Control and Coordination Grade 12 PDF

Control and Coordination Grade 12 Ms. Fathima Comparing the endocrine system and nervous system  5.1.1 Compare the features of the Lesson Objective nervous system and the endocrine system  Different parts of the body perform different functions, ye...

Control and Coordination Grade 12 Ms. Fathima Comparing the endocrine system and nervous system  5.1.1 Compare the features of the Lesson Objective nervous system and the endocrine system  Different parts of the body perform different functions, yet the body works as one. This is because the body has systems that help coordinate activities such as the regulation of substances and response to stimuli In order to achieve this there are two types of coordination systems in the body  nerves that transmit information in the  chemical messengers (hormones) that are form of electrical impulses. These nerves carried in the blood these hormones and make up the nervous system their network make up the endocrine system  The Endocrine System A hormone is a chemical substance produced by an endocrine gland and carried by the blood They are chemicals which transmit information from one part of the organism to another and bring about a change They alter the activity of one or more specific target organs Hormones are used to control functions that do not need instant responses The endocrine glands that produce hormones in animals are known collectively as the endocrine system A gland is a group of cells that produces and releases one or more substances (a process known as secretion)  The human nervous system consists of the The Nervous System following: Central nervous system (CNS) – the brain and the spinal cord It allows us to make sense of our Peripheral nervous system (PNS) – all of surroundings and respond to them and the nerves in the body to coordinate and regulate body functions Information is sent through the nervous system as nerve impulses – electrical signals that pass along nerve cells known as neurones A bundle of neurones is known as a nerve Neurones coordinate the activities of sensory receptors (eg. those in the eye), decision-making centres in the central nervous system, and effectors such as muscles and glands Nervous communication  5.2.1 Describe the structure and function of a sensory neurone and a Lesson Objective motor neurone and state that intermediate neurones connect sensory neurons and motor neurons.  Neurones There are three main types of neurone: sensory, relay and motor Sensory neurones carry impulses from receptors to the CNS (brain or spinal cord) Intermediate (aka relay) neurones are found entirely within the CNS and connect sensory and motor neurones Motor neurones carry impulses from the CNS to effectors (muscles or glands)  Neurones Each type of neurone has a slightly different structure Motor neurones have: A large cell body at one end, that lies within the spinal cord or brain A nucleus that is always in its cell body Many highly-branched dendrites extend from the cell body, providing a large surface area for the axon terminals of other neurones Sensory neurones have the same basic structure as motor neurones, but have: A cell body that branches off in the middle of the cell - it may be near the source of stimuli or in a swelling of a spinal nerve known as a ganglion  Neurones A neurone has a long fibre known as an axon The axon is insulated by a fatty sheath with small, uninsulated sections along its length (called nodes of Ranvier) The sheath is made of myelin, a substance that is made by specialised cells known as Schwann cells Myelin is made when Schwann cells wrap themselves around the axon along its length This means that the electrical impulse does not travel down the whole axon, but jumps from one node to the next This means that less time is wasted transferring the impulse from one cell to another Their cell bodies contain many extensions called dendrites This means they can connect to many other neurones and receive impulses from them, forming a network for easy communication Motor neurones have a cell body that lies within the brain or spinal cord. Many highly-branched cell processes extend from the cell body. These are called dendrites. Dendrites receive impulses from other neurones and conduct them towards the cell body. A single long axon transmits impulses away from the cell body.  The function of a motor neurone is to transmit impulses from the central nervous system to effector organs, such as muscles or glands. Intermediate neurones (also known as relay or interneurones) have numerous, short fibres. Each fibre is a thread like extension of a nerve cell. Intermediate neurones occur in the central nervous system.  They connect sensory neurones and motor neurones. Sensory neurones have a single long dendron, which brings impulses towards the cell body, and a single axon which carries impulses away from the cell body.  Sensory neurones transmit impulses from receptors to the spinal cord or brain.  5.2.2 Outline the role of sensory Lesson Objective receptor cells in detecting stimuli and stimulating the transmission of impulses in sensory neurons.  