3.7:Cell Respiration
Aerobic cell respiration:
glucose + oxygen  carbon dioxide + water + energy
3.7.1 Define cell respiration.
Cell respiration is the controlled release of energy from organic compounds in cells to form ATP.
3.7.2: State that, in cell respiration, glucose in the cytoplasm is broken down by
glycolysis into pyruvate, with a small yield of ATP.
IB Question: In the cytoplasm of the cell, glucose is broken down into pyruvate in a process
called glycolysis. State one product of glycolysis. [1]
ATP / NADH + H+ / 2 NADH / reduced NAD [1]
3.7.3 Explain that, during anaerobic cell respiration, pyruvate can be converted in the
cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP
IB Question: List two end products of aerobic cell respiration. [2]
aerobic respiration;
Carbon dioxide , water, ATP
IB QUESTION: Distinguish between the process of anaerobic respiration in yeast and humans.
[2]
yeast: pyruvate to ethanol and carbon dioxide;
humans: pyruvate to lactic acid; [2]
Award [1 max] if products are appropriately linked to organisms without the mention of
pyruvate.
3.7.4 Explain that, during aerobic cell respiration, pyruvate can be broken
down in the mitochondrion into carbon dioxide and water with a large yield of ATP.
IB Question: Using a table, compare aerobic and anaerobic respiration in a eukaryotic cell. [5]
Award [1] for each correct row, up to [5 max].
Aerobic respiration Anaerobic respiration
occurs in mitochondria occurs in cytoplasm;
requires 2 O occurs without 2 O ;
both produce pyruvate from glucose (glycolysis);
uses fatty acids/lipids/amino acids doesn’t use fatty acids;
(Krebs cycle) produces 2 CO and 2 H O (fermentation) produces ethanol / 2 CO
(in yeast) ;
(Krebs cycle) produces 2 CO and 2 H O (fermentation) produces lactate in
animals (humans) ;
NADH produced in both;
large amount of ATP (36 per glucose
molecule) produced
small amount of ATP (2 per glucose
molecule) produced; [5 max]
IB Question: Explain the process of aerobic cell respiration. [8]
cell respiration produces energy;
controlled release of energy;
by breakdown of organic molecules/glucose;
energy from them is used to make ATP;
aerobic respiration is in mitochondria;
requires oxygen;
pyruvate is produced by glycolysis / glucose broken down;
pyruvate is broken down in the mitochondria;
into carbon dioxide and water;
large production of ATP;
per molecule/mass of glucose;
much higher production of ATP than in anaerobic respiration; [8 max]
IB Question: Compare anaerobic cellular respiration and aerobic cellular respiration. [5]
Direct comparisons must be made to achieve a mark.
anaerobic in the absence of oxygen whereas aerobic in the presence of oxygen;
both may produce 2 CO ;
both produce ATP;
aerobic releases considerably more ATP per glucose molecule than anaerobic;
anaerobic/fermentation in plants produces alcohol / anaerobic in animals produces
lactic acid neither produced in aerobic respiration;
glucose can be the substrate for both;
glucose can be the substrate for both;
anaerobic entirely in cytoplasm whereas aerobic requires mitochondria/specialized
region of membrane;
glucose is broken down into pyruvate in the cytoplasm in both; [5 max]
3.8: Photosynthesis
carbon dioxide + water  glucose + oxygen
3.8.1 State that photosynthesis involves the conversion of light energy into
chemical energy.
IB Question: i. State the principal conversion of energy that occurs in photosynthesis.
[1]
ii. State the molecule necessary for this conversion of energy.
(i) light (energy) to chemical (energy)/ATP/glucose/NADPH/sugar; [1]
(ii) chlorophyll [1]
[1]
3.8.2 State that light from the Sun is composed of a range of wavelengths (colours).
IB Question: Outline the difference in absorption of red, blue and green light by chlorophyll for
the process of photosynthesis.
[1]
red and blue light is absorbed and green light is reflected / blue light is absorbed
the most and green light is absorbed the least [1]
3.8.3 State that chlorophyll is the main photosynthetic pigment.
3.8.4: Outline the differences in absorption of red, blue and green light by
chlorophyll.
3.8.5 State that light energy is used to produce ATP, and to split water molecules (photolysis) to
form oxygen and hydrogen.
3.8.6: State that ATP and hydrogen (derived from the photolysis of water) are used
to fix carbon dioxide to make organic molecules.
IB QUESTION: Outline how light energy is used and how organic molecules are made in
photosynthesis.
[6]
chlorophyll is the (main) photosynthetic pigment;
absorbs (mainly) red and blue light;
green light is reflected;
light energy absorbed is converted into chemical energy;
ATP produced;
water split;
to form oxygen and hydrogen;
ATP and hydrogen used to fix carbon dioxide to make organic molecules; [6 max]
3.8.7 Explain that the rate of photosynthesis can be measured directly by the production of
oxygen or the uptake of carbon dioxide, or indirectly by an increase in biomass..
IB Question: Explain how the rate of photosynthesis can be measured. [5]
rate can be measured by the disappearance of raw materials / 2 CO (in solution);
rate of change of 2 CO can be measured (indirectly) by pH change;
rate can be measured by the appearance of products/ 2 O /starch;
rate can be measured by measuring rate of change of biomass;
description of apparatus to measure the rate of photosynthesis / annotated diagram;
explanation of expected experimental outcome: e.g. increased photosynthesis in
an aquatic plant – more 2 O bubbles counted per unit time; [5 max]
IB Question: Explain how photosynthesis can be measured both directly and indirectly. [3]
(a) directly:
by production of oxygen / measuring the
volume/number of bubbles of gas produced;
by measuring the uptake of carbon dioxide;
changes in pH;
⎧⎨⎩
Do not accept “production of gas”.
indirectly:
by measuring the increase in biomass;
by measuring the production of glucose / starch / other suitable molecule; [3 max]
Award [2 max] if only indirect measurements or direct measurements are addressed.
Apply ECF if direct and indirect is confused for more than one method.
3.8.8: Outline the effects of temperature, light intensity and carbon dioxide
concentration on the rate of photosynthesis.
Effect of Temperature on rate of photosynthesis
Effect of light intensity on rate of photosynthesis
Effect of carbon dioxide concentration on rate of photosynthesis
IB Question: Outline how three different environmental conditions can affect the rate of
photosynthesis in plants. [6]
light: [2 max]
rate increases with increasing light;
it reaches maximum then plateaus;
as all chloroplast molecules are working at optimal pace;
temperature: [2 max]
rate increases with increasing temperature;
to a maximum/optimum temperature;
but then falls off rapidly;
as enzymes are denatured above the optimal temperature;
carbon dioxide: [2 max]
rate increases with increasing carbon dioxide level;
it reaches maximum then plateaus;
as photosynthesis operating at optimal level; [6 max]
Award any of the above points if clearly drawn in a diagram.
IB Question: Outline the effects of temperature, light intensity and carbon dioxide concentration
on the rate of photosynthesis. [6]
Award credit for the following points if annotated on sketched graphs.
all three variables can be classified as limiting factors;
as temperature increases, photosynthetic rate increases;
maximum rate of photosynthesis at optimum temperature;
at (very) high temperatures photosynthesis slows/stops;
as light intensity increases, photosynthetic rate increases;
at high light intensity, photosynthesis stops increasing;
minimum light intensity necessary for photosynthesis to occur;
(because concentration is rarely high) 2 CO is the main rate-limiting variable;
as concentration of 2 CO rises, photosynthetic rate rises (up to a certain point); [6 max]