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Photosynthesis Flashcards

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AP® Biology flashcards Biology 101 flashcards
0
Q

Why do plants need to take up magnesium ions from the soil?

A

To use in the synthesis of chlorophyll and as an activator for many enzymes

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1
Q

In addition to CO2 and water, which two essential elements are required by flowering plants to produce nucleic acids?

A

Nitrogen and phosphorous

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2
Q

Why can waterlogged soil have an adverse effect of the health of plants?

A

Waterlogged soil can reduce the uptake of mineral ions, as this type of soil is poorly aerated.

The reduced supply of oxygen to roots inhibits the efficient active transport of mineral ions into plants

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3
Q

Define autotroph

A

Organisms that use light or chemical energy and inorganic molecules to synthesise complex organic molecules.

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4
Q

Define heterotroph

A

Organisms that ingest and digest complex organic molecules releasing the chemical potential energy stored in them.

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5
Q

Light energy is used during photosynthesis to produce…

A

Complex organic molecules

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6
Q

Explain how respiration in plants and animals depends upon the products of photosynthesis.

A

Photoautotrophs and hetreotrophs can release the chemical potential energy in complex organic molecules which were made during photosynthesis.

They use oxygen, which was first released into the atmosphere as a product of photosynthesis, for aerobic respiration.

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7
Q

In plants photosynthesis is a…

A

Two-stage process taking place in chloroplasts.

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8
Q

Explain how the structure of chloroplasts enables them to carry out their functions.

A

The inner membrane contains transport proteins which was control the entry and exit of substances between the cytoplasm and then stroma.

The grana provide a surface area for photosynthetic pigments, electron carriers, and ATP synthase, all involved in the Light-dependent reaction.

The photosynthetic pigments are arranged into photosystems to allow for maximum absorption of light energy.

Proteins embedded in the grana hold the photosystems in place
The stroma contains enzymes needed to catalyse the reactions in the light-independent stage.

The stroma surround the grana, so the products of the light-dependent reaction, needed in the light- independent reaction, can readily pass into the stroma.

Chloroplasts can make some of the proteins they need for photosynthesis using the genetic instructions on their chloroplast DNA, and the chloroplast ribosomes to assemble the proteins.

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9
Q

Define the term photosynthetic pigment.

A

Molecules that absorb light energy.

Each pigment absorbs a range of wavelengths in the visible region and has its own distinct peak of absorption.

Other wavelengths are reflected.

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10
Q

Explain the importance of photosynthetic pigments in photosynthesis.

A

They are substances that absorb certain wavelengths of light and reflect others.

They appear to us the colour of the wavelength they reflect.

There are many different pigments that act together, to capture as much light energy as possible.

They are in thylakoid membranes, arranged in funnel shaped structures called photosystems, held in place by proteins

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11
Q

The light-dependent stage takes place in ___________and that the light-independent stage takes place in the _________.

A

Thylakoid membranes

Stroma

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12
Q

Outline how light energy is converted to chemical energy (ATP and reduced NADP) in the light-dependent stage

A

When a photon hits a chlorophyll molecule the energy of the photon is transferred to two electrons and they become excited.

These electrons are captured by electron acceptors and passed down a series of electron carriers embedded in the thylakoid membranes.

Energy is released as electrons pass down the chain of electron carriers. This pumps protons across the thylakoid membrane into the thylakoid space where they accumulate.

A proton gradient is formed across the thylakoid membrane and the protons flow down their gradient, through proteins associated with ATP synthase enzymes.

This flow of protons is chemiosmosis, and it produces a force which joins ADP to Pi to produce ATP. The kinetic energy from the proton flow is converted to chemical energy in the ATP molecules, which is used in the light-independent stage of photosynthesis.

The making of ATP using light energy is called photophosphorylation, of which there are two types- cyclic and non cyclic.

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13
Q

Explain cyclic photophosphorylation

A
  • Uses only photosystem I (P700)
  • The excited electrons pass to an electron acceptor and back to the chlorophyll molecule from which they were lost
  • No photolysis of water
  • No generation of reduced NADP

• Small amounts of ATP formed
o May be used in light-independent stage
o May be used in guard cells, which contain only PS1, to
bring in K+ ions, so water will follow by osmosis,
causing the guard cells to swell and open the stomata.

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14
Q

Explain non-cyclic photophosphorylation

A

• Uses PS1 (P700), and PSII (P670).

  1. Light strikes PSII, exciting a pair of electrons that leave the chlorophyll molecule from the primary pigment reaction centre
  2. The electrons pass along a chain of electron carriers and the energy released is used to synthesise ATP
  3. Light has also struck PSI, and a pair of electrons have also been lost
  4. These electrons, along with protons (from the photolysis of water as PSII), join with NADP, which becomes reduced NADP
  5. The electrons from PSI replace those lost at PSII
  6. Electrons from photolysed water replace those lost by oxidised chlorophyll at PSI
  7. Protons from photolysed water take part in chemiosmosis to make ATP and are then captured by NADP in the stroma. They will be used in the light-independent stage.
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15
Q

Explain the role of water in the light-dependent stage.

