What is Cell signalling? - answer-When cells communicate by signalling, one cell releases a chemical•This chemical is detected by another cell•The second cell then responds to this signal
What are the two Cell signalling systems - answer-There are 2 major systems of communication:
Neuronal ...
OCR A-Level Biology
What is Cell signalling? - answer-When cells communicate by signalling, one cell
releases a chemical•This chemical is detected by another cell•The second cell then
responds to this signal
What are the two Cell signalling systems - answer-There are 2 major systems of
communication:
Neuronal System•
via Network of neurons•
Quick signals•
Rapid responses
Hormonal System•Uses blood to transport signals•Endocrine glands secrete
hormones directly into blood•Carried all over the body•recognized by specific
target cells•Enables long-term responses to be coordinated•Specific target cells
have receptors that have a shape that is complementary to the shape of the
hormone
What is homeostasis?/ What factors are controlled (5) - answer-Homeostasis is the
regulation of internal environments with a certain range
Temperature• Blood glucose concentration• Blood salt concentration •Water
content• Blood pressure• Blood carbon dioxide partial pressure (blood pH)
What is negative feedback? (2) - answer-A response to a change in the body that
counteracts or opposes the initial change.
eg thermoregulation and Blood sugar regulation
What is positive feedback? (1) - answer-Response that causes change to
increase,Destabilizes the system, Usually more harmful•Does not lead to
homeostasis•Can be useful in •Eg: childbirth (oxytocin )Uterine contractions
What are endotherms? - answer-Animals who maintain body temperature through
metabolic heat, independent of external temperature eg mammals and birds
Advantage and disadvantages of Endotherms (2) - answer-Advantages ○Constant
body temperature regardless of external environment
○Activity possible in cooler temperatures○
Able to inhabit cooler parts of the world•
Disadvantages:○lot of energy intake used to maintain body temperature
○More food required
○Less energy from food can be used for growth
What are ectotherms? - answer-Animals whose body temperature is determined by
their environment/ Behavioral changes
lizards
Advantages and disadvantages of Ectotherms - answer-Advantages
Less food used in respiration○
Less food required○
,Greater proportion of energy derived from food can be used for growth•
disadvantages:
○Less active in cooler temperatures
○May not be capable of activity during cold winters
What is Excretion and what is metabolic waste? - answer-Excretion = the removal of
metabolic waste products from the body.
Metabolic waste = Unneeded byproducts produced as a result of normal
metabolism. That need to be removed from the body as they can become toxic in
large quantities eg co2 , urea
Why does CO2 need to be excreted? - answer-Excess CO2 is toxic•High levels of
carbon dioxide Reduce the oxygen carrying capacity of the red blood
cells○Combines with haemoglobin to form carbaminohaemaglobin, which has a
lower affinity for oxygen
why are Nitrogenous compounds such as protein excreted and how? - answer-The
body is unable to store amino acids or proteins•
its wasteful to excrete amino acids•transported to the liver and deaminated•The
removed amine groups initially forms the very toxic ammonia•This is then
converted to the less toxic urea, ornithine cycle which is transported to the kidneys
for excretion•The remaining keto acid can be directly respired, or converted to a
carbohydrate or fat
Blood flow in the Liver which type of Blood and how? - answer-Oxygenated Blood
from the aorta via Hepatic artery•
Deoxygenated Blood from the digestive system via Hepatic portal vein○has
digestive products
Exit via the hepatic vein
•Sinusoids○Oxy and deoxy blood mix in vessels called sinusoids○Join together to
form the hepatic(central) vein○Blood flowing by sinusoids come into contact with
the liver cells(Hepatocytes)
What are Liver Cell called and what are Kupffer cells - answer-Hepatocytes
Specialised macrophages• in sinusoids•Break down and recycle old red blood
cells•Haemoglobin is broken down into bilirubin○This is the brown pigment in
faeces
Liver function and diagram (3) - answer-Detoxification of Blood
Storage of Glycogen
Breakdown of Erythrocytes
Production of plasma protein
deamination of amino acids
kidney function / functional unit of kidney - answer-The kidney's role is to filter
blood and remove excess ions/water to produce urine. The functional unit of the
kidney is the nephron.
,Nephron structure (6) - answer-nephrons spread across the cortex and medulla of
the kidney. Blood enters the organ via the renal artery and exits via the renal vein.
