Obtaining Energy and Removing Waste

Obtaining Energy and Removing Waste

Middle School

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Learning Objectives

• Describe how food is broken down and moves through the digestive system.

• Explain how food molecules change in reactions to support growth and release energy.

• Model how cellular respiration breaks down food to release energy.

• Explain how matter is conserved during digestion and cellular respiration.

• Compare how plants and animals get matter and energy for survival.

Key Vocabulary

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Digestion

The breakdown of food into molecules the body can use for energy, growth, and cell repair.

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Nutrient

A substance in food that is essential for providing energy and materials for growth and survival.

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Cellular Respiration

A reaction that uses oxygen (O₂) to release the energy stored in food molecules inside cells.

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Chemical Reaction

A process that rearranges the atoms of substances to form new substances with different chemical properties.

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Molecule

A group of two or more atoms that are held together by chemical bonds to form a substance.

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Atom

The basic unit of a chemical element and the smallest particle of matter that can exist.

Key Vocabulary

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Conservation of Matter

The principle of Conservation of Matter states that matter cannot be created or destroyed.

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Peristalsis

Peristalsis is the series of wave-like muscle contractions that move food through the digestive tract.

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Villi

Villi are tiny, finger-like projections lining the small intestine that absorb nutrients from digested food.

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Kidneys

The kidneys are vital organs that work to filter waste products from the blood.

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Photosynthesis

Photosynthesis is the process plants use to make their own food using light energy.

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Xylem & Phloem

Xylem and Phloem are the essential plant tissues responsible for transporting water and nutrients.

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Energy and Nutrients from Food

Energy from Food

• Food provides the energy your body needs, which is measured in units called Calories.

• This energy powers every activity you do, such as running, jumping, and even thinking.

• Energy is stored inside complex food molecules that contain the element carbon.

Nutrients from Food

• Nutrients are substances in food that your body uses to grow, repair, and survive.

• Different nutrients have different jobs, such as protein which is used to build strong muscles.

• Calcium is another important nutrient that your body uses to help build and strengthen bones.

Multiple Choice

What is the main purpose of food for the human body?

• To provide the body with energy and nutrients.

• To help the body build strong muscles only.

• To measure the amount of carbon in food molecules.

• To give the body a source of calcium only.

Multiple Choice

How does the body's use of energy from food differ from its use of nutrients?

• Energy powers activities, while nutrients are used to build and repair the body.

• Energy is measured in Calories, while nutrients are measured in carbon.

• Energy is used for building bones, while nutrients are used for thinking.

• Energy comes from protein, while nutrients come from Calories.

Multiple Choice

A student is training for a long-distance running event. Which statement best explains why their diet is important for both performance and recovery?

• They need Calories from food for energy to run and protein to repair their muscles.

• They only need calcium from food to make their bones stronger for running.

• They only need a lot of energy from food because running uses up Calories.

• They need complex food molecules that contain carbon to make them run faster.

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The Process of Digestion

Mechanical Digestion

• Mechanical digestion is when food is physically broken down into much smaller pieces.

• This happens when you chew, mash, and grind food with your teeth and tongue.

• Your stomach also plays a part by mashing and churning the food you eat.

Chemical Digestion

• Chemical digestion is when chemical reactions break down food into small molecules.

• These reactions change the food chemically, making it easier for your body to absorb.

• For instance, saliva in your mouth contains substances that start this chemical process.

Multiple Choice

What is the primary function of mechanical digestion?

• To physically break down food into smaller pieces.

• To change food into new substances using chemicals.

• To absorb nutrients directly into the body.

• To use saliva to begin breaking down food.

Multiple Choice

Which statement best describes the process of chemical digestion?

• It uses chemical reactions, like those started by saliva, to break food into small molecules.

• It physically mashes and churns food inside the stomach.

• It only involves using the teeth and tongue to grind up food.

• It makes food pieces smaller without changing them chemically.

Multiple Choice

If the stomach could no longer mash and churn, what would be the most likely effect on digestion?

• Overall digestion would be less effective because food would not be broken down into smaller pieces in the stomach.

• It would have no effect on digestion because the teeth already chewed the food.

• Chemical digestion would stop completely because the stomach releases all the chemicals.

• The body would absorb food more quickly because it would be in the stomach for less time.

The Path of Food: Mouth, Esophagus, and Stomach

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The Mouth

• Digestion starts here with your teeth and your tongue.

