Photosynthesis Quiz for Biology Class

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Questions and Answers

What do autotrophic organisms primarily use as their source of energy for synthesis?

Organic compounds

Chemical reactions

Mineral nutrients

Sunlight (correct)

Which of the following best describes photoautotrophs?

Organisms that rely entirely on chemical reactions for energy

Organisms that only use organic materials for energy

Organisms that convert light energy into chemical energy (correct)

Organisms that assimilate energy from the soil

In the overall equation for photosynthesis, where does the oxygen produced originate?

From carbon dioxide molecules

From water molecules (correct)

From soil minerals

From glucose molecules

Which process involves breaking down complex organic molecules to release energy?

Heterotrophic nutrition Signup and view all the answers

What is the primary role of photosynthesis in the ecosystem?

To produce glucose and release oxygen Signup and view all the answers

What is the primary purpose of the tight arrangement of bundle sheath cells around the vascular bundles in C4 plants?

To isolate bundle sheath cells from oxygen. Signup and view all the answers

Which group of organisms primarily consists of autotrophs?

Plants and photosynthetic bacteria Signup and view all the answers

How does the spatial separation of light-dependent and light-independent reactions benefit C4 plants?

It prevents photorespiration. Signup and view all the answers

What are chemoautotrophs primarily characterized by?

Their use of chemical reactions for energy Signup and view all the answers

What role do plasmodesmata play in C4 plants?

They allow rapid movement of metabolites between cells. Signup and view all the answers

Which of the following is NOT a product of photosynthesis?

Carbon dioxide Signup and view all the answers

In what way do C4 plants manage carbon dioxide during periods of low supply?

By storing carbon dioxide in bundle sheath cells. Signup and view all the answers

What is the main advantage of C4 plants having stomata that may close at midday?

To reduce water loss. Signup and view all the answers

What is the primary function of the stroma in chloroplasts?

Location for light-independent reactions Signup and view all the answers

Which component of chloroplasts directly facilitates the light-dependent reactions of photosynthesis?

Thylakoids Signup and view all the answers

What is the primary role of the granal membranes in chloroplasts?

Provide surface area for ATP production Signup and view all the answers

Which pigment is the most important for capturing light energy in photosynthesis?

Chlorophyll a Signup and view all the answers

What role does the magnesium atom play in chlorophyll?

Forms part of the structure Signup and view all the answers

Which process occurs in the stroma of chloroplasts?

Calvin cycle Signup and view all the answers

What is the significance of the proteins that hold photosynthetic pigments in chloroplasts?

They form the photosystems Signup and view all the answers

Which elements are found in chloroplast pigments besides carbon, hydrogen, and oxygen?

Magnesium and nitrogen Signup and view all the answers

What is the primary result of protons flowing through the ATP synthase complex?

Production of ATP Signup and view all the answers

Which process exclusively uses photosystem I?

Cyclic photophosphorylation Signup and view all the answers

What occurs during cyclic photophosphorylation?

Electrons are recycled back to the original chlorophyll molecule Signup and view all the answers

How does non-cyclic photophosphorylation differ from cyclic photophosphorylation?

It involves both photosystem I and photosystem II Signup and view all the answers

What role do the electrons play in photosystem II during non-cyclic photophosphorylation?

They replace lost electrons in photosystem I Signup and view all the answers

What is required for photophosphorylation to occur?

Light Signup and view all the answers

What happens to the excess protons that accumulate in the thylakoid space?

They flow back through ATP synthase Signup and view all the answers

In the light-independent stage of photosynthesis, what molecule do the excited electrons ultimately reduce?

NADP+ Signup and view all the answers

What is the role of the special pair of chlorophyll a molecules in a photosystem?

They serve as the reaction centre. Signup and view all the answers

What process describes the addition of an inorganic phosphate to ADP during the light dependent stage of photosynthesis?

Photophosphorylation Signup and view all the answers

Which photosystem is associated with the light absorption peak of 700 nm?

Photosystem I (PSI) Signup and view all the answers

What is the primary function of photosystems in chloroplasts?

To capture and funnel light energy. Signup and view all the answers

What do the electrons taken up by an electron carrier during photoactivation of chlorophyll represent?

They are in an excited state. Signup and view all the answers

During the process of photolysis, what are water molecules split into?

Oxygen, protons, and electrons Signup and view all the answers

Where does the light dependent stage of photosynthesis primarily take place?

Thylakoids Signup and view all the answers

What role do accessory pigments play in photosystems?

They absorb light and transfer energy to chlorophyll. Signup and view all the answers

What is the main reason photosynthesis is considered temperature sensitive?

It involves both chemical and photochemical processes. Signup and view all the answers

What is the primary goal of regulating environmental conditions in glasshouses for crop production?

To determine and optimize the limiting factors for photosynthesis. Signup and view all the answers

Which factor is mentioned as a potential limiting factor in photosynthesis?

Temperature. Signup and view all the answers

What can happen if the optimal level of a specific factor in photosynthesis is exceeded?

