Biology- Light dependent reactions

what allows plants to collect solar energy?

Light-absorbing pigment molecules in their leaves

What happens to the light energy absorbed by pigments in plants

it is converted into chemical energy during the light dependent reactions of photosynthesis

What law explains why absorbed energy cannot disappear

The first law of thermodynamics- energy cannot be created or destroyed, only transformed

what is the purpose of the light-dependent reactions

To convert light energy into ATP and NADPH, which power the calvin cycle

Where do the light dependent reactions take place in the plants

In the thylakoid membranes of the chloroplasts

What are photosystems

Large protein-pigment complexes that harvest light energy for photosynthesis

What is the special chlorophyll pair in photo system ll called

P700

What do ATP and NADPH store

chemical energy used in the calvin cycle to make sugars

What is non-cyclic photophosphorylation

the “Standard“ light-dependent reaction where electrons are removed from water passed through PSll and PSl, and end up in NADPH while also producing ATP

What are the products of non-cyclic photophosphorylation

ATP, NADPH, and O2 

What happens when light is absorbed by PSll

energy is transferred to P680, exciting an electron to a high energy level

What replaces the electron lost by P680

An electron from the splitting of water (H20)

What is released when water is split in PSll

Oxygen (O2), protons (H+), and electrons

What happens to the excited electron from PSll

It travels down an electron transport chain, losing energy

How is ATP produced during the light reactions

Energy from the ETC pumps H+ ions into the thylakoids lumen, as they flow back into the stroma through ATP synthase, ATP is made by chemiosmosis

What contributes to the proton (H+) gradient

H+ ions from water splitting and H+ pumped into the lumen during electron transport

What happens to the electron when it reaches PSl

It joins the P700 special pair and is re-energized by light absorption

What replaces the electron lost by P700 in PSl

An electron arriving from PSll via the electron transport chain

where does the high energy electron from PSl go next

down a short second electron transport chain to NADP+

What is formed at the end of PSl electron transport chain

NADPH, from NADP and electrons

How is cyclic photophosphorylation different from non-cyclic

electrons cycle back to PSl instead of going to NADP, only ATP is produced

describe the energy change of electrons during the light reactions

electrons start at low energy in water, are boosted twice by light and end at high energy in NADPH

Why are electron transfers “downhill“ in energy

Because light boosts electrons to high energy levels, allowing spontaneous energy release as they move along the chain

What is a photosystem

A complex of proteins and pigments in the thylakoids membrane that harvests light and converts it into chemical energy

What are the two main photosystems

photosystem ll and photosystem l

what are the primary pigments in photosystems

chlorophyll a, chlorophyll b, and carotenoids

How do pigments transfer absorbed light energy

through resonance energy transfer passing energy from one pigment to the next until it reaches the reaction center

What happens when energy reaches the reaction center

the special pair of chlorophyll a releases an electron to a primary electron acceptor

where does splitting occur

in PSll