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AP® Biology flashcards Biology 101 flashcards
1
Q

Photosynthesis

A

is the process
that converts
solar energy into
chemical energy

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2
Q

Autotrophs

A

sustain themselves without eating

anything derived from other organisms.

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3
Q

Autotrophs are the producers of

A

the biosphere,
producing organic molecules from CO2 and other
inorganic molecules

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4
Q

Almost all producers are photoautotrophs

A

using
the energy of sunlight to make organic molecules
through photosynthesis

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5
Q 
Photosynthesis occurs in
plants, algae, certain other
protists (single-celled
eukaryotes), and some
prokaryotes
A

These organisms feed not
only themselves but also
most of the living world

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6
Q

Heterotrophs

A

obtain their organic material from

consuming all or parts of other organisms

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7
Q

Almost all heterotrophs, including humans

A

depend

on photoautotrophs for both food and oxygen.

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8
Q

The Earth’s supply of fossil fuels was formed from
the remains of organisms that died hundreds of
millions of years ago

A

Fossil fuels therefore represent stores of solar

energy captured by producers in the distant past.

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9
Q

The green color of plants is

from

A

chlorophyll, the green

pigment within chloroplasts

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10
Q

Although all green parts of a

plant contain chlorophyll,

A

leaves are the major site of

photosynthesis.

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11
Q

Chloroplasts are found mainly

in cells of the mesophyll

A

the

interior tissue of the leaf.

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12
Q

Each mesophyll cell contains

A

30–40 chloroplasts

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13
Q

stomata.

A

CO2 enters and O2 exits the
leaf through microscopic
pores called stomata

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14
Q

The chlorophyll is in the membranes of thylakoids (connected

sacs in the chloroplast)

A

thylakoids may be stacked in columns

called grana

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15
Q

The thylakoids are surrounded by stroma

A

a dense interior fluid

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16
Q

Photosynthesis is a complex series of reactions

that can be summarized as the following equation:

A

6 CO2 + 12 H2O + Light energy  C6H12O6 + 6 O2 + 6 H2O

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17
Q

Chloroplasts split H2O into hydrogen and oxygen.

A

The electrons of hydrogen are incorporated into

sugar molecules and oxygen is released.

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18
Q

Photosynthesis is a redox process in which H2O

A

is
oxidized and CO2
is reduced.

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19
Q

Photosynthesis is an endergonic process

A

the

energy boost is provided by light

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20
Q

Photosynthesis reverses the direction of

A

electron

flow seen in cellular respiration

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21
Q

Photosynthesis consists of

A 
The light reactions (the photo part) and the
Calvin cycle (the synthesis part).
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22
Q

The light reactions (in the thylakoids)

A 
– Split H2O
– Release O2
– Reduce NADP+
to NADPH
– Generate ATP from ADP by
photophosphorylation
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23
Q

The Calvin cycle (in the stroma)

A

– forms sugar from CO2
, using ATP and
NADPH

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24
Q

Chloroplasts are solar-powered chemical factories

A

Their thylakoids transform light energy into the

chemical energy of ATP and NADPH

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25
Q

Light is a type of
electromagnetic
radiation wave

A 
Light can also be
considered
discrete particles
of energy called
photons
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26
Q

Pigments are substances that absorb visible light

A

Leaves appear green
because chlorophyll
reflects and transmits
green light

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27
Q

Chlorophyll a is

A

the main

photosynthetic pigment.

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28
Q

Accessory pigments, such as

chlorophyll b

A

broaden the spectrum

used for photosynthesis.

29
Q

Accessory pigments called

carotenoids

A

absorb excessive light

that would damage chlorophyll.

30
Q

A spectrophotometer

A

measures a pigment’s

ability to absorb various wavelengths

31
Q

This machine sends light through pigments and

A

measures the fraction of light transmitted at each

wavelength.

32
Q

An absorption spectrum

A

is a graph plotting a

pigment’s light absorption versus wavelength

33
Q

An action spectrum

A

profiles the relative
effectiveness of different wavelengths of radiation
in driving a process

34
Q

Absorption spectra

show that violet-blue

A

and red light work best

for photosynthesis

35
Q

When a pigment absorbs light,

A

it goes from a

ground state to an excited state, which is unstable

36
Q

When excited electrons fall back to the ground

state, photons are given off

A

an afterglow called

fluorescence

37
Q

If illuminated, an isolated solution of chlorophyll

A

will

fluoresce, giving off light and heat.

38
Q

In chloroplasts a photosystem consists of

A

1) a reaction-center complex (a type of protein
complex) surrounded by,
2) light-harvesting complexes

39
Q

The light-harvesting complexes (pigment

molecules bound to proteins)

A

transfer the energy

of photons to the reaction center.

