Coordination and Response
Sensitivity and Response to Changes in their environment
Sensitivity is the ability to recognise and respond to changes in external and internal conditions.
- In order to function properly and efficiently, organism have different control and communication
systems that ensure their internal conditions are kept relatively constant
Physiological control systems maintain the internal environment within restricted limits
- Known as homeostasis
- This is critically important for organisms as it maintains optimal conditions for enzymes
A change in conditions is called a stimulus.
To produce a coordinated response to that stimulus, there must be a receptor that can recognise the stimulus,
and an effector, a mechanism to carry out the response.
Coordination means detecting and responding appropriately to a particular stimulus.
Coordination and Response in flowering plants
Tropisms
Plants need to be able to grow in response to certain stimuli
- E.g. plants need to be able to grow in response to light so their leaves can absorb the max amount of
light for photosynthesis
- They also need to be able to response to gravity to ensure that shoots grow upwards and roots down
The directional growth responses made by plants in response to light and gravity are called tropisms
● Towards the stimulus = positive tropism
● Away from the stimulus = negative tropism
Light response = phototropism
● If the growth is towards light, it is called positive phototropism (shoots)
● If the growth is away from the light, it is called negative phototropism (roots)
Gravity response = geotropism
● Roots are positive geotropism
● Shoots are negative geotropism
Tropisms are controlled by plant hormones called auxins.
- These hormones are made in the tips of the shorts and roots and diffuse away from the tips.
- Further back along a shoot, the hormones stimulate cells to elongate so that the shoot grows longer
The growth of shoots towards light can be explained by the response of auxin to the light
● When all sides of a shoot receive the same amount of light, equal amounts of auxin diffuse down all
sides of the shoot. So cells all around the shoot are stimulated equally and elongated.
○ This means that the shoot will grow straight up
, ● When the light on the shoot comes mainly from the side auxin on that side of the shoot moves across
the shoot to the shaded side. The cells on the shaded side of the shoot will receive more auxin, and
so grow longer, than those on the bright side.
○ This causes the shoot to curve as it grows, so that it grows towards the light
The hormone is also made in root tips. However, it has the opposite effect on root cells compared with
shoot cells, because it reduces how much the cells elongate
● When roots are pointing straight down, all the sides of the root receive the same amount of hormone,
so all cells elongate by the same amount
● When the root is growing at an angle to the force of gravity, gravity causes the hormone to collect on
the lower side. This reduces the amount of elongation of cells on the lower side of the root, so that the
root stats to curve as it grows until it is in line with the force of gravity
REMEMBER
Auxin causes shoots to curve by the elongation of existing cells, not by the production of more cells
, **What does a coordinated response require**
Stimulus → Receptor → Effector → Response
Stimulus
External:
1. Loud sound
2. Bright light
Internal:
1. Rise or drop in core body temperature
2. Rise or drop in blood glucose level
Receptors
- Detect internal changes
- E.g. osmoreceptors in the hypothalamus
- E.g. in blood sugar - Pancreas
Sense organs
Sense organ Sense Stimulus Receptor
Skin Touch Pain/pressure Pressure receptors
Tongue Taste Food/drink Chemoreceptors
Nose Smell Gases Chemoreceptors
Eyes Sight Light Photoreceptors
Ears Hearing Noise Pressure receptors
Balance Movement/position of head
Effectors
- Cause changes to happen
- E.g. muscles
- E.g. glands
Sensitivity and Response to Changes in their environment
Sensitivity is the ability to recognise and respond to changes in external and internal conditions.
- In order to function properly and efficiently, organism have different control and communication
systems that ensure their internal conditions are kept relatively constant
Physiological control systems maintain the internal environment within restricted limits
- Known as homeostasis
- This is critically important for organisms as it maintains optimal conditions for enzymes
A change in conditions is called a stimulus.
To produce a coordinated response to that stimulus, there must be a receptor that can recognise the stimulus,
and an effector, a mechanism to carry out the response.
Coordination means detecting and responding appropriately to a particular stimulus.
Coordination and Response in flowering plants
Tropisms
Plants need to be able to grow in response to certain stimuli
- E.g. plants need to be able to grow in response to light so their leaves can absorb the max amount of
light for photosynthesis
- They also need to be able to response to gravity to ensure that shoots grow upwards and roots down
The directional growth responses made by plants in response to light and gravity are called tropisms
● Towards the stimulus = positive tropism
● Away from the stimulus = negative tropism
Light response = phototropism
● If the growth is towards light, it is called positive phototropism (shoots)
● If the growth is away from the light, it is called negative phototropism (roots)
Gravity response = geotropism
● Roots are positive geotropism
● Shoots are negative geotropism
Tropisms are controlled by plant hormones called auxins.
- These hormones are made in the tips of the shorts and roots and diffuse away from the tips.
- Further back along a shoot, the hormones stimulate cells to elongate so that the shoot grows longer
The growth of shoots towards light can be explained by the response of auxin to the light
● When all sides of a shoot receive the same amount of light, equal amounts of auxin diffuse down all
sides of the shoot. So cells all around the shoot are stimulated equally and elongated.
○ This means that the shoot will grow straight up
, ● When the light on the shoot comes mainly from the side auxin on that side of the shoot moves across
the shoot to the shaded side. The cells on the shaded side of the shoot will receive more auxin, and
so grow longer, than those on the bright side.
○ This causes the shoot to curve as it grows, so that it grows towards the light
The hormone is also made in root tips. However, it has the opposite effect on root cells compared with
shoot cells, because it reduces how much the cells elongate
● When roots are pointing straight down, all the sides of the root receive the same amount of hormone,
so all cells elongate by the same amount
● When the root is growing at an angle to the force of gravity, gravity causes the hormone to collect on
the lower side. This reduces the amount of elongation of cells on the lower side of the root, so that the
root stats to curve as it grows until it is in line with the force of gravity
REMEMBER
Auxin causes shoots to curve by the elongation of existing cells, not by the production of more cells
, **What does a coordinated response require**
Stimulus → Receptor → Effector → Response
Stimulus
External:
1. Loud sound
2. Bright light
Internal:
1. Rise or drop in core body temperature
2. Rise or drop in blood glucose level
Receptors
- Detect internal changes
- E.g. osmoreceptors in the hypothalamus
- E.g. in blood sugar - Pancreas
Sense organs
Sense organ Sense Stimulus Receptor
Skin Touch Pain/pressure Pressure receptors
Tongue Taste Food/drink Chemoreceptors
Nose Smell Gases Chemoreceptors
Eyes Sight Light Photoreceptors
Ears Hearing Noise Pressure receptors
Balance Movement/position of head
Effectors
- Cause changes to happen
- E.g. muscles
- E.g. glands
