6: Homeostasis for A-Level Biology (Edexcel)

In mammals, what is the regulation of the internal conditions of the body within narrow limits called?

Homeostasis

Maintains optimal conditions for cellular processes despite external environmental changes.

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Why must body temperature remain relatively constant in mammals?

To maintain optimum enzyme activity.

Enzymes have specific temperature optima; large deviations reduce reaction rates or cause denaturation.

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Why is maintaining a stable blood pH important for metabolism?

Enzyme structure and function depend on pH.

Changes in pH alter ionic bonds and hydrogen bonds, affecting enzyme active sites.

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Why must blood glucose concentration be carefully regulated?

To ensure a constant respiratory substrate supply.

Glucose is the main fuel for respiration and ATP production in cells.

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How does blood glucose concentration affect the water potential of the blood?

High glucose lowers blood water potential.

Increased solute concentration causes water to move out of cells by osmosis.

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What type of control mechanism returns a physiological variable back to its set level after deviation?

Negative feedback

The response counteracts the initial change and restores the original condition.

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True or False:

Negative feedback amplifies the original stimulus to produce a stronger response.

False

Negative feedback reduces deviation from the set point rather than increasing it.

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Fill in the blank:

Negative feedback restores conditions to their ______ level after a disturbance.

original

Also called the set point in physiological control systems.

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What term describes the normal level around which a physiological variable fluctuates in homeostatic control?

Set point

Examples include normal body temperature or blood glucose concentration.

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True or False:

Mammals use separate negative feedback mechanisms to correct increases and decreases from the set point.

True

Different responses are triggered depending on whether the variable rises or falls.

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Why do separate mechanisms for opposite deviations improve homeostatic control?

Greater precision of regulation.

For example, different mechanisms act to raise or lower body temperature.

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Fill in the blank:

Homeostatic systems maintain the internal environment within restricted ______.

limits

These limits allow enzymes and cells to function efficiently.

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What general type of system do mammals use to regulate internal conditions such as temperature, pH and glucose?

Physiological control systems

These involve receptors, coordination centres and effectors working together.

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True or False:

Positive feedback always stabilises a physiological variable around its normal level.

False

Positive feedback increases the change rather than reversing it (e.g., childbirth contractions).

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What variable is regulated to maintain a stable internal supply of glucose for respiration in mammals?

Blood glucose concentration

Maintained by negative feedback mainly involving insulin and glucagon.

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Which organ is primarily responsible for regulating glucose levels in the blood?

Liver

The liver stores glucose as glycogen and releases glucose when blood levels fall.

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What process converts excess glucose into glycogen for storage in the liver and muscles?

Glycogenesis

Stimulated mainly by insulin when blood glucose concentration rises.

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What process breaks down glycogen into glucose when blood glucose concentration falls?

Glycogenolysis

Mainly stimulated by glucagon and adrenaline.

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What metabolic pathway produces glucose from non-carbohydrate molecules such as glycerol and amino acids?

Gluconeogenesis

Occurs mainly in the liver when glucose supply is low.

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Which hormone is released from pancreatic β cells when blood glucose concentration rises?

Insulin

Promotes uptake and storage of glucose in tissues.

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Which hormone is secreted from pancreatic α cells when blood glucose concentration falls?

Glucagon

Stimulates the release of glucose into the bloodstream.

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What hormone released during stress or exercise rapidly increases blood glucose concentration?

Adrenaline

Prepares the body for the “fight or flight” response.

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When insulin binds to receptors on target cells, what type of proteins are inserted into the membrane to increase glucose uptake?

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Channel proteins

These proteins allow facilitated diffusion of glucose into cells.

Which storage carbohydrate is synthesised in the liver when insulin activates enzymes that convert glucose into a storage form?

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Glycogen

Allows excess glucose to be stored without affecting osmotic balance.

# True or False: Insulin lowers **blood glucose concentration** by increasing the conversion of glucose to **glycogen** in the liver.

True ## Footnote Insulin activates enzymes involved in glycogenesis.

# True or False: Glucagon lowers **blood glucose concentration** by increasing **glucose uptake** into cells.

False ## Footnote Glucagon raises blood glucose by promoting glycogen breakdown and gluconeogenesis.

When glucagon binds to receptors on **liver cells**, which **stored molecule** is broken down to release glucose?

Glycogen ## Footnote This process is glycogenolysis.

Besides **glycogen breakdown**, which two types of molecules can be converted into glucose during **gluconeogenesis**?

Glycerol and amino acids ## Footnote These molecules are converted into glucose in the liver.

Which enzyme in the **second messenger model** converts ATP into **cyclic AMP** after hormone binding?

Adenylate cyclase ## Footnote Activated when glucagon or adrenaline binds to membrane receptors.

Which intracellular **signalling molecule** acts as the **second messenger** in glucagon and adrenaline signalling?

cAMP ## Footnote Cyclic AMP activates protein kinase enzymes inside the cell.

