B1.2 Flashcards
What is homeostasis?
maintaining a stable environment
What 3 things does homeostasis control?
osmoregulation- regulating water content
need balance between water gained (e.g food and drink) and lost (e.g in sweat)
thermoregulation - regulating body temperature
need to get rid of excess body heat when cold but retain heat when cold
blood glucose regulation -
need to keep glucose in blood at steady level
How does homeostasis work?
negative feedback keeps all things steady
changes in environment trigger response to counteract the changes
internal environment stays at the level cells work best
only works within certain limits - if too much change, may not be possible to counteract it
How is body temperature controlled?
enzymes work best at around 37oc
hypothalamus in brain controls it
when change detected, response in dermis
if too hot:
erector muscles relax, hairs lie flat
sweat produced in sweat glands - when it evaporates, transfers skin heat to environment and cools you down
blood vessels close to skin dilate (vasodilation) - more blood flow near surface and more heat lost through radiation
if too cold:
erector muscles contract, hairs on end - traps insulating layer of air to keep you warm
very little sweat produced - no heat lost through evaporation
blood vessels close to skin contract (vasoconstriction)- less blood flow near surface, less heat lost through radiation
What are hormones?
Where are they produced?
chemical messengers which travel in blood to activate target cells
produced in endocrine glands
travel all over body but only effect certain cells in certain places (target cells)
target cells have right receptors to respond to hormones
organ containing target cells is target organ
travel at speed of blood
What are neurones?
nerve cells that transmit information as electrical impulses around body
have branched endings (dendrons) to connect with other neurones
electrical impulse passed along axon of cell
myelin sheath- acts as electrical insulator, stops impulse getting lost and speeds it up
neurones long- speeds up impulse, one long neurone quicker than lots of small ones)
synapse (gap) - connection between two neurones
nerve impulse transmitted by neurotransmitters, diffuse across gap and start impulse in next neurone
What is the difference between hormones and nerves?
nerves: very fast act for short time act on very precise area electrical message
hormones: slower message act for long time act in more general way chemical message
What are chromosomes and genes?
chromosomes- long lengths of coiled up DNA
23 pairs in nucleus of human cells
carry genes
genes- short section of DNA
control development of different characteristics e.g hair colour
different versions of same gene - give different versions of characteristic. called alleles
two copies of each chromosome so two of each gene- two alleles same or two different
What are sense organs and stimuli?
sense organs detect stimuli
stimulus- change in environment you may have to respond to
5 sense organs - eyes, ears, nose, tongue, skin
all contain different receptors (group of cells sensitive to stimulus) that change stimulus energy (e.g light energy) into electrical impulses
stimulus can be: light, sound, touch, pressure, chemical or change in pressure/ temperature
What receptors do the sense organs contain?
eyes- light receptors
ears- sound and “balance” receptors
nose - smell receptors, sensitive to chemical stimuli
tongue - taste receptors sensitive to chemical stimuli, bitter, sweet, sour, savoury, salt
skin- sensitive to touch (pressure) and temperature change
What is the CNS and how does it work?
central nervous system- consists of brain and spinal chord
coordinates a response
when stimulus detected by receptors in sense organ, information sent as electrical impulses along sensory neurone
CNS then coordinates a response- decides what to do about stimulus and tells something to do it
CNS sends information to effector along motor neurone, effector responds accordingly
What are the different types of neurone and what do they do?
sensory neurone- long dendrons and short axons
carry nerve impulses from receptor in sense organs to CNS
relay neurones- short dendrons and axons
carry nerve impulses from sensory neurones to motor neurones
motor neurones - many short dendrons, one long axon
carry nerve impulses from CNS to effectors
effectors- muscles and glands, respond in different ways
muscles contract in response to a nervous impulse, glands secrete substances e.g hormones
What are reflexes?
automatic responses to certain stimuli to reduce chances of being injured
example: if light shone in your eye, pupils automatically get smaller so less light gets in eye
What is a reflex arc and how does it work?
