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GCSE Biology Homeostasis and response summary (AQA)

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GCSE Biology Summary Notes: Homeostasis and Response Topic (AQA) Unlock your potential and ace your GCSE Biology with these comprehensive summary notes, meticulously crafted to cover the Homeostasis and Response topic as per the AQA curriculum. Dive into the fascinating world of how living org...

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Institution GCSE
Education GCSE
Module Biology
School year 1

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GCSE Biology.
Paper 2
Homeostasis and response
 Homeostasis refers to the body's ability to regulate its internal conditions
within a narrow range, ensuring stability and optimal functioning.
 It involves maintaining variables such as temperature, pH, and blood
glucose levels at specific set points to support cellular activities.
 Homeostasis relies on control systems that include receptors, effectors,
and a control centre (often the brain or a specific organ).
 Receptors detect changes in the internal or external environment, such
as temperature or blood sugar levels.
 The control centre processes this information and sends signals to
effectors, which are muscles or glands that carry out the necessary
responses.
 Negative feedback mechanisms are crucial in homeostasis. They work
to counteract changes in internal conditions.
 When a variable deviates from its set point, the control system triggers
responses that bring it back to the desired level.
 For example, when body temperature rises (e.g., due to exercise), sweat
glands produce sweat to cool the body, returning temperature to the
normal range.
 Examples of Homeostasis: (more explanation on each of them in
later slides)
 Thermoregulation: The body maintains a constant core temperature
(~37°C) through processes like shivering or sweating.
 Blood Sugar Regulation: The pancreas regulates blood glucose levels
by releasing insulin to lower high levels and glucagon to raise low levels.
 Response to Stimuli: Organisms also respond to external stimuli to
ensure survival and adaptation.
 Responses can be categorized as behavioural (e.g., moving into the shade
when it's hot) or physiological (e.g., pupils constricting in response to
bright light).
 Disruptions in homeostasis can lead to health issues. For instance,
uncontrolled blood sugar levels can result in diabetes.
 Understanding homeostasis is crucial in healthcare, as it helps diagnose
and treat various medical conditions.

,Thermoregulation
 The core temperature of the body is typically maintained at around 37
degrees Celsius in humans.
 This temperature is essential for enzymatic reactions and metabolic
processes within cells.
 Thermoregulation relies on specialized receptors, primarily found in
the skin, that detect changes in external temperature.
 Effectors, such as sweat glands and muscles controlling blood vessel
constriction or dilation, play a crucial role in responding to temperature
fluctuations.
 Thermoregulation operates through a negative feedback loop.
 When the body detects a deviation from the set temperature (e.g., an
increase due to exercise or external heat exposure), it triggers responses
to counteract the change and restore normal temperature.
 Responses to Heat:
 When the body temperature rises above the set point:
 Sweat glands are activated to produce sweat, which evaporates and cools
the skin.
 Blood vessels near the skin's surface dilate (vasodilation), allowing more
heat to dissipate through radiation.
 Breathing rate may increase to release excess heat.
 Responses to Cold:
 When the body temperature falls below the set point:
 Sweat production decreases, conserving body fluids.
 Blood vessels constrict (vasoconstriction) to reduce heat loss.
 Muscles may contract involuntarily (shivering) to generate heat through
increased metabolic activity.
 The hypothalamus, located in the brain, acts as the control centre
for thermoregulation.
 It receives input from temperature receptors and orchestrates responses
to maintain temperature equilibrium.
 In addition to physiological responses, organisms may exhibit behavioural
adaptations to regulate body temperature.
 Examples include seeking shade when it's hot or wearing warm clothing in
cold weather.
 Dysregulation of thermoregulation can lead to health issues such as
heatstroke or hypothermia.

Control of water levels
 Water is a critical component of all living organisms, making up a
significant portion of their body mass.
 It plays essential roles in various biological processes, such as
transportation of nutrients, temperature regulation, and chemical
reactions within cells.
 Osmosis is the passive movement of water molecules across a selectively
permeable membrane (like a cell membrane) from an area of lower solute
concentration to an area of higher solute concentration.

,  Osmosis helps regulate the water content in cells and tissues.
 Role of Kidneys:
 In vertebrates, including humans, the kidneys play a central role in
controlling water levels.
 They filter blood to remove waste products and excess water,
forming urine.
 The amount of water reabsorbed by the kidneys is adjusted based on the
body's hydration needs.
 Hormonal Regulation:
 Hormones, such as antidiuretic hormone (ADH), play a key role in
regulating water levels.
 When the body detects dehydration or increased blood solute
concentration, ADH is released, causing the kidneys to reabsorb
more water, reducing urine output, and conserving water.
 Thirst Mechanism:
 The sensation of thirst is another important mechanism for controlling
water levels.
 When the body detects dehydration, it signals the brain, leading to the
sensation of thirst, prompting individuals to drink fluids to replenish water
levels.
 Excretion of Excess Water:
 In addition to regulating water reabsorption, the body can excrete excess
water when necessary.
 This is especially important during periods of excess hydration or
when blood solute levels are too low.
 Maintaining the right balance of water is crucial for overall health.
 Dehydration can lead to symptoms such as thirst, dry mouth, and
decreased urine output, while overhydration can result in water
intoxication and electrolyte imbalances.

 Adaptations in Different Environments:
 Different species have adapted to varying environments in terms of water
regulation.
 Desert organisms may have efficient water-conserving mechanisms, while
aquatic animals may excrete excess water more readily.

The kidneys
 The kidneys are bean-shaped organs located in the lower back, one on
each side of the spine.
 They are part of the urinary system and are responsible for filtering
waste products and excess substances from the bloodstream to
form urine.
 The primary function of the kidneys is to filter blood to remove metabolic
waste products, excess salts, and excess water from the body.
 These waste products and excess substances are excreted from
the body in the form of urine.
 The functional units of the kidneys are called nephrons.

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