14 - Response To Stimuli

    Cards (40)

    • How does responding to the environment help organisms survive?
      1. Animals increase their chances of survival by responding to changes in their external environment i.e. avoiding places too hot or cold
      2. They also respond to changes in their internal environment to ensure conditions are always optimal for their metabolism
      3. Plants also increase their chances of survival by responding to changes in their environment
    • What is a stimulus?
      Any change in the internal or external environment
    • What are Receptors?
      Receptors detect stimuli - they can be cells or proteins on cell surface membranes
    • What are Effectors?
      Effectors are cells that brings about a response to a stimulus, to produce an effect. Effectors include muscle cells and cells found in glands e.g. the pancreas
    • What are the 3 types of neurones?
      1. Sensory Neurones -> transmit electrical impulses from receptors to the central nervous system (CNS = Brain & Spinal Cord)
      2. Motor Neurones -> transmit electrical impulses from the CNS to effectors
      3. Relay Neurones -> transmit electrical impulses between sensory neurones & motor neurones
    • How does the Nervous System respond to stimuli?
      1. A stimulus is detected by receptor cells, causing an electrical impulse to be sent along a sensory neurone
      2. When an electrical impulse reaches a synapse, a neurotransmitter takes the information to the next neurone, carrying on the electrical impulse
      3. The CNS (the coordinator) processes the information & sends impulses along motor neurones to an effector
    • 2 systems of the Nervous System:
      • Central NS (brain & spinal cord)
      • Peripheral NS (connects CNS to rest of body)
      PNS has 2 sub-divisions:
      • Somatic NS (controls conscious activities)
      • Autonomic NS (controls unconscious activities)
      ANS has 2 further sub-divisions:
      • Sympathetic NS (gets body ready for action, 'fight or flight')
      • Parasympathetic NS (calms body down, 'rest and digest')
    • How do reflexes work?
      1. A reflex is where your body responds to a stimulus without making a conscious decision to respond
      2. Info travels fast from receptors to effectors, it protects organisms due to how rapid it is
      3. The pathway of neurones is called a reflex arc - it goes from sensory neurone -> relay -> motor
      4. If there is a relay neurone involved in a simple reflex arc, you can override the reflex e.g. your brain telling you to withstand the heat
    • Reflex Arc Example- the hand-withdrawal response to heat
      • Thermoreceptors in the skin detect the heat stimulus
      • The sensory neurone carries impulses to the relay neurone
      • The relay neurone connects to the motor neurone
      • The motor neurone sends impulses to the effector (your bicep muscle)
      • Your muscle contracts to withdraw your hand, stopping it being damaged
    • What are 3 attributes of Nervous System Communication?
      • Localised - At the neurone end, neurotransmitters are secreted directly onto target cells
      • Short-Lived - Neurotransmitters are quickly removed after secretion
      • Rapid - Electrical impulses are really fast, allowing animals to react quickly to stimuli
    • What ways to plants respond to environmental change?
      • They sense the direction of light to maximise light absorption for photosynthesis
      • They can sense gravity, so roots & shoots grow in the right direction
      • Climbing plants have a sense of touch, so they can find things to climb up & reach sunlight
      • Phototropism is the growth of a plant in response to light
      • Shoots are positively phototropic & grow towards light
      • Roots are negatively phototropic & grow away from the light
      • Gravitropism is the growth of a plant in response to gravity
      • Shoots are negatively gravitropic & grow upwards
      • Roots are positively gravitropic & grow downwards
    • Describe how a plant shoot responds to directional light:
      1. Indoleacetic Acid (IAA) is an auxin produced in the tip of shoots
      2. IAA moves via diffusion/active transport to the shaded part of the shoot
      3. This stimulates growth of the shaded side by elongating the cells
      4. The shoot bends towards the light stimulus, maximising light absorption for photosynthesis
    • Describe how a plant root responds to directional light:
      1. Indoleacetic Acid (IAA) is an auxin produced in the tip of roots
      2. IAA moves via diffusion/active transport to the shaded part of the root
      3. IAA has a inhibiting effect in roots so the root bends downwards, away from the light & anchoring the plant
    • Describe how a plant shoot responds to gravity:
      1. Indoleacetic Acid (IAA) is an auxin produced in the tip of shoots
      2. IAA moves via diffusion/active transport to the underside of the shoot
      3. IAA stimulates growth on the underside of the shoot by elongating cells
      4. Shoot bends upwards and grows up
    • Describe how a plant root responds to gravity:
      1. Indoleacetic Acid (IAA) is an auxin produced in the tip of roots
      2. IAA moves via diffusion/active transport to the underside of the root
      3. IAA inhibits growth in roots, so the roots grows downward
    • What is Taxis + an example:
      • Taxis is when organisms move towards or away from a directional stimulus
      • Example: Woodlice show a tactic response to light (phototaxis) - they move away from light, helping them stay concealed away from predators in the day & keeps them in damp conditions
    • What is Kineses + an example:
      • Kineses is the organisms' movement is affected by a non-directional stimulus.
