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Dr Bhavsar's A level Biology (OCR, A) > Module 5 Homeostasis and excretion essential notes > Flashcards

Module 5 Homeostasis and excretion essential notes Flashcards

1
Q

Explain, with examples, why it important to maintain the internal conditions of organisms

A
  1. Maintain the shapes of proteins, so biological functions can
  2. continue for example enzymes in metabolism Maintain diffusion gradients. If concentrations of substances are not maintained, rates of supply/removal to/from cells
  3. will be insufficient for continued function Substrates for metabolic reactions. For example respiration requires a continual supply of glucose. Photosynthesis requires a continuous supply of water
  4. Prevent build-up of toxic substances
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2
Q

Give examples of internal conditions that need to be maintained within certain limits

A
  1. Carbon dioxide concentration
  2. Water/salt balance
  3. Blood glucose concentration
  4. Blood urea concentration
  5. Core body temperature
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3
Q

Explain why homeostasis requires coordination between organs

A
  1. The cells, tissues and organs of organisms are highly specialised
  2. Responses require the internal or external conditions to be detected with specialised sensor organs which have receptor proteins
  3. Communication systems allow the sensor to stimulate the effector organ
  4. Effector organs function to make a response (that helps maintain the internal conditions)
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4
Q

State the ways in which cells/tissue/organs can communicate with each other

A
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5
Q

Describe how cells signalling changes cell behaviour

A
  1. A chemical signal is received by the cell
  2. It attaches to a complementary protein receptor
  3. A second messenger is produced that changes the activity of proteins in the cell
  4. OR signals to the nucleus alter the types of proteins synthesised
  5. The cell may perform a new function, which changes cell behaviour
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6
Q

Describe how negative feedback is used to maintain homeostasis

A
  1. A sensor/receptor detects a change away from the setpoint norm
  2. A communication system is used to to stimulate the effector
  3. The effector, when stimulated, responds by acting to reverse the detected change
  4. This produces a fluctuation around the setpoint norm as shown:
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7
Q

Compare positive feedback to negative feedback

A
  1. Positive feedback is where changes are detected
  2. But effectors act to increase the detected change (not reverse it)
  3. Positive feedback systems cannot be used for homeostasis
  4. Examples include blood clotting and hormonal control of uterine contractions during childbirth
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8
Q

Explain why organisms need to carry out thermoregulation

A
  1. In order for proteins and enzymes (metabolism) to function
  2. Enzymes need to have the right tertiary structure
  3. So that active sites and substrates are complementary
  4. Collisions between substrates and enzymes also need to have sufficient energy and be frequent enough
  5. The temperature at which enzymes function best is their optimum temperature
  6. Core body temperature is maintained near the optimum temperature of enzymes
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9
Q

Describe the consequences of body temperature rising too high

A
  1. Proteins and enzymes become denatured as their kinetic energy is too high
  2. Their shape is different so they cannot carry out their function
  3. (Enzymes are no longer complementary to their substrate)
  4. So metabolic reactions cannot occur at rates required for tissues and organs to function
  5. This is called hyperthermia
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10
Q

Describe the consequences of body temperature falling too low

A
  1. Proteins and enzymes do not have enough kinetic energy to function properly
  2. For example, enzymes and substrates collide too infrequently, or with insufficient energy
  3. Rates of metabolic reactions are too slow
  4. Cells, tissues and organs may not function normally
  5. This is called hypothermia
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11
Q

State the ways in which thermal energy can be transferred in living organisms

A
  1. Exothermic metabolic reactions (gain of heat energy)
  2. Radiation (gain or loss)
  3. Conduction through solids (gain or loss)
  4. Convection through water or air (gain or loss)
  5. Evaporation of water (loss of heat energy)
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12
Q

Describe the key features of ectotherms

A
  1. Examples include invertebrates, fish, amphibians and reptiles
  2. Gain heat mostly from the environment
  3. Little physiological mechanisms for thermoregulation
  4. More fluctuation in body temperature
  5. Aquatic ectotherms rely on the high specific heat capacity of water for their thermoregulation
  6. Terrestrial ectotherms require behavioural adaptations for thermoregulation (air temperature can vary much more)
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13
Q

