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Life Sciences 141 > Chapter Five > Flashcards

Chapter Five Flashcards

1
Q

What is photosynthesis

A

Process where plants use light from the sun; water from the roots and CO2 from the air and turn it into energy to allow them to live

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2
Q

Why is photosynthesis the most important life process

A

Without it plants could die and even become extinct

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3
Q

Explain the end of photosynthesis fully

A
  • Completion = O2 released and carbs are produced which are commonly known as glucose
  • These sugar molecules contain energy that living organisms need to survive
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4
Q

What is the balanced equation for photosynthesis

A

6CO2 + 6H2O —–> C6H1206 + 6O2

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5
Q

Explain how plants used the produced carbs

A
  • Used as fuel for their own cellular respiration
  • Glucose molecules are also used as the building blocks for the cellulose cell wall
  • If a plant produces more sugar / glucose than needed the excess may be stored as starch
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6
Q

What are the non-photosynthetic plant parts

A
  • Roots; flowers; fruits; seeds and others couldn’t grow without the sugar shipments from the green leaves and stems
  • Indirectly instrumental in plant reproduction ( pollination )
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7
Q

What parts are involved in photosynthesis

A
  • The leaves
  • Stomata
  • Roots
  • Mesophyll
  • Chloroplasts
  • Stroma
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8
Q

Explain each part involved in photosynthesis

A
  1. Leaves = broad, flat surface expose great SA to sunlight
  2. Stomata = small regulated openings where gaseous exchange of CO2 and O2 occurs
  3. Roots = absorption of water
  4. Mesophyll = Middle layer that contains abundant chloroplasts
  5. Chloroplasts = organelles of photosynthesis in plants and algae
  6. Stroma = inner fluid of chloroplasts that is gelatinous and contains ribosomes; DNA and enzymes
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9
Q

Where does photosynthesis primarily take place

A

The leaves

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10
Q

Where does water evaporate from in plants

A

Stomata

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11
Q

What are photosystems

A

Clusters of pigments and proteins that participate in photosynthesis

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12
Q

Explain the stroma fully

A
  • Inside = 10 to 100 grana
  • Each granum has a stack of 10-20 pancake shaped thylakoids
  • The thylakoid has an inner compartment called a thylakoid space
  • Thylakoid space = enclosed by a thylakoid membrane that’s studded with photosynthetic pigments
  • Thylakoid membrane has photosystems
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13
Q

What are the 2 stages that photosynthesis takes place in

A
  1. Light dependant reactions
  2. Carbon reactions ( Calvin cycle )
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14
Q

Explain light dependent reactions fully

A
  • Take place in thylakoid membrane
  • Chlorophyll absorbs energy from the sunlight and then converts it into chemical energy with the use of water
  • Releases O2 from hydrolysis of water as a product
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15
Q

Explain carbon reactions fully

A
  • Occurring stroma
  • Chemical energy derived from the light dependant reactions drives both the capture of carbon in CO22 molecules and the subsequent assembly of sugar molecules
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16
Q

What do carbon and light reactions use

A

Carrier molecules to transport the energy from one to the other

17
Q

Explain light energy fully

A
  • Sun emits enormous amounts of electromagnetic radiation ( solar energy )
  • Portion humans can see = visible light
  • Solar energy travels in a way that can be described and measured as waves
  • Scientists can determine the amounts of energy of a wave by measuring its wavelength
  • Wavelength = distance between 2 consecutive similar points in a series of waves
18
Q

Explain the electromagnetic spectrum; photons

A
  1. Electromagnetic spectrum = the range of all possible wavelengths of radiation
  2. Photons = discrete packets of kinetic energy
19
Q

Identify and explain the components of sunlight that reaches the earths surface

A
  1. Ultraviolet radiation photons = can damage DNA, cause sunburn, and skin cancer
  2. Visible light = provides energy that powers photosynthesis
  3. Infrared radiation = contains too little energy per photon to be useful to organisms – most of this energy is converted immediately to heat
20
Q

