Plant and Animal responses Flashcards
CHEMICAL DEFENCES: Tannins
-phenolic compounds located in cell vacuoles or in surface wax of plants
-toxic to microorganisms and larger herbivores
-in upper epidermis of leaves and make leaf taste bad
-in roots they prevent infiltration by pathogenic microorganisms
CHEMICAL DEFENCES: alkaloids
-organic nitrogen containing bases that have important physiological effects on animals
-include nicotine, quinine, strychnine and morphine
-derived from amino acids
-feeding deterrents to animals as taste bitter
-located in growing tips and flowers
-in peripheral cell layers of stems and roots
CHEMICAL DEFENCES: pheromones
-any chemical substance released by one living thing which affects the behaviour or physiology of another living thing
Define tropism
directional growth response to in which direction of response is determined by direction of external stimulus
TYPES RESPONSE: phototropism
-shoots grow toward light which enable them to photosynthesise
TYPES RESPONSE: geotropism
-roots grow towards pull of gravity
-this anchors them in soil and helps them to take up water which is needed for support (keeps cells turgid) as raw material for photosynthesis and helps cool plant
-also be minerals such as nitrates in water, needed for synthesis of amino acids
TYPES RESPONSE: chemotropism
-on a flower, pollen tubes grow down style attracted by chemicals, towards ovary where fertilisation can take place
TYPES RESPONSE: thigmotropism
-shoots of climbing plants such as ivy wind around other plans or solid structures to gain support
Positive v negative response
-if plant responds towards stimulus it is positive tropic response
-if plant responds away from stimulus it is still a tropic response but negative
Nastic responses
-non directional response to external stimuli
-e.g. sensitive plant, Mimosa pudica responds to touch with sudden folding of leaves
What are plant hormones
-they coordinate plant response to environmental stimuli
-they are chemical messengers that can be transported away from their site of manufacture to act in other parts of plant
-they are not produced by endocrine glands but by cells in a variety of tissues in the plant
Mechanism of plant hormones
-when hormones reach target cells, bind to receptors on plasma membrane
-specific hormones have specific shapes which can only bind to specific receptors with complementary shapes on membranes of particular cells
-this specific binding ensures hormones only act upon correct tissues
-some hormones can amplify each others effects and some even cancel each other out
-hormones can influence cell division, elongation or differentiation
HORMONES: cytokinins
-promote cell division
-delay leaf senescence
-overcome apical dominance
-promote cell expansion
HORMONES: abscisic acid
-inhibits seed germination and growth
-causes stomatal closure when plant stressed by low water availability
HORMONES: auxins
-promote cell elongation
-inhibit growth of side shoots
-inhibit leaf abscission (leaf fall)
HORMONES: gibberellins
-promote seed germination
-promote growth of stems
HORMONES: ethene
-promote fruit ripening
How do hormones move around plant
-either by active transport, diffusion or mass flow in phloem sap or xylem vessels
Define apical dominance
-inhibition of lateral buds further down shoot by chemicals produced by apical bud at tip of plant shoot
Describe role of auxins and how they were tested
-plant hormones responsible for regulating plant growth
-if you break tip off plant, plant starts to grow side branches from lateral buds that were previously dormant
-auxin levels drop when tip removed and buds grow
-to test this, scientists applied paste containing auxins to cut end of shoot and lateral buds did not grow
-however, when they applied a ring of auxin transport inhibitor below apex of shoot, lateral buds grew
-suggests that normal auxin level in lateral buds inhibits growth, whereas low auxin levels promote growth
-the two variables - auxin levels and growth inhibition - may have no effect on each other both could be affected by third variable
Describe abscisic acid
-inhibits bud growth
-high auxin shoot may keep abscisic acid levels high in bud
-when tip removed, source of auxin, abscisic acid levels drop and bud starts to grow
Describe cytokinins
-promote bud growth
-directly applying cytokinins to buds can override apical dominance effect
-high levels of auxin make apex a sink for cytokinins produced in root - most cytokinins goes to shoot apex
-when apex removed, cytokinins spread evenly around plant
Describe the research for gibberellins and stem elongation
-researchers compared GA1 levels of tall pea plants and dwarf pea plants which were genetically identical apart from tall=dominant Le and dwarf=dominant le allele
-found that plants with higher GA1 levels were taller
-to show GA directly causes stem growth, researchers found how GA formed
-the Le gene responsible for producing enzyme enzyme that converted GA20 to GA1
-researchers found pea plant with mutation blocking gibberellin production between ent-kaurene and GA12-aldehyde in synthesis pathway produce no gibberellin and only grow 1cm tall
-it was confirmed GA1 causes stem elongation
Describe how gibberellins cause stem elongation
-cause growth in internodes by stimulating cell elongation (by loosening cell walls) and cell division (by stimulating production of protein that controls cell cycle)
List the gibberellin synthesis pathway
ent-kaurene
GA12-aldehyde
GA12
GA53
GA44
GA19
GA20
enzyme by Le allele acts here
GA1
Describe how gibberellins control seed germination
-when seeds absorbs water, embryo releases gibberellins which travel to aluerone layer in endosperm region of speed
-gibberellin enables production of amylase which can break down starch into glucose
