Photosynthesis Study Guide for A Level Biology

Key Points

Explains the light-dependent and light-independent reactions of photosynthesis.
Includes diagrams illustrating the structure of chloroplasts and the photosynthetic process.
Covers the role of chlorophyll and accessory pigments in capturing light energy.
Discusses factors affecting the rate of photosynthesis, such as light intensity and carbon dioxide concentration.

elvani chinnaya

8 pages

Language:English

Type:Study Guide

Photosynthesis

elvani chinnaya

8 pages

Language:English

Type:Study Guide

Photosynthesis

1 | P a g e h t t p s : / / w w w . c i e n o t e s . c o m /

Photosynthesis (chapter 12):

 Photosynthesis is the fixation of CO

and its subsequent reduction to carbohydrate, using

hydrogen from water, taking place in the chloroplast; where two reactions are involved:

light dependent reactions and light independent reactions

 The photosynthetic pigments involved fall into two categories: primary pigments

(chlorophylls) and accessory pigments (carotenoids) of which are arranged in light-

harvesting clusters called photosystems (I and II), where several hundred accessory

pigment molecules surround a primary pigment molecule to pass absorbed light energy

towards the primary pigment – the reaction centre

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 Light dependent reactions – thylakoids (holds ATP synthase):

 Light energy is necessary for the synthesis of ATP in photophosphorylation and the

splitting of water (photolysis – photosystem II) into hydrogen ions (combine with a

carrier molecule NADP to make reduced NADP) and oxygen – waste product

 Photophosphorylation of ADP to ATP are of two types: cyclic and non-cyclic

 Cyclic phosphorylation:

 Only involves photosystem I

 Light absorbed by photosystem I passed to the primary pigment resulting to

the excitation of an electron for which is emitted from the chlorophyll

molecule (photoactivation) and captured by an electron acceptor to be

passed onto the electron transport chain

 Protons from photolysis pumped into the membrane space to synthesise

ATP from ADP and an inorganic phosphate group (Pi) by the process of

chemiosmosis for which goes to the light independent stage (Calvin cycle) to

produce complex organic molecules

 Non-cyclic phosphorylation:

 Involves both the photosystems

 Light is absorbed by both photosystems resulting to excited electrons

emitted from the primary pigments of both reaction centres, which are then

absorbed by electron acceptors and pass along the ETC

 The primary pigment of photosystem I absorbs electrons from photosystem

II for which receives replacement electrons from the splitting of water

(photolysis)

 Protons from photolysis pumped into the membrane space to synthesise

ATP from ADP and an inorganic phosphate group (Pi) by the process of

3 | P a g e h t t p s : / / w w w . c i e n o t e s . c o m /

chemiosmosis for which goes the light independent stage (Calvin cycle) to

produce complex organic molecules

 Light independent reaction (Calvin cycle) – stroma :

 Carbon dioxide reaches the inside of a palisade mesophyll cell from the external

atmosphere through the stomata by diffusion down a concentration gradient, and

passes through air spaces; dissolves in film of water on cell surface then diffuses

through cell wall / surface membrane of palisade cells

 Using a series of enzyme-controlled reactions:

 Fixation of carbon dioxide by combination with RuBP, a 5C compound,

(carboxylation) – using Rubisco enzyme – to form an unstable 6C

intermediate, resulting to 2 molecules of GP, a 3C compound; using ATP and

reduced NADP from the light dependent reaction reduces GP to TP for

which most of it regenerates to form RuBP while others undergo

rearrangement of carbons to form pentose sugars / lipids / amino acids /

hexose sugars; ATP is required for the phosphorylation of ribulose

phosphate into ribulose bisphosphate

 Role of accessory pigment in photosynthesis: passes energy to primary pigment; absorb

light wavelengths that primary pigment does not; forms part of the light-harvesting cluster

of pigments (photosystem)

Overview

Photosynthesis Study Guide for A Level Biology

Photosynthesis explores the biochemical process by which plants convert light energy into chemical energy. This study guide is tailored for A Level Biology students, featuring detailed explanations of light-dependent and light-independent reactions, along with diagrams for visual learners. Key topics include the role of chlorophyll, the Calvin cycle, and factors affecting photosynthesis rates. Ideal for students preparing for exams or seeking a comprehensive understanding of plant biology. Key Points Explains the light-dependent and light-independent reactions of photosynthesis. Includes diagrams illustrating the structure of chloroplasts and the photosynthetic process. Covers the role of chlorophyll and accessory pigments in capturing light energy. Discusses factors affecting the …

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FAQs of Photosynthesis Study Guide for A Level Biology

What are the stages of photosynthesis?

Photosynthesis consists of two main stages: the light-dependent reactions and the light-independent reactions, also known as the Calvin cycle. The light-dependent reactions occur in the thylakoid membranes of chloroplasts, where light energy is converted into ATP and NADPH. The Calvin cycle takes place in the stroma, where carbon dioxide is fixed into organic molecules using the energy from ATP and NADPH produced in the first stage.

How do chlorophyll and accessory pigments function in photosynthesis?

Chlorophyll primarily absorbs light in the red and blue-violet regions of the spectrum, reflecting green light. Accessory pigments, such as carotenoids, absorb different wavelengths of light that chlorophyll does not, thus enhancing the overall efficiency of photosynthesis. These pigments work together in light-harvesting complexes to funnel energy to the reaction centers where photosynthesis occurs.

What factors influence the rate of photosynthesis?

The rate of photosynthesis is influenced by several factors including light intensity, carbon dioxide concentration, and temperature. At low light intensities, light is the limiting factor, while at higher intensities, other factors like temperature or carbon dioxide levels may limit the rate. Understanding these factors is crucial for optimizing plant growth and agricultural practices.

What is the significance of the Calvin cycle in photosynthesis?

The Calvin cycle is essential for converting carbon dioxide into glucose, which serves as an energy source for plants. This cycle uses ATP and NADPH generated from the light-dependent reactions to reduce 3-phosphoglycerate into glyceraldehyde-3-phosphate, a precursor for glucose and other carbohydrates. The cycle's efficiency is vital for plant growth and energy storage.

What role does water play in photosynthesis?

Water is crucial in photosynthesis as it is split during the light-dependent reactions to release oxygen and provide electrons. This process, known as photolysis, occurs in photosystem II and helps generate ATP and NADPH. The availability of water directly impacts the rate of photosynthesis, making it an essential resource for plant health.