2.19: Know the Word Equation and the Balanced Chemical Symbol Equation for Photosynthesis

PHOTOSYNTHESIS: Production of Carbon compounds (Glucose) in cells by using light energy from the Sun

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EQUATION OF PHOTOSYNTHESIS:

Carbon Dioxide       +       Water       →       Glucose       +       Oxygen           6CO2                          H2O                    C6H12O6                     6O2

2.18: Understand the Process of Photosynthesis and its Importance in the Conversion of Light Energy to Chemical Energy

PHOTOSYNTHESIS: Production of Carbon compounds (Glucose) in cells using light energy from the Sun

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• Light energy from the sun is absorbed by Chlorophyll to produce Glucose which is stored as Starch for growth, and Oxygen as a waste product
• Glucose produced in Photosynthesis is passed down the food chain from one organism to another, hence why Plants are called Producers (bottom of the food chain)
• While Photosynthesis only occurs under the presence of sunlight, aerobic respiration occurs at all times of day and uses Glucose produced from Photosynthesis to produce energy (used for cell growth) and Carbon Dioxide (waste product or used for Photosynthesis)

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EQUATION OF PHOTOSYNTHESIS:

Carbon Dioxide       +       Water       →       Glucose       +       Oxygen          6CO2                         6H2O                    C6H12O6                     6O2

2.20: Understand how Varying Carbon Dioxide Concentration, Light Intensity and Temperature affect the Rate of Photosynthesis

PHOTOSYNTHESIS: Production of Carbon compounds (Glucose) in cells using light energy from the Sun

FACTORS THAT AFFECT RATE OF PHOTOSYNTHESIS:

FACTOR	EXPLANATION
CARBON DIOXIDE	As the concentration of Carbon Dioxide increases, the rate of Photosynthesis will increase As Carbon Dioxide is a reactant in Photosynthesis, the increase in Carbon Dioxide concentration will allow more Photosynthesis to occur, hence increasing the rate of Photosynthesis However, as concentration of Carbon Dioxide increases beyond a certain point, rate of Photosynthesis with plateau as another factor will be the limiting factor
TEMPERATURE	As temperature increases towards optimum, the rate of Photosynthesis will increase This is because the increase in temperature towards optimum will allow optimum enzyme activity for Photosynthesis-related enzymes, hence increasing the rate of photosynthesis However, as temperature increases above optimum, enzymes involved in Photosynthesis will denature, therefore causing the rate of Photosynthesis to decrease
LIGHT INTENSITY	As light intensity increases, the rate of Photosynthesis will increase As Photosynthesis can only occur under the presence of light, the increase in light intensity will therefore allow more Photosynthesis to occur, increasing the rate of Photosynthesis However, as light intensity increases beyond a certain point, the rate of Photosynthesis will plateau as another factor is the limiting factor

2.21: Describe the Structure of the Leaf and Explain How it is Adapted for Photosynthesis

DIAGRAM OF LEAF STRUCTURE:

                                    

Diagram showing the Structure of a Leaf

STRUCTURE OF THE LEAF:

STRUCTURE	DESCRIPTION
WAX CUTICLE	Outermost protective layer that prevents Water loss via evaporation
UPPER EPIDERMIS	Thin and transparent layer of cells to allow light to enter Palisade Mesophyll
PALISADE MESOPHYLL	Layer tightly packed with Chloroplasts to maximise light absorption for Photosynthesis
SPONGY MESOPHYLL	Layer containing internal air spaces to increases surface area to volume ratio for the diffusion of gases (mainly Carbon Dioxide)
LOWER EPIDERMIS	Layer containing: Guard cells: cells that flank and control the opening and closing of Stomata by absorbing and losing Water to regulate gas exchange and prevent water loss (via transpiration) Stomata: mouth-shaped opening flanked and controlled by Guard cells to regulate gas exchange and prevent Water loss (via transpiration)

*ADAPTATIONS FOR PHOTOSYNTHESIS (FEATURES):

FEATURE	ADAPTATION
LARGE SURFACE AREA (LEAF)	Increases surface area to volume ratio (SA:V) for diffusion of Carbon Dioxide and absorption of light for Photosynthesis
THIN	Short diffusion length which increases the rate of diffusion of Carbon Dioxide into leaf cells, e.g Chloroplasts
CHLOROPHYLL	Tightly packed and present in large amounts in Palisade Mesophyll to maximise light absorption for Photosynthesis
NETWORK OF VEINS	Supports the leaf and transports Water for Photosynthesis and Transpiration (via Xylem), and Carbohydrates produced by Photosynthesis (via Phloem) from sources to sinks
STOMATA	Regulates gas exchange by allowing Carbon Dioxide to diffuse into the leaf for use in Photosynthesis, and Oxygen to diffuse out as waste product of Photosynthesis

2.22: Understand that Plants Require Mineral Ions for Growth, and that Magnesium Ions are needed for Chlorophyll and Nitrate Ions are needed for Amino Acids

MINERAL IONS:

MINERAL ION	FUNCTION
MAGNESIUM	Needed to build Chlorophyll for growth Deficiency: Leaves turn yellow
NITRATE	Needed to produce Amino acids to build Protein and DNA Deficiency: Leaves turn yellow and stunted growth

2.23: Practical: Investigate Photosynthesis, Showing the Evolution of Oxygen from a Water Plant, the Production of Starch and the Requirements of Light, Carbon Dioxide and Chlorophyll

