Plant Nutrition

6.1 :Photosynthesis

1. Understand that photosynthesis is the process by which plants make carbohydrates from raw materials using energy from light?

                   The process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds.

The process:

1. Light absorption: Chlorophyll absorbs light energy, primarily in the red and blue wavelengths.
2. Energy conversion: The absorbed light energy is converted into chemical energy, stored in ATP and NADPH molecules.
3. Carbon fixation: Carbon dioxide from the atmosphere is incorporated into organic molecules, primarily glucose, using the energy stored in ATP and NADPH.
4. Glucose production: The final product of photosynthesis is glucose, a simple sugar that serves as the primary energy source for the plant.

Equation

There are four factors which are necessary for the process of photosynthesis

• Water
• Carbon dioxide
• Sunlight

2. State that chlorophyll is a green pigment that is found in chloroplasts?

Chlorophyll is a green pigment essential for photosynthesis, the process by which plants convert sunlight into chemical energy. It is primarily found in the chloroplasts of plant cells, specifically in the thylakoid membranes within the chloroplasts.

There are two main types of chlorophyll:

• Chlorophyll a: This is the primary pigment involved in photosynthesis. It absorbs light primarily in the red and blue wavelengths, reflecting green light, which is why plants appear green.
• Chlorophyll b: This is an accessory pigment that helps to broaden the range of wavelengths of light that can be absorbed by the plant.

• Chlorophyll molecules are composed of a porphyrin ring, which contains a magnesium atom at its center, and a long hydrocarbon tail called a phytol chain. The porphyrin ring is responsible for absorbing light, while the phytol chain anchors the chlorophyll molecule to the thylakoid membrane.
• During photosynthesis, chlorophyll molecules absorb sunlight, which excites the electrons in the porphyrin ring. These excited electrons are then transferred through a series of electron carriers, ultimately producing ATP (adenosine triphosphate), a molecule that stores energy, and NADPH (nicotinamide adenine dinucleotide phosphate), a reducing agent. The energy stored in ATP and NADPH is then used to convert carbon dioxide into glucose, a sugar molecule that serves as the primary energy source for the plant.

Chlorophyll is a green pigment found in chloroplasts. It helps plants make their own food through a process called photosynthesis.

• Chloroplasts: These are tiny structures inside plant cells.
• Photosynthesis: This is the process where plants use sunlight, water, and carbon dioxide to make glucose (sugar).
• Chlorophyll: It absorbs sunlight and turns it into energy that plants can use.

Because chlorophyll reflects green light, plants appear green to us.

3. State that chlorophyll transfers light energy into chemical energy for the formation of glucose and other Carbohydrates?

             Chlorophyll is a green pigment found in plants that plays a crucial role in photosynthesis. It absorbs sunlight and transfers this light energy into chemical energy, which is used to form glucose and other carbohydrates. This process is essential for plant growth and survival.

4. Outline the subsequent use and storage of the carbohydrates made in photosynthesis, limited to:

(a) starch as an energy store

(b) cellulose to build cell walls

(c) glucose used in respiration to provide energy

(d) sucrose for transport through the plan

 

Carbohydrates produced through photosynthesis are essential for plant growth and survival. They are stored and used in various forms for different functions:

(a) Starch as an Energy Store

• Storage: Starch is a complex carbohydrate stored in plant cells, primarily in plastids like amyloplasts.
• Location: It is commonly found in roots, stems, and seeds.
• Function: Starch serves as a long-term energy reserve for the plant. When the plant needs energy, it breaks down starch into glucose, which can be used in cellular respiration.

(b) Cellulose to Build Cell Walls

• Structure: Cellulose is a complex carbohydrate composed of glucose units linked together in a linear chain.
• Function: It forms the primary structural component of plant cell walls.
• Role: Cellulose provides rigidity, support, and protection to plant cells.

(c) Glucose Used in Respiration to Provide Energy

• Cellular Respiration: Glucose is broken down in the process of cellular respiration to produce ATP (adenosine triphosphate), the primary energy currency of cells.
• Function: ATP provides energy for various cellular activities, such as growth, movement, and transport.