      • Example: Woodlice show a kinetic response to humidity. In high humidity, they move slowly and turn less often so they stay where they are. In dry conditions, they become faster and turn more often so they move into a new area, potentially with higher humidity.
      • This improves the organisms chance of survival as higher humidity is advantageous to conserve water & remain concealed
    • How would you use a Choice Chamber to investigate Animal Response?
      1. Make a choice chamber using given equipment
      2. Cover 1 half with black paper to create dark condition
      3. Place damp filter paper over 1 light & dark condition
      4. Place a drying agent (i.e. anhydrous calcium chloride) on the remaining quarters
      5. Place 10 maggots in the centre of the chamber & cover with a lid
      6. After 10 minutes, take off the lid and record the number of maggots in each condition
      7. Repeat. You should find maggots move towards the dark, damp condition
    • What do receptors being specific mean?
      They only detect one particular stimulus, e.g. light, pressure or glucose concentration.
    • What are the different types of receptors:
      • Cells - e.g. photoreceptors in the eye
      • Proteins on Surface Cell Membranes - e.g. glucose receptors in the pancreas
    • What does the potential difference in a receptor mean?
      • When a nervous system receptor is in its resting state, there is a difference in charge inside & outside of the cell.
      • This is generated by ion pumps or ion channels.
      • The voltage across the membrane is the potential difference
    • What occurs in a receptor when a stimulus is detected?
      • Cell membrane become more permeable, allowing more ions to move in and out of the cell
      • This alters the potential difference
      • The change in potential difference is called the generator potential
    • How is an action potential produced?
      • If the generator potential is big enough, it triggers the electrical impulse along the neurone
      • This will only occur if the size of the generator potential exceeds the threshold level
      • Action potentials are all one size, so the strength of the stimulus is measured by the amount of action potentials.
    • Pacinian Corpuscles:
      1. They are mechanoreceptors, responding to pressure in your skin
      2. They contain the end of a sensory neurone wrapped in layers of lamellae
      3. When the Pacinian corpuscle is stimulated, the lamellae is deformed & press on the sensory neurone
      4. This deforms stretch-mediated sodium channels, causing them to open and Na+ ions diffuse into the cell
      5. Creating the generator potential
    • Photoreceptors:
      1. Light enters through the pupil, the amount of light being controlled by muscles around the iris
      2. Light rays are focused onto the retina by the lens. The retina contains rod & cone cells.
      3. The fovea is an area with lots of photoreceptor cells
      4. Nerve impulses from the photoreceptors cells are carried to the brain by the optic nerve, which is a bundle of neurones.
      5. Where the optic nerve leaves the eye is the blind spot, as there's no photoreceptor cells.
    • How do photoreceptors convert light into electrical impulses?