Describe the features of endo therms

A
  1. Endotherms are mammals and birds
  2. They maintain a constant body temperature, independent of environmental temperature
  3. They use energy from metabolic processes to gain heat
  4. Physiological adaptations to maintain thermoregulation
  5. Maintain a more constant body temperature
  6. Which means they use much more energy
  7. So have higher calorific (energy) requirement
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14
Q

Describe how ectotherms use behavioural adaptations to carry out thermoregulation

A
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15
Q

Describe the overall mechanism of thermoregulation in endotherms

A
  1. Temperature homeostasis is carried out by negative feedback
  2. Temperature sensors in the hypothalamus of the brain detect a change in blood temperature away from the setpoint norm
  3. When the temperature falls below the setpoint norm, the heat gain centre of the hypothalamus is stimulated
  4. When the temperature rises above the setpoint norm, the heat loss centre of the hypothalamus is stimulated
  5. The nervous system is used to communicate with effector organs
  6. Effector organs that reverse the detected change are stimulated
  7. Body temperature returns to setpoint norm
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16
Q

State the ways in which endotherms can gain and lose heat energy

A
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17
Q

Explain how sweating affects thermoregulation in endotherms

A
  1. Sweat glands are stimulated by the nervous system to secrete more sweat onto the skin surface The body’s thermal energy is used up to break hydrogen bonds between water molecules
  2. Water evaporates and the body’s temperature is reduced
  3. More sweating reduces body temperature
  4. Reduced sweating increases body temperature
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18
Q

Explain how feathers or hair can be used in thermoregulation

A
  1. Hair and feathers act as thermal insulators They prevent the loss of heat by reducing convection currents near the skin
  2. Erector pili muscle in the skin can be stimulated to contract
  3. Hairs or feathers stand up
  4. And increase the insulating effect
  5. Trapping heat near the skin and raising body temperature
  6. When erector pili muscles are relaxed, the hairs or feather lie close to the skin
  7. And heat is lost from the body, reducing body temperature
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19
Q

Explain how shivering raises body temperature

A
  1. The skeletal muscles (that generate movement) are stimulated by the nervous system when body temperature falls below the setpoint norm
  2. This makes these muscles contract more
  3. Increased muscle contraction requires muscle mitochondria to produce more ATP
  4. As respiration increases (and not being 100% energy efficient) more energy is lost as heat
  5. This is transferred to the rest of the body, raising body temperature
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20
Q

State the main metabolic wastes and how they are removed

A
  1. Excretion is the removal of metabolic waste substances
  2. Carbon dioxide is a waste product of respiration
  3. It is removed via the lungs (respiratory system)
  4. Urea is a waste product of protein metabolism (excess amino acids)
  5. It is removed by the kidneys via urine production
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21
Q

State the key functions of the liver

A
  1. Carbohydrate metabolism (glycogen synthesis, glucose homeostasis)
  2. Transamination (converting one amino acid into another)
  3. Deamination of excess amino acids
  4. Detoxification (converting ammonia into urea, ornithine cycle)
  5. Production of bile for lipid digestion
  6. Production of blood plasma proteins
22
Q

Describe how the structure of the liver is related to its function

A
  1. The liver is supplied with deoxygenated blood rich in the products of digestion (many amino acids, fatty acids and carbohydrates) by the hepatic portal vein
  2. The liver is supplied with oxygenated blood via the hepatic artery (oxygen for respiration of liver cells)
  3. As the blood flows past the liver cells, they carry out their metabolic functions
  4. Reduced blood glucose, added lipids for storage in adipose tissue, balance of amino acids ready for cells to use
  5. Excess amino acids used to produce urea
  6. Blood leaves the liver in the hepatic vein
23
Q

Describe the structure of liver lobules

A
  1. The liver is composed of hexagonal structures called lobules
  2. Each has branches of the hepatic portal vein and the hepatic artery on the outside
  3. The blood mixes and flows past rows of liver cells (hepatocytes) called sinusoids
  4. The restructured blood flows into a branch of the hepatic vein (central vein) at the centre of the lobule towards the heart
  5. Additionally bile ductules collect bile produced and transport it to the gall bladder in the bile duct
  6. Kupffer cells are liver macrophages, which destroy pathogens that may be in the blood
24
Q

