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Plant & Animal Responses

Plant and Animal Responses 

 

  • Differences between parasympathetic (PS) and sympathetic (S) nervous system 

    • PS has very few nerves leading out of the CNS while S has numeros leading separate effectors

    • Ganglia in the S nervous system in just prior to the CNS while PS ganglia are in the effector tissue 

    • Short preganglionic neuron and long post ganglionic in the S system and Long preganglionic and short postganglionic in the PS system

    • The neurotransmitter differs: Noradrenaline is used as a neurotransmitter in the S system while in the PS acetylcholine is used instead 

    • S acts to increase heart rate and dilate pupils etc as ‘fight or flight’ but PS acts as a relaxer to decrease etc. thus antagonistic 

  • Structure: Initial into CNS and PNS then PNS divides to give the motor and sensory neurons and the the motor divides to give Somatic and Autonomic and Autonomic dived to give Sympathetic and Parasympathetic 

  • Brain: 

 

  • Cerebrum: Largest and organises higher thought processes (memory, conscious). 2 hemispheres connected via the corpus callosum. The outer layer is the cerebral cortex and is made of nerve cell bodies 

    • Divided into sensory areas which receive input from a variety of sensory receptors indirectly as well as the association area which compares inputs which previous experience to determine what an input may be. Additionally there are motor areas which are where there may be action potentials generated to send to various effector muscles

    • Parietal Lobe: Processing touch, pain as well as the sense of limb positions 

    • Temporal Lobe: Understanding language, memory facial recognition and visual perception

    • Occipital Lobe: Visuospatial and distance and depth perception

    • Frontal Lobe: Higher level function, social understanding and expression language 

  • Cerebellum: Coordinates movement and balance. It contains over half the neurons of the brain and it is involved with balance and fine coordination of movement and as such it receives information from numerous receptors in order to process information accurately. Fine movements include balance when riding a bike etc, as well as judging the position of objects relative to other objects, tension of fine muscles in order to use a tool etc.It is also responsible for the coordination of antagonistic muscles when walking 

    • These actions require learning and once learnt the connections are built into the pons and enable action and movement easily and are subconscious  

  • Hypothalamus and Pituitary Complex: which organises homeostatic responses and controls physiological processes. Acts by negative feedback and contains its own sensory receptors and acts by negative feedback to maintain a constant internal environment (hypothalamus sits just above the pituitary gland)

    • Vital for regulation of temperature as the hypothalamus will detect changes in core temperature and it will receive sensory input from temperature receptors in the skin and will then initiate responses to regulate or mitigate these changes and thick can occur either though hormonal or nervous system 

    • It is also vital for osmoregulation, the hypothalamus will contain osmoreceptors that monitor the water potential in the blood. When the osmoregulatory centre initiates a response that brings a reversal of the change. The response will be mediated by the hormonal system 

    • Pituitary gland (PG) acts in conjunction with the hypothalamus. PG consists fo 2 lobes 

      • Posterior Lobe is connected to the hypothalamus by specialised neurosecretory cells. Hormones such as ADH are manufactured in the hypothalamus and pass down the neurosecretory cells and they then release the given hormone into the blood 

      • Anterior Lobe produces hormones itself, these are released into the blood in response to releasing factors produced by the hypothalamus. These releasing factors are hormones that need to be transported a short distance from the hypothalamus. Anterior pituitary gland hormones control responses to stress, growth, reproduction and lactation

  • Medulla Oblongata: coordinates many of the autonomic responses. Controls non-skeletal muscles by sending action potentials out through the autonomic nervous system and contains centres for regulating the vital processes such as the cardiac centre for heart rate as well as the vasomotor centre for circulation and blood pressure and the respiratory centre for control fo depth of breathing 

  • Reflexes: Example Specific cases 

    • Blinking: Example of a cranial reflex but is a direct process that does not require any processes of the higher brain. Also known as the corneal reflex, sensory neuron from the cornea enters the pons, there is then a synapse which connects this neuron to a relay neuron and then again to a motor neuron and this action potential will then pass to a motor neuron which will pass out of the brian to the facial muscle and stimulate the eyelid to blink. 

      • Overriding: the sensory neuron will als carry the action potential to myelinated neurons in the pons, these neurons carry the action potential to the sensory region of the brain to inform higher centres that the stimulus has occurred which allows the reflex to be overridden by conscious control as the higher brain can send inhibitory signals to the motor centre in the pons 

    • Knee Jerk reflex: Example of a spinal reflex, muscle spindles will detect the increase in muscle length and if unexpected then will act as a stimulus and trigger sensory neuron triggering action potential directly to a motor neuron. Cannot be inhibited as no relay. 

