Chapter 14 - Stimuli and response Flashcards
What is meant by tropism
The response of a plant to a directional stimulus
What is the impact of IAA on shoot cells and root cells
Shoot cells elongate
Growth of root cells is inhibited
Explain the process of positive phototropism
- Only in shoots
- IAA (type of auxin) moves to shaded side of shoot
- Causing cell elongation in these cells
- Shoots bend and so grow towards light
Explain the process of negative phototropism
- Only in roots
- IAA moves to shaded side
- Inhibits cell growth
- Roots grow away from light
Ask sir about this
Explain the process of positive geotropism
- IAA moves to underside of root
- Inhibits cell growth
- Roots grows towards gravity
What is meant by taxes
When a mobile organism moves towards or away from a directional stimulus
Can be positive or negative, positive towards negative away from
What is meant by kinesis
When a mobile organism changes their rate of movement in response to a non-directional stimulus
Explain the choice chamber practical
Woodlice
Record rate of movement and final position
What is meant by a reflex
A rapid response to a stimulus without conscious control
Draw diagram of a reflex from stimulus to response
In folder
What are advantages of reflexes
- Help organisms avoid damage
- Very fast reaction
- Doesn’t need to be learned (protect infants)
What is a pacinian capuscle
The receptor that detects pressure, touch and vibration in the skin
Explain how the pacinian corpuscle detects pressure
- Pressure causes the lamellae to stretch and deform
- Stretch mediated sodium ions channels open
- Sodium ions diffuse into neurone
- A large stimulus will open more sodium ion channels
- If threshold is reached then action potential is initiated
Draw and label the human eye
Folder
What is the forea
The area behind the retina that has lots of photoreceptors, which are mostly cones
What is the blind spot
The area behind the retina that has no photoreceptors
How does the eye detect light
- Light is focused on retina by the lens
- Light is absorbed by pigments in the photoreceptors
- Causes some of the sodium ions channels to open creating a generator potential
- If this reaches threshold, action potential, bipolar neurone, optic nerve, central nervous system
Explain the role of rods
- Monochromatic so only detect one pigment (black and white)
- More sensitive time low intensity of light
- Low visual acuity (resolution/detail)
- Mostly in peripheral part of retina (edges)
Explain what cones do
- They’re trichromatic, so have red, green and blue optical pigments, allowing colour vision
- Less sensitive to low intensity light
- Higher visual acuity
Why do cones have higher visual acuity and are less sensitive to low light than rods
Each cone has its own bipolar neurone so need a stronger stimulus to reach threshold, whereas many rods join to a single bipolar neurone so the opposite
Explain the order of the heart beat
- Sinoatrial node (SAN) initiates the heart beat
- Sends an electrical impulse across the atria
- Atria contract
- Non-conductive tissue prevents the electrical impulse reaching the ventricles
- Atrioventricular nose delays electrical impulse, allowing atria to contract and empty before ventricles contract
- AVN sends the electrical impulse down the bundle of His and along the purkyne fibres
- Ventricles contract from the base upwards
What is different about the left ventricle
- Has highest blood pressure
- Most cardiac muscle
- Contracts with a greater force
- Pumps blood to the whole body
Explain how heart rate is slowed down in the body
- Chemoreceptors detect high blood oxygen, low blood CO2 and high pH, or baroreceptors detect high blood pressure
- Receptors send nerve impulses to medulla oblongata in brain
- Medulla oblongata sends nerve impulses along parasympathetic neurone
- Parasympathetic neurones secrete acetylcholine
- Heart rate slows down
Explain how heart rate is sped up in the body
- Chemoreceptors detect low blood oxygen, high blood CO2 and low pH, or baroreceptors detect low blood pressure
- Receptors send nerve impulses to medulla oblongata
- Medulla oblongata sends nerve impulses along sympathetic neurones
- sympathetic neurones secrete noradrenaline
- Heart rate speeds up
Explain the process of negative geotropism
- IAA moves to underside of shoot
- Causes cell elongation
- Shoot grows away from gravity
What is the photosynthetic pigment in cones called
Iodopsin
What is the photosynthetic pigment in rods called
Rhodopsin