(d) Sucrose for Transport Through the Plant

• Transport: Sucrose is a disaccharide composed of glucose and fructose.
• Function: It is the primary form of sugar transported throughout the plant from photosynthetic cells to other parts, such as roots and storage organs.
• Transport Vessels: Sucrose is transported through phloem vessels.

5. State the word equation and balanced chemical equation for photosynthesis?

The general balanced reaction for Photosynthesis Formula according to Kamen and Ruban (1941) is

            6CO₂        +    6H₂O   →   C₆H₁₂O₆   +    6O₂   +     6H₂O

 

  (Carbon dioxide )    (Water)              (Glucose)        (Oxygen)       (Water)

Photosynthesis is the process of converting the energy in which solar energy is converted into the form of light which is used in the production of carbohydrate molecules.

Here are a few solved problems of photosynthesis.

Problem 1: Write the complete balanced reaction for Photosynthesis both in symbol and word equation.

Solution

The balanced reaction for photosynthesis in word form is

Carbon dioxide + Water → Glucose   + oxygen.

The balanced reaction for photosynthesis in symbol form is

6CO₂ + 6H₂O   → C₆H₁₂O₆ + 6O₂ + 6H₂O

6. Investigate the necessity for chlorophyll, light and carbon dioxide for photosynthesis, using appropriate controls?

Chlorophyll:

• Take a potted plant with variegated leaves (leaves that have both green and white patches, like the leaf on the left) and destarch the plant by keeping it in complete darkness for two days (about 48 hours).
• Place it in sunlight for a few days, so that it can form some new starch. Finally, perform the starch test on one of the leaves (add a few drops of iodine to the leaf.)

 

• The green parts (i.e. the parts with chlorophyll) will turn blue-black, and the white parts will be orange-brown. This shows that starch is only formed where chlorophyll is present. Hence, photosynthesis can only occur in the presence of chlorophyll.

Light:

• Destarch a plant.
• Cut out a strip of opaque black paper and clip it a section of one of the leaves.
• Leave the plant in sunlight for a few days.
• Perform the starch test and observe.
• The areas that turn blue-black (and hence contain starch) are the areas exposed to sunlight, and the orange-brown area was the section covered by paper. This shows that light is necessary for photosynthesis.

Carbon dioxide:

• Destarch two potted plants.
• Cover both plants in transparent plastic bags; place a petri dish of sodium hydrogen carbonate in one, and a petri dish of soda lime . Sodium hydrogen carbonate gives off carbon dioxide, and soda lime absorbs carbon dioxide from the air.
• Leave these two plants in sunlight for a day (at least 6 hours). Perform the starch test on a leaf from each plant.
• You will find that the leaf from the plant with sodium hydrogen carbonate turns blue-black, and the leaf from the plant with soda lime turns orange-brown. This shows that carbon dioxide is necessary for photosynthesis.

7. Describe and explain the effect of varying light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis?

The Effect of Varying Factors on Photosynthesis Rate

Photosynthesis, the process by which plants convert sunlight into chemical energy, is influenced by several environmental factors.

These factors include light intensity, carbon dioxide concentration, and temperature.

Light Intensity

• Effect:
  • As light intensity increases, the rate of photosynthesis generally increases until a certain point. Beyond this point, increasing light intensity has little or no effect on the rate.
• Explanation:
  • More light energy is available to drive the photosynthetic reactions, leading to a higher rate. However, at very high light intensities, other factors, such as the availability of water or carbon dioxide, may become limiting.

Carbon Dioxide Concentration

• Effect:
  • As the concentration of carbon dioxide increases, the rate of photosynthesis generally increases until a certain point. Beyond this point, increasing carbon dioxide concentration has little or no effect on the rate.
• Explanation:
  • Carbon dioxide is a reactant in photosynthesis. Higher concentrations provide more substrate for the reactions, leading to a higher rate. However, at very high concentrations, other factors, such as light intensity or temperature, may become limiting.

