9.1 Flashcards
How do the nervous and chemical control systems interact to maintain homeostasis
changes in the body are detected by sensers/receptors which then sends a message to effectors, these then work to either reverse the change or increase it
why does water potential need to be maintained
to avoid osmotic effects that could damage or destroy cells
why does temperature need to be maintained
maintains optimum activity of enzymes
maintains integrity of membranes
controls movement of substances into and out of the cells
why does the pH need to be maintained
for structures of protein molecules to remain stable
allows enzymes to function at their optimum
structure of cell membrane is maintained
what are the mechanisms controlled in homeostasis
pH
temperature
water potential
define homeostasis
the maintenance of a state of dynamic equilibrium in the body, despite changes in external or internal conditions
what are sensors/receptors
specialised cells that are sensitive to specific changes in the environment
what are effectors
systems (usually muscles or glands) that work to either reverse, increase or decrease changes in a biological system
define negative feedback system
a way of maintaining a condition by recognising an increase by receptors and as a result effectors are stimulated to decrease it to maintain dynamic equilibrium
what are the effectors for hormonal communication
target organs
what are the effectors for nervous system communication
muscles and glands
define positive feedback system
effectors work to increase an effect that has triggered a response
explain the positive feedback system of contractions of the uterus during labour
brain stimulates pituitary to release oxytocin
oxytocin makes uterus contract harder pushing baby against cervix
baby pushes against cervix - cervix stretches
stretch receptors in cervix send impulses to brain
why are chemical messengers used in homeostasis control
effect lasts over a long period of time
reach the entire body
where are hormones released from
endocrine glands
outline what hormones do
organic chemicals produced in endocrine glands and released into the blood carried through the transport system to parts of the body that they bring about changes which may be widespread or specifically targeted
what are endocrine glands
produce hormones
do not have ducts
release hormones directly into the blood stream
what are exocrine glands
produce chemicals (e.g.enzymes) and release them along small tubes or ducts
what are the common forms of hormones
proteins, peptides, steroids
how are glands well adapted
always have a rich blood supply of capillaries to release their hormones and chemicals into
how is hormone release controlled by the nervous system
the endocrine gland is directly stimulated by a nerve resulting in the release of the hormone and doesn’t release the hormone when not stimulated
how is hormone release controlled by response to chemical stimulus in a negative feedback loop
increase in stimulating chemical -> increase in hormone release -> decrease in stimulating chemical -> hormone release decreased -> increase in stimulating chemical
what is the pituitary gland
a small gland in the brain that has an anterior lobe and a posterior lobe and produces and releases secretions that affect the activity of most endocrine glands
what is the hypothalamus
small area in the brain directly above the pituitary gland that controls the activities of the pituitary gland and coordinates the autonomic nervous system
what are neurosecretory cells
nerve cells that produce secretions from the ends of their axons which either stimulate or inhibit release of hormones
what is the role of neurosecretory cells 1
produce substances that stimulate or inhibit the release of hormones from the anterior pituitary
what is the name of the substances produced from neurosecretory cells 1
releasing factors or release-inhibiting factors
what is the role of neurosecretory cells 2
produce secretions that are stored in the posterior pituitary and are released later as hormones
what cells is the hypothalamus made up of
neurosecretory cells 1/2
what hormones are released from the anterior pituitary
- thyroid-stimulating hormone
- growth hormone (GH)
- adrenocorticotrophic hormone (ACTH)
- follicle stimulating hormone (FSH)
- luteinising hormone (LH
- prolatin
what hormones are released by the posterior pituitary
- oxytocin
- antidiuretic hormone (ADH)
what is the role of thyroid-stimulating hormone
controls the secretion of thyroxin and triiodothyronine from the thyroid gland
what is the role of growth hormone (GH)
stimulates the growth of body cells and increases the build up of proteins
what is the role of adrenocorticotrophic hormone (ACTH)
controls secretion of some of the hormones of the adrenal cortex of the adrenal glands
what is the role of follicle stimulating hormone (FSH)
in females - stimulates ovaries to produce oestrogen and development of ova in the menstrual cycle
in males - stimulates the testes to produce sperm
what is the role of luteinising hormone (LH)
in females - stimulates ovulation and formation of corpus luteum and prepares uterus for implanting
in males - stimulates the testes to produce testosterone
what is the role of prolactin
stimulates and maintains production of milk by the mammary glands
what is the role of antidiuretic hormone (ADH)
decreases the urine volume by affecting the tubules of the kidney, can cause arteries to constrict after hemorrhage to prevent excess blood loss and raising blood pressure
what is the role of oxytocin
stimulates the muscles of the uterus to contract during labour and the contraction of cells in the mammary tissue
how do hormones work when they are not lipid soluble
if hormones are not lipid soluble they cannot cross the cell membrane so it binds to a receptor on the cell membrane which triggers a series of membrane-bound reactions that result in formation of a second chemical messenger inside the cell that then activates enzymes within the cell
what is cyclic AMP (cAMP)
formed from ATP