      1. Light enters the eye, hits the photoreceptors and is absorbed by light-sensitive optical pigments
      2. Light bleaches the pigments, causing a chemical change & altering the membrane permeability to Na+ ions
      3. Creates the generator potential and sends the nerve impulse along a bipolar neurone, which connect photoreceptors to the optic nerve
    • Rod Cells:
      • Mainly concentrated in the peripheral parts of the retina
      • Monochromatic vision
      • Very sensitive to light/Works well in dim light (Many rods join one neurone so weak generator potentials combine to reach threshold for action potential)
      • Low visual acuity (Many rods join one neurone so light from two points can't be told apart)
    • Cone Cells:
      • Packed together in the fovea
      • Trichromatic vision (There are 3 types of cone: red-sensitive, green & blue. When they're stimulated in different proportions you see different colours)
      • Less sensitive to light/Works well in bright light (One cone per neurone so it takes more light to trigger action potential)
      • High visual acuity (One cone per neurone means brain can distinguish two points close together as 2 separate points)
    • What qualities does cardiac muscle have?
      • Myogenic - It can contract & relax without receiving contractions from nerves
      • Non-tiring - Lots of mitochondria to maintain regular beating
    • Part 1 - Heartbeat:
      1. Sinoatrial Node (in the wall of right atrium) sends out regular waves of electrical activity to the atrial walls.
      2. Causes the right & left atria to contract at the same time
      3. A band of non-conducting collagen tissue prevents the waves of electrical activity from passing from the atria to the ventricles
      4. The waves instead are transferred from SAN to the atrioventricular node (AVN)
    • Part 2 - Heartbeat:
      1. The AVN passes on the electrical activity onto the bundle of His. However, there is a slight delay before the AVN reacts to ensure the atria is empty before the ventricles contract
      2. The bundle of His is a group of muscle fibres responsible for conducting waves between the ventricles to the apex (bottom) of the heart.
      3. The bundle splits into finer muscle fibres in the left & right ventricles walls, called the Purkyne tissue
      4. The Purkyne tissue carries the waves into ventricle walls causing them to contract simultaneously, from the bottom up.
    • How is Heart Rate controlled?
      • The SAN generates electrical impulses that cause the cardiac muscles to contract
      • Heart rate is unconsciously controlled by the medulla oblongata
      • Animals need to alter their heart rate to respond to internal stimuli
      • Stimuli are detected by pressure & chemical receptors
      • Electrical impulses from receptors are sent to the medulla along sensory neurones. The medulla processes the info + sends impulses to the SAN along sympathetic or parasympathetic neurones
    • What receptors respond to pressure?
      Baroreceptors are found in the aorta & the carotid arteries. They're stimulated by high or low blood pressure
    • What receptors respond to chemicals?
      Chemoreceptors are found in the aorta, the carotid arteries & the medulla. They monitor the oxygen levels in the blood and also CO2 and pH levels (which are indicators of O2 levels)
    • How does the body respond to High Blood Pressure?
      1. Baroreceptors in the aorta /carotid artery detect high blood pressure
      2. Impulses are sent to the medulla oblongata
      3. This sends impulses along the parasympathetic nervous system
      4. These secretes acetylcholine which binds to receptors on the SAN
      5. The heart rate slows and this reduces blood pressure
    • How does the body respond to Low Blood Pressure?
      1. Baroreceptors in the aorta /carotid artery detect low blood pressure
      2. Impulses are sent to the medulla oblongata
      3. This sends impulses along the sympathetic nervous system
      4. These secretes noradrenaline which binds to receptors on the SAN
      5. The heart rate speeds up and this increases blood pressure
    • How does the body respond to High Blood O2, low CO2 or high pH levels?
      1. Chemoreceptors in the aorta /carotid artery detect chemical changes in the blood
      2. Impulses are sent to the medulla oblongata
      3. This sends impulses along the parasympathetic nervous system
      4. These secretes acetylcholine which binds to receptors on the SAN
      5. The heart rate slows and O2, CO2 and pH levels return to normal
    • How does the body respond to Low Blood O2, high CO2 or low pH levels?
      1. Chemoreceptors in the aorta /carotid artery detect chemical changes in the blood
      2. Impulses are sent to the medulla oblongata
      3. This sends impulses along the sympathetic nervous system
      4. These secretes noradrenaline which binds to receptors on the SAN
      5. The heart rate increases and O2, CO2 and pH levels return to normal