Macronutrients and Nutrient Essentiality

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Questions and Answers

What defines primary macronutrients in plants?

Required in large amounts (correct)

Required in tiny amounts

Required in moderate amounts

Always non-essential for growth

Which of the following is NOT a criterion for determining the essentiality of a nutrient in plants?

Component of Important Molecules

Ability to substitute with other elements (correct)

Necessary for Life Cycle Completion

Key Role in Metabolism

Which macronutrient serves as the backbone of many biomolecules such as starch and cellulose?

Carbon (correct)

Phosphorus

Nitrogen

Potassium

What amount of micronutrients is required by plants?

Less than 0.02% by dry weight Signup and view all the answers

What experimental approach is used to determine nutrient essentiality in plants?

Hydroponics and Nutrient Deficiency Trials Signup and view all the answers

Which criterion for nutrient essentiality indicates that elements are directly involved in vital metabolic processes?

Key Role in Metabolism Signup and view all the answers

What happens when essential elements are absent from a plant?

Visible deficiency symptoms appear Signup and view all the answers

Which macronutrient is involved in the photosynthesis process by being fixed as a photo-assimilate?

Carbon Signup and view all the answers

What role does chlorophyll play in plants?

It aids in the absorption of energy from sunlight. Signup and view all the answers

Which photosystem absorbs light at a maximum wavelength of 700 nm?

Photosystem I Signup and view all the answers

What is produced as a byproduct of photolysis during the light-dependent reactions?

Oxygen Signup and view all the answers

In which part of the plant does the light-dependent reaction of photosynthesis occur?

In the thylakoid membranes Signup and view all the answers

What process occurs after chlorophyll loses an electron during the light-dependent reaction?

Photolysis of water Signup and view all the answers

Which chlorophyll is specifically mentioned as being involved in Photosystem II?

Chlorophyll-a Signup and view all the answers

What accumulates inside the thylakoid lumen during photolysis?

Hydrogen ions Signup and view all the answers

Which of these forms of chlorophyll is NOT mentioned in the content?

Chlorophyll-x Signup and view all the answers

Which pigment group primarily acts as accessory pigments in photosynthesis?

Carotenoids Signup and view all the answers

What is one of the significant roles of carotenoids in plants?

Absorbing light energy Signup and view all the answers

What distinguishes phycobilins from chlorophyll and carotenoids?

They are water-soluble Signup and view all the answers

Which type of carotenoid is responsible for the red/orange color in plants?

Carotenes Signup and view all the answers

In the light reactions of photosynthesis, how do plants enhance their efficiency over bacteria?

By utilizing two interconnected photosystems Signup and view all the answers

What color of light does phycoerythrin primarily absorb?

Dim & blue-green light Signup and view all the answers

What are the primary products formed during photosynthesis?

Glucose and oxygen Signup and view all the answers

What is a defining characteristic of xanthophylls compared to carotenes?

They are more abundant Signup and view all the answers

Where do light-dependent reactions of photosynthesis predominantly take place?

In the thylakoid membrane Signup and view all the answers

Which process in bacteria involves cyclic photophosphorylation?

Generation of ATP via electron transport Signup and view all the answers

Which of the following are the two main compounds produced in light-dependent reactions?

NADPH and ATP Signup and view all the answers

What is the function of chlorophyll in photosynthesis?

To absorb light energy Signup and view all the answers

What is the role of NADP+ in light-dependent reactions?

It serves as an electron carrier Signup and view all the answers

What primarily enables nutrient absorption through root hairs in plants?

Concentration gradients and diffusion Signup and view all the answers

Which statement is true about Photosystem I and Photosystem II?

Photosystem II absorbs at 680 nm, while Photosystem I absorbs at 700 nm. Signup and view all the answers

Which of the following describes the Calvin Cycle?

It synthesizes organic molecules from CO2. Signup and view all the answers

What is the significance of the electron transport chain (ETC) in photosynthesis?

It transfers electrons between proteins Signup and view all the answers

Which cation exchange capacity (CEC) range is associated with high clay content and greater nutrient retention?

11 - 50 Signup and view all the answers

What is the role of mycorrhizal associations in nutrient absorption?

