Detailed, comprehensive & thorough HSC Module 8 Biology notes with many diagrams to assist your learning. These notes were made by a student that consistently ranked in the top 3 biology students in their cohort.
Homeostasis
- process by which body maintains a constant internal environment
→ everything is kept relatively stable
- works to maintain the internal environment
- variables:
● body temp
● water availability
● CO2 conc.
● blood glucose levels
Stimulus Response Model
- body's way of detecting a change in its external or internal environment, & reacting
accordingly
, 1. Stimulus: something occurs to cause a change in the environment
2. Receptor: internal body receptors, including chemo-, thermo-, mechano-, & osmoreceptors,
detect the change within the internal environment
3. Control centre: the receptor sends a signal to the control centre (brain & spinal chord) to alert
about the change, the control centre compares the information fro the receptors to normal
internal levels
4. Effector: the CNS sends a signal to the effector, either muscles of glands, directing them to
rectify the imbalance within the body
5. Response: the body is restores to its original balance state
NEGATIVE FEEDBACK LOOP
- information produced by the feedback causes a reversal in the effect of the stimulus
, Thermoregulation
- internal regulation of an animal’s body temperature
- hypothalamus regulates body temp
- uses negative feedback loop
Endotherms Ectotherms
warm-blooded cold-blooded
- largely create our heat by adjusting - rely on external sources of temperature to
processes in our body heat up or cool down
- rely mainly on physiological sources of heat - depend solely on the environment for heat
to regulate temperature regulation
- can still depend on environment/behavioural
adaptations - e.g. behavioural adaptation: reptiles & many
insects find sunny places to maximise their
exposure to the sun
1. STIMULUS - change in body temp
2. RECEPTOR - thermoreceptors
- in the skin: detect external temp changes & are triggered frequently
- in hypothalamus: cluster of temp sensitive cells that monitor the body’s internal temp
by measuring the temp of blood
→ initiate a regulatory response
→ can affect amount of heat the organism generates or loses
3. CONTROL CENTRE - hypothalamus
- receives info
- sends out impulses (via motor neurons) to activate the particular physiological
response, required to re-achieve balance
4. EFFECTOR
● temp decrease
- nerve impulses trigger piloerection, shivering & vasoconstriction
- nervous system coordinates behavioural responses including sheltering &
putting on clothes
- hypothalamus secretes thyroid hormone & triggers pituitary & thymus glands to
secrete hormones which increase cell metabolism
● temp increase
- nerve impulses trigger sweating & vasodilation
- nervous system triggers behavioural response, sheltering & removing clothing
- reduction in rate of cell metabolism
5. RESPONSE
- will try to reverse the original change in temp
,Responding to Cold
Reduce Heat Loss Increase Heat Production
Physiological Piloerection Shivering
- hairs erect on skin - muscle cells perform respiration
- trap air close to skin, in order to break down glucose
preventing heat loss via & produce energy
convection of air - respiration releases heat
Vasoconstriction Increasing Metabolism
- blood vessels constrict - main source of heat production
→ less blood travels near when body at rest
skin’s surface - endocrine system can be used
- less heat is lost from blood to influence production of heat
via metabolism
Behavioural - seeking shelter - voluntary movement
- putting on clothing
Responding to Hot
Increase Heat Loss Reduce Heat Production
Physiological Sweating Decreasing metabolism
- from eccrine gland & apocrine - hypothalamus reduces rate of
gland cellular respiration in body’s
- draws heat from skin to internal organs
evaporate sweat
→ converts liquid to gas
Vasodilation
- blood actively loses heat to
external environment
Behavioural - covering body in water - decreasing activity
- swimming in cool water
- removing clothes
- moving into shade
, Osmoregulation
- method by which plants maintain water balance
Plant Adaptation
★ STOMATA
- pores found on underside of leaves
- allow for gas exchange b/w plant tissue & environment
- allow transpiration (water vapour escapes) to occur
→ w/o a steady water supply, transpiration can lead to water loss
→ w/o water, plant cells lose their turgor, wilt & eventually die
- source of CO2 which a plant requires for photosynthesis
- while stomata open in day for intake of CO2 when most
photosynthesis occurs, this allows increased water loss to external
environment
MESOPHYTES
Land plants which are Closed Stomata
adapted to neither - achieved by decreasing amount of water in guard cells so that they
particularly dry nor close the gap
particularly wet - controlled by hormone abscisic acid
environments - plants will close their stomata when it is hottest (eg. midday) & leave
them open at all other time
e.g. roses
→ allows the leaf to maximise photosynthesis whilst minimising
water loss
Waxy Cuticle
- provides a waterproof barrier which help to reduce water loss
- thicker the cuticles, better at reducing water loss
Vacuoles
- organelles which store large amount of water
Transpiration
- water is transpired by a plant via stomata
→ water concentration in these areas will be low
→ since osmosis occurs across a concentration gradient, water will
travel into these areas to even out the concentration
- hot day: stomata are open for photosynthesis, transpiration can
occur at a much higher rate due to the rise in temperature
- when this occurs, water conc drops in stomata
→ loses turgor
→ stomata closes
- ensures water conc is kept near its preferred level
Reduced Stomata
- fewer stomata
XEROPHYTES → less potential for water vapour to evaporate out of plant
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