6 Organisms respond to changes in their environments

• The nervous system is made up of the central nervous system (CNS) and peripheral nervous system (PNS).
• Gravitropism


  Plants respond to gravity by growing either upwards or downwards
• Organisms increase their chance of survival by responding to changes in the environment
• Stimulus is a detectable change in the environment
• IAA (Indole-3-acetic acid)

  A type of auxin that controls cell elongation in plants
• Receptors


  Cells that can detect changes in the environment
• Phototropism


  Plants respond to light by growing towards the light source
• Reflex is an example of a rapid auto...
• Tropism

  1. Plants respond to their surroundings via growth

  2. Tropisms can be positive (towards the stimulus) or negative (away from the stimulus)
• Gravitropism


  Root moves to the lower side causing the upper side to elongate and the root to bend down towards gravity, resulting in positive gravitropism which increases survival by anchoring the plant
• Taxes


  Organism moves towards a favorable stimulus or away from an unfavorable stimulus
• Receptors

  • Pacinian corpuscles
  • Rods
  • Cones
• Rods

  Photoreceptors in the eye that process images in black and white, detect light at low intensities, providing low visual acuity
• Kinesis

  Organism changes speed of movement and direction to stay within favorable conditions
• Reflex arc

  Consists of three neurons: sensory neuron, relay neuron, and motor neuron, with only two synapses, leading to a rapid response
• Simple responses

  • Taxes
  • Kinesis
• Pacinian corpuscles

  Pressure receptors found deep in the skin, detecting changes in pressure
• A reflex is a rapid automatic response to protect animals from danger
• Receptors are cells that detect changes in the environment or stimuli, responding to specific stimuli and leading to action potentials
• Taxes

  • Earthworm moving away from light (negative phototaxis)
• Cones


  Photoreceptors in the eye that process color images, providing high visual acuity
• Proportion of cone cells detecting a stimulus determines the colors perceived in vision
• Photoreceptor cells


  Cells responsible for detecting light
• Non-conductive tissue separating atria and ventricles


  Prevents direct depolarization transmission, directs wave through Bundle of His and Purkinje fibers
• Cardiac muscle is myogenic, contracting and relaxing independently, but the speed of contraction is controlled by the nervous system
• Nervous system involvement in heart rate control

  Medulla oblongata in the brain controls heart rate through the autonomic nervous system
• Cardiac cycle

  Initiated by SAN releasing depolarization wave, causing atria to contract first, followed by AVN releasing another wave, leading to ventricular contraction
• Total utility is the sum of marginal utility for each unit consumed
• Cone cells are photoreceptor cells containing three types of iodopsin pigment for red, green, and blue, absorbing different wavelengths of light
• At night time, vision is limited due to the absence of adequate light sources, resulting in reduced clarity and the ability to see only in black and white
• Iodopsin is broken down only in high light intensity, allowing color vision
• Wave of depolarization reaching AVN


  Causes release of another wave, leading to ventricular contraction
• Parts involved in controlling heart rate

  • Sinoatrial node (SAN)
  • Atrioventricular node (AVN)
  • Bundle of His
  • Purkinje fibers
• Contraction sequence of ventricles

  Starts from apex and moves upwards, aiding in efficient blood ejection
• Changes in blood pH are detected by chemoreceptors, changes in blood pressure are detected by pressure receptors, both found in the walls of the aorta and carotid artery
• Stimuli affecting heart rate

  pH and blood pressure
• Increased heart rate helps remove acidic compounds by allowing dissolved carbon dioxide to reach the lungs faster for exhalation
• Low blood pressure may result in insufficient oxygenated blood supply to cells, increasing heart rate helps counteract this
• Resting potential inside the axon is -70 millivolts, maintained by sodium-potassium active transport pump which pumps potassium ions in and sodium ions out, creating an electrochemical gradient
• High respiratory rate can decrease blood pH due to excess carbon dioxide from aerobic respiration or lactic acid from anaerobic respiration, which can denature enzymes