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Photosynthesis Flashcards

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Biology 101 flashcards
1
Q

What are heterotrophic organisms?

A

Organisms that obtain energy from ingesting and digesting complex organic molecules (from other organisms).

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2
Q

What are autotrophic organisms?

A

Organisms that make their own organic compounds from inorganic molecules.

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3
Q

What are photoautotrophs?

A

A type of autotrophic organism that have special photosynthetic pigments that can convert light energy into chemical bond energy.

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4
Q

What is the shape of a chloroplast?

A

Biconvex

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5
Q

What is evidence for the endosymbiont theory regarding chloroplasts?

A

The presence of 70s ribosomes and circular DNA suggests that chloroplasts may have descended from a photosynthetic prokaryote (cyanobacteria).

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6
Q

What is the purpose of starch granules in the chloroplast?

A

Starch granules contain a storage polysaccharide for the end-product of photosynthesis.

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7
Q

What is the stroma of the chloroplast?

A

Colourless dense fluid containing soluble enzymes for the light-independent stage of photosynthesis.

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8
Q

What is the purpose of circular DNA in the chloroplast?

A

Has genetic code for proteins required in photosynthesis such as rubisco.

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9
Q

What is a thylakoid membrane in the chloroplast?

A

A pair of close membranes with a fluid-filled space between, made from equal parts protein and lipid.
Contains photosystems for photosynthesis.

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10
Q

What is a granum (grana) in the chloroplast?

A

Thylakoid membranes arranged in stacks for a larger surface area for light absorption.
Grana are the site of the light-dependent stage of photosynthesis.

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11
Q

What are intergranal lamella in the chloroplast?

A

Thylakoid membranes connecting adjacent grana.

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12
Q

Why are there lipid droplets in the choroplast stroma?

A

Formed as a result of the breakdown of aged membranes.

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13
Q

What does the chloroplast envelope comprise of?

A

The outer and inner membranes.

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14
Q

What are pigments?

How can they be identified in a sample?

A

Molecules that absorb specific wavelengths of light and reflect others.
Pigments can be extracted and identified using chromatography.

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15
Q

What is the primary pigment?

A

Chlorophyll A.

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16
Q

What are some examples of accesory pigments?

A

Chlorophyll B.
Carotenoids such as beta-carotene..
Xanthophylls

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17
Q

What is the structure of chlorophyll A?

A

Flat light-absorbing head containing a magnesium ion (Mg2+) prosthetic group at its centre.
Long hydrocarbon tail.

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18
Q

What are the two different absorption peaks that chlorophyll A can have?

A

680nm or 700nm.

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19
Q

What is significant about beta-carotene?

A

The most widespread carotenoid pigment.
Makes carrots orange.
Broken down to form vitamin A.

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20
Q

What colour of light do plants gain the most energy from?

A

Blue.

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21
Q

What is the structure of a photosystem?

A

Lots of accessory pigment molecules surrounding a central primary pigment molecule called the reaction centre.
This structure spans the thylakoid membrane.

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22
Q

What are the two types of photosystem and how are they different?

A

PSI absorbs best at 700nm as it has the 700nm version of chlorophyll A as its reaction centre.
PSII absorbs best at 680nm as it has the 680nm version of chlorophyll A as its reaction centre.

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23
Q

What is the purpose of the accessory pigments in a photosystem?

A

To “funnel” energy towards the reaction centre. Accessory pigments increase the range of wavelengths of light that can be absorbed by the photosystem. (broaden the absorbtion spectrum)

24
Q

What is an absorption spectrum?

A

A graph showing which wavelengths of light are absorbed by a pigment.

25
Q

What is an action spectrum?

A

A graph showing which wavelengths of light are actually used the most in photosynthesis.

26
Q

What effect do accessory pigments have on the absorption spectrum?

A

They widen it.

27
Q

What is ATP?

A

A phosphorylated nucleotide used as the universal currency of energy.
Energy is released and stored by the addition and subtraction of inorganic phosphate.

28
Q

What is NADP?

A

A coenzyme used for redox reactions.

NADP+ can be reduced with hydrogen into its energised form.

29
Q

How is NADP used in photosynthesis?

A

NADPH is produced by NADP reductase (enzyme) in non-cyclic photophosphorylation and is then used in the calvin cycle.

30
Q

What is photolysis?

