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IB HL Biology > 2.9 Photosynthesis > Flashcards

2.9 Photosynthesis Flashcards

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1
Q

Equation for photosynthesis

A
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2
Q

What is photosynthesis?

A

The reaction of carbon dioxide and water using energy from light to produce carbohydrates (carbon compounds) and releasing oxygen as a waste product.

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3
Q

The first photosynthetic organisms were simple, ___ cells

A

Prokaryotic

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4
Q

Where does photosynthesis take place?

A

In chloroplasts

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5
Q

What are chloroplasts?

A

The tiny organelles in plant or algae cells where photons (the fundamental particle of light) are captured.

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6
Q

Why does the chloroplast look green?

A

Because chlorophyll a and chlorophyll b, the pigments that capture the photons, reflect green light and absorb most of the other wavelengths in the visible light spectrum.

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7
Q

What pigments are there other than chlorophyll that are also involved in photosynthesis?

A

-Pigments such as xanthophyll and carotenoids.

-They reflect yellow and orange light respectively.

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8
Q

Diagram showing chlorophyll (a green pigment that can be found in chloroplasts in plant cells)

A

.

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9
Q

What is the color of leaves on a plant determined by?

A

The color of light from the visible spectrum that is reflected

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10
Q

What light does chlorophyll absorb and reflect?

A

Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours

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11
Q

Graph showing the absorption spectrum of chlorophyll a and b

A
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12
Q

Define the action spectrum

A

The action spectrum shows the efficiency of photosynthesis or rate of photosynthesis achieved over the various wavelengths of light from the visible spectrum.

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13
Q

Define the absorption spectrum

A

The absorption spectrum shows which wavelength of visible light is absorbed by a particular photosynthetic pigment such as chlorophyll a or b measured by a spectrometer.

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14
Q

What is the action spectrum a good indicator of?

A

-Of which wavelengths are most efficient in photosynthesis.

-Some wavelengths cause a higher photosynthetic rate than others.

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15
Q

Action spectrum showing the different rates of photosynthesis that occur at different wavelengths of visible light

A
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16
Q

When asked to draw the action spectrum for photosynthesis, what must you ensure is included?

A

-The x-axis is labeled light wavelength or frequency and the y -axis is labeled rate of photosynthesis.

-The curve increases, decreases, and then increases again to decrease again.

-One peak is approximately 425 nm in the blue region.

-The second peak is approximately 670 nm in the red region.

-The first peak is higher than the second peak.

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17
Q

Consider that a plant X has a unique photosynthetic pigment.

The leaves of this plant appear to be yellow.

Which wavelengths of visible light are being absorbed by this pigment?

A

Blue and red

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18
Q

Halobacterium has a photosynthetic membrane that is coloured purple.

Its photosynthetic action spectrum is exactly complementary (opposite to) the action spectrum for green plants.

What wavelengths of light do the Halobacterium photosynthetic pigments absorb?

A

-Green and yellow

-If the action spectrum is opposite that of normal green plants it means that only green and yellow are absorbed because those are the colours reflected by green plants.

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19
Q

What does the action spectrum of photosynthesis record?

A

The amount of photosynthesis occurring at each wavelength

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20
Q

What is photolysis?

A

-The stage of photosynthesis in which water is split by light (photo – light and lysis – splitting).

-The energy in photons is used to split water molecules.

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21
Q

What does photolysis generate?

A

Hydrogen ions, electrons and oxygen

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22
Q

What is the equation for photolysis?

A
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23
Q

What are the electrons that are produced from photolysis used for?

A

-The electrons are used to generate ATP.

-Both the ATP (produced by the movement of electrons through a chain of carriers) and the hydrogen ions are used in the later stages of photosynthesis, while oxygen is a waste product that diffuses out of the plant.

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24
Q

Simplified diagram of photolysis

A
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25
Q

Where is the oxygen we breathe in produced from?

A

From water used in the photolysis reaction

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26
Q

In which process of photosynthesis is light directly involved?

A

-The splitting of water (photolysis)

-Photolysis, or the splitting of water by light energy, takes place during the light-dependent reactions.

-Using energy from the sun, water is split into electrons, H+ and an oxygen atom.

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27
Q

The energy absorbed from light is used to turn ___ and ___ into ___ and ___.

A

Carbon dioxide

Water

Carbohydrates

Other carbon compounds.

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28
Q

Is photosynthesis an anabolic or catabolic reaction?

A

Anabolic (small molecules (carbon dioxide and water) are joined together to form large molecules (sugars)

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29
Q

What is the Calvin cycle?