Explain the energy flow fully

A
  • Living things access energy by breaking down carbohydrate molecules
  • Carbohydrates are storage molecules for energy in all living things
  • Although energy can be stored in molecules like ATP, carbohydrates are much more stable and efficient reservoirs for chemical energy
  • Photosynthetic organisms also carry out the reactions of respiration to harvest the energy that they have stored in carbohydrates, for example, plants have mitochondria in addition to chloroplasts.
21
Q

Explain photosynthesis fully

A
  • The two parts of photosynthesis—the light-dependent reactions and the Calvin cycle—have been described, as they take place in chloroplasts.
  • However, prokaryotes, such as cyanobacteria, lack membrane-bound organelles.
  • Prokaryotic photosynthetic autotrophic organisms have infoldings of the plasma membrane for chlorophyll attachment and photosynthesis
  • It is here that organisms like cyanobacteria can carry out photosynthesis
22
Q

Explain the Calvin cycle fully

A
  • After the energy from the sun is converted and packaged into ATP and NADPH, the cell has the fuel needed to build food in the form of carbohydrate molecules.
  • The carbohydrate molecules made will have a backbone of carbon atoms.
  • Where does the carbon come from? The carbon atoms used to build carbohydrate molecules come from carbon dioxide, the gas that animals exhale with each breath.
  • The Calvin cycle is the term used for the reactions of photosynthesis that use the energy stored by the light-dependent reactions to form glucose and other carbohydrate molecules.
23
Q

Explain generating another energy carrier : NADPH

A
  • The remaining function of the light-dependent reaction is to generate the other energy-carrier molecule, NADPH.
  • As the electron from the electron transport chain arrives at photosystem I, it is re-energized with another photon captured by chlorophyll.
  • The energy from this electron drives the formation of NADPH from NADP+ and a hydrogen ion (H+).
  • Now that the solar energy is stored in energy carriers, it can be used to make a sugar molecule.
24
Q

Explain generating another energy carrier : ATP

A
  • In the light-dependent reactions, energy absorbed by sunlight is stored by two types of energy-carrier molecules: ATP and NADPH
  • The energy that these molecules carry is stored in a bond that holds a single atom or group of atoms to the molecule.
  • For ATP, it is a phosphate group, and for NADPH, it is a hydrogen atom.
  • When these molecules release energy into the Calvin cycle, they each lose either atoms or groups of atoms to become the lower-energy molecules ADP and NADP
25
Q

Explain the interworking of the Calvin cycle discovery

A
  • In plants, carbon dioxide (CO2) enters the leaf through the stomata and diffuses into the mesophyll cells and into the stroma of the chloroplast—the site of the Calvin cycle reactions where sugar is synthesized.
  • The reactions are named after Melvin Calvin, the scientist who discovered them, and reference the fact that the reactions function as a cycle.
    • Others call it the Calvin-Benson cycle to include the name of another scientist involved in its discovery, Andrew Benson.
26
Q

Explain light and photosynthesis

A
  • Light energy enters the process of photosynthesis when pigments absorb the light.
  • In plants, pigment molecules absorb only visible light for photosynthesis.
  • Different kinds of pigments exist, and each absorbs only certain wavelengths (colors) of visible light.
  • Pigments reflect the color of the wavelengths that they cannot absorb.
  • All photosynthetic organisms contain a pigment called chlorophyll a, which humans see as the common green colour associated with plants
  • Each type of pigment can be identified by the specific pattern of wavelengths it absorbs from visible light, which is its absorption spectrum.
27
Q

Explain chlorophyll A

A

Absorbs wavelengths from either end of the visible spectrum (blue and red), but not from green
- Because green is reflected, chlorophyll appears green

  • Major pigment
  • Plants; algae; Cyanobacteria
28
Q

Explain chlorophyll B

A

Absorbs blue and red-orange light, the colours reflected are yellow-green

  • Accessor y pigment
  • Plants and green algae
29
Q

Explain carotenoids

A

Absorb blue-green region and violet region and will reflect red, yellow and orange region

