Plant and Energy - 04/08

LO 24.1: Summarize the inputs & outputs of the light & carbon reactions using NADPH, glucose or other organic carbons, H2O, O2, CO2, and ATP; LO 24.2: Predict the possible consequences for the production of ATP & NADPH if a component or process in the photosynthesis pathway is altered

Which step of photosynthesis does rubisco catalyze?

the first step of the Calvin cycle

How does increasing water availability affect ATP and NADPH production during photosynthesis?

It increases ATP and NADPH production

What is the effect of higher light intensity on ATP and NADPH production?

Higher light intensity increases ATP and NADPH production

How does placing plants in the dark affect ATP and NADPH production?

It decreases ATP and NADPH production

What happens to ATP and NADPH production when Photosystem II (PSII) is inhibited

ATP and NADPH production decreases

How does decreasing water availability impact ATP and NADPH production during photosynthesis?

It decreases ATP and NADPH production

Why was oxygen highly toxic to early life?

Because oxygen is highly reactive

What adaptation did some lineages develop in response to increased oxygen?

They adapted to tolerate and use oxygen

What is aerobic respiration?

Respiration that uses oxygen

Why was aerobic respiration considered a key innovation?

It allowed organisms to efficiently produce energy using oxygen

What is photosynthesis?

A biochemical process that converts light energy into chemical energy (ATP) to create organic molecules (carbohydrates) for later use

What organisms are photosynthesis found in?

Bacteria, Protists, Plants

What are the major inputs for photosynthesis?

Light energy (photons), Water (H₂O), Carbon dioxide (CO₂)

What are the major outputs of photosynthesis?

Oxygen (O₂) & Carbohydrates

What is chloroplast?

The cellular structure (organelle) responsible for photosynthesis

What factors influence the density of chloroplasts in plant cells?

Species, age, light exposure, and tissue function

Does chloroplast density remain constant across all plant cells?

No, it varies depending on species, age, light exposure, and tissue function

How many membranes do plant chloroplasts have?

Two (double membranes)

Do chloroplasts have their own DNA?

Yes, chloroplasts have their own DNA for replication

How is chloroplast DNA different from the organism’s DNA?

Chloroplast DNA is distinct from the DNA found in the cell nucleus

What is the formula of photosynthesis?

Energy + water + CO₂ —> sugar + O₂

What is the function of the light dependent reactions?

To capture light energy and convert it into chemical energy in the form of ATP and NADPH, while producing oxygen from water

What are the inputs of light dependent reactions?

Light, energy, and water

What are the outputs of light dependent reactions?

NADPH, ATP, O₂

What is photosynthetically active radiation (PAR)?

Light within the 400-700 nm wavelength range that plants use for photosynthesis

Can pigments other than chlorophyll capture light for plants?

Yes, other pigments can augment light capture

Besides aiding light capture, what other roles might plant pigments have?

They may serve additional functions beyond light capture

What are carbon reactions in biochemistry?

A set of biochemical reactions that fix carbon by transforming atmospheric carbon into organic molecules and creating carbohydrates

Which carbon fixation cycle is present in all plants?

The Clavin cycle (also called the C3 cycle)

Why are carbon reactions sometimes called “light independent reactions“?

Because they do not directly require light, but the Calvin cycle only occurs when light is present

What enzyme initially catalyzes the Calvin cycle?

RuBisCo

What is the role of Rubisco in the Calvin cycle?

It catalyzes the conversion of CO₂ to organic molecules

What molecules provide the energy needed for the remaining steps of the Calvin cycle?

ATP & NADPH

How many ATP are used in the regeneration of RuBP?

6 ATP —> 12 ADP

How many CO₂ molecules enter the cycle?

6 CO₂

Where does the Calvin Cycle begin?

With CO₂ entering and being fixed by RuBisCO

What happens to ATP after it is used?

It becomes ADP

What is ATP used for in the Calvin Cycle?

