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Bio Component 1 > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

Describe the method of studying the density of stomata

A
  1. Apply clear nail polish to the lower epidermis of a leaf between the veins and allow it to dry
  2. Using forceps, peel the nail polish from the leaf to produce a replica of the lower epidermis
  3. Place the replica on a microscope slide and count the number of stomata using the microscope
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2
Q

Other than the presence of stomata, give 3 adaptations of the leaf for photosynthesis

A
  1. Large surafce area: absorbs as much light as possible
  2. Thin: light penetrates all levels
  3. Air spaces in the spongey mesophyll: allows CO2 to diffuse into photosynthesising cells
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3
Q

Biochemical reactions in cells often involve cyclic metabolic pathways which occur in compartments (such as chloroplasts) inside cells. Why is this important?

A
  • Reactions can occur in small volume/ isolation of enzymes/reactants
  • Membranes isolate reactions within organelles, keeping products seperate from the cytoplasm
  • Mitochondria can be positioned close to areas needing ATP, and organelles ca move within the cytoplasm
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4
Q

State the location and function of the light dependent stage of photosynthesis

A

Thylakoid membrane and thylakoid space of chloroplast
Involves the conversion of light energy into chemical energy (ATP and NADPH)

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5
Q

State the location and function of the light independent stage of photosynthesis

A

Stroma of chloroplast
Uses the prducts of the light dependent reaction (ATP and NADPH) to produce organic molecules such as glucose

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6
Q

Where are photosynthetic pigments located?

A

Within the thylakoid membranes of chloroplasts

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7
Q

During photosynthesis, different wavelengths of light strike the leaf and are absorbed by varous pigments. What is the role of the pigments?

A

Capture light energy from the sun and convert it into chemical energy

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8
Q

What are the 2 main types of photosynthetic pigments in flowering plants?

A

Primary pigments and accessory pigments

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9
Q

What is the primary pigment and which wavelengths does it absorb?

A

Chlorophyll a absorbs blue and red wavelengths of light

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10
Q

What are the secondary pigments and which wavelengths do they absorb?

A
  • Chlorophyll b absorbs blue and red wavelengths of light
  • Carotenoids absorb violet/blue light (xanthophyll & carotene)
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11
Q

Why are accessory pigments important?

A

They absorb wavelengths of light not absorbed by the primary pigments
This ensures a wider range of wavelengths are absorbed, increasing the efficiency of photosynthesis

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12
Q

What macronutrient is needed to produce chlorophyll a?

A

Magnesium ions

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13
Q

Describe how chromatography can be used to separate photosynthetic pigments

A
  1. Tear up leaves and grind with acetone to form a dark green pigment solution
  2. Use capillary tube to spot the pigment on to chromatography paper
  3. Place the chromatography paper into a solvent
  4. Remove the chromatography paper once the solvent has travelled to the top of the strip. Observe the different distances the pigments have travelled
  5. Calculate the Rf value for each pigment
  6. Identify each pigment by comparing Rf values to known values
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14
Q

Why do we add acetone when grinding leaves during chromatography?

A

Acetone dissolves the phospholipid membrane to extract the pigment

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15
Q

How do you calculate the Rf value?

A

distance travelled by the pigment/distance travelled by solvent

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16
Q

Where are photosystems located?

A

On the thylakoid membranes of chloroplasts

17
Q

What is the role of photosystems?

A
  • Absorb photons of light energy
  • Act as transducers, transferring this light energy to high energy electrons
  • This energy is then used to fuel proton pumps and synthesise ATP
18
Q

Describe the photosystem structure

A

Accesssory pigments are grouped into clusters with associated proteins, forming an antenna complex
These pigments absorb photons of light energy and funnel this energy down the antenna complex to the reaction centre
Chlorophyll a molecules are found in the reaction centre, below the antenna complex
When photons of light energy reach chlorophyll a, electrons are excited to become high energy electrons

19
Q

At what wavelength does photosystem I best absorb light?

A

700nm

20
Q

At what wavelength does photosystem II best absorb light?

A

680nm

21
Q

What 6 things does the light dependent reaction involve?

A
  • Requires light energy
  • Takes place in the thylakoid membranes and thyakoid space
  • Involves the synthesis of ATP from ADP and Pi (via photophosphorylation)
  • Involves the splitting of water using light (photolysis)
  • Involves the reduction of NADP to form redNADP
  • Releases oxygen gas as a by product
22
Q

What are the 2 light dependent reactions in higher plants?

