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
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
27
Q
What are the stages of noncyclic photophosphorylation
in PSI?
A
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
36
Q
Describe the stages in the
Calvin Cycle
A
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
Q
Why does the Calvin cycle
need to turn 6 times to make
one hexose sugar?
A
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
40
Q
How does light intensity
affect the rate of
photosynthesis?
A
• 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
Q
What is the effect of
changing the light intensity
on the Calvin cycle?
A
- GP cannot be reduced to TP
- TP levels fall and GP
accumulates - If TP levels fall, RuBP cannot be
regenerated
42
Q
What is the effect of
changing the CO2
concentration on the Calvin
cycle?
A
- RuBP cannot accept it, and
accumulates - GP cannot be made
- Therefore, TP cannot be made
