LIGHT DEPENDENT REACTIONS Flashcards
PHOTOSYNTHESIS
What are accessory pigments? (1)
light-absorbing molecules that pass on the energy they absorb to chlorophyll molecules at the start of photosynthesis.
what are the common types of photosynthetic pigments? (3)
-chlorophylls
-carotenes
-others
what photosynthetic pigments come underneath chlorophylls? (2)
Chlorophyll a - green
chlorophyll b - green
what photosynthetic pigments come underneath carotenes? (2)
B - carotene - orange
Xanthophyll - yellow
what photosynthetic pigments come underneath others? (2)
phycoerithrin - red
fucoxanthin - brown
what is the purpose of photosynthetic pigments? (1)
to absorb light energy and convert it into chemical energy.
what is meant by hydrophilic? (1)
having an affinity for water and soluble in water.
what is meant by hydrophobic? (1)
substances that repel water, they are mainly insoluble in water but can be soluble in lipids.
what are the two parts of a chlorophyll molecule? (2)
-the head of the molecule is a hydrophilic ring structure with a magnesium atom in its centre.
-attached to this is a long hydrophobic hydrocarbon tail
what does the arrangement of a chlorophyll molecule mean? (1)
means that chlorophyll molecules are attached to the membranes of the chloroplast by their long tails whilst the heads lie flat on the membrane surface to absorb the maximum amount of light.
what is the absorption spectrum? (1)
shining light of different wavelengths through a solution of the pigment and measuring how much is absorbed - the graph of the amount of light absorbed at each wavelength is known as the absorption spectrum.
what is the action spectrum? (1)
by plotting a graph of the rate of photosynthesis of a green plant at different wavelengths.
why are the action spectrum and absorption spectrum very similar? (1)
this provides good evidence to support the model of light being trapped by these pigments and used in photosynthesis.
why do plants need more than one absorption pigment? (1)
a combination of two or more pigments means that a greater range of wavelengths can be absorbed efficiently.
What are the main properties of the structure of chloroplast? (6)
- has outer and inner membranes
-contains 70s ribosomes
-the liquid is called the stroma
-has a stack of disks (grana) and individually called a thykloid
-have DNA
-contains a lamella (between granium)
where is chlorophyll found in a chloroplast? (1)
within the thylakoid
what is autotrophic nutrition? (1)
the synthesis of larger organic molecules from simpler inorganic compounds as carried out by plants during photosynthesis
what is the word equation for photosynthesis? (1)
Carbon dioxide + water + light energy —-> organic compounds (sugars) + oxygen
where do light dependent reactions take place? (1)
occurs in the grona
what is a summary of light dependent reaction? (3)
light energy is used directly to split water (photolysis). Hydrogen is then removed and retained by the photosynthetic specific hydrogen acceptor (NADP+). At the same time ATP is generated for ADP and phosphate, dissolving energy from light - this is known as photophosphorylation.
do chlorophylls occur haphazardly? (1)
chlorophylls do not occur haphazardly but are grouped together in structure called photosystems held in the thylakoid membranes of the grana.
what is photosystem 1? (1)
has a reaction activated at the wavelength 700nm (also known as P700)
What is photosystem 2? (1)
has a reaction activated by the light wavelength of 680nm (also known as P680)
What occurs in the first stage of photosystem 2? (1)
the excited electrons from photosystem 11 are picked up by, and passed along a chain of electron carriers. As these excited electrons pass, some of the energy causes the pumping of hydrogen ions (protons) from the chloroplasts matrix into the thylakoid spaces, there they accumulate - incidentally causing the pH to drop. The result is a proton gradient that is created across the thylakoid membrane, and which sustains the synthesis of ATP.