They increase the root surface area for nutrient absorption. Signup and view all the answers

Which nutrient is released from organic debris through microbial decomposition?

Nitrogen Signup and view all the answers

Which process creates negative pressure helping to draw water and minerals into plant roots?

Transpiration Signup and view all the answers

How do soil microbes enhance potassium (K) solubilization in soil?

Via acidolysis and chelation Signup and view all the answers

What is one way microbes facilitate the acquisition of iron by plants?

Through rhizosphere acidification Signup and view all the answers

Which microbial activity is involved in enhancing sulfur nutrition for plants?

Releasing S from sulfate esters Signup and view all the answers

Study Notes

Macronutrients

Primary macronutrients are required in the largest amounts
Secondary macronutrients are required in moderate amounts
Micronutrients are also known as trace minerals
Micronutrients are required in tiny amounts

Determining Nutrient essentiality

To be considered essential, a nutrient must meet several criteria:
- Necessary for life cycle completion: The absence of an essential element prevents the plant from completing its life cycle and leads to visible deficiency symptoms.
- Non-substitutable: These elements cannot be replaced by others, even if they have similar properties.
- Key role in metabolism: Essential elements are directly involved in vital metabolic processes within the plant.
- Seed Viability: Without essential elements, plants are unable to produce viable seeds.
- Component of Important Molecules: Essential elements form part of critical plant compounds, like Mg²⁺ in chlorophyll.

Experimental Approaches to Determine Essentiality

Hydroponics and Nutrient Deficiency Trials: These trials involve growing plants in a controlled environment with specific nutrient solutions, allowing for the manipulation of nutrient levels and observation of their effects. By omitting a specific nutrient, researchers can determine its essentiality by observing growth and development compared to control plants receiving all essential nutrients.
Nutrient Reintroduction Studies: If a plant exhibits deficiency symptoms after being deprived of a specific nutrient, reintroducing that nutrient should reverse the symptoms and restore normal growth. This helps confirm the essentiality of the nutrient.
Radioisotope Tracing: By using radioactive isotopes of specific nutrients, researchers can trace their movement and uptake within the plant. This helps understand how nutrients are utilized and transported throughout the plant's system.
Genetic Studies: Examining plant genotypes with mutations affecting specific nutrient uptake or metabolism can reveal the role of specific element and demonstrate its essentiality.

Functions of Macro and Micronutrients in the Plant Body

Carbon (C):
- On average, the dry weight (excluding water) of a plant cell is composed of 50% Carbon.
- Serves as the backbone of many biomolecules such as starch and cellulose (the main structural component of the plant cell wall).
- Carbon is fixed as photo-assimilate through photosynthesis using carbon dioxide drawn from the atmosphere.

Soil and nutrient absorption

Soil cation exchange capacity (CEC) is a measure of its ability to hold onto nutrients
- CEC ranges from 1-10 for high sand content soils. Nitrogen and potassium are more likely to leach from these soils. These soils have a low water holding capacity.
- Soils with high clay content (CEC range 11-50) have a higher capacity to hold nutrients and a higher water holding capacity.

Mechanism of nutrient absorption in plants

Root Surface Absorption: Nutrients enter the root system primarily through the root hairs and apical regions, utilizing concentration gradients and diffusion.
Mycorrhizal Associations: Fungal hyphae extend into the soil, increasing the surface area for nutrient absorption and accessing nutrient-depleted areas.
Transpiration-Driven Flow: The process of transpiration creates a negative pressure that helps draw water and dissolved minerals from the soil into the roots.

Role of microbes in nutrient absorption

Microbes play significant roles in plant acquisition of ammonium (NH4+) and nitrate (NO3−).
- Ammonium is generated by bacterial or fungal decomposition of organic debris and can be oxidized by nitrifying bacteria to nitric oxides and nitrates.
Microbes are essential for making phosphorus available to plants.
- A wide variety of bacteria and fungi species are capable of solubilizing inorganic P and/or mineralizing organic P, releasing bioavailable P for plant absorption.
Microbes can enhance mineral weathering and increase K solubilization in soil, mainly through acidolysis, chelation, and exchange reactions, in which microbe-secreted organic acids play an important role.
Many bacterial and fungal species in the rhizosphere are capable of releasing sulfur from sulfate esters, enhancing plant sulfur nutrition.
Inoculation of AM fungus Funneliformis mosseae to Poncirus trifoliata seedlings resulted in enhanced growth promotion and suppression of Mg deficiency symptoms.
Rhizosphere acidification, stimulated or directly contributed by microbes, facilitates plant iron acquisition.
Fungi are capable of increasing plant fitness under Cu deficient and toxic conditions.
Microbes can influence the availability of manganese to plants.

