Photosynthesis Part 2

Chlorophyll & Chloroplasts

KEY QUESTION: What role do pigments play in the process

of photosynthesis?

Our lives, and the lives of nearly every living thing on the surface of Earth, are made possible by the sun and the process of photosynthesis. In order for photosynthesis to occur, light energy from the sun must somehow be captured.

Light

The sun’s energy travels to Earth in the form of light. Sunlight, which our eyes perceive as “white” light, is actually a mixture of different wavelengths. Our eyes see the different wavelengths of the visible spectrum as different colors: shades of red, orange, yellow, green, blue, indigo, and violet.

Pigments

Light-absorbing compounds are known as pigments. Photosynthetic organisms primarily use the pigment chlorophyll to capture the energy in sunlight. The principal pigment of green plants is known as chlorophyll. Two types of chlorophyll, a and b, are found in plants, and are available to absorb different parts of the visible light spectrum, primarily blue-violet and red. Chlorophyll does not absorb the color green. Leaves appear green because they reflect these wavelengths. Plants also have red and orange carotene pigments, which we can only see when leaves begin to die during the fall.

Chloroplasts

The plant organelle known as a chloroplast is where photosynthesis takes place. Within chloroplasts are grana, which are stacks of thylakoids that contain chlorophyll. The rest of the fluid outside of this is called stroma. The number of chloroplasts per cell varies across different plants. Chloroplasts can sometimes move within plants, as well as duplicate themselves.

Multiple Choice

What role do pigments play in the process of photosynthesis?

• Pigments release light energy.
• Pigments convert light energy into heat.
• Pigments reflect light energy.
• Pigments absorb light energy.

Multiple Choice

What visible light does chlorophyll does not absorb?

This light is reflected, hence why plants have this color.

• yellow
• blue
• green
• red

Multiple Choice

The main pigment of green plants is

• hemoglobin
• carotene
• chlorophyll
• melanin

Multiple Choice

What pigment is responsible for the red and orange color, which can be seen in the winter?

• carotenoid (carotene)

• anthocyanin
• melanin
• chlorophyll

Match

Match the following

• Grana (granum)

• Contains chlorophyll

• Inner liquid of the chloroplast

• Organelle for photosynthesis

Stacks of thylakoids

Thylakoids

Stroma

Chloroplast

• Stacks of thylakoids

• Thylakoids

• Stroma

• Chloroplast

Labelling

Label the chloroplast

Drag labels to their correct position on the image

Thylakoid

Stroma

Grana

Energy Collection

The light energy collected by a cluster of pigments, including chlorophyll, is transferred to the reaction center in the center of the cluster where a particular chlorophyll molecule is excited and releases energized electrons. These high-energy electrons are vital to later steps of photosynthesis.

High-Energy Electrons

KEY QUESTION: What are electron carrier molecules?

Specific molecules called electron carriers are necessary to convey the highly reactive and high-energy electrons that are produced by chlorophyll. The electron carrier moves the electrons with their energy to other molecules where they are

needed. Nicotinamide adenine dinucleotide phosphate, or NADP+, is one such electron carrier. When it accepts two high-energy electrons, NADP+ also bonds a hydrogen ion, which turns it into NADPH. Now the captured energy can be moved to the location in the chloroplast where sugars are manufactured.

Overview of Photosynthesis

​KEY QUESTION: What are the reactants and products of photosynthesis?

Photosynthesis uses the energy of sunlight to convert water and carbon dioxide (low-energy reactants) into high-energy sugars and oxygen (products).

Light-Dependent Reactions

The Light-dependent Reactions need sunlight. The sunlight energy is captured by pigments in the thylakoid membrane. The energy is used to convert ADP into ATP and NADP⁺ into NADPH. These sources of energy are important for other steps in photosynthesis. Also, water is split apart, which makes more electrons available, and produced oxygen (O₂) and hydrogen ions (H⁺).

Multiple Choice

Where does the light dependant reaction take place?

• thylakoid membrane of the chloroplasts
• cytoplasm
• nucleus
• mitochondria

Multiple Choice

What are the reactants (what is needed) of the light-dependent reaction of photosynthesis?

• water and light energy
• carbon dioxide and ATP
• chlorophyll and NADPH
• glucose and oxygen

Multiple Choice

What are the products of the light-dependent reaction of photosynthesis?

• Carbon dioxide and water
• Glucose and oxygen
• Starch and cellulose
• ATP and NADPH (high energy molecules)

  (oxygen as waste)

Multiple Choice

ADP is converted into what during the light-dependant reaction, and NADP+ is converted into what?

• ATP and NADPH
• ADP and NADP+
• ADP and NADPH
• ATP and NADP+

Multiple Choice

What is the primary goal of the light-dependent reaction of photosynthesis?

• To produce oxygen as a byproduct
• To regulate the temperature of the plant
• To convert light energy into chemical energy (high energy molecules)

• To convert chemical energy into light energy

Light-Independent Reactions

The Light-independent Reactions (Calvin cycle) occur in the stroma and do not use sunlight. The energy in ATP and NADPH, produced in the light-dependent reactions, is used to “fix” carbon dioxide. That is, carbon dioxide (CO₂) is combined with H⁺ to produce sugars, primarily glucose (C₆H₁₂O₆).

The plant makes these sugars asfood for itself.

Multiple Choice

How is the light-independent reaction different from the light dependent reaction?

• The light-independent reaction produces ATP, while the light-dependent reaction produces NADPH.
• The light-independent reaction does not require light, while the light-dependent reaction does.
• The light-independent reaction occurs in the thylakoid membrane, while the light-dependent reaction occurs in the stroma.
• The light-independent reaction converts carbon dioxide into glucose, while the light-dependent reaction converts water into oxygen.

Multiple Choice

What is produced by the light-dependent reaction and used in the light-independent reaction to "fix" carbon dioxide into glucose?

• ATP and NADPH
• ATP and NADH
• ADP and NADP+
• ATP and NADP+

Multiple Choice

What are the three reactants of the light-independent reaction?

• carbon dioxide, ATP, NADPH
• chlorophyll, sunlight, water
• starch, cellulose, glucose
• oxygen, glucose, water

Multiple Choice

What is the product of the light-independent reactions?

• ATP
• oxygen
• carbon dioxide
• glucose

Labelling

Label the process of photosynthesis

Drag labels to their correct position on the image

H₂0

Light

Glucose (sugars)

CO₂

O₂

Multiple Choice

What are ATP and NADPH used for in photosynthesis?

• ATP and NADPH are used for protein synthesis.
• ATP and NADPH are used as energy carriers.
• ATP and NADPH are used for DNA replication.
• ATP and NADPH are used as building blocks for glucose.

Categorize

Options (8)

Occurs in Thylakoid

Occurs in Stroma

Requires light

Does not require light

Reactants: Water + Light / Products: Oxygen + NADPH + ATP

Reactants: CO₂ + NADPH + ATP / Products: Sugars (Glucose)

Organize these options into the right categories

Determine the following as a light-dependent reaction or light-independent reaction.

Light-dependent reaction

Light-independent reaction