Biology Unit 4, ATP and Photosynthesis

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Questions
1 (a) Name two pigment molecules found in chloroplasts.
(b) Explain the role of pigment molecules.
(a) Describe the effects of different wavelengths of light on the rate of
photosynthesis.
(b) Pigments are present in photosystems I and II. Where are the photosystems
located in the chloroplasts and how do photosystems I and II differ?
(c) A number of plants have additional pigments, which may mask the colour of
the chlorophylls. These plants often appear to have `red' leaves, such as
copper beech. What benefit might this confer on the plant?
2 (a) What are the three products of the lightdependent stage of photosynthesis?
(b) During the lightdependent stage, the pH of the thylakoid space is lower than
that of the stroma. Why is this?
(a) What is the role of this difference in pH?
(b) ATP is synthesized via a process called photophosphorylation during the
lightdependent stage of photosynthesis. This may occur via cyclic or
noncyclic photophosphorylation. The photosystems and end products of
noncyclic photophosphorylation are identified in the table below. Identify
those of cyclic photophosphorylation.
cyclic noncyclic
Photosystem
s (i) PSII & PSI
involved
End O2, ATP &
(ii)
products NADPred
(c) Chloroplasts in some guard cells have only photosystem I. Why would these
chloroplasts be unable to form sugars?
3 The diagram below summarizes the lightindependent stage of photosynthesis.
(a) Between which two substances in the cycle does
(i) carbon dioxide enter and
(ii) reduced NADP enter?
(b)

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Name the enzyme that fixes carbon dioxide.
(c) What is the role of reduced NADP in the cycle?
(d) What is the name of the cycle?
(e) Where in the chloroplast does the cycle occur?
4 During the lightindependent stage of photosynthesis, six molecules of carbon
dioxide combine with six molecules of ribulose bisphosphate to give twelve
molecules of glycerate phosphate. These are each reduced, giving twelve
molecules of glyceraldehyde phosphate (triose phosphate).…read more

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The rate of photosynthesis is limited by a number of factors. The figure below
shows the effects of light intensity at different carbon dioxide concentrations and
temperatures.…read more

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The diagram below summarizes the movement of materials within chloroplasts
and between them and the cytoplasm. Identify substances (a) to (e) from the
diagram that follows.
8 The volume of oxygen released by an aquatic plant was calculated in mm3 h­1 for
two different light intensities at different temperatures. The results obtained are
illustrated below.
(a) Describe the results obtained at
(i) low light intensity and
(ii) high light intensity.
(b) Explain the difference in the results.…read more

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Light intensity is inversely proportional to the square of the distance from the
source: if the distance is increased by a factor of 2 the intensity falls by a
2
factor of 1/2 = 1/4 or 25%. This is called the inverse square law.
Leaf discs extracted from young spinach leaves and that have been submerged in water float
when illuminated with a bench lamp.…read more

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ACTIVITY NOTES
Answers to questions
1 (a) Chlorophyll a, chlorophyll b, carotene,
xanthophylls, phaeophytin.
(b) To absorb certain wavelengths of light, exciting electrons for use in the lightdependent stage of photosynthesis.
(c) Wavelengths of about 400­450 nm (blue) and
650­700 nm (red) give high rates of photosynthesis but wavelengths of about
500­650 nm (green) are reflected.
(d) The photosystems are on the granal and thylakoid lamellae, PSII is mainly on granal lamellae but PSI mainly on
thylakoid lamellae.…read more

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Because carbon dioxide from respiration is being used in photosynthesis, so no carbon dioxide is taken up ­ or
because oxygen from photosynthesis is being used in respiration, so no oxygen is released.
6 (a) By dissolving lipids and denaturing proteins the
hot alcohol prevented further reactions. Thus, at whatever step had been reached, the lightindependent stage was
fixed at the time the cells were dropped into the hot alcohol.
(b) The separation of substances in one direction is oneway chromatography.…read more

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H2O.
(b) O2 .
(c) ATP (or NADPred).
(d) NADPred (or ATP).
(e) CO2.
8 (a) (i) The rate barely increases from about 1.0 mm3
h­1 to 1.5 mm3 h­1 with a rise in temperature and declines after 30 °C.
(ii) The rate increases with temperature,
approximately doubling for every 10 °C rise in temperature up to 30 °C, after which the rate decreases.…read more

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