triggers increased cellular respiration, increased contraction of muscle, relaxation of smooth muscle in blood vessels
how does adrenaline work
it is not lipid soluble therefor it binds to receptor on the cell surface membrane
this activates membrane-bound proteins which activates adenylate cyclase for the formation of cAMP
how do lipid soluble hormones work
the hormone passes through the membrane and inside the cell where it binds to a receptor and forms a hormone-receptor complex which can then pass through pores in the nuclear membrane so that it then acts as a transcription factor
what hormones are commonly lipid soluble
oestrogen and testosterone
why do plants need hormones
the rely on them to communicate between different parts of the plant and respond to factors such as light and gravity
what different factors of light affect plants
direction of light
intensity of light
length of exposure to light
what factors effect the growth of plants
gravity
water
temperature
light
what is a tropism
plant growth responses to environmental cues
what are auxins
plant hormones that act as powerful growth stimulants and are involved in apical dominance, stem and root growth, and tropic responses to unilateral light
how do auxins move down the plant from the shoots to the roots
active transport and calcium ions
what is apical dominance
suppression of growth in lateral shoots so that one main stem grows fastest
what does the response of a plant to auxin depend upon
concentration of hormone and the region of the plant
explain the elongation of plant cells using hormones
the molecule IAA binds to specific receptors on the cell surface membrane
activates pumping of H+ ions into the cell wall spaces to increase pH to 5
this provides the optimum pH for the enzyme that breaks bonds between cellulose microfibrils
the microfibrils slide past each other easily making the cell wall flexible
the cell then absorbs water by osmosis and due to turgor pressure the flexible cell wall elongates and expands
why do plant cells become more rigid over time
as the cell matures the IAA is destroyed and the pH rises, the enzyme is inhibited, bonds form between cellulose microfibrils and becomes rigid
how do plants grow towards light
light on one side of the plant is stronger than the other
light causes auxin to move laterally across the shoot away from the light
producing a greater concentration on the unilluminated side
the shoot tip acts as a photoreceptor
cell growth and elongation occurs on the dark side
resulting in shoot bending towards the light
until it grows directly towards the light and auxin concentration becomes even so it grows straight towards the light
what do gibberellins do
affect internodes of stems
stimulate elongation of growing cells
promote growth of fruit
how are gibberellins involved in seed germination
the are involved in breaking dormancy of seeds and stimulating formation of enzymes in seeds
what do cytokinins do
promote cell division in apical meristem and cambium
what is abscission
the shedding of leaves, flower parts or fruits from a plant after the formation of an abscission zone across the stem attaching the organ to the plant
what name is given to hormones which work together, completing each other and giving a greater response
synergy
what name is given to hormones that have opposite effects and the balance between them determines the outcome
antagonism
what hormones work antagonistically together to maintain apical dominance
auxins and cytokinins
what 2 plant hormones have a synergy
auxins and gibberellins
how do auxins and cytokinins work antagonistically in the growth of plants
initially high concentrations of auxin to promote growth of lead shoot and as this increases cytokinins are inhibited until auxin concentration decreases then cytokinins become dominant and lateral buds are activated and grow
what would happen to a plant that wasn’t given any light
the metabolism of a plant is severely disrupted and no chlorophyll is formed and no photosynthesis takes place and eventually the plant dies
what is photomorphogenesis
the process by which the form and development of a plant is controlled by the levels and type of light
what is the wavelength of light
580-660nm
what is the wavelength of far red light
700-730nm
what do plants use to detect red light and far red light
phytochromes
what are phytochromes
plant pigment that reacts with different types of light and affects the response of the plant
does red light stimulate or inhibit germination
red light stimulates germination
does far red light stimulate or inhibit germination
far red light inhibits germination
what phytochrome absorbs red light
Pr
what phytochrome absorbs far red light
Pfr
what occurs to Pr when is it exposed to red light
it is converted to Pfr
what occurs when Pfr when it is exposed to far red light
it is converted to Pr
what occurs to phytochromes as a seed germinates
as a seedling is germinating is it only exposed to far red light so it has Pr then as soon as it breaks through the surface of the soil it is exposed to red light and Pr is converted to Pfr
what occurs to the formation of Pr and Pfr in the dark
Pfr is converted to Pr
is Pr or Pfr more biologically active
Pfr
is Pr or Pfr more stable
Pr
what is the photoperiod
amount of light an organism is exposed to in the 24hour period
what are short-day plants
plants flowering when days are short and nights are long
what are long-day plants
plants flowering when days are long and nights are short
what are day-neutral plants
plants where flowering is not affected by the length of time they are exposed to light or dark
how does red light affect flowering of plants
inhibits flowering of short-day plants
stimulates flowering of long-day plants
what are etiolated plants
plants that grow in the dark with long internodes, thin stems, small or unformed leaves and white or pale yellow in colour
what are the typical characteristics of a germinating plant
- rapid stem lengthening but little thickening
- relatively little root growth
- no leaf growth
- no chlorophyll
