BIOLOGYINDEEP

• 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 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;

• 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!!!<33 u="">

• 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]

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