Describe the key specialisations of hepatocytes

A
  1. Many mitochondria to provide ATP for all the biosynthetic metabolic reactions (protein synthesis, exocytosis)
  2. Lots of Golgi apparatus for the modification of secretion of plasma proteins
  3. Contain the enzymes needed to carry out all the metabolic reactions, such as deamination and detoxification
25
Q

Describe the production of urea from excess amino acids

A
  1. The amino group of excess amino acids are removed (deamination)
  2. The ammonia produced is highly toxic, and highly soluble
  3. In the Ornithine cycle, ammonia is converted to urea
  4. Which is less toxic, and less soluble
  5. This is released into the blood
  6. To be removed from the blood by the kidneys into urine (which leaves the body)
26
Q

Give examples of the role of the liver in detoxification

A
  1. Converting metabolic wastes into less harmful substances for excretion
  2. For example converting ammonia into urea (ornithine cycle)
  3. For example the breakdown of toxic hydrogen peroxide to harmless water and oxygen (catalase enzyme)
  4. For example the detoxification of alcohol and drug molecules (alcohol dehydrogenase enzyme)
27
Q

Describe the overall position and function of the kidneys

A
  1. There are two kidneys
  2. Each is supplied with oxygenated blood high in urea (from the liver, then heart) in the renal artery
  3. The kidneys filter out the urea and unwanted waste molecules into urine
  4. They return useful substances like glucose, amino acids, water and ions back to the blood
  5. This filtered blood leaves the kidneys in the renal vein to return to the heart
  6. The urine leaves the kidneys in the ureter and collects in the bladder
28
Q

Describe the main regions of the kidney

A
  1. The kidney is surrounded by the capsule
  2. The outermost layer is the cortex, appearing dark due the dense network of capillaries
  3. The next layer in is the medulla, which is lighter as it has the tubules of the nephrons (which collect urine)
  4. The innermost region is the pelvis, where the urine collects, appearing the lightest part
29
Q

Summarise how the different structures of the nephron contribute to the filtering of blood

A
  1. The Bowman’s capsule carries out the process of ultrafiltration,
  2. urea and other molecules removed from blood The proximal convoluted tubule carries out selective reabsorption of important biological molecules (glucose and amino acids)
  3. The distal convoluted tubule rebalances the ion concentrations of the blood
  4. The Loop of Henle carries out the reabsorption of water back into the blood
  5. The collecting duct carries the urine towards the ureter
30
Q

Describe the process of ultrafiltration at the Bowman’s capsule

A
  1. The afferent arteriole of the glomerulus is wider than the efferent arteriole
  2. This causes high pressure in the glomerulus capillaries This forces small molecules (urea, water, glucose, amino
  3. acids) and ions into the lumen of the capsule
  4. Removing these substances from the blood and into the filtrate
31
Q

Describe the adaptations of the Bowman’s capsule

A
  1. The Bowman’s capsule has three layers through which filtration occurs
  2. First is the capillary endothelium
  3. Next is the basement membrane
  4. Third are the fenestrations of the podocytes
  5. These barriers limit the size of molecule that can pass through to around 69, 000 RMU
  6. Which means blood cells and large proteins remain in the blood during the process
32
Q

Describe the role of the proximal convoluted tubule the functioning of the kidney

A
  1. The proximal convoluted tubule carries out selective reabsorption of glucose, amino acids and mineral ions back into blood
  2. Some water is also reabsorbed here
  3. Active transport of sodium ions out of tubule cells
  4. Results in movement of glucose and amino acids into the tubule cells by facilitated diffusion (cotransport with sodium ions)
  5. glucose , amino acids and mineral ions then diffuse into the blood capillaries
  6. Water moves out of the filtrate and into the blood by osmosis
  7. Cells of the PCT have many mitochondria (for active transport)
  8. Cells of the PCT have microvilli (to increase their surface area)
33
Q

Describe the role of the Loop of Henle in reabsorbing the remaining water in the filtrate/urine

