Unit 10: Biological Molecules and Metabolic Pathways
Unit 10C: Explore the factors that can affect the pathways and the rate of
photosynthesis in plants.
Vocational Scenario:
I am carrying out a work experience placement at Pugh’s Garden Centre in Trefforest. My supervisor has
asked me to produce a report about the factors that can affect the rate of photosynthesis in plants,
including the stages involved in the process. I am expected to complete a relevant investigation into a
factor that affects the rate of photosynthesis, and my supervisor has allocated time for me to complete
this as part of my work experience placement.
Introduction:
Photosynthesis is an important process that takes place in plants and some bacteria cells. It is important
as it's how plant make their food and get energy. Through this process, plants use the energy from
sunlight and convert carbon dioxide from the atmosphere and water from the ground into glucose,
which provides them with energy. Once the water is converted it helps regulate the water balance of
the plant and releases oxygen into the atmosphere. This is necessary for all living organisms and helps us
to survive
Word equation:
Light
Carbon dioxide + Water ---------------> Glucose + Oxygen
Chlorophyll
Chemical equation:
Light
6CO2 + 6H2O ----------------> C6H12O6 + 6O2
Chlorophyll
Chloroplasts:
Chloroplasts are essential in the process of photosynthesis as this is where photosynthesis occurs. They
are small organelles surrounded by membranes, that are found in all plant cells as well as some algal
cells. I will be explaining their structure in depth:
,Structure of chloroplasts:
Outer membrane:
The outer membrane of the chloroplast surrounds the whole chloroplast and acts as barrier and
regulates the movement of molecules. Whilst it controls the passage of substances, it selectively allows
smaller molecules and ions to enter and exit the chloroplast.
Inner membrane:
The inner membrane of the chloroplasts lies inside the outer membrane. It also regulates the
movements of substances in and out of the chloroplast but more specifically in the cytoplasm and the
stroma with the assistance of protein carriers.
Intermembrane space:
In between the outer membrane and inner membrane there is an area called the intermembrane space
and it is about 15nm.
Lamella:
These are folds that are in the inner membrane that are usually piled up on top of each other
repeatedly.
Stroma:
Fluid filled space that contains enzymes, starch, oil, DNA and ribosomes and surrounds the thylakoid
membrane.
Thylakoid membrane:
Thylakoid Lumen:
This thylakoid membrane surrounds this inner space, and it is where the light dependent reaction takes
place.
,Thylakoid Grana:
Stacks of disk like structures that are all joined together by lamellae
Phospholipid bilayer:
Like all cellular membranes, the thylakoid membrane is made of phospholipids that are arranged in a
bilayer that separates the thylakoid from the environment.
Photosynthetic Pigments:
Photosynthetic pigments like chlorophylls and carotenoids are crucial for capturing light energy during
photosynthesis in plants and algae. Chlorophylls, including chlorophyll a and b, absorb light primarily in
the blue and red wavelengths, while carotenoids absorb in the blue and green.
Functions of chloroplast:
Chloroplasts have multiple functions in plant cells:
1. Photosynthesis: Chloroplasts are primarily responsible for photosynthesis, the process by which
plants convert light energy into chemical energy (glucose) using carbon dioxide and water. This
process occurs in specialised structures within chloroplasts called thylakoids and stroma.
2. Synthesis of Organic Molecules: Besides glucose, chloroplasts synthesise other organic
molecules essential for plant growth and metabolism, such as lipids, amino acids, and vitamins.
3. Storage of Starch: Chloroplasts store excess glucose in the form of starch, which serves as a
reserve energy source for the plant.
4. Pigment Production: Chloroplasts produce pigments like chlorophylls and carotenoids, which are
essential for capturing light energy during photosynthesis and protecting the plant from excess
light.
5. Oxygen Production: During photosynthesis, chloroplasts release oxygen as a byproduct, which is
essential for aerobic respiration in plants and other organisms.
Function of thylakoids:
Thylakoids, the membranous structures within chloroplasts, serve several crucial functions in
photosynthesis:
1. Light Absorption: Thylakoids contain chlorophyll and other photosynthetic pigments that absorb
light energy. This absorption starts the process of photosynthesis.
2. Electron Transport: Thylakoids contain protein complexes involved in the electron transport
chain. These complexes help with the movement of electrons, which is essential for producing
energy carriers (ATP and NADPH) during the light-dependent reactions of photosynthesis.
3. Generation of Proton Gradient: During electron transport, protons (H⁺ ions) are pumped into
the thylakoid lumen, creating a proton gradient across the thylakoid membrane.
