IB DP Biology A1.1 Water IB Style Questions For HL Paper 2

Explanation:

a) Outline how water acts as a coolant when sweating.

Water acts as a coolant during sweating due to its high specific heat capacity and high heat of vaporization. When the body becomes too hot, sweat glands release water (sweat) onto the skin. As sweat evaporates, it absorbs heat from the body, cooling it down. This process occurs because:

• Evaporation of water requires energy (heat), which is taken from the skin’s surface.
• Since water has a high heat of vaporization, it can absorb a lot of heat before it changes from liquid to gas.
• This cooling effect helps regulate body temperature and prevent overheating.

b) Describe how the kidney regulates water when the body is dehydrated.

When the body is dehydrated, the kidneys play a crucial role in conserving water to maintain fluid balance. The process works as follows:

1. 1. Increased Antidiuretic Hormone (ADH) secretion: The hypothalamus detects dehydration, signaling the pituitary gland to release more ADH (also called vasopressin) into the bloodstream.
   2. ADH effects on kidneys: ADH acts on the nephrons in the kidneys, specifically the collecting ducts, making them more permeable to water.
   3. Water reabsorption: As a result, more water is reabsorbed from the urine back into the bloodstream, concentrating the urine and reducing water loss.
   4. Conservation of water: This process helps maintain body water levels and prevents excessive fluid loss during dehydration.

c)Explain how water is transported from the soil to the atmosphere in flowering plants.

Water is transported from the soil to the atmosphere in a process called transpiration, which involves several steps:

1. Root absorption: Water is absorbed from the soil by the plant’s roots through osmosis.
2. Xylem transport: Water moves from the roots up through the xylem vessels to the leaves, using a combination of root pressure and capillary action.
3. Evaporation from leaves: Once the water reaches the leaves, it evaporates from the stomata (small pores on the leaf surface) into the atmosphere. This evaporation is driven by sunlight and heat.
4. Transpiration pull: As water evaporates from the stomata, it creates a vacuum that pulls more water up from the roots through the xylem, continuing the cycle.

——————————————-Markscheme—————————————————

(a) a. evaporation of water / water molecules separate / water changes to vapour/gas;
b. hydrogen bonds broken by heat / thermal energy;
c. heat removed from body/skin with evaporation/breaking of hydrogen bonds;
d. water’s high (latent) heat of evaporation makes it efficient (at removing heat)/OWTTE;

(b) a. ADH (secreted) if body/blood is dehydrated/hypertonic/solute concentration too high;
b. more aquaporins / aquaporins open (in collecting duct);
c. collecting duct more permeable to water/reabsorbs more water (from filtrate/urine);
d. water reabsorbed by osmosis/water reabsorbed because medulla is hypertonic;
e. (reabsorbed) water passes (from filtrate) to blood / blood solute concentration reduced;
f. less water lost in urine / smaller volume of (more concentrated) urine;
g. negative feedback / less/no ADH secreted when blood solute concentration returns to normal;

(c) a. root takes up water by osmosis;
b. root hair cells increase surface area (for uptake);
c. active transport of salts/ions/minerals into root increases uptake of water;
d. water enters xylem (vessels) in root/ water transported up plant in xylem;
e. water lost by transpiration/evaporation from leaves;
f. low/negative (hydrostatic) pressure generated in leaves/xylem (vessels);
g. water moved up in xylem by transpiration pull/tension/suction;
h. cohesion/hydrogen bonding between water molecules (so water column does not break);
i. root pressure/active transport of ions into (root) xylem can move water up in xylem;
j. capillary action due to adhesion of water molecules to xylem wall (can refill xylem);
k. xylem vessels reinforced/strengthened by wood/lignin (to prevent collapse);