Molecules Needed by the Cells

Molecules Needed by the Cells

Middle School

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Learning Objectives

• Define metabolism and explain the process of cellular respiration.

• Identify the key molecules cells need to function, including glucose and amino acids.

• Describe how different body systems work together to support all of your cells.

• Explain how chemical reactions in your body release energy from food.

Key Vocabulary

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Metabolism

The sum of all chemical reactions in an organism that are necessary to sustain life.

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Cellular Respiration

The process where cells use oxygen to release energy stored within food molecules.

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Molecule

A group of atoms bonded together, which is the smallest unit of a chemical compound.

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Glucose

A simple sugar that serves as an important source of energy for all living organisms.

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Amino Acid

These are the essential building blocks that link together in long chains to form proteins.

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Digestive System

The body system responsible for breaking down food into smaller molecules for the body.

Key Vocabulary

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Respiratory System

The system responsible for taking in oxygen and removing carbon dioxide from the body.

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Circulatory System

The system that transports oxygen, nutrients, and other substances throughout the body.

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Energy

The power derived from using physical or chemical resources in the body to live.

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Oxygen

A gas that is essential for releasing energy in our cells and is transported by blood.

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What is Metabolism?

Breaking Down Molecules

• Our bodies break down complex molecules from the food we eat.

• This process releases the energy stored inside these food molecules.

• We use this energy for everything, from running to thinking.

Building New Molecules

• The energy released is then used to build new, useful molecules.

• These new molecules help our bodies grow and repair any damage.

• Some of these new molecules are used to store energy for later.

Multiple Choice

What is the primary function of metabolism?

• To break down molecules for energy and use that energy to build new molecules.

• To only convert food directly into energy for running and thinking.

• To only build new molecules for the body to grow and repair damage.

• To create complex molecules that the body can store for later use.

Multiple Choice

What is the relationship between breaking down molecules and building new molecules in the body?

• The energy released from breaking down molecules is used to build new ones.

• Building new molecules releases the energy needed to break down food.

• Breaking down molecules is a process that happens only during exercise.

• Building new molecules and breaking down molecules are separate, unrelated processes.

Multiple Choice

If a body could successfully break down food and release its energy, but was unable to use that energy to build new molecules, what would be a likely result?

• The body would have no energy for activities like running or thinking.

• The body would not be able to effectively grow or repair damage.

• The body would stop breaking down molecules from food.

• The body would immediately use all released energy for physical activity.

Molecules for Life

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Carbohydrates

• ​These are the body's main and quickest source of energy.

• ​​Glucose is a simple carbohydrate that our cells use for fuel.

• ​They provide the immediate energy needed for your daily activities.

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Proteins

• ​Proteins are made from smaller units called amino acids.

• ​​They are essential for building and repairing body parts like muscles.

• ​Your skin and nails are also made mostly of proteins.

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Lipids (Fats)

• ​Lipids, also known as fats, store energy for long-term use.

• ​​They help to keep your body warm by providing insulation.

• ​These molecules also play a key role in protecting your organs.

Multiple Choice

What is the primary function of carbohydrates?

• To provide the body's main and quickest source of energy.

• To build and repair body parts like muscles and skin.

• To store energy for long-term use and provide insulation.

• To be used as the building blocks for lipids and fats.

Multiple Choice

Which statement best compares the primary roles of proteins and lipids?

• Proteins are used for building and repairing tissues, while lipids are used for storing energy long-term.

• Proteins are the body's quickest source of energy, while lipids are made from amino acids.

• Both proteins and lipids are primarily used to provide immediate fuel for cells.

• Lipids are used to repair muscles and skin, while proteins provide insulation to keep the body warm.

Multiple Choice

An animal needs to survive a long, cold winter hibernation without eating. Which molecule is most critical for it to store in its body, and why?

• Lipids, because they provide both long-term energy storage and insulation.

• Carbohydrates, because they are the quickest source of energy for the body's cells.

• Proteins, because they are needed to repair any muscle damage during the long rest.

• Glucose, because it is a simple sugar that provides fuel for all activities.

Body Systems at Work

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Digestive System

• This system breaks down large food molecules into much smaller ones.

• Carbohydrates and proteins become glucose and amino acids your body can use.

• These small molecules are then absorbed directly into your blood stream.

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Respiratory System

• This system is responsible for bringing oxygen into the body.

• You get this essential oxygen from the air you breathe in.

• Oxygen is necessary for releasing the energy stored inside food molecules.

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Circulatory System

• This system acts as a transportation highway throughout your entire body.

• It includes your heart, blood, and all of your blood vessels.

• It transports glucose, amino acids, and oxygen to every single cell.

Multiple Choice

What is the primary function of the digestive system?

• To break down food into smaller molecules the body can use.

• To transport oxygen and nutrients to every cell.

• To bring oxygen into the body from the air.

• To release energy stored inside food molecules.

Multiple Choice

How do nutrients from food and oxygen from the air reach the body's cells?

• They are transported through the bloodstream by the circulatory system.

• They are absorbed directly into the cells from the lungs and stomach.

• They are converted into energy before leaving the digestive system.

• They are moved around the body by the respiratory system.

Multiple Choice

Based on the information provided, what is the most likely reason that cells need both oxygen and glucose?

• Oxygen is needed to unlock the energy stored in molecules like glucose.

• Oxygen combines with food to make it small enough to enter the blood.

• The heart uses oxygen as its primary fuel to pump blood.

• The digestive system needs oxygen to break down carbohydrates and proteins.

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Cellular Respiration: Releasing Energy

• Cellular respiration is a chemical reaction that releases energy for your cells.

• This reaction happens inside tiny cell structures called the mitochondria.

• It uses two ingredients: glucose from food and oxygen from the air.

• This process rearranges matter to provide the energy needed for life.

Multiple Choice

What is the main purpose of cellular respiration?

• To release energy from food for the cell to use

• To create glucose and oxygen for the cell

• To store large amounts of energy as matter

• To get rid of carbon dioxide from the cell

Multiple Choice

What two things are required for the chemical reaction of cellular respiration to happen?

• Energy and carbon dioxide

• Glucose from food and oxygen from the air

• Mitochondria and new molecules

• Chemical reactions and water

Multiple Choice

If a cell has plenty of glucose but is unable to take in oxygen, what would be the most likely outcome?

• The cell would not be able to release a large amount of energy.

• The cell would create more glucose to make up for the lack of oxygen.

• The cell would start using carbon dioxide to produce energy.

• The cell would release more energy to find a new oxygen source.

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Common Misconceptions

Misconception	Correction
Metabolism is only about burning calories or losing weight.	It includes all chemical reactions like building muscle and repairing cells.
Your body only uses energy when you are moving.	Your body constantly uses energy, even when you are asleep.
Food is the same thing as energy.	Food contains stored chemical energy released by cellular respiration.
Breathing and respiration are the same thing.	Breathing is moving air. Respiration releases energy in cells.

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Summary

• Metabolism breaks down molecules for energy and builds them for growth.

• Food provides carbohydrates for energy and proteins for building materials.

• Your organ systems work together to deliver oxygen and nutrients to cells.

• Cellular respiration uses glucose and oxygen to release energy for your body.

Poll

On a scale of 1-4, how confident are you about explaining how food gives your body energy?

• 1 - Not confident at all

• 2 - A little confident

• 3 - Mostly confident

• 4 - Very confident