Transcript of Aqa A2 Biology Unit 5
Muscle Contraction Homeostasis By Beelal Simreekheea Nerves and Sensory Reception Genetics Taxes is a simple response whose direction is determined by the direction of the stimulus. Taxes are classified according to whether the movement is towards the stimulus (positive taxis) or is moving away (negative taxis) Examples of taxis include phototaxis, chemotaxis and even hydrotaxis Taxes and Kineses both examples of orientation behavior Kinesis is the response in which an organism will increase its random movements to escape an unpleasant surrounding and this can continue until it reaches more favorable conditions where these movements will stop. An examples being wood lice which lose water from their bodies in dry conditions and to prevent that they move more rapidly until they reach an area which is damper than the previous surrounding Tropisms work in the same way as Kinesis and Taxes however it involves plants which are not able to move from one area to another. The plant most likely will grow towards the stimulus i.e. more sunlight in order to provide itself with efficient living conditions. One example of tropism is through a hormonal response as plants do not have a nervous system and therefore rely on growth hormones or plant growth factors such as indoleacetic acid (IIA). Tropism + Kinesis + Taxes Tropism Taxes Kinesis Reflex arc Stimulus Receptor Coordinator/ Relay Neurone Effector Response Muscle or glands are examples of effectors Sensory Nervous SystemA detectable alteration in the internal or external environment of an organism that produces some change in that organism. Examples include a change in temperature or even change in light intensity Sensory neurone Motor Neurone A cell adapted to a change in the environment Pacinian Corpuscle and Rod + Cone Cells Specific to a single type of stimulus i.e. responds to only mechanical pressure Produces a generator potential by acting as a transducer Generator potential is also known as a nerve impulse and is the function of a receptor as it converts stimulus energy into impulses which the body can read. Occurs deep int the skin and are most abundant on the fingers, the soles of the feet and the external genitalia. The sensory neurone ending at the centre of the Pacinian corpuscle has a special type of sodium channel occurring in its plasma membrane Has a stretch-mediated sodium channel In its normal state, the specialized sodium channels around the corpuscle are too small to allow sodium ions through. At this moment the neurone around the Pacinian Corpuscle has a resting potential When pressure is applied to the Pacinian Corpuscle, it changes shape and the membrane around the neurone becomes stretched This stretching widens the sodium channels in the membrane and sodium ions diffuse into the neurone The influx of sodium ions changes the potential of the membrane as it becomes depolarised thereby producing a generator potential. This creates an action potential that passes along the neurone to the CNS. Rod cells cannot differentiate between different wavelengths of light ==> have poor visual acuity However in large quantities in comparison to cone cells Cone cells can differentiate between different wavelengths ==> therefore has a high visual acuity More than one rod cell attached to a single bipolar cell whereas cone cells are each attached to their own bipolar cell. Greater number of rod cells at the periphery of the retina whereas there are more cone cells at the fovea (the part of the retina opposite the pupil) Pigment in rod cells (rhodopsin) is broken down==> has low Ea therefore can be broken down in low light intensityFull transcript
Cone cells contain a pigment (iodopsin) which requires high Ea ==> can only be broken down in high light intensity. Passes the nerve impulse to the coordinator Nervous Organisation Nervous System Peripheral Nervous System CNS Spinal Cord Brain Sensory Nervous System Motor Nervous System Voluntary Nervous System Autonomic Nervous System carries nerve impulses to body muscles and is under conscious control Carries nerve impulses to glands, smooth and cardiac muscle and is an involuntary action Control of Heart Rate Controlled by the autonomic nervous pathway which has two divisions.
These divisions work in antagonistic pairs Parasympathetic Sympathetic Stimulates effectors to speed up activity. Inhibits effectors and therefore slows down any activity Changes to heart rate controlled by medulla oblongata in the brain. It has two centres, one which speeds up activity by increasing SAN impulses and the other decreases activity by doing the opposite