It can denature enzymes and harm the plants. Signup and view all the answers

How much can tomato yields be increased by raising CO2 concentration to 1000 ppm?

20% or more. Signup and view all the answers

What role do enzymes play in photosynthesis according to the information provided?

They facilitate the chemical processes during the light independent stage. Signup and view all the answers

Why is precise control of environmental conditions essential in glasshouses?

To avoid the wasteful use of energy and resources. Signup and view all the answers

What is the average CO2 concentration in the atmosphere?

400 ppm. Signup and view all the answers

Study Notes

Photosynthesis Overview

Photosynthesis is essential for all living organisms, providing energy captured from sunlight
Autotrophic nutrition: Organisms build complex organic molecules (e.g., lipids, carbohydrates, proteins) from simple inorganic molecules (e.g., carbon dioxide, water) using energy (light or chemical reactions). Plants, algae, and some bacteria are autotrophs.
Heterotrophic nutrition: Organisms break down complex organic molecules to simpler, soluble molecules. Examples include animals, fungi, and some bacteria.
Photoautotrophs: Organisms use light energy to drive photosynthesis (e.g., green plants, algae, photosynthetic bacteria).
Chemoautotrophs: Organisms use energy from chemical reactions for photosynthesis (e.g., some bacteria involved in the nitrogen cycle).

Photosynthesis Equation

The overall equation for photosynthesis: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
The equation 6CO₂ + 12H₂O + light → C₆H₁₂O₆ + 6O₂ + 6H₂O is a more precise representation

Photosynthesis Stages

Light harvesting takes place in chloroplasts via chlorophyll, carotenoids, xanthophyll.
Light-dependent stage: Captures light energy, splits water (photolysis), produces ATP and reduced NADP.
Light-independent stage (Calvin cycle): Uses ATP and reduced NADP to convert carbon dioxide into carbohydrates, occurs in stroma of chloroplasts.

Leaf Structure Adaptations

Large surface area for light absorption.
Thin lamina (leaf blade) for short diffusion distances.
Transparent cuticle and epidermis to allow light through
Numerous stomata for gaseous exchange.
Air spaces in spongy mesophyll for CO₂ and water diffusion.
Network of vascular bundles (xylem and phloem) for water transport and sugar delivery

Chloroplast Structure

Chloroplasts have a double membrane (envelope)
Stroma: Fluid-filled space where the light-independent reactions occur.
Grana: Stacks of thylakoids where light-dependent reactions happen.

Chloroplast Pigments And Light Harvesting

Chlorophylls (a and b). Absorbs red and blue light well
Carotenoids, Xanthophylls which are accessory pigments absorbing other wavelengths than chlorophylls, and transferring the energy to chlorophyll a for use in the light-dependent stage.
Absorption spectrum: Graph showing the amount of light absorbed by a pigment at different wavelengths.
Action spectrum: Graph showing the rate of photosynthesis at different wavelengths.

Light Dependent Stage

Photoactivation of chlorophyll: Electrons are excited by light to a higher energy level.
Photolysis of water: Water molecules split into Protons, Electrons and oxygen.
Electron transport chain: Electrons pass through a series of protein complexes generating ATP via chemiosmosis.
ATP and reduced NADP, are produced which are required for the light-independent stage.
Cyclic photophosphorylation: Electrons return to the chlorophyll molecules, generating only ATP.
Non-cyclic photophosphorylation: Electrons are accepted by NADP from the photosystem I, generating ATP and reduced NADP, that is eventually used to fuel the light-independent (Calvin cycle) reactions.

Light Independent Stage (Calvin Cycle)

Carbon fixation: CO₂ combines with RuBP (ribulose bisphosphate) using the enzyme rubisco to form an unstable six-carbon compound.
Reduction: The unstable six-carbon compound breaks down into two three-carbon molecules (glycerate 3-phosphate, GP). ATP and reduced NADP provide energy needed to reduce GP to triose phosphate (TP).
Regeneration of RuBP: Some TP molecules are used to regenerate RuBP using ATP, ensuring the cycle can continue.

C4 Pathway

C4 plants have a spatial separation of carbon fixing and the Calvin cycle to minimise photorespiration and maximize carbon fixation in hot, dry climates such as in maize and sugarcane.
The C4 plants fix carbon using an enzyme that has a higher affinity for carbon dioxide and less for oxygen in the mesophyll layer of the leaf where light is captured.
PEP carboxylase is not affected by oxygen and has high efficiency at fixing carbon under high temperature.

Limiting Factors

Limiting factors: Factors that restrict the rate of photosynthesis when they are present at less than optimal levels. Common limiting factors include light intensity, CO₂ concentration, and temperature.
Light compensation point: The light intensity at which the rate of carbon dioxide uptake equals the rate of carbon dioxide release.

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Description

Test your knowledge on photosynthesis and the role of autotrophic organisms. This quiz covers essential concepts, including energy sources, the definition of photoautotrophs, and the biological processes involved in oxygen production. Perfect for students looking to reinforce their understanding of this fundamental topic.