Photosynthesis in Higher Plants

Carbon dioxide

Carbon dioxide

________ is the major limiting factor for photosynthesis.

water splitting complex

The ________ is associated with the PS II, which itself is physically located on the inner side of the membrane of the thylakoid.

primary CO2 acceptor

The ________ is a 3- carbon molecule phosphoenol pyruvate (PEP) and is present in the mesophyll cells.

membrane system

The ________ is responsible for trapping the light energy and also for the synthesis of ATP and NADPH.

pigments of photosystem

The electrons are not used up as they pass through the electron transport chain, but are passed on to the ________ PS I.

ATP

Like in respiration, in photosynthesis too, ________ synthesis is linked to the development of a proton gradient across a membrane.

breakdown of chlorophyll

An increase in incident light beyond a point causes the ________ and a decrease in photosynthesis.

photosystem

Each ________ has all the pigments (except one molecule of chlorophyll a) forming a light- harvesting system also called antennae.

intermembrane space

In respiration, protons accumulate in the ________ of the mitochondria when electrons move through the ETS.

LHC

The ________ is made up of hundreds of pigment molecules bound to proteins.

bundle sheath cells

The ________ are rich in an enzyme Ribulose bisphosphate carboxylase- oxygenase (RuBisCO), but lack PEPcase.

3 carbon molecule

The ________ is transported back to the mesophyll where it is converted to PEP again, thus, completing the cycle.

Glucose

________ is usually stored as starch.

Chemiosmosis

________ requires a membrane, a proton pump, a proton gradient and ATP synthase.

C3

The ________ and C4 plants respond differently to CO2 concentrations.

RuBisCO

________ has a much greater affinity for CO2 when the CO2: O2 is nearly equal.

inner side

Since the splitting of the water molecule takes place on the ________ of the membrane, the protons or hydrogen ions that are produced by the splitting of water accumulate within the lumen of the thylakoids.

O2

Some organisms do not release ________ during photosynthesis.

Photophosphorylation

________ is the synthesis of ATP from ADP and inorganic phosphate in the presence of light.

Cyclic photophosphorylation

________ also occurs when only light of wavelengths beyond 680 nm is available for excitation.

PS I

When only ________ is functional, the electron is circulated within the photosystem and phosphorylation occurs due to the cyclic flow of electrons.

ATP synthase enzyme

The ________ consists of two parts: one called the CF0 is embedded in the thylakoid membrane and forms a transmembrane channel that carries out facilitated diffusion of protons across the membrane.

NADP reductase enzyme

The ________ is located on the stroma side of the membrane.

linear relationship

There is a(n) ________ between incident light and CO2 fixation rates at low light intensities.

photorespiratory pathway

In the ________, there is no synthesis of ATP or NADPH.

Photosynthesis

________ is under the influence of several factors, both internal (plant) and external.

chlorophyll

Though ________ is the major pigment responsible for trapping light, other thylakoid pigments like ________ b, xanthophylls and carotenoids, which are called accessory pigments, also absorb light and transfer the energy to ________ a.

NADPH

Along with the ________ produced by the movement of electrons, the ATP will be used immediately in the biosynthetic reaction taking place in the stroma, responsible for fixing CO2, and synthesis of sugars.

Joseph Priestley

________ (1733- 1804) 1770 performed a series of experiments that revealed the essential role of air in the growth of green plants.

Melvin Calvin

The use of radioactive 14C by ________ in algal photosynthesis studies led to the discovery that the first CO2 fixation product was a 3- carbon organic acid.

Priestley

________ discovered oxygen in 1774.

green plants

In ________, H2O is the hydrogen donor and is oxidised to O2.

photosystem II

In ________ the reaction centre chlorophyll absorbs 680 nm wavelength of red light causing electrons to become excited and jump into an orbit farther from the atomic nucleus.

blue green

Chlorophyll a (bright or ________ in the chromatogram)- is the chief pigment associated with photosynthesis.

ATP synthase

________ has a channel that allows the diffusion of protons back across the membrane.

‘ Kranz

________ means ‘ wreath and is a reflection of the arrangement of cells.

C4 plants

The ________ respond to higher temperatures and show a higher rate of photosynthesis while C3 plants have a much lower temperature optimum.

Carboxylation

________ is the fixation of CO2 into a stable organic intermediate.

form of bond

Living organisms have the capability of extracting energy from oxidisable substances and storing this in the ________ energy.

membranous system

Within the chloroplast, there is a(n) ________ consisting of grana, the stroma lamellae, and the matrix stroma.

RuBisCO

________ is the most abundant enzyme in the world and is characterised by the fact that its active site can bind to both CO2 and O2- hence the name.

ATP

The products of the light reaction are ________, NADPH and O2.

carbon dioxide

They are allowed to grow in a(n) ________- enriched atmosphere that leads to higher yields.

photosynthesis

Some ________ does take place at the other wavelengths of the visible spectrum.

C4 plants

In the ________, it does not take place in the mesophyll cells but does so only in the bundle sheath cells.

photorespiratory pathway

In the ________, there is neither synthesis of sugars, nor ATP.

ATP

The process through which ________ is synthesised by cells (in mitochondria and chloroplasts) is named phosphorylation.

Priestley observed that a candle burning in a closed space

a bell jar, soon gets extinguished

Priestley hypothesized as follows

Plants restore to the air whatever breathing animals and burning candles remove

Now consider the interesting experiments done by T.W Engelmann (1843

Chlorophyll a (bright or blue-green in the chromatogram)

is the chief pigment associated with photosynthesis

The two photosystems are connected through an electron transport chain, as seen earlier

in the Z scheme

The ATP synthase enzyme consists of two parts

one called the CF0 is embedded in the thylakoid membrane and forms a transmembrane channel that carries out facilitated diffusion of protons across the membrane

Since then CO2 assimilation during photosynthesis was said to be of two main types

those plants in which the first product of CO2 fixation is a C3 acid (PGA), i.e., the C3 pathway, and those in which the first product was a C4 acid (OAA), i.e., the C4 pathway

The studies very unexpectedly showed that the acceptor molecule was a 5-carbon ketose sugar

ribulose bisphosphate (RuBP)

RuBisCO is the most abundant enzyme in the world and is characterised by the fact that its active site can bind to both CO2 and O2

hence the name

RuBisCO has a much greater affinity for CO2 when the CO2

O2 is nearly equal

This takes place when the C4 acid from the mesophyll is broken down in the bundle sheath cells to release CO2

this results in increasing the intracellular concentration of CO2

If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value

it is the factor which directly affects the process if its quantity is changed