Photosynthesis

what is photosynthesis

uses the suns energy to convert inorganic substances into complex organic molecules- which can then be used as a source of energy

what is the equation for photosynthesis

6CO2 + 6H20 → C6H12O6 + 6O2

what is the ultimate source of energy for living organisms

the sun

what are autotrophs

organisms that can synthesise complex organic molecules from inorganic molecules and an energy source

what are photoautotrophs

use energy from sunlight

give examples of autotrophs

plants, algae, bacteria and some archaea

what are chemoautotrophs

use inorganic molecules for energy

no sunlight needed

among the first lifeforms on earth

describe heterotrophs

obtain complex organic molecules by eating other organisms

what is the site of photosynthesis

chloroplasts

what are the two stages of photosynthesis

1. light dependant stage

2. light independent stage

where does the light dependant stage of photosynthesis take place

on the thylakoid membrane within chloroplasts

describe the light dependant reaction of photosynthesis

energy from sunlight is absorbed and used to form ATP

hydrogen from water is used to reduce coenzymes NADP to reduced NADP (NADPH)

how many types of photosystems are there

2

what are the types of photosystems

PSi

PSii

describe photosystems

in the thylakoid membranes hundreds of photosynthetic pigment molecules act together in a harvesting cluster cause a photosystem

captures light energy

what do the 2 photosystems contain

chlorophyll A

describe PSi

contains p700 chlorophyll A

peak absorbtion at 700nm

describe psii

contains p680 chlorophyll A

peak absorption at 680nm

describe the interaction between photons and photosystems

photon strikes the accessory pigment molecule

light energy is passed down to the reaction centre

special pair is excited and released from the reaction centre

what are the aims of light dependant reactions

1. split water to release hydrogen ions to provide reducing power (photolysis)

2. provide energy in the form of ATP for use in the light independent reactions in the reduction of co2 to carbohydrate (photophosphorylation)

what are the features of the chloroplast

stroma lamellae

ribosomes

thylakoid

chloroplast dna

stroma

starch grain

describe the role of the stroma lamellae in chloroplasts

keeps the grana sacks separated and suspended

describe the thylakoid in chloroplasts

chlorophyll is found here

site for light reactions

made of individual grana

describe the stroma in chloroplasts

surrounds thylakoid membranes

describe the role of the starch grain in chloroplasts

energy storage for excess carbohydrates

state the process of light dependant reaction

ps2 followed by sp1

ps2 absorbs photons

excited electrons are released from reaction centre of ps2 and passed to ETC- ps2- atp produced

photolysis - electrons produced→ ps2

ps1 absorbs photons - excited electrons are released- passed to ETC-

NADP reductase accepts electrons and hydrogen ion (from photolysis)

NADP→ NADPH

describe photolysis

H2O→ 2 H+ + 2e- + ½ O2

electrons replace electrons lost from reaction centre of ps2

hydrogen ions produces are combined with NADP and an electron from PSI to form NADPH

describe cyclic phosphorylation

electrons leaving ETC after PS1 are returned to PS1 instead of being used to reduce NADP

ATP produced without electrons being supplied from PS2

where does the light independent stage of photosynthesis occur

the stroma of chloroplasts

what is required/ produced in the light independent stage of photosynthesis

co2 used as a raw material

ATP and NADPH are required

organic molecules are produced

state the calvin cycle

co2 (1C) combines with RUBP (5C) by RUBISCO - forms 6C molecule which splits into GP

GP (3C) - converted to TP (3C) - using hydrogen ion from NADPH and energy from ATP

majority of TP is used to regenerate RUBP - calvin cycle continues

calvin cycle does 3 cycles- 1/6 TP per 3 cycles is used to synthesise organic molecules

what is the effect of reducing light intensity on the calvin cycle

reduces rate of light dependant stage

reduced quantity of ATP and NADPH

concentration of GP increases and concentration of TP decreases

less TP to regenerate RUBP

what is the effect of temperature on photosynthesis

as temp increases, rate of enzyme activity increases until proteins denature

carbon fixation cannot happen if enzymes are denatured

stomata close to avoid water loss- stops the diffusion of co2 into the plant- reduces rate of light independent reaction

why is water not a limiting factor in photosynthesis

for water potential to be low enough to limit the rate of photosynthesis - the stomata would already be closed and ceased photosynthesis

what is the effect of light intensity on photosynthesis

light is needed as an energy source

as light intensity increases, ATP and NADPH are produced at a higher rate

what is the effect of co2 concentration on photosynthesis

needed as a source of carbon

increasing co2 conc. increases rate of carbon fixation in the calvin cycle- therefore increased rate of GP production and therefore TP

low conc. = less fixation and reduced GP and therefore TP

describe using leaf discs to measure the volume of o2 produced

all leaves have the same SA

easier to measure - leaves float to the surface

however- still dont measure the volume of O2 produced

describe a simple photosynthometer to measure the volume of o2 produced

simple to set up

measure distance of bubble in a capillary tube

air may lead→ grease with vaseline

can only use for small plants

describe the use of a photosynthometer

measure distance of bubble/fluid

easy to repeat

temperature changes

air leaks

how is an o2 probe more accurate than a syringe

removes human error

how do you use indicators to measure rate of photosynthesis

uses a control

co2- acidic - produced from respiration- higher o2 conc. in the dark

light- more photosynthesis- more o2 produced- alkali

describe the hydrogen carbonate indicator

purple- more o2 produced- more light, more photosynthesis

yellow- less respiration- more co2 stored- acidic