Photosynthesis

Chapter 8

What is the primary source of energy on Earth?

Solar energy

What wavelengths of light do plants use as their energy source?

Blue and red wavelengths

What is photosynthesis in simple terms?

The conversion of light energy to chemical energy using chlorophyll, carbon dioxide and water

What does photosynthesis use to build up complex chemicals from simple ones?

Light

What is the name of the green pigment plants use for photosynthesis?

Chlorophyll

What form of energy does photosynthesis turn light into?

ATP (adenosine triphosphate)

What kinds of organisms use photosynthesis?

Autotrophs, mainly green plants

What is the word equation for photosynthesis?

Carbon dioxide + water → Glucose + oxygen

What is the balanced chemical equation for photosynthesis?

6CO2 + 6H2O → C6H12O6 + 6O2

Where in the cell does photosynthesis take place?

The chloroplasts

What is the name of the jelly like substance in the chloroplasts?

Stroma

What is suspended in the stroma?

The thylakoid membrane

What are the two forms of the thylakoid membrane?

Single sheets called lamella and stacks called granum (pl. grana)

What does chlorophyll do?

Traps light energy and passes it onto other substances

What are the two stages of photosynthesis?

The light-dependent stage

The light-independent stage

Where does the light-dependent stage of photosynthesis occur?

On the thylakoid membrane

What is another name for the light-independent stage?

The Calvin cycle

Where does the light-independent stage of photosynthesis occur?

In the stroma

What are the three parts of the light-dependent stage of photosynthesis?

Pathway 1

Pathway 2

The formation of NADPH

What is another name for Pathway 1?

Cyclic photophosphorylation

What does it mean if Pathway 1 is cyclic?

The energised electrons that leave the chlorophyll eventually return to the chlorophyll molecule, having lost their extra energy

How does Pathway 1 of the light-dependent stage of photosynthesis work?

The chlorophyll absorbs light energy and passes it to an electron, which then gets ejected as a high-energy electron. This high-energy electron, gets accepted by an electron accepter, which passes it on to the electron transport chain. As the high-energy electron passes along the electron transport chain, its excess energy gets used to produce ATP. By the end of the chain, the electron has lost its excess energy and is now a low-energy electron again. This electron then returns to the chlorophyll. The ATP produced is used in the light-independent stage

How does an electron become high-energy?

The chlorophyll absorbs light and passes it onto the electron

Where does the electron acceptor send high-energy electrons?

To the electron transport chain

In Pathway 1, where does the low-energy electron return to?

The chlorophyll

What is another name for Pathway 2?

Non-cyclic photophosphorylation

What does it mean if Pathway 2 in non-cyclic?

The electrons that leave the chlorophyll do not return, and are instead replaced by electrons by a different source

How does the chlorophyll replace missing electrons?

By pulling electrons from surrounding water molecules, causing them to break down

What is photolysis?

Splitting water by light

How does Pathway 2 of the light-dependent stage of photosynthesis work?

High-energy electrons are passed to the electron transport chain, where they combine ADP and P to form ATP. The electrons that have passed through the electron transport chain are now low energy and replace the high-energy electrons that have left the chlorophyll

What is produced when a high-energy electron travels down the electron transport chain?

ADP and P, that join to form ATP

What is produced by Pathway 1 of the light-dependent stage of photosynthesis?

ATP

How is oxygen produced in Pathway 2?

Oxygen atoms from the carbon dioxide and water join into pairs, creating oxygen gas

What do plants do with the oxygen they produce?

It is either used immediately in respiration or any excess gets diffused out into the atmosphere

What can diffused oxygen be used for?

Respiration by other organisms or for combustion

What happens with the hydrogen from water in Pathway 2 during the light-dependent stage of photosynthesis?

The hydrogen ions enter the proton pool

What compound accepts the high-energy electrons from the chlorophyll?

An electron acceptor

What is produced during Pathway 2 of the light-dependent stage of photosynthesis?

ATP and oxygen

How is NADP- formed?

NADP+ from the light-independent stage picks up two excited electrons that were produced by the chlorophyll and held by the electron acceptor

What is the formula for NADP-?

NADP+ + 2e- = NADP-

How is NADPH formed?

NADP- picks up a hydrogen ion from the proton pool

What is the purpose of NADPH?

It transports hydrogen to the light-independent stage

How does the light-independent stage of photosynthesis work?

