Cell Structure

Cell Structure

Middle School

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Learning Objectives

• Identify the main parts, called organelles, inside of plant and animal cells.

• Describe the job that each of the most important cell organelles does.

• Compare the similarities and differences between plant cells and animal cells.

• Explain how the different organelles work together to keep the cell alive.

Key Vocabulary

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Organelle

A specialized structure inside a cell that performs a specific and essential job for the cell's function.

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Cell Membrane

The thin, flexible barrier around a cell that controls what substances can enter or leave the cell.

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Cytoplasm

The entire region inside the cell membrane but outside of the nucleus, including all the organelles.

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Nucleus

The large organelle that acts as the cell's command center by storing DNA and directing all activities.

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Ribosome

A tiny cellular structure responsible for assembling proteins by following instructions encoded in the cell's DNA.

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Endoplasmic Reticulum

A network of membranes that helps produce, fold, and process both proteins and lipids for the cell.

Key Vocabulary

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Golgi Apparatus

This organelle sorts, modifies, and packages proteins and lipids for transport to their final destinations.

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Mitochondrion

The powerhouse of the cell, this organelle breaks down food molecules to release energy that the cell can use.

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Chloroplast

A specialized organelle in plant cells that performs photosynthesis to create sugars from sunlight energy.

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Vacuole

A membrane-bound sac used for storing water, food, and waste materials within the cell.

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Cell Wall

The rigid and protective outer layer found only in plant cells, providing structural support and shape.

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Outer Boundary and Inside Space

Cell Membrane

• The cell membrane is a thin, flexible barrier that surrounds and protects the entire cell.

• Its main function is to control all substances that enter and leave the cell.

• This regulation helps the cell maintain a stable and balanced internal environment for its functions.

Cytoplasm

• The cytoplasm is the jelly-like substance that fills the entire space inside the cell.

• It supports and holds all of the cell's internal structures, which are called organelles.

• Many essential chemical reactions that keep the cell alive happen within the cytoplasm.

Multiple Choice

What are the primary roles of the cell membrane and the cytoplasm?

• To serve as the cell's protective barrier and its internal, jelly-like filling.

• To hold the cell's genetic material and produce energy.

• To help the cell move and to store water for later use.

• To break down waste materials and to build proteins.

Multiple Choice

What is the relationship between the cell membrane's ability to control substances and the chemical reactions in the cytoplasm?

• By regulating substances, the membrane helps the cytoplasm keep a balanced environment needed for chemical reactions.

• The cytoplasm provides the energy for the cell membrane to transport substances.

• The cell membrane holds the organelles, while the cytoplasm protects them from harm.

• The cytoplasm's jelly-like nature gives the cell membrane its flexible shape.

Multiple Choice

If a cell's membrane was damaged and could no longer maintain a balanced internal environment, what would be the most likely consequence for the cell?

• The organelles would float out of the cell.

• The chemical reactions essential for life would be disrupted.

• The cell would immediately stop producing energy.

• The cytoplasm would lose its jelly-like consistency.

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The Information Center: Nucleus

• The nucleus is the cell's information center because it holds the DNA.

• It acts as the command center, directing all cell activities like growth.

• Inside the nucleus is the nucleolus, which builds parts for ribosomes.

• The nuclear envelope has pores to control what moves in and out.

Multiple Choice

What is the primary role of the nucleus in a cell?

• To act as the command center that directs all cell activities

• To build parts for the cell's ribosomes

• To control what materials enter and exit the cell

• To store water and nutrients for the cell

Multiple Choice

What is the specific function of the nuclear envelope?

• It contains the DNA to direct all cell activities.

• It is where parts of ribosomes are built.

• It controls which materials can enter and exit the nucleus.

• It helps the cell grow and reproduce.

Multiple Choice

Based on the functions of the nucleus and its parts, what would most likely happen if the pores of the nuclear envelope were to become blocked?

• The DNA would be unable to direct cell activities.

• The nucleolus would stop making ribosome parts.

• Ribosome parts would be unable to exit the nucleus, halting key cell activities.

• The nucleus would run out of energy to function.

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Types of ER

Rough ER

• ​It is a network of membranes connected to the nucleus that looks like flattened sacs.

• ​​It is called ‘rough’ because it is covered with tiny dots called ribosomes.

• ​The ribosomes on its surface are responsible for building new proteins for the cell.

• ​The Rough ER then helps to fold and modify these newly made proteins correctly.

Smooth ER

• ​This network of membranes looks more like a series of connected tubes.

• ​​It is called ‘smooth’ because it does not have any ribosomes on its surface.

• Its main job is to create lipids, which are fats.

• ​It also detoxifies harmful substances and performs other special tasks for the cell.

Multiple Choice

What is the primary function of the ribosomes located on the surface of the Rough ER?

• To build new proteins for the cell.

• To create lipids and fats for the cell.

• To detoxify harmful substances in the cell.

• To connect the membranes to the cell nucleus.

Multiple Choice

What is the main difference between the Rough ER and the Smooth ER in terms of their structure and function?

• The Rough ER has a tube-like shape for detoxification, while the Smooth ER has flattened sacs for making proteins.

• The Rough ER is connected to the nucleus to make lipids, while the Smooth ER is not.

• The Rough ER has ribosomes to make proteins, while the Smooth ER lacks ribosomes and makes lipids.

• The Rough ER is covered in fats to make it smooth, while the Smooth ER is covered in ribosomes.