A

When light energy is absorbed by PSII, some is used by an enzyme to split water molecules into 4H+, 4e- and an oxygen molecule (O2).

31
Q

Where are the products of photolysis used?

A

Oxygen is a waste product and leaves the chloroplast.
The electrons replace those lost from PSII.
The protons help to reduce NADP along with the electrons lost from PSI.

32
Q

How is a proton gradient produced in photophosphorylation?

A

The excited electron from the photosystem is passed to a primary electron acceptor, and then passed down an ETC (electron transport chain) where it loses energy through a series of redox reactions.
The energy from the excited electron is used by proton pumps to pump H+ ions into the thylakoid space from the stroma, creating a proton gradient. (electrochemical gradient)

33
Q

What is the process of chemiosmotic synthesis in photophosphorylation?

A

The electrochemical gradient across the thylakoid membrane allows protons to diffuse through ATP synthase, which drives the phosphorylation of ADP to ATP.

34
Q

Where does the excited electron from PSII go after the ETC?

A

It replaces the lost electron from PSI.

35
Q

Where does the excited electron from PSI go in non-cyclic photophosphorylation?

A

It is used by NADP reductase to reduce NADP into NADPH.

36
Q

Where does the excited electron from PSI go in cyclic photophosphorylation?

A

The electron is passed on to the electron carriers (acceptor) normally used by PSII.

37
Q

Why would cyclic phosphorylation occur instead of non-cyclic?

A

If there is a shortage of NADP (oxidised).

If there is a shortage of water for photolysis.

38
Q

What is the key difference in cyclic as opposed to non-cyclic photophosphorylation?

A

Only PSI is used.
Only ATP is formed, not reduced NADP.
No oxygen is produced.

39
Q

Where does the calvin cycle occur in the chloroplast?

A

The stroma.

The calvin cycle is the light-independent stage of photosynthesis.

40
Q

What are the three phases of the calvin cycle?

A

Carbon fixation.
Reduction and Phosphorylation.
Regeneration.

41
Q

What happens in the carbon fixation stage of the calvin cycle?

A

Carbon dioxide is fixed to RuBP (ribulose bisphosphate) by the enzyme rubisco. This forms a 6-carbon molecule that immediately splits into 2 GP molecules (glycerate-3-phosphate).

42
Q

What happens in the reduction and phosphorylation stage of the calvin cycle?

A

Reduced NADP oxidises into NADP, reducing GP.
ATP goes to ADP, phosphorylating GP.
This forms TP. (triose phosphate)

43
Q

What happens in the regeneration stage of the calvin cycle?

A

5 TP molecules are regenerated into 3 RuBP molecules using 3ATP.
These RuBP molecules are then used by rubisco in carbon fixation.

44
Q

How many TP molecules are produced in 3 turns of the calvin cycle?

A

1 (5 are used to regenerate 3 RuBP molecules).

45
Q

How many TP molecules are required to produce 1 glucose molecule, and therefore, how many turns of the calvin cycle produce 1 glucose?

A

2 TP are required to make 1 glucose.

This requires 6 turns of the calvin cycle.

46
Q

How many ATP and NADPH molecules are required to produce one glucose molecule?

A

18ATP and 12 NADPH

47
Q

How many carbons does RuBP have?

A

5

48
Q

What is GP used to make?

A

Amino acids

49
Q

What can a combination of TP and GP make?

A

Lipids

50
Q

What factors can limit the rate of photosynthesis?

A 
Light intensity.
Availability of water.
Availability of carbon dioxide.
Availability of chlorophyll/chloroplasts/palisade cells.
Temperature.
51
Q

What is the law of limiting factors?

A

When a process is affected by more than one factor it is limited by the factor that is nearest its minimum value. It is that limiting factor which directly affects the process if the factor is changed.

52
Q

What is the compensation point on a graph of oxygen production against light intensity for a plant?

A

The point at which the rate of oxygen production (photosynthesis) is equal to the rate of oxygen consumption (aerobic respiration), so no net oxygen is released by the plant.

53
Q

What can a combination of two TP molecules make?

A

Hexose sugars like glucose

54
Q

What does Rubisco stand for?

A

ribulose bisphosphate carboxylase

55
Q

What is the method of energy transfer when photosynthetic pigments absorb light from the sun?

A

Electrons in the pigment are excited to a higher energy level.
The primary pigments pass excited electrons to the ETC.

BIO (33 decks)

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