- Stomata are tiny pores mostly on the underside of leaves, responsible for CO₂ intake for photosynthesis.
- In darkness, stomata close to reduce water loss by transpiration; in light, they reopen to allow CO₂ entry.
- Transpiration occurs alongside photosynthesis, thus "transpiration is the price the plant pays for photosynthesis."
- The opening and closing of stomata depend on the movement of water in and out of guard cells, which have a thick inner and thin outer wall.
Definitions [9]
Define the following term:
Photolysis of water
Releasing electrons and dividing the water molecule (H2O) into its two components (Hydrogen and Oxygen). Photolysis is the term used to describe this reaction, which is characterised by the fracturing of molecules by light (photo = light, lysis = breaking).
Definition: Photosynthesis
Photosynthesis is the process by which living plant cells, containing chlorophyll, produce food substances (glucose and starch) from carbon dioxide and water by using light energy. Plants release oxygen as a byproduct during photosynthesis.
Define the following term:
Chloroplast
Chloroplasts are indeed miniature ovoid structures that are encased in a double membrane. Nevertheless, the response could offer a more succinct definition: Chloroplasts are the cellular organelles that are responsible for the process of photosynthesis in plant cells. They are the sites where photosynthesis occurs and contain thylakoids.
Define the following term:
Thylakoids
Thylakoids are indeed very small compartments that are present within chloroplasts. They are the locations where the light-dependent reactions of photosynthesis take place and contain chlorophyll. Nevertheless, the response could be simplified to enhance its clarity.
Define Photosynthesis.
In the presence of chlorophyll, photosynthesis is the process by which green plants and certain other organisms convert carbon dioxide and water into glucose (a form of sugar) using light energy, typically from the sun. As a byproduct, this process generates oxygen.
Definition: Photophosphorylation
Photophosphorylation is the process of converting ADP into energy-rich ATP by adding an inorganic phosphate (Pi), using energy from light (photons).
Definition: Photolysis
Photolysis occurs in the grana of a chloroplast and is defined as the splitting of H2O molecules into hydrogen ions and oxygen in the presence of light.
Definition: Polymerisation
The process of conversion of many simpler and smaller molecules into a complex, bigger molecule is termed as polymerisation. For example, conversion of several glucose molecules into a starch molecule.
Define the following term:
Polymerisation
Most green plants use glucose as soon as it occurs during photosynthesis to make starch. Polymerisation is the process by which several glucose molecules are turned into one starch molecule.
The process by which monomer molecules combine together to form a polymer is called polymerisation.
The process by which monomer molecules combine together to form a polymer is called polymerisation.
Chemica Equations [1]
Chemical Equation: Photosynthesis
The balanced chemical equation is: \[6\mathrm{CO}_{2}+12\mathrm{H}_{2}\mathrm{O}\frac{\text{light energy}}{\text{chlorophyll}}\mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6}+6\mathrm{H}_{2}\mathrm{O}+6\mathrm{O}_{2}\uparrow\]
Key Points
Key Points: Concept of Photosynthesis
- Photosynthesis converts sunlight into chemical energy using CO₂ and water, producing glucose and releasing oxygen as a byproduct.
- Green plants are autotrophs (make their own food); all other organisms are heterotrophs. All life depends on sunlight for energy.
- Three essentials for photosynthesis: chlorophyll, light, and CO₂.
- Experiment 1 - Variegated leaf tested for starch showed that photosynthesis occurs only in green parts in the presence of light.
- Experiment 2 - Leaf part enclosed with KOH-soaked cotton (absorbs CO₂) tested negative for starch → proved CO₂ is necessary for photosynthesis.
Key Points: Chlorophyll
- Chlorophyll is the green pigment in plants, found in chloroplasts.
- It is located in the thylakoid walls inside the chloroplasts.
- Chloroplasts are mainly present in mesophyll cells of leaves.
- There are nine types of chlorophyll, but chlorophyll a and chlorophyll b are the most common.
- Chlorophyll absorbs blue and red light for photosynthesis and reflects green light.
Key Points: Stomatal Function and Movement
Key Points: Opening and Closing of Stomata (Theories)
- Two main theories explain stomatal movement: the potassium ion concentration theory (recent) and the Sugar concentration theory (old).
- K⁺ Ion Theory: In light, ATP from photosynthesis pumps K⁺ ions into guard cells, increasing osmotic pressure, causing water inflow and stomatal opening.
- At night, K⁺ ions leak out, guard cells lose turgor, become flaccid, and the stomata close.
- Sugar Theory: Photosynthesis produces glucose, which increases osmotic pressure in guard cells, leading to water uptake and turgidity, opening the stomata.
- In both theories, stomatal closure occurs when water is lost from guard cells, making them flaccid and closing the pore.
Key Points: Process of Photosynthesis
- Photosynthesis mainly occurs in mesophyll cells (palisade and spongy) of leaves, using chlorophyll to trap sunlight.
- Carbon dioxide enters the leaf via stomata by diffusion down a concentration gradient.
