2.4 Responding To The Environment Flashcards
(128 cards)
0
Q
What is positive tropism?
A
When the growth is towards the stimulus
1
Q
What is a tropism?
A
A directional growth response in which the direction of the response is determined by the direction of the external stimulus
2
Q
What is negative tropism?
A
When the growth is away from the stimulus
3
Q
If the stimulus is light, what type of tropism occurs?
A
Phototropism
4
Q
If the stimulus is gravity, what type of tropism occurs?
A
Geotropism
5
Q
If the stimulus is chemical, what type of tropism occurs?
A
Chemotropism
6
Q
If the stimulus is water, what type of tropism occurs?
A
Hydrotropism
7
Q
If the stimulus is air, what type of tropism occurs?
A
Aerotropism
8
Q
Give an example of thigmotropism
A
Ivy winding around another plant to gain support
9
Q
What are nasties?
A
Also called nastic responses
They are non-directional responses
10
Q
What are plant hormones?
A
Chemical messengers that can be transported away from their site of manufacture to act in other parts of the plant
- Some hormones stay in the cells that make them and exert their effect there
11
Q
Where are plant hormones made?
A
By cells in a variety of tissues in the plant
12
Q
How can hormones move around the plant?
A
- Active transport
- Diffusion
- Mass flow in the phloem sap or in xylem vessels
13
Q
What can hormones influence?
A
Cell division, cell elongation or cell differentiation
14
Q
What effect do auxins have?
A
- Promote cell elongation
- Inhibit growth of the side shoots
- Inhibit leaf abscission (leaf fall)
15
Q
What effect do cytokinins have?
A
Promote cell division
Promote bud and shoot growth
Prevent leaf senescence (By making the leaf act as a sink for phloem transport, so the leaf is guaranteed a good supply of nutrients)
16
Q
What effect do gibberellins have?
A
- Promote seed germination
- Promote growth of stems
17
Q
What effect does abscissic acid have?
A
- Inhibits seed germination and growth
- Causes stomatal closure when the plant is stressed by low water availability
- Inhibits bud growth
18
Q
What effect does ethene have?
A
Promotes fruit ripening
19
Q
Where are auxins made?
A
They are made continually in the shoot apex and young leaves (apical meristems)
20
Q
Explain how IAA causes positive phototropism
A
- Light is detected by photoreceptors
- These set off a chain of reactions, leading to the redistribution of IAA
- More IAA moves to the shaded side of the stem
- IAA causes the cells to elongate by loosening the structure of the cell wall
- Because the cells on the shaded side have a higher concentration of IAA, they stretch more than the cells in the light
- This causes the shoot to bend towards the light
21
Q
How do auxins cause cells to elongate?
A
- They promote the active transport of hydrogen ions into the cell wall (via an ATPase enzyme on the plasma membrane)
- The resulting low pH provides optimum conditions for wall-loosening enzymes (expansins) to work
- These enzymes break bonds within the cellulose so the walls become less rigid and can expand as the cell takes on water
- At the same time, the increased hydrogen ions also disrupt hydrogen bonds within cellulose
22
Q
What is apical dominance?
A
The growth of the main central stem of a plant, with reduced production of lateral sheets/branches
- Controlled by auxins
23
Q
Where are apical meristems found and what are they responsible for?
A
- Located at the tips of roots and shoots
- Responsible for the roots and shoots getting longer
24
Where are lateral bud meristems found and what are they responsible for?
- In the buds
| - Could give rise to side shoots
25
Where are lateral meristems found and what are they responsible for?
- Found in a cylinder near the outside of roots and shoots
| - Responsible for the roots and shoots getting wider
26
Where are intercalary meristems found and what are they responsible for?
- Only in some plants
- Located between the nodes (where the leaves and bud branch off the stem)
- Responsible for the shoot getting longer
27
What happens if cytokinin production drops?
The supply of nutrients to the leaf dwindles and senescence begins
- Usually followed by leaves being shed
28
Define apical dominance?
The growing apical bud at the tip of the shoot inhibits growth of lateral buds further down the shoot
29
How can you prove apical dominance?
- If you break the shoot tip off a plant, the plant starts to grow side branches from lateral buds that were previously dormant
- Apply a paste containing auxins to the cut end of the shoot (the lateral buds did not grow)
30
What is the role of cytokinins in apical dominance?
