energy for biological processes Flashcards
1
Q
Why do living organisms
need energy?
A
For metabolic activities: • Active transport, which is essential for the uptake of nitrates by root hair cells, loading sieve tube cells, the selective reabsorption of glucose and amino acids in the kidney, and the conductions of nerve impulses • Anabolic reactions e.g. building polymers like proteins, polysaccharides, and nucleic acids essential for growth and repair • Movement brought about by cilia, flagella, or the contractile filaments in muscle cells
2
Q
Define the following:
- Autotrophic
2. Heterotrophic
A
1. Organisms that synthesise complex organic molecules from inorganic molecules via photosynthesis 2. Organisms that acquire nutrients by the ingestion of other organisms
3
Q
What is photosynthesis?
A
Synthesis of complex organic molecules using light • Light is trapped by chlorophyll molecules • This energy is used to drive the synthesis of glucose from carbon dioxide and water 6CO2 + 6H2O ⇌ C6H12O6 +6O2
4
Q
What is respiration?
A
Breakdown of complex organic molecules linked to the synthesis of ATP • The energy stored within the bonds of the organic molecules is used to synthesise ATP C6H12O6 + 6O2 →6CO2 +6H2O
5
Q
Describe the bonds in small
inorganic molecules
A
• e.g. water and carbon dioxide
• Strong bonds that release a lot of
energy when they form, but require
a lot of energy to brea
6
Q
Describe the bonds in
organic molecules
A
e.g. glucose and amino acids • Contain many more bonds than small inorganic molecules • Weaker bonds than inorganic molecules • Release less energy when they form, and require less energy to be broken
7
Q
Describe what happens in
respiration in terms of bond
energy
A
Large organic molecules broken down into small inorganic molecules • Total energy required to break all the bonds in the complex organic molecules is less than the total energy released in the formation of all the bonds in the smaller inorganic products • The excess energy is used to synthesise ATP
8
Q
What is the importance of
carbon-hydrogen bonds?
A
• The carbon-hydrogen bonds is a non-polar bond which does not require a lot of energy to break • The carbon and hydrogen released then form strong bonds with oxygen atoms (forming CO2 and H2O), resulting in the releases of large quantities of energy • The reverse happens in photosynthesis; the energy required to build molecules in photosynthesis comes from the Sun
9
Q
What is chemiosmosis?
A
The synthesis of ATP driven by a flow of protons across a membrane • Protons diffuse from a region of high concentration to a region of low concentration through a partially permeable membrane • The movement of protons releases energy that is used in attach Pi to ADP, forming ATP • It depends on the creation of a proton concentration gradient. The energy to do this comes from excited electrons
10
Q
How are electrons raised to
higher energy levels
(excited)?
A
• Electrons in pigment molecules (e.g. chlorophyll) are excited by absorbing light from the Sun • High energy electrons are released when chemical bonds are broken in respiratory substrate molecules (e.g. glucose)
11
Q
Describe an electron
transport chain
A
Made up of a series of electron carrier, each with progressively lower energy levels • As high energy electrons move from one carrier in the chain to another, energy is released • This energy is used to pump protons across a membrane, creating a concentration difference across the membrane, and therefore a proton gradient • The proton gradient is maintained because the membrane is impermeable to hydrogen ions
12
Q
How do protons move down
their concentration
gradient?
A
The membrane is impermeable to hydrogen ions • Protons have to move through hydrophilic membrane channels linked to the enzyme ATP synthase (catalyses the formation of ATP) • Flow of protons through these channels provides the energy used to synthesise ATP
13
Q
Describe the membranes in
chloroplasts
A
They provide a large surface area to
maximise the absorption of light
essential in the first step of
photosynthesis
14
Q
A
The membranes form flattened sacs called thylakoids which are stacked to form grana • The grana are joined by membranous channels called lamellae • The fluid enclosed in the chloroplast is called the stroma, and is the site of the many chemical reactions resulting in the formation of complex organic molecules
15
Q
What is a pigment?
A
Molecules that absorb specific
wavelengths of light
16
Q
What is a photosystem?
A
Protein complexes involved in the
absorption of light and electron
transfers in photosynthesis
17
Q
What is the primary pigment
in photosynthesis?
A
• Chlorophyll A
• Mainly absorbs red and blue light
and reflects green lights
18
Q
What are the accessory
pigments?
