Plant and animal responses 5.5 Flashcards
What is leaf senessence?
It is the colour change in leaves caused by the breakdown of chlorophyll
What is leaf abscission?
It is the shedding of leaves, fruits and flowers to reduce transpiration to survive harsher conditions
Why does leaf abscission and senessence happen?
It is the plants responses to stress
What is tropism?
Directional growth towards an external stimulus
What are the 5 types of tropism?
- phototropism
- geotropism
- hydrotropism
- chemotropism
- thigmotropism
What happens during phototropism?
It is the growth response of a plant in response to light, causing positive tropism in the shoots and negative phototropism in the roots
What happens during geotropism?
It is the growth response of a plant in response to gravity, causing positive geotropism in the roots and negative tropism in the stem
The stem grows against gravity
What happens during hydrotropism?
It is the growth response of a plant in response to water, causing positive tropism in the roots
What happens during thigmotropism?
It is the growth response of a plant in response to physical contact, causing positive tropism
Plants cling to physical structures
What happens during chemotropism?
It is the growth response of a plant in response to chemicals, causing positive or negative tropism in the roots
They can either grow towards minerals or away from acids
What is a nastic response?
A non directional response to an external stimulus
What is an example of a nastic response?
Thigmonasty
mimosa plants fold their leaves in response to touch
Why are plant growth regulators considered hormones?
- transported from site of manufacture to target tissues
- bind to receptors on plasma membrance of specific tissue
- complimentary shape
- molecules that influence development in plants
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What is synergism?
When 2 or more plant hormones act together to rienforce and amplify the effects
What is antagonism?
When 2 or more plant hormones have opposing actions that diminish each others effects
What do plant hormones usually influence?
Cell elongation, differentation and division
What are the 5 plant hormones?
- auxin
- gibberellin
- cytokinins
- ethene
- abscisic acid
What are the effects of auxin?
- promotes cell elongation
- inhibits lateral growth
- inhibits leaf absission
What are the effects of gibberellins?
- promotes seed germination
- promotes growth of stems/ cell elongation
- stimulates cell division
loosens cell walls
stimulates cell cycle protein
What are the effects of abscisic acid?
- inhibits seed germination and growth
- causes stomatal closure when the plant is stressed by low water availibility
What are the effects of ethene?
Promotes fruit ripening
What are the effects of cytokinins?
- promotes cell division
- delays leaf abscission and senescence
- overcomes apical dominance
- promotes cell expansion
What does the removal of the apical bud cause?
lateral growth
What is the apical bud and what does it do?
- top bud on a plant
- causes apical dominance which promotes vertical growth and inhibits lateral growth
contains lots of auxin, causing cytokinins to accumulate
What causes apical dominance?
- there is a lot of auxin in the bud
- this causes cytokinins to accumulate near the shoot
- it increases the ABA in the rest of the plant which inhibits lateral growth
- this causes apical dominance
What happens when you remove the top bud?
- remove the top bud
- cytokinins then spread out more evenly along the plant
- it decreases the ABA so lateral bud growth is stimulated
- which leads to no apical dominance
What is the role of abscisic acid during apical dominance?
Inhibit lateral bud growth
High levels of auxins keep abscisic acid levels high
What is the role of cytokinins during apical dminance?
Stimulates growth
High levels of auxin cause cytokinins to move to the shoot apex
What is the chemical needed to create tall plants?
GA1 as it directly causes stem growth
Gibberellin
What is the Le gene?
It is the gene needed to create the enzyme that converts GA20 into GA1
Why are dwarf plants short?
They lack the Le gene to convert GA20 into GA1
Contain recessive le allele instead
Why is the plant without the na allele short?
it cannot turn nt-kaurene into GA12-aldehyde to create GA1
What happens when you graft a dwarf plant with one that does not contain the na allele?
It lead to the tall plant as the dwarf plant has the na allele and the other plant has the Le allele so together they can creat GA1
How are gibberellins used commercially?
- used to develop bigger fruit
- allows for stem elongation so fruit have more space to grow (grapes)
- speeds up germination for brewing?
- allows sugar cane stalks to grow more to increase production
- lodging (shorter stems so plants don’t snap)
How are auxins used commercially?
- promotes rapid shoot growth so stem cannot support leaves and the plant dies (weed killer)
- on flowers to promote ovule growth so fruit grows with no seeds
- as a rooting powder to encourage root growth in plant cuttings
How is ethene used commercially?
- fruit ripening
- stops fruit from ripening
How does auxin cause cell elongation in the shoots?
