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  4. Main Organs of Photosynthesis

Main Organ for Photosynthesis

 
2.4 Main Organ for Photosynthesis
 
The image is a graphic explaining the necessity of photosynthesis in plants. The background is light yellow with blue accents. The title at the top reads ‘the Necessity of Photosynthesis in Plants’ in white text on a blue background. Below the title, there are several bullet points: - Plants are autotrophic organisms that produce their own food through photosynthesis. - The product of photosynthesis, which is glucose, is used by other organisms to generate energy through oxidation of food. - The glucose produced can be used to form cellulose. - The glucose produced can be converted into sucrose and transported to other parts of plant for metabolism or storage in the form of starch. - Glucose can be converted into amino acids, proteins or fats for metabolism or
 
 
The Necessity of Photosynthesis in Plants
  • Plants are autotrophic organisms that produce their own food through photosynthesis.
  • The product of photosynthesis, which is glucose, is used by other organisms to generate energy through oxidation of food.
  • The glucose produced can be used to from cellulose.
  • The glucose produced can be converted into sucrose and transported to other parts of plant for metabolism or storage in the form of starch.
  • Glucose can be converted into amino acids,proteins or fats for metabolism or storage.
 
Chemical Reaction of Overall Photosynthesis Process
\(12\text{H}_2\text{O}+6\text{CO}_2\xrightarrow[\text{chlorophyll}]{\text{light energy}}\text{C}_6\text{H}_{12}\text{O}_6+6\text{O}_2+6\text{H}_2\text{O}\)
 
Process of Photosynthesis
  • Photosynthesis needs chlorophyll to absorb light energy from the sun, carbon dioxide from the atmosphere and water from the soil.
  • Oxygen is released as a by-product.
  • Besides the leaf being the main photosynthesis organ, young stem and other green parts of the plants are also able to carry out photosynthesis.
 
The Relation of Internal Leaf Structure Adaptation with Photosynthesis
Aspect Explaination
Leaf shape
  • Broad-increases surface area to absorb more sunlight.
  • Thin-allow penetration of sunlight to reach lower layer of cells in leaf.
Epidermis
  • Transparent-allow sunlight to penetrate into leaf.
  • Cuticle-to reduce water loss from leaf.
Palisade mesophyll
  • Cells which have abundant of chloroplasts-can carry out photosynthesis.
  • Cylindrical shape of cells-more cells can be arranged compactly.
  • Cells arranged compactly-absorb sunlight maximally for photosynthesis.
Spongy mesophyll
  • Cells which have chloroplasts-can carry out photosynthesis.
  • Irregular shaped of cells and loosely arranged-to form air spaces for transpiration and gaseous exchange.
Xylem
  • Transport water and mineral salts from roots to mesophyll for photosynthesis.
Phloem
  • Transport organic products from leaves to other parts of plants.
Stoma
  • Pore that formed from two guard cells.
  • For gaseous exchange and transpiration.
 
Chloroplast Structure

This image is a detailed diagram of a chloroplast, highlighting its internal structures. The outer membrane surrounds the chloroplast, while the inner membrane is located just inside it. Inside the chloroplast, there are stacks of disc-shaped structures called thylakoids, which are grouped together in stacks known as granum. The stroma is the fluid-filled space surrounding the thylakoids. Lamellae are the structures that connect different grana.

  • The function of chloroplast is as a site for photosynthesis.
  • A chloroplast contains chlorophyll to absorb sunlight and converts it into chemical energy during photosynthesis.
  • Kloroplas terdiri daripada:
    • Thylakoids:
      • Disc-shaped sacs containing chlorophyll.
      • In thylakoid membrane, there are photosynthetic pigments that trap sunlight.
      • Light-dependent reaction occurs in the thylakoid.
    • Granum:
      • A disc-shaped stack of thylakoids.
      • This arrangement increases the surface area for optimal photosynthesis.
    • Stroma:
      • Colourless fluid surrounding granum in the chloroplast.
      • Site for light-independent reaction to take place which produces glucose.
 
