Nervous and hormonal control (part 2) Flashcards
What is a stimulus?
Any change in the internal or external environment
What do receptors do?
Receptors detect stimuli – they can be cells or proteins on cell surface membranes
What do effectors do?
They bring about a response to a stimulus to produce an effect
Eg muscles cells
How do receptors communicate with effectors?
Via the nervous or hormonal system
How does the eye respond to dim light?
- Light receptors in the eyes detect a lack of light
- The CNS processes information
- The radial muscles in the iris are stimulated by the motor neurones
- The radial muscles contract to dilate the pupils
How does the eye respond to bright light?
- Light receptors in the eyes detect bright light
- The CNS processes the information
- The circular muscles in the iris are stimulated by the motor neurones
- The circular muscles contract to constrict the pupils
What is the hormonal system comprised of?
Glands and hormones
What is a gland?
A group of cells that are specialised to secrete a useful substance such as a hormone
Eg the pancreas secretes insulin
What is a hormone?
A ‘chemical messenger’ – many are proteins or peptides but some are steroids
When are hormones secreted?
When a gland is stimulated
How can glands be stimulated x2
- By a change in concentration of a substance eg another hormone
- Electrical impulses
Describe how hormones trigger a response in target cells (use blood glucose):
- Receptors on pancreas cells detect low blood glucose concentration
- The pancreas releases the hormone glucagon into the blood
- Target cells in the liver detect glucagon and convert glycogen into glucose
- Glucose is released into the blood so glucose concentration increase
Differences between nervous and hormonal system x4:
- Nervous uses electrical impulses, hormonal uses chemicals
- Nervous has a faster response, hormonal has a slower response
- Nervous has a localised response, hormonal has a widespread response
- Nervous has a short-lived response, hormonal has a long-lived response
Nervous system: What are photoreceptors?
Light receptors in the eye
What part of the eye controls the amount of light entering?
The muscles of the iris
What part of the eye contains photoreceptors?
The retina
Which part of the retina has an abundance of photoreceptors?
The fovea
Name the two types of photoreceptors:
Rods and cones
Where are rods found + what do they do?
Mainly found in the peripheral parts of the retina
They deliver information in black and white
Where are cones found + what do they do?
In the fovea
They deliver information in colour
What are the three types of cone?
Red-sensitive, blue-sensitive, green-sensitive
What happens to rod cells when stimulated by light?
They become hyperpolarised
What is the light-sensitive pigment found in rod cells called and what is it made of?
Rhodopsin is made of retinal and opsin
What happens to rod cells in the dark?
- Sodium ions diffuse into the rod cells, depolarising the cell
- Neurotransmitters are released across the synapse to the bipolar neurone
- Inhibitory response occurs so the bipolar neurone does not depolarise, and no action potential is fired
What happens to rod cells in the light?
- Rhodopsin absorbs light and breaks down into retinal and opsin
- Opsin activated a cascade of reactions that result in the closing of cation channels
- Sodium cannot diffuse into the rod cells, so the cell membrane becomes hyperpolarised
- No release of neurotransmitters so there is no inhibition of the bipolar neurone, so it depolarises, delivering an action potential to the brain via the optic nerve
What is a tropism?
A plants growth response to an external directional stimulus
What is a positive/negative tropism?
Positive = grow towards the stimulus Negative = grow away from the stimulus
Relationship between roots/shoots and light:
Shoots are positively phototropic
Roots are negatively phototropic
Relationship between roots/shoots and gravity:
Shoots are negatively geotropic
Roots are positively geotropic
How are plant responses brought about?
They respond using growth factors that either speed up or slow down plant growth
Where are growth factors produced?
In growing regions of the plant eg shoot tips and move to where needed
How do auxins stimulate growth in shoots?
By cell elongation – cells walls become lose and stretchy so get longer
What do high concentrations of auxins do to roots?
Inhibit growth
Name 4 other growth factors:
Gibberellins – stimulate flowering
Cytokinin – stimulate cell division
Ethene – stimulates fruit ripening
ABA – stimulates leaf fall
What is IAA?
An important auxin produced in the tips of shoots in flowering plants
How does IAA control cell elongation and growth?
When IAA enters the nucleus of a cell it can regulate the transcription of genes involved in elongation and growth
How is IAA transported over short distances?
Active transport and diffusion
How is IAA transported over short distances?
Active transport and diffusion
How is IAA transported over longer distances?
Phloem
How do plants detect light?
Using photoreceptors called phytochromes
Where are phytochromes found?
Leaves, seeds, roots, and stems
What two states do phytochromes exist in?
Pr and Pfr
What light + wavelength does Pr absorb?
Pr absorbs red light at a wavelength of 660nm
What light and wavelength does Pfr absorb?
Far-red light at a wavelength of 730nm
What is Pr converted to in red light?
Converted quickly into Pfr
What is Pfr converted to in far-red light?
Converted quickly into Pr
What happens to Pfr in darkness?
Slowly converted into Pr
