HESI A2 Biology Study Guide 2023
Cellular respiration is the process inside of cells that converts nutrients (such as sugars, amino acids, and
fatty
... [Show More] acids) into ATP (adenosine triphosphate), which is used throughout the organism for energy. Large
molecules are broken into smaller molecules, which releases both energy and waste.
Aerobic respiration occurs in the presence of Oxygen and has four main stages:
Glycolysis: Larger sugar molecule is broken down into 2 smaller sugar molecules in the cytoplasm.
Net gain of 2 ATP and 2 NADH
Formation of Acetyl CoA: Pyruvate undergoes oxidative decarboxylation to form Acetyl coenzyme
A. 1 CO2 is released as waste. Net gain of 2 NADH.
Citric acid cycle: also known as Krebs cycle. The 2 small sugar molecules produced during
glycolysis are oxidized forming new products. Gain of 2 ATP, 6 NADH, 2 FADH2.
Electron transport chain: redox reaction involving the electrons removed during glycolysis and the
Krebs cycle. Protons are pumped across the mitochondrial membrane to form a gradient, which
drives the synthesis of 34 ATP.
Anaerobic respiration is a type of cellular respiration which occurs when oxygen is not present. This process
is most commonly performed by bacteria and Achaea. These organisms use this process to obtain energy
because they live in environments with low oxygen levels. Example: Achaea called methanogens use
carbon dioxide to accept electrons. Methanogens can be found in soil and the digestive systems of animals
called ruminants, which includes cows and sheep.
Anaerobic respiration, similar to aerobic cellular respiration, uses electrons from the fuel molecules to pass
through the electron transport chain, which drives ATP synthesis. The electron transport chain moves
electrons to create a proton gradient that allows for the synthesis of ATP. Electron transport chains are
used for extracting energy. This can happen in plants, where the energy from the sunlight is used to create
glucose and oxygen through photosynthesis in the chloroplast. Eukaryotes perform this process in the
mitochondria.
Fermentation is another type of cellular respiration which occurs in the absence of Oxygen. Organisms
capable of fermentation include prokaryotes, yeast, and multicellular organisms such as humans.
Feature
Aerobic Respiration
Anaerobic Respiration
Oxygen requirement
Yes, always
No, never
Waste products
Carbon dioxide and water
Carbon dioxide and ethanol
Efficiency in releasing energy
from glucose
Very efficient
(most of the energy is released
from glucose)
Less efficient
(some energy locked in ethanol
is not released)
Some energy released as heat
Yes
Yes, but less than that for
aerobic respiration [Show Less]