Chlorophyll

Chlorophyll is a mixture of chlorophyll-a and chlorophyll-b.
It is essential for photosynthesis.
The green color pigment absorbs light energy, allowing plants to perform photosynthesis and release oxygen.
Other photosynthetic organisms contain other forms of chlorophyll.

Stages of Photosynthesis

Photosynthesis occurs in three stages:
- Capturing energy from sunlight.
- Using the energy to make ATP and reduce NADP+ to NADPH
- Using ATP and NADPH to power the synthesis of organic molecules from CO2.

Light Dependent Reactions

Provide energy for the Calvin Cycle (light-independent reactions).
Essential for the survival of plants and, consequently, all aerobic life forms.
Take place in the thylakoid membrane and require a continuous supply of light energy.
Chlorophylls absorb this light energy, which is converted into chemical energy through the formation of ATP and NADPH.
In this process, water molecules are also converted to oxygen.

Key Components Involved in Light Dependent Reactions

Chlorophyll: The pigment that absorbs light.
Photosystems: Large complexes of pigment and protein molecules present within the plant cells, responsible for capturing light energy.
- Photosystem I is located in the stroma lamellae and at the edges of the grana. It absorbs light at 700 nm (P700).
- Photosystem II is located predominantly in the grana lamellae. It absorbs light at 680nm (P680).
Electron Transport Chain (ETC): A series of proteins that transfer electrons.

Site of Light-Dependent Reactions

The internal thylakoid membrane is highly organized and contains the structures involved in these reaction. For this reason, they are also referred to as the thylakoid reactions.

Carotenoids

Fat-soluble yellow, orange, brown, or red pigments present in all photosynthetic plants.
Contribute to autumn leaf colors alongside anthocyanins.
Found in some flowers & fruits like carrots, tomatoes, pumpkins, etc.
Act as accessory pigments, absorbing light in the blue-violet range of the spectrum.
Transfer captured light energy to chlorophyll, facilitating photosynthesis.
Protect chlorophyll molecules from photooxidation.
Two types of Carotenoid:
- Carotenes (C40H56): Red/orange – hydrocarbons (terpenes). Common examples include carotenes, phytotene, lycopene, and neurosporine. Hydrolysis of beta-carotene yields vitamin-A.
- Xanthophylls (C40H56O2): Brown/yellow – oxygenated hydrocarbons, more abundant than carotenes. They differ from carotenes in having oxygen. Major examples include lutein, violaxanthin, zeaxanthin, and neoxanthein. Fucoxanthin is present in diatoms and brown algae. Lutein gives yellow color to autumn leaves.

Carotenoids are significant in two ways:

They absorb solar energy & transmit it to neighboring pigment molecules.
They protect chlorophyll molecules from photooxidation.

Phycobilins

Red or blue accessory photosynthetic pigments found in cyanobacteria and red algae.
Differ from chlorophyll & carotenoids in being water soluble.
Similar to the porphyrin part of chlorophylls, except that Mg is absent and tetrapyroles are linear rather than cyclic.

Two major groups of phycobilins:

Phycoerythrin: Red, absorbs dim and blue-green light that reaches ocean depths.
Phycocyanin: Blue colored, absorbs orange and red light.

Photosystem Function in Light Reactions

Bacteria use a single photosystem to generate ATP via electron transport. This process then returns the electrons to the reaction center. This is called cyclic photophosphorylation.
Plants utilize two interconnected photosystems to enhance the efficiency of photosynthesis and overcome the limitations of cyclic photophosphorylation.
This process includes the oxidation of water and electron transfer.

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Explore the key concepts of macronutrients, micronutrients, and their roles in plant health. This quiz will help you understand the essential criteria that nutrients must meet for plants to thrive. Test your knowledge on plant nutrition fundamentals.