Sensory Receptor Cells A cell that responds to a stimulus is called a receptor cell Receptor cells are transducers – they convert energy in one form (such as light, heat or sound) into energy in an electrical impulse within a sensory neurone  Sensory Receptor Cells Receptor cells are often found in sense organs (eg. light receptor cells are found in the eye) Some receptors, such as light receptors in the eye and chemoreceptors in the taste buds, are specialised cells that detect a specific type of stimulus and influence the electrical activity of a sensory neurone Other receptors, such as some kinds of touch receptors, are just the ends of the sensory neurones themselves  Sensory Receptor Cells When receptor cells are stimulated, they are depolarised If the stimulus is very weak, the cells are not sufficiently depolarised and the sensory neurone is not activated to send impulses If the stimulus is strong enough the sensory neurone is activated and transmits impulses to the CNS  5.2.3 Describe the sequence of events that results in an action Lesson Objective potential in a sensory neurone, using a chemoreceptor cell in a human taste bud as an example.  Chemoreceptors Chemoreceptors, specialised sensory receptors in our sense organs, recognise the chemical stimuli by which organisms collect information about their internal and external environments. The senses of taste and smell are the most familiar examples of chemoreception in humans. Humans have approximately 100,000 chemoreceptor cells in taste buds, located on the upper surface of the tongue, soft palate, upper oesophagus and epiglottis. The sense of smell also relies on chemoreceptors located in the nose and these play a crucial role in distinguishing more subtle differences in taste.  Taste buds are composed of a cluster of between 50 and 150 columnar taste receptor cells grouped together a bit like a bunch of bananas. Each taste bud can detect sweet, sour, salty, umami or bitter tastes. Slender processes (microvilli) extend from the outer ends of the receptor cells through the taste pore. At their inner end, each taste receptor cell synapses (connects) with an afferent nerve that transmits information to the brain.  Dissolved chemicals from food enter the taste bud through the taste pore and bind to the receptor cells, causing a change in the shape of the chemoreceptor protein on the cell surface. This change in shape causes chemical-gated sodium channels in the cells to open. There is an influx of sodium ions into the cells This causes the cell membrane to depolarise. This depolarisation is transmitted to the taste neurones, resulting in an action potential that is ultimately transmitted to the medulla oblongata in the brain, where it is recognised as a specific taste. An example of the sequence of events that results in an action potential in a sensory neurone Chemoreceptors in the taste buds that detect salt (sodium chloride) respond directly to sodium ions If salt is present in the food (dissolved in saliva) being eaten: Sodium ions diffuse through highly selective channel proteins in the cell surface membranes of the microvilli of the chemoreceptor cells This leads to the depolarisation of the chemoreceptor cell membrane The increase in positive charge inside the cell is known as the receptor potential If there is sufficient stimulation by sodium ions and sufficient depolarisation of the membrane, the receptor potential becomes large enough to stimulate voltage-gated calcium ion channel proteins to open As a result, calcium ions enter the cytoplasm of the chemoreceptor cell and stimulate exocytosis of vesicles containing neurotransmitters from the basal membrane of the chemoreceptor The neurotransmitter stimulates an action potential in the sensory neurone The sensory neurone then transmits an impulse to the brain  When receptors (such as chemoreceptors) are stimulated, they are depolarised If the stimulus is very weak or below a certain threshold, the receptor cells won’t be sufficiently depolarised and the sensory neurone will not be activated to send impulses If the stimulus is strong enough to increase the receptor potential above the threshold potential then the receptor will stimulate the sensory neurone to send impulses This is an example of the all-or-nothing principle An impulse is only transmitted if the initial stimulus is sufficient to increase the membrane potential above a threshold potential Rather than staying constant, threshold levels in receptors often increase with continued stimulation, so that a greater stimulus is required before impulses are sent along sensory neurones  5.2.4 Describe and explain changes to the membrane potential of neurones, including: how the resting potential is maintained. Lesson Objective the events that occur during an action potential how the resting potential is restored during the refractory period This occurs in the following stages: 1.Resting potential - The membrane is at rest and polarised at around -70 mV. 2.Stimulus - Voltage-gated Na+ channels open, so more Na+ flows into the axon making the inside less negative. 3.Depolarisation - If the threshold potential of around -55 mV is reached, more Na+ channels open causing an influx of Na+. 4.Repolarisation - At around +30 mV, Na+ channels close and K+ channels open, so K+ flows out of the axon and the membrane starts repolarising. 5.Hyperpolarisation - An excess of K+ leaves the axon, dropping the potential below the -70 mV resting level. 