L15: Nutritional Categories

Question 1

How are nutrional categoeis defines

Answer 1

source, electrons (reducing equivalents), carbon

Question 2

Phototrophs

Answer 2

– use light as an energy source (i.e., in photophosphorylation)
– some phototrophs can switch to a chemotrophic strategy during
dark period

Question 3

Chemotrophs

Answer 3

– obtain (conserve) energy from biochemical reactions
– breaking and forming of chemical bonds
– aerobic/anaerobic respiration, fermentation, methanogenesis
– biochemical energy can be conserved by formation of energy-
storage compounds i.e., ATP, carbohydrate polymers i.e.,
glycogen, polyhydroxybutyrate, etc
– biochemical energy can be interconverted with membrane
potential

Question 4

What do cells use energy for

Answer 4

energise cytplamic membrane via electron flow and maintenance of proton gradeint

*the gradeint interconverted with ATP, NAD(P)H

Question 5

Autotrophs needs energy

Answer 5

to fuel carbon fixation

Question 6

diazatrophs need energy…

Answer 6

to feul N2 fixation

Question 7

Organotrophs

Answer 7

obtain electrons from organic compounds

Question 8

Lithotrophs

Answer 8

obtain electrons from inorganic compounds

Question 9

What happens to ep

Answer 9

– electrons are transferred to coenzymes such as NAD + or
NADP +, reducing them to NAD(P)H
– in phototrophs this is often light-driven
– in chemotrophs it is mediated by enzymatic reactions
– some electrons are used to reduce compounds in the cell
– some electrons are dumped onto electron acceptors and form
waste products (respiration, methanogenesis, fermentation)

Question 10

What happens to NAD(P)H

Answer 10

– source of electrons for enzymatic reactions requiring reducing
equivalents, thus for biosynthesis (all cells)
– source of electrons for the electron transport chain, to fuel the
proton gradient and thus ATP synthesis, in chemotrophs that use
respiration (aerobic or anaerobic)

Question 11

chemolithotrophs, photolithotrophs and lithotrophs

Answer 11

hemolithotrophs:
– organisms that use inorganic compounds as the source of energy nd electrons
– chemolithoautotrophs and chemolithoheterotrophs

Photolithotrophs:
– organisms that use light energy and obtain electrons from inorganic compounds
– photolithoautotrophs and photolithoheterotrophs

lithoautotrophs are common because organisms that fix CO 2
often obtain electrons from inorganic compound

Question 12

Organotropjs

Answer 12

Photoorganotrophs:
– organisms that use light energy and obtain electrons from
organic compounds
– photoorganoheterotrophs and photoorganoautotrophs

Chemoorganotrophs:
– organisms that use organic compounds as the source of energy
and reducing equivalents (electrons)

Question 13

chemoORGANOtrophs

Answer 13

organisms that use organic compounds as the source of energy
and electrons
– organoheterotrophs are common because many organisms
utilize the same compound as source of carbon and electrons
– chemoorganoheterotrophs may utilize the same compound as
source of carbon, electrons and energy
– chemoorganoautotrophs utilize organic compounds as their
source of electrons and energy but not carbo

Question 14

Hetertrophs

Answer 14

– assimilate organic compounds as C source for growth
– may or may not use organic compounds as energy and/or
electron sources
– take up organic compounds and then use them as the source of
carbon in their own biosynthetic reactions
– sugars, organic, amino, nucleic and fatty acids, etc
– some CO 2 may be re-fixed via enzymes like PEP carboxylas

Question 15

Autotrophs

Answer 15

obtain carbon from inorganic sources (CO 2 , CH 4 )

Question 16

What is mixotrophy

Answer 16

switching between metabolic strategies based on conditions

Question 17

List the life strategies

Answer 17

Chemolithoautotrophs
Photoautotrophs
Photoheterotrophs
Chemoorganoheterotrophs
Chemolithoheterotrophs

Question 18

Phototrophs

Answer 18

energy from light, carbon from CO 2

– photolithoautotrophs
–e- ’s come from inorganic compounds (H 2 O, H 2 S, H 2 , etc)
– plants, cyanobacteria, green & purple sulfur bacteria etc

– photoorganoautotrophs
–organisms that would use organic electron donors and fix CO 2
at the same time may not exist
–organisms that can use organic electron donors and can fix CO 2
exist but are not known to do these at the same time in nature

Question 19

Chemolithoautotrophs

Answer 19

– energy and reducing equivalents from oxidation of inorganic
compounds
– carbon source CO 2 or CH 4
– S-oxidizing bacteria, hydrogen bacteria, nitrifiers, iron bacteria

Question 20

Photoheterotrophs

Answer 20

– energy from light, carbon (and electrons) by assimilation of
organic compounds
– P/S bacteria and archaea that cannot fix CO 2
– mostly (only?) photoorganoheterotrophs
– photolithoheterotrophism is possible (in the lab) but may only
occur rarely in nature (not known)

Question 21

Chemoorganoheterotrophs

Answer 21

– energy and reducing equivalents from oxidation of organic
compounds
– obtain carbon by assimilation of organic compounds
– very common in bacteria, animals and other organisms referred to
simply as heterotrophs i.e., fungi etc.

Question 22

Chemolithoheterotrophs

Answer 22

– energy and reducing equivalents from oxidation of inorganic
compounds i.e., H 2 gas
– obtain carbon by assimilation of organic compounds
– among the chemolithoautotrophic groups are some exceptions
that do not seem to fix CO 2 (some Achromatium sp. isolates), and
thus would have to be chemolithoheterotrophs