They promote bud growth
- Directly applying cytokinin to buds can override the apical dominance effect
- High concs of auxin make the shoot apex a sink for cytokinins produced in the roots (so most of the cytokinin goes to the shoot apex)
- When that is removed, cytokinin spreads more evenly around the plant, promoting growth in the buds
31
What experiment did Ken Thimann and Folke Skoog come up with to do with apical dominance?
They applied a ring if auxin transport inhibitor below the apex of the shoot
- Since the lateral buds grew, they suggested that normal auxin concs in lateral buds inhibit growth whereas low auxin concs promote growth
32
What experiment was done to prove that gibberellins caused stem elongation?
- They chose a pea plant which lacks gibberellin because it lacks the precursor molecule which becomes gibberellin
- They chose another pea plant which cannot convert the precursor into gibberellin because it lacks the enzyme required
Neither plant produces gibberellin and they only grow to about 1cm
However, if you graft the 2 shoots together, it grows tall
33
What commercial uses are there for auxins?
- When taking cuttings, the end can be dipped in rooting powder before planting to encourage root growth (rooting powder contains auxins, a fungicide and talcum powder)
- Treating unpollinated flowers with auxin can promote growth of seedless fruit. Applying auxin promotes ovule growth, which triggers automatic production of auxin by tissues in the developing fruit, helping to complete the developmental process
- Artificial auxins are used as herbicides to kill weeds. They are transported in the phloem to all parts of the plant and they can act within the plant for longer because they are not a close fit to the enzymes that break them down. They promote shoot growth so much that the stem cannot support itself, buckles and dies
34
What is the commercial role of gibberellins in fruit production?
- They delay senescence in citrus fruit, extending the time fruits can be left unpicked, and making them available for longer in the shops
- Gibberellins acting with cytokinins can make apples elongate to improve their shape
- Without gibberellins, bunches of grapes are very compact; this restricts the growth of individual grapes. With gibberellins the grape stalks elongate, they are less compacted and the grapes get bigger
35
What is the commercial role of gibberellins in brewing?
- To make beer you need malt, which is usually produced in a malthouse at a brewery
- When barley starts to germinate, the aleurone layer of the seed produces amylase enzymes that break down stored starch into maltose
- Usually, the genes for amylase production are switched on by naturally occurring gibberellins
- Adding gibberellins can speed up the process
- Malt is then produced by drying and grinding up the seeds
36
What is the commercial role of gibberellins in sugar production?
- Spraying sugar cane with gibberellins stimulates growth between the nodes, making the stems elongate
- This is useful because sugar cane stores sugar in the cells of the internodes, making more sugar available from each plant
37
What is the commercial role of gibberellins in plant breeding?
- They can induce speed formation in young trees, which speeds up the process of breeding plants with the desired characteristics
- Seed companies who want to harvest dress from biennial plants (which flower only in their second year of life) can add gibberellins to induce seed production in the first year
38
Why might it be useful to stop plants making gibberellins?
- It can keep flowers short and stocky
- Ensures that the internodes of crop plants stay short, helping to prevent lodging (lodging happens in wet summers - stems bend over because of the weight of water collected on the ripened seed heads, making the crop difficult to harvest)
39
What is the commercial role of cytokinins?
- They can be used to prevent yellowing of lettuce leaves after they have been picked (because they delay leaf senescence)
- They are used in tissue culture to help mass produce plants. They promote bud and shoot growth from small pieces of tissue taken from a parent plant, which produces a short shoot with a lot of side branches. This can be split into lots of small plants, each of which is grown separately
40
What are the commercial roles of ethene?
- Speeding up fruit ripening in apples, tomatoes and citrus fruits
- Promoting fruit drop in cotton, cherry and walnut
- Promoting female sex expression in cucumbers, reducing the chance of self-pollination (pollination makes cucumbers taste bitter) and increasing the yield
- Promoting lateral growth in some plants, yielding compact flowering stems
41
How can ethene be sprayed onto a plant?
2-chloroethylphosphonic acid can be sprayed on solution directly onto plants
- It is easily absorbed
- It slowly releases ethene inside the plant
42
Why can restricting ethene's effects on a plant be useful?
- Storing fruit in a low temp with little oxygen and high CO2 conc prevents ethene synthesis and thus prevents fruit ripening
- This means fruits can be stored for longer
- Silver salts (another inhibitor of ethene synthesis) can increase the shelf life of cut flowers
43
What is the cerebrum?
