5.6 Photosynthesis

what is photosynthesis?

a physiological process used by plants, algae and some types of bacteria to convert light energy from sunlight into chemical energy

what is autotropic nutrition?

when organisms use this chemical energy to synthesise large organic molecules from simple inorganic molecules such as water and carbon dioxide

what are organisms that photosynthesise called?

photoautotrophs or producers

what is the equation for photosynthesis?

6CO₂ + 6H₂O + energy from photons →(chlorophyll)→ C₆H₁₂O₆ + 6O₂

what is carbon fixation?

the process by which carbon dioxide is converted into sugars

what does carbon fixation need?

it is endothermic, so need energy

it also needs electrons; the addition of electrons is a reduction reaction

what is photolysis?

where light energy splits water molecules into hydrogen, water and electrons

What are heterotrophs and how do they obtain energy?

non-photosynthetic organisms such as fungi, animals, many protoctists and many types of bacteria

they obtain energy by digesting complex organic molecules of food to smaller molecules that they can use as respiratory substrates

what is the compensation point?

when photosynthesis and respiration occurs at the same rate therefore there are no net gain or loss of carbohydrate

what is the compensation period?

the time plant takes to reach compensation point

why is the compensation period different for different plant species?

plants have different requirements for light intensity

e.g. shade plants have a shorter period because they can utilise light of lower intensity

what are plant chloroplasts shape and size?

they are disc shaped and around 2-10 um long

what is the width of the intermembrane space?

10-20 nm

where does the light dependent stage occur?

the grana

what is the stroma?

a fluid filled matrix

what does the stroma contain?

enzymes that catalyse reactions in the light-independent stage, starch grains, oil droplets, small ribosomes and DNA

what does the stroma in DNA contain?

genes that code for proteins needed for photosynthesis

what are thylakoids?

flattened disc-like sacs

the membrane is less permeable

what are photosystems?

funnel-shaped structures within thylakoid membranes

what are photosynthetic pigments?

they absorb light of a particular wave length, and reflects other wave lengths

the energy captured is funnelled down to the primary pigment reaction centre

what are chlorophylls?

a mixture of pigments that all have similar molecule structure

what are chlorophylls molecular structure?

it consists of a porphyrin group, in which a magnesium atom and a long hydrocarbon chain

what do the two forms of chlorophyll a appear as?

green-blue

where are the two forms of chlorophyll a situated?

at the centre of photosystems

what colour does chlorophyll a absorb?

red

where is P₆₈₀ found and what is its peak of absorption?

it is found in photosystem II and its peak of absorption is light of wavelength 680 nm

where is P₇₀₀ found and what is its peak of absorption?

it is found in photosystem I and its peak of absorption is light of wavelength 700 nm