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Plants and the Environment > lecture 4 Photosynthesis > Flashcards

lecture 4 Photosynthesis Flashcards

1
Q

What does Photosynthesis mean?

A

“Synthesis using light” and it is process of biological importance which involves conversion of solar energy of the chemical energy producing organic compounds

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2
Q

The photosynthetic process takes place in what kind of plants?

A

Under natural conditions, the photosynthetic process takes place in plants that are continuously responding to internal and external change

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3
Q

What does the amount of light CO2 determine?

A

The amount of light CO2 determine the photosynthetic response of plants and multiple level of control over the process of photosynthesis allows plants to grow successfully in changing environments and diverse habitats.

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4
Q

What are plant physiologists interested in?

A

Plant physiologists are interested to understand the effect of environmental factors such as light, CO2 concentration and temperature on photosynthesis

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5
Q

The photosynthetic process is important for? but why?

A

The photosynthetic process is important for agronomists because plant productivity and crop yield depends on photosynthetic efficiency in a dynamic environment

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6
Q

What are the names for the 3 major steps in the process of photosynthesis?

A

1) The light reactions
2) uptake of carbon dioxide
3) Carbon dioxide fixation

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7
Q

What does step 1 involve?

A

involves the light reactions which capture light energy to be used for reduction of NADP and formation of ATP. These energy rich compounds are later used in the synthesis of sugars and complex organic molecules

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8
Q

What does step 2 involve?

A

Involves the uptake and diffusion of carbon dioxide to the reaction centre in the chloroplast

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9
Q

What does step 3 involve?

A

Is the fixation of carbon dioxide to synthesize carbohydrate, involving the calvin cycle

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10
Q

In the light reaction, visible light is absorbed by?

A

the chlorophyll molecules which are located in thylakoid membranes of the chloroplast

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11
Q

How are the light photons captured?

A

The light photons are captured by chlorophyll (a and b) the green pigment molecules and the excitation energy is transferred to a chemical acceptor

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12
Q

What is the result of the photosynthetic electron transfer process?

A

the end result is the production of reducing power (NADPH) and the synthesis of ATP

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13
Q

What happens in the chemical reactions in which water is oxidized to oxygen?

A

NADP is reduced, and ATP is formed, take place in the thylakoid membrane, are known as thylakoid reactions

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14
Q

What is the chemical energy of NADPH and ATP later used for?

A

The chemical energy of NADPH and ATP is later used for the fixation of carbon dioxide into carbohydrates.

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15
Q

What is leaf used for in photosynthesis?

A

Leaf - the primary site of photosynthesis and internal structure of the chloroplast

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16
Q

In chloroplast, light energy is converted into?

A

chemical energy by two different photosystems.

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17
Q

What are these photosystems and what do they do?

A

These photosystems are known as photosystem and photosystem 2, which carry out early energy storage reactions in the process of photosynthesis.

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18
Q

Explain Photosystem 1

A

Photosystem 1 absorbs far-red light of wavelength greater than 680 nm and produces strong reductant capable of reducing NADP+

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19
Q

Explain Photosystem 2

A

Photosystem 2 absorbs the light of 680 nm and produces very strong oxidant capable of oxidizing water.

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20
Q

What do both Photosystems have?

A

Both photosystems have specific antenna pigments and photochemical reaction centre which are linked by an electron transport chain

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21
Q

What is the fraction of the captured light also used for?

A

Fraction of the captured light is also used for light-dependant ATP synthesis, known as photophosphorylation.

22
Q

What is the process of the uptake of carbon dioxide?

A

The uptake of carbon dioxide is a diffusion process

23
Q

How do the Carbon dioxide molecules move?

A

Carbon dioxide molecules move by diffusion down a concentration gradient from the atmosphere into the leaf entering through the stomata

24
Q

What are the stomata?

A

The stomata are pores of the leaf surface, each of which are formed by two guard cells responsible for opening and closing like a valve, which is controlled by changes in turgor pressure inside the guard cells.

25
Q

What happens to the carbon dioxide molecules do after they pass through the stomata?

A

After passing through stomata, the carbon dioxide molecules diffuse through the intercellular spaces, entering the mesophyll cells which contain the chloroplasts. Once in the chloroplast, the fixation process can take place using a special enzyme - Rubisco.

26
Q

What does C3 fixation refer to?

A

C3 fixation refers to the production of a 3 carbon compound (Phosphoglycerate) as the first stable product of photosynthesis

27
Q

What do a number of important crop plants and major natural vegetation plants in the sub-tropics do instead of C3 fixation?

A

C4 fixation

28
Q

What is Net photosynthesis?

A

Net photosynthesis is a function of a both photosynthesis and respiration i.e

Net Photosynthesis = Gross Photosynthesis – Gross Respiration
↓ ↓ ↓
Net uptake of CO2 =Gross uptake of CO2 by fixation – Gross evolution of CO2 by dark and photo-respiration

29
Q

What is the most abundant enzyme?