- The largest and most recognisable part of the brain
- Responsible for the elements of the nervous system that are associated with being human, including thought, imagination and reasoning
- It is divided into 2 hemispheres, which are connected via the corpus callosum
44
What is the cerebral cortex?
The outermost layer of the cerebrum
- It is folded
- It consists of a thin layer of nerve cell bodies
It is subdivided:
- Sensory areas: receive impulses indirectly from the receptors
- Association areas: compare input with previous experiences in order to interpret what input means and judge an appropriate response
- Motor areas: send impulses to effectors
45
What is the cerebrum in control of?
- Conscious thought and emotional responses
- The ability to override some reflexes
- Features associated with intelligence, such as reasoning and judgement
46
What does the cerebellum control?
The coordination of movement and posture
47
What is the function of the medulla oblongata?
- Controls non-skeletal muscles, so it is effectively in control of the autonomic nervous system
- Regulatory centres for a number of vital processes are found in the medulla oblongata including:
- The cardiac centre, which regulates heart rate
- The respiratory centre, which controls breathing and regulates the rate and depth of breathing
48
What is the function of the hypothalamus?
- Controls most of the body's homeostatic mechanisms
- Sensory input from temp receptors and osmoreceptors is received by the hypothalamus and leads to the initiation of automatic responses that regulate body temp and blood water potential
- Controls much of the endocrine function of the body because it regulates the pituitary gland
49
What do neurones from the cerebellum do?
They carry impulses to the motor areas so that motor output to the effectors can be adjusted appropriately
50
Where does the cerebellum process sensory information from?
- The retina
- The balance organs in the inner ear
- Specialised fibres in muscles called spindle fibres (info about muscle tension)
- The joints
51
What area of the brain controls speech?
Cerebrum
52
What are the 3 types of muscle?
- Cardiac
- Smooth/involuntary
- Skeletal/voluntary/striated
53
How do muscles cause a bone (at a joint) to move?
By producing a force when they contract
- Work in antagonistic pairs
- 1 muscle is stimulated to contract, the other muscle relaxes
54
What does the ligament do?
It holds bones together to avoid dislocation
55
What does cartilage do and where is it found?
- Found at the end of bones, where the bones meet
- Reduces friction as the bone moves
- Acts as a shock absorber
56
What does the synovial membrane do?
It produces synovial fluid
57
What does synovial fluid do?
- Lubricates the joint
| - Provides nutrients to cartilage cells
58
What happens when the triceps (in the arm) is stimulated?
- It shortens, pulling on the tendon and shortening the arm
| - Since the triceps is an extensor, it straightens the arm
59
What do tendons do and what are the made of?
- They join muscles to bones
| - Made of tough, inelastic collagen
60
What happens when the biceps is stimulated?
- It shortens
- This pulls on the tendon which bends the arm
- This is called flexion, and the biceps is a flexer
61
What kind of joint is an elbow joint?
A synovial joint
62
What is a neuromuscular junction?
- A specialised synapse
- Occurs at the end of a motor neurone where it meets the muscle fibre
- Release of acetylcholine, following depolarisation at the neuromuscular junction, stimulates contraction of the muscle fibre
63
What is a motor unit?
A cluster of muscle cells
| - Stimulation of neuromuscular junctions causes them to contract
64
What is gradation of response?
The more motor units stimulated, the greater the force of contraction
65
What stimulates muscular contraction?
Impulses arriving at the neuromuscular junction
66
What happens when an action potential arrives at the neuromuscular junction?
- Calcium channels open and calcium ions flood into the cell
- The increased conc. of Ca^2+ in the cell stimulates the vesicles which contain the neurotransmitter acetylcholine
- These move towards the presynaptic membrane and fuse with it
- Acetylcholine is released by exocytosis and diffuses across the synaptic cleft
- It binds to the receptors on the postsynaptic membrane
- This results in sodium channels opening
- Na^+ floods into the muscle cells
- The postsynaptic membrane depolarises
- If the threshold value is reached, an action potential is generated
- This travels along the muscle cell membrane and into special structures called T-tubules
- The T-tubules channel the action potential into the cell, towards the sarcoplasmic reticulum
- The organelle releases stored calcium ions into the cell cytoplasm in response to the depolarisation
- This increase in the conc of calcium ions in the muscle cell cytoplasm causes the cell to contract
- The acetylcholine is recycled by enzyme action (acetylcholinerase) and returned to the neurone
67
Where is muscle fibre found and why?
