Photosynthesis Quiz - Plant Biology

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Questions and Answers

What is the approximate amount of Photosynthetically Active Radiation (PAR) in full sunlight?

1000 umole photons m2/s

4000 umole photons m2/s

3000 umole photons m2/s

2000 umole photons m2/s (correct)

Chlorophyll appears green to us because it primarily absorbs which wavelengths of light?

Green and yellow

Red and blue (correct)

Blue and green

Yellow and red

Which of the following is NOT a component of a chloroplast?

Stroma lamellae

Mitochondria (correct)

Thylakoid

Stroma

What is the primary function of the Thylakoid membrane in photosynthesis?

Light reactions (A) Signup and view all the answers

What is the main product of the Calvin cycle?

Glyceraldehyde-3-phosphate (G3P) (B) Signup and view all the answers

Which of the following statements accurately describes the role of accessory pigments in photosynthesis?

They absorb light energy and transfer it to chlorophyll. (C) Signup and view all the answers

What is the net equation for photosynthesis?

6 CO2 + 6 H2O → C6H12O6 + 6 O2 (B) Signup and view all the answers

What is the primary function of the enzymes in the stroma of a chloroplast?

Fixing carbon dioxide into carbohydrates. (C) Signup and view all the answers

What is the primary photosynthetic pathway used by all plants?

Calvin Cycle (D) Signup and view all the answers

Under which specific conditions does photorespiration occur?

Low CO2 concentration (C) Signup and view all the answers

What is the function of RuBP in photosynthesis?

To capture and fix carbon dioxide (D) Signup and view all the answers

Which of the following is a disadvantage of photorespiration?

Loss of RuBP from the Calvin Cycle (C) Signup and view all the answers

What is the primary difference between C3 and C4 plants?

C3 plants use only the Calvin Cycle, while C4 plants use both Hatch-Slack and Calvin Cycles. (D) Signup and view all the answers

What is the role of PEP in C4 plants?

To capture and fix carbon dioxide in the Hatch-Slack Pathway. (A) Signup and view all the answers

Which of the following is an example of a C4 plant?

Maize (C) Signup and view all the answers

Why are C4 plants more effective at photosynthesis in hot, dry climates?

Their ability to fix carbon dioxide at lower concentrations. (D) Signup and view all the answers

Why do C4 plants have a higher water use efficiency compared to C3 plants?

C4 plants use the enzyme PEP carboxylase, which has a higher affinity for CO2, allowing them to keep their stomata closed for longer periods. (C) Signup and view all the answers

Which of the following statements accurately describes the difference between C3 and C4 plants in terms of their photosynthetic efficiency?

C3 plants are more efficient at lower CO2 concentrations, while C4 plants are more efficient at higher CO2 concentrations. (C) Signup and view all the answers

C4 plants are particularly well-suited for which of the following environmental conditions?

High temperatures and low water availability. (C) Signup and view all the answers

What is the primary reason for the decreased photosynthetic efficiency of C3 plants at higher temperatures?

Increased photorespiration caused by the competing reaction of Rubisco with oxygen at higher temperatures. (C) Signup and view all the answers

What is the role of PEP carboxylase in C4 plants?

It fixes CO2 into a four-carbon compound, malate, which is transported to bundle sheath cells. (B) Signup and view all the answers

How do CAM plants differ from C3 and C4 plants in terms of their stomatal activity?

CAM plants open their stomata only at night and close them during the day, unlike C3 and C4 plants. (D) Signup and view all the answers

What is the primary factor that determines the maximum yield of a crop under optimal growth conditions?

The amount of light intercepted by the leaf canopy. (A) Signup and view all the answers

What role does the accumulation of intercepted PAR play in crop biomass accumulation?

It is directly proportional to the amount of biomass accumulated. (A) Signup and view all the answers

Study Notes

Photosynthesis Overview

Photosynthesis is the process where plants convert light energy into biomass.
Photosynthetically Active Radiation (PAR) is light energy between 400 and 700nm wavelengths.
PAR is approximately 50% of incoming solar radiation.
In full sunlight, PAR is about 2000 μmol photons/m²/s.
Solar radiation is composed of 50% PAR, 47% infra-red radiation, and 3% ultraviolet radiation.