A
  1. The ascending limb actively transports sodium and chloride
  2. ions out of the filtrate and into the tissue fluid This reduces the water potential of the medulla
  3. Water moves down a water potential gradient out of the descending limb and the collecting duct into the tissue fluid It then moves by osmosis into the capillaries back into the blood
  4. The remaining filtrate enters the collecting duct
34
Q

Describe the role of the distal convoluted tubule in the function of the kidney

A
  1. The distal convoluted tubule rebalances the composition of the blood before it leaves the kidney
  2. If required, The cells of the distal convoluted tubule actively transport sodium ions out of the filtrate (from where the diffuse into the blood)
  3. Chloride ions will move with the sodium ions down an electrochemical gradient, into the blood
  4. The DCT can also adjust the pH of the blood
  5. Cells of the DCT have many mitochondria (to carry out active transport)
35
Q

Explain the role of the collecting duct in the function of the kidneys

A
  1. The role of the collecting duct is in osmoregulation of the blood The permeability of the walls of the collecting duct can be controlled by the hormone ADH (antidiuretic hormone)
  2. If the blood water levels need to be increased the walls of the CD become more permeable to water
  3. More water leaves across the CD walls by osmosis and urine becomes hypertonic (concentrated)
  4. If the blood water levels need to be reduced the permeability of the CD walls are reduced
  5. More water remains in the CD and leaves the kidneys via the ureter (urine is hypotonic, dilute)
36
Q

Summarise the process by which the water potential of the blood is maintained

A
  1. The water potential of the blood is maintained by osmoregulation
  2. Osmoregulation is a homeostatic process carried by negative feedback
  3. The hypothalamus detects the water potential of the blood
  4. The hormone ADH is used to stimulate the effector organ
  5. The walls of the collecting ducts in the kidneys are the effector
  6. Which can be controlled to regulate the blood water potential
37
Q

Describe how water potential is raised when it falls too low

A
  1. Water potential of the blood falls below setpoint norm
  2. This is detected by osmoreceptors in the hypothalamus (in the brain)
  3. Hypothalamus then stimulates the pituitary gland to release antidiuretic hormone (ADH)
  4. ADH circulates in the blood and causes the walls of the CD to become more permeable to water
  5. More water leaves the urine in the collecting duct by osmosis, and re-enters blood
  6. Blood water potential increases towards setpoint norm
38
Q

Describe how water potential is reduced when it gets too high

A
  1. Water potential of the blood rises above setpoint norm
  2. This is detected by osmoreceptors in the hypothalamus (in the brain)
  3. Hypothalamus then inhibits the release of antidiuretic hormone
  4. (ADH) from the pituitary gland
  5. ADH levels in the blood reduce, causing the wall of the CD to become less permeable to water
  6. More water remains in the urine in the collecting duct and is lost during urination
  7. Blood water potential decreases towards setpoint norm
39
Q

Explain how ADH affects the permeability of the walls of the collecting duct

A
  1. ADH is a peptide hormone (polar)
  2. It diffuses out of the blood and binds to a complementary receptor protein…
  3. …in the membrane of the cells of the collecting duct (target cells)
  4. A second messenger is produced in the cell (cyclic AMP)
  5. This causes aquaporins (water channel proteins) to be inserted into the collecting duct wall cells
  6. This increases how much water can leave the collecting duct by osmosis
  7. Thus raising blood water potential
40
Q

Explain why urine can be tested for substances present in the body

A
  1. If any substances are present in the body and transported in the blood
  2. If they are smaller than 69,000 RMU
  3. Will be filtered out of the blood by ultrafiltration at the
  4. Bowman’s capsule
  5. Unless they are selectively reabsorbed they will end up in the urine
  6. The urine therefore indicates the presence of substances that have been in the blood
  7. For diagnostic or investigative purposes
41
Q

Describe the use of monoclonal antibodies in testing for

pregnancy

A
  1. The hormone hCG (human chorionic gonadotropin) is produced during pregnancy hCG is a small peptide hormone that circulates in the blood Antibodies that are complementary in shape to hCG can be produced
  2. These can be immobilised on pregnancy tests
  3. Urine from a pregnant person will contain hCG which will bind to the antibodies on the test
  4. This will cause a colour change that indicates the presence of the hCG
  5. There is also an additional strip that confirms the antibody test is functional
42
Q