  • Responses: 

    • Fight or Flight: Pupils may dilate, Heart rate and blood pressure can increase, arterioles to the muscle and liver are dilated and blood glucose levels will increase. Hairs will stand up on the surface of the skin and ventilation rate and depth increases as well as Endorphins being released to prevent the 

    • This occurs as inputs feed into sensory receptors in the cerebrum and the cerebrum passes signals to the association centres. The cerebrum stimulates the hypothalamus and increases activity in the sympathetic nervous system and stimulates the release of hormones such as adrenaline from the pituitary gland 

  • Mechanism of Adrenaline action: 

    • Adrenaline binds to a receptor on the plasma membrane. 

    • This receptor is associated with a G protein on the inner surface of the plasma membrane and thus stimulates adenyl cyclase 

    • Adenyl cyclase converts ATP to cyclic AMP (cAMP) which is the second messenger inside the cell 

    • cAMP causes an effect inside the cell by activating enzyme action and an enzyme cascade though the exact final effect is dependent upon the cell that the adrenaline binds to 

  • Hormones of Pituitary: 

    • Corticotropin-releasing hormone from the hypothalamus causes the release of adrenocorticotropic hormone. The ATCH passes around the blood and stimulates the adrenal cortex to release corticosteroid hormones such as glucocorticoids which regulate carbohydrate metabolism

    • Thyrotropin-releasing hormone causes a release of thyroid-stimulating hormone which stimulates the thyroid gland to release more thyroxine which acts to increase metabolic rate.

  • Heart Rate Regulation: 

    • Heart rate is controlled by the SAN which has a set frequency carrying from person to person and this can be varied by the cardiovascular centre in the medulla oblongata. 

    • Nerves from the medulla oblongata supply the SAN and these are part of the autonomic nervous systems and these initiate a contraction 

    • Action potentials are sent down a sympathetic nerve of the Accelerans nerve causing the release of the neurotransmitter noradrenaline at the SAN causing an increase in heart rate 

    • Action potentials can be sent down the vagus nerve to release acetylcholine which acts to reduce the heart rate 

    • The receptors vary:

      • Some can be stretch receptors which detect the movement of limbs and send impulses to the cardiovascular centre informing it that more O2 may be needed soon leading to an increase in heart rate

      • Chemoreceptors in the carotid arteries as well as the brain and aorta monitor blood pH as when there is exercise there is more carbon dioxide produced increasing the carbonic acid level of the blood which reduced blood pH and as a result pH change is detected by the chemoreceptors which causes the cardiac centre to increase the heart rate to remove CO2 from blood 

      • Stretch receptors in the walls of the carotid sinus also monitors blood pressure and an increase ijn blood pressure during exercise etc. will reduce the heart rate to lower blood pressure 

 

Muscle: 

  • 3 types 

    • Involuntary (smooth) muscle made of numerous individual cells which are tapered at each end and contain a nucleus as well as bundles of actin and myosin

    • Cardiac with individual cells forming long fibres which branch to form cross bridges between fibres. Joined by intercalated discs which is probably the best thing to look out for on a scan if you are given an identification based question. Is the only muscle that rarely will fatigue if at all.

    • Voluntary (skeletal or striated) muscle is the muscle at joints in the skeleton and the muscle that contracts to innovate the skeleton. Muscles are found in antagonistic pairs which assure that when one contracts the other will elongate etc. Each is multinucleated as this provides the ATP 

    • And is surrounded by sarcolemma. Appears in a patterned arrangement.

 

 

  • Structures:

    • Distance between two Z lines is a sarcomere 

    • Muscle cell cytoplasm is called the sarcoplasm 

      • A Band: The entire myosin filament length including the slight crossover with the actin (THINK: A - Ammi - all myosin myofilament) 

      • H Zone: The length of the entire myosin filament excluding the overlapping region with the actin 

      • I Band: All of the actin filament excluding the cross over region with the myosin. 

      • Z line: The centre of the actin myofilament, the region holding this together 

    • In a contraction the H Zone size decreases and the I band size decreases as the Z line is brought closer to the Myosin

  • ATP: 

    • Part of the myosin head can hydrolyse ATP (using ATPase?) into ADP and an inorganic Phosphate which releases energy 

    • This provides the energy for the myosin head to move and form a cross bridge with the actin filament 

    • There is an initial movement (after the binding of the myosin head to the actin), power stroke, where the myosin head tilts backwards and the actin filament is thus pushed/pulled further closer to the Z line. 

