Why is photosynthesis described as indirect evidence for evolution?

All photoautotrophs share chlorophyll and a similar process, so it is inferred they inherited it from a common ancestor.

What absorbs light in photosynthesis?

Chlorophyll (and accessory pigments).

How is ATP made in the chloroplast?

Protons diffuse down an electrochemical gradient through ATP synthase.

Where is ATP synthase found in chloroplasts?

Embedded in the thylakoid membranes.

What does ATP synthase catalyse?

The formation of ATP from ADP and inorganic phosphate.

Give two reasons photosynthesis is not 100% efficient.

Light is reflected or transmitted; only some wavelengths are absorbed; energy lost as heat; limiting factors.

State the equation for Rf.

Rf = \frac{distance moved by pigment}{distance moved by solvent front}

Why do pigments separate in chromatography?

They have different solubilities in the solvent, so they move different distances.

Why might shade-tolerant plants contain more chlorophyll b?

It absorbs a different range of wavelengths, so more of the dim light is absorbed.

Does an Rf value have a unit?

No, it is a ratio and is always less than or equal to 1.

Photosynthesis overview and pigmentsAQA A-Level Biology: Flashcards

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What is a photoautotroph?

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What is a photoautotroph?: An organism that makes organic molecules from inorganic molecules using light energy.
Why is photosynthesis described as indirect evidence for evolution?: All photoautotrophs share chlorophyll and a similar process, so it is inferred they inherited it from a common ancestor.
What absorbs light in photosynthesis?: Chlorophyll (and accessory pigments).
What is the light energy absorbed by chlorophyll linked to?: The production of ATP.
How is ATP made in the chloroplast?: Protons diffuse down an electrochemical gradient through ATP synthase.
Where is ATP synthase found in chloroplasts?: Embedded in the thylakoid membranes.
What does ATP synthase catalyse?: The formation of ATP from ADP and inorganic phosphate.
Give two reasons photosynthesis is not 100% efficient.: Light is reflected or transmitted; only some wavelengths are absorbed; energy lost as heat; limiting factors.
State the equation for Rf.: $R_f = \frac{\text{distance moved by pigment}}{\text{distance moved by solvent front}}$
Why do pigments separate in chromatography?: They have different solubilities in the solvent, so they move different distances.
Why might shade-tolerant plants contain more chlorophyll b?: It absorbs a different range of wavelengths, so more of the dim light is absorbed.
Does an Rf value have a unit?: No, it is a ratio and is always less than or equal to 1.
Which colour of light is mainly reflected by chlorophyll?: Green.

Exam questions on Photosynthesis overview and pigments

Cyanobacteria, algae, mosses and flowering plants all carry out photosynthesis. In every group, light is absorbed by chlorophyll, and the energy is used to make ATP by a very similar set of reactions involving membrane-bound proteins.
Explain how the similarities in photosynthesis between these groups suggest that photoautotrophs share a common ancestor.2 marks
Isolated chloroplasts were kept in the dark in a buffer at pH 4 until the space inside their thylakoids also reached pH 4. They were then transferred to a buffer at pH 8 containing ADP and inorganic phosphate, still in the dark. ATP was made for a short time.
Explain why ATP was made in this experiment even though there was no light.2 marks
A student separated the photosynthetic pigments from the leaves of two plants by thin-layer chromatography. The solvent front travelled 9.0 cm from the origin. The extract from a plant grown in full sun gave spots at 8.1 cm (carotene), 6.3 cm (chlorophyll a) and 5.4 cm (chlorophyll b) from the origin. The extract from a shade-tolerant plant gave the same three spots, but its chlorophyll b spot was much larger and darker.
Calculate the Rf value of chlorophyll a in the extract from the plant grown in full sun. Show your working.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).