A

-The name for the light-independent reactions: a cycle of chemical reactions where CO 2 is assimilated to make sugars.

-Carbon dioxide + water → carbohydrates + oxygen

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30
Q

How many stage does photosynthesis involve?

A

Two

31
Q

What is the first stage of photosynthesis?

A

-Light-dependent reaction which requires light and occurs on the thylakoids of chloroplasts.

-Photolysis takes place at this stage.

32
Q

What is the second stage of photosynthesis?

A

-Light-independent reaction that has no light requirement and takes place in the stroma of chloroplasts.

-It involves carbon fixation to produce carbohydrates.

33
Q

Diagram showing a summary of photosynthesis

A
34
Q

What are the raw materials and products of photosynthesis?

A

Water and carbon dioxide are the raw materials and oxygen and carbohydrates are the products of photosynthesis

35
Q

What is needed in photosynthesis to convert carbon dioxide into organic molecules?

A

ATP and hydrogen from the splitting of water

36
Q

Define limiting factor

A

A limiting factor is a factor that restricts the rate of a reaction when present in a low amount.

37
Q

Why does photosynthesis have limiting factors?

A

-As the process of photosynthesis is catalyzed by enzymes, it works best at an optimum temperature.

-Additionally, since light, water, and carbon dioxide are required for photosynthesis to occur, these will also influence the rate at which the process can take place.

38
Q

Water as a limiting factor to photosynthesis

A

-It is worth noting that water is a limiting factor, but only under extreme conditions.

-If water becomes so scarce that the plant is likely to die, photosynthesis will stop.

39
Q

What are the three factors that can limit the rate of photosynthesis?

A

-Light

-Carbon dioxide

-Temperature

40
Q

Explain how light intensity is a limiting factor for photosynthesis

A

-At night when there is very little light, the rate of photosynthesis slows down.

-When the sun comes up, the rate of photosynthesis increases – but only up to a certain point.

-Beyond this point, the chemical reactions of photosynthesis cannot go any faster, so any further increase in light intensity does not increase the rate.

-Photosynthesis operates via a certain number of photosystems that capture photons.

-If they are all occupied, the rate of reaction cannot rise any more.

41
Q

Graph showing the effect of light intensity on the rate of photosynthesis

(Here the rate is expressed as the uptake of CO2. Another method to measure the rate of photosynthesis would be to measure the production of oxygen.)

A
42
Q

Explain how carbon dioxide is a limiting factor for photosynthesis

A

-Carbon dioxide is a raw material in the production of carbohydrates, which takes place in the light-independent reaction.

-Once all the active sites of the enzymes involved in this cyclic process are occupied with a substrate, any further increase in carbon dioxide concentration will not increase the rate (the graph levels off).

43
Q

Graph showing the effect of carbon dioxide concentration on the rate of photosynthesis

A
44
Q

Explain how temperature is a limiting factor for photosynthesis

A

-The optimum temperature of photosynthesis differs enormously for plants.

-It can range from almost freezing for certain lichens and mosses in the tundra of Siberia, to 35 °C in the tropical rainforests of Costa Rica and Brazil.

-In both cases, when the temperature increases beyond the optimum level, enzymes start to denature, hence the rate of photosynthesis decreases.

-When all enzymes are denatured, photosynthesis stops.

45
Q

Graph showing the effect of temperature on the rate of photosynthesis

A
46
Q

Until what point can a factor be said to be limiting and when does this stop?

A

-As far as an increase in a particular factor causes an increase in the rate of photosynthesis, that factor is said to be limiting.

-However, once the rate remains constant (when the graph levels off), it indicates that some other factor is limiting or the plant has reached its maximum potential.

47
Q

What is the rate of photosynthesis limited by at optimum temperature?

A

By light intensity and carbon dioxide concentration

48
Q

At very high light intensity and optimum temperature, what will increasing the carbon dioxide concentration do?

A

It will further increase the rate of photosynthesis, but only up to a certain point; then the rate of photosynthesis will reach a plateau.

49
Q

What should you consider when designing an experiment to investigate the effect of limiting factors on photosynthesis?

A

-Choose a plant material that allows easy control of variables and collection of data. Would it be better to use an aquatic plant or a terrestrial plant?

-Finalise your independent variable first (it could be either temperature, light intensity or carbon dioxide concentration), then list all other variables that you have to keep constant throughout the experiment.

-After checking the amount of time you have for the experiment, decide on how many levels of the independent variable you will include, as well as the number of repeats for each value. You should have at least 3–5 different levels of the independent variable.

