Food, energy and cellular respiration

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Lesson notes

Energy Needs of Organisms

All living things need energy to survive.
Plants are producers: they get energy from the sun via photosynthesis and store it as chemical energy in glucose.
Animals are consumers: they must eat food to obtain energy.
Food provides both energy and matter for growth and repair.

Cellular Respiration Overview

Cellular respiration is the process by which cells break down glucose to release stored chemical energy.
It requires glucose and oxygen.
We get oxygen by breathing and glucose by eating.
Respiration occurs in all living organisms, including plants and decomposers.

Getting the ingredients for cellular respiration

Products of Cellular Respiration

Cellular respiration releases energy, carbon dioxide, and water.
Energy is the main useful product; carbon dioxide and water are waste products.
Carbon dioxide is removed from the body by breathing out.
Water can be felt when breathing on your hand.

Chemical Equation for Respiration

The equation for respiration is: glucose + oxygen → carbon dioxide + water + energy.
This is the opposite of photosynthesis in terms of reactants and products.
Photosynthesis stores energy in glucose; respiration releases that energy.

Cellular respiration: changes in matter and energy

Energy Currency: ATP

Cellular respiration converts chemical energy in glucose into ATP.
ATP is the molecule that powers cellular work.
In animals, ATP energy is converted to mechanical and heat energy.
This energy enables activities like muscle movement and heart pumping.

Importance of Food: Energy

Food labels show calories, a measure of energy released by respiration.
Simple sugars provide quick energy but can lead to a 'crash'.
Complex carbohydrates take longer to break down, providing sustained energy.
A balanced diet ensures a constant energy supply.

Importance of Food: Matter

Food provides matter for growth and repair.
Proteins are broken into amino acids to build muscles, enzymes, hormones, etc.
Nutrients like iron are needed for hemoglobin to carry oxygen.
The atoms from food rearrange to become the molecules of our body.

Molecules built from food

Circulation and Respiration Link

Blood carries oxygen and glucose to cells, and carries carbon dioxide away from them.
Cellular respiration itself happens inside mitochondria within each cell.
The heart keeps blood moving so this delivery and removal can continue nonstop.

Testing for Carbon Dioxide

Carbon dioxide can be detected using limewater.
Bubbling gas through clear limewater turns it milky if CO2 is present.
Human breath contains CO2 from respiration.
Atmospheric air has very little CO2 (0.03%).

Testing breath for carbon dioxide with limewater

Respiration vs. Breathing

Breathing is the physical act of inhaling and exhaling air.
Respiration is the metabolic process that releases energy from glucose.
Breathing supplies oxygen for respiration and removes carbon dioxide.
Do not confuse the two terms.

Slides

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Practice questions

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1.What is the main purpose of cellular respiration?
Easy
- ATo release energy from glucose
- BTo produce glucose
- CTo absorb sunlight
- DTo exchange gases
2.A student eats cereal with milk for breakfast. The food is broken down and used in the student's cells during cellular respiration. An incomplete model of the reaction is shown: two reactants react to form carbon dioxide, water, and energy. Which pair of reactants correctly completes the model?
Medium
- AFood molecule + oxygen → carbon dioxide + water + energy
- BOxygen + energy → carbon dioxide + water + food molecule
- CEnergy + food molecule → carbon dioxide + water + oxygen
- DFood molecule + energy → carbon dioxide + water + energy
3.Cellular respiration occurs only in animals.
Easy
True or false?
4.Which of the following is NOT a product of cellular respiration?
Easy
- AGlucose
- BCarbon dioxide
- CWater
- DEnergy
5.Breathing and respiration are the same thing.
Easy
True or false?
6.Which molecule is the main energy currency of the cell?
Easy
- AATP
- BGlucose
- CCarbon dioxide
- DOxygen
7.Which of the following is a by-product of respiration that is removed by breathing out?
Medium
- ACarbon dioxide
- BOxygen
- CGlucose
- DATP
8.Plants do not undergo cellular respiration because they make their own food.
Easy
True or false?

