Ecosystems

Metabolism
All chemical reactions in a cell → arranged into metabolic pathways
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 StructureCuctile → 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 numbersTotal 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 biomassTotal 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 energyAmount 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…