Clear, concise, effective summary notes covering all points in Topic 12: Energy and Respiration of the new 2022-24 CIE A Level Biology syllabus. A must-have revision tool that helped me achieve an A* in A-Level Biology.
Topic 12: Energy and respiration
Energy
● need for energy
Transport of substances eg. active transport, exocytosis, Na-K pump (3 Na+
out for 2 K- in)
Movement eg. chromosome movement, muscle contraction
by active potentials
Anabolic reactions synthesis of larger biological molecules eg. DNA,
proteins
Homeostasis birds & mammals
● sources of energy
Autotrophs Heterotrophs
synthesise own E. by converting inorganic obtain E. from already-made organic compounds
compounds to organic compounds
from photosynthesis from ingesting food
light E. from sun → chemical potential E. in
carbs. → broken down by respiration →
ATP & E./modified & combined → other
essential organic compounds
● ATP
○ small, soluble molecule providing ST store of chemical energy used by cells as work
○ adenine + ribose (5C) + 3 Pi
○ described as ‘universal energy currency’
■ universal – used by all organisms
■ currency – used & reused in circulation for different purposes
○ features that make ATP suitable as universal energy currency
small but sufficient amount of E. released from drive metabolic reactions while keep E. usage low
complete ATP hydrolysis
hydrolysis quick & easy allows cell to respond to sudden ↑ E. demand
stable molecule in cellular pH only broken down by enzyme eg. ATPase → E. not
wasted
recyclable → ATP + H2O ⇔ ADP + Pi + E. same molecule can be reused elsewhere in cell
soluble moves easily w/in cells → can transport E. to
different parts of cell
forms phosphorylated intermediates of metabolic make them more reactive → ↓ Ea needed for
compounds reaction
, ○ ATP hydrolysis
■ ATP → ADP → AMP → adenosine
■ 30.5 kJmol-1 + 30.5 kJmol-1 + 14.2 kJmol-1 = 75.2 kJmol-1 E. released from complete
hydrolysis (3 H2O needed)
○ ATP synthesis
■ body does not store large amounts of ATP → makes them as it needs E.
■ E. used, H2O released
■ carried out by substrate-linked phosphorylation & chemiosmosis
Substrate-linked phosphorylation Chemiosmosis
transferring a Pi directly from organic generates ATP from ATP synthase using flow of
intermediate/substrate molecule to ADP H+s down electrochemical gradient
during glycolysis & Krebs cycle during oxidative phosphorylation &
light-dependent stage
Aerobic respiration
● overview of stages
Glycolysis glucose phosphorylated & then in cytoplasm
broken down into 2 pyruvate
compounds
Link reaction pyruvate decarboxylated & in mitochondrial matrix
dehydrogenated into acetyl CoA
Krebs cycle acetyl CoA converted into CO2 in mitochondrial matrix
w/ intermediates recycled
Oxidative phosphorylation energy created by electron in inner membrane of
transport chain (ETC) used to mitochondria
carry out chemiosmosis to
create an electrochemical
gradient that makes ATP
● electron shuttles
○ carry e-s & H+s from glycolysis, link reaction, Krebs cycle to ETC in reduced state & then
recycled
■ ∴ aka. hydrogen carriers
■ NB. reduced ≡ ↑ e-/H+
○ by coenzymes NAD+ (nicotinamide adenine dinucleotide) & FAD
■ coenzyme – molecule necessary for enzyme function but does not take part in
reaction itself
■ 1 molecule carries 2e-
○ NAD+ + 2H ⇔ NADH (reduced) + H+
■ occurs in all stages
○ FAD + 2H ⇔ FADH2 (reduced)
■ occurs in Krebs cycle & oxidative phosphorylation
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