-this provides substrate for respiration for embryo and so it grows
-glucose also used for protein synthesis
Where does plant growth occur
-plant cells can only divide and expand in groups of immature cells that are still capable of dividing
(meristems)
-apical meristems - at tips or apices of roots and shoots; responsible for roots and shoots getting longer
-lateral bud meristems - found in buds; give rise to side shoots
-lateral meristems - forming cylinder near outside of roots and shoots and are responsible for roots and shoots getting wider
-intercalary meristems - located between nodes where leaves and buds branch off stem. Growth between nodes responsible for some shoots getting longer
How can we investigate phototropic responses
-using experimental plant and control plant with 10 replicates
-control plant is illuminated from all sides, while experimental has illumination from just one side
-in each plant, shoots and roots are marked every 2mm at start
-after several days look at results
-shoot has bent toward light because shady side of shoot has elongated more than illuminated side
-mean and standard deviation of lengths between marks has increased on shady side
How can we investigate geotropic responses
-a control plant constantly spun (very slowly) by machine called klinostat to ensure effect of gravity applied equally to all sides
-for experimental plant klinostat is not switche don so gravity only applied to on side
-in experimental plant, root bends downwards because upper side of root elongated more than lower side
-shoot bends upwards because lower side of shoot elongated more than upper side
-in control, both root and shoot grow horizontally
How are the effect of plant hormones on phototropism investigated
-Darwin’s experiments confirmed that shoot tip was responsible for phototropic responses
-Boysen-Jensen work confirmed water and/or solutes need to be able to move backwards from shoot tip for phototropism to work
-when permeable gelatine block inserted behind shoot tip, shoot still showed positive phototropism
-when impermeable mica block inserted, no phototropic response
How was the role of auxin as the chemical messenger confirmed
-using a series of different concentrations of auxins (e.g. IAA) created by serial dilution gives shoot curvature in proportion to amount of auxin
-auxins are produced at apex of shoot
-auxin travels to cells in zone of elongation, causing them to elongate and make shoot grow
-when light equal on all sides, auxin simply promotes shoot growth evenly
-light shining on one side of shoot appears to cause auxins to move to shaded side causing cells there to elongate more quickly, and shoot bends toward light
-extent to which cells elongated is proportional to concentration of auxins
Describe the mechanism of auxins
-auxin increases stretchiness of cell wall by promoting active transport of H+ by ATPase enzyme on plasma membrane, into cell wall
-the resulting low pH provides optimum conditions for wall loosening enzymes (expansins) to work
-these enzymes break bonds within cellulose (at same time, increased hydrogen ions disrupt hydrogen bonds within cellulose) so walls become less rigid and can expand as cell takes in water
Explain the research on how light causes the redistribution of auxins
-two enzymes identified - phototropin 1 and phototropin 2 - whose activity is promoted by blue light
-blue light is main component of white light that causes the phototropic response
-hence, lots of phototropin 1 activity on light side but progressively less toward dark
-this gradient thought to cause redistribution of auxins through their effect on PIN proteins
these transmembrane proteins can be found dorsally, ventrally or laterally on plasma membrane of cells and they control efflux of auxin from each cell, essentially sending auxin in different directions in shoot, depending on their location
How is activity of PIN proteins controlled
-controlled by PINOID molecule
-one theory suggests that phototropins affect activity of PINOID which then affects PIN activity
-however evidence from ARABIDOPSIS suggests this may only work for pulse induced phototropism (short bursts of light) with another independent mechanism able to operate in continuous light
Explain the effect of auxin in geotropic responses of roots
-in a root lying flat, Went discovered that auxin accumulates on lower side where is inhibits cell elongation
-the upper side continues to grow and root bends downwards
-this effect of auxin in roots is in contrast to that in the shoot where auxin promotes cell elongation on lower side, making shoot lying flat bend upwards
-this happens because root and shoot cells in elongation zone exhibit different responses to same concentration of auxin
-concentrations that stimulate growth in shoot=inhibit root growth
COMMERCIAL USES: auxins
-can be used to prevent leaf and fruit drop and to promote flowering for commercial flower production
-useful if there are too many small fruit that will be difficult to sell - fruit produces fewer, larger fruit
- cuttings - dipping end of cutting in rooting powder (containing auxins) before planting it encourages root growth
-seedless fruit - 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 developing fruit, helping to complete developmental process
-herbicides - used as herbicides, man made auxins hard to break down and can act within plant for longer. Promote shoot growth too much that stem cannot support itself, buckles and dies
COMMERCIAL USES: cytokinins
-because cytokinins can delay leaf senescence they are sometimes used to prevent yellowing of lettuce leaves after been picked
-used in tissue culture to help mass produce plants
