6: Homeostasis for A-Level Biology (OCR B

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)