EXAM 3: Photosynthesis

photosynthesis

plants can make their own food using light energy from the sun

photosynthesis

takes place in the chloroplasts, Chloroplasts are tiny green structures found in the green parts of plants

glucose and oxygen

during photosynthesis, what does carbon dioxide and water are converted into what?

Producers

plants are producers

make or produce the beginnings of most of the food energy on earth

consumer

Animals are consumers

eats part of a plant, takes the plant’s stored food energy

primary consumers

animals that eat plants directly (chemicals pass to organisms that eat plants)

secondary consumers

animals that get their food energy by eating other animals

decomposers

break down and take energy from dead things into their bodies

decomposers

enrich the soil, helping plants to grow and create more food energy

mesophyll

the cells in a middle layer of leaf tissue, primary site of photosynthesis

stomata

small pores found on the surface of leaves, and they let CO₂ diffuse into the mesophyll layer and O₂ diffuse out

each individual mesophyll cell

contains organelles called chloroplasts, which are specialized to carry out the reactions of photosynthesis

thylakoids

disc-like structures within each chloroplast

thylakoid

contains green-colored pigments called chlorophylls that absorb light

light dependent reactions and Calvin cycle (light-independent reactions)

photosynthesis consists of two reactions, which are?

thylakoids

where do light dependent reactions occur?

stroma

where do light independent reactions occur?

light-dependent reactions

redox reactions

electron transport

ATP synthesis using a proton gradient

light-dependent reactions

reduce the electron acceptor NADP+ to NADPH

light dependent reactions

generate ATP from ADP by phosphorylation

light dependent reactions

split H₂O and release O₂

light energy

can be converted to other forms of energy

photons

light also behaves as though it consists of discrete particles called:

reflected

transmitted

absorbed: the energy is transferred to the compound

when a photon of light interacts with a compound, it can be:

electrons

when a photon of light is absorbed, where is energy transferred to?

high energy state

energy from the light propels the electrons from a photosystem into a:

in the thylakoid membrane of chloroplast

in plants there are two photosystems, Photosystem 1 and Photosystem 2, where are they located?

pigments

each photosystem is made of many different:

absorption pigments

transfer the energy from sunlight to another pigment

chloroplasts

Pass the photon energy to another pigment that absorbs a similar or wavelength of light

it is raised to higher orbital

when an electron absorbs a photon,

released

is energy absorbed or released when electrons return to the ground state

pigment absorbs a photon of light, it becomes excited, meaning that it has extra energy and is no longer in its normal, or ground state

What does it mean for a pigment to absorb light

chlorophyll a

chlorophyll b

carotenoids

what are the three photosynthetic pigments

chlorophyll a

the key light capturing pigment in the chloroplast

chlorophyll b

an accessory pigment in the chloroplast

carotenoids

a separate group of accessory pigments

photosystems

have light harvesting complexes and a reaction center

light-harvesting complexes

photosynthetic pigments bound to transmembrane proteins

antenna complex

numerous lights harvesting complexes

reaction center

transmembrane proteins and very specific type of chlorophylls (surrounded by antenna complex)

Photon absorbed a pigment in the antenna complex→ excited pigment

excited pigment returns to ground state→ energy released is absorbed by adjacent pigment

transfer of energy continues until it reaches the reaction center chlorophylls

light energy transferred to the reaction center chlorophylls is converted into excited electrons

excited electrons from the reaction center chlorophylls are transferred to an electron acceptor

Photosystem in light dependent reactions

oxidized

losing electrons causes chlorophyll to become oxidized

Are reaction center chlorophylls oxidized or reduced?

reduced

electron acceptor gains electrons and becomes reduced

the electron acceptor is

light energy

is used to oxidize reaction center chlorophylls (and reduce the primary electron acceptor)

PS I or P700- reaction center chlorophyll absorbs light at 700nm

PS II or 680: reaction center chlorophyll absorbs light at 680 nm

What are the two types of photosystems

P680 because shorter wavelengths carry more energy than longer ones

What photosystem requires more energy to excite electrons in the reaction center chlorophylls- P700 or P680

Photosystem II (PS II)

it is names as second because it was discovered after PS I

functions first in the path of electron flow

excited (high energy) state

when the P680 photosystem II absorbs energy, it enters an

excited electrons from photosystem II (P680) are transferred to an electron transport chain (ETC) within the thylakoid membrane

Translocate H⁺ ions into the thylakoid

Buildup of protons within the thylakoid→ creates an electrochemical gradient

H⁺ ions return to the stroma

ATP synthase uses the passage of H⁺ ions to catalyze the synthesis of ATP (from ADP+Pi)

PS II Steps

photophosphorylation

light as energy source for ATP production

mitochondrial intermembrane space

the thylakoid space is equivalent to

both create electrochemical gradients

why is the electron transport chain in mitochondria similar to photosynthesis in thylakoids

mitochondrial matrix

the stroma is equivalent to the

endergonic

it requires energy to pump protons against their concentration gradient

movement of H+ into the thylakoid space is

the newly de-energized electrons from photosystem II are taken up by photosystem I

excited electrons from photosystem I → be transferred to a carrier molecule and used to reduce NADP+

forms NADPH (later for Calvin Cycle)

Electrons from reaction center chlorophyll need to be replaced

photosystem I in light dependent reaction steps

ferredoxin (Fd)

electron carrier, reduces NADP+ to NADPH

CO₂ combines with its acceptor, RuBP forming 3PG

3PG is reduced to G3P in a two-step reaction requiring ATP and NADPH

About one-sixth of the G3P molecules are used to make sugars- the output of the cycle

The remaining five-sixths of the G3P molecules are processed in the series of reactions that produce RuMP

RuMP is converted to RuBP in a reaction requiring ATP. RuBP is ready to accept another CO₂₊

Steps of Calvin Cycle

photosynthesis and cellular respiration are near-opposite processes

photosynthesis versus cellular respiration