HESI A2 Biology Study Guide 2023
Cellular respiration is the process inside of cells that converts nutrients (such as sugars, amino acids, and
fatty acid... [Show More] s) 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
3 | P a g e
© 2017 All Rights Reserved. www.ReadyForTheHESI.org
Antibiotics
Antibiotics are a kind of medicine used to treat bacterial infections. Not all bacteria are bad or unhealthy.
Humans and other animals actually have a healthy ecosystem of bacteria, called normal flora. These are
the good kind of bacteria.
Pathogenic bacteria are the type which can cause infection. Some bacteria will cause infection no matter
where they are, but others are safe in some areas of the body, but become infectious when they wander to
a new location in the body. An example of this is if the bacteria in the gut, or intestines, were to try and live
in the bladder or another organ. This is what happens in case of a urinary tract infection. The body’s immune
system must try to fight and destroy the invading bacteria.
Antibiotics are chemicals that enter and stick to
certain parts of the bacterial cell. The parts where
the antibiotics can attach can be the
proteins/sugars in the bacterial cell wall or the
important enzymes that make new bacterial DNA
or proteins. This act of blocking these parts
interferes with the bacteria’s ability to survive and
multiply. If the correct antibiotic is used, the
bacteria will stop growing or die.
Without antibiotics, bacteria can grow and
multiply, especially if the immune system canno [Show Less]