A

RuBisCO is the most abundant enzyme (Protein) in the world since it is present in every plant that undergoes photosynthesis

30
Q

Where is the enzyme RuBisCO located?

A

The enzyme RuBisCO is located in the stroma of chloroplasts and used in the Calvin Cycle to catalyze the first major step of carbon fixation.

31
Q

What is the structure of RuBP

A

RuBP (Ribulose 1,5 - biphosphate) is a five carbon sugar, which reacts with CO2 in the first step of the Calvin cycle.

32
Q

What does the enzyme RuBisCO do?

A

RuBisCO catalyzes the carboxylation of RuBP with carbon dioxide and requires Mg2+ for its activity.

33
Q

what is the photosynthetic rate of temperate plants

A

Temperate plants 1.5 - 6.0

E.g. wheat 5.0

34
Q

what is the photosynthetic rate of Tropical plants?

A

Tropical plants 3.0 -12.0

35
Q

What causes the difference?

A

Another fixation pathway

Tropical plants use the C4 fixation pathway

C4 fixation is an additional pathwar

Complete fixation include both PEP carboxylase and RuBisCO

36
Q

What is the difference between the C3 and C4 carbon cycles in relation to cells?

A

C3 leaves have only mesophyll cells that contained chloroplasts but C4 leaves have two distinct chloroplast containing cells, mesophyll and bundle shealth.

37
Q

What are the 3 stages of the C4 cycle?

A

1) Fixation of CO2 by the PEP in the mesophyll to form C4 acids (malate or asparate).
2) Transport of C4 acids to bundle sheath cells
3) Decarboxylation of C4 acids and generation of CO2, which is then reduced to carbohydrate via the Calvin cycle

38
Q

How can C4 plants overcome the harmful effects of high temperature?

A

because high activity of PEP carboxylase enables them to reduce stomatal aperture.

39
Q

What is the second beneficial feature for C4 plants?

A

suppression of photorespiration resulting from the concentration of CO2 in bundle sheath cells.

40
Q

What is Crassulacean Acid Metabolism (CAM plants e.g. cacti, pineapple and vanila)?

A

A different form of C4 fixation

CAM plants have competitive advantage in arid climates

Conserving water improves their water use efficiency

41
Q

Why is the carbon dioxide fixation pathway catalysed by RUBISCO given the term C3

a) It involves three steps
b) It involves three compounds
c) The first stable product has three carbons
d) It requires three cycles for completion
e) None of these

A

c) The first stable product has three carbons

42
Q

To make up the complete RUBISCO protein, subunits are derived from the following organelles:

a) The nucleus
b) The nucleus and chloroplast
c) The nucleus and mitochondrion
d) The chloroplast and mitchondrion

A

b)The nucleus and chloroplast

43
Q

Identify one of the conditions that promotes photorespiration in C3 systems:

a) Low carbon dioxide concentrations
b) High carbon dioxide concentrations
c) Lower light
d) Lower temperature
e) None of these

A

a)Low carbon dioxide concentrations

44
Q

In the Kranz anatomy of C4 plants, where does fixation via RUBISCO and the Calvin cycle occur?

a) In the leaf mesophyll cell
b) In the palisade cell
c) In the epidermis
d) In the bundle sheath cell
e) None of these

A

d)In the bundle sheath cell

45
Q

Identify a factor which contributes LEAST to the development of the atmospheric window:

a) amount of cloud
b) depth of ozone layer
c) atmospheric pollution
d) elevated atmospheric carbon dioxide
e) prevailing wind

A

e)prevailing wind

46
Q

In photosynthesis, which of the following does NOT occur?

a) electron transfer
b) energy transfer
c) light harvesting
d) light adsorption
e) photolysis of water

A

d)light adsorption

47
Q

Identify a role for PEP carboxylase:

a) breaks down starch
b) closes stomata
c) provides a secondary fixation mechanism
d) synthesis of carbonates
e) none of these

A

c)provides a secondary fixation mechanism

48
Q

Under what conditions would C4 plants outperform C3 plants?

a) higher light intensities
b) lower temperatures
c) higher carbon dioxide levels
d) lower levels of nitrogen
e) none of these

A

a)higher light intensities

49
Q

Step 2 in the process of photosynthesis is:

a) light harvesting
b) light energy converted to chemical energy
c) uptake and diffusion of carbon dioxide to the reaction centre in the chloroplast
d) fixation of carbon dioxide
e) photolysis of water

A

c)uptake and diffusion of carbon dioxide to the reaction centre in the chloroplast

50
Q

In the light harvesting complex of a higher plant, what is the molecule at the reaction centre?

a) chlorophyll b
b) Riboflavin
c) Phytochrome
d) a carotenoid
e) a special form of chlorophyll a

A

e) a special form of chlorophyll a

Plants and the Environment (12 decks)

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