The Cell

The Cell

Middle School

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Learning Objectives

• Provide evidence that living things are made of cells, the basic units of life.

• Explain the three parts of the Cell Theory and the role of the microscope.

• Describe how organelles contribute to the overall function of a cell.

• Compare and contrast prokaryotic, eukaryotic, plant, and animal cells.

• Describe how a single-celled organism performs all of its essential life functions.

Key Vocabulary

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Cell

A cell is the most basic structural and functional unit of all known living organisms.

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Unicellular

A unicellular organism is a living being that is made up of only one single cell.

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Multicellular

A multicellular organism is a living being that consists of many different types of cells.

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Cell Theory

Cell theory is the scientific idea that all living things are composed of one or more cells.

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Organelle

An organelle is a specialized structure within a cell that performs a specific, important job or function.

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Prokaryote

A prokaryote is a simple, single-celled organism that does not have a distinct, membrane-bound nucleus.

Key Vocabulary

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Eukaryote

A eukaryote is an organism whose cells contain a nucleus and other organelles enclosed within membranes.

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Cell Membrane

The cell membrane selectively controls which substances, like nutrients and waste, can pass into and out of the cell.

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Cell Wall

A rigid layer outside the cell membrane provides structural support and protection to plant and bacterial cells.

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Nucleus

The nucleus acts as the cell's control center, containing the genetic material, or DNA, for the organism.

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Mitochondria

Often called the powerhouse of the cell, mitochondria are responsible for generating most of the cell's energy.

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Chloroplast

Found in plant cells and some protists, chloroplasts are the specific site where photosynthesis occurs to make food.

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Cells: The Basic Units of Life

• All living things, from bacteria to animals, are made of cells.

• A living thing can be unicellular or multicellular with many cells.

• In multicellular organisms, different cells are specialized to do specific jobs.

• For instance, muscle cells contract for movement and nerve cells send signals.

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Multiple Choice

What is the fundamental unit that makes up all living things?

• A cell

• A muscle

• A nerve

• An organism

Multiple Choice

What is the primary reason why multicellular organisms have many different types of cells?

• Different cells are needed to perform specific, specialized jobs.

• Some cells are unicellular while others are multicellular.

• All cells need to be able to contract for movement.

• Having different cells makes an organism look more complex.

Multiple Choice

If an organism's nerve cells stopped performing their specialized job, what would be the most likely consequence?

• The organism would not be able to send signals throughout its body.

• The organism's muscles would be unable to get smaller.

• The organism would immediately become a single-celled organism.

• The organism's cells would all become identical to each other.

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Discovering Cells and the Cell Theory

• The invention of the microscope in the 1600s made the discovery of cells possible.

• Robert Hooke named the box-like structures he saw in cork "cells."

• Antoni van Leeuwenhoek was the first to observe living, single-celled organisms.

• The Cell Theory states that all new cells come from pre-existing cells by division.

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Multiple Choice

What is a central principle of the Cell Theory?

• All new cells are formed from pre-existing cells.

• All living things are made of boxes called cork.

• All cells can be seen without a microscope.

• All single-celled organisms are non-living.

Multiple Choice

How did the invention of the microscope lead to the discovery of cells?

• It allowed scientists to see objects too small to be seen with the naked eye.

• It proved that all cells come from cork.

• It was used to create the first living organisms.

• It helped Robert Hooke name single-celled organisms.

Multiple Choice

Which piece of evidence suggests that new cells arise from existing ones?

• Observation of living organisms suggested that they could grow and divide.

• Observation of box-like structures in cork proved that all things have cells.

• Discovery was more important than suggesting cells grow and divide.

• Hooke's use of the name 'cell' was the most critical part.

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The Two Main Types of Cells

Prokaryotic Cells

• These simple cells, like bacteria, are defined by the absence of a nucleus.

• Their genetic material, or DNA, floats freely throughout the cell's cytoplasm.

• They have a very simple structure with only a few specialized parts called organelles.

Eukaryotic Cells

• These complex cells make up organisms like protists, fungi, plants, and animals.

• Their defining feature is a nucleus, which encloses and protects the cell's DNA.

• They contain many different types of specialized structures known as organelles.

Multiple Choice

What is the main defining feature that distinguishes prokaryotic cells from eukaryotic cells?

• The presence or absence of a nucleus.

• The type of organisms they are found in.

• The complexity of their specialized parts.

• The way their genetic material is stored.

Multiple Choice

How does the location of genetic material (DNA) compare between prokaryotic and eukaryotic cells?

• The nucleus contains the DNA in a eukaryotic cell, while the DNA floats freely in a prokaryotic cell.

• Both cell types have a nucleus, but only one uses it to store DNA.

• Prokaryotic cells store their DNA in organelles, while eukaryotic cells store it in the cytoplasm.

• The DNA is located in the cytoplasm in both cell types, but it is more complex in eukaryotic cells.

Multiple Choice

A scientist discovers a new single-celled organism. The cell has a very simple structure, contains only a few organelles, and its DNA floats freely in the cytoplasm. What is the best conclusion the scientist can make?

• It is a prokaryotic cell because its simple structure and lack of a nucleus are defining features of prokaryotes.

• It is a eukaryotic cell because it is a newly discovered organism, and most organisms are eukaryotes.

• It is a prokaryotic cell because all simple cells belong to bacteria.