Carbon dioxide from the atmosphere or cellular respiration diffuses into the stroma. Protons and neutrons are added to the CO2, which forms glucose.

What diffuses into the stroma?

Carbon dioxide

What is another name for hydrogen ions?

Protons

What do hydrogen ions, electrons and CO2 produce?

Glucose

What happens to NADPH in the light-independent stage of photosynthesis?

It turns back to NADP+ and returns to the thylakoid membrane

Where is energy for the formation of glucose acquired?

ATP from the light-dependent stage

What happens as ATP breaks down to ADP + P?

Energy is released

What is the surface area of a leaf called?

The lamina

Why is the lamina so large?

To catch as much sunlight as possible

What is the petiole of a leaf?

The stalk attaching it to the twig or branch

What are stipules?

Leaf-like structures at the base of a leaf

Why are leaves thin?

So that light doesn’t have far to penetrate and so that CO2 and O2 don’t have far to diffuse

What are the external features of a leaf?

The petiole, stipule, midrib, lamina and cuticle

What are the veins of a leaf and why do they contain?

Vascular bundles containing xylem and phloem

What do veins do?

Carry in the water needed for photosynthesis and carry glucose away from the leaves to be stored

Why does xylem do?

It brings water and dissolved minerals from the roots via the stem

What does phloem do?

Transports sugars (glucose) up and down the plant from leaves to parts of the plant where it’s required or stored

What is cuticle made of?

It is waxy

What is the role of the cuticle?

To keep water in and keep pathogens out

What are the internal features of a leaf?

The upper and lower epidermis, vein, stomata, the spongy layer and the palisade layer

What is the upper epidermis?

A thin layer of flattened cells that marks the upper boundary of the leaf

Does the upper epidermis contain chloroplasts?

No

What are the stomata?

Holes in the epidermis

What do the stomata allow?

They allow and control gaseous exchange

What gaseous exchange happens during the day and why?

CO2 diffuses in and O2 diffuses out, as more photosynthesis takes place than respiration

What is the compensation point?

The point where oxygen escapes from the plant as more oxygen is produced by photosynthesis than is used in respiration

What gaseous exchange happens during the night and why?

O2 diffuses in and CO2 diffuses out, because only respiration takes place

What controls the size of the opening of the stomata?

Guard cells

When do guard cells allow the stomata to open?

When the cells are turgid due to water being drawn in by osmosis

When do guard cells keep the stomata closed?

When they are flaccid due to water diffusing in a process called transpiration

What is the palisade layer comprised of?

One or two layers of tightly packed cells in vertical columns

Why are palisade cells rich in chloroplasts?

Because they are the first to catch the light

Where does most photosynthesis take palace within the leaf?

In the palisade layer

What is the spongy layer composed of?

Irregularly shaped cells with lots of space between them

Why is there a lot of space between the cells in the spongy layer?

To allow for gaseous exchange

Does the lower epidermis have a waxy cuticle?

No

What epidermis contains more stomata?

The lower epidermis

What are trichomes and what are some examples?

Outgrowths, such as nettle stings and hairs

What is the apparent rate of photosynthesis?

The oxygen being released into the atmosphere

What is the actual rate of photosynthesis?

The oxygen used in respiration plus the oxygen released into the atmosphere

What are limiting factors in measuring the rate of photosynthesis?

Light intensity, CO2 concentration, temperature, etc.

What are conditions used to grow plants in horticulture?

Day length, light intensity, frequency of light, temperature, CO2 concentration and nutrients

How does day length affect plants?

It regulates their growth patterns and the longer they’re exposed to light, the longer they’ll photosynthesise for. As the days get shorter, they prepare for winter, and as the acts get longer, they grow and produce offspring

How does light intensity affect plants?

It increases the rate of photosynthesis, which increases the growth rate of plants

How does the frequency of light affect plants?

Red and blue wavelengths are the most effective for increased photosynthesis

What is the optimum temperature for plants?

About 40°C

What does paraffin produce?

CO2 and ethylene

How does CO2 concentration affect photosynthesis?

An increased concentration of CO2 increases the rate of photosynthesis

What does ethlyene do?

Speeds up the ripening of fruit

What are some important nutrients for plants?

CO2, water, nitrates, phosphates, potassium, etc.

What is hydroponics?

A process of growing the roots directly in water to precisely control the concentration of nutrients