- Surrounding the end of the neurone
| - To increase the area over which signals are received
68
What proteins are muscle filaments made of?
Actin and myosin
69
What are some features of smooth muscle?
- It is slow to fatigue
- It is controlled by the autonomic nervous system
- Not controlled consciously
- With training, humans can learn to control some smooth muscles
70
Where is smooth muscle particularly important and what does it do there?
In the digestive system (intestine walls)
| Its rhythmic contractions help to move food along the digestive tract (peristalsis)
71
Where is cardiac muscle found?
In the ventricle and atrium walls in the heart
72
What are the 3 types of cardiac muscle?
- Atrial muscle
- Ventricular muscle
- Specialised excitatory and conductive muscle fibres
73
What are some features of cardiac muscle?
- Myogenic (capable of stimulating contraction without nerve impulse)
- Contracts rhythmically throughout its lifespan
- Doesn't become fatigued
- Longer duration of contraction than skeletal muscles
- Rate of contraction is controlled by the autonomic system
- It is striated
- Contractions are powerful
74
What are some features of skeletal muscle?
- Covers the skeleton
- Allows bones to be moved relative to one another
- Usually attached to bones by a tendon
- Controls skeletal muscles by sending messages from the CNS to the muscle tissue
- Contractions are quick and powerful
- Fatigues quickly
75
What is skeletal muscle used for?
- Maintaining posture
| - Voluntary movement of the skeleton at joints
76
What do muscle cells form?
Fibres of about 100 μm in diameter
77
What is each muscle fibre surrounded by?
A cell surface membrane called the sarcolemma
78
What is muscle cell cytoplasm also known as and what does it contain?
```
Sarcoplasm
Organelles, including:
- many mitochondria
- an extensive sarcoplasmic reticulum
- a number of myofibrils
```
79
What are myofibrils?
- The contractile elements
- Consist of a chain of smaller contractile units called sarcomeres
- Sarcomeres are arranged end to end for the entire length of the myofibril
- There are 2 types of protein myofilaments within them: thin actin and thick myosin
- These run the length of the cell
- They are arranged in an interlocking pattern
- Exhibit a distinctive striated pattern under the microscope
- The pattern of banding on them is caused by the sarcomeres
80
What is skeletal muscle composed of?
A series of bundles
| - Groups of muscle fibres which are surrounded by connective tissue containing blood vessels and nerves
81
Describe muscle fibres
The cells within them fuse during development to form a very long, strong, multinucleated cell (can withstand very high tension)
82
What is each sarcomere formed from?
- Thousands of protein filaments
- These can slide together due to the interlocking structure of the thick and thin filaments
- This shortens the sarcomere
83
What is a sarcomere?
- The smallest contractile unit of a muscle
| - A region of myofibril that lies between 2 Z-lines
84
What changes when a sarcomere is viewed under a microscope whilst contracting?
The sarcomere shortens
- I-band = shortens
- Z-lines = no change
- H-zone = shortens
- A-band = no change
85
What are Z-lines?
- Lines that define the limits of the sarcomere
| - Appear as thin, dark lines under a microscope
86
What are I-bands?
- Regions that contain only actin filaments
- They are the lightest coloured bands of the sarcomere when viewed under a microscope
- They are at the edges of the sarcomere
87
What is the A-band?
- The same length as the myosin filaments
- Contains both the H-zone and the M-line
- Actin and myosin interlock within the A-band
88
What is the H-zone?
- Lies within the A-band
- The region of the A-band that only contains myosin filaments
- The H-zone ends where myosin and actin filaments begin to interlock
89
What is the M-line?
- Found at the centre of the myosin filaments
| - There are no myosin heads in this region of the myosin filaments
90
Describe the structure of thin filaments
- 2 strands coiled around each other
- Mainly made of the protein F actin
- Each strand is composed of G actin (globular protein) subunits
- Tropomyosin (a rod-shaped protein) molecules coil around F actin, reinforcing it
- A troponin complex is attached to each tropomyosin molecule
- Each troponin complex consists of 3 polypeptides
- 1 binds to actin, 1 to tropomyosin and 1 to calcium ions
91
Describe the structure of thick filaments
- Bundles of the protein myosin
- Each myosin molecule consists of a tail and 2 protruding heads
- Each thick filament consists of many myosin molecules whose heads stick out from opposite ends of the filament
92
What happens to the sarcomere during muscle contraction?