• They perform mechanical digestion by chewing up the food.

• Saliva begins the process of chemical digestion in your mouth.

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The Esophagus

• This is the muscular tube food enters after you swallow.

• It moves food down from the mouth to the stomach.

• Muscle contractions called peristalsis push the food along.

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The Stomach

• This organ is a temporary storage container for the food.

• It has an acidic fluid that is called gastric juice.

• The gastric juice continues the process of chemical digestion.

Multiple Choice

What is the primary role of the stomach as described in the food's path?

• To act as a storage container and continue chemical digestion.

• To move food down from the mouth using muscle contractions.

• To perform mechanical digestion by chewing up food.

• To begin the process of chemical digestion using saliva.

Multiple Choice

How do the digestive functions of the mouth and the esophagus compare?

• The mouth uses both mechanical and chemical digestion, while the esophagus only moves the food.

• The mouth only performs chemical digestion, while the esophagus performs mechanical digestion.

• The mouth is a muscular tube, while the esophagus is a storage container.

• The mouth uses gastric juice, while the esophagus uses saliva.

Multiple Choice

Based on the information provided, what would most likely happen if the muscular contractions called peristalsis stopped working?

• The stomach would not be able to use gastric juice.

• Chemical digestion in the mouth would stop.

• Food would get stuck in the esophagus.

• Teeth would no longer be able to chew the food.

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The Path of Food: The Intestines

Small Intestine

• ​This long tube is where most chemical digestion is completed and nutrients are absorbed by the body.

• ​​Its walls are covered in tiny, finger-like projections called villi, which help in absorption.

• ​Villi pass nutrients from the intestine into the blood, which carries them to the rest of the body.

Large Intestine

• ​After the small intestine, leftover materials move into the large intestine for further processing.

• ​​Here, most of the water is absorbed from the waste products, making them more solid.

• ​The solid waste is then stored until it is ready to be eliminated from the body.

Multiple Choice

What is the main purpose of the small intestine?

• To complete digestion and absorb nutrients into the body.

• To absorb water from waste products, making them solid.

• To store solid waste until it is ready to be eliminated.

• To move food from the stomach to the intestines.

Multiple Choice

What is the specific function of the villi in the small intestine?

• They pass nutrients from the intestine into the blood.

• They help to solidify waste by absorbing water.

• They move waste from the small to the large intestine.

• They break down food using chemical digestion.

Multiple Choice

If the large intestine stopped performing its main function, what would be the most likely result?

• The body would not be able to absorb enough nutrients.

• Waste products would be too liquid and not solid enough.

• Nutrients would not be able to pass into the blood.

• Digestion would not be completed before waste is formed.

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What is Cellular Respiration?

• Cellular respiration is a chemical reaction in cells that releases energy from food.

• During this process, food molecules like glucose react with oxygen inside the cell.

• The reaction releases stored energy for activities like growth and movement.

• It also produces new molecules: carbon dioxide (CO₂) and water (H₂O).

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Multiple Choice

What is the main purpose of cellular respiration?

• To create water for the cell to store

• To produce oxygen for the cell to breathe

• To release energy from food for the cell to use

• To convert carbon dioxide into food

Multiple Choice

Which statement best describes what happens during the process of cellular respiration?

• Food and oxygen are used to create carbon dioxide and water.

• Carbon dioxide and water are used to create food and oxygen.

• Energy is used to turn water and oxygen into food.

• Oxygen is used to break down carbon dioxide into water.

Multiple Choice

If a cell did not have access to enough oxygen, what would be the most likely result?

• The cell would produce more carbon dioxide than usual.

• The cell would start making its own food from water.

• The cell would not be able to release as much energy for activities.

• The cell would have too much unused water.

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Building a New You: Matter is Conserved

• Atoms are not created or destroyed, just rearranged in chemical reactions.

• The food you eat contains atoms like carbon, hydrogen, and oxygen.

• Digestion breaks down food, rearranging atoms to form new molecules.

• These new molecules build your body, helping you grow and heal.

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Multiple Choice

What happens to atoms during a chemical reaction like digestion?

• They are rearranged to form new molecules.

• They are completely destroyed and disappear.

• They are turned into energy and used up.

• New atoms are created to build new things.

Multiple Choice

What is the relationship between the food you eat and the growth of your body?

• To break down food and rearrange its atoms into new molecules the body can use.