Which **enzyme** is activated by cyclic AMP to trigger **enzyme cascades** leading to glycogen breakdown?

Protein kinase ## Footnote This amplifies the hormonal signal inside the cell.

# Fill in the blank: The **second messenger** produced from ATP during glucagon signalling is \_\_\_\_\_\_.

cAMP ## Footnote cAMP transmits the signal from the membrane receptor into the cell.

Which **autoimmune disease** results from the destruction of **pancreatic β cells**?

Type I diabetes ## Footnote Leads to little or no insulin production.

Which **metabolic disorder** occurs when body cells become less responsive to **insulin**?

Type II diabetes ## Footnote Often associated with obesity and lifestyle factors.

What is the main **treatment** used to control blood glucose levels in people with **Type I diabetes**?

Insulin therapy ## Footnote Delivered by injections or insulin pumps.

What **lifestyle intervention** is commonly used to control **Type II diabetes** before medication?

Dietary control ## Footnote Often combined with exercise and weight reduction.

# True or False: Type II diabetes is commonly associated with reduced **sensitivity of body cells** to **insulin**.

True ## Footnote This condition is called insulin resistance.

In **Required Practical 11**, what instrument is used to measure **light absorbance** when determining glucose concentration?

Colorimeter ## Footnote Used to produce a calibration curve from a dilution series.

What **graph** is produced from known glucose concentrations to determine the concentration of an **unknown urine sample**?

Calibration curve ## Footnote Absorbance values are plotted against concentration.

What is meant by the regulation of the **water potential** of the **blood** in mammals?

Osmoregulation ## Footnote Maintains stable blood water potential despite changes in water intake or loss.

Which region of the **brain** detects changes in the **water potential** of the blood?

Hypothalamus ## Footnote Osmoreceptors in this brain region monitor blood water potential.

Which part of the **pituitary gland** releases **antidiuretic hormone** into the bloodstream?

Posterior pituitary ## Footnote ADH is synthesised in the hypothalamus but stored and released from the posterior pituitary.

What **hormone** increases the permeability of **kidney tubules** to water during osmoregulation?

Antidiuretic hormone (ADH) ## Footnote ADH alters the permeability of collecting ducts and distal convoluted tubules.

# True or False: When **blood water potential** decreases, more **ADH** is released.

True ## Footnote Lower water potential means blood is more concentrated, triggering increased ADH secretion.

What is the **functional unit** of the **kidney** responsible for filtering blood and forming urine?

Nephron ## Footnote Each kidney contains around one million nephrons.

What is the **fluid** produced when **blood is filtered** in the renal corpuscle called?

Glomerular filtrate ## Footnote Formed by ultrafiltration in the glomerulus and Bowman's capsule.

What **process** forces water and small solutes from the **glomerulus** into the Bowman's capsule?

Ultrafiltration ## Footnote Driven by high hydrostatic pressure in the glomerular capillaries.

# Fill in the blank: The \_\_\_\_\_\_ convoluted tubule is responsible for reabsorbing all glucose from the filtrate.

proximal ## Footnote Selective reabsorption of glucose occurs via co-transport with sodium ions.

Which section of the **nephron** establishes a **sodium ion concentration gradient** in the medulla?

Loop of Henle ## Footnote Countercurrent multiplier mechanism maintains the medullary gradient.

# True or False: The **descending limb** of the **loop of Henle** is permeable to water but not to sodium ions.

True ## Footnote Water leaves by osmosis as the filtrate moves into the increasingly concentrated medulla.

# True or False: The **ascending limb** of the **loop of Henle** allows water to leave the filtrate.

False ## Footnote The ascending limb is impermeable to water but actively transports sodium ions out.

What **transport mechanism** moves **sodium ions** out of the ascending limb of the loop of Henle?

Active transport ## Footnote This creates the high salt concentration in the medulla.

# Fill in the blank: The gradient of **sodium ions** in the kidney \_\_\_\_\_\_ helps draw water out of the collecting duct.

medulla ## Footnote A steep osmotic gradient enables water reabsorption when ADH is present.

Which part of the **nephron** becomes more permeable to **water** when ADH levels rise?

Collecting duct ## Footnote ADH inserts aquaporin channels into the membrane.

Which **nephron segment** reabsorbs large amounts of **water and glucose** from the filtrate?

Proximal convoluted tubule ## Footnote Reabsorption here occurs via active transport and osmosis.

# True or False: High **ADH levels** produce a large volume of **dilute urine**.

False ## Footnote High ADH increases water reabsorption, producing small volumes of concentrated urine.

# Fill in the blank: When **blood water potential** rises, \_\_\_\_\_\_ ADH is released.

less ## Footnote Reduced ADH makes the collecting duct less permeable to water, producing dilute urine.

6: Homeostasis Flashcards

Explain how organisms maintain stable internal conditions through regulation. (57 cards)