A Level Biology Revision Lesson 212:

Photosynthesis - The Light Dependent Reactions.

Task 1. Check Where this Lesson fits into your Exam Specification!

Task 2. Watch the Revision Lessons in Full.


Check Your Spec!

★ AQA A Level Biology Specification Reference: - The light-dependent reaction in such detail as to show that: chlorophyll absorbs light, leading to photoionisation of chlorophyll. Some of the energy from electrons released during photoionisation is conserved in the production of ATP and reduced NADP. The production of ATP involves electron transfer associated with the transfer of electrons down the electron transfer chain and passage of protons across chloroplast membranes and is catalysed by ATP synthase embedded in these membranes (chemiosomotic theory). Photolysis of water produces protons, electrons and oxygen.


★ CIE A Level Biology Specification Reference: - 13.1 Photosynthesis as an energy transfer process Light energy absorbed by chloroplast pigments in the light dependent stage of photosynthesis is used to drive reactions of the light independent stage that produce complex organic compounds. a) explain that energy transferred as ATP and reduced NADP from the light dependent stage is used during the light independent stage (Calvin cycle) of photosynthesis to produce complex organic molecules b) state the sites of the light dependent and the light independent stages in the chloroplast c) describe the role of chloroplast pigments (chlorophyll a, chlorophyll b, carotene and xanthophyll) in light absorption in the grana. f) describe the light dependent stage as the photoactivation of chlorophyll resulting in the photolysis of water and the transfer of energy to ATP and reduced NADP (cyclic and non-cyclic photophosphorylation should be described in outline only).


★ Edexcel A Level Biology (Biology A – Salters-Nuffield) Specification Reference: - Topic 5: On the Wild Side: This topic builds an appreciation that photosynthesis is the primary process that underpins the majority of ecosystems, and provides students with an understanding of how ecosystems work. 5.5 Understand the overall reaction of photosynthesis as requiring energy from light to split apart the strong bonds in water molecules, storing the hydrogen in a fuel (glucose) by combining it with carbon dioxide and releasing oxygen into the atmosphere. 5.6 Understand how phosphorylation of ADP requires energy and that hydrolysis of ATP provides an immediate supply of energy for biological processes. 5.7 Understand the light-dependent reactions of photosynthesis including how light energy is trapped by exciting electrons in chlorophyll and the role of these electrons in generating ATP, reducing NADP in photophosphorylation and producing oxygen through photolysis of water. 5.9 Understand the structure of chloroplasts in relation to their role in photosynthesis.

★ Edexcel A Level Biology (Biology B) Specification Reference: - Topic 5: Energy for Biological Processes. 5.7 Photosynthesis: i Know the structure of chloroplasts, including: envelope, stroma, grana and lamellar structure. Light-dependent stage: ii Understand the role of the thylakoid membranes in the light dependent stage of photosynthesis. iii Understand that the processes of cyclic and non-cyclic photophosphorylation result in the production of reduced NADP, ATP and oxygen.

★ OCR A Level Biology (Biology A) Specification Reference: - 5.2 Energy for biological processes. 5.2.1 Photosynthesis: (b) the structure of a chloroplast and the sites of the two main stages of photosynthesis. The components of a chloroplast including outer membrane, lamellae, grana, thylakoid, stroma and DNA. (c) (i) the importance of photosynthetic pigments in photosynthesis. To include reference to light harvesting systems and photosystems. (d) the light-dependent stage of photosynthesis. To include how energy from light is harvested and used to drive the production of chemicals which can be used as a source of energy for other metabolic processes (ATP and reduced NADP) with reference to electron carriers and cyclic and non-cyclic photophosphorylation AND the role of water.

★ OCR A Level Biology (Biology B) Specification Reference: - Module 4: Energy, reproduction and populations: 4.3 Photosynthesis, food production and populations - 4.3.1 Photosynthesis, food production and management of the environment : (a) (i) the ultrastructure of the chloroplast - To include the location of the components for the light-dependent reaction in the thylakoid membranes (light harvesting complexes, photosystems, electron transport chain and ATP synthase) and the location of the enzymes for the light-independent reactions in the stroma. (b) the process of the light-dependent stage of photosynthesis. To include the transfer of light energy to chemical energy in the form of ATP and reduced NADP (details of cyclic and non-cyclic photophosphorylation are not required).


★ WJEC A Level Biology Specification Reference: - Energy for Life: 2. Photosynthesis uses light energy to synthesise organic molecules. Learners should be able to demonstrate and apply their knowledge and understanding of: (a) the distribution of chloroplasts in relation to light trapping (b) chloroplasts acting as transducers converting the energy of light photons into the chemical energy of ATP. (c) the process of light harvesting and the absorption of various wavelengths of light by chlorophyll and associated pigments and the energy transfer to reaction centres. (d) the basic features of Photosystems I and II. (e) cyclic and non-cyclic photophosphorylation as sources of electrons for the electron transport chain. (f) photolysis as a source of electrons for Photosystem II. (g) the reduction of NADP by the addition of electrons and hydrogen ions in the stroma maintaining the proton gradient.

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