Intermediates in these pathways are called metabolites
Catabolic reactions (e.g. respiration) release energy
Anabolic reactions (e.g. photosynthesis) use up energy
Leaf Structure
Phototropism → growth towards light
Large leaf surface area → captures more light
Thin leaves → few cell layer → more light captured
by chlorophyll
Leaf mosaic increases leaf exposure to light
Internal Structure
Cuctile → reduces H2O loss by evaporation
Palisade mesophyll → chloroplast can move around
cell for max light absorption
Spongy mesophyll → allows diffusion of gases
through leaves
Phloem sieve tube → removes products of photosynthesis
Chloroplast
Thylakoid membrane: light-dependent → large surface
area
Associated with chlorophyll, accessory pigments, ETC, enzymes
Grana: stacks of thylakoid membranes
Enclose hydrogen reservoir used in chemiosmosis
Lamella: tubular extensions forming a network between grana
Stroma: RuBP carboxylase catalyses light independent reaction
Starch granule → insoluble storage carbohydrate
product of photosynthesis
Light Dependent Reaction
In Thylakoid Membrane / Granum
IMG 5-14-6
Chemiosmosis/Photophosphorylation produces ATP
//H+ from photolysis remain in thylakoid space
ETC releases energy
Used to pump H+ from stroma into thylakoid space
By active transport and electrochemical gradient
H+ conc in thylakoid space > stroma
H+ ions pass back from space between two mitochondrial
membranes
Through pores which are associated with the enzyme ATP
synthetase
Energy from the ETC will be used to produce ATP
Diffuse down conc gradient across thylakoid membrane
Produces ATP by photophosphorylation
Light Independent Reaction
In Stroma (Calvin Cycle)
IMG 5-14-6
Summary WITH IMG!!!!!!!!!!!!!!!
The light dependent reaction takes place in the chloroplast and
is important to produce ATP and NADPH + H+. Both molecules and carbon dioxide
(CO2) are needed in the light independent reaction (Calvin Cycle) to produce a
hexose sugar, such as glucose, from RuBP.
Glucose is used to in the mitochondrion to produce the energy
molecule ATP. NAD+ is also needed for respiration, but is not produced by
photosynthesis.
PARP (Poly-ADP-Ribose-Polymerase) and PARG
(Poly-ADP-Ribose-Glycohydrolase) are important if the plant is exposed to
excessive stress factors (such as extreme temperatures). Note: knowledge about
PARP and PARG is not required for your exam.
IMG
Picture 5-1 from Bayer research.
Genetic engineering improves crop yields,
Braving the drought [view article]
Energy Transfer
Ecological pyramids
Pyramids of numbers
Total number of organisms in a food chain at each trophic level
Highest number at the bottom (usually producers, then consumers)
Pyramid will be inverted if lots of small animals are feeding
off one large plant
Pyramids of biomass
Total biomass of organisms in a food chain at each trophic
level
Always pyramid shaped
Organisms multiplying rapidly may have biomass less than primary
consumers
Dry mass is measured / H2O stores no energy and varies in
different organisms
Pyramid of energy
Amount of energy transferred to each level of a food chain in
an ecosystem
Always pyramid-shaped / no energy loss
Transfer of energy between trophic levels
Food chains and food webs
Energy is used to produce new cells / remains fixed in that
organism
Energy is passed on to the next trophic level through feeding
Producers are photoautotrophs (plants)
Transduce light energy into chemical P.E. by forming new
tissues and storing organic compounds (starch, glucose, lipids, proteins)
Consumers are herbivores, carnivores and omnivores
Decomposers are detritivores and saprophytes
Break down dead complex organic molecules into simple inorganic
molecules
Food chains are feeding relationships and linked with each
other to form complex food webs
Some organisms feed on different trophic levels / leaves and
insects
Some organisms feed on different foods when they are larvae
(leaves) and when they are adult (nectar produced by different flowers)
Energy transfer and efficiency
2% of light energy is converted to chemical P.E. by
photosynthesis
Rest is lost reflection from leaves / heat loss / not all
wavelengths are utilised / light strikes non-photosynthetic structures
10% of that are passed on along trophic levels
Rest is lost in respiration / as heat/faeces/urine
Chemical P.E. / generates heat / stores energy by forming
organic matter (new cells)
Mammals are homeothermic / must maintain constant body temp
Warm environment / less energy maintains body temp / more
organic matter stored / more transferred to consumer
Small organisms / large surface area:volume ratio / lose high
amounts of energy
Carnivores fix organic matter more efficiently than herbivores
Herbivores feed on plants
Thus, take up cellulose and lignin / difficult to digest
Thus, more food passes through gut and is lost as faeces
Trout fix organic matter most efficiently, they are
Poikilotherms → must NOT maintain constant body
temp
More energy is used to fix organic matter
Carnivores are harvested while they are still young and grow
rapidly
Trout transfer most energy to consumer (human) in terms of food
[EXAM] Number of food chains is limited
Due to energy losses (at each trophic level)
In respiration/egestion/excretion/movement/as heat
(Too) little energy is left to sustain higher trophic levels/to
be passed on
Ecosystem
Ecosystem
Five Kingdoms
Human Activity
Inheritance
Nutrient Cycle
Photosynthesis
Selection
Variation
Content
Metabolism
Leaf Structure
Chloroplast
Light Dependent Reaction
Chemiosmosis/Photophosphorylation produces ATP
Light Independent Reaction
Summary WITH IMG!!!!!!!!!!!!!!!
Energy Transfer
Ecological pyramids
Transfer of energy between trophic levels
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