3.6.1.1 survival and response Flashcards
Suggest two advantages of simple reflexes
- Rapid;
- Protect against damage to body tissues;
- Do not have to be learnt;
- Help escape from predators;
- Enable homeostatic control;
What is a stimulus?
A detectable change in the internal or external environment of an organism.
Why is the ability to respond to stimuli advantageous.
It increases the chances of survival
Stimuli are detected by…
receptors
A response is controlled by a…
coordinator e.g. brain
A response (e.g. hormone secretion) is produced by an…
effector
The two modes of communication between cells in large multicellular organisms are…
- Hormonal communication
2. Nervous communication
What is the sequence of events leading from a stimulus to a response?
Stimulus >Receptor > Coordinator > Effector >Response
Define taxis.
A directional response in which a whole organism moves towards or away from a stimulus.
Movement of a whole organism towards light (e.g. algae) is called…
Phototaxis (positive)
Positive taxis is…
Movement towards a stimulus by a whole organism.
Negative taxis is…
Movement away form a stimulus by a whole organism.
Define kinesis.
Random movement of a whole organism in response to a non-directional stimuli e.g. temp or humidity. This may be an increase/decrease in speed or turning frequency.
Define tropism
the growth of part of a plant in response to a directional stimulus e.g. light, gravity, water
When plant shoots grow towards light we call it…
positive phototropism
When plant shoots grow away from gravity we call it…
negative gravitropism
When plant roots grow away from light we call it…
negative phototropism
Why do woodlice increase their rate if turning if they exit favourable conditions?
To increase the probability that they will re-enter the favourable conditions.
Why do woodlice decrease their rate of turning and move rapidly after spending a while in unfavourable conditions?
To increase the chances that they will pass through the unfavourable conditions and enter more favourable.
Woodlice move in response to stimuli via the process of…
kinesis
When roots grow towards water we call it…
positive hydrotropism
As well as taking in water the function of roots is to…
anchor plants into the ground
The growth responses (tropisms) of plants are controlled by hormone like substances called…
plant growth factors
How do plant growth factors differ from hormones?
- They are produced by cells located throughout the plant (not just a particular organ/gland)
- They tend to affect the tissues that release the growth factors rather than ‘target’ tissues.
Are plant growth factors released in large or small quantities?
small
Name the main plant growth factor…
Indoleacetic Acid (IAA)
Describe the process of positive phototropism in a flowering plant shoot.
- Cells in the shoot tip produce IAA.
- IAA is usually evenly transported down the shoot,
- Light causes the movement of IAA to the shaded side of the shoot.
- There is more IAA on the shaded side vs light side.
- IAA causes shaded side shoot cells to elongate!!
- Unequal growth causes the shoot to bend towards light.
Describe the process of negative phototropism in a flowering plant root.
- Cells in the root tip produce IAA.
- IAA is usually evenly transported down the root,
- Light causes the movement of IAA to the shaded side of the root.
- There is more IAA on the shaded side vs light side.
- IAA inhibits cell elongation in roots!!
- Unequal growth causes the root to bend away from light (into the ground).
How is IAA transported around plant tissues?
Carrier proteins (active transport)
What effect does gravity have on IAA carrier proteins in the cells of the plant?
It alters their distribution - more IAA gathers on the lower side of horizontal shoots/roots causing shoots to grow up and roots to grow down.
Describe the process of positive gravitropism in a flowering plant root.
- Cells in the root tip produce IAA.
- IAA is usually evenly transported down the root,
- Gravity causes the movement of IAA to the lower side of the root (due to a change in carrier protein distribution).
- There is more IAA on the lower side vs upper side.
- IAA inhibits cell elongation in roots!!
- Unequal growth causes the root to bend away from gravity (into the ground).
What is the hypothesis that tries to explain how IAA causes shoot cell elongation?
Acid Growth Hypothesis
Explain the acid growth hypothesis that allows IAA to allow cell elongation to occur.
- H+ ions are actively transported from the cytoplasm into the spaces of the cell wall.
- The increase in H+ makes conditions around the cell wall more acidic.
- This increases the plasticity of the cell walls allowing for elongation.
The simplest type of nervous response is called a…
reflex arc
The 2 major divisions of the nervous system are:
- The central nervous system
2. The peripheral nervous system
The central nervous system consists of…
the brain
spinal cord
The peripheral nervous system consists of…
pairs of nerves that come out of the brain or spinal cord.
The pairs of neurones that make up the peripheral nervous system are called…
sensory neurones
motor neurones
What is the function of a sensory neurone?
they carry nerve impulses from receptors to the central nervous system.
What is the function of a motor neurone?
they carry nerve impulses away from the central nervous system to effectors
What is the function of the voluntary nervous system?
it carries nerve impulses to the body muscles and is under conscious (voluntary) control.
What is the function of the autonomic nervous system?
It carries nerve impulses to glands, smooth muscle and cardiac muscle and is under subconscious (involuntary) control.
Why are reflex arcs referred to as simple reflexes?
They only involve 3 neurones.
Recall the main stages of a reflex arc.
- Stimulus
- Receptor
- Sensory neurone
- Relay neurone
- Motor neurone
- Effector
- Response