- The heads on the myosin filaments form cross-bridges with the surrounding actin filaments by attaching themselves to binding sites on the actin
- The head group then bends, causing the thin filament to be pulled along and so overlap more with the thick filament. This is the power stroke. ADP and Pi are released
- The cross-bridge is then broken as new ATP attaches to the myosin head
- The head group moves backwards as the ATP is hydrolysed to ADP and Pi
- It can then form a cross-bridge with the thin filament further along and bend again
93
What is the myosin filament formed from?
A number of myosin proteins wound together
| - Each ends in a myosin head, which contains an ATPase
94
How do calcium ions allow muscles to contract?
- The muscle is stimulated
- Calcium ions are released
- At high concs. calcium ions bind to troponin
- Troponin changes shape
- This moves the tropomyosin away from the binding sites on the actin
- Myosin heads attach to the actin
- The power stroke occurs
- The sarcomere shortens
- Myosin heads break down ATP
- Calcium ions are actively transported back into the sarcoplasmic reticulum when nervous stimulation stops
95
What is the coordination of responses to stimuli from the external environment a result of?
Brain activity - assesses the most appropriate responses
96
What is the 'fight or flight' response?
- The full range of coordinated responses of animals to situations of perceived danger
- The combined nervous and hormonal response has dramatic effects on the whole organism, making it ready for actions that lead to the confrontation of the danger to escape it
97
What physiological changes occur due to the fight or flight response?
- Pupils dilate
- Heart rate and blood pressure increase
- Arterioles to the digestive system and skin are constricted whilst those to the muscles and liver are dilated
- Blood glucose levels increase
- Erector pili muscles in the skin contract, making hairs stand up
- Ventilation rate and depth increase
- Endorphins (natural painkillers) are released in the brain
- Sweat production increases
98
How is the fight or flight response caused?
- A visual or auditory stimulus is detected
- The cerebral understanding of a threat activates the hypothalamus
- This stimulates increased activity in the sympathetic nervous system
- It triggers the release of the hormone adrenaline from the adrenal medulla into the blood
- The hypothalamus also releases corticotropin-releasing factor (CRF) into the pituitary gland
- This stimulates the release of adreno-corticotropin hormone (ACTH) from the anterior pituitary gland
- This hormone stimulates the release of a number of different corticosteroid hormones from the adrenal cortex
- Some of these hormones help the body to resist stressors
99
What is a stressor?
- A stimulus that causes that stress response
| - It causes wear and tear on the body's physical or mental resources
100
What is meant by behaviour?
Behaviour is described as the responses of an organism to its environment which increase its chances of survival
101
What is genetically determined behaviour?
A reflex response to a stimulus
102
What is innate behaviour?
Any animal response that occurs without the need for learning
- It is an inherited response, similar in all members of the same species and is always performed in the same way in response to the same stimulus
103
Compare innate and learned behaviours
- I: genetically determined and so the environment has no impact on behavioural response, L: determined by the relationship between the genetic make-up of the individual and environmental influences
- I: passed on to offspring by reproduction, L: not passed on to offspring via reproduction but may be by teaching
- I: rigid and inflexible, L: can be altered by experience
- I: patterns of behaviour are the same in all members of a species, L: considerable variety is shown between members of a species
- I: unintelligent in the sense that the organism probably has no sense of the purpose of the behaviour, L: learned behaviours form the basis of all intelligent and intellectual activity
104
What are the 3 types of innate behaviour that invertebrates rely on for their survival?
Reflexes, kineses, taxes
105
What are escape reflexes?
Involuntary responses which follow a specific pattern in response to a given stimulus
106
What is a kinesis?
- An orientation behaviour where the rate of movement increases when the organism is in unfavourable conditions
- The behaviour is non-directional, meaning that the response is to change the rate of movement overall in relation to the intensity of the stimulus, not in any particular direction
107
What is a taxis?
A directional orientation response
The direction of movement is described in relation to the stimulus which triggers the behavioural response
- Positive phototaxis is towards light stimulus
- Positive chemotaxis is towards a specific chemical
108
How do more complicated behaviours occur?
By combining genetically determined and learned responses to stimuli
109
What is learned behaviour?
- Animal responses that change or adapt with experience
- There is a range of learned behaviours identified, from simply learning not to respond to a repeated stimulation, to the ability to consider a problem and formulate a response
110
What type of animals does learned behaviour provide the greatest survival benefit to?
