Biology- Photosynthesis

Overall symbol equation for ps

6CO2 + 6H2O → C6H12o6 + 6O2

What form of energy is captured?

What form of energy is a flow of electrons?

What form of energy are ATP and glucose?

Light (photons)

Electrical

Chemical

What are the main stages of ps

Light dependant reaction LDR

Light independent reaction LIR

3 ways which leaf structure is adapted for ps

Link structure to function

• Waxy cuticle/guard cells → reduce water loss

• Palisade mesophyll→ stacked (closely packed) lots of them in small space for max light absorption

• Spongy mesophyll→ air spaces provide a quicker diffusion pathway

Chloroplast structure (diagram labelled)

How is a chloroplast adapted for ps

• Contain DNA and ribosomes- to quickly manufacture some proteins needed for the LDR

• Thylakoids have large surface area- for attachment of many chlorophyll molecules, electron carreirs and ATP synthase enzymes

• ATP synthase molecules are found in thylakoid membrane to catalyse production of ATP in the LDR

• Proteins in the thylakoid membrane hold chlorophyll in a specific orientation to allow it to absorb more light

How does chromatography of leaf pigments work

• Sample is placed on to chromatography paper, the bottom of which is placed into a solvent

• The solvent travels up the chromatography paper, taking any pigments (which are soluble in the solvent) with it

• Different pigments will be carried different distances by the solvent due to their solubility, and so the pigments are separated out

Formula for Rf value

What does it allow us to do

Allows for comparison between samples between different leaves

Rf values of pigments (carotenoids, chlorophyll a, chlorophyll b)

High → low

• Carotenoids have the highest Rf values (close to 1)

• Chlorophyll a

• Chlorophyll b

Processes in LDR Light energy is used to power

LDR

Summary: The LDR provides a source of reducing power (NADPH) and energy (ATP) for the LIR

O2 from photolysis is used in respiration or lost via the stomata

Why cant plants use ATP produced in LDR as only source of ATP

• LDR only occurs in the light

• Produces little ATP

Absorption spectrum table for chlorophyll a, b, carotenoid

Why is LIR needed

• as light energy from the sun is only available during the day, LDR is limited to when it can proceed

• A long term store of energy is produced in LIR using energy from ATP and reducing power from NADPH

Can LIR take place in the dark

Yes

But nor indefinitely as relies on the products of the LDR

How does CO2 for LIR enter leaf

What is this process called

• Diffuses into leaf via stomata and dissolves in water around the walls of the mesophyll cells

• It then diffuses through the plasma membrane, cytoplasm and chloroplast membranes where the carbon is used to produce organic molecules

• This process is called carbon fixation and takes place in the stroma of chloroplasts

LIR (Calvin cycle)

3 factors which affect rate of ps

What is a limiting factor

The factor which is at its least favourable value

Graph to show effect of CO2 on ps

• Present in atmosphere at 0.04% conc therefore often the limiting factor

• Growers of greenhouse crops enrich the carbon dioxide conc of the air to 0.1% to provide higher yields

Graph to show how temp affects ps

Graph to show how light intensity affects ps

What is light compensation point

What affect will increasing LI above the compensation point

• The light intensity at which rate of ps is = to rate of respiration

• will increase rate of ps but have no affect on respiration

• So increasing vol of oxygen will be given of and CO2 taken up until the light saturation point when another factor becomes limiting