Zadanie 8, Paper 2, maj 2022, TZ2, Biologia IB HL

(a) Simple diffusion down a gradient through the bilayer, for example oxygen or carbon dioxide. ✔

Osmosis is net water movement towards lower water potential/higher solute concentration across a selectively permeable membrane. ✔

Facilitated diffusion uses a membrane protein for passive transport, for example glucose through a carrier. ✔

Active transport uses energy to move a substance against its gradient, for example the sodium–potassium pump. ✔

Endocytosis encloses material in membrane vesicles, for example phagocytosis of bacteria. ✔

Exocytosis releases vesicle contents by membrane fusion, for example neurotransmitter release. ✔

(b) Osmoregulation keeps internal solute concentrations within a controlled range. ✔

Glomerular filtration transfers water and small solutes into Bowman’s capsule. ✔

The proximal tubule selectively reabsorbs useful solutes such as glucose, salts and amino acids. ✔

The loop of Henle maintains a concentrated medulla OR actively transports salts. ✔

Water can leave the descending limb by osmosis. ✔

Concentrated blood or dehydration triggers increased ADH release; hypothalamic osmoreceptor detection is optional. ✔

ADH increases collecting-duct permeability or water reabsorption. ✔

Urine becomes more concentrated OR its volume is reduced. ✔

Breakdown of excess amino acids produces nitrogenous waste. ✔

Toxic ammonia is converted to the less toxic compound urea, principally in the liver, not the kidney. ✔

Urea is excreted in urine. ✔

(c) Nocturnal activity or burrowing reduces exposure to daytime heat. ✔

Structures such as large ears can aid dry heat loss and reduce the need for evaporative cooling. ✔

Longer loops of Henle can support concentrated urine. ✔

More ADH can be released when osmotic conditions require it OR urine can be more concentrated OR urine volume can be lower. ✔

Stored fat can yield metabolic water when oxidized, as in camels. ✔

Reduced sweating lowers water loss. ✔

Other valid adaptations, such as a pale coat that reduces solar heat gain. ✔

Quality: the response is clear on first reading, concise and contains little repetition or irrelevant material. ✔

Part (a):1 per valid process with its example,maximum 4; water itself is the osmosis example. Part (b):any 7,maximum 7; annotated diagrams may earn points. Part (c):any 4,maximum 4; accept other valid desert adaptations. Award 1 independent quality mark. Total 16. Pumps are not passive channels, urea is less toxic rather than non-toxic, and synthesis of urea is distinguished from its renal excretion.