6 - Coordination and Responding to Stimuli Flashcards
What is a stimulus?
Any change in the internal or external environment
What are receptors?
- Detect a stimulus
- Receptors in the sense organs are groups of cells that detect external stimuli
- e.g. Rod and cone cells in the eye detect changes in light
What are effectors?
- Cells that bring about a response to a stimuli
- Include muscle cells and cells found in glands (e.g. the pancreas)
- Effectors respond in different way (muscles contract whereas glands secrete hormones)
How do receptors and effectors communicate?
Via the nervous system, the hormonal system or both
What are sense organs?
The eyes, ears, nose, tongue and skin
What is the CNS?
- Central nervous system
- Made of neurons
- Consists of the brain and spinal chord only
- The job is to coordinate a response
- The high speed electrical impulses produce a rapid response
- When receptors detect and stimulus they send electrical impulses along sensory neurons to the CNS
- The CNS sends electrical impulses to an effector along a motor neuron
What are the neurons in the CNS?
Sensory, Relay, Motor
What are reflexes?
Automatic responses to certain stimuli which reduce changes of being injured
e.g. if a bright light is shone in the eye the pupil automatically get smaller to stop them being injured
Give an example of the reflex arc
- Cupcake candle burns finger
- Stimulation of pain in the receptors
- Impulses travel along the sensory neuron
- Impulses are passed along a relay neuron via a synapse
- Impulses travel along a motor neuron via a synapse
- When impulses reach muscles it contracts
What is the reflex arc?
Stimulus - Receptor - Sensory neuron - relay neuron - Motor Neuron - Effector - Response
What is the reflex arc?
Stimulus - Receptor - Sensory neuron - relay neuron - Motor Neuron - Effector - Response
What is the role of the cornea?
Refracts light into the eye
- Transparent with no blood vessels to supply it with oxygen so oxygen diffuses in from the outer surface
What is the role of the conjunctiva?
Lubricates and protects the surface of the eye
What is the role of the iris?
Controls the diameter of the pupil allowing how much light is let in
What is the role of the lens?
Focuses light on the retina (the light-sensitive part covered in light receptors called rods and cones)
Rods and Cones
Rods - more sensitive in dim light but can’t sense colour
Cones - sensitive to colours but aren’t so good in dim light. Found all over the retina but are loads at the fovea
What is the role of the optic nerve?
Carries impulses from the receptors to the brain
How does the eye adjust to bright light?
- Bright light triggers a reflex that makes the pupil smaller, allowing less light in
- Light receptors detect light and send a message along sensory neurons to the brain. The message travels along a relay neuron to a motor neuron which tells circular muscles to contract
- The opposite happens in dark light
How does the eye look at distant objects?
- Ciliary muscles relax
- Suspensory ligaments pull tight
- This makes the lens go thin (less curved)
How does the eye look at near objects?
- Ciliary muscles contract
- Slackens the suspensory ligaments
- The lens becomes fat (more curved)
Long-sighted people
- Unable to focus on near objects
- The cornea or lens doesn’t bend the light enough or the eyeball is too short
- The images of near objects are brought into focus behind the retina
Short-sighted people
- Unable to focus on distant objects
- The cornea or lens bends the light too much or the eyeball is too long
- The images of distant objects are brought into focus in front of the retina
Short-sighted people
- Unable to focus on distant objects
- The cornea or lens bends the light too much or the eyeball is too long
- The images of distant objects are brought into focus in front of the retina
What are hormones?
Chemicals released directly into the blood
- Carried in the blood plasma to other parts of the body but only affect particular cells (called target cells) in particular places
- Control things in organs and cells that need constant adjustment
- Produced in various glands
- Travel slowly and last for a long time
ADH
Source - Pituitary gland (brain)
Role - Controls water content
Effect - Increases water permeability of the kidney tubules to water
Adrenaline
Source - Adrenal glands (on top of kidney)
Role - Readies the body for a ‘fight or flight’ response
Effect - Increases heart rate, blood flow to muscles and blood sugar levels
Insulin
Source - Pancreas
Role - Helps control blood sugar lever
Effect - Stimulates the liver to turn glucose into glycogen for storage
Testosterone
Source - Testes
Role - Male sex hormone
Effect - promotes male secondary characteristics (e.g. facial hair)
Progesterone
Source - Ovary
Role - Supports pregnancy
Effect - Maintains the lining of the uterus
Oestrogen
Source - Ovaries
Role - Female sex hormone
Effect - Controls the menstrual cycle and promotes female secondary characteristics (e.g. widening of hips)
Nerve characteristics
- Fast message
- Acts for a short time
- Acts on a precise area
Hormone characteristics
- Slow message
- Acts for a long time
- Acts in a more general way
What is homeostasis?
The maintenance of a constant internal environment
Water - A balance between water gain and water lost
Temperature - Lose heat when you’re hot, gain it when you’re cold
Describe the water lost on a hot day
- Sweat a lot
- Produce less urine but more concentrated
- Lose more water through breath by breathing faster
Describe the water lost on a cold day
- Little sweat
- Produce more urine which is pale and more diluted
How is a body temperature maintained?
- Optimum temperature is 37*C
- The brain detects the temperature
How is a body temperature maintained?
- Optimum temperature is 37*C
- The brain detects the temperature
What happens to the skin when you’re hot?
- Lots of sweat (when it evaporates it transfers heat from you to the environment cooling you down)
- Blood vessels close to the surface of the skin widen (vasodilation) which allows more blood to flow near the surface so it can radiate more heat to the surroundings)
- Hairs lie flat
What happens to the skin when you’re cold?
- Very little sweat produced
- Blood vessels near the surface constrict (vasoconstriction) so less heat can be transferred form the blood to the surroundings
- Shivering which generates more heat in the muscles
- Hairs stand on end to trap an insulating layer of air which helps keep you warm
Why do smaller organisms cool down quicker?
- Bigger surface area to volume ration meaning there is more area for the heat to transfer across
- Animals in cold climates are often round to keep their surface area to a minimum, reducing heat loss
Why do smaller organisms cool down quicker?
- Bigger surface area to volume ration meaning there is more area for the heat to transfer across
- Animals in cold climates are often round to keep their surface area to a minimum, reducing heat loss
How do plants respond to stimuli in their environment?
- Sense light and grow towards it to maximise photosynthesis
- Sense gravity so roots and shoots grow in the right direction
- Climbing plants have a sense of touch so they can find things to climb and reach the sunlight
How do plants respond to stimuli in the presence of predators?
- White clover plant produces substances that are toxic to cattle to avoid being eaten
How do plants respond to stimuli in abiotic stress?
Abiotic stress = anything that is harmful but non-living e.g. a drought
- Carrots produce antifreeze proteins at low temperatures to bind ice crystals and lower the temperature that water freezes at to stop ice crystals from growing
What are auxins?
Plant hormones that control growth at the tips and shoots
- Produced in the tips and diffuses back to stimulate the cell elongation process which occurs in cells just behind the tips
- Promotes growth in the shoot but inhibits the growth in the root
What is gravitropism/geotropism?
When the stimulus for plant growth is gravity
- Shoots are negatively geotropic/gravitropic (grow away from gravity)
- Roots are positively geotropic/gravitropic (grow towards gravity
What is phototropism?
When the stimulus for plant growth is light
- Shoots are positively phototrophic (grow towards light)
- The cell grows faster on the shaded side so the shoot bends towards the light