Describe how urine can be tested for anabolic steroids and drugs

A
  1. For smaller molecules such as steroid hormones and or drug molecules
  2. Mass spectrometry is carried out on urine samples
  3. This technique first separates all the individual substances in the urine (gas chromatography)
  4. Then analyses each one’s molecular structure (mass spectroscopy)
43
Q

State the possible consequences of kidney failure

A
  1. Toxic wastes/substances accumulate in blood and tissue fluid - reducing cell function and causing cell death
  2. Water is not removed increasing blood pressure, damaging arteries, and thus reducing oxygenated blood supply to tissues and organs
  3. Mineral ion and pH balance is lost, affecting the function of cells and proteins of tissues and organs
44
Q

Explain how kidney function can be measured

A
  1. Creatine is a store of phosphate in muscle cells
  2. Can be used to regenerate ATP for muscle contraction
  3. Creatine is metabolised to an unusable product creatinine
  4. This is not reabsorbed in the kidneys
  5. The levels of creatinine in the blood determine the estimated glomerular filtration rate
  6. eGFR of below 60 indicates kidney disease
  7. Over time kidney damage causes more substances to get filtered out of blood as the Bowman’s capsule gets damaged
45
Q

Explain the general principle of how dialysis treats kidney dysfunction

A
  1. Dialysis is carried out to remove toxic substances from the blood
  2. While making sure the glucose, amino acids and water potential are maintained close to setpoint norms
  3. Dialysis fluid is composed of the right concentrations of molecules and ions according to setpoint norms
  4. And is allowed to exchange substances with the blood across partially permeable membranes
  5. Wastes at a high concentration in the blood diffuse into the dialysis fluid
  6. Other substances may diffuse in either direction depending on if their blood levels are too high or too low
46
Q

Describe haemodialysis

A
  1. An artery and vein are connected to a dialysis machine
  2. The dialyser allows the blood to exchange substances with the dialysis fluid across a partially permeable membrane (simple diffusion)
  3. Urea, excess ions, and other waste substances diffuses from blood into dialysis fluid
  4. A countercurrent flow system is used increase the efficiency of diffusion in the dialyser
47
Q

State the key features/advantage s/disadvantages of hemodialysis

A
  1. Usually done in hospitals (can be done at home)
  2. Can take about 8 hours (inconvenient)
  3. Has to be repeated several times a week
  4. Requires careful diet management (monitor fluid intake, reduced protein and salt intake)
  5. Substances diffuse across artificial membrane
  6. Long term dialysis can have serious effects of health
48
Q

Describe peritoneal dialysis

A
  1. The peritoneum is a fluid-filled cavity in the abdomen bounded by the peritoneal membrane
  2. It is permeated by blood capillaries
  3. Filing the peritoneal cavity with dialysis fluid
  4. Allows exchange (diffusion) with the blood
  5. Urea and other wastes diffuse into the dialysis fluid
  6. The fluid is then removed, allowing excretion of urea and other wastes
49
Q

State the key features/advantage s/disadvantages of peritoneal dialysis

A
  1. Can be done at home while patient can move around
  2. More convenient than having to go to hospital Can be done while sleeping
  3. Substances move across biological membranes
  4. Long term dialysis can have serious effects of health
50
Q

Describe the process of a kidney transplant

A
  1. The blood vessels of the ‘new’ kidney are joined with the renal artery and renal veins of the recipient
  2. The donor kidney ureter is inserted into the recipient’s bladder
  3. It should now function as a normal kidney
51
Q

State the key features/advantage s/disadvantages of kidney transplant

A
  1. Risk of tissue rejection (non-self antigens, immune response)
  2. The donor kidney’s antigens will be more similar if they are a blood type match, for example a close relative
  3. Or the recipient can be treated with immunosuppressants
  4. But immunosuppressants can result in more infectious diseases developing
  5. Transplanted organs may fail after a number of years

Dr Bhavsar's A level Biology (OCR, A) (20 decks)

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