorylation.
- Lactate fermentation is a type of anaerobic respiration which occurs in animals and produces lactate.
- Glucose is converted into pyruvate via glycolysis. Reduced NAD from glycolysis transfers hydrogen to pyruvate, forming lactate and NAD which can then be reused in glycolysis.
- Lactic acid can build up in cells, and is broken down by converting it back into pyruvate. Liver cells can convert it directly into glucose which can be used for respiration or stored.
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- Homeostasis is the maintenance of a constant internal environment. Responses in the body occur due to negative feedback.
- Reducing body temperature: Sweating - water evaportaes from the surface of the skin cooling it. Hairs lie flat - erector pilli muscles relax so less air is trapped and heat can be lost easily. Vasodilation - arterioles dilate, increasing blood flow through the capillaries, so more heat is lost from the skin via radiation.
- Increasing body temperature : Shivering - muscles contract in spasms, more heat is produced from increased respiration. Hormones released - adrenaline and thyroxine increase metabolism so more heat is produced. Hairs stand up - erector pilli muscles contract, trapping more air and preventing heat loss. Vasoconstriction - arterioles constrict, so less blood flows through capillaries, reducing heat loss.
- Proteins called transcription factors controll the transcription of genes. They bind to DNA near the start of genes and increase or decrease the rate of transcription. The thyroid hormone receptor decreases transcription of a protien that increases metabolic rate at normal temperature. At cold temperatures, thyroxine is released which binds to the thyroid hormone receptor, making it an activator, increasing transcription rate, increasing production of metabolic rate protein production, so metabolic rate increases, increasing body temperature.
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Nervous and Hormonal Systems
- The nervous system consists of 3 types of neurone. Sensory neurones transmit electrical impulses from receptors to the CNS. Motor neurones transmit electrical impulses from the CNS to effectors. Relay neurones transmit electrical impulses between sensory and motor neurones.
- Stimulus, Receptors, CNS, Effectors, Response.
- The hormonal system sends information as chemical signals and is made up of glands and hormones. Glands are groups of cells that secrete hormones. Hormones are chemical messengers that can be proteins or peptides. Glands can be stimulated by a change in concentration of a specific substance or electrical impulses. Hormones diffuse directly out of the blood but will only bind to specific receptors on the membrane of cells.
- Stimulus, Receptors, Hormone, Effectors, Response.
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Receptors in the Nervous System
- Photoreceptors are in your eye and convert light into electrical impulses. When light hits a photoreceptor it is absorbed by light sensitive pigments causing a chemical change in them (this is called bleaching), and triggers a nerve impulse along a bipolar neurone.
- There are 2 types of photoreceptor - rod cells which see in black and white, and cones - see information in colour.
- Rod cells hyperpolarise when stimulated by light. They contain a substance called rhodopsin which can be split into retinal and opsin, this is called bleaching and is caused by light energy. The bleaching of rhodopsion causes the sodium ion channels to close so they are still activley transported out of the cell but can't diffuse back in. This causes the inside of the membrane to become negativley charged (hyperpolarisation), which causes the rod cell to stop releasein neurotarbsmitters, so the bipolar neurone is no longer inhibited. This allows the bipolar neurone to depolarise, creating a change in potential difference which can cause an action potential if it reaches the threshold.
- When it is dark the bipolar neurone is inhibited by the neurotransmitters released due to the fact that the sodium can diffuse back into the membrane so it is only a little bit negative.
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Neurones in the Nervous System
- Neurone cell membranes become depolarised when they are stimulated. This excites the neurone cell membrane causing sodium ion channels to open. This means that the membrane is more permeable to sodium and they diffuse in down the electrochemical gradient, making the inside of the membrane less negative.
- Depolarisation is when enough sodium ions enter the membrane to cause the action potenital to reach the threshold.
- Repolarisation is when the sodium ion channels close and the potassium channels open. The membrane is more permeable to potassium ions so they diffuse out of the neurone down the concentration graident, making the neurone get back to its resting potential.
- Hyperpolarisation is when potassium ion channels are too slow to close so the potential difference inside the neurone becomes more negative than the resting potenital.
- Depolarisation occurs in a wave down a neurone, jumping from node to node. A refactory period (when channels do not open to create a time delay so that action potentials dont overlap) occurs behind the action potential.
- Action potenitals go faster in myelinated neurones, because they act as insulators and have Shwann cells that contain nodes of ranvier so that the action potenital can 'jump'. The depolarisation of the next neurone along is called saltatory conduction and is really fast.
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Synapses in the Nervous System
- Nerve impulses are transmitted between neurones using the space between them called synapses.
- An action potential causes an influx of calcium ions into the synaptic knob. These trigger the release of neurotransmitters in synaptic vesicles which fuse to the presynaptic membrane, releasing the neurotransmitters into the synaptic cleft via exocytosis.
- The neurotransmitters trigger an action potenital in the postsynaptic neurone, as it binds to receptors on the post synaptic membrane, causing sodium ion channelsa to open in the post synaptic neurone, creating depolarisation and generating an action potenital in the adjactent neurone.
- The neurotransmitter is then broken down by Acetlycholine Esterase, which then allows it to diffuse back across the presynaptic membrane so that it does not trigger another action potential.
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Responses in Plants
- Phototropism is the growth of a plant in response to light. Geotropism is the growth of a plant in response to gravity.
- Plants detect light using photoreceptors called phytochromes, which are molecules that absorb light. Pr absorbs red light and Pfr absorbs far red light. Pr is converted into Pfr when eposed to red light and vice versa. Pfr is also converted back into Pr when in darkness, but this is much slower.
- The levels of Pr and Pfr determine things such as growth and flowering times.
- The detection of light in the plant can cause it to bend towards the light. Auxins are hormones that are released in response to light and diffuse to the side of the plant with less light. They can then stimulate cell growth and cause elongation of the side furthest away from the light, causing the plant to bend towards the light, so that it can photosynthesis at a maximum.
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Brain Structure and Function
- The Cerebrum is the largest part of the brain and is divided into two halves called hemispheres. It allows you to thik, see, learn and feel.
- The Hypothalamus controlls body temperature and produces hormones that controll the pituitary gland.
- The Medulla controlls breathing and heart rate and is at the base of the brain.
- The Cerebellum controlls coordination and movement. It has a folded cortex and is under the cerebrum.
- Hubel and Wiesel investigated visual cortex development by stitching the eyes shut of kittens and unstitching a few after several months to see if they developed sight. They discvered that cats have a critical period for sight.
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Drugs and Disease
- Parkinsons is a brain disorder that affects motor skills and is caused by a lack of dopamine in the system. Drugs such as L-Dopa and MDMA can be used to replace the dopamine.
- The Human Genome Project is a long study that identified all of the genes in human DNA. The information is accessible by everyone and is stored on databases. It can be used to target new drugs at specific genes to see what effects they have.
- Genetically modified microorganisms: the gene is located using restriction enzymes and is copied using PCR and is then inserted into a plasmid and transferred into microorganusms that are grown in large containers. The protein can then be purified and used as a drug.
- Genetically modified plants: the gene is located using restrcition enzymes and then amplified using PCR. The gene is then added to a bacterium that infects a plant cell. The plant is then grown and the gene is in ever cell. The protein can be purified from plant tissues.
- Genetically modified animals: the gene is located using a restriction enzyme and is amplified using PCR. The gene is then injected into the nucleus of a fertilised animal egg cell and implated into the mother. Once it has grown into a whole animal the gene is expressed in each cell and the protein can be purified from the milk.
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