A2 - Unit 1 - Photosynthesis Flashcards
What are autotrophs?
Organisms that use light energy or chemical energy and inorganic molecules (carbon dioxide and water) to synthesise complex organic molecules
What are heterotrophs?
Organisms that ingest and digest complex organic molecules, releasing the chemical potential energy stored in them
What is photosynthesis?
The process whereby light energy from the Sun is transformed into chemical energy and used to synthesise large organic molecules from inorganic substances
What equation summarises photosynthesis?
6CO2 + 6H2O (+light energy) —> C6H12O6 + 6O2
What equation summarises aerobic respiration?
C6H12O6 + 6O2 —> 6CO2 + 6H2O (+ energy, some as ATP)
Where does photosynthesis take place?
Photoautotrophs have special organelles within their cells called chloroplasts
What are photosynthetic pigments?
Molecules that absorb light energy
Each pigment absorbs a range of wavelengths in the visible region and has its own distinct peak of absorption
Over wavelengths are reflected
What is the structure of a chloroplast?
Vary in shape and size but most are disc-shaped and between 2-10 um long
Each is surrounded by a double membrane - an envelope
Intermembrane space between the inner and the outer membrane
Outer membrane permeable to many small ions
Inner membrane less permeable and had transport proteins embedded in it, folded into lamellae which are stacked up like piles of pennies
Each stack of lamellae called a granum
What are the two distinct regions inside each chloroplast?
Stroma
Grana
What is the stroma in a chloroplast?
A fluid-filled matrix.
The reactions of the light-independent stage of photosynthesis occur in the stroma where necessary enzymes are located
Within the stroma are starch grains and oil droplets, as well as DNA and prokaryote-type ribosomes
What are the grana in chloroplasts?
Stack of flattened membrane compartments, called thylakoids
These are sites of light absorption and ATP sysnthesis during the light-dependent stage of photosynthesis
The thylakoids can only be seen using an electron microscope
Give 7 thing which help the chloroplasts be adapted for their role
Inner membrane with its transport proteins
Many grana
Photosynthetic pigments
Proteins embedded in the grana
Fluid-filled stroma contains enzymes
Grana are surrounded by the stroma
Chloroplasts can make some of the proteins they need
How is the inner membrane of a chloroplast adapted for its role?
With its transport proteins can control entry and exit of substances between the cytoplasm and the stroma inside the chloroplasts
How does having many grana help a chloroplast perform its function?
Many grana, consisting of stacks of up to 100 thylakoid membranes provide a large surface area for the photosynthetic pigments, electron carriers and ATP synthase enzymes, all of which are involved in the light-dependent reaction
How are the photosynthetic pigments in chloroplasts adapted for their role?
They are arranged into special structures called photosystems, which allow maximum absorption of light energy
How do proteins in the grana help chloroplasts be adapted for their role?
The proteins hold the photosystems in place
Why do the chloroplasts have a fluid-filled stroma?
It contains the enzymes needed to catalyse the reactions of the light-independent stage of photosynthesis
Why are the grana surrounded by the stroma in the chloroplasts?
So the products of the light-dependent reaction, which are needed for the light-independent reaction, can readily pass into the stroma
How can chloroplasts make some of the proteins they need for photosynthesis?
Using the genetic instructions in the chloroplast DNA, and the chloroplast ribosomes to assemble the proteins
What happens when light hits chlorophyll?
Causes a pair of electrons associated with the magnesium to become excited
What are the two forms of chlorophyll a and what colour do they appear?
P680 and P700
Yellow-green
Each absorbs red light at a slightly different wavelength
What is the primary pigment reaction centre?
The pigment which is found in the centre of a photosystem, which is chlorophyll A (P680 or P700)
Which photosystem is P680 found in?
Photosystem II
Its peak of absorption is light at a wavelength of 680nm
Which photosystem is P700 found in?
Photosystem I
Its peak of absorption is light at a wavelength of 700nm
