Photosynthesis- BP Flashcards
What is photosynthesis?
using light energy to make glucose (and other biological molecules)
occurs in plants and algae (both have chloroplast)
Adaptation of plant for photosynthesis?
leaf located near top of plant = closer to light
leaf is thin and wide = large surface area for light, short diffusion distance for CO2
has many veins = connect to xylem to bring in water
has stomata for gas-exchange (CO2/O2)
has air spaces to support ease of gas-exchange
palisade cells located near top of leaf close to the light
palisade cells are large = large surface area for light
palisade cells have a thin cell wall = short diffusion distance for CO2
palisade cells contain many chloroplasts (site of photosynthesis)
palisade cells have a large vacuole = pushes chloroplast to edge of cell closer to light
Structure of chloroplast?
site of photosynthesis
has a double membrane (outer and inner)
contains discs called thylakoids (contain chlorophyll)
a stack of thylakoids = granum
thylakoids are surrounded by a fluid material called stroma
How does photosynthesis take place?
In 2 stages
light dependent stage = in thylakoid membrane, makes ATP and reduced NADP
light independent stage = in stroma, uses the ATP and reduced NADP to make glucose
Describe the light independent stage?
involves the calvin cycle
RuBP (5 carbon) joins with CO2 (using rubisco) to make 2 lots of GP (3 carbon)
the GP is reduced into TP (3 carbon)
this uses energy from ATP and hydrogen atom from reduced NADP
the TP can be used to reform RuBP (uses energy from ATP)
the TP can also be used to form glucose (carbohydrate)
TP can also be used to form amino acids (proteins) and fatty acids
TP can also be used to form glycerol
fatty acids and glycerol will form a lipid
photosynthesis/calvin cycle = produces all the main biological molecules
What are the limiting factors for photosynthesis?
Light
CO2
Temperature
: as these increase the rate of photosynthesis also increases
Effect of limiting Light on the calvin cycle?
RuBP decreases – being converted into GP but not being reformed from TP (no ATP)
GP increases – not converted into TP (no ATP/reduced NADP) but is being formed from RuBP
Effect of limiting CO2 on the calvin cycle?
RuBP increases – not converted into GP (no CO2) but is being reformed from TP
GP decreases – not being formed from RuBP (no CO2) but being converted into TP
What is the compensation point in plants?
the point in the day (light intensity) when the CO2 taken in by photosynthesis equals the amount given out by respiration = no net gas exchange
at low light intensity: rate of respiration > rate of photosynthesis [CO2 released]
at high light intensity: rate of photosynthesis > rate of respiration [CO2 absorbed]
How to measure rate of photosynthesis?
measure amount of CO2 used or measure amount of O2 produced, in a certain time
one method = photosynthometer
photoionisation?
light hits chlorophyll
chlorophyll absorbs the light if correct wavelength
electrons become excited and are lost from the chlorophyll (photoionisation)
Photophosphorylation?
electrons enter an electron carrier system
electrons move down the system releasing energy
this pumps protons from stroma into thylakoid space
protons accumulate in thylakoid space, then diffuse back into stroma
they pass through ATP Synthase which joins ADP and Pi to make ATP (mechanism = chemiosmosis, process = photophosphorylation)
the electron ends up by joining with NADP to form reduced NADP
Photolysis?
light also hits water
causes photolysis (breakdown of water due to light)
forms: H+, e-, O2
the H+ joins with the reduced NADP (now carries a hydrogen atom: H+ and e-)
the e- replaces electrons lost from chlorophyll
O2 given off as waste
Describe the light dependant stage
light hits chlorophyll
chlorophyll absorbs the light if correct wavelength
electrons become excited and are lost from the chlorophyll (photoionisation)
electrons enter an electron carrier system
electrons move down the system releasing energy
this pumps protons from stroma into thylakoid space
protons accumulate in thylakoid space, then diffuse back into stroma
they pass through ATP Synthase which joins ADP and Pi to make ATP (mechanism = chemiosmosis, process = photophosphorylation)
the electron ends up by joining with NADP to form reduced NADP
light also hits water
causes photolysis (breakdown of water due to light)
forms: H+, e-, O2
the H+ joins with the reduced NADP (now carries a hydrogen atom: H+ and e-)
the e- replaces electrons lost from chlorophyll
O2 given off as waste
draw and label a chloroplast
inner membrane
outer membrane
thylakoid disks
grana
stroma
lamellae