A
• Chlorophylls B and carotenoids • Carotenoids appear yellow and orange and absorb blue light • Not directly involved in light dependent reactions, but absorb wavelengths that are not well absorbed by chlorophylls and pass the associated energy to chlorophyll A at the base of the photosystem • Carotene (orange) and Xanthophyll (yellow) are the main carotenoids • Carotenoids are important for photo-protection
19
Q
What is the role is of
accessory pigments?
A
• They are embedded in the thylakoid membrane of the chloroplast • These and other proteins and pigments for a light harvesting system (aka antennae complex)
20
Q
What is photo-protection?
A
In high light intesisties, the accessory pigments dissipate the energy that they have absorbed instead of passing it to chlorophyll A, to protect the chlorophyll A
21
Q
What is the role of the light
harvesting system (antennae
complex)?
A
• To absorb, or harvest, light energy of different wavelengths and transfer this energy quickly and efficiently to the reaction centre • Chlorophyll A is located in the reaction centre, which is where reactions in photosynthesis take place The light harvesting system and reaction centre are collectively known as a photosystem
22
Q
A
Absorption spectrum - shows the absorption spectrum for the photosynthetic pigments Action spectrum - Profiles the relative performance of different wavelengths to promote photosynthesis
23
Q
How are chloroplasts
adapted to carry out their
role in photosynthesis?
A
• The inner membrane can control entry and exit of substances between the cytoplasms and the stroma with its transport proteins • Many Trajan consisting of stacks of thylakoid membranes providing a large SA for photosynthetic pigments, electron carrier and ATP synthase • Photosynthetic pigments are arranged into special structures called photosystems which allow maximum absorption of light • Proteins in the Trajan hold the photosystems in places • The fluid filled stroma contains enzymes that catalyse all the light independent reactions • Grana are surrounded by the stroma so products of the light dependent reactions which are needed for the light independent stages can pass easily into the stroma • Chloroplasts can make some of the proteins they need for photosynthesis using genetic instructions in the chloroplast DNA, and the chloroplast ribosomes assemble the proteins
24
Q
What are the two stages of
photosynthesis?
A
Light dependent stage - energy from sunlight is absorbed and used to form ATP. Hydrogen from water is used to reduce coenzyme NADP to reduced NADP Light-independent state - hydrogen from reduced NADP and CO2 is used to build organic molecules e.g. glucose. ATP supplies the required energy
25
What is non-cyclic
| photophosphorylation?
The synthesis of ATP and reduced
NADP involving photosystems I and
II
26
What are the stages of noncyclic photophosphorylation
| in PSII?
```
1. The light absorbed excites
electrons at the reaction centres
of the photosystems
2. The excited electrons are
released from the reaction centre
of PSII and are passed to an
electron transport chain. ATP is
produced by chemiosmosis
3. The electrons lost from the
reaction centre and PSII are
replaced from water molecules
broken down using energy from
the Sun
```
27
What are the stages of noncyclic photophosphorylation
| in PSI?
```
1. Excited electrons are released
from the reaction centre at PSI,
passed to another electron
transport chain, and ATP is again
produced by chemiosmosis
2. The electrons lost form this
reaction are replaced by
electrons that have just travelled
along the first electron transport
chain after being released from
PSII
3. The electrons leaving the
electron transport chain
following PSI are accepted,
along with a hydrogen ion, by
the coenzyme NADP, forming
reduced NADP
4. Reduced NADP provides the
hydrogen or reducing power in
the production of organic
molecules, e.g. glucose, in the
light-independent stage which
follows
```
28
What is photolysis?
```
Water molecules are split into
hydrogen ions, electrons, and
oxygen molecules using energy from
the Sun
H2O → 2H+ + 2e- +0.5O2
```
29
Detail the process of
| photolysis
```
• The oxygen-evolving complex
which forms part of PSII is an
enzyme that catalyses the break
down of water
• Here water molecules are split into
hydrogen ions, electrons and
oxygen molecules using energy
from the sun
• The electrons released replace the
electrons lost from the reaction
centre PSII
• This is why water along with light
and CO2 is a raw material for
photosynthesis
```
30
What happens to the H+
| ions released in photolysis?
```
They are leased into the lumen of
the thylakoids, increasing the
proton concentration across the
membrane
• As they move back through the
membrane down a concentration
and electrochemical gradient, they
drive the formation of more ATP
• Once H+ ions are returned to the
stroma, they combine with NADP
and an electron from PSI to form
reduced NADP
• This is used in the lightindependent reactions of
photosynthesis - this removed H+
ions from the stroma so it helps to
maintain the proton gradient
across the thylakoid membranes
```
31
What is cyclic
| photophosphorylation?
