Type of respiration Oxygen needed? Products Relative energy released Aerobic yes carbon dioxide + water large Anaerobic in yeast no ................... smal...

This question compares aerobic and anaerobic respiration and tests the aerobic respiration equation.

(a) Completed row for anaerobic respiration in yeast (2 marks, one for each product):

So the products are alcohol (ethanol) [1] and carbon dioxide [1].

(b) Respiration is the series of chemical reactions in cells [1] that break down nutrient molecules such as glucose to release energy [1].

(c) Aerobic respiration releases more energy because the glucose is completely / fully broken down (to carbon dioxide and water) [1]; in anaerobic respiration the glucose is only partly broken down, so a large amount of energy remains locked in the products (ethanol or lactic acid) [1].

(d) Any two processes that require energy [1 each, max 2]: growth / building large molecules (protein synthesis), muscle contraction / movement, active transport, cell division, or maintaining a constant body temperature.

(e) The balanced equation for aerobic respiration [1 for each correct part]:

\[ C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O \]

That is glucose plus oxygen (\(6O_2\)) [1] gives carbon dioxide (\(6CO_2\)) [1] plus water (\(6H_2O\)) [1].

(f) Yeast makes bread dough rise because the yeast respires anaerobically and produces carbon dioxide gas [1]; the bubbles of this gas are trapped in the dough, making it expand and rise [1].

Exam tip: balance the respiration equation by matching the six carbons, twelve hydrogens and six oxygens of glucose; the same six oxygen molecules that go in come out combined as CO₂ and H₂O.