- Water is absorbed by roots, transported via the stem to mesophyll cells of the leaves.
- Using light energy, chlorophyll helps synthesize glucose (C₆H₁₂O₆) from CO₂ and H₂O, releasing O₂ as a by-product.
- The balanced chemical equation is: \[6\mathrm{CO}_{2}+12\mathrm{H}_{2}\mathrm{O}\frac{\text{light energy}}{\text{chlorophyll}}\mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6}+6\mathrm{H}_{2}\mathrm{O}+6\mathrm{O}_{2}\uparrow\]
Key Points: Light Reaction
- Light Harvesting Complexes (LHC) - Made up of hundreds of pigment molecules bound to proteins. Found in PS I and PS II. Help absorb different wavelengths of light for efficient photosynthesis.
- Antennae System - In each photosystem, all pigments except one chlorophyll a molecule form the antennae (light-harvesting system). They absorb light and pass energy to the reaction centre.
- Reaction Centre - The single chlorophyll a molecule that directly participates in the photochemical reaction. It is different in PS I and PS II.
- PS I - Reaction centre = P700 (absorbs light at 700 nm).
- PS II - Reaction centre = P680 (absorbs light at 680 nm).
- Steps of Light Reaction - Light absorption → Water splitting → Oxygen release → ATP and NADPH production.
Key Points: Products of Photosynthesis
- Glucose is used immediately, stored as starch, converted into sucrose, or used to make fats and proteins.
- Water produced may be reused in further photosynthesis.
- Oxygen mostly diffuses out, but some is used in photorespiration.
- Synthesized food is temporarily stored as starch in the leaf.
- At night, starch is converted back to sugar and translocated to other plant parts.
Key Points: Factors Affecting Photosynthesis
- Blackman’s Law of Limiting Factors states that the rate of photosynthesis is controlled by the factor in the least supply.
- Light affects photosynthesis through intensity, quality, and duration; it shows a linear increase at low intensity and saturation at about 10% of full sunlight.
- Carbon dioxide is the major limiting factor; increasing CO₂ concentration increases photosynthesis up to a limit, after which it may become harmful.
- Temperature controls enzymatic reactions (dark reactions); C₄ plants work better at higher temperatures, while C₃ plants have a lower optimum temperature.
- Water affects photosynthesis indirectly; water stress causes stomatal closure, reducing CO₂ availability and decreasing photosynthesis.
- All factors work together, but usually one limiting factor determines the overall rate of photosynthesis.
Key Points: Experiments on Photosynthesis
- Priestley (1770) - Plants take up CO₂ and release O₂; plants restore what animals and candles remove from the air.
- Ingenhousz (1779) - O₂ release occurs only in sunlight and only by the green parts of plants.
- Theodore de Saussure (1804) - Water is an essential requirement for photosynthesis.
- Julius von Sachs (1854) - Green parts produce glucose, stored as starch; chlorophyll is located in chloroplasts.
- T.W. Engelmann (1888) - Plotted the first action spectrum of photosynthesis; bacteria accumulated in blue and red light regions.
- C.B. van Niel (1931) - Photosynthesis is a light-dependent reaction; H from an oxidisable compound reduces CO₂ to form sugar. O₂ comes from H₂O, not CO₂.
- Hill (1937), Calvin (1954-55), Hatch & Slack (1965) - Hill: O₂ evolves in light reaction, Calvin: traced carbon fixation pathway, Hatch & Slack: discovered C4 pathway.
Key Points: Carbon Cycle
- Carbon is a key element of living organisms and is found in air, water, soil, rocks, and oceans (major reservoirs).
- The carbon cycle is the movement of carbon between the atmosphere, organisms, and the Earth through natural processes.
- Photosynthesis fixes CO₂ into organic matter, which passes through food chains.
- CO₂ returns to the atmosphere through respiration, decomposition, and combustion.
- Carbon sinks & humans: Fossil fuels and rocks store carbon, but human activities increase CO₂, causing global warming.
Important Questions [48]
- The Diagram Given Below Represents an Experiment to Prove the Importance of A Factor in Photosynthesis. Answer the Questions that Follow :
- Cochlea, Malleus, Pinna, Stapes, Incus
- Formalin, Iodine, DDT, Lime
- The Leaf Turns Blue Black Except in the Covered Region. as the Region Didnot Receive Light, Photosynthesis Did Not Occur. Hence No Starch Was Formed There. the Uncovered Region
- The Diagram Given Below Represents an Experiment to Prove the Importance of a Factor in Photosynthesis. Answer the Questions that Follow
- The Diagram Given Below Represents an Experiment to Prove the Importance of a Factor in Photosynthesis. Answer the Questions that Follow : Draw a Neat, Labelled.
- State the main functions of the following: Medulla Oblongata
- State the Main Functions of the Following: Cytokinins
- Draw a neat and well-labeled diagram of the apparatus you would set up to show that oxygen is given out during photosynthesis.
- Arrange and rewrite the terms in the group in the correct order to be in a logical sequence beginning with the term that is underlined: Snake, Rabbit, Cabbage, Hawk.