Synthesis of ATP involving only
| photosystem I
32
Describe the process of
| cyclic photophosphorylation
```
The electrons leaving the electron
transport chain after PSI can be
returned to PSI, instead of being
used to form reduced NADP
• This means PSI can still lead to the
production of ATP without any
electrons being supplied from PSII
• Reduced NADP is not produced
when this happens
```
33
Where does the lightindependent stage (Calvin
cycle) of photosynthesis
take place?
```
• In the stroma of the chloroplasts
• The stroma conains all the
enzymes needed for fixing the
carbon dioxide to produce
complex organic molecules
```
34
Describe the Calvin cycle
```
A metabolic pathway that
regenerates the starting material -
after molecules enter and leave the
cycle
• CO2 is captured and modified by
the addition of hydrogen to form
carbohydrate
```
35
What are the chemicals
| involved in the Calvin cycle?
```
• Ribulose Biphosphate (RuBP)
which is a 5-carbon carbon
dioxide acceptor compound
• The enzyme ribulose biphosphate
carboxylase (RuBisCO)
• Glycerate 3-phosphate (GP)
• Triose phosphate (TP)
```
36
Describe the stages in the
| Calvin Cycle
```
1. CO2 absorbed from the
atmosphere is combined with
RuBP in a process called fixing.
This is catalysed by the enzyme
RuBisCO
2. An unstable 6-carbon compound
is produced, which rapidly
breaks down to two molecules of
GP
3. The GP is then converted to TP
by reduction using H+ ions from
reduced NADP, and ATP from the
light-dependent stage
4. The TP can then be used to
manufacture the large organic
molecules needed by the plant
e.g. carbohydrates, amino acids,
lipids etc.
5. However most of the TP (5 out of
every 6) is recycled to produce
more RuBP. This process
requires more ATP (produced by
the light-dependent stage)
```
37
Why does the Calvin cycle
need to turn 6 times to make
one hexose sugar?
```
1. 3 turns of the cycle produces 6
molecules TP because 2
molecules of TP are made for
every 1 CO2 molecules used
2. 5 out 6 of these TP molecules
are used to regenerate RuBP
3. For 3 turns of the cycle, only 1
TP is produced that’s used to
make a hexose sugar
4. A hexose sugar has 6 carbons
though, so 2 TP molecules are
needed to form one hexose
sugar
5. There fore the cycle must turn 6
times to produce 2 molecules of
TP that can be used to make 1
hexose sugar
6. 6 turns of the cycle needed 18
ATP and 12 reduced NADP from
the light-dependent reaction
```
38
What does the law of
| limiting factors state?
```
The law of limiting factors states that
at any given moment, the rate of a
metabolic process is limited by the
factor present in its least favourable
(lowest) value
```
39
How is light important in
| photosynthesis?
```
• Causes stomata to open
• Excites electrons in chlorophyll
molecules
• Causes photolysis of water
• Photophosphorylation produces
ATP and reduced NADP for the
fixation of carbon dioxide
• Light also causes tomato to open
so gas exchange can happen
```
40
How does light intensity
affect the rate of
photosynthesis?
```
• At a constant favourable
temperature and constant suitable
CO2 concentration, light intensity
is the limiting factor
• When light intensity is low, rate of
photosynthesis is low
• As light intensity increases, the
rate of photosynthesis
• At a certain point, even as light
intensity increases, the rate of
photosynthesis doesn’t increase -
another factor is now limiting the
process
```
41
What is the effect of
changing the light intensity
on the Calvin cycle?
1. GP cannot be reduced to TP
2. TP levels fall and GP
accumulates
3. If TP levels fall, RuBP cannot be
regenerated
42
What is the effect of
changing the CO2
concentration on the Calvin
cycle?
1. RuBP cannot accept it, and
accumulates
2. GP cannot be made
3. Therefore, TP cannot be made
43
What are the effects of
changing temperature on
the Calvin cycle?
```
• 25-30˚C: If plants have enough
water and CO2 and a sufficient
light intensity, the rate of
photosynthesis increases as
temperature increases
• >30˚C: Growth rates may reduce
due to photorespiration: oxygen
competes with CO2 for the
enzyme RuBisCO’s active site.
Reduces amount of CO2 being
accepted by RuBP and so
reduced the quantity of GP and
therefore of TP being produced,
whilst whilst initially causing an
accumulation of RuBP. However
due to the lack of TP, RuBP cannot
be regenerated
• >45˚C: Enzymes involved in
photosynthesis may be denatured.
This reduces the concentrations of
GP and TP, and eventually RuBP
as it cannot be regenerated
```
