Biology Unit 3.2 - Photosynthesis Flashcards by Mac Hughes

What is photosynthesis?

Process where chloroplasts containing photosynthetic pigments absorb light energy at particular wavelengths of light

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How are chloroplasts distributed within a leaf?

Found in mesophyll cells, predominantly in the palisade mesophyll, and guard cells

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How are chloroplasts distributed within cells?

Cells orientate themselves to best suit light conditions:

In low light intensity they spread out to maximise surface area for light absorption
In high light intensity they arrange themselves in vertical columns so light strikes them edge-on

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What is the waxy cuticle?

Waxy and waterproof upper layer which limits water loss

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What is the upper epidermis?

Layer that protects the leaf, produces the waxy cuticle and allows light through to the palisade mesophyll

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What is palisade mesophyll?

Large, rectangular cells whose main function is photosynthesis

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What is spongy mesophyll?

Cells with many air spaces between them, allowing for the circulation of gases

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What is the lower epidermis?

Transparent layer containing no chloroplasts

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What are stomata?

Tiny pores which allow carbon dioxide to diffuse into the leaf and oxygen to diffuse out

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What are guard cells?

Cells guarding the stomata which open and close the stomatal pores by adjusting their turgor

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What are chloroplasts?

Organelle containing chlorophyll which trap light energy and convert it into chemical energy, which have their own DNA and a double membrane, surrounding a stroma containing folded internal membranes called thylakoids, which are the site of photosynthesis

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What did Thomas Engelmann discover in 1883?

He found that aerobic bacteria need oxygen and that they can move to regions with higher oxygen concentrations. Oxygen is produced during photosynthesis, with most oxygen being produced in the red and blue regions of the visible light spectrum, meaning most photosynthesis occurs here

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What are the two main types of pigments?

Chlorophylls which appear in the red and blue-violet regions, and carotenoids which appear in the blue-violet region, and are split into two sub-groups: carotenes and xanthophylls

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What is chromatography?

The separating of one type of molecule from another

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How do you calculate Rf values?

Divide the distance moved by the pigment from the origin by the distance moved by the solvent from the origin

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What are absorption spectra?

Graphs which shows how much light a particular pigment absorbs

Why do plants contain more than one type of photosynthetic pigment?

Allows the plant to absorb a wider range of wavelengths of light equalling more photosynthesis

What are action spectra?

Graphs which show the rate of photosynthesis at different wavelengths of light

How is light harvested?

Thylakoids are grouped in clusters called antenna complexes, which are special proteins that help funnel light energy until they reach chlorophyll a, the reaction centre

Explain the antenna complex and reaction centre…

There are two types of reaction centres - Photosystem I and Photosystem II - where light striking the reaction centre sets up a flow of excited electrons

Explain the light-dependent stage…

Occurs in the thylakoid membranes and consists of three main reactions:
* Photolysis which splits water molecules through the use of a photon of light
* ATP is synthesised from ADP and Pi during photophosphorylation
* NADP is reduced to form reduced NADP

Explain the non-cyclic pathway…

Involves PS I and PS II
Light excites electrons in PS II
Electron is accepted by an electron acceptor
Electron is passed along an elecron transport system and provide energy for the photophosphorylation of ADP and Pi
Electrons retrun to the reaction centre and are accepted by PS I
Electrons lost from PS II are replaced by photolysis, where light splits water forming oxygen, electrons, and protons
Electrons are passed to PS II, and protons are passed to NADP
At the same time electrons in PS I become excited, and are passed to an electron acceptor, with some being passed to NADP

Explain cyclic photophosphorylation…

Generates ATP through the use of PS I
Light is absorbed by PS I and passed to chlorophyll a
Electrons are passed to a higher energy level and are received by an electron acceptor
Electrons pass along a chain of electron carriers
This generates energy for ATP production via chemiosmosis

Explain chemiosmosis…

Excited electrons pass from electron acceptors to the transport system
Electrons are passed from electron carrier to electron carrier
Provides electron energy to drive the one type of proton pumps in the thylakoid membrane
Protons are pumped into the thylakoid cavity
Concentration gradient produced allows diffusion of protons back out of the cavity through stalked particles attached to ATP synthetase
Electrochemical gradient provides sufficient energy to join ADP to Pi to form ATP by chemiosmosis

Explain the light-independent stage...

ATP and reduced NADP produced are used in the Calvin cycle, where ATP is used as an energy source and reduced NADP provides reducing power to reduce carbon dioxide and fix the carbon into carbohydrate

Explain the Calvin cycle...

* Ribulose biphosphate (RuBP) combines with carbon dioxide, catalysed by rubisco, forming a 6C compound * Compound splits into to glycerate-3-phosphate (GP) molecules * GP is phosphorylated by ATP and then reduced by NADP to form triose phosphate (TP) * Some TP is built up into glucose and then starch * Results in the regeneration of RuBP

What is autoradiograph analysis?

Investigation into the sequence of events in the light-independent stage: * Alga Chlorella was exposed to 14CO2 * After intervals of 5 seconds and 30 secondsa sample was added to hot ethanol * Radioactive compounds were seperated by paper chromatography

What are the optimal conditions for photosynthesis?

* High light intensity as more energy is provided to the light-dependent stage * Certain wavelengths work best with chlorophyll absorption peaks in the red and blue-violet regions * Temperature of 25 degrees celsius, with lower temperatures resulting in inactivity and higher temperatures resulting in denaturation * Increased carbon dioxide concentration increase photosynthesis

How is light a limiting factor?

At low light intensity it is a limiting factor as light is needed as an energy source for photolysis As the light intensity increases the rate of photosynthesis increases until the saturation point is reached

How is carbon dioxide concentration a limiting factor?

At low concentrations it is a limiting factor as it is used in the light-independent stage Increased concentration will increase the rate of photosynthesis until the saturation point is reached

How is temperature a limiting factor?

At low temperatures it is a limiting factor as temperature influences enzyme activity which controls photosynthesis Rate of photosynthesis will increase until the enzymes' optimum temperature is reached

What is the law of limiting factors?

When a reaction is affected by more than one factor the rate is limited by the factor which is nearest its minimum value, where if a value is increased the rate will increase until another factor becomes limiting

How can yield of growth be increased?

* Carbon dioxide can be added to the air of glasshouses * Lamps can be installed to increase light intensity and day length * Heaters and cooling systems can be installed to maintain optimum temperatures

How do you investigate the effect of light intensity on photosynthesis?

Through the use of immobilised algae, bathed in hydrogen carbonate indicator: * Yellow - Rate of photosynthesis is lower than the rate of respiration, causing carbon dioxide concentration to increase * Red - Rate of photosynthesis and respiration are equal * Purple - Rate of photosynthesis is greater than rate of respiration, causing carbon dioxide concentration to decrease

Explain nitrogen deficiency in plants...

* Absorbed by the roots by active transport * Transported as nitrates in the xylem, and as amino acids in the phloem * Used to synthesise amino acids, nucelic acids, and ATP * Symptoms of deficiancy inlcude reduced growth and chlerosis, which first appear in older leaves

Explain magnesium deficiancy in plants...

* Absorbed as ions and tranposrted in the xylem * Used in chlorophyll production and ATPase activation * Needed by all tissues, especially plants as their form a part of the chlorophyll molecule * Deficiancy causes chlorosis between the veins of older leaves due to existing magnesium being transported to newer leaves