Main Stages in Photosynthesis
Light-Dependent Reactions (Occurs in the Thylakoids)
  • In light-dependent reactions,chlorophyll absorbs light energy to becomes active and then releases electrons.
  • At the same time,photolysis of water occurs in which a water molecule is splitted into hydrogen ion,oxygen and molecules.
  • The oxygen gas produced is released into atmosphere.
  • The electron released from water molecule will replace the electrons released from the chlorophyll.
  • The electrons flow from chlorophyll eventually received by hydrogen ions and NADP+ to form hydrogen atoms and NADPH.
  • During the flow of electrons from chlorophyll to hydrogen ions,some energy released from the electrons is used to synthesis ATP.
  • The hydrogen atoms,NADPH and ATP produced from the light-dependent reactions will be used by the light independent reaction in stroma.
Light-Independent Reactions (Occurs in the Stroma)
  • Carbon dioxide gas diffuses into chloroplast.
  • The hydrogen atom, NADPH and ATP produced from the light-dependent reactions are used to reduce the carbon dioxide to produce glucose and water. 
  • The reduction process requires enzymes found in the stoma. 
  • The glucose produced form starch by condensation.
The Overall Reaction for Photosynthesis can be Represented by the Following Chemical Reaction

 
 
The Simillarities between the Light-Dependent and Light Independent Reactions
  • Occurs in daytime.
  • Occurs in chloroplasts.
  • Involves chemical reactions with enzymes.
 
The Differences of Light-Dependent and Light-Independent Reactions
Light-Dependent Reaction  Light-Independent Reaction
Require light energy. Do not require light energy. 
Occurs in granum and thylakoid. Occurs in stroma.
Photolysis of water takes place. Photolysis of water does not take place. 
Produce ATP and NADPH. Do not produce ATP and NADPH.
Produce oxygen and water molecule. Produce glucose.
 
Environmental Factors that Affect the Rate of Photosynthesis
Carbon Dioxide Concentration
  • The increase in carbon dioxide concentration increases the photosynthesis rate as long as there are no other limiting factors such as surrounding temperature and light intensity.
  •  At P, photosynthesis rate is constant.
  • As the concentration of carbon dioxide increases after P, the rate of photosynthesis remains unchanged.
  • This is due to light intensity becoming the limiting factor.
  • The graph below shows the relationship between the rate of photosynthesis and carbon dioxide concentration.

The image is a graph showing the relationship between carbon dioxide concentration (%) and the rate of photosynthesis (cm/min). The x-axis represents the carbon dioxide concentration, while the y-axis represents the rate of photosynthesis. There are two curves on the graph: 1. A higher curve labeled ‘30°C at a high light intensity.’ 2. A lower curve labeled ‘30°C at a low light intensity.’ Both curves start at the origin and rise, but the high light intensity curve reaches a higher rate of photosynthesis than the low light intensity curve. Point P is marked on the x-axis, indicating a specific carbon dioxide concentration
Light intensity
  • Light is needed in the light-dependent reaction.
  • If the concentration of carbon dioxide and temperature are constant, the rate of photosynthesis increases until it reaches its maximum point at noon.
  • Graph I shows that the rate of photosynthesis increases with the increase of light intensity until it reaches a light saturation point at P.
  • After point P, the increase in light intensity (from P to Q) is no longer increases the rate of photosynthesis because it is limited by other factors such as temperature and carbon dioxide concentration.
  • Graph II shows when the concentration of carbon dioxide in the environment is increased to 0.13%, the rate of photosynthesis also increases.
  • The graph below shows the relationship between the rate of photosynthesis and light intensity.