6.Refractory period - Various ion pumps and channels work together to restore the membrane back to the resting potential. Transmission of Nerve Impulses Neurones transmit electrical impulses, which travel extremely quickly along the neurone cell surface membrane from one end of the neurone to the other Unlike a normal electric current, these impulses are not a flow of electrons These impulses, known as action potentials, occur via very brief changes in the distribution of electrical charge across the cell surface membrane Action potentials are caused by the rapid movement of sodium ions and potassium ions across the membrane of the axon There are channel proteins in the axon membrane that allow sodium ions or potassium ions to pass through These open and close depending on the electrical potential (or voltage) across the axon membrane and are known as voltage- gated channel proteins (they are closed when the axon membrane is at its resting potential) Resting potential In a resting axon (one that is not transmitting impulses), the inside of the axon always has a slightly negative electrical potential compared to the outside of the axon This potential difference is usually about - 70mV (i.e. the inside of the axon has an electrical potential about 70mV lower than the outside) This is called the resting potential Several factors contribute to maintaining the resting potential:  The all-or-nothing principle Reaching the threshold potential triggers an action potential that proceeds in a uniform, self-propagating fashion - it's an all-or-nothing response. The all-or-nothing principle of action potentials is characterised by: The threshold phenomenon - Once the threshold potential is reached, an action potential is always triggered, regardless of the stimulus' strength. No partial response - Without reaching the threshold potential, no action potential is initiated. Action potentials are always the same size - A stronger stimulus doesn't increase the size of the action potential, but it does increase the frequency of action potentials generated. Action potentials When an action potential is stimulated (eg. by a receptor cell) in a neurone, the following steps occur: Sodium channel proteins in the axon membrane open Sodium ions pass into the axon down the electrochemical gradient (there is a greater concentration of sodium ions outside the axon than inside. The inside of the axon is negatively charged, attracting the positively charged sodium ions) This reduces the potential difference across the axon membrane as the inside of the axon becomes less negative – a process known as depolarisation This triggers voltage-gated sodium channels to open, allowing more sodium ions to enter and causing more depolarisation  This is an example of positive feedback (a small initial depolarisation leads to greater and greater levels of depolarisation) If the potential difference reaches around -50mV (known as the threshold value), many more channels open and many more sodium ions enter causing the inside of the axon to reach a potential of around +30mV An action potential is generated The depolarisation of the membrane at the site of the first action potential causes current to flow to the next section of the axon membrane, depolarising it and causing sodium ion voltage-gated channel proteins to open The 'flow' of current is caused by the diffusion of sodium ions along the axon from an area of high concentration to an area of low concentration This triggers the production of another action potential in this section of the axon membrane and the process continues In the body, this allows action potentials to begin at one end of an axon and then pass along the entire length of the axon membrane  Repolarisation and the Refractory Period Very shortly (about 1 ms) after an action potential in a section of axon membrane is generated, all the sodium ion voltage-gated channel proteins in this section close, stopping any further sodium ions diffusing into the axon Potassium ion voltage-gated channel proteins in this section of axon membrane now open, allowing the diffusion of potassium ions out of the axon, down their concentration gradient This returns the potential difference to normal (about -70mV) – a process known as repolarisation There is actually a short period of hyperpolarisation This is when the potential difference across this section of the axon membrane briefly becomes more negative than the normal resting potential The potassium ion voltage-gated channel proteins then close and the sodium ion channel proteins in this section of the membrane become responsive to depolarisation again Until this occurs, this section of the axon membrane is in a period of recovery and is unresponsive This is known as the refractory period  During the refractory period, a section of the axon is unresponsive. This is very important as it ensures that ‘new’ action potentials are generated after, rather than before or during the original action potential. This makes the action potentials discrete events and means the impulse can only travel in one direction. This is essential for the successful and efficient transmission of nerve impulses along neurones.  5.2.5 Describe and explain the rapid transmission of an impulse in a Lesson Objective myelinated neurone with reference to saltatory conduction.  