Temperature

• Effect:
  • The rate of photosynthesis increases with increasing temperature up to an optimal point. Beyond this point, increasing temperature can denature enzymes involved in photosynthesis, leading to a decrease in the rate.
• Explanation:
  • Higher temperatures increase the kinetic energy of molecules, leading to faster reaction rates. However, excessively high temperatures can denature enzymes, rendering them inactive.

8. Investigate the effect of varying light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis using submerged aquatic plants and hydrogen carbonate indicator solution?

Hypothesis: The rate of photosynthesis in submerged aquatic plants is influenced by light intensity, carbon dioxide concentration, and temperature.

Materials:

• Submerged aquatic plants (e.g., Elodea)
• Test tubes
• Hydrogen carbonate indicator solution
• Light source
• Thermometer
• Ice bath
• Hot water bath

Procedure:

1. Set up the experiment:
   • Fill several test tubes with hydrogen carbonate indicator solution.
   • Place a piece of Elodea into each test tube.
   • Seal the test tubes with a cork or rubber stopper.
2. Vary light intensity:
   • Place some test tubes at different distances from a light source.
   • Record the distance from the light source for each test tube.
3. Vary carbon dioxide concentration:
   • Add different amounts of sodium bicarbonate to some of the test tubes.
   • Sodium bicarbonate will release carbon dioxide into the solution.
4. Vary temperature:
   • Place some test tubes in an ice bath to lower the temperature.
   • Place other test tubes in a hot water bath to raise the temperature.
   • Record the temperature of each test tube.
5. Observe and record:
   • Observe the color change of the hydrogen carbonate indicator solution in each test tube.
   • A color change from yellow to purple indicates the presence of carbon dioxide, suggesting that photosynthesis is occurring.
   • Record the time it takes for the color change to occur in each test tube.

Analysis:

• Light intensity: As light intensity increases, the rate of photosynthesis should also increase. This is because more light energy is available to drive the photosynthetic reactions.
• Carbon dioxide concentration: As the concentration of carbon dioxide increases, the rate of photosynthesis should also increase. This is because carbon dioxide is a reactant in photosynthesis, and a higher concentration provides more substrate for the reaction.
• Temperature: The rate of photosynthesis generally increases with temperature up to an optimal point. Beyond this point, increasing temperature can denature enzymes involved in photosynthesis, leading to a decrease in the rate.

Conclusion:

By analyzing the results, you can conclude how light intensity, carbon dioxide concentration, and temperature affect the rate of photosynthesis in submerged aquatic plants. You can also compare the effects of these factors to determine which has the greatest impact on the photosynthetic rate under specific conditions.

9. Identify and explain the limiting factors of photosynthesis in different environmental conditions?

limiting factors of photosynthesis:

Light:

• There is a linear relationship between the incident light and the rate of photosynthesis.
• After a certain light intensity, a further increase in light intensity does not increase the photosynthesis but rather causes the breakdown of chlorophyll, and a decrease in the rate of photosynthesis is observed.

Carbon dioxide :

• It’s concentration is the major limiting factor.
• If the concentration of carbon dioxide is low photosynthesis can not occur.

Temperature:

• the dark reaction of photosynthesis is controlled by enzymes and hence is much sensitive to temperature.

Water:

• It exerts its effect on the plant as a whole rather than directly affecting photosynthesis.
• Due to less water the stomata are closed and the available carbon dioxide is reduced.
• It also reduces the surface area by causing the leaves to wilt.

6.2 leaf structure

A leaf is attached to the stem through a leaf stalk, which continues into the leaf as midrib. There is a network of veins that deliver water and salts to the leaf cells. The leaf lamina is the broad surface of the leaf.

Internal structure of dicot leaf

 

Internal structure of moncot leaf

• Cuticle

The cuticle is a waxy, waterproof substance secreted by the upper epidermis cells. It prevents water loss and provides moisture.

• Epidermis

These are closely fitted cells present on the upper and lower layer of the leaf. Upper epidermis is thin and transparent to allow the free passage of light. They do not have any chloroplasts, and they also prevent the entry of disease-causing organisms e.g. bacteria, fungi. The lower epidermis acts as a protective layer. Stomata are present on the lower epidermis.

