2.38: Understand the Role of Diffusion in Gas Exchange

DIFFUSION: Net Movement of Particles Down the Concentration Gradient (High Concentration to Low Concentration)

ROLE OF DIFFUSION IN GAS EXCHANGE

In Alveoli

EXPLANATION During Inhalation, Oxygen Enters Alveoli High Concentration of Oxygen in Alveoli, Low Concentration of Oxygen in Blood Capillaries Oxygen will Diffuse out of Alveoli Down the Concentration Gradient Into Blood Capillaries Oppositely, There is High Concentration of Carbon Dioxide in Blood Capillaries (from Waste of Respiration) and Low Concentration of Carbon Dioxide in Alveoli Carbon Dioxide will Diffuse out of Blood Capillaries Down the Concentration Gradient into Alveoli This is how Net Exchange of Gases Take Place

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

AEROBIC RESPIRATION:  Breakdown of Glucose to release Energy in the Presence of Oxygen

EQUATION:

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

 

GAS EXCHANGE:

• Oxygen is Taken in by Respiring Cells (Mitochondria) and Carbon Dioxide is Produced as Waste Products

PHOTOSYNTHESIS: Conversion of Light Energy from the Sun into Chemical Energy by Chlorophyll such as Glucose, which is then stored as Starch

EQUATION:

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

 

GAS EXCHANGE:

• Carbon Dioxide is Taken in by Photosynthesizing Cells (Chloroplast) and Oxygen is Produced as Waste Products (If not Used for Aerobic Respiration)

2.40: Understand that Respiration Continues during the Day and Night, but that the Net Exchange of Carbon Dioxide and Oxygen Depends on the Intensity of Light

PLANTS

• Plants Respire during the day and night, But they can Only conduct Photosynthesis during the Day when Light is Present

PROCESS	DAY	NIGHT
RESPIRATION	✓	✓
PHOTOSYNTHESIS	✓	✗

PLANTS AND GAS EXCHANGE

• Using the Table Above, the Reactants and Products of Aerobic Respiration and Photosynthesis will Reverse Each Other

PROCESS	CARBON DIOXIDE	OXYGEN
RESPIRATION	Out	In
PHOTOSYNTHESIS	In	Out

NET GAS EXCHANGE

DURING THE DAY

Net Exchange of Gases During the Day

Respiration takes Place All the Time so Carbon Dioxide will be Taken in by Respiring Cells, and Carbon Dioxide will be Produced as a Waste Product In Daytime, Light is Present which Allows Photosynthesis to Occur, So Carbon Dioxide will be Taken In by Photosynthesizing Cells in Plants and Oxygen will be Produced as a Waste Product Oxygen is Being Both Used and Produced, and Carbon Dioxide is Being Both Used and produced, Causing the Net Exchange of Gases to be Balanced During the Day

DURING THE NIGHT

Net Exchange of Gases During the Night

Respiration takes Place All the Time so Carbon Dioxide will be Taken in by Respiring Cells, and Carbon Dioxide will be Produced as a Waste Product At Night, Light is Not Present so Photosynthesis will Not Occur, So Carbon Dioxide will Not be Taken In by Photosynthesizing Cells in Plants and Oxygen will Not be Produced as a Waste Product Oxygen Will be Used by Respiration, Carbon Dioxide will be Produced by Respiration So Net Exchange of Oxygen will have an Increased Input and Net Exchange of Carbon Dioxide will have an Increased Output

2.41: Explain How the Structure of the Leaf is Adapted for Gas Exchange

Diagram:

                              

ADAPTATIONS FOR GAS EXCHANGE:

FEATURE	ADAPTATION
INTERNAL AIR SPACES IN SPONGY MESOPHYLL LAYER	Increases the Surface Area to Volume Ratio for the Absorption of Carbon Dioxide
GUARD CELLS AROUND STOMATA	Allows the Size of the Stomata to be Adjusted to Allow Carbon Dioxide to Diffuse in, Oxygen to Diffuse Out. E.g, Opens during the Day to Allow the Diffusion of Carbon Dioxide for Photosynthesis
FLATTENED SHAPE	Larger Surface Area to Absorb More Light and Carbon Dioxide for Photosynthesis
THIN	Short Distance of Diffusion for Carbon Dioxide to Diffuse into Leaf Cells and for Oxygen to Diffuse out of Leaf Cells
STOMATA	Can Open to Allow Diffusion of Carbon Dioxide into the Leaf for Photosynthesis, and the Diffusion of Oxygen and Water Vapour Out of the Leaf

