Topic 6.1 - Survival, Response, and Receptors Flashcards
Includes response mechanisms in plants
What do receptors do?
Detect stimuli
What can receptors be?
Cells or proteins on cell surface membranes
What are effectors?
Cells that bring about a response to stimulus to produce an effect
Give examples of types of effectors cells
Muscle cells and cells found in glands e.g. pancreas
How do receptors communicate with effectors?
Via nervous system and/or hormonal system
Name 3 types of neurones
- Sensory neurones
- Motor neurones
- Intermediate/relay neurones
What do sensory neurones do?
Transmit electrical impulses from receptors to the CNS - the brain and spinal cord
What do motor neurones do?
Transmit electrical impulses from CNS to effectors
What do relay neurones do?
Transmit electrical impulses between sensory neurones and motor neurones
State the 5 stages of a response to a stimulus

What the central nervous system (CNS) made up of?
Brain and spinal cord
What is the peripheral nervous system (PNS) made up of?
Neurones that connect the CNS to the rest of the body
What does the somatic nervous system control?
Conscious activities e.g running and playing video games
What does the autonomic nervous system control?
Controls unconscious activities e.g. digestion
What does the sympathetic nervous system do?
Gets the body ready for action - ‘flight or fight’ system
What does the parasympathetic nervous system do?
Calms the body down - ‘rest and digest’ system
What is a reflex?
When body responds to stimulus without making a conscious decision to respond
What is a reflex arc?
Pathway of neurones linking receptors to effectors in a reflex
Describe the simple reflex arc for a hand-withdrawal response to heat
- Thermoreceptors in skin detect heat stimulus
- Sensory neurone carries impulses to relay neurone
- Relay neurone connects to motor neurone
- Motor neurone sends impulses to effector
- Muscle contracts to withdraw your hand and stop it being damaged

Explain how nervous communication is localised
When electrical impulse reaches end of neurone = neurotransmitters are secreted directly onto target cells
Explain how nervous communication is short-lived
Neurotransmitters are quickly removed once they’ve done their job
State the 2 types of responses that simple mobile organisms have to keep them in a favourable environment
- Tactic (taxes)
- Kinetic (kineses)
Define taxes
Organisms move towards or away from a directional stimulus e.g. light
Define kineses
Organisms’ movement is affected by non-directional stimulus e.g. humidity
Give an example of taxes
- e.g. woodlice show tactic response to light (phototaxis)
- Move away from light source
- Helps them to survive because it keeps them concealed under stones during the day (where they’re safe from predators) & keeps them in damp conditions (reduces water loss)
Give an example of kineses
- e.g. woodlice show kinetic response to humidity
- In high humidity they move slowly and turn less often so they stay where they are
- When air gets drier they move faster and turn more often so more likely to move into new area
- Response increases chance woodlouse will move to area with higher humidity
- Improves survival chances of organisms by reducing their water loss & keeps them concealed
Explain the importance of relfex actions (3)
- Automatic / involuntary
- Prevents injury
- Role in homeostasis
Why do flowering plants respond to changes in their environment?
Increases their chances of survival
Give examples of how flowering plants respond to changes in environment
- They sense direction of light and grow towards it to maximise light absorption for photosynthesis
- Sense gravity so roots and shoots grow in right direction
- Climbing plants have a sense of touch = find things to climb up and reach sunlight
What is tropism?
Response of plant to directional stimulus
How do plants respond to stimuli?
By regulating their growth
What is positive tropism?
Growth towards stimulus
What is negative tropism?
Growth away from stimulus
Name 4 types of tropisms
- Phototropism
- Gravitropism
- Hydrotropism
- Responds to water
- Chemotropism
- Responds to chemicals
What is phototropism?
Growth of plant in response to light
Describe how the shoots and roots respond to light
- Shoots are positively phototropic and grow towards light
- Roots are negatively phototropic and grow away from light

What is gravitropism (aka geotropism)?
Growth of plant in response to gravity
Describe how the shoots and roots respond to gravity
- Shoots are negatively gravitropic and grow upwards
- Roots are positively gravitropic and grow downwards
What do plants use to respond to directional stimuli?
growth factors
What are growth factors?
Hormone-like chemicals that speed up or slow down plant growth
Where are growth factors produced?
In growing regions of plant (e.g. shoot tips, leaves)
& move to where they’re needed in other parts of plant
What do auxins (growth factors) do?
- Stimulate growth of shoots by cell elongation
- Where cell walls become loose and stretchy so cells get longer
What is indoleacetic acid (IAA)?
Important auxin that’s produced in tips of shoots in flowering plants
Describe how IAA is moved around a plant
Moves by diffusion and active transport over short distances & via phloem over long distances
Describe where IAA moves to control phototropism
IAA moves to more shaded parts of shoots and roots so there’s uneven growth
Phototropism
State what happens to IAA and its effect in a shoot
- IAA concentration increases on the shaded side
- cells elongate and the shoot bends towards the light