This image is a graph showing the relationship between light intensity (measured in Lux) and the rate of photosynthesis (measured in cm³/min). There are two curves, Graph I and Graph II. Graph I represents the rate of photosynthesis at 0.03% CO₂ concentration at 30°C, while Graph II represents the rate at 0.13% CO₂ concentration at 30°C. Both graphs show an initial increase in the rate of photosynthesis with increasing light intensity, but they level off at different points, labeled P and Q respectively.
Temperature
  • The reactions in photosynthesis are catalysed by enzymes.
  • Therefore, changes of surrounding temperature will affect enzyme activity and also the rate of photosynthesis.
  • The optimum temperature is different for different plant species but in general, the optimum temperature is between 25°C to 30°C.
  • A very high temperature denatures the enzymes and the process of photosynthesis is stopped.
  • The graph below shows the relationship between the rate of photosynthesis and temperature.

 

The image is a graph showing the relationship between temperature (°C) and the rate of photosynthesis (cm/min). The x-axis represents temperature, ranging from 0 to 40°C, while the y-axis represents the rate of photosynthesis, ranging from 0 to 100 cm/min. The graph shows a curve that starts low at 0°C, rises gradually, peaks sharply around 30°C, and then drops steeply towards 40°C.
 
The Effect of Different Light Intensities and Light Colours on the Rate of Photosynthesis
  • The rate of photosynthesis in plants is different throughout the day.
  • Other than the light intensity factor, the rate of photosynthesis is also affected by the colour of light.
  • Light spectrum consists of seven colours in a certain sequence (violet, indigo, blue, green, yellow, orange and red).
  • Each colour has a different wavelength.
  • The rate of photosynthesis is the highest in red and blue light.
  • All of the red light is absorbed by chlorophyll.
  • The blue light is absorbed by carotenoid pigments before being transferred to the chlorophyll.
  • These two lights have enough amount of energy to excite electrons in the light-dependent reaction.
 

 

 

 

The views expressed in the notes here are those of the contributor and don’t necessarily represent the views of pandai.

Main Organ for Photosynthesis

 
2.4 Main Organ for Photosynthesis
 
The image is a graphic explaining the necessity of photosynthesis in plants. The background is light yellow with blue accents. The title at the top reads ‘the Necessity of Photosynthesis in Plants’ in white text on a blue background. Below the title, there are several bullet points: - Plants are autotrophic organisms that produce their own food through photosynthesis. - The product of photosynthesis, which is glucose, is used by other organisms to generate energy through oxidation of food. - The glucose produced can be used to form cellulose. - The glucose produced can be converted into sucrose and transported to other parts of plant for metabolism or storage in the form of starch. - Glucose can be converted into amino acids, proteins or fats for metabolism or
 
 
The Necessity of Photosynthesis in Plants
  • Plants are autotrophic organisms that produce their own food through photosynthesis.
  • The product of photosynthesis, which is glucose, is used by other organisms to generate energy through oxidation of food.
  • The glucose produced can be used to from cellulose.
  • The glucose produced can be converted into sucrose and transported to other parts of plant for metabolism or storage in the form of starch.
  • Glucose can be converted into amino acids,proteins or fats for metabolism or storage.
 
Chemical Reaction of Overall Photosynthesis Process
\(12\text{H}_2\text{O}+6\text{CO}_2\xrightarrow[\text{chlorophyll}]{\text{light energy}}\text{C}_6\text{H}_{12}\text{O}_6+6\text{O}_2+6\text{H}_2\text{O}\)
 
Process of Photosynthesis
  • Photosynthesis needs chlorophyll to absorb light energy from the sun, carbon dioxide from the atmosphere and water from the soil.
  • Oxygen is released as a by-product.
  • Besides the leaf being the main photosynthesis organ, young stem and other green parts of the plants are also able to carry out photosynthesis.
 