INVESTIGATING PHOTOSYNTHESIS

Diagram showing Experiment to Investigate the Effect of Light intensity on Photosynthesis in Pond Weed

METHOD: Place pond weed in a beaker of water Change the independent variable Leave for 5 Minutes to allow pond weed to adapt to environment Count the number of air bubbles produced in a fixed period of time Increase or decrease the independent variable by a fixed increment (e.g, distance of lamp to change light intensity) Repeat process to obtain a range of data and analyse results

INDEPENDENT VARIABLES: LIGHT INTENSITY Use a lamp and change light intensity by adjusting the distance between lamp and pond weed CARBON DIOXIDE CONCENTRATION To increase Carbon Dioxide concentration, add Sodium Bicarbonate into beaker of Water To decrease Carbon Dioxide concentration, add Sodium Hydroxide into beaker of Water CHLOROPHYLL Use variegated plant - Green plant containing Chlorophyll, and White plant without Chlorophyll

2.40B: Understand the Role of Diffusion in Gas Exchange

DIFFUSION: Passive net movement of particles down the concentration gradient (from region of high concentration to region of low concentration) until equilibrium

ROLE OF DIFFUSION IN GAS EXCHANGE

Diagram showing the Role of Diffusion during Gas Exchange in Alveoli

EXPLANATION For diffusion in gas exchange to be efficient, high concentration gradient needs to be maintained between Alveoli and blood capillaries As a result of gas exchange, Oxygen diffuses from the Alveoli into the bloodstream where it is transported and consumed by cells via cellular respiration, producing Carbon Dioxide as a waste product that diffuses out into the Alveoli to be exhaled Hence, during inhalation, Oxygen enters the Alveoli which results in a high concentration of Oxygen relative to the bloodstream, causing Oxygen to continuously diffuse out from the Alveoli into blood capillaries down the concentration gradient Correspondingly, there is a high concentration of Carbon Dioxide (produced as a waste product in cellular respiration) in the bloodstream relative to the Alveoli, therefore continuously diffusing out into the Alveoli down the concentration gradient to be exhaled out of the lungs A high concentration gradient is maintained between Alveoli and bloodstream to allow continuous gas exchange (diffusion of Oxygen and Carbon Dioxide) to occur

2.42B: Understand How the Structure of the Leaf is Adapted for Gas Exchange

STRUCTURE OF PLANT LEAF:

                                 

Diagram showing Cross-section of Plant Leaf

ADAPTATIONS FOR GAS EXCHANGE:

FEATURE	ADAPTATION
STOMATA	Opens to allow the diffusion of Carbon dioxide into the leaf for Photosynthesis, and the diffusion of waste products of Oxygen and Water vapour out of the leaf - gas exchange
GUARD CELLS AROUND STOMATA	Controls the opening and closing of Stomata depending on the time of day to enable gas exchange - e.g, Guard cells become turgid during daytime to open Stomata and allow diffusion of Carbon Dioxide into the leaf for Photosynthesis (due to presence of sunlight)
THIN	Minimises the diffusion length of Carbon Dioxide into the leaf (for Photosynthesis), and Oxygen and Water (waste product of Photosynthesis) out of the leaf, therefore increasing the rate of gas exchange
FLATTENED SHAPE	Larger surface area to volume ratio increases the rate of absorption of sunlight and Carbon Dioxide for use in Photosynthesis, therefore increasing rate of gas exchange
INTERNAL AIR SPACES IN SPONGY MESOPHYL	Larger internal surface area to volume ratio for absorption of Carbon Dioxide into the leaf (for Photosynthesis), therefore increasing the rate of gas exchange

2.41B: Understand Gas Exchange (of Carbon Dioxide and Oxygen) in Relation to Respiration and Photosynthesis

*AEROBIC RESPIRATION: Breakdown of Glucose in the presence of Oxygen to produce Carbon Dioxide and Water to release energy; occurs in the Mitochondria of the cell
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• As a result of gas exchange, Oxygen diffuses from the Alveoli into the bloodstream where it is transported and consumed by cells via cellular respiration, producing Carbon Dioxide as a waste product that diffuses out into the Alveoli to be exhaled from Lungs

EQUATION:

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*PHOTOSYNTHESIS: Production of Carbon compounds (Glucose) in cells by using light energy from the Sun

• As a result of gas exchange, Carbon Dioxide diffuses through the Stomata into plant cells where it is transported and consumed by Chloroplasts via photosynthesis, producing Oxygen as a waste product that diffuses out through the Stomata into the Atmosphere

EQUATION:

2.43B: Describe the Role of Stomata in Gas Exchange

STOMATA: Mouth-shaped opening flanked and controlled by Guard cells to regulate gas exchange and prevent Water loss (via transpiration)

DURING THE DAY	DURING THE NIGHT
Stomata During the Day	Stomata During the Night
During the daytime, high light intensity will stimulate Guard cells to absorb Water via osmosis Guard cells become turgid, causing thick inner walls to split open Stomata opens Net exchange of gases occur (Carbon Dioxide will diffuse in, and Oxygen and Water vapour will diffuse out)	During the night, low light intensity will stimulate Guard cells to lose Water via osmosis Guard cells become flaccid, causing thick inner walls to split close Stomata closes Net exchange of gases does not occur