    • Another ATP molecule will be used to break the cross bridge and then the ATP will again be hydrolysed such that it binds to the open binding site on the actin (this site is different to the original the filament moved along) 

  • ATP supply must be maintained: 

    • Aerobic respiration and Bohr effect so more oxygen in heavily respiring tissue 

    • Anaerobic respiration in the sarcoplasm of the muscle tissue which releases slightly more ATP 

    • Creatine phosphate stores, in the sarcoplasm they act as a reserve tore of phosphate groups which can be transferred from the creatine phosphate to ATP molecules which creates ATP rapidly this uses the enzyme creatine phosphotransferase and this supports muscular contraction for slightly longer.

 

Contraction: Neuromuscular Junction 

  • Contraction stimulates by somatic for skeletal muscle

  • Acts differently from the synapse in between neurons 

  • Stimulation:

    • An action potential arriving at the presynaptic bulb stimulates voltage gated calcium ion channels to open 

    • This stimulates calcium ions rapidly diffusion from high to low concentration gradient via the voltage gated calcium ion channels 

    • This then stimulates the movement of vesicles of acetylcholine towards the axon presynaptic membranes and then release via exocytosis into the synapse 

    • Acetylcholine then diffuses across the synapse and binds with the receptors of the sarcolemma 

    • This stimulates the opening of sodium ion channels in the muscle in order to to allow sodium ions to diffuse into the muscle which leads to a depolarisation of the membrane/sarcolemma

    • A wave of depolarisation then spreads across the sarcolemma down transverse tubules (T-tubules) 

    • The action potential then travels to the sarcoplasmic reticulum which stores calcium ions. 

    • The action potential stimulates the release of calcium ions into the sarcoplasm 

    • These calcium ions then bind to troponin and this stimulates a conformational change which leads to the tropomyosin being pulled aside 

      • The tropomyosin would be covering the binding sites of the actin filament 

    • As the actin binding sites are exposed the myosin heads bind to the actin, forming cross bridges in the process, pull the actin filament past the myosin filament 

    • Millions of cross bridges are formed between the actin and myosin. Once the contraction occurs the calcium ions are transported back to the sarcoplasmic reticulum allowing the muscle to relax

 

Plant Responses: 

  • Types of Responses: known as tropisms (directional growth response) or nastic responses (non directional such as the mimosa which fold upon being touched) 

  • CHEMICAL DEFENCES:

    • Tannins - toxic chemicals in which can be found in the upper epidermis of the leave and make the leaves taste bad. They can also be in the roots to prevent infiltration

    • Alkaloids - derived from amino acids they are feeding deterrent as they taste bitter and can be located in growing tips and flowers and peripheral cell layers stems and roots 

    • Pheromones affect the behaviour or physiology of another plant 

  • Chemotropism: a directional growth response stimulated by a chemical stimulus located outside of the organism 

  • Thigmotropism: based on sensation an example is shoots climbing up plants or objects such as ivy 

  • A response in the direction of the stimulus is positive (and vice versa) 

  • Equally there is thigmonasty which is the response to touch in a non-directional manner 

  • A nastic response is one that is non-directional 

  • Hormones are key for the regulation of the expression of these responses : 

    • Cytokinins: promote cell division and cell expansion and can act to overcome apical dominance and delay leaf senescence 

    • Abscisic Acid: Inhibits seed germination and growth and causes stomatal closure when there is water stress, and causes leaf abscission 

    • Auxins: Promote cell elongation and inhibit the growth of side-shoots as well as preventing leaf abscission also promote PARTHENOCARPY (seedless fruit growth) 

    • Gibberellins: Promote seed germination and stem growth, delay senescence in citrus fruits

    • Ethene: Promotes fruit ripening - also weakens the cell walls and promotes leaf abscission

  • C) When the tip of a plant is cut, lateral buds soon begin to grow. As a result Scientists assumed that the logical explanation is that auxin present in the buds inhibits lateral growth if these buds and thus upon auxin concentration decreasing the lateral buds are able to grow: they tested this by adding a auxin paste around the lateral bud heads and they did not grow, but then they questioned whether perhaps upon the shoot site being open to o2 a different hormone were produced to enable the bud lateral bud to grow as a result a inhibiting ring was placed on the shoot and the buds still grew. As a result scientists concluded normal or high auxin levels inhibit the growth of a  the buds while low auxin levels promote the growth 