A
  • Non-cyclic photophosphorylation
  • Cyclic photophosphorylation
23
Q

Describe what happens at photosystem II during non-cyclic photophosphorylation

A
  • Photons of light are absorbed by PSII and passed to chloropyll a in the reaction centre
  • This excites 2 electrons on chlorophyll a to a higher energy level, causing them to be emitted, passed to electron acceptors and then transferred along a chain of carriers (including a proton pump) to photosystem I
  • As the electrons move along the chain, they release energy, which is used to pump hydrogen ions (protons) from the stroma across the thylakoid membrane into the thylakoid space
  • This creates an elecrochemical gradient due to the high H+ concentration in the thylakoid space and low concentration in the stroma
  • H+ flow down this proton gradient, through a proton channel connected to ATP synthase providing energy for the formation of ATP from ADP and Pi
24
Q

Describe when happens at photosystem I during non-cyclic photophosphorylation

A
  • Photons of light energy are absorbed by PSI, causing 2 electrons in chlorophyll a to be raised to a higher energy level, emitted, and passed to another electron acceptor
  • The elecron acceptor transfers the electrons to protons outside the thylakoid membrane into the stroma, which then reduce NADP to NADPH
  • The use of H+ to reduce NADP lowers their concentration in the stroma, helping to maintain the electrochemical gradient between the thylakoid space and the stroma
  • The emitted electrons do not return to their original source so this process is known as non-cyclic photophosphorylation
25
Q

Describe photolysis (happens during non-cyclic photophosphorylation)

A
  • Photolysis is the splitting of water using light
  • It occurs in the thylakoid space
  • Water splits into oxygen, protons and electrons
  • The electrons replace those lost by photosystem II, making the chlorophyll molecule stable
  • The protons help to maintain the electrochemical gradient between the thylakoid space and the stroma
26
Q

Where/when does cyclic photophosphorylation occur?

A

Occurs in bacteria and primitive plants. Higher plants also use this pathway to provide extra ATP , especially when CO2 is in short supply, or if levels of reduced NADP are high

27
Q

Describe cyclic photophosphorylation

A
  • Only photosystem I is involved. Light energy is absorbed at PSI and channelled to chlorophyll a
  • Electrons in the chlorophyll a become excited, energised and released. They are accepted by an electron acceptor and eventually passed along the same tranfer chain as that used by the electrons from PSII
  • Protons are pumped into the thylakoid space and ATP is produced from ADP + Pi
  • The same chhemiosmotic theory as that used to describe the Z scheme is believed to be involved in the productionn of ATP
  • Electrons excited and released form PSI return to PSI
28
Q

How is the light independent stage linked to the light dependent stage?

A

The light independent stage (Calvin cycle) uses ATP and reduced NADP from the light dependent stage to fix carbon dioxide into organic molecules

29
Q

Describe the light independent stage (Calvin Cycle)

A
  • CO2 from the atmosphere is fixed with RuBP (5C)
  • The enzyme RuBisCo catalyses this reaction
  • Results in the formation of an unstable 6C compound which splits into two molecules of Glycerate-3-phosphate (3C)
  • Glycerate-3-phosphate is then reduced using reduced NADP produced during the light dependent stage
  • ATP from the light dependent stage is also required. ATP is hydrolysed and the phosphate transferrred to Glycerate-3-phosphate, resulting in the formation of 2 molecules of triose phosphate (3C)
  • One carbon atom of the 6 available is removed from the Calvin cycle and can be used to produce organic molecules such as glucose
  • Five carbon atoms remain in the Calvin cycle and are used to regenerate RuBP so the cycle can begin again
30
Q

Name 2 symptoms of a deficiency of nitrates

A
  • Reduced growth of organs
  • Chlorosis - yellowing leaves due to inadequate chlorophyll production so plant no longer able to absorb light energy
31
Q

Name a symptom of a deficiency of magnesium

A

Pronounced chlorosis between veins of older leaves as existing magnesium is moved and transported to new leaves

32
Q

Name a symptom of deficiency of phosphates

A

Stunting of plant growth

33
Q

What are the 3 limiting factors of photosynthesis?

A
  • Temperature
  • CO2 concentration
  • Light intensity
34
Q

How does an increase in temperature affect the rate of photosynthesis?

A

An increase in temperature generally enhances enzyme activity, thereby increasing the rate of photosythesis

35
Q

The light dependent stage is much less dependent on enzyme activity than the light independent stage. Explain the implications of this on the overall rate of photosynthesis

A

An increase in temperature speeds up the LIS more than it speeds up the LDS. The supply of products from the LDS will not be able to keep up with the demand from the LIS. The overall rate of photosynthesis will become limited by the supply of reduced NADP and ATP

36
Q

Describe a physical change that could occur in the leaf that might result in the rate pf photosynthesis decreasing at very high carbon dioxide concentrations

A
  • Carbon dioxide diffuses into leaves and dissolves in water
  • The enzyme carbonic anhydrase catalyses this reaction
  • Carbonic acid is formed which dissociates to form H+ ions and HCO3- ions
  • The accumulation of H+ ions causes cells to become more acidic
  • The acidity denatures enzymes in mesophyll cells in the leaves
37
Q

Explain the effect that an increase in light intensity will have on the yield of photosynthates

A

As the light dependent reaction speeds up, ATP and reduced NADP are produced at a faster rate. They enter the Calvin cycle and organic molecules are produced at a faster rate

38
Q

Describe a physical change that could occur in a leaf that might result in the plateau at high light intensity. Explain the advantage of this to the plant

A

At high light intensity, temperatures are also high so stomata close to reduce transpiration/wilting

Bio Component 1 (6 decks)

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