Chlorophyll

The mesophyll of leaves is the main photosynthetic tissue in plants.
Mesophyll cells contain chloroplasts, which hold chlorophyll pigments.
Chlorophyll absorbs primarily red and blue light wavelengths, reflecting green light.

Leaf Cross-Section

A leaf cross-section illustrates the key structures involved in photosynthesis.
Key leaf structures include the epidermis, mesophyll, xylem, phloem, guard cells, and stomata.

Chloroplast Structure

Chloroplasts contain several key organelles:
- Inner and outer membranes
- Grana (stacks of thylakoids)
- Thylakoid lumen
- Stroma (surrounds grana)
- Stroma lamellae (connections between grana)

Organelles in a Chloroplast

Stroma: the inner membrane that encloses the chloroplast, containing enzymes that convert CO2 into carbohydrates and the location of the Calvin cycle.
Thylakoid: flat, sac-like membrane structures within the stroma, often stacked into grana; the site of light reactions.
Stroma lamellae: thylakoid extensions that connect the individual grana.

Photosynthetic Pigments

Chlorophyll a and chlorophyll b are the most abundant pigments.
Carotenoids and phycocyanin are accessory pigments.

Process of Photosynthesis

Photosynthesis involves a complex series of chemical reactions that convert CO2 and H2O into carbohydrates (C6H12O6).
The chemical equation is: 6CO2 + 6H2O → C6H12O6 + 6O2
Light reactions convert light energy to chemical energy, splitting water into oxygen and hydrogen ions.
The light reactions produce ATP, NADPH, and oxygen.
The Calvin cycle uses ATP and NADPH (from light reactions) to fix CO2 into a carbohydrate.
The product of the Calvin cycle is glyceraldehyde-3-phosphate (G3P).

Output of Calvin Cycle

Glyceraldehyde-3-phosphate (G3P) combines to form fructose.
Fructose is then rearranged to form glucose or combines with fructose to form sucrose for transport throughout the plant.
Glucose will undergo respiration to release energy (ATP).

Types of Photosynthesis

C3 plants fix CO2 only via the Calvin cycle. Examples include rice, soybeans, and sunflowers.
- C3 plants are shade-loving and thrive in cooler temperatures.
C4 plants use two pathways: the Hatch-Slack pathway in the mesophyll cells and the Calvin cycle in bundle sheath cells. Examples include maize, sugarcane, and tropical grasses.
- C4 plants are adapted to hotter, drier climates.
CAM plants have specialized stomatal activity patterns, opening stomata at night to reduce water loss. Examples include cacti, orchids, and pineapples.

Photorespiration

Photorespiration occurs under low CO2 conditions, where rubisco binds to oxygen instead of CO2.
This is considered a wasteful process as it releases CO2 and less carbon is returned to the chloroplast.

Radiation Use Efficiency

The maximum crop yield under optimum growth conditions depends on the amount of PAR intercepted by the leaf canopy.
Crop biomass accumulation is proportional to the accumulation of intercepted PAR.
Radiation use efficiency (RUE) represents how much biomass is produced from each absorbed PAR.

Factors Affecting Photosynthesis Rate

Nitrogen, moisture, and temperature are major factors that influence the rate of photosynthesis.

Nitrogen

Nitrogen is essential for chlorophyll formation, thus impacting photosynthesis.
If nitrogen is deficient, plants can exhibit chlorosis, stunting plant growth.
Reduced leaf size due to nitrogen deficiency reduces light energy capture.

Moisture

Water is necessary for plant cell expansion, division, and differentiation.
Drought reduces leaf canopy expansion, leading to decreased photosynthesis.

Temperature

Photosynthesis generally increases with temperature up to an optimum.
Exceeding the optimum temperature for a plant decreases photosynthetic rates.
This occurs because membrane-bound electron transport processes become unstable, affecting the supply of reducing power, thus causing decreased photosynthesis.
Plants have different optimal temperatures for photosynthesis based on adaptation to different environments.

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Description

Test your knowledge on key concepts related to photosynthesis, including the role of chloroplasts, light absorption, and the Calvin cycle. This quiz covers essential topics such as the differences between C3 and C4 plants, the function of enzymes in chloroplast stroma, and the significance of accessory pigments. Prepare to dive deep into the fascinating world of plant biology!