  • Now they feel other hormones such as Abscicic acid and cytokines amy also play a role 

  • D) Gibberellins: responsible for stem elongation and seed germination. Stem elongation. Tested by applying gibberellic acid to many dwarf plants and they grew taller, however just because they can does not mean that they do in nature. Compared the levels of Gibberellic acid in tall pea plants and dwarf pea plants and found that in the taller plants there was  a greater concentration of Gibberellin. They still had to show that it was the Gibberellin which directly caused the growth. Thus they chose  a pea plant with a mutation that blocks gibberellin production and they only grew to 1 cm they then took a cutting and used GA to attempt to grow it tall and did thus proving that GA caused growth 

  • They also promote seed germination as wehen the seed absorbs water gibberellin release is stimulated which travels to the aleurone layer in the endosperm. Here the gibberellin enables the production of amylase which breaks down starch to glucose which provides a respiratory substrate for glucose and so it grows 

  • NOTE: meristematic tissue sites are the only places where plant growth is feasible as the cell wall otherwise prevents this from occurring

  • Experiments: 

    • Photo and geotropism 

      • Photo: Control and test control has light from all aspects and test has unidirectional light leav for several days observe diff 

      • Geo Use a klinostat which is slowly rotating and have the control rotate at a constant speed and the test switched off with te shoot horizontal view after a few days test will have root directed down and the control will be equally distributed 

      • To investigate auxin on shoots etc 

        • A control was used with unidirectional light and left for a few days 

        • The tip was removed and left for a few days with unidirectional light

        • The tip was covered by an opaque cap with unidirectional light

        • The tip was covered with a transparent cap with unidirectional light

        • The base was covered with an opaque shield 

        • ^^ all conducted by Darwin 

        • Boysen-Jensen then 

        • Separated the tip and stem with a gelatin block and then a mica block the mica block was impermeable 

        • Results showed that when the tip was exposed to light and present it bent toward it and the latter 2 experiments showed that when separated with gelatin it still bent but when separated with impermeable mica it did not so something must be diffusing 

        • Went then carried out the practical using blocks with and without auxin and found that when auxin was present it stimulated growth and if only half a block was used it stimulated a bend to the side that it was not placed on equally for blocks with no auxin no growth was seen 

        • Diff auxin concs can also be tested 

        • Equally auxin has the inverse effect in the roots as it stimulates growth downard and has a role in the positive geotropic response as it inhibits cell elongation on the lower side of the root and thus causes a downward bend as due to gravity it will fall to the side of the root furthest down 

  • Commercial Uses: 

    • Auxin: Can be used to prevent leaf and fruit drop and to promote flowering for commercial production (if in high conc will promote fruit drop so low is used) Auxin can also be used with cuttings and the end may be dipped in rooting powder before planting to encourage growth. It can be used for seedless fruit as auxin will promote ovule growth which can lead to a the product being seedless (must be unpollinated flowers). Also can be used as herbicides in order to stimulate shoot growth at an increased rate such that the plant cannot support itself and so dies 

    • Cytokinins: Can be used in preventing yellowing of lettuce leaves after being picked as they are used to delay leaf senescence. They can also be used in tissue culture to promote bud and shoot growth with many side branches. Which can be cut and taken as cuttings and grown separately 

    • Gibberellins: 

      • Fruit: act to delay senescence in citrus fruit and this extends the time they can be left unpicked. They can also be used with cytokines to extend a fruit and improve shape. They are also used in grapes and other fruit grown in bunches to make the stem longer such that they are les compact and the individual fruits grow longer 

      • Brewing: The addition of gibberellins can increase the speed of barley seed germination and thus the generation of malt that is required in order to make beer

      • Sugar Production: spraying gibberellins between the nodes of sugar canes can increase the amount of sugar available as the sugar is often stored in the internodes.

      • Plant breeding: In order to produce plants with favourable characteristics gibberellins can be used on conifer plants to encourage the formation of a seed earlier as otherwise they traditionally mature late and are not reproductively active for a long time. Additionally using gibberellin inhibitors in some plants can be useful for short stocky plant to prevent lodging etc. 

      • Ethene: As a gas can be sprayed in solution as 2-chloroethylphosphonic acid which can be added and this then slowly releases ethene in the plant. This can speed up fruit ripening in apples, citrus fruits or tomatoes as well as promoting fruit drop in numerous fruits. Promoting female expression in cucumbers to reduce the risk of self-pollination as well as promoting lateral growth in some plants. In addition restricting ethene synthesis and thus preventing ripening is vital in transport of fruit etc. 

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