In between, it passes through tiny capillaries that surround the continuous tube
constituting the nephron. Function•Filter out waste products
Bowman's Capsule-Ultrafiltration ,Filter blood •Proximal Convoluted Tubule (PCT)
selective reabsorption Re-absorbs valuable substances, such as glucose•
Loop of Henle Creates low water potential in the medulla○Allows water to be
reabsorbed•Distal Convoluted Tubule (DCT)○osmoregulation○Varies the amount of
water reabsorbed into the Blood
Compostion of Nephron - answer-PCT○In the PCT fluid composition is altered by
reabsorption 100% sugars, most salts and water○85% of water is reabsorbed•
Descending Limb○the water potential decreased
Salts added- Water removed•Ascending Limb○In the ascending limb water potential
is increased○Salts are removed by active transport•Collecting Duct○In the
collecting duct water potential is decreased again- Water removed
What is the basement membrane? - answer-Fine mesh of collagen fibers and
glycoproteins- Acts as a filter to prevent the passage of molecules with a RMM of
over 69,000-
Most proteins are held in the capillaries of the glomerulus
Epithelial cells of the Bowman's capsule structure
How is glomerular filtrate formed - answer-Podocytes-Finger like projections called
major processes make gaps between cells Filtrate from blood can pass into the
lumen of the Bowman's capsule• High pressure forces some water and solutes
through the basement membrane and into the Bowman's capsule•This liquid is now
known as the 'glomerular filtrate'
What is Selective Reabsroption - answer-high pressure forces water and solutes
through the basement membrane and into the Bowman's capsule•This liquid is now
known as the 'glomerular filtrate'What is left in the capillary?•Proteins•Blood
cells•Molecules bigger than 69,000 RMM will remain in the blood.Selective
reabsorption•As fluid moves along the nephron, substances are removed•Sodium-
Potassium pumps move sodium ions from the cells lining the PCT into the tissue
fluid•This reduced the concentration of sodium ions in the cytoplasm
•Sodium ions are transported to cell, with glucose or amino acids, by facilitated
diffusion•As gluc and amin acid conc rise , these substances diffuse out into the
tissue fluid•Process may be enhanced by the active removal of glucose and amino
acids•Tissue fluids substances diffuse into the blood and are carried
away•Reabsorption of salts, glucose and amino acids reduced the water potential in
cells and increases it in the tubule fluid•Water enter cells•
Adapations for selective reabosrption - answer-Microvilli increase surface area•
Membrane contains co-transporter proteins that transport glucose and amino acids
with sodium ions in facilitated diffusion
•Many mitochondria( for ATP generated)
, How does the loop of Henle reabsorb water - answer-Salts can be transferred from
the descending limb to the ascending limb•
Increases concentration of salts in the tubule fluid•
Salts diffuse out into the surrounding medulla tissue•
Medulla tissue has a very low water potential•
Amount of water reabsorbed controls water potential of blood
Process of water reabsorption - answer-As the fluid moves down, the water potential
falls○Water is lost to surrounding tissue fluid○Sodium and chloride ions diffuse into
the tubule•As the fluid moves up the ascending limb, the water potential rises○At
the base, sodium and chloride ions diffuse out○Sodium and chloride ions are
actively transported out○Wall of the ascending limb is impermeable to water○Fluid
loses salt, but not water, when moving up the ascending limb
Explain the hair pin counter current multiplier - answer-Close arrangement of the
ascending and descending limb•Increases the efficiency of salt transfer from the
ascending to descending limb•Salt concentrations build up in the surrounding
tissue•Movement of salts into the medulla creates a low water potential•Removal of
ions from the ascending limb means at the top, urine is dilute•Water is then
reabsorbed, according to the needs of the body
How is water content of blood controlled - answer-Brain releases antidiuretic
hormone •ADH travels to the collecting duct
the Cell have membrane bound receptors for ADH•ADH binds to
receptors•Aquaporins sent in vesicles to the cell surface membrane•Aquaporins
inserted into cell surface membrane•Walls of collecting duct more permeable to
water•More water moves into the medulla by osmosis•Water potential of the blood
rises back to the set level•Brain stops releasing ADH
what are 3 treatments of Kidney failure - answer-Renal Transplants• •Kidney
surgically attached to blood supply and bladder•Patient take immunosuppressant
drugs to prevent rejection
Dialysis•Waste removed from blood by passing it over a dialysis
membrane•Partially permeable membrane allows the exchange of substances
between blood and dialysis fluid•Any excess substances diffuse out of the blood and
into the dialysis fluid
Treatment Haemodialysis•Blood from an artery is passed into a machine and
dialyzed•Heparin added to avoid clotting•Performed at a clinic•Three times a week
Explain peritoneal dialysis - answer-Uses filter in the abdominal
membrane•Permanent tube implanted in the abdomen•Dialysis solution fills space
between organs and membrane•Solution drained after several hours•Patient able
to walk around•Can be carried out at home
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