HESI A2 Biology Study Guide

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Ready For The

HESI A2

Biology Study

Guide

• Chapter summaries

• Biology vocabulary

• HESI-style Biology Practice

Questions

• Diagrams and explanations

• 24/7 Email Support

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HESI A2 Biology Study Guide

Cellular respiration

Cellular respiration is the process inside of cells that converts nutrients (such as sugars, amino acids, and

fatty 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

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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 cannot

battle the bacteria. If enough antibiotic is present,

the bacterial cell is crippled and stops growing,

known as bacteriostatic, or it simply dies, known

as the bactericidal effect. Antibiotics do not affect

viruses, fungi or parasites as they bind only to

bacterial cell targets.

Some bacteria have the ability to become antibiotic resistant. This happens when bacteria have

overexposure to antibiotics. The bacteria no longer are affected by the antibiotic because it undergoes

mutations.

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Cells and tissues

The basic building block of the body is the cell. Cells can perform a wide variety of functions, depending on

the specialized type of cell that it is. Every type of cell plays a vital role in growth, development, and

maintenance of the body.

Cells from all organisms, ranging from humans to plants to bacteria, share certain characteristics. There

are two categories that cells fall into: prokaryotic and eukaryotic. Prokaryotic cells are single-celled

organisms from the domains Bacteria and Archaea. “Pro-” means before and “kary-” means nucleus, hence

prokaryotic cells lack a nucleus and other membrane-bound organelles. Eukaryotes are made of two or

more cells. “Eu-” means true, which means that eukaryotic cells have a nucleus. All types of cells share

four key components: plasma membrane, cytoplasm, DNA and ribosomes.

Prokaryotic cells have DNA, but it is not housed in a

nucleus. The majority of the DNA in prokaryotic cells is

found in a central region of the cell called the nucleoid.

Bacteria are a specific type of prokaryotic cell. Most

bacteria are surrounded by a rigid cell wall, which

provides an extra layer of protection, helps the cell

maintain its shape and prevent dehydration. Many

bacteria have an outermost capsule that is sticky and

helps the cell attach to its surroundings. Some bacteria

also have a flagellum. It is a whip-like structure that acts

like a motor to help the bacteria to move. Fimbriae are

hair-like structures that are used to attach to other

surfaces or host cells. Sometimes bacteria have pili,

which allows the cell to transfer DNA to other bacteria or

helps with locomotion (movement).

Eukaryotic cells are significantly more complex

compared to prokaryotic cells. They contain a variety

of different compartments that have specialized

functions, and are separated by layers of

membrane. This organization allows each

compartment to maintain its respective conditions

and do what it needs to carry out its job. These

compartments are called organelles. Unlike

prokaryotic cells, eukaryotic cells have a nucleus,

membrane-bound organelles, and multiple linear

chromosomes. Eukaryotic cells have an array of

organelles that are important for energy balance,

metabolism, and gene expression.

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