Phototropism
State what happens to IAA and its effect in a root
- IAA concentration increases on the shaded side
- Growth is inhibited so root bends away from light

Describe where IAA moves to control gravitropism
IAA moves to the underside of shoots and roots, so there’s uneven growth
Gravitropism
State what happens to IAA and its effect in a shoot
- IAA concentration increases on lower side
- cells elongate so shoot grows upwards

What is a potential difference?
The difference in charge across a membrane due to the movement and isolation of different
Receptors only detect …
one particular stimulus
Describe a receptor in its resting state (not being stimulated)
There’s a difference in charge between inside and outside of cell
What is the difference in charge between inside and outside of receptor cell generated by and what does this mean?
- Difference is generated by ion pumps and ion channels
- Means there’s a potential difference (voltage) across the membrane
Describe how a generator potential is created
- When stimulus is detected, cell membrane is excited and becomes more permeable
- Allows more ions to move in & out = alerting potential difference
- Change in potential difference due stimulus = generator potential
Explain how a bigger stimulus results in a bigger generator potential being produced
Bigger stimulus excites membrane more = bigger movement of ions and bigger change in potential difference.
State when an action potential is generated
If generator potential is big enough i.e. reaches threshold level, it’ll trigger an action potential
Describe the size of action potentials
Action potentials are all same size (all or nothing theory)
How is the strength of a stimulus measured?
By frequency of action potentials
What type of receptors are Pacinian corpuscles?
Mechanoreceptors
(Detect mechanical stimuli e.g. pressure, vibrations)
Pacinian corpuscles the contain end of a _____ neurone
Pacinian corpuscles contain the end of a sensory neurone
(Called sensory nerve ending)
What is the sensory nerve ending wrapped in?
Lamellae
Describe what happens when a Pacinian corpuscle is stimulated
- When the Pacinian corpuscle is stimulated the lamellae are deformed and press on the sensory nerve ending
- = the sensory neurone’s cell membrane to stretch
- This deforms (stretch-mediated) sodium ion channels
- This opens the channels = greater pressure & allows for Na+ to diffuse into the cell creating a generator potential

Where are photoreceptors found?
Retina
What is the fovea?
An area of retina where there’s loads of photoreceptors
Nerve impulses from photoreceptor cells are carried from retina to brain by ___ ___ (bundle of neurones)
Optic nerve
What do photoreceptors do?
Convert light into electrical impulse
What happens when light enters the eye?
It hits photoreceptors and is absorbed by light-sensitive pigments
What happens when light bleaches pigments?
- Causes chemical change and alters membrane permeability to sodium ions
- Generator potential is created & if it reaches threshold = nerve impulse is sent along bipolar neurone

What do bipolar neurones do?
Connect photoreceptors to optic nerve, which takes impulses to brain
Name the 2 types of photoreceptor the human eye has
- Rods
- Cones
Where are rods found?
Found in peripheral parts of retina
Where are cones found?
Cones packed together in fovea
Why do rods and cones give information in different colours?
Rods and cones contain different optical pigments making them sensitive to different wavelengths of light
Rods give information in ____
Black and white (monochromatic vision)
Cones give information in ____
Colour (trichromatic vision)
Name the 3 types of cones (each containing a different pigment)
- Red-sensitive
- Green-sensitive
- Blue-sensitive
When stimulated in different proportions = see different colours
State which one is more sensitive to light: rods or cones?
Rods
Explain why rods are very sensitive to light (work well in dim light)
- because many rods join one neurone, so many weak generator potentials combine to reach threshold and trigger action potential
- & rhodopsin can be broken down easily (pigment needs to be broken down in order to create an action potential) (called spatial summation)

Explain why cones are less sensitive than rods (work best in bright light)
- because one cone joins one neurone
- Takes more light to reach threshold and trigger action potential
- & requires lots of light intensity to breakdown iodopsin

Which one gives a higher visual acuity (ability to tell apart points
that are close together): rods or cones?
Cones
Explain why cones give a high visual acuity
- because cones are close together and one cone joins one neurone
- When light from 2 points hits 2 cones, 2 action potentials (one from each cone) go to the brain
- Can distinguish 2 points that are close together as 2 separate points

Explain why rods give a low visual acuity
- Give low visual acuity because many rods join same neurone
- Which means light from 2 points close together can’t be told apart

Explain why it takes time for the rod cells to recover their sensitivity to light after moving into darkness. (2)
- rhodopsin bleached / broken down by light
- time for resynthesis