Revision notes

## Cellular Respiration: Energy from Food - **Cellular respiration** is the process cells use to break down food molecules (like glucose) and release energy stored in ATP. - **Overall reaction** (aerobic): Glucose + Oxygen → Carbon dioxide + Water + ATP (energy) - **Key point**: Energy is released slowly in controlled steps, not all at once like burning. ### Types of Respiration - **Aerobic respiration**: Uses oxygen (O₂) as the final electron acceptor. Produces up to ~29–30 ATP per glucose. Much more efficient than anaerobic. - **Anaerobic respiration**: Uses an inorganic molecule other than oxygen (e.g., sulfate) as electron acceptor. Still produces ATP, but less than aerobic. - **Fermentation** (not respiration): No external electron acceptor; produces only 2 ATP per glucose. ### Main Stages (Aerobic) 1. **Glycolysis** (in cytosol): Splits one glucose (6C) into two pyruvate (3C each). Produces **2 net ATP** and **2 NADH**. No oxygen needed. - Reaction: Glucose + 2 NAD⁺ + 2 ADP + 2 Pi → 2 pyruvate + 2 NADH + 2 ATP + 2 H⁺ + 2 H₂O 2. **Pyruvate oxidation** (in mitochondria): Each pyruvate is converted to acetyl-CoA, producing NADH and CO₂. 3. **Krebs cycle** (in mitochondria): Acetyl-CoA is fully oxidized to CO₂. Produces ATP, NADH, and FADH₂. 4. **Electron transport chain & oxidative phosphorylation** (inner mitochondrial membrane): NADH and FADH₂ donate electrons, creating a proton gradient that drives ATP synthase. Most ATP is made here. ### Key Terms - **ATP (adenosine triphosphate)**: The main energy currency of the cell. Energy is released when the third phosphate bond is broken. - **Glycolysis**: "Sugar splitting" – first step of respiration, occurs in cytosol, breaks glucose into pyruvate. - **Aerobic**: Requires oxygen. - **Anaerobic**: Does not require oxygen; uses other electron acceptors. - **Mitochondria**: Organelle where most of aerobic respiration occurs (Krebs cycle and ETC). - **NADH / FADH₂**: Electron carriers that transfer high-energy electrons to the electron transport chain. - **Oxidative phosphorylation**: Process that uses the electron transport chain and chemiosmosis to produce ATP. ### Efficiency - Aerobic respiration yields up to **29–30 ATP** per glucose. - Anaerobic (glycolysis only) yields **2 ATP** per glucose. - Aerobic is about **15 times more efficient** than anaerobic alone.

Cellular respiration: The process of oxidizing biological fuels using an inorganic electron acceptor (often oxygen) to produce ATP, which stores chemical energy for cellular activities.
ATP (adenosine triphosphate): The main energy currency of the cell; energy is released when the bond of its third phosphate group is broken, forming ADP and a free phosphate.
Glycolysis: A metabolic pathway in the cytosol that splits one glucose molecule into two pyruvate molecules, producing a net gain of 2 ATP and 2 NADH; occurs with or without oxygen.
Aerobic respiration: Cellular respiration that requires oxygen (O₂) as the final electron acceptor; produces carbon dioxide, water, and a large amount of ATP.
Anaerobic respiration: Cellular respiration that uses an inorganic molecule other than oxygen (e.g., sulfate) as the final electron acceptor; yields less ATP than aerobic respiration.
Mitochondria: Organelles in eukaryotic cells where the Krebs cycle and oxidative phosphorylation take place; the site of most ATP production in aerobic respiration.
NADH: An electron carrier molecule that transfers high-energy electrons to the electron transport chain, where they are used to produce ATP.
FADH₂: An electron carrier similar to NADH; donates electrons to the electron transport chain, contributing to ATP production.
Oxidative phosphorylation: The process in which ATP is formed using the energy released by the electron transport chain and chemiosmosis; produces most of the ATP in aerobic respiration.
Electron transport chain: A series of protein complexes in the inner mitochondrial membrane that transfer electrons from NADH and FADH₂ to oxygen, creating a proton gradient used to make ATP.

Flashcards

What is cellular respiration?

Cellular respiration is the process of oxidizing biological fuels (like glucose) using an inorganic electron acceptor (often oxygen) to produce ATP, which stores chemical energy for cellular activities.

What is the main purpose of cellular respiration?

The main purpose is to release chemical energy from nutrients and convert it into ATP, which cells use to power processes like biosynthesis, movement, and transport.

What does ATP stand for and why is it important?

ATP stands for adenosine triphosphate. It stores chemical energy in a form that cells can use; breaking the bond of its third phosphate group releases energy for cellular work.

What is the difference between aerobic and anaerobic cellular respiration?

Aerobic respiration uses oxygen as the final electron acceptor; anaerobic respiration uses an inorganic molecule other than oxygen (e.g., sulfate). Both produce ATP, but aerobic yields much more.

What is the overall chemical equation for aerobic cellular respiration?

Glucose + 6 O2 → 6 CO2 + 6 H2O + energy (ATP). The energy released is used to form ATP from ADP and phosphate.

Where does glycolysis occur in the cell?

Glycolysis occurs in the cytosol (cytoplasm) of cells.

What are the inputs and net outputs of glycolysis?

Inputs: glucose, 2 NAD+, 2 ADP, 2 π. Net outputs: 2 pyruvate, 2 NADH, 2 ATP (net), 2 H+, 2 H2O, and energy.

How many ATP molecules are produced per glucose during glycolysis?

Glycolysis produces 4 ATP total, but 2 are used in the preparatory phase, so the net gain is 2 ATP per glucose.

What happens to pyruvate after glycolysis in aerobic respiration?

Pyruvate is transported into the mitochondria, where it is oxidized and enters the citric acid cycle (Krebs cycle).

What are the main products of the citric acid cycle?

The citric acid cycle produces CO2, ATP (or GTP), NADH, and FADH2.

What is the role of the electron transport chain in aerobic respiration?

The electron transport chain uses electrons from NADH and FADH2 to pump protons across a membrane, creating a chemiosmotic gradient that drives ATP synthase to produce most of the ATP.

What is oxidative phosphorylation?

Oxidative phosphorylation is the process in which ATP is formed using the energy released by the electron transport chain and chemiosmosis; it produces most of the ATP in aerobic respiration.

How many ATP molecules can be produced from one glucose molecule in aerobic respiration?

The theoretical maximum is 38 ATP, but actual yields are about 29–30 ATP per glucose due to energy losses.

Why is aerobic respiration more efficient than anaerobic respiration?

Aerobic respiration yields up to 15 times more ATP per glucose (about 30 ATP) than anaerobic respiration (2 ATP).

What are the waste products of aerobic cellular respiration?

The waste products are carbon dioxide (CO2) and water (H2O).

What types of molecules can be used as fuel in cellular respiration?

Common fuels include sugars (like glucose), amino acids, and fatty acids.

What is the role of oxygen in aerobic respiration?

Oxygen acts as the final electron acceptor in the electron transport chain, allowing the production of large amounts of ATP.

What is the difference between cellular respiration and fermentation?

Cellular respiration uses an external electron acceptor (like oxygen) and produces ATP via an electron transport chain; fermentation does not use an external electron acceptor and yields only 2 ATP per glucose.

Where do the post-glycolytic reactions (Krebs cycle and oxidative phosphorylation) occur in eukaryotic cells?

They occur in the mitochondria.

What is the meaning of the term 'glycolysis'?

Glycolysis literally means 'sugar splitting' and refers to the breakdown of glucose into two pyruvate molecules.

What is the initial step of glycolysis?

Glucose is phosphorylated using one ATP to form glucose-6-phosphate, which increases its reactivity.

What is the net ATP yield from anaerobic respiration (glycolysis only)?

Anaerobic respiration (glycolysis) yields a net of 2 ATP per glucose molecule.

Do plants carry out cellular respiration?

Yes, plants respire; plant respiration accounts for about half of the CO2 generated annually by terrestrial ecosystems.

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