homeostasis
maintenance of a constant internal environment
involves an optimum point
-temp
-pH
-water potential
processes of life
metabolism
response
homeostasis
growth
reproduction
excretion
nutrition
optimal conditions external
temp
toxins
humidity
light intensity
optimal conditions internal
temp
water potential
pH
metabolic substrate
if not optimum conditions
enzymes denature
tertiary structure changed
can no longer make substrate complexes
or not enough successful collisions
water potential changes
change in the volume of cells due to osmosis-expand and shrink
influenced by glucose concentration
glucose conc affects supply of glucose for respiration
controlling homeostasis
1-optimum
2-receptor
3-coordinator
4-effector
positive feedback
amplifacation of a response
-conditions change
-change detected
-response reinforces change
so conditions are changed and cycle continues
positive feedback example
stretch in the cervix from the baby
nerve impulse to the brain
brain stimulates the release of oxytocin
causes the uterus to contract
stretching the cervix
negative feedback
restoration of set point
ideal conditions
increase/decrease detected
decrease/increase occurs
example of negative feedback
oven
heat goes over set temp
fan turns off
heat goes under set temp
fan goes on
hormones release
endocrine glands can be stimulated to release hormones by nerves or other hormones
pituitary gland particularly secretes hormones that affect other glands
pituritry and hypothalomus
found in brain
hypothalamus often controls pituitary
hypothalomus contains neurosecretry cells
a group of which stimulate or inhibit the release of hormones from the anterior pituitary
-release factors or release inhibiting factors
another group of neurosecretery produce secretions that are stored in the posterior pituitary and released as hormones /
anterior lobe hormones x6
thyroid stimulating hormone
-secretion of thyroxin
growth hormones (GH)
-stimulates growth
adrenocorticotrophic hormone (ACTH)
-controls adrenal cortex
follicle stimulating hormone (FSH)
-stimulates oestrogen and sperm
leueinising hormone (LH)
-stimulates ovulation
prolactin
-milk production
posterior lobe hormones x2
antidiuretic hormone (ADH)
-decreases urine volume
oxytocin
-stimulates muscle contraction in the uterus
second messenger
-hormones bind to receptors on target cells
-triggers intracellular membrane bound reactions
-stimulates the release of second messenger
-which activates enzymes to alter the metabolism of a cell
second messenger e.g
adrenaline binds to a receptor
activating to an enzyme- adenyl cyclase which converts atp to cyclic AMP
the cAMP acts as second messenger
triggers different responses e.g increased respiration
hormone enters through cell
hormones pass through the membrane and bind to a receptor inside the cell
they form a hormone-receptor complex which passes into the nucleus and acts as a transcription factor to regulate gene expression
oestrogen
tropisms
growth of a plant in response to a stimulus
plant grows towards or away from stimuli
e.g
positive phototropism - plant grows towards light
negative gravitropism - plant grows away from light
hydrophobic - water
plant hormones
auxins
cytokinins
gibberellins
auxins
produced in young shoots (e.g IAA)
plant growth factor
released from terminal bud
move down plant - active transport + calcium ions
control gravitropism and photo
inhibit growth of side plants- apical dominance (growth only in stem)
control the amount of cytokines
cytokinins
promote bud growth
produced from base of shoot
promote cell devision in the meristems and cambium
work with ethene in the abcisiion of leaves flowers and fruits
how does IAA work
iaa diffuses to zone of elongation
bind to specific receptor sites on the cell membrane -active pumping of H+ ions into the cell wall spaces
changes pH to 5 which is the optimum for enzymes that break myofibrils bonds
so more water can be absorbed by osmosis causing cell walls to stretch elongating the cell