passage of information in a reflex from receptor to effector
neurones go through spinal chord or unconscious part of brain
when stimulus detected by receptors, impulses sent along sensory neurone to CNS
in CNS, sensory neurone, passes on message to relay neurone
relay neurones relay impulse to motor neurone
impulses travel along motor neurone to effector
effector responds (e.g muscle moves hand)
you don’t have to think about it, quicker than normal responses
What practical can investigate external stimuli?
one person blindfolded, other person uses two points of paperclip fixed distance apart to touch the blindfolded person’s skin
how many points felt depends on area of skin and how sensitive
really sensitive places, both points felt when closer together as more touch receptors
less sensitive area, both points felt when further apart as fewer touch receptors
What happens if blood glucose levels too high/low?
controlled by insulin and glucagon
when too high:
insulin secreted by pancreas, added to blood
glucose removed from blood by liver
insulin causes liver to turn glucose into glycogen
glucose levels removed, pancreas stops secreting insulin
when too low:
glucagon secreted by pancreas and added to blood
glucose added to blood by liver
glucagon causes liver to turn glycogen into glucose
glucose levels increased, pancreas stops secreting glucagon
What is type 1 diabetes and how is it managed?
pancreas produces little or no insulin- blood sugar can rise to dangerously high level
controlled by:
limiting intake of food rich in simple carbohydrates (e.g sugars) which can cause rapid increase of blood glucose level
injecting insulin (into subcutaneous fat) into blood- usually at meal times, glucose removed from blood quickly once digested
how much insulin needed depends on diet and activity, healthy diet and regular exercise reduces amount needed
What is type 2 diabetes and how is it managed?
pancreas doesn’t produce enough insulin or person becomes resistant to it so cells don’t respond properly to the hormone
blood sugar levels rise
obese people increased risk
can be controlled with healthy diet, regular exercise and losing weight
if needed, medication and insulin injections can be used
How do you work out BMI?
BMI = body mass/ (height)2 obese = bmi over 30
How do plants respond to stimuli?
respond by regulating growth
called tropism- positive tropism is growing towards a stimulus
phototropism- growth of plant in response to light. shoots positively photoropic- grow towards light
gravitropism/geotropism- growth of plant in response to gravity. roots positively geo/gravitropic- grow donwards
How do plants and roots show positive tropism?
shoots positively phototropic
auxin produced in shoots
shoot tip exposed to light, more auxin accumulates on shaded side
causes cells to elongate faster on shaded side, shoot bends towards light
enables plants to absorb more light for photosynthesis so provides them with more sugar and energy for growth
roots positively geo/gravitropic
when root growing sideways, gravity causes unequal distribution of auxin in tip so more on lower side
in root, extra auxin inhibits growth so cells on top elongate faster and root bends downwards
enables plants to extend roots deep into soil so they are well anchored. they absorb more water and minerals for photosynthesis too
what are plant hormones?
auxin and gibberellin
auxin controls growth at top of shoots and roots
produced in tips and diffuses backwards, causing cells just behind tip to elongate
if tip of shoot removed, no auxin so shoots stop growing
gibberellin is another plant hormone
stimulates seed germination, stem growth and flowering
stem elongation causes plant stem to grow and helps plant grow tall
if both hormones work together they will have a big impact on plant growth
How are plant hormones used commercially?
selective weedkillers
most weeds broad leaved, selective weedkillers developed from plant hormones will only affect broad-leaved plants
disrupts normal growth patterns so kills them while leaving grass and crops untouched
rooting powder
add to cuttings, they produce roots rapidly and start growing as new plants
enables growers to produce clones of plants quickly
fruit ripening
can use plant hormones to control
fruit can be picked while still unripe and if you add ripening hormone, the fruit will ripen on the way to shop so fresh on shelves
seedless fruits
normally only grows on pollinated plants
if you add growth hormone to unpollinated plants, the fruit will grow but the seeds won’t
used in seedless citrus fruits
and seedless grapes, though usually plant fertilised first
What experiments can interpret experimental data on plant hormones?
cover 3 different parts of plant shoot
the bending of the shoot only prevented when tip covered so auxin must be produced there
proves auxin produced in tips
remove the plant tip and place in block of agar , the agar soaks up the auxin from the tip
place agar block on one side of shoot in darkness and the shoot will bend away from the side with the auxin
shows auxin causes faster growth on shoot where it’s concentration highest