-promote bud and shoot growth from small pieces of tissue taken from plant parent - produces short shoot with lot of side branches which can be split into lots of small pieces
-each of these then grown separately
COMMERCIAL USES: gibberellins; fruit production
-gibberellins delay senescence in citrus fruit, extending time fruit can be left unpicked and making them available for longer in the shops
-gibberellins acting with cytokinins can make apples elongated to improve their shape
-without gibberellins bunches of grapes are very compact which restricts growth of individual grapes
-with gibberellins grape stalk elongates, less compacted and grape gets bigger
COMMERCIAL USES: gibberellins; brewing
-to make beer you need malt which is usually produced in malthouse at brewery
-when barley seeds germinate, the aluerone layer of seed produces amylase enzymes that break down stored starch into maltose
-usually genes for amylase production are switched on by naturally occurring gibberellins
-adding gibberellins can speed up process
-malt produced by drying and grinding seeds
COMMERCIAL USES: gibberellins; sugar production
-spraying sugar cane with gibberellins stimulates growth between nodes, making stems elongate
-useful as sugar cane stores sugar in cells of internodes, making more sugar available from each plant
COMMERCIAL USES: gibberellins; plant breeding
-plant breeders job to produce plants with desired characteristics by breeding together other plants usually over many generations
-however in conifer plants this can take particularly long time because conifers spend long as juveniles before becoming reproductively active
-gibberellins can speed up process by inducing seed formation on young trees
-seed companies that want to harvest seeds from biennial plants can add gibberellins to induce seed production
-stopping plants making gibberellins also useful
-spraying with gibberellin synthesis inhibitors can keep flowering short and stocky - desirable in poinsettias
-also ensures internodes of crop plant stay short, helping prevent lodging
-lodging occurs in wet summers - stem bend over because of weight of water collected on ripened seed heads making crop difficult to harvest
How is ethene applied
-ethene is a gas so cannot be sprayed directly, scientists developed 2-chlorethylphosophonic acid which can be sprayed in solution, so is easily absorbed and slowly releases ethene inside plant
COMMERCIAL USES: ethene
-speed up fruit ripening in apples, tomatoes, citrus fruit
-promoting fruit drop in cotton, cherry, walnut
-promoting female sex expression in cucumbers, reducing chance of self pollination (bitter taste) and increase yield
-promoting lateral growth in some plants, yielding compact flowering stems
Why is restricting ethene effects useful
-storing fruit at low temperature with little oxygen and high carbon dioxide levels prevents ethene synthesis and thus prevents fruit ripening
-means fruits can be stored for longer - essential when shipping unripe bananas from caribbean
-other inhibitors of ethene synthesis such as silver salts, can increase shelf life of cut flowers
Summarise the role of the nervous system
-successful organism must be able to respond to changes in the environment
-these changes could be in internal or external environment
-communication system must enable: cell signalling between all part of body, coordination of range of effectors to carry out responses to sensory input, suitable responses, detection of changes in environment
-many environmental changes require rapid and well coordinated responses to ensure survival
-this may involve wide array of responses such as coordinated muscle action, control of balance, temperature regulation etc
Describe the divisions of the nervous system
-most obvious division of nervous system is into central nervous system and peripheral nervous system
-the PNS further divided into sensory system and motor system
-motor system divided into somatic nervous system and autonomic nervous system
-these divisions help us describe nervous actions and to understand coordination processes
-CNS - brain and spinal cord
-PNS- sensory nervous system and motor system
-MOTOR SYSTEM - somatic nervous system and autonomic nervous system
Describe the brain of the CNS
-human brain contains about 86 billion neurones
-much of brain is composed of relay neurones which have multiple connections enabling complex neural pathways
-most of these cells are non myelinated cells and tissue looks grey in colour - known as grey matter
Describe the spinal cord of the CNS
-also has many non myelinated relay neurones making up central grey matter
-however spinal cord also contains large numbers of myelinated neurones making up an outer region of white matter
-these myelinated neurones carry action potentials up and down the spinal cord for rapid communication over longer distances
-spinal cord is protected by vertebral column
-between each of these vertebrae, peripheral nerves enter and leave spinal cord carrying action potentials to and from rest of body
Describe the peripheral nervous system
-role of the peripheral nervous system is to ensure rapid communication between the sensory receptors, CNS and effectors
-the PNS is composed of sensory and motor neurones
-these usually bundled together in connective tissue sheath to form
Describe the sensory nervous system
-sensory fibres entering CNS are dendrons of sensory neurones
-these neurones conduct action potentials from the sensory receptors into CNS
-these neurones have their cell body in dorsal root leading into spinal cord and short axon connecting to other neurones in CNS
What is the motor nervous system
-conducts action potentials from the CNS to effectors
-further subdivided according to functions of motor neurones
