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Chapter – 13 Co-ordination and response Key Words: Stimuli: Change in the organism’s environment which is sensed by special cells called neurons or receptors. Eg. Sensory receptors or sensory neuron Sensed Information is passed to the effectors. Effectors are muscles or glands Involuntary actions: Not under conscious control, because the impulses are transmitted faster, without thinking. Eg. Blinking of eyes Voluntary action: Is something that you do consciously eg. Reading book Synapse: A junction between tow nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter Gravitropism: - A response in which a plant grows towards or away from gravity Phototropism: - A response in which a plant grows towards or away from the direction from which light is coming 1 Co-ordination is between the effectors and receptors There are two ways of sending information from receptors to effectors Nervous system Endocrine system There are two organ system which continuously work to detect and respond to stimuli Nervous system: Impulses passed through nerves at a faster rate and the impulses are electrical impulses Endocrine system: the impulses are chemicals (Hormones) carried through the blood but transmitted slowly (hormones secreted in to blood directly) CNS: Brain and spinal cord (orders other part of the body to perform certain job) PNS: Nerves and receptors- Main job is to detect stimuli and send impulses to CNS according to stimuli Neurons: (Nerve cells) Neurons act as wires to transmit electrical impulses all over the body. Bundle of neurons is called nerve 2 There are three types of neurons: Sensory Neuron: Take electrical impulses from sensory receptors Relay Neuron: Located at the CNS, Take impulse from sensory neuron to motor neuron and even send to brain 3 Motor neuron: transmit electrical impulses from CNS to effectors. Neurons have three basic parts like specialized cells. Nucleus , Cytoplasm , Cell Membrane In the neuron they long thin fibers stretching from the cell body. Dendrons/Dentrites (Short fibers): Pick nerve impulses from other neuron to the cell body then passed it to the axon. Axon: It’s the longest fiber one meter long, Axon passes impulses to other neuron. Axon is covered with Myelin Sheath this is made of fat and proteins. Insulates nerve fibre. Carry these impulses much faster. 4 Reflex Arc : The pathway along which the nerve impulses passes. Sensory neuron. Relay neuron. Motor neuron. Reflex action: Hand touches heat. Sensory receptor senses. Send electrical impulses through sensory neuron. Relay neuron. Relay neuron passes impulses to motor neurons and to the brain. The Motor neuron takes the impulses to the effectors Reflex action: Voluntary and Involuntary Involuntary actions, not under conscious control, because the impulses are transmitted faster, without thinking. Eg. Blinking of eyes Voluntary action is something that you do consciously eg. Reading book 5 6 Synapses: Junction between two nerve cells where impulses pass by diffusion Inside a sensory neuron an axon contain hundreds of tiny vacuoles These contain chemical substances called neurotransmitter When an impulse arrives along the axon of the sensory neuron It causes the vesicle to move to the membrane and empty their content to synaptic cleft Neurotransmitter quickly diffuses across the tiny gap Attaches the receptor molecules in the cell membrane of relay neuron Neurotransmitter binds to the receptors Triggers the nerve impulses in the relay neuron Till it reaches the next synapse Similar process across to transmit the impulse to the motor neuron 7 Synaptic cleft: In the reflex arc the three neurons involved in it is not connected with each other this gap between them are called as synaptic cleft 8 Co-ordination and response in plants Plants have the ability to detect stimulus Respond (Tropism) By growing or bending In the direction or away from the direction Phototropism: Response of a plant to grow towards or away from light Geotropism/Gravitropism: Response of a plant to grow toward or away from gravity Towards the direction of stimulus positive response Away from the direction of stimulus Negative response Auxin: Tropisms are controlled by a chemical called Auxin Plant Hormone Produced at the tip of the shoot Diffuses downwards 9 Role in phototropism: When sun shines on the right side of the plant shoot Auxin deposits on the opposite side (Left side) Makes the cells on the left side to grow faster than the right side The shoot will bend towards the sun light Role in Geotropism/Gravitropism: Auxin settles at the end of the root Dose not allow the tip of the root grow longer Allows the cells at the middle of the root grow faster This pushes the root deeper to the soil Root gets longer Grows in the direction of gravitational pull Roots: Positive geotropism/gravitropism Negative phototropism Shoot: Positive phototropism Negative geotropism 10 Experiment: 1 1. Tip of coleoptiles is cut and replaced Still grows towards the light Auxin diffuses downwards 2. Tip of coleoptiles is cut and separated by a piece of agar Still grows towards light Auxin diffuses downwards 3. Tip of coleoptiles is cut and separated by a piece of Mica Dose not grows towards light Auxin cannot diffuse through mica Result: The response to light is caused by diffusion of substance made at the tip 11 Experiment: 2 Response to gravity in a coleus shoot The stem is kept in horizontal position in the dark Auxin tends to collect on the lower side of the stem This causes faster growth Curves up away from gravity Because there is no light 12