Photosynthesis Content: Overview of photosynthesis

Photosynthesis

Content:

Overview of photosynthesis

The light-dependent reaction

The light-independent reaction

Required practical 7: 

Use of chromatography to investigate the pigments isolated from leaves of different plants,

eg

, leaves from shade-tolerant and shade-intolerant plants or leaves of different colours.

Required practical 8

:

Investigation

into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts.

Overview of photosynthesis

Explain how the plant leaf is adapted to carry out photosynthesis.

Describe the main stages of photosynthesis.

Describe the structure of chloroplastOutline the role chloroplast plays in photosynthesis.

KEYWORDS: ATP, cuticle, chloroplast, chlorophyll, mesophyll, stoma, stroma, grana, thylakoid

Synoptic links: 2.3 Energy & ATP + 3.4 Eukaryotic cell structure

WORDS

Stoma

Pore in the leaf to allow gas exchange to occur.

Stroma

Fluid filled area within a chloroplast where the light independent stage of photosynthesis takes place.

What is photosynthesis?

All life on Earth depends on

photosynthesis

. The process is described by the following word and symbol equations:

These equations are summaries of a complex two-step process that takes place in the

chloroplasts

of green plants. The end products are not just glucose, but complex organic molecules such as carbohydrates, amino acids, lipids and nucleic acids.

carbon

dioxide

+ water

oxygen + glucose

light energy

6CO

2

+ 6H

2

O

6O

2

+ C

6

H

12

O

6

light energy

Why do plants photosynthesize?

Photosynthesis is an essential biological process. This is because it produces:

energy for processes in the organism

complex organic molecules needed for growth

oxygen, which is then used for respiration.

The oxygen produced is released into the atmosphere and is available for other organisms.

If the plant is eaten, the organic molecules are used to provide energy to organisms higher up the food chain.

There are not just advantages for the plant itself:

Leaves and photosynthesis

Adaptations of the leaf

Adaptation

How they aid photosynthesis

Large surface area

Absorb

as much light energy as possible.

Arrangement of leaves

Minimise

overlapping & avoids shadowing.ThinMost light absorbed in first few micrometres. Short diffusion pathway

Transparent cuticle & epidermis Maximise light penetrating to mesophyll.

Adaptation

How they aid photosynthesis

Long narrow mesophyll cells packed with chloroplast

Absorb

as much light energy as possible.Lots of stomata

Maximise gas exchange

& short diffusion pathway.

Guard cells

Controls opening & closing of stomata depending upon light intensity.Many air spacesRapid diffusionNetwork of xylem & phloem

Supplies leaf with water & carries sugars away.

Structure of the chloroplast

Plant photosynthetic tissues

Plant anatomy

Functions of photosynthetic structures

Photosynthetic Pigments

Photosynthetic pigments

The light dependent reaction

Explain the process of oxidation and reduction.

Explain how ATP is made during the light dependent reaction.

Describe the role of photolysis.Explain how chloroplasts are adapted to carry out the light dependent reaction.

KEYWORDS: ATP, photolysis, reduction, oxidation, photoionisation

, thylakoids, electron carrier,

chemiosmotic

theory, NADP, NADPH

Oxidation & reduction – always together

Oxidation (oxidised)

Addition of oxygen

Loss of electrons,

Loss of hydrogenEnergy given outReduction (reduced)Loss of oxygenGains electrons

Gains hydrogen

Energy taken in

The light dependent stage of photosynthesis

Water is split by light to produce oxygen.

This is

PHOTOLYSIS

.

Water Oxygen

Animation

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120072/bio13.swf::

Photosynthetic%20Electron%20Transport%20and%20ATP%20Synthesis

Cyclic and non-cyclic photophosphorylation

http://

highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter39/cyclic_and_noncyclic_photophosphorylation.html

WORDS

Photophosphorylation

Use of light energy to combining ADP and inorganic phosphate into ATP.

Non - cyclic photophosphorylation

Series of reactions involving the production of NADPH. The electron is used up in the process.

Chemiosmosis

Creation of ATP from ADP and inorganic phosphate by moving hydrogen ions through the ATP-synthase down the concentration gradient.

Cyclic photophosphorylation

The excited electron passes its energy to the proton pump causing chemiosmosis to occur. The electron is cycled.

Describe the light dependent stage of photosynthesis

Cyclic phosphorylation

Electron transport chain

Electrons

NADP Reduced NADP

ATP synthase

chemiosmosis

The light independent reaction

Explain how carbon dioxide is incorporated into organic molecules.