Providing energy for reactions (reduction and regeneration)

What is NADPH used for in the Calvin Cycle?

Providing electrons (reducing power)

How many NADPH are used in the cycle?

12 NADPH —> 12 NADP⁺

What leaves the cycle to form more complex sugars?

2 G3P

Where do ATP and NADPH come from?

Light-dependent reactions

Which enzyme is involved in the reduction phase of the Calvin cycle?

G3P dehydrogenase

Name an enzyme involved in the light-dependent reactions of photosynthesis

ATP synthase (produces ATP using the proton gradient)

What happens to carbon dioxide and water during photosynthesis?

Carbon dioxide (CO₂) is fixed into organic molecules (like glucose) during the Calvin cycle, while water (H₂O) is split in the light-dependent reactions to release oxygen (O₂), electrons, and protons

Which of the following statements is true for the Calvin cycle?

The Calvin cycle depends on the products of the light reactions

What happens to photosynthesis rate when light intensity increases?

Photosynthesis rate increases because more light energy is available for the light-dependent reactions, up to a saturation point

What happens when light intensity decreases?

Photosynthesis rate decreases due to less energy for converting CO₂ and water into glucose

How does an increase in carbon dioxide concentration affect photosynthesis?

Photosynthesis rate increases as more CO₂ is available for the Calvin cycle, enhancing carbon fixation

How does a decrease in CO₂ concentration affect photosynthesis?

Photosynthesis rate decreases because CO₂ is a substrate for carbon fixation, so less CO₂ limits the process

What is the effect of increasing temperature on photosynthesis?

Photosynthesis rate increases up to an optimum temperature because enzyme activity speeds up

What happens when temperature decreases?

Photosynthesis rate slows down as enzyme activity decreases and biochemical reactions become less efficient

What happens when temperature increases?

Photosynthesis rate sharply decreases due to enzyme denaturation and damage to photosynthetic structures

How does increasing water availability influence photosynthesis?

Photosynthesis rate increases because water is a raw material and stomata remain open for CO₂ uptake

How does decreasing water availability affect photosynthesis?

Photosynthesis rate decreases as stomata close to conserve water, reducing CO₂ intake and causing water stress

What happens when oxygen concentration increases?

Photosynthesis rate can decrease due to increased photorespiration, which competes with carbon fixation

What about when oxygen concentration decreases?

Photorespiration is reduced, potentially increasing photosynthesis efficiency, especially in C3 plants

How does increasing nutrient availability affect photosynthesis?

Photosynthesis rate increases as nutrients support chlorophyll production and enzyme function

What happens when nutrient availability decreases?

Photosynthesis rate decreases due to limited chlorophyll and enzyme synthesis

What is the effect of increasing chlorophyll concentration?

Photosynthesis rate increases because more light energy can be absorbed

What if chlorophyll concentration decreases?

Photosynthesis rate decreases due to less light absorption

How are NADPH and ATP used in the Calvin cycle?

NADPH provides reducing power (electrons) and ATP provides energy to convert CO₂ into glucose

What molecule is released as a waste product during the light reactions?

Oxygen (O₂)

What happens to ATP production if ATP synthase is inhibited?

ATP production stops because protons cannot flow back into the stroma to drive ATP synthesis, even if the proton gradient exists

How does a shortage of NADP⁺ affect NADPH and ATP production?

NADPH production decreases as NADP⁺ is the final electron acceptor; this can cause electron backup and reduce ATP production indirectly

What happens to ATP production if photosystem II (PSII) is damaged or inhibited?

Electron flow slows or stops, reducing the proton gradient needed for ATP synthase, so ATP production decreases

How does a malfunction in photosystem I (PSI) affect NADPH production?

Electrons cannot be transferred to NADP⁺ efficiently, so NADPH production decreases

What is the effect on ATP and NADPH if the electron transport chain (ETC) between PSII and PSI is blocked?

Electron flow is interrupted, reducing both proton gradient formation (less ATP) and electron availability for NADPH synthesis