2.43: Describe Experiments to Investigate the Effect of Light on Net Gas Exchange from a Leaf, Using Hydrogen - Carbonate Indicator

HYDROGENCARBONATE INDICATOR: Used to Show Carbon Dioxide Concentration in a Solution

COLOUR AND CARBON DIOXIDE LEVELS:

COLOUR	CARBON DIOXIDE CONCENTRATION
YELLOW	High
RED	Atmospheric
PURPLE	Low

INVESTIGATING EFFECT OF LIGHT ON GAS EXCHANGE

Plant in Hydrogencarbonate Indicator to Test Effect of Light on Gas Exchange

METHOD: Set Up Apparatus as Shown Above Add Plant into Beaker of Hydrogencarbonate Indicator Set Distance of Light to Beaker Allow the Plant to Adapt to Light Intensity for a Few Minutes Record Colour of Indicator Alter the Distance of the Lamp to the Beaker and Continue until a Range of Distance is Experimented

RESULT: The Closer the Lamp is to the Plant, the Stronger the Light Intensity, So the More Light Energy there is for Chlorophyll to Conduct Photosynthesis, therefore, the More Carbon Dioxide intake causing the Indicator to be Purple as Rate of Photosynthesis Will be Greater than Rate of Respiration, Resulting in Low Levels of Carbon Dioxide The Further the Lamp is to the Plant, the Weaker the Light Intensity, So Less Light Energy there is for Chlorophyll to Conduct Photosynthesis, therefore, Rate of Respiration is Higher than Rate of Photosynthesis so High Levels of Carbon Dioxide, causing the Indicator to turn Yellow

2.42: Describe the Role of the Stomata

STOMATA: Located in the Lower Epidermis, It Controls Gas Exchange in the Leaf as it Opens and Closes Depending on How Turgid the Guard Cells Are

DURING THE DAY	DURING THE NIGHT
Stomata During the Day	Stomata During the Night
Guard Cells will Absorb Water by Osmosis (Due to High Light Intensity) and become Turgid Thick Inner Walls Will Split Open Stomata Opens Net Exchange of Gases Occur	Guard Cells will Lose Water by Osmosis (Due to Low Light Intensity) and become Flaccid Thick Inner Walls Will Stick Together Stomata Closes Net Exchange of Gases Do Not Occur

2.44: Describe the Structure of the Thorax, Including the Ribs, Intercostal Muscles, Diaphragm, Trachea, Bronchi, Bronchioles, Alveoli and Pleural Membrane

THORAX: Part of the Body Between the Neck and Abdomen

Diagram:

                     

STRUCTURE OF THORAX:

STRUCTURE	DESCRIPTION
RIBS	Bone Structure that Protects Internal Organs such as the Lungs
INTERCOSTAL MUSCLE	Muscles between the Ribs to control it during Inhalation and Exhalation
DIAPHRAGM	Sheet of Muscle at the Bottom of the Thorax that Helps with Inhalation and Exhalation
TRACHEA	Windpipe that Connects the Mouth and Nose to the Lungs
BRONCHI	Thick Tubes that Divides into Two Bronchi, with One Bronchus for Each Lung
BRONCHIOLES	Bronchi will Split to Form Smaller Tubes Called Bronchioles that are in the Lungs, Connected to Alveoli
ALVEOLI	Tiny Air Sacs where Gas Exchange Takes Place
PLEURAL MEMBRANE	Sticks the Outside of the Lungs to Inside of the Chest Cavity so Lungs Follow Chest Movement, Lubricates the Lungs to Reduce Friction

2.46: Explain How Alveoli are Adapted for Gas Exchange by Diffusion Between Air in the Lungs and Blood in Capillaries

ALVEOLI: Tiny Air Sacs where Gas Exchange Takes place

Diagram:

                                         

ADAPTATIONS:

FEATURE	ADAPTATION
FOLDED	Increases the Surface Area to Volume Ratio for the Diffusion of Gases (Efficient Rate of Gas Exchange)
THIN CELL WALLS	One Cell thick so the Distance of Diffusion is short, Increasing the Rate of Diffusion of Gases
STRONG CONCENTRATION GRADIENT	Each Alveolus is Surrounded by Blood Capillaries which Maintains a Strong Concentration Gradient and Blood Supply, Allowing Oxygen to Diffuse Out and Carbon Dioxide to Diffuse In
EACH ALVEOLUS IS VENTILATED	Access to the Lungs Helps Remove Waste Carbon Dioxide and Replenishing Oxygen Levels in the Alveolar Air, Also Allows the Maximum Concentration Gradient between the Blood and the Air in the Alveoli