4. ATP Synthesis: The proton gradient generated across the thylakoid membrane drives ATP
synthesis by ATP synthase, an enzyme embedded in the membrane. ATP produced in this
, manner serves as a source of energy for the Calvin cycle, the light-independent reactions of
photosynthesis.
5. Oxygen Evolution: Thylakoids are where the water-splitting reaction occurs during the light-
dependent reactions, resulting in the release of oxygen as a byproduct. This oxygen is crucial for
aerobic respiration in plants and other organisms.
Photosystem:
Photosystems are areas found in plant cells that produce energy, particularly within chloroplasts.
They're made up of proteins and pigments, including chlorophyll, which give plants their green colour.
These structures capture sunlight and convert it into chemical energy during photosynthesis. Picture
them as solar panels on a roof, but for plants. They work together with other parts of the cell to produce
the sugars plants need to grow and thrive.
Structure of Photosystem:
There are two areas of photosystem: Photosystem II and Photosystem I
Photosystem II (PSII):
PSII is a protein complex made from more than 20 subunits, including chlorophyll a molecules and other
pigments. It is found in the thylakoid membrane. The centre of PSII contains a reaction centre composed
of chlorophyll a molecule known as P680, which absorbs light energy most effectively at a wavelength of
around 680 nm.
Photosystem I (PSI)
Similar to PSII, PSI is a multi-subunit protein structure that includes pigments and chlorophyll a
molecule. Also, the thylakoid membrane contains it. The PSI reaction centre is home to a molecule
called P700, or chlorophyll, which is best suited for absorbing light with a wavelength of about 700 nm.
Function of Photosystem:
Photosystem II (PSII):
The take-up of photons to generate electrons is the very first phase of the light-dependent processes,
which is carried out by the PSII. PSII collects light energy, which stimulates the electrons in the reaction
centre and causes them to travel to an electron acceptor molecule. The photosynthetic electron
transport chain's electron flow is started by this step.
The capability of PSII to break water molecules and release oxygen as a byproduct is one of its unique
characteristics. Electrons lost from PSII's reaction centre during electron transport are replaced by those
obtained through this process, which is referred to as photolysis. It also helps to create a proton
gradient by releasing protons (H+) into the thylakoid lumen.
Unit 10C: Explore the factors that can affect the pathways and the rate of
photosynthesis in plants.
Vocational Scenario:
I am carrying out a work experience placement at Pugh’s Garden Centre in Trefforest. My supervisor has
asked me to produce a report about the factors that can affect the rate of photosynthesis in plants,
including the stages involved in the process. I am expected to complete a relevant investigation into a
factor that affects the rate of photosynthesis, and my supervisor has allocated time for me to complete
this as part of my work experience placement.
Introduction:
Photosynthesis is an important process that takes place in plants and some bacteria cells. It is important
as it's how plant make their food and get energy. Through this process, plants use the energy from
sunlight and convert carbon dioxide from the atmosphere and water from the ground into glucose,
which provides them with energy. Once the water is converted it helps regulate the water balance of
the plant and releases oxygen into the atmosphere. This is necessary for all living organisms and helps us
to survive
Word equation:
Light
Carbon dioxide + Water ---------------> Glucose + Oxygen
Chlorophyll
Chemical equation:
Light
6CO2 + 6H2O ----------------> C6H12O6 + 6O2
Chlorophyll
Chloroplasts:
Chloroplasts are essential in the process of photosynthesis as this is where photosynthesis occurs. They
are small organelles surrounded by membranes, that are found in all plant cells as well as some algal
cells. I will be explaining their structure in depth:
,Structure of chloroplasts:
Outer membrane:
The outer membrane of the chloroplast surrounds the whole chloroplast and acts as barrier and
regulates the movement of molecules. Whilst it controls the passage of substances, it selectively allows
smaller molecules and ions to enter and exit the chloroplast.
Inner membrane:
The inner membrane of the chloroplasts lies inside the outer membrane. It also regulates the
movements of substances in and out of the chloroplast but more specifically in the cytoplasm and the
stroma with the assistance of protein carriers.
Intermembrane space:
In between the outer membrane and inner membrane there is an area called the intermembrane space
and it is about 15nm.
Lamella:
These are folds that are in the inner membrane that are usually piled up on top of each other
repeatedly.
Stroma:
Fluid filled space that contains enzymes, starch, oil, DNA and ribosomes and surrounds the thylakoid
membrane.
