Photosynthesis - Textbook

What is light trapped by?

Chlorophyll molecules

Reactants of respiration

glucose and oxygen

Products of respiration

water and carbon dioxide

Reactants of photosynthesis

water and carbon dioxide

products of photosynthesis

glucose and oxygen

what does whether a reaction is endothermic or exothermic depend on?

the total number and strength of bonds that are broken or formed during the reaction

is photosynthesis endothermic or exothermic?

endothermic

why is photosynthesis endothermic?

it requires light energy to react with carbon dioxide and water to produce glucose and oxygen

What does light provide energy for?

The construction of organic molecules like glucose

How is ATP primarily synthesised?

Chemiosmosis

What is chemiosmosis?

Involves the diffusion of protons from a region of high concentration to low concentration through a partially permeable membrane

What does the movement of protons achieve?

The release of energy that is used in the attachment of an inorganic phosphate ion to ADP, forming ATP

2 ways that electrons can be excited

1. electrons present in pigment molecules are excited by absorbing light from the sun

2. high energy electrons are released when chemical bonds are broken in respiratory substrate molecules

Where are the excited electrons passed onto?

An electron transport chain (ETC)

What is an electron transport chain made up of?

A series of electron carriers, each with progressively lower energy levels

What happens when electrons move between carriers?

Energy is released

What is the energy released used for?

To pump protons across a membrane, creating a concentration difference across the membrane

How is the proton gradient maintained?

As a result of the impermeability of the membrane to hydrogen ions

What is the only way protons can move back through the membrane down thir concentration gradient?

Through the hydrophilic membrane channels linked to the enzyme ATP synthase

Use of ATP in photosynthesis

To synthesise glucose and other organic molecules

Photosynthesis symbol equation

6CO2 + 6H2O → C6H12O6 + 6CO2

Where does photosynthesis take place?

In the chloroplasts

What provides a large surface area within the chloroplasts?

The network of membranes

What are thylakoids?

The membranes forming flattened sacs

What is a stack of thylakoids called?

Grana

What are grana joined by?

Membranous channels called lamellae

What is the fluid enclosed in the chloroplast called?

The stroma

What is the pigment in photosynthesis?

Chlorophyll

What does chlorophyll mainly do?

Absorb red and blue light and reflects green

What is the primary pigment?

Chlorophyll a

Name the other pigments embedded in the thylakoid membrane of the chloroplast?

Chlorophyll b, xanthophylls, carotenoids

Role if a light harvesting system

To absorb, or harvest, light energy of different wavelengths and transfer this energy quickly and efficiently to the reaction centre

Where is chlorophyll a located?

In the reaction centre

2 stages of photosythesis

1. Light-dependent stage

2. Light-independent stage

What happens in the light-dependent stage?

Energy from sunlight is absorbed and used to form ATP. Hydrogen from water is used to reduce the coenzyme NADP to reduced NADP.

What happens in the light-independent stage?

Hydrogen from reduced NADP and carbon dioxide is used to build organic molecules such as glucose. 

What photosystems are involved in non-cyclic photophosphorylation?

PSI and PSII

What happens in non-cyclic photophosphorylation?

1. PSI absorbs light at a higher wavelength than PSII.

2. The light absorbed excites electrons at the reaction centres of the photosystems. 

3. The excited electrons are released from the reaction centre of PSII and are passed to the ETC. 

4. ATP is produced by chemiosmosis. 

5. The electrons lost from the reaction centre at PSII are replaced from water molecules broken down using energy from the sun.