C1.3 Photosynthesis Flashcards
What is photosynthesis?
Synthesis of food in a series of reactions using light energy and carbon dioxide.
What type of energy conversion occurs during photosynthesis?
Light energy to chemical energy.
Where is the chemical energy from photosynthesis stored?
Biomass, within the bonds of the organic compounds.
What are the raw materials of photosynthesis?
Carbon dioxide and water.
What are the products of photosynthesis?
Glucose and oxygen.
What are autotrophs?
Organisms that make their own food.
Which type of organisms carry out photosynthesis?
Plants, algae, and cyanobacteria.
What is a heterotroph?
An organism that obtains its food from other organisms.
Why do chloroplasts contain pigments?
To absorb light energy for photosynthesis.
Why do chloroplasts contain multiple photosynthetic pigments?
To absorb a wide range of wavelengths to ensure efficient photosynthesis.
How is oxygen produced during photosynthesis?
By the splitting of water.
What is the main photosynthetic pigment?
Chlorophyll.
What colour of visible light has the shortest wavelength?
Violet (400nm).
What colour has the longest wavelength?
Red (700nm).
How does light wavelength affect photosynthesis?
Absorption of light varies with wavelength, affecting the rate of photosynthesis.
How do pigments absorb visible light?
The pigment molecules absorb photons, causing an electron to become ‘excited’ and jump to a higher energy level.
Which wavelengths do not provide enough energy to ‘excite’ an electron?
Green (so it is not absorbed).
What are the two main groups of pigments?
Chlorophylls and carotenoids.
What do carotenoids do?
Surround chlorophyll and absorb similar & different wavelengths of light, expanding the range of absorbed wavelengths.
What is an absorption spectrum?
Shows how much light is absorbed by different pigments at different wavelengths.
What is an action spectrum?
A graph that shows the rate of photosynthesis at different wavelengths of light.
What are the similarities between an absorbance spectrum and an action spectrum?
Both have two main peaks (at blue-violet and red regions) and a trough in the green-yellow region.
What wavelengths does chlorophyll absorb?
Blue-violet and red (green is reflected).
What wavelengths do carotenoids absorb?
Mainly blue-violet range.
What wavelengths produce the highest rates of photosynthesis?
Blue-violet and red.
What are the two types of chromatography?
Paper chromatography and thin-layer chromatography.
What are photosystems?
Clusters of chlorophyll and accessory pigments, with a reaction centre that absorbs light and emits an excited electron.
Where are photosystems located?
Thylakoid membrane.
What processes take place in the thylakoid membrane?
Light-dependent reactions: Photolysis of water, synthesis of ATP by chemiosmosis, reduction of NADP.
What is photolysis?
The splitting of water using light energy, producing protons, electrons, and oxygen.
Where does photolysis occur exactly?
Photosystem II.
What is the chemical equation of photolysis?
2H₂O → O₂ + 4H⁺ + 4e⁻.
What are the electrons produced by photolysis used for?
Replacement of electrons lost from the reaction centre in photosystem II and subsequent reactions of the light-independent reaction.
What is chemiosmosis?
Movement of protons across a membrane, driving ATP synthesis.
What is the role of the proton gradient in the thylakoid membrane?
The proton gradient powers ATP synthase to produce ATP.
What is the function of ATP synthase?
It synthesises ATP from ADP and inorganic phosphate, using energy from the proton gradient.
Define photophosphorylation.
Light energy being used to phosphorylate ADP to produce ATP.
What are the two types of photophosphorylation?
Cyclic (only photosystem I involved) and non-cyclic (both photosystem I and II).
What is the main purpose of non-cyclic photophosphorylation?
To produce ATP, NADPH, and O₂, which are needed for the Calvin cycle.
What happens to electrons in non-cyclic photophosphorylation?
Electrons are excited in PSII, travel through the electron transport chain to PSI, and reduce NADP⁺ to NADPH.
Why does cyclic photophosphorylation occur?
When the plant needs more ATP than NADPH or when the Calvin cycle runs out of NADP+.
How does cyclic photophosphorylation differ from non-cyclic photophosphorylation?
Uses only Photosystem I, only ATP is produced, and no water is split.
Describe how NADP is reduced during the light-dependent reactions.
NADP+ gains two electrons from photosystem I and one proton from the stroma to become NADPH.
What are the useful end-products of the light-independent reactions?
ATP & reduced NADP (NADPH).
Is the oxygen produced during the light-independent reactions a useful or waste product?
A waste product.
Describe the function of Rubisco.
The enzyme responsible for carbon fixation in the Calvin cycle, attaching CO2 to RuBP.
Where do the light-independent reactions/Calvin cycle take place?
Stroma of chloroplasts.
What are the three main phases of the Calvin cycle?
- Carbon fixation - CO2 combining with RuBP using Rubisco. 2. Synthesis of triose phosphate. 3. Regeneration - some triose phosphates leave to form glucose.
What are the main products of the Calvin cycle?
Glucose, regenerated RuBP, ADP, and NADP+.
Why is the Calvin Cycle a cycle?
Because it starts and ends with the same molecule.
Why do light-independent reactions stop when there is no light?
Because they need ATP and NADPH produced by light-dependent reactions.
Define carbon fixation.
When CO2 is attached to an organic molecule (RuBP) in photosynthesis.
Describe the regeneration of RuBP in the Calvin cycle.
5 triose phosphate molecules are converted to 3 RuBP molecules.
How many turns of the Calvin cycle are needed to produce 1 molecule of glucose?
6 turns.
What fraction of triose phosphate is used to regenerate RuBP?
5/6 (1/6 used to synthesis organic molecules like glucose).
What products, other than glucose, are synthesised from Calvin cycle intermediates?
Carbohydrates, amino acids, and other carbon compounds.
Why can’t the light-dependent reactions continue without CO₂?
The light-independent reactions rely on CO₂, and a lack of it prevents the Calvin cycle from functioning.
