Responding to the Environment Flashcards
What is any change in temperature, light intensity or pressure called?
A stimulus
What is tactic response?
Directional movement in response to a stimulus.
The direction of the stimulus affects the response.
What is kinetic response?
Non-directional (random) movement in response to a stimulus.
What are receptors?
Receptors detect stimuli- they can be cells, or proteins on cell surface membranes.
What are effectors?
Cells that bring about a response to a stimulus, to produce an effect.
Receptors communicate with effectors via the nervous system or the hormonal system, or both.
What are the three main neurones?
Sensory neurone
Motor neurone
Relay neurone
What is the role of the sensory neurone?
Transmit electrical impulses from receptors to the central nervous system (CNS).
What is the role of the motor neurone?
Transmit electrical impulses from the CNS to effectors.
What is the role of the relay neurones?
Transmit electrical impulses between sensory neurones and motor neurones.
Give the simple 5 step sequence to nervous communication.
Stimulus Receptors CNS Effectors Response
What are the chemicals that allow for a signal to cross a synapse?
Neurotransmitters.
Why is a nervous response short lived?
When an electrical impulse reaches the end of a neurone, neurotransmitters are secreted directly onto cells so the response is localised.
Neurotransmitters are quickly removed once they’ve done their job.
Electrical impulses are very fast.
What is a simple reflex?
A simple reflex is a rapid, involuntary response to a stimulus , the pathway of response goes through the spinal cord but not the conscious parts of the brain so its automatic.
What is the reflex arc?
The pathway of neurones linking receptors to effectors in a simple reflex is called a reflex arc.
Three neurones are involved: a sensory neurone, a reflex neurone and a motor neurone.
What is a gland?
A group of specialised cells that are specialised to secrete a useful substance, such as a hormone e.g the pancreas secretes insulin.
What is a hormone?
Chemical messengers- many hormones are proteins or peptides (e.g insulin) and some are steroids (e.g progesterone).
When are hormones secreted?
When a gland is stimulated.
Glands can be stimulated by a change in the concentration of a specific substance.
They can also be stimulated by electrical impulses.
What are target cells?
Hormones diffuse directly into the blood and are taken round the body in the circulatory system.
They diffuse out of the blood all over the body but each hormone will only bind to specific receptors for that hormone, found on the membranes of some cells (target cells).
The hormones trigger a response in the target cells (the effectors).
Why is the effects of hormones longer lasting than the nervous system?
Hormones aren’t released directly onto their target cells- they must travel in the blood to get there.
They aren’t broken down as quickly as neurotransmitters so the effects last longer.
Hormones are transported all over the body so the response may be widespread if the target cells are widespread.
Nervous system key points
Electrical impulses carried by neurones
Fast response
Localised effect
Short lived
Hormonal system key points
Hormones carried in blood
Slow response
Widespread effect
Long-lasting effect
Kinesis
Kinesis takes the form of an increase in movement, but this is non directional
This takes place when the response of an organism is proportional to the intensity of a stimulus
The greater the intensity of the stimulus the faster it moves
Taxis
This is a directional response to a stimulus
It can be a positive taxis (towards) or negative (away)
Chemotaxis (stimulus are chemical stimulus)
Light
Phototropic
Gravity
Gravitropic
Water
Hydrotropic
How do plants grow towards light?
Auxins accumulate on darkened side
Encourage growth on this side
Causes curving towards light
Give two types of cell that act as effectors.
Muscle and cells in glands
Give two types of stimuli that trigger hormone secretion.
A change in the concentration of a specific substance/another hormone, electrical impulses
What is a chemical mediator?
A chemical mediator is a chemical messenger that acts locally.
What are the differences between chemical mediators and hormones?
Chemical mediators are secreted from cells that are all over the body (not just glands).
Their target cells are right next to where the chemical mediator’s produced, meaning they stimulate a local response.
They only have to travel a short distance to their target cells, so produce a quicker response than hormones.
What are two types of chemical mediator?
Histamine
Prostaglandins
What is histamine?
A chemical mediator that’s stored in mast cells and basophils.
It’s released in response to the body being injured or infected.
It increases the permeability of the capillaries nearby to allow more immune system cells to move out of the blood to the infected/injured area.
What are prostaglandins?
A group of chemical mediators produced by most cells in the body.
They’re involved in inflammation, fever, clotting and blood pressure regulation.
What do plants respond to?
Light
Gravity
Water
What are plant growth factors?
They exert their influence by affecting growth.
Unlike animal hormones, they are made by cells located throughout the plant rather than specific organs.
Unlike animal hormones, some plant growth factors affec the tissues that release them rather than acting on a distant target organ.
Give an example of a plant growth factor.
IAA (indoleacetic acid)