Thylakoid membrane:
Thylakoid Lumen:
This thylakoid membrane surrounds this inner space, and it is where the light dependent reaction takes
place.
,Thylakoid Grana:
Stacks of disk like structures that are all joined together by lamellae
Phospholipid bilayer:
Like all cellular membranes, the thylakoid membrane is made of phospholipids that are arranged in a
bilayer that separates the thylakoid from the environment.
Photosynthetic Pigments:
Photosynthetic pigments like chlorophylls and carotenoids are crucial for capturing light energy during
photosynthesis in plants and algae. Chlorophylls, including chlorophyll a and b, absorb light primarily in
the blue and red wavelengths, while carotenoids absorb in the blue and green.
Functions of chloroplast:
Chloroplasts have multiple functions in plant cells:
1. Photosynthesis: Chloroplasts are primarily responsible for photosynthesis, the process by which
plants convert light energy into chemical energy (glucose) using carbon dioxide and water. This
process occurs in specialised structures within chloroplasts called thylakoids and stroma.
2. Synthesis of Organic Molecules: Besides glucose, chloroplasts synthesise other organic
molecules essential for plant growth and metabolism, such as lipids, amino acids, and vitamins.
3. Storage of Starch: Chloroplasts store excess glucose in the form of starch, which serves as a
reserve energy source for the plant.
4. Pigment Production: Chloroplasts produce pigments like chlorophylls and carotenoids, which are
essential for capturing light energy during photosynthesis and protecting the plant from excess
light.
5. Oxygen Production: During photosynthesis, chloroplasts release oxygen as a byproduct, which is
essential for aerobic respiration in plants and other organisms.
Function of thylakoids:
Thylakoids, the membranous structures within chloroplasts, serve several crucial functions in
photosynthesis:
1. Light Absorption: Thylakoids contain chlorophyll and other photosynthetic pigments that absorb
light energy. This absorption starts the process of photosynthesis.
2. Electron Transport: Thylakoids contain protein complexes involved in the electron transport
chain. These complexes help with the movement of electrons, which is essential for producing
energy carriers (ATP and NADPH) during the light-dependent reactions of photosynthesis.
3. Generation of Proton Gradient: During electron transport, protons (H⁺ ions) are pumped into
the thylakoid lumen, creating a proton gradient across the thylakoid membrane.
4. ATP Synthesis: The proton gradient generated across the thylakoid membrane drives ATP
synthesis by ATP synthase, an enzyme embedded in the membrane. ATP produced in this
, manner serves as a source of energy for the Calvin cycle, the light-independent reactions of
photosynthesis.
5. Oxygen Evolution: Thylakoids are where the water-splitting reaction occurs during the light-
dependent reactions, resulting in the release of oxygen as a byproduct. This oxygen is crucial for
aerobic respiration in plants and other organisms.
Photosystem:
Photosystems are areas found in plant cells that produce energy, particularly within chloroplasts.
They're made up of proteins and pigments, including chlorophyll, which give plants their green colour.
These structures capture sunlight and convert it into chemical energy during photosynthesis. Picture
them as solar panels on a roof, but for plants. They work together with other parts of the cell to produce
the sugars plants need to grow and thrive.
Structure of Photosystem:
There are two areas of photosystem: Photosystem II and Photosystem I
Photosystem II (PSII):
PSII is a protein complex made from more than 20 subunits, including chlorophyll a molecules and other
pigments. It is found in the thylakoid membrane. The centre of PSII contains a reaction centre composed
of chlorophyll a molecule known as P680, which absorbs light energy most effectively at a wavelength of
around 680 nm.
Photosystem I (PSI)
Similar to PSII, PSI is a multi-subunit protein structure that includes pigments and chlorophyll a
molecule. Also, the thylakoid membrane contains it. The PSI reaction centre is home to a molecule
called P700, or chlorophyll, which is best suited for absorbing light with a wavelength of about 700 nm.
Function of Photosystem:
Photosystem II (PSII):
The take-up of photons to generate electrons is the very first phase of the light-dependent processes,
which is carried out by the PSII. PSII collects light energy, which stimulates the electrons in the reaction
centre and causes them to travel to an electron acceptor molecule. The photosynthetic electron
transport chain's electron flow is started by this step.
The capability of PSII to break water molecules and release oxygen as a byproduct is one of its unique
characteristics. Electrons lost from PSII's reaction centre during electron transport are replaced by those
obtained through this process, which is referred to as photolysis. It also helps to create a proton
gradient by releasing protons (H+) into the thylakoid lumen.
