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Plant Biology - Prokaryotes and Viruses

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    Study Guide Plant Biology – Prokaryotes and Viruses 1. Reproduction Bacteria reproduce mainly by asexual reproduction , which means only one parent cell is involved. In this process, a single bacterial cell divides into two new cells. Even though bacteria do not reproduce sexually like plants or animals, they can exchange genetic material (DNA) with each other. These methods are much simpler than the complex processes of mitosis and meiosis seen in eukaryotic cells. 1.1 Asexual Reproduction Bacteria use several types of asexual reproduction. The three most common ones are explained below. 1.1. 1. Binary Fission (Most Common) This is the main way bacteria reproduce. • First, the bacterial chromosome copies itself. • The two copies move to opposite ends of the cell. • The cell wall then grows inward and splits the cell into two identical cells. • There is no mitosis and no microtubules involved. • The entire process is very fast and usually takes 30 minutes to 3 hours . 1.1. 2. Fragmentation • This occurs in bacteria that grow in long chains or filaments. • The filament breaks into smaller pieces. • Each fragment can grow into a complete new bacterial cell.

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    Study Guide 1.1. 3. Budding • A small outgrowth called a bud forms on the parent cell. • The bud pinches off from the parent. • It then grows and develops into a new bacterial cell. 1.2 Gene Exchange in Bacteria Because bacteria do not have a nucleus , they cannot reproduce sexually. However, they still exchange DNA in several ways. This exchange increases genetic diversity and helps bacteria adapt to new environments. 1.2. 1. Conjugation • Two bacterial cells connect using a structure called a sex pilus . • This pilus acts like a bridge between the cells. • DNA is transferred from the donor cell to the recipient cell. 1.2. 2. Transformation • Some DNA exists freely in the environment. • This DNA usually comes from dead bacteria or is released by living ones. • Other bacteria can take up this free DNA and use it as their own. 1.2. 3. Transduction • This method involves bacteriophages , which are viruses that infect bacteria. • When a virus moves from one bacterial cell to another, it may carry bacterial DNA with it. • That DNA is then introduced into the new host cell. • Scientists use this same process in biotechnology to insert new genes into organisms.

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    Study Guide 1.3 Mutation • Mutations are random changes in a bacterium’s DNA. • These changes can affect how the bacterium responds to its environment. • Harmful mutations usually cause the bacterium to die. • Helpful mutations give the bacterium an advantage and spread quickly as bacteria reproduce rapidly. Key Takeaway Bacteria may be simple organisms, but they are extremely efficient at reproducing and sharing genetic information. This ability helps them survive, adapt, and evolve rapidly in changing environments. 2. Prokaryote Metabolism Prokaryotes are the most metabolically diverse organisms on Earth . This means they have many different ways to get energy and carbon , which they need to build cells and stay alive. Most eukaryotes (plants, animals, fungi) follow similar metabolic pathways. In contrast, prokaryotes use a wide variety of materials and pathways , some of which are not used by any other organisms. All organisms need: • Carbon to build molecules like proteins and DNA • Energy to power life processes Scientists use different terms to describe how organisms get their energy and carbon. These terms are sometimes used inconsistently, which can be confusing. The table below summarizes the most common metabolic terms. 2.1 Purpose of this image:

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    Study Guide This table explains how organisms are classified based on: • Energy source (sunlight or chemicals) • Carbon source (carbon dioxide or organic compounds) • Electron source (inorganic or organic molecules)

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    Study Guide It helps students understand terms like: • Photoautotroph • Chemoheterotroph • Lithotroph • Organotroph 2.2 Photosynthesis in Prokaryotes Some prokaryotes can make their own food using photosynthesis . However, not all photosynthetic prokaryotes work the same way as plants. 2.3 Cyanobacteria (Blue - Green Algae) Cyanobacteria are important photosynthetic prokaryotes . Key features: • They use chlorophyll a , the same pigment found in plants. • They also contain accessory pigments called phycobilins : o Phycocyanin (blue) o Phycoerythrin (dark red) These pigments help cyanobacteria capture light energy more efficiently. Some cyanobacteria grow on melting snow in cold regions, turning the snow pink or red in spring. Photosynthesis in cyanobacteria: • Takes place on thylakoid - like membranes • Uses water as the hydrogen donor • Releases oxygen as a by - product , just like plants Cyanobacteria are common in marine plankton . Long ago, their photosynthesis helped change Earth’s atmosphere from oxygen - free to oxygen - rich , allowing oxygen - using eukaryotes to evolve.

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    Study Guide 2.4 Purple and Green Bacteria These bacteria also perform photosynthesis, but in a different way . Important points: • They are anaerobic (do not use oxygen) • They do not produce oxygen • Their pigments include bacteriochlorophylls and carotenoids • They do not have phycobilins Types: • Purple sulfur & green sulfur bacteria o Use sulfur compounds as electron donors • Purple nonsulfur & green nonsulfur bacteria o Use organic compounds like alcohols and fatty acids Green sulfur bacteria are photolithoautotrophs , meaning: • Photo → energy from sunlight • Auto → carbon from CO ₂ • Litho → electrons from inorganic compounds Scientists believe: • Purple bacteria are ancestors of Photosystem II • Green bacteria are ancestors of Photosystem I 2.5 The Nitrogen Cycle and Prokaryotes Prokaryotes are essential to the nitrogen cycle . They move nitrogen into , through , and out of ecosystems .

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    Study Guide This diagram visually explains: • Nitrogen fixation • Nitrification • Ammonification • Denitrification 2.6 Nitrogen Fixation • Only prokaryotes can fix atmospheric nitrogen (N ₂ ). • They convert N ₂ into ammonia (NH ₃ / NH ₄⁺ ) . • Some nitrogen is used by bacteria; the rest enters the soil.

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    Study Guide Where nitrogen - fixers live: • Free - living soil bacteria • Root nodules of legumes • Symbiotic relationships (lichens, cycads, ferns) • Cyanobacteria in lakes and oceans 2.7 Nitrification This is a two - step process : 1. Ammonia → Nitrite (NO ₂⁻ ) 2. Nitrite → Nitrate (NO ₃⁻ ) • Done by chemolithoautotrophs • Energy released is used to fix CO ₂ • Plants can absorb nitrate , but nitrite is toxic 2.8 Ammonification (Mineralization) • Carried out by saprophytic bacteria and fungi • Breaks down nitrogen - containing organic matter • Releases ammonia back into the soil Without this process: • Nutrients would become locked up • Life would eventually stop 2.9 Denitrification • Converts nitrate back into N ₂ or N ₂ O • Done by anaerobic bacteria • Occurs when oxygen is limited in soil • Nitrate replaces oxygen as the electron acceptor

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