• It is a eukaryotic cell because it has specialized parts called organelles.

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The Cell as a System

• A cell is a complex system where parts work together for life processes.

• These individual parts of the cell are known as organelles.

• The cell membrane controls what enters and leaves to maintain a stable environment.

• Specialized organelles break down food to release energy for all cell functions.

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Multiple Choice

Which statement best describes a cell?

• A complex system where different parts work together.

• A single, simple part that performs one job.

• A storage container for food and water.

• The basic unit of energy for an organism.

Multiple Choice

How does the cell membrane contribute to maintaining a stable environment within the cell system?

• By breaking down food to release energy.

• By controlling what enters and leaves the cell.

• By giving the cell a rigid, unchanging shape.

• By producing all the parts the cell needs.

Multiple Choice

If a cell's specialized organelles were unable to break down food, what would be the most likely consequence for the cell as a whole?

• The cell would not have the energy to carry out its life processes.

• The cell membrane would become more effective at its job.

• The cell would begin to store more food than it needs.

• The cell would have too much energy and stop working.

Inside the Eukaryotic Cell: Key Organelles

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The Nucleus

• ​It acts as the 'control center' of the entire cell.

• ​​It contains the cell's genetic material, also known as DNA.

• ​The nucleus directs all activities that happen inside the cell.

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The Mitochondria

• ​These are known as the 'powerhouses' of the eukaryotic cell.

• ​​They perform cellular respiration to break down different kinds of nutrients.

• ​This important process releases energy for the cell to use.

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The Ribosomes

• ​Ribosomes are responsible for building essential molecules known as proteins.

• ​​These proteins are vital for the cell's growth and repair.

• ​They also help in carrying out important chemical reactions.

Multiple Choice

Which organelle acts as the 'control center' of a eukaryotic cell by directing all its activities?

• The Nucleus

• The Mitochondria

• The Ribosomes

• The Cell Wall

Multiple Choice

What is the primary way mitochondria provide power for the cell?

• By breaking down nutrients to release energy

• By storing the cell's genetic material

• By building proteins for growth and repair

• By directing all the cell's activities

Multiple Choice

If a cell's mitochondria were damaged, what is the most likely impact on the cell's ribosomes?

• Protein production by ribosomes would stop due to a lack of energy.

• The nucleus would begin to break down nutrients to create energy.

• The cell would use the genetic material in the nucleus for energy.

• Ribosomes would start performing cellular respiration.

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Key Differences: Plant vs. Animal Cells

Plant Cells

• ​Plant cells possess a rigid cell wall made of cellulose for structural support.

• ​​They contain chloroplasts, which are the sites of photosynthesis.

• ​Photosynthesis allows plants to produce their own food using sunlight.

Animal Cells

• ​Animal cells have a flexible cell membrane but lack a cell wall.

• ​​They do not have chloroplasts and cannot perform photosynthesis.

• ​They obtain energy by consuming food from other organisms.

Multiple Choice

Which feature provides structural support to plant cells but is not found in animal cells?

• A rigid cell wall

• A flexible cell membrane

• A method for consuming food

• The ability to move

Multiple Choice

Why are plant cells able to produce their own food, unlike animal cells?

• They have chloroplasts, which are needed for photosynthesis.

• They have a cell wall that absorbs sunlight.

• They get energy from the soil through their roots.

• They have a cell membrane that creates energy.

Multiple Choice

Based on the functions of their different structures, what would most likely happen to a plant if its cells were missing cell walls?

• The plant would lose its rigid structure and have difficulty standing upright.

• The plant would start consuming other organisms for energy.

• The plant would be unable to perform photosynthesis.

• The plant's cells would become more flexible, which is an advantage.

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The Paramecium: A Unicellular Eukaryote

• A paramecium is a complex, single-celled organism called a eukaryote.

• It is covered in tiny hairs called cilia that help it swim.

• Cilia also sweep food into an opening called the oral groove.

• A contractile vacuole pumps out excess water from the cell.

Multiple Choice

Which statement best describes a paramecium?

• A complex, single-celled organism

• A type of multi-celled plant

• A part of an animal's digestive system

• A simple, non-living particle

Multiple Choice

What are two primary functions of the cilia on a paramecium?

• Movement and feeding

• Breathing and reproduction

• Pumping water and sensing light

• Protection and creating energy

Multiple Choice

What would most likely happen to a paramecium if its contractile vacuole stopped working?

• It would fill with excess water and could burst

• It would be unable to find or consume food

• It would be unable to swim or move

• It would lose all its cilia and become smooth

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Common Misconceptions

Misconception	Correction
Single-celled organisms are just simple blobs.	They are complex, with specialized organelles for all life functions.
All cells are the same.	Cells have many shapes and sizes and are specialized for different functions.
Cells are static and inactive.	Cells are constantly active, carrying out reactions, transporting materials, and reproducing.
Everything inside a living thing is a cell.	Cells produce non-cellular structures like bone matrix or tree bark.

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Summary

• All living things are made of one or more cells.

• Cells are the basic unit of life and come from other cells.

• Cells can be prokaryotic (no nucleus) or eukaryotic (with a nucleus).

• In eukaryotes, organelles like mitochondria and the cell membrane work as a system.

• Plant cells have a cell wall for support and chloroplasts to make food.

• A single-celled paramecium can perform all of life's essential functions.

Poll

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