-If you have decided to measure the amount of oxygen produced as an indication of rate of photosynthesis, avoid counting bubbles; consider measuring the volume of gas produced, which is more accurate. Alternatively, you may use a data logger and oxygen or carbon dioxide sensor to collect data (if you have them at school).

50
Q

Diagram of an example setup for an experiment to investigate the effects of different light intensities on the photosynthetic rate in an aquatic plant

A
51
Q

Describe the earliest photosynthetic organisms on Earth and how they evolved

A

-It has been hypothesised that the earliest photosynthetic organisms (prokaryotes called cyanobacteria) appeared on Earth around 2700 million years ago.

-It took several hundred millions of years before other organisms, such as single-celled algae and primitive plants, arrived on the scene.

-So, it took a long time before their contribution to the atmospheric oxygen concentration became apparent.

52
Q

Graph showing a rise of the oxygen concentration over the last 3.5 billion years

A
53
Q

What may have the oxygen released from photosynthesis been used for (in the early atmosphere- look at graph on previous flashcard)?

A

The oxygen released from photosynthesis may have been used in the oxidation of minerals, such as iron, and ended up in sediments and rocks

54
Q

When did eukaryotes appear and how did this affect the oxygen concentration in the Earth’s atmosphere?

A

-At around 2,100 million years ago, eukaryotes appeared and from then on, algae and other organisms living in the oceans have increased the oxygen concentration, also called partial pressure, in the water.

-Once the oceans and deposits were saturated, the Earth’s atmospheric oxygen started to build up.

-You will see that there is a peak around 300 million years before present – this coincides with the evolution of multicellular organisms and the colonisation of land.

55
Q

What can the changes in oxygen content of the Earth’s atmosphere, oceans and rock deposition be attributed to?

A

Photosynthesis

56
Q

Which organisms contributed to the rise in oxygen concentration during the first 2 billion years of the Earth’s existence?

A

Cyanobacteria

57
Q

What is chromatography?

A

A technique used to separate mixtures of substances based on the movement of the different substances on a piece of paper by capillary action.

58
Q

What are the two phases that chromatography makes use of for the separation process?

A

A mobile phase and a stationary phase

59
Q

What is the stationary and mobile phase in the case of paper chromatography?

A

The paper is the stationary phase while the solvent used to develop the chromatogram is the mobile phase.

60
Q

How are the pigments separated in paper chromatography?

A

They are commonly separated using an alcohol solvent mixture.

61
Q

Despite the fact that a leaf might look green, it can contain several different pigments, such as ___

A

-Chlorophylls, beta-carotene and xanthophyll

-These can be separated using paper chromatography

62
Q

What can be used to separate the different pigments in a leaf?

A

Paper chromatography

63
Q

Describe how the different pigments in a leaf can be separated using paper chromatography

A

-The pigment is first extracted from the leaves by using a suitable solvent that dissolves most plant pigments.

-A sample of the extract is then placed on chromatography paper and transferred to a container with the chromatography solvent.

-The pigments move at different rates on the stationary phase, so they separate out to form a chromatogram.

64
Q

Diagram of a paper chromatography setup.

25 refers to the 25 ml of the solvent placed in the container, and the 10 is the 10ml above the solvent, where the initial spot should be placed.

A
65
Q

What is the retention factor (Rf)?

A

-The ratio of the distance moved by a pigment to the distance moved by the solvent

-It is a constant

66
Q

What is the equation to find the Rf value?

A

R f = distance travelled by sample/distance travelled by solvent

67
Q

What can be deduced by comparing the R f value to known R f values of plant pigments?

A

The pigments present in the plant extract can be deduced

68
Q

How is thin layer chromatography different from paper chromatography?

A

In thin layer chromatography, the stationary phase is usually silica gel, aluminium oxide or cellulose instead of paper.

69
Q

What is the advantage of thin layer chromatography over paper chromatography?

A

It gives a better result as well-defined and well-separated spots are obtained.

70
Q

Required practical for 2.6: Investigating pigments present in plant leaves through chromatography

A
71
Q

Which substance can be used to dissolve pigments in paper chromatography?

A

Ethanol

72
Q

What is the function of the acetone used in paper chromatography to separate photosynthetic pigments?

A

It dissolves pigments, allowing them to travel up the paper strip.

73
Q

Visible light has a range of wavelengths with ___ being the shortest wavelength and ___ the longest.

A

Violet

Red

IB HL Biology (68 decks)

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