• Mesophyll

The Mesophyll cell has two types: spongy mesophyll and palisade mesophyll cells. Palisade mesophyll cells are perpendicular to the upper epidermis. These are thin, tall and tightly packed. They are rich in chloroplasts, making themselves a photosynthesizing tissue. The dense packing of these cells allows the absorption of the maximum amount of light energy for the manufacture of food. The chloroplasts in them are present on the edge of the cell so more light energy can be absorbed. Spongy mesophyll cells are scattered.

The air spaces present between them aid the process of diffusion of gases through the leaf. The air spaces are saturated with water vapor, so water diffuses out of the leaf. During the day time, the rate of photosynthesis is high. Thus, the concentration of carbon dioxide decreases in the air spaces, and carbon dioxide diffuses in through the stomata. Oxygen is produced as a by-product, so when its concentration rises in the air spaces, it diffuses out. There are more chloroplasts in palisade mesophyll cells compared to the spongy mesophyll cells, as it is located on the top, and it will receive direct sunlight.

• Stomata

In between the lower epidermis cells, there are small openings known as Stomata. They are open during the daylight but are closed during the night time. When they are open, carbon dioxide gas diffuses into the leaf. When stomata close, carbon dioxide stops diffusing in, and the process of photosynthesis stops. Guard cells are surrounding the stomata, and they regulate the stomata by opening and closing them. They aid gaseous exchange and help in preventing water loss by transpiration.

• Vascular Bundles

The transport systems of the cells are vascular bundles (veins). The xylem vessels transport water and mineral salts in and out of the cell. The phloem tissue transports organic products of photosynthesis i.e. glucose. Bundle sheath cells form a protective covering around the vascular bundle.

6:3  Mineral  nutrition

• Explain the importance of nitrate ions for making amino acids, required for the production of proteins?

Nitrate ions (NO₃⁻) are essential for plant growth and development, particularly in the synthesis of amino acids. Amino acids are the building blocks of proteins, which are crucial for various cellular functions, including enzymes, structural components, and transport proteins.

Here’s how nitrate ions play a role in amino acid synthesis:

1. Nitrate Assimilation: Plants absorb nitrate ions from the soil through their roots. These ions are then transported to the leaves, where they undergo a process called nitrate assimilation.
2. Reduction to Nitrite: Nitrate ions are reduced to nitrite ions (NO₂⁻) by the enzyme nitrate reductase.
3. Reduction to Ammonium: Nitrite ions are further reduced to ammonium ions (NH₄⁺) by the enzyme nitrite reductase.
4. Amino Acid Synthesis: Ammonium ions are incorporated into amino acids through various metabolic pathways. The most common pathway is the glutamate synthase cycle, where ammonium ions are combined with α-ketoglutarate to form glutamate, a key amino acid. Other amino acids can then be synthesized from glutamate through transamination reactions.

In summary, nitrate ions are essential for providing the nitrogen atoms needed to build amino acids. Without sufficient nitrate ions, plants would be unable to synthesize proteins, leading to stunted growth, reduced yield, and other negative consequences.

• Explain the importance of magnesium ions for making chlorophyll?

Magnesium ions (Mg²⁺) are essential for the synthesis of chlorophyll, the green pigment responsible for photosynthesis in plants.

Here’s how magnesium ions play a role in chlorophyll synthesis:

1. Porphyrin Ring Formation: The core structure of chlorophyll is a porphyrin ring, which contains a central magnesium atom. The magnesium ion is crucial for the stability and function of the porphyrin ring.
2. Light Absorption: The porphyrin ring, with its central magnesium ion, is responsible for absorbing sunlight and converting it into chemical energy. The magnesium ion helps to coordinate the electron transfer processes that occur during photosynthesis.

Without magnesium ions, plants would be unable to produce chlorophyll, and therefore, they would be unable to carry out photosynthesis. This would lead to stunted growth, reduced yield, and ultimately, death of the plant.