- promotes active transport of H+ ions into the cell wall which decreases pH
- it enables optimum conditions for the enzymes (expansis)
- this breaks the bonds in the cellulose cell wall as the H+ ions disrupt the H bonds in the cellulose
- it becomes less rigid and expands as water moves in via osmosis
How does auxin cause geotropism in the roots?
- auxin accumulates on he bottom of the roots
- it inhibits cell elongation so roots grow downwards
- auxin conc. is much lower in the roots compared to the shoots
What tropism experiment did Charles and Francis Darwin do and what did it discover?
- they cut off/ covered he shoot tips
- the tip is sensitive to light
What tropism experiment did Boysen-Jensen do and what did it discover?
- cut off te tip and replaced it with different materals separating it
- chemical messenger has the ability to move
- separating part of the shoot from the rest of the plant
- chemical acts on shady side and encourages growth
What tropism experiment did Paal do and what did it discover?
- removing the tip and placing it to one side
- chemical travels in a downward direction
What tropism experiment did Went do and what did it discover?
- cut the tip off and placed it onto agar and then placed the agar on the shoot with no tip
- chemical messanger can diffuse and can be stimulated artificially
How does seed germination happen?
- when conditions are correct the seed begins to absorbe water
- embryo releases gibberellin which stimulates production of amylase
- amylase breaks starch down into glucose
- glucose is used in respiration to release energy
- energy is used for cellular recations to allow for germination
What are examples of smooth muscle?
- blood vessels
- eyes
- intestines
- uterus
- bladder
- cardiac muscles
- respiratory system
What is peristalsis?
The unvoluntary and smooth contraction and relaxation of the intestines
What are the two main divisions of the nervous system?
The central nervous system and the peripheral nervous system
What is the PNS divided into?
The somatic nervous system and the autonomic nervous system
What does the CNS consist of?
Brain and the spinal cord and relay neurones
What is the role of the PNS?
To ensure rapid communication between sensory receptors, the CNS and the effectors
What are the characteristics of the somatic nervous system?
- effectors are skeletal muscles
- 1 nerone
- acetylcholine as neurotransmitter
- heavily myelinated neurons
- stimulatory responses
- quick responses
What are characteristics of the sympathetic nervous system?
- prepares body for activity
- ‘fight or flight’
- ganglia just outside CNS
- uses noradrenaline as a neurotransmitter
- neurons are lightly myelinated
- most active during times of stress
Eg/ increases heart rate, dialates pupils
What are the characteristics of the parasympathetic nervous system?
- decreases activity/ conserves energy
- ‘rest and digest’
- ganglia in effector tissue
- uses acetylcholine as neurotransmitter
- neurons are lightly myelinated
- most active during sleep or relaxation
Eg/ increases digestive activity, decreases heart rate
What are the characteristics of the autonomic nervous system?
- effectors are involuntary muscles
- 2 neurones
- acetylcholine and noradrenaline as neurotransmitters
- lightly myelinated
- stimulatory or inhibitory responses
- slower responses
- splits into parasympathetic and sympathetic nervous systems
What does the brain consist of?
- medulla oblongata
- cerebellum
- cerebrum cortex
- hypothalamous
What is the role of the medulla oblongata?
It controls vital functions like heart and ventilation rates, peristalsis and blood pressure
What is the role of the cerebellum?
Controls balance and muscle coordination
What is the role of the cerebrum cortex?
It controls the bodies voluntary behaviour such as learning, personality, memory, decision making, intelligence and sensory input
What is the role of the hypothalamus?
It recieves sensory information and contains centres that control factors such as temperature and blood solute concentration. It also produces ADH and stores it in the pituitary glands
What are the clues that an action is a reflex?
- involves only three neurones
- coordinated by medulla oblangata
What are the clues that an action is involuntary or autonomic?
- does not use the cerebrum cortex
- does not use decision making
What are the characteristics of a reflex?
- involuntary responses
- very rapid
- not learned
- controls everyday actions
What is the pathway of the knee jerk reflex?
- receptors at the knee detect the stimulus of the touch
- action potencial sent down sensory neurone
- passes the relay neurone in the spinal chord
- goes down the motor neurone to the effector which causes the quadriceps to contract
- this reflex helps with balance whilst walking
What is the pathways for a cranial reflex (blink reflex)?
- receptors at the eye detect the stimulus of the touch
- action potencial sent down sensory neurone
- passes the relay neurone in the medulla oblongata
- goes down the motor neurone to the effector which causes the eyelid muscles to contract
Where are alkaloids found and what do they do?
- growing tips and flowers
- feeding deterrents as they taste bitter
- derived from amino acids
What do pheromones do?
- secreted by the plant
- affect the behaviour or physiology of another organism