Speed of Conduction of Impulses The speed of conduction of an impulse refers to how quickly the impulse is transmitted along a neurone It is determined by two main factors: the presence or absence of myelin (ie. whether or not the axon is insulated by a myelin sheath) the diameter of the axon  Myelination In unmyelinated neurones, the speed of conduction is very slow By insulating the axon membrane, the presence of myelin increases the speed at which action potentials can travel along the neurone: In sections of the axon that are surrounded by a myelin sheath, depolarisation (and the action potentials that this would lead to) cannot occur, as the myelin sheath stops the diffusion of sodium ions and potassium ions Action potentials can only occur at the nodes of Ranvier (small uninsulated sections of the axon) The local circuits of current that trigger depolarisation in the next section of the axon membrane exist between the nodes of Ranvier This means the action potentials ‘jump’ from one node to the next This is known as saltatory conduction This allows the impulse to travel much faster (up to 50 times faster) than in an unmyelinated axon of the same diameter  5.2.6 Explain the importance of the Lesson Objective refractory period in determining the frequency of impulses  Summary: The refractory period After a neurone fires an action potential, it enters a recovery phase known as the refractory period. During the refractory period, the neurone's membrane can't generate another action potential. This is because sodium ion (Na+) channels remain closed during repolarisation, preventing depolarisation. The refractory period's essential roles include: Ensuring action potentials don't overlap. Limiting the frequency at which impulses are transmitted. Guaranteeing that impulses travel in only one direction. The refractory period is therefore crucial for transmitting nerve impulses as distinct signals. This also means there is a minimum time between action potentials occurring at any one place along a neurone The length of the refractory period is key in determining the maximum frequency at which impulses can be transmitted along neurones (between 500 and 1000 per second)  5.2.7 Describe the structure of a Lesson Objective cholinergic synapse and explain how it functions, including the role of calcium ions.  Cholinergic Synapses Where two neurones meet, they do not actually come into physical contact with each other A very small gap, known as the synaptic cleft, separates them The ends of the two neurones, along with the synaptic cleft, form a synapse  Synapse structure The key structures in a synapse include: 1.Presynaptic neurone - This neurone releases neurotransmitters into the synapse. 2.Synaptic knob - The section at the end of the presynaptic neurone that contains the organelles needed for neurotransmitter production, like mitochondria to release energy. 3.Synaptic vesicles - These sacs within the synaptic knob store neurotransmitters until they are released. 4.Synaptic cleft - The gap between the presynaptic and postsynaptic neurones' membranes. 5.Postsynaptic neurone - This neurone receives the neurotransmitters and can generate new action potentials. 6.Neurotransmitter receptors - These specific molecules on the postsynaptic membrane bind with the neurotransmitters.  Synaptic transmission – basic mechanism Electrical impulses cannot ‘jump’ across synapses When an electrical impulse arrives at the end of the axon on the presynaptic neurone, chemical messengers called neurotransmitters are released from vesicles at the presynaptic membrane The neurotransmitters diffuse across the synaptic cleft and bind temporarily with receptor molecules on the postsynaptic membrane This stimulates the postsynaptic neurone to generate an electrical impulse that then travels down the axon of the postsynaptic neurone The neurotransmitters are then destroyed or recycled to prevent continued stimulation of the second neurone, which could cause repeated impulses to be sent Cholinergic synapses and the role of acetylcholine Cholinergic synapses are specific types of synapses that use acetylcholine (ACh) as their neurotransmitter. After ACh binds to receptors and triggers a response: 1.ACh is broken down by the enzyme acetylcholinesterase into choline and ethanoic acid (acetate). 2.These breakdown products are then reabsorbed into the presynaptic knob via active transport. 3.They can then be recycled to synthesise more ACh. 4.ACh is transported into synaptic vesicles, ready for another action potential. It is important to remove neurotransmitters like ACh from the synaptic cleft to prevent the stimulus from being maintained and to allow another stimulus to affect the synapse. This prevents continuous stimulation and allows for neurotransmitter recycling. Muscle contraction  5.3.1 Describe the ultrastructure of striated muscle with reference to Lesson Objective sarcomere structure using electron micrographs and diagrams.  