The Relation of Internal Leaf Structure Adaptation with Photosynthesis
Aspect Explaination
Leaf shape
  • Broad-increases surface area to absorb more sunlight.
  • Thin-allow penetration of sunlight to reach lower layer of cells in leaf.
Epidermis
  • Transparent-allow sunlight to penetrate into leaf.
  • Cuticle-to reduce water loss from leaf.
Palisade mesophyll
  • Cells which have abundant of chloroplasts-can carry out photosynthesis.
  • Cylindrical shape of cells-more cells can be arranged compactly.
  • Cells arranged compactly-absorb sunlight maximally for photosynthesis.
Spongy mesophyll
  • Cells which have chloroplasts-can carry out photosynthesis.
  • Irregular shaped of cells and loosely arranged-to form air spaces for transpiration and gaseous exchange.
Xylem
  • Transport water and mineral salts from roots to mesophyll for photosynthesis.
Phloem
  • Transport organic products from leaves to other parts of plants.
Stoma
  • Pore that formed from two guard cells.
  • For gaseous exchange and transpiration.
 
Chloroplast Structure

This image is a detailed diagram of a chloroplast, highlighting its internal structures. The outer membrane surrounds the chloroplast, while the inner membrane is located just inside it. Inside the chloroplast, there are stacks of disc-shaped structures called thylakoids, which are grouped together in stacks known as granum. The stroma is the fluid-filled space surrounding the thylakoids. Lamellae are the structures that connect different grana.

  • The function of chloroplast is as a site for photosynthesis.
  • A chloroplast contains chlorophyll to absorb sunlight and converts it into chemical energy during photosynthesis.
  • Kloroplas terdiri daripada:
    • Thylakoids:
      • Disc-shaped sacs containing chlorophyll.
      • In thylakoid membrane, there are photosynthetic pigments that trap sunlight.
      • Light-dependent reaction occurs in the thylakoid.
    • Granum:
      • A disc-shaped stack of thylakoids.
      • This arrangement increases the surface area for optimal photosynthesis.
    • Stroma:
      • Colourless fluid surrounding granum in the chloroplast.
      • Site for light-independent reaction to take place which produces glucose.
 
Main Stages in Photosynthesis
Light-Dependent Reactions (Occurs in the Thylakoids)
  • In light-dependent reactions,chlorophyll absorbs light energy to becomes active and then releases electrons.
  • At the same time,photolysis of water occurs in which a water molecule is splitted into hydrogen ion,oxygen and molecules.
  • The oxygen gas produced is released into atmosphere.
  • The electron released from water molecule will replace the electrons released from the chlorophyll.
  • The electrons flow from chlorophyll eventually received by hydrogen ions and NADP+ to form hydrogen atoms and NADPH.
  • During the flow of electrons from chlorophyll to hydrogen ions,some energy released from the electrons is used to synthesis ATP.
  • The hydrogen atoms,NADPH and ATP produced from the light-dependent reactions will be used by the light independent reaction in stroma.
Light-Independent Reactions (Occurs in the Stroma)
  • Carbon dioxide gas diffuses into chloroplast.
  • The hydrogen atom, NADPH and ATP produced from the light-dependent reactions are used to reduce the carbon dioxide to produce glucose and water. 
  • The reduction process requires enzymes found in the stoma. 
  • The glucose produced form starch by condensation.
The Overall Reaction for Photosynthesis can be Represented by the Following Chemical Reaction

 
 
The Simillarities between the Light-Dependent and Light Independent Reactions
  • Occurs in daytime.
  • Occurs in chloroplasts.
  • Involves chemical reactions with enzymes.
 
The Differences of Light-Dependent and Light-Independent Reactions
Light-Dependent Reaction  Light-Independent Reaction
Require light energy. Do not require light energy. 
Occurs in granum and thylakoid. Occurs in stroma.
Photolysis of water takes place. Photolysis of water does not take place. 
Produce ATP and NADPH. Do not produce ATP and NADPH.
Produce oxygen and water molecule. Produce glucose.
 