A

Water is a source of:

Hydrogen ions to be used in chemiosmosis to produce ATP.

Electrons to replace those lost by oxidised chlorophyll.

The oxygen produced comes from water.

16
Q

Outline how the products of the light-dependent stage are used in the light-independent stage (Calvin cycle) to produce triose phosphate (TP)

A
  1. CO2 diffuses into the leaf through the open stomata
  2. CO2 combines with 5c Ribulose biphosphate, catalysed by Rubisco
  3. This forms two molecules of glycerate 3-phosphate
  4. GP is reduced (using Reduced NADP from the light-dependent stage) and phosphorylated (using ATP from the light dependent stage) to form Triose Phosphate
  5. 5/6 molecules of TP are recycled by phosphorylation (using ATP from the light dependent stage) to three molecules of RuBP.
17
Q

Explain the role of carbon dioxide in the light-independent stage (Calvin cycle).

A

Carbon dioxide is the source of carbon and oxygen for the production of all large organic molecules.

18
Q

Triose Phosphate can be used to make…

A

Carbohydrates, lipids and amino acids.

19
Q

Most TP is recycled to…

A

Rubulose biphosphate

20
Q

Describe the effect on the rate of photosynthesis, and on levels of GP, RuBP and TP, of changing carbon dioxide concentration

A

• Lots of CO2
o More CO2 fixation
o More GP
o More Triose Phosphate
o More regeneration of Ribulose Biphosphate
o However, open stomata may lead to increased
transpiration, so the plant may wilt if the water loss
exceeds water uptake. This leads to a stress response,
and following the release of abscisic acid, the stomata
close, reducing the CO2 uptake, and therefore the rate of
photosynthesis.

• Little CO2- affects light-independent, not dependent.
o RuBP will accumulate
o Less GP
o Less TP

21
Q

Describe the effect on the rate of photosynthesis, and on levels of GP, RuBP and TP, of changing light intensity

A

• Lots of light
o More excitation of electrons
o So, more photophosphorylation
o More ATP and reduced NADP produced
o More GP reduced and phosphorylated to TP
o More TP phosphorylated to RuBP

• Little light
            o GP cannot be changed to TP
            o Levels of TP will fall 
            o GP will accumulate 
            o Less RuBP
            o Less CO2 fixed
            o Less GP formed
22
Q

Describe the effect on the rate of photosynthesis, and on levels of GP, RuBP and TP, of changing temperature.

A

• High temperature
o Little effect on light dependent- not dependent on
enzymes except for photolysis of water.
o Light-independent is a series of biochemical steps, each
catalysed by a specific enzyme.
o Above 25°C, photorespiration exceed photosynthesis, as
the oxygenase activity of Rubisco. increases more than
the carboxylase activity.
o ATP and reduced NADP from the light-dependent
reaction are dissipated and wasted
o Reduces the overall rate of photosynthesis
o High temps may also denature proteins
o High temp= high water loss

This may lead to stomata closure, and the reduction of photosynthesis due to less CO2

23
Q

Discuss limiting factors in photosynthesis with reference to carbon dioxide concentration, light intensity and temperature.

A

Carbon dioxide concentrations
• Growers can increase the amounts of CO2 in their
greenhouses by burning methane or oil -fired heaters.
• This will increase the rate of photosynthesis, providing that
nothing else is limiting the process

Light intensity
• Light causes
o Stomata to open
– CO2 can diffuse in
o Trapped by Chorophyll
– Excites electrons
o Splits water molecules to produce protons
• The electrons and protons are used in
photophosphorylation, which produced ATP to fix CO2

Temperature
• The calvin cycle is very much affected by temperature as it
is enzyme-catalysed.
o At too higher temperatures, the enzymes work less
effectively, and O2 successfully competes for the active
site of rubisco, preventing it from accepting CO2
• Also, as too higher temperatures, more water is lost from
the stomata, leading to a stress response where the
stomata close, limiting the availability of CO2

24
Q

Explain what is meant by Blackman’s law of limiting factors

A

When a process is controlled by a number of factors, the factor in least supply will limit the rate of the process

25
Q

Lis the three main factors affecting the rate of photosynthesis

A

CO2 concentration

Light intensity

Temperature

26
Q

Under normal environmental conditions, what is a limiting factor at very low rates of photosynthesis?

A

Light intensity

27
Q

How many carbon atoms has Ribulose biphosphate

A

5

28
Q

How many carbon atoms has glycerate 3-phosphate?

A

3

29
Q

Explain what would happen if all the glyceraldehyde 3-phosphate was converted to other carbohydrates

A

The process would stop, since the acceptor molecule for carbon dioxide, Ribulose biphosphate, must be regenerated in order to fix the Carbon dioxide from the atmosphere

Biology (13 decks)

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