Animals:
- With a longer lifespan and so time to learn
- With an element of parental care of the young, which involves learning from parents
- Living for a part of the time at least with other members of the species in order to learn from them
111
What is habituation?
Animals learn to ignore certain stimuli because repeated exposure to the stimulus results in neither reward nor punishment
- Avoids wasting energy in making escape responses to non-harmful stimuli
- Avoids causing stress
112
What is imprinting?
- A form of learning to recognise a parent or other complex stimulus, which is often limited to a sensitive (receptive) period in an animals development
- It ensures that the infant animal is in a position to learn the skills possessed by the parent
113
What is classical conditioning?
- A form of adaptive learning in which an innate response is modified
- The animal learns to respond to a stimulus that is different from the usual stimulus
- Animals can learn to relate a pair of events and respond to the first in anticipation of the second
- This type of learning is passive and involuntary
114
What is operant conditioning?
A form of adaptive learning in which an animal learns to carry out a particular action in order to receive a reward or to avoid an unpleasant experience
115
What is latent (exploratory) learning?
- Behaviour that is not directed towards a particular outcome
- Animals explore new surroundings and learn information that has no apparent value at the time, but may be useful for survival in the future
116
What is insight learning?
- A form of learning in which an animal integrates memories of 2 or more earlier actions to produce a response to gain a reward
- More complex than the associative learning seen in classical or operant conditioning
- Based on the ability to think and reason in order to solve problems
- Once solved, the solution to the problem is remembered
117
What are primates?
- Mammals
| - Include the apes and monkeys as well as more primitive lemurs
118
What are some features of primates?
- Most live in family groups where the young remain until they reach sexual maturity
- The organisation of the groups usually shows a hierarchy where different individuals have different status and roles within the group
- Such hierarchies lead to social control within the group which protects all group members
- They have large brains with a highly developed cerebral cortex
- This is linked to social development and interaction
119
What is the social organisation in gorillas?
- Mountain gorillas live in stable groups of around 10 individuals
- This usually consists of 1 mature dominant male, a number of adult females and their offspring
- The dominant male protects the other members of the group, leads them in search of food and is the only male that mates with the mature females
- As younger males reach sexual maturity they leave the group to live alone until they are mature enough to attract females
- As younger females mature they either stay with the same group or join another
120
How is gorilla offspring cared for?
By the mother
- During the 1st 5 months the infant remains in constant contact with the mother, sucking at hourly intervals
- By the age of 12 months, infants will venture as far as 5m from the mother
- During this period the female protects the young gorilla as it learns the social and other skills necessary to live independently
- Further learning takes place after the age of 2, as juvenile gorillas play together and imitate the adult behaviour of foraging for food
- The male is important in the development of the young gorillas from the age of 3 to 6 years, both in terms of protection from older males within the group, and in play as a source of learning new skills
121
How do gorillas communicate?
- A variety of calls, displays and grunts are used to signal danger to other members of the group, to issue threats to predators or other groups, and in play fighting displays as juveniles learn how to behave as adults
- Facial expressions are also very important, especially in terms of recognition of other members of the group
122
What are the advantages of social behaviour in primates?
- Females give birth to only 1 (or very few) infants at a time. The maternal care and group protection enhances the survival rate of the young
- The young learn through observation of and play with the other members of the group. Learned behaviour is vital to the survival of primates
- The final relatively large brain size slows the maturation of primates. The security of the group enhances the survival and learning of immature young
- Knowledge and protection of food sources is shared with the group
- Greater ability to detect and deter predators is achieved by groups of individuals working together
123
What is dopamine?
- A hormone
- A neurotransmitter
- Precursor molecule in the production of adrenaline and noradrenaline
124
What can low levels of dopamine be associated with?
Parkinson's disease
125
What can high levels of dopamine be associated with?
- Mental health conditions such as schizophrenia
| - Compulsive gambling
126
What is the range of activities affected by dopamine due to?
The number of and variation within dopamine receptors
- There are 5 different dopamine receptors
- Each of these is coded for by a separate gene
127
How does leaf abscission occur?
- Levels of cytokinin in the plant drop in response to lower water availability of nutrients and changing day lengths
- The plant withdraws nutrient supplies from the leaf
- Auxin levels in the leaf drop in response to a drop in cytokinin
- Another hormone, antagonistic to auxin, called ethene, is activated and ethene production increases
- This stimulates the production and release of cellulase enzymes in the abscission zone of the leaf