Environmental Factors that Affect the Rate of Photosynthesis
Carbon Dioxide Concentration
  • The increase in carbon dioxide concentration increases the photosynthesis rate as long as there are no other limiting factors such as surrounding temperature and light intensity.
  •  At P, photosynthesis rate is constant.
  • As the concentration of carbon dioxide increases after P, the rate of photosynthesis remains unchanged.
  • This is due to light intensity becoming the limiting factor.
  • The graph below shows the relationship between the rate of photosynthesis and carbon dioxide concentration.

The image is a graph showing the relationship between carbon dioxide concentration (%) and the rate of photosynthesis (cm/min). The x-axis represents the carbon dioxide concentration, while the y-axis represents the rate of photosynthesis. There are two curves on the graph: 1. A higher curve labeled ‘30°C at a high light intensity.’ 2. A lower curve labeled ‘30°C at a low light intensity.’ Both curves start at the origin and rise, but the high light intensity curve reaches a higher rate of photosynthesis than the low light intensity curve. Point P is marked on the x-axis, indicating a specific carbon dioxide concentration
Light intensity
  • Light is needed in the light-dependent reaction.
  • If the concentration of carbon dioxide and temperature are constant, the rate of photosynthesis increases until it reaches its maximum point at noon.
  • Graph I shows that the rate of photosynthesis increases with the increase of light intensity until it reaches a light saturation point at P.
  • After point P, the increase in light intensity (from P to Q) is no longer increases the rate of photosynthesis because it is limited by other factors such as temperature and carbon dioxide concentration.
  • Graph II shows when the concentration of carbon dioxide in the environment is increased to 0.13%, the rate of photosynthesis also increases.
  • The graph below shows the relationship between the rate of photosynthesis and light intensity.

This image is a graph showing the relationship between light intensity (measured in Lux) and the rate of photosynthesis (measured in cm³/min). There are two curves, Graph I and Graph II. Graph I represents the rate of photosynthesis at 0.03% CO₂ concentration at 30°C, while Graph II represents the rate at 0.13% CO₂ concentration at 30°C. Both graphs show an initial increase in the rate of photosynthesis with increasing light intensity, but they level off at different points, labeled P and Q respectively.
Temperature
  • The reactions in photosynthesis are catalysed by enzymes.
  • Therefore, changes of surrounding temperature will affect enzyme activity and also the rate of photosynthesis.
  • The optimum temperature is different for different plant species but in general, the optimum temperature is between 25°C to 30°C.
  • A very high temperature denatures the enzymes and the process of photosynthesis is stopped.
  • The graph below shows the relationship between the rate of photosynthesis and temperature.

 

The image is a graph showing the relationship between temperature (°C) and the rate of photosynthesis (cm/min). The x-axis represents temperature, ranging from 0 to 40°C, while the y-axis represents the rate of photosynthesis, ranging from 0 to 100 cm/min. The graph shows a curve that starts low at 0°C, rises gradually, peaks sharply around 30°C, and then drops steeply towards 40°C.
 
The Effect of Different Light Intensities and Light Colours on the Rate of Photosynthesis
  • The rate of photosynthesis in plants is different throughout the day.
  • Other than the light intensity factor, the rate of photosynthesis is also affected by the colour of light.
  • Light spectrum consists of seven colours in a certain sequence (violet, indigo, blue, green, yellow, orange and red).
  • Each colour has a different wavelength.
  • The rate of photosynthesis is the highest in red and blue light.
  • All of the red light is absorbed by chlorophyll.
  • The blue light is absorbed by carotenoid pigments before being transferred to the chlorophyll.
  • These two lights have enough amount of energy to excite electrons in the light-dependent reaction.
 

 

 

 

The views expressed in the notes here are those of the contributor and don’t necessarily represent the views of pandai.
Chapter : Structure and Leaf Function
Topic : Main Organs of Photosynthesis
Form 5 Biology
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