• To remove all atoms from food so the body has pure energy.

• To create new types of atoms that the body needs to grow.

• To store food in the stomach without changing its atomic structure.

Multiple Choice

A student scrapes her knee. Over the next week, the wound heals and new skin forms. Which statement best explains where the building blocks for the new skin came from?

• The atoms that make up the new skin came from the rearranged atoms of the food she ate.

• The new skin cells were created from nothing by the body's healing power.

• The atoms from the air were used to create the new skin cells.

• The body converted energy directly into new atoms for the skin.

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Removing Waste: The Excretory System

• The excretory system collects and removes waste from your body using several organs.

• Your respiratory system removes the waste gas carbon dioxide (CO₂) when you exhale.

• The urinary system's kidneys filter waste from your blood to produce urine.

• Your skin helps remove excess salt and water from the body as sweat.

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Multiple Choice

What is the main purpose of the excretory system?

• To collect and remove waste from the body

• To break down food for energy

• To pump blood throughout the body

• To help the body move

Multiple Choice

What do the kidneys, lungs, and skin have in common?

• They all produce urine to be removed.

• They are all part of the respiratory system.

• They are all organs that help remove waste from the body.

• They all remove the exact same type of waste.

Multiple Choice

During intense exercise, a person breathes heavily and sweats a lot. Which two waste removal functions are most active?

• The kidneys filtering blood and the lungs removing oxygen.

• The respiratory system removing carbon dioxide and the skin removing sweat.

• The skin removing sweat and the kidneys producing less urine.

• The urinary system producing urine and the respiratory system adding carbon dioxide.

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Plant Energy and Transport

• Plants make their own food through a process called photosynthesis.

• They use sunlight, water (H₂O), and carbon dioxide (CO₂) to create glucose.

• This glucose provides the energy for the plant's growth and repair.

• Xylem transports water, while phloem transports the glucose (food).

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Multiple Choice

What is photosynthesis?

• The process plants use to make their own food using sunlight.

• The way plants absorb nutrients from the soil.

• The method plants use to release water vapor.

• The system that transports food throughout the plant.

Multiple Choice

What is the relationship between xylem and phloem in a plant?

• Xylem transports water, and phloem transports glucose.

• Xylem transports glucose, and phloem transports water.

• Both xylem and phloem transport water to the leaves.

• Both xylem and phloem transport glucose from the leaves.

Multiple Choice

If a plant's access to water was blocked, what would be the most likely consequence for the plant's energy production?

• The plant would not be able to create glucose for energy.

• The plant's leaves would not be able to absorb sunlight.

• The plant would have too much water in its leaves.

• The plant would not be able to transport glucose to its cells.

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A Closer Look: Celiac Disease

• Celiac disease is a digestive disorder where gluten damages the small intestine.

• This damage prevents the body from properly absorbing nutrients from your food.

• Malabsorption can lead to weight loss, fatigue, and other health problems.

• Treatment requires a strict, lifelong diet that is completely free of gluten.

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Multiple Choice

In a person with Celiac disease, which part of the body is directly damaged by gluten?

• The stomach

• The small intestine

• The liver

• The large intestine

Multiple Choice

What is the primary consequence of the damage to the small intestine in Celiac disease?

• It causes the body to reject all food.

• It stops the body from absorbing nutrients properly.

• It makes the body digest food too quickly.

• It leads to an immediate increase in weight.

Multiple Choice

Based on the information, what is the best explanation for why a strict, gluten-free diet is required for treating Celiac disease?

• To help the body produce more gluten on its own.

• To increase a person's appetite and energy levels.

• To prevent damage to the small intestine and allow the body to absorb nutrients.

• To cure the disease so that gluten can be eaten again later.

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Common Misconceptions

Misconception	Correction
Digestion only happens in the stomach.	Digestion begins in the mouth and continues in the small intestine.
Food “disappears” or turns into energy.	The atoms in food are rearranged. Matter is conserved and energy is released.
Plants get their food from the soil.	Plants create their own food through photosynthesis.
All body waste is solid.	Waste is also removed as urine, carbon dioxide, and sweat.

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Summary

• Digestion breaks down food, which reacts with oxygen during cellular respiration to release energy.

• The atoms in food are conserved and rearranged for an organism's growth and repair.

• The digestive system absorbs food; the excretory system removes waste like CO₂.

• Plants make their own food but use cellular respiration to get energy from it.

Poll

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