Describe the role of ATP & NADPH in the light independent reactions.

Describe the events in the Calvin cycle.

KEYWORDS: ATP, NADP, NADPH, Calvin cycle, stroma, stoma, RuBP, rubisco, GP, TP, organic compound

Chloroplast

Animation

http://

highered.mcgraw-hill.com/sites/0070960526/student_view0/chapter5/animation_quiz_1.html

GP

T

P

T

P

Making complex molecules

Pairs of TP molecules combine to form hexose sugars, such as

glucose

, some of which may isomerize to form

fructose

.

Triose phosphate

is a three-carbon sugar that can be used to make a variety of complex biological molecules.

TP can be converted to

glycerol and this may be combined with fatty acids to make

lipids.These monosaccharides can combine to form disaccharides such as sucrose, and polysaccharides such as cellulose and starch.

Describe the light

independent

stage of photosynthesis

Reduced NADP

ATPRibulose

bisphosphate

carboxylase/

oxygenase

(Rubisco)Glycerate-3-phosphate (GP)Triose phosphate (TP)Ribulose bisphosphate

(RuBP)Hexose sugars (glucose)GlycerolFatty acidsAmino acidsLipids

Summary of photosynthesis

light- dependent reactions

light- independent reactions

light

carbohydrates, other complex molecules

Calvin cycle song

https://

www.youtube.com/watch?v=OYSD1jOD1dQ

Investigating rate of photosynthesis

Outline how you can investigate photosynthesis qualitatively.

Outline how you can investigate photosynthesis

quantitatively.Complete both safely.

KEYWORDS: limiting factor, rate of reaction, light intensity,

What are limiting factors?

The

law of limiting factors

states that:

Factors that can limit the rate of photosynthesis include:

At any given moment, the rate of a physiological process is limited by the factor that is at its least favourable value.

This factor is called a

limiting factor

because it limits the rate at which the process can take place. Changing the levels of other factors will not alter the rate of the process.

CO

2

concentration.

temperature

light intensity

What will affect the rate of reaction?

What reactants are needed?

Where do reactants come from?

What affects enzyme efficiency?Where do the products go?

Are we really measuring photosynthesis?

Oxygen is produced in the light-dependent stage of photosynthesis. However, at all light intensities, plants

respire

. Respiration uses oxygen.

In other words, the amount of oxygen produced by the plant is excess to that which the plant uses for respiration.

When the rate of photosynthesis is determined by measuring the amount of oxygen formed, what is actually being measured is the

net release of oxygen

, which represents how much the rate of photosynthesis exceeds the rate of respiration.

Respiration

: C

6H12O6 + 6O2 ® 6H2

O + 6CO

2

Qualitative

Counting the bubbles on Elodea/

Cabomba

.

Quantitative

Colour change of hydrogen carbonate due to pH change.

Effect of light intensity

Plotting light intensity

Volume of oxygen can be plotted against

light intensity

instead of distance. This can be measured with a lightmeter as the lamp is moved closer. A graph like this one is obtained:

What relationship does this graph show between light intensity and oxygen and why could this be? What does this mean in terms of limiting factors?

volume of oxygen produced in 5 mins (mm

3

)

light intensity (lux)

Comparing different types of plant

The graph shows the growth of two types of crop at varying light intensities.

light intensity

(arbitrary units)

rate of photosynthesis

(arbitrary units)

crop B

crop A

How is the growth of the two crops similar?

From this data, suggest which crop would be better suited to grow in a sunny climate, which in a cloudy climate and why.

What other issues might these climates create?

Why is temperature important?

The

light-independent reaction

of photosynthesis is controlled by

enzymes

. Temperature affects enzyme reactions.

As temperature increases, collision frequency between reactant particles and between reactant and enzyme increases. This increases the rate of reaction up to the optimum temperature.

Beyond the optimum temperature however, enzymes begin to be

denatured

. Their tertiary structure breaks down, changing the shape of the active site so that reactant molecules no longer fit.

up to optimum temperature

enzyme denatured at high temperature

Effect of temperature

Atmospheric carbon dioxide

Carbon dioxide

is essential for the photosynthesis process. It is used during the

light-independent

stage to carboxylate

ribulose bisphosphate

.

The normal concentration for atmospheric carbon dioxide varies between 0.03

% and 0.04 %.Plants are adapted to survive in varying concentrations of CO2, but the higher the value, the higher the rate of photosynthesis.

Plants may therefore be able to remove some of the CO2 released by human activity from the air.

Effect of carbon dioxide concentration