- A potted plant with variegated leafes was kept in dark for 24 hours and then placed in bright sunlight. Answer the following questions.
- Study the diagram given below and fill in the blanks with suitable words: In order to prove that carbon dioxide is necessary for (a) ______, a potted plant is placed in dark for 48 hours the leaves.
- Cytoplasm : Cytokinesis : : Nucleus : _____
- The diagrams given below represent the relationship between a mouse and a physiological process that occurs in green plants. Study the diagrams and answer the questions that follow
- Give biological reasons for the following statements : In some xerophytes leaves are modified into spines
- Give appropriate biological/technical terms for the following: An apparatus that measures the rate of water uptake in a cut shoot due to transpiration.
- The individual flattened stacks of membranous structures inside the chloroplasts are known as
- The Following Diagram Demonstrates a Physiological Process Taking Place in Green Plants. the Whole Set up Was Placed in Bright Sunlight for Several Hours. Study the Diagram and Answer the Questions that Follow
- Briefly Explain the Following Terms: Photophosphorylation
- the exact location of the Thylakoids
- The diagram below shows two test-tubes A and B. Test-tube A contains a green water plant. Test-tube B contains both a green water plant and a snail. Both testtubes are kept in sunlight. Answer the questions that follow
- The process of conversion of ADP into ATP during photosynthesis.
- Identify the Odd One in Each Set : Transpiration, Photosynthesis, Phagocytosis, Guttation
- The Figure Given Below Represents an Experimental Setup with a Weighing Machine to Demonstrate a Particular Process in Plants. the Experimental Setup Was Placed in Bright Sunlight
- A Potted Plant Was Taken in Order to Prove a Factor Necessary for Photosynthesis. the Potted Plant Was Kept in the Dark for 24 Hours.
- Give One Example Of An Aquatic Plant Used in the Laboratory to Demonstrate O2 Liberation During Photosynthesis
- Expand the Following Biological Abbreviations: ATP
- To Test a Leaf for Starch, the Leaf is Boiled in Water to (1) _________. It is Then Boiled in Methylated Spirit To (2) ________. The Leaf is Dipped in Warm Water to Soften It. It is Placed in a Petri Dish, and (3) _____ Solution is Added. the Region of the Leaf Which Contains Starch, Turns (4) ________And the Region While Does Not Contain Starch, Turns (5) __________.
- Differentiate Between the Following Pairs on the Basis of What is Indicated in the Brackets. Leaf and Liver [Form in Which Glucose is Stored]
- Give Biological Explanations For Plants Growing in Fertilized Soil Are Often Found to Wilt If the Soil is Not Adequately Watered.
- Give Suitable Biological Reasons for the Following Statements : All Life on Earth is Supported by Photosynthesis.
- Expand the Following Biological Abbreviations : Atp
- Given Below is an Experiment Setup to Demonstrate a Particualr Tropic Movement in Germinating Seeds. Study the Diagram and Answer the Questions that Follow :
- Given Below is an Experiment Setup to Demonstrate a Particualr Tropic Movement in Germinating Seeds. Study the Diagram and Answer the Questions that Follow :
- Given Below is an Experiment Setup to Demonstrate a Particualr Tropic Movement in Germinating Seeds. Study the Diagram and Answer the Questions that Follow :
- Given Below is an Experiment Setup to Demonstrate a Particualr Tropic Movement in Germinating Seeds. Study the Diagram and Answer the Questions that Follow :
- Given Below is an Experiment Setup to Demonstrate a Particualr Tropic Movement in Germinating Seeds. Study the Diagram and Answer the Questions that Follow
- Mention the Exact Location of the Following : Thylakoids
- The Diagram Given Below Represents an Experiment to Prove the Importance of A Factor in Photosynthesis. Answer the Questions that Follow Name the Factor Studied in this Experiment.
- Draw a neat, labelled diagram of a chloroplast.
- A potted plant with variegated leaves was taken in order to prove a factor necessary for photosynthesis. The potted plant was kept in the dark for 24 hours.
- Which one of the following helps in the opening of stomata?
- State the Main Function of The Lenticels
- Expand the abbreviation - NADP.
- The Solvent Used to Dissolve the Chlorophyll Pigments While Testing a Leaf for Starch is Soda Lime.
- Expand the abbreviation: ADP
- Phosphate, RNA, Sugar, Nitrogenous base
- Write the overall chemical equation for photosynthesis.
Concepts [13]
- Concept of Photosynthesis
- Chlorophyll: The Vital Plant Pigment
- Regulation of Stomatal Opening for Carbon Dioxide Intake
- Opening and Closing of Stomata
- Process of Photosynthesis
- Light Reaction
- Light-Independent Phase of Photosynthesis
- Adaptations in Leaves to Perform Photosynthesis
- Products of Photosynthesis
- Factors Affecting Photosynthesis
- Experiments on Photosynthesis
- Significance of Photosynthesis
- Carbon Cycle