  • Plants; algae; bacteria; archaea
30
Q

Explain carbon fixation

A
  • The Calvin cycle reactions can be organized into three basic stages: fixation, reduction, and regeneration.
  • In the stroma, in addition to CO2, two other chemicals are present to initiate the Calvin cycle: an enzyme abbreviated RuBisCO, and the molecule ribulose bisphosphate (RuBP).
  • RuBP has five atoms of carbon and a phosphate group on each end.
  • RuBisCO catalyzes a reaction between CO2 and RuBP, which forms a six-carbon compound that is immediately converted into two three-carbon compounds.
  • This process is called carbon fixation because CO2 is “fixed” from its inorganic form into organic molecules.
31
Q

Explain reduction reaction and ATP; NADH

A
  • ATP and NADPH use their stored energy to convert the three-carbon compound, 3-PGA, into another three-carbon compound called G3P.
  • This type of reaction is called a reduction reaction because it involves the gain of electrons.
  • A reduction is the gain of an electron by an atom or molecule.
  • The molecules of ADP and NAD+, resulting from the reduction reaction, return to the light-dependent reactions to be re-energized.
  • One of the G3P molecules leaves the Calvin cycle to contribute to the formation of the carbohydrate molecule, which is commonly glucose (C6H12O6).
  • Because the carbohydrate molecule has six carbon atoms, it takes six turns of the Calvin cycle to make one carbohydrate molecule (one for each carbon dioxide molecule fixed).
  • The remaining G3P molecules regenerate RuBP, which enables the system to prepare for the carbon-fixation step.
  • ATP is also used in the regeneration of RuBP.
32
Q

Explain chemiosmosis and ATP synthase

A
  • The buildup of hydrogen ions in the thylakoid space forms an electrochemical gradient because of the difference in the concentration of protons (H+) and the difference in the charge across the membrane that they create.
  • This potential energy is harvested and stored as chemical energy in ATP through chemiosmosis
  • Chemiosmosis: the movement of hydrogen ions down their electrochemical gradient through the transmembrane enzyme ATP synthase.
  • The hydrogen ions are allowed to pass through the thylakoid membrane through an embedded protein complex called ATP synthase.
  • The energy generated by the hydrogen ion stream allows ATP synthase to attach a third phosphate to ADP, which forms a molecule of ATP in a process called photophosphorylation.
  • The flow of hydrogen ions through ATP synthase is called chemiosmosis because the ions move from an area of high to low concentration through a semi-permeable structure.
33
Q

Explain how light dependent reactions work

A
  • The overall purpose of the light-dependent reactions is to convert light energy into chemical energy
  • This chemical energy will be used by the Calvin cycle to fuel the assembly of sugar molecules
  • The light-dependent reactions begin in the photosystem
  • A pigment molecule in the photosystem absorbs one photon at a time.
  • A photon of light energy travels until it reaches a molecule of chlorophyll
  • The photon causes an electron in the chlorophyll to become “excited.” The energy given to the electron allows it to break free from an atom of the chlorophyll molecule.
  • Chlorophyll is therefore said to “donate” an electron
  • To replace the electron in the chlorophyll, a molecule of water is split
34
Q

Explain the splitting

A
  • This splitting releases an electron and results in the formation of oxygen (O2) and hydrogen ions (H+) in the thylakoid space.
  • Each breaking of a water molecule releases a pair of electrons and therefore can replace two donated electrons.
  • The replacing of the electron enables chlorophyll to respond to another photon.
  • The oxygen molecules produced as byproducts find their way to the surrounding environment.
  • The hydrogen ions play critical roles in the remainder of the light-dependent reactions.
  • The purpose of the light-dependent reactions is to convert solar energy into chemical carriers that will be used in the Calvin cycle.
  • In eukaryotes and some prokaryotes, two photosystems exist. The first is called photosystem II, which was named for the order of its discovery rather than for the order of the function.
35
Q

What happens after the photon hits

A
  • After the photon hits, photosystem II transfers the free electron to the first in a series of proteins inside the thylakoid membrane called the electron transport chain.
  • As the electron passes along these proteins, energy from the electron fuels membrane pumps that actively move hydrogen ions against their concentration gradient from the stroma into the thylakoid space.
  • After the energy is used, the electron is accepted by a pigment molecule in the next photosystem, which is called photosystem I

Life Sciences 141 (22 decks)

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