40
Q

A special pair of
chlorophyll a
molecules in the
reaction center is

A 
excited by photons
from the light
harvesting complex
and donates
electrons to the
primary electron
acceptor
41
Q

There are two interconnected types of photosystems:

A
  • Photosystem II (PS II)

- Photosystem I (PS I)

42
Q

Photosystem II (PS II)

A

functions first (the numbers
reflect order of discovery) and is best at absorbing a
wavelength of 680 nm (its chlorophyll a is called
P680)

43
Q

Photosystem I (PS I)

A

is best at absorbing a
wavelength of 700 nm (its chlorophyll a is called
P700)

44
Q 
Photosystem II
A photon hits a pigment and
its energy is passed among
pigment molecules until it
excites P680.
A 
An excited electron from
P680 is transferred to the
primary electron acceptor.
P680’s electrons are
replaced by electrons from
a water molecule.
45
Q 
Photosystem II
Each electron “falls”
down an electron
transport chain from
the primary electron
acceptor of
Photosystem II
A

The electron transport chain establishes a proton
gradient across the thylakoid membrane that
drives ATP synthesis

46
Q

In Photosystem I

A

light energy excites P700 to pass
an electron to its primary acceptor, this electron is
replaced by the electron transport chain

47
Q

photosystem 1
A second electron transport chain transfers
electrons to NADP+ reducing it to NADPH

A

The result of the light reaction is that ATP and NADPH
are supplied to the Calvin Cycle where they are used
to produce sugars

48
Q

The Calvin Cycle:

A

Making Sugar

49
Q

The Calvin cycle was described in
the 1950’s by Andrew Bensen,
James Bassham and Melvin Calvin

A

The Calvin cycle uses ATP and
NADPH (from light reactions) to
convert CO2
to sugar

50
Q

The Calvin Cycle

A

The cycle is similar to that in the
citric acid cycle – the final product
of the reaction is an initial reactant.

51
Q

The Calvin cycle has three phases

A
  1. CO2 acceptor fixes carbon
  2. Reduction of the sugar
  3. Regeneration of the CO2 acceptor
52
Q

Phase 1: Carbon fixation:

A 
In the first phase, the carbon in
CO2
is attached to the 5-carbon
sugar ribulose bisphosphate
(RuBP) by the enzyme rubisco
53
Q

(Rubisco)

A

Ribulose bisphosphate carboxylase

oxygenase

54
Q

(Rubisco

A

Most abundant protein on Earth

55
Q

Rubisco is relatively inefficient

A 
fixing only 3 molecules/second
and
It is not very specific (occasionally
binds O2
instead of CO2
56
Q

calvin cycle

Phase 2: Reduction

A 
In the second phase, ATP
phosphorylates the sugar and NADPH
donates electrons to raise the potential
energy of the sugar. One molecule of
the sugar glyceraldehyde 3-phosphate
(G3P) leaves the cycle
57
Q

Phase 3:

Regeneration

A

In the third phase,
additional G3P is
rearranged into
molecules of RuBP.

For the net production of
one molecule of G3P
the cycle must fix three
molecules of CO2

58
Q

Alternative Mechanisms to Fix

Carbon in Hot, Dry Climates

A

Dehydration is a problem sometimes requiring
trade-offs with other metabolic processes,
especially photosynthesis.

59
Q

On hot, dry days, plants close stomata, which

conserves H2O but also limits photosynthesis

A

Closing stomata reduces access to CO2 and

causes O2 to build up within cells.

60
Q

Photorespiration

A

An apparently detrimental process called
photorespiration occurs while the stomata are
closed and O2 builds up in the mesophyll cells.

61
Q

Photorespiration

A 
• Rubisco binds O2
instead of CO2
• Additional CO2
is produced but lost from the leaf
• ATP is consumed
• Photosynthetic rate is reduced
62
Q

The version of the Calvin cycle
shown previously fixes carbon
first in

A

a 3-carbon sugar –plants
that use this method are called
C3 plants

63
Q

C4 plants

A 
minimize
photorespiration by using an
enzyme, PEP carboxylase,
with a higher affinity for CO2
than that of rubisco
64
Q

In C4 plants PEP carboxylase fixes
CO2
in 4-carbon compounds

A

These are exported from mesophyll
cells to bundle sheath cells, where
they release CO2
for the Calvin cycle

65
Q

Comparison: C3 – C4 Plants

A 
C3
- carbon fixed first in a 3-carbon sugar
C4
- a 4-carbon sugar is the first product
- CO2
fixed first by PEP carboxylase
(instead of rubisco)
- Calvin cycle occurs in bundle sheath cells
66
Q

CAM Plants
Some plants fix carbon
by crassulacean acid
metabolism (CAM)

A 
1. CAM plants open their
stomata at night,
incorporating CO2
into
organic acids.
2. During the day, the
stomata close and the
CO2
is released from
the organic acids for
use in the Calvin cycle.
67
Q 
Each day the Earth’s
atmosphere receives
enough energy to supply
all of humanity’s energy
consumption for 25 years!
A

Only ~1% of the solar
energy that reaches Earth
is converted to chemical
energy by plants

68
Q

Significance of Photosynthesis

A

About 50% of sugars made in photosynthesis are
consumed in the cellular respiration of the plant.
The remainder are synthesized into proteins, lipids
and other molecules for the plant.
Some products are stored in roots, seeds and fruits

biology 171 exam 2 (4 decks)

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