Striated muscle Striated muscle makes up the muscles in the body that are attached to the skeleton 'Striated' means it is striped/streaky in appearance Striated muscle is made up of muscle fibres A muscle fibre is a highly specialised cell-like unit: Each muscle fibre contains an organised arrangement of contractile proteins in the cytoplasm Each muscle fibre is surrounded by a cell surface membrane Each muscle fibre contains many nuclei – this is why muscle fibres are not usually referred to as cells Structure of striated muscle The different parts of a muscle fibre have different names from the equivalent parts of a normal cell:  Cell surface membrane = sarcolemma  Cytoplasm = sarcoplasm  Endoplasmic reticulum = sarcoplasmic reticulum (SR) The sarcolemma has many deep tube-like projections that fold in from its outer surface:  These are known as transverse system tubules or T- tubules  These run close to the SR The sarcoplasm contains mitochondria and myofibrils  The mitochondria carry out aerobic respiration to generate the ATP required for muscle contraction  Myofibrils are bundles of actin and myosin filaments, which slide past each other during muscle contraction The membranes of the SR contain protein pumps that transport calcium ions into the lumen of the SR Myofibrils Myofibrils are located in the sarcoplasm Each myofibril is made up of two types of protein filament: Thick filaments made of myosin Thin filaments made of actin These two types of filament are arranged in a particular order, creating different types of band and line  The striped appearance of skeletal muscle is due to an interlocking arrangement of the two types of protein filaments, known respectively as thick and thin filaments – they make up the myofibrils. These protein filaments are aligned, giving the appearance of stripes (alternating light and dark bands). This can be seen in highly magnified electron micrographs  5.3.2 Explain the sliding filament Lesson Objective model of muscular contraction including the roles of troponin, tropomyosin, calcium ions and ATP.  Structure of thick & thin filaments in a myofibril The thick filaments within a myofibril are made up of myosin molecules These are fibrous protein molecules with a globular head The fibrous part of the myosin molecule anchors the molecule into the thick filament In the thick filament, many myosin molecules lie next to each other with their globular heads all pointing away from the M line The thin filaments within a myofibril are made up of actin molecules These are globular protein molecules Many actin molecules link together to form a chain Two actin chains twist together to form one thin filament A fibrous protein known as tropomyosin is twisted around the two actin chains Another protein known as troponin is attached to the actin chains at regular intervals  The sliding filament model Muscles cause movement by contracting During muscle contraction, sarcomeres within myofibrils shorten as the Z discs are pulled closer together This is known as the sliding filament model of muscle contraction An action potential arrives at the neuromuscular junction Calcium ions are released from the sarcoplasmic reticulum (SR) Calcium ions bind to troponin molecules, stimulating them to change shape This causes troponin and tropomyosin proteins to change position on the actin (thin) filaments Myosin binding sites are exposed on the actin molecules The globular heads of the myosin molecules bind with these sites, forming cross-bridges between the two types of filament The myosin heads move and pull the actin filaments towards the centre of the sarcomere, causing the muscle to contract a very small distance ATP hydrolysis occurs at the myosin heads, providing the energy required for the myosin heads to release the actin filaments  The myosin heads move back to their original positions and bind to new binding sites on the actin filaments, closer to the Z disc The myosin heads move again, pulling the actin filaments even closer to the centre of the sarcomere, causing the sarcomere to shorten once more and pulling the Z discs closer together The myosin heads hydrolyse ATP once more in order to detach again As long as troponin and tropomyosin are not blocking the myosin-binding sites and the muscle has a supply of ATP, this process repeats until the muscle is fully contracted Control and Co-ordination in Plants  5.4.1 Explain the role of auxin in Lesson Objective elongation growth by stimulating proton pumping to acidify cell walls.  The Role of Auxin in Elongation Growth Plant hormones (also known as plant growth regulators) are responsible for most communication within plants Auxins are a type of plant growth regulator that influence many aspects of growth, including elongation growth which determines the overall length of roots and shoots The principle chemical in the group of auxins made by plants is IAA (indole 3-acetic acid) and this chemical is often simply referred to as ‘auxin’ Auxins are a class of plant hormones that regulate growth in plants Auxin (IAA) is synthesised in the growing tips of roots and shoots (ie. in the meristems, where cells are dividing) Growth in these meristems occurs in three stages: Cell division by mitosis Cell elongation by absorption of water Cell differentiation Auxin (IAA) is involved in controlling growth by elongation  Controlling growth by elongation Auxin molecules bind to a receptor protein on the cell surface membrane Auxin stimulates ATPase proton pumps to pump hydrogen ions from the cytoplasm into the cell wall (across the cell surface membrane) This acidifies the cell wall (lowers the pH of the cell wall) This activates proteins known as expansins, which loosen the bonds between cellulose microfibrils At the same time, potassium ion channels are stimulated to open This leads to an increase in potassium ion concentration in the cytoplasm, which decreases the water potential of the cytoplasm This causes the cell to absorb water by osmosis (water enters the cell through aquaporins) This increases the internal pressure of the cell, causing the cell wall to stretch (made possible by expansin proteins) The cell elongates