Energy and Respiration for A Level Biology Students PDF

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Energy and respiration (chapter 12):

 Energy in living organisms needed for:

 Anabolic reactions:

 Protein synthesis / DNA replication / glycogenesis / polymerisation

 Cellular work:

 Active transport / movement of chromosomes / sliding filaments /

movement of vesicles

 Movement

 Maintenance of body temperature in endotherms

 Glucose is stable due to its activation energy – lowered by enzymes and raising the energy

level of glucose by phosphorylation

 These reactions are all reversible; the interconversion of ATP and ADP is given by:

 Features of ATP that make it suitable as the universal energy currency:

 Loss of phosphate / hydrolysis, leads to energy release

 Small packets of energy

 Small / water-soluble, so can move around cell

 Immediate energy donor

 Acts as link between energy-yielding and energy-requiring reactions

 High turnover

 Excess energy during transfer and reactions are converted into thermal energy

 Four stages in aerobic respiration:

 Glycolysis – cytoplasm:

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 Glucose phosphorylated by ATP

 Raises energy level / overcomes activation energy to form fructose bisphosphate

 Lysis / splitting of glucose / hexose

 Breaks down to two TP (triose phosphate)

 6C (hexose bisphosphate) into 2 3C (triose phosphate) which is then

dehydrogenated; hydrogen transferred to NAD

 2 reduced NAD formed from each TP

 4 ATP produced; final net gain of 2 ATP

 Pyruvate produced

 Link reaction – mitochondrial matrix:

 Pyruvate passes by active transport from the cytoplasm through the outer and

inner membranes of a mitochondrion

 Undergoes decarboxylation, dehydrogenation (hydrogen transferred to NAD) and

combined with coenzyme A (CoA) to give acetyl coenzyme A

 Role of CoA:

 Combines with acetyl group in the link reaction

 Delivers acetyl group to the Krebs cycle

 Acetyl group combines with oxaloacetate

 Krebs cycle – mitochondrial matrix:

 Reactions are catalysed by enzymes

 Acetyl CoA combines with a four-carbon compound (oxaloacetate) to form a six-

carbon compound (citrate)

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 Citrate is decarboxylated and dehydrogenated – through intermediate compounds

– to yield CO

(waste gas) and hydrogens are accepted by hydrogen carriers (NAD

and FAD) to form reduced NAD and reduced FAD

 Oxaloacetate is regenerated to combine with another acetyl CoA

 Two CO

are produced

 One FAD and three NAD molecules are reduced

 One ATP molecule is generated (substrate-level phosphorylation)

 Oxidative phosphorylation – inner mitochondrial membrane:

 Reduced NAD / FAD are passed to the electron transport chain (ETC) on the inner

membrane of the mitochondria (cristae)

 Hydrogen released from reduced NAD / FAD and splits into electron and proton

 Electrons are passed along the electron carriers on the ETC

 Energy released from the electrons, pumps protons into the intermembrane space

 Proton gradient is set up

 Protons diffuse back through the membrane – through ATP synthase – down the

potential gradient

 Oxygen acts as the final electron acceptor; acts as proton acceptor to form water;

allows ETC to continue and ATP to be produced

Overview

Energy and Respiration for A Level Biology Students

Energy and respiration are crucial topics in A Level Biology, focusing on how living organisms convert energy for cellular processes. This resource provides detailed explanations of aerobic and anaerobic respiration, including glycolysis, the Krebs cycle, and oxidative phosphorylation. Ideal for A Level students preparing for exams, it covers essential concepts and mechanisms involved in energy production. The document also discusses the role of ATP and NAD in cellular respiration, making it a comprehensive study aid for understanding metabolic pathways. Key Points Explains the four stages of aerobic respiration: glycolysis, link reaction, Krebs cycle, and oxidative phosphorylation. Details the role of ATP as the universal energy currency in living organisms. Covers anaerobic respir…

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FAQs

What are the main stages of aerobic respiration?

Aerobic respiration consists of four main stages: glycolysis, the link reaction, the Krebs cycle, and oxidative phosphorylation. Glycolysis occurs in the cytoplasm, where glucose is broken down into pyruvate, yielding a net gain of ATP. The link reaction takes place in the mitochondrial matrix, converting pyruvate into acetyl CoA. The Krebs cycle further processes acetyl CoA, producing CO2 and reducing NAD and FAD. Finally, oxidative phosphorylation occurs in the inner mitochondrial membrane, where the electron transport chain generates ATP using the energy from electrons.

How does ATP function as an energy currency in cells?

ATP, or adenosine triphosphate, serves as the primary energy currency in cells due to its ability to release energy when its phosphate bonds are hydrolyzed. This process occurs when ATP loses a phosphate group, converting into ADP (adenosine diphosphate) and releasing energy for cellular activities. ATP is small and water-soluble, allowing it to easily move within cells to provide immediate energy for processes such as active transport, muscle contraction, and biosynthesis. Its high turnover rate ensures a constant supply of energy for cellular functions.

What is the significance of the Krebs cycle in cellular respiration?

The Krebs cycle, also known as the citric acid cycle, is a crucial part of cellular respiration that occurs in the mitochondrial matrix. It processes acetyl CoA derived from carbohydrates, fats, and proteins, generating energy-rich molecules such as NADH and FADH2. These molecules are essential for the electron transport chain, where they contribute to ATP production through oxidative phosphorylation. Additionally, the Krebs cycle produces CO2 as a waste product, which is expelled from the organism. Its role in linking metabolic pathways makes it vital for energy production.

What are the differences between aerobic and anaerobic respiration?

Aerobic respiration requires oxygen and occurs in the presence of it, producing a high yield of ATP through the complete oxidation of glucose. In contrast, anaerobic respiration occurs in the absence of oxygen, resulting in lower ATP yields and the production of byproducts such as lactic acid or ethanol. While aerobic respiration involves multiple stages including glycolysis, the Krebs cycle, and oxidative phosphorylation, anaerobic respiration primarily relies on glycolysis followed by fermentation processes. This distinction is crucial for understanding how different organisms adapt to varying oxygen availability.

How do respiratory substrates affect energy production?

Respiratory substrates, such as carbohydrates, fats, and proteins, significantly influence the amount of energy produced during respiration. Carbohydrates, particularly glucose, are commonly used for energy, yielding a moderate amount of ATP. Fats, however, have a higher energy value due to their greater number of C-H bonds, resulting in more ATP production per gram. Proteins can also be utilized as energy sources, but this occurs less frequently and typically under conditions of starvation. Understanding the energy values of these substrates is essential for comprehending metabolic efficiency.

Key Points

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