Multiple Choice

If a disease caused all the ribosomes on the Rough ER to disappear, what would be the most likely outcome for the cell?

• The folding of new proteins would stop, but the production of lipids would continue.

• The production of lipids would stop, but the folding of new proteins would continue.

• Both protein folding and lipid production would stop immediately.

• The cell would begin to detoxify substances more slowly.

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Processing & Shipping: Golgi & Vesicles

• The Golgi apparatus is like the cell's post office that receives proteins from the ER.

• ​It sorts, modifies, and packages proteins into vesicles for delivery.

• Vesicles are small bubbles that act as delivery trucks, moving materials.

Multiple Choice

What is the main role of the Golgi apparatus and vesicles in a cell?

• To create energy for the cell to use.

• To store the cell's genetic information.

• To sort, package, and transport materials for delivery.

• To control all of the cell's activities.

Multiple Choice

What is the direct relationship between the Golgi apparatus and vesicles?

• Vesicles deliver proteins to the Golgi apparatus for creation.

• The Golgi apparatus sorts and packages materials into vesicles for transport.

• Vesicles provide the energy for the Golgi apparatus to function.

• The Golgi apparatus is a type of large vesicle for storage.

Multiple Choice

What would most likely happen if a cell's Golgi apparatus stopped functioning correctly?

• The cell would not be able to produce any proteins in the endoplasmic reticulum.

• Proteins would not be sorted and packaged for delivery to their proper destinations.

• Vesicles would be unable to move materials to the cell membrane.

• The cell would run out of energy because materials are not being delivered.

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Energy for the Cell

Mitochondria

• ​Mitochondria are known as the powerhouses of the cell, releasing usable energy for cellular functions.

• ​​They achieve this by breaking down food molecules, such as sugars, in a specific process.

• ​This vital process is called cellular respiration and is found in most living things.

Chloroplasts

• ​Chloroplasts are special organelles that are found only in the cells of plants.

• ​​They perform photosynthesis by using sunlight to convert water and CO₂ into food.

• ​They are filled with green chlorophyll, which is the pigment that captures light energy.

Multiple Choice

What is the primary role of mitochondria within a cell?

• To release usable energy by breaking down food molecules.

• To create food for the cell using sunlight and water.

• To store the cell's genetic information.

• To control what enters and leaves the cell.

Multiple Choice

How do mitochondria and chloroplasts differ in terms of which organisms they are found in?

• Mitochondria create food, while chloroplasts release energy from food.

• Mitochondria are in most cells, while chloroplasts are only in plant cells.

• Mitochondria use sunlight, while chloroplasts use sugars.

• Mitochondria perform photosynthesis, while chloroplasts perform cellular respiration.

Multiple Choice

If a healthy plant were moved from a sunny location to a completely dark room, which organelle would be most affected and why?

• The chloroplasts, because they need sunlight to produce food through photosynthesis.

• The mitochondria, because they cannot perform cellular respiration without light.

• The chloroplasts, because they would be unable to break down sugars in the dark.

• The mitochondria, because they can only get energy from chlorophyll.

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Storage and Cleanup

• Vacuoles are storage compartments for water, food, and other materials.

• Plant cells have a large central vacuole that helps support the plant, while animal cells have smaller vacuoles that store water, nutrients, and waste.

• Lysosomes are the cell's cleanup crew, breaking down waste products.

• They use powerful enzymes to recycle old and worn-out cell parts.

Multiple Choice

What are the primary functions of vacuoles and lysosomes within a cell?

• Storing materials and breaking down waste

• Producing energy and transporting proteins

• Controlling cell activities and making food

• Helping the cell move and providing structural support

Multiple Choice

What is a key difference between the vacuoles in plant cells and those in animal cells?

• Plant cells have one large vacuole, while animal cells have many small ones.

• Animal cells use vacuoles for firmness, while plant cells do not.

• Plant cells have lysosomes, while animal cells have vacuoles.

• Animal cells store water in vacuoles, while plant cells store nutrients.

Multiple Choice

What would most likely happen inside an animal cell if its lysosomes stopped working?

• The cell would run out of water and nutrients.

• The cell would lose its firmness and shape.

• Waste materials would build up and damage the cell.

• The cell would be unable to store any food.

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Shape, Support, and Protection

Cytoskeleton

• A network of protein fibers that gives the cell its shape and internal organization.

• It assists in the movement of different organelles that are present within the cell.

• It also plays an important role during the process of cell division.

Cell Wall

• A tough, rigid outer layer found only in plant cells, outside the cell membrane.

• It provides the cell with structural support and protection from any external factors.

• This gives plant cells a fixed, boxy shape that helps plants stand upright.

Multiple Choice

What is the main purpose of structural components like the cytoskeleton and cell wall?

• To provide the cell with shape, support, and protection.

• To control the process of cell division.

• To assist in the movement of organelles.

• To generate energy for cellular activities.

Multiple Choice

What is a key difference between the cell wall and the cytoskeleton?

• The cell wall is a rigid outer layer, while the cytoskeleton is a network of internal fibers.

• The cell wall helps organelles move, while the cytoskeleton provides a fixed shape.

• The cell wall is found in all cells, while the cytoskeleton is only in plant cells.

• The cell wall assists with cell division, while the cytoskeleton protects the cell.

Multiple Choice

If a plant cell's cell wall remained perfectly intact but its cytoskeleton was damaged, what would be the most likely result?

• