Home Page Textbooks Prentice Hall Biology (California) Section 19.1: Bacteria

Prentice Hall Biology (California)

1st Edition

Kenneth R. Miller, Levine

ISBN: 9780132013529

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Section 19.1: Bacteria

Exercise 1

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There are two kingdoms that consist only of prokaryotes. These are the kingdoms **Archaebacteria** and **Eubacteria**. Each kingdom has their own similarities and differences.

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Members of kingdom Eubacteria consist of unicellular prokaryotes with cell walls that contain peptidoglycan. Many species contain a single membrane that surrounds their cytoplasm. In some cases, they may also have two separate cell membranes.

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On the other hand, members of kingdom Archaebacteria also consist of unicellular prokaryotes with cell walls. However, their cell walls lack peptidoglycan. One of their distinctive features is that they are capable of surviving in most extreme environments.

Exercise 2

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Prokaryotes are identified by characteristics such as shape, chemical nature of cell walls, movement, and the way they obtain energy.

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The identification of prokaryotes can be based on many observable characteristics such as their shape (spherical, rod-shaped, spiral) and their cell wall composition (e.g. peptidoglycan).

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Prokaryotes can also be identified based on the mode of locomotion and mode of nutrition. They may possess locomotive structures such as cilia or flagella. They may also be autotrophic or heterotrophic in terms of obtaining energy.

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Aside from that, prokaryotes can also be identified based on how they process the energy they obtain. Some species may undergo fermentation, others may undergo cellular respiration, and some may even be capable of performing both.

Exercise 3

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Bacteria play an important ecological role in the environment as the **decomposers**. They help break down organic matter into simpler substances that can be taken up by other organisms.

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Therefore, decomposers such as bacteria help in the recycling of nutrients in the ecosystem. Without them, dead organic matter will accumulate and may cause the ecosystem to collapse.

Exercise 4

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Most prokaryotes usually have a cell wall, which may contain a thick layer of peptidoglycan or may contain little to no peptidoglycan at all. Prokaryotes also have a single cell membrane; however, in some cases, they may also have two separate cell membranes.

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One of the distinctive features of all prokaryotes is the lack of membrane-bound organelles such as nuclei. Therefore, their DNA as well as their cytoplasmic constituents (such as ribosomes) are floating freely in their cytoplasm.

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In some prokaryotes, the presence of locomotive structures such as cilia and flagella can be observed. These structures are used in the movement of the prokaryote. Conjugative pili may also be present, which are used for bacterial conjugation.

Exercise 5

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Prokaryotes can be classified into two categories based on how they obtain energy. The first category are **phototrophs**, which can obtain their energy by deriving it from sunlight.

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The second category are **chemotrophs**, which obtain their energy from organic chemical compounds in the environment. Unlike phototrophs, they cannot obtain energy from sunlight.

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Furthermore, prokaryotes can also be classified based on how they obtain their carbon source. **Autotrophs** obtain their carbon from carbon dioxide (CO$_2$) in the atmosphere, while **heterotrophs** obtain their carbon from organic chemical substances in the environment.

Exercise 6

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Gram-positive bacteria possess a cell wall that contains a thick layer of peptidoglycan that protects them. However, they are vulnerable to drugs that target the cell wall by inhibiting peptidoglycan synthesis.

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On the other hand, Gram-negative bacteria also possess a cell wall with a thin layer of peptidoglycan. However, they are more resistant to drugs against the cell wall because they possess two separate cell membranes – inner and outer membrane.

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The outer membrane, in particular, is what gives Gram-negative bacteria their drug resistance. The outer membrane contains a layer called the lipopolysaccharide (LPS) layer that prevents drugs from diffusing into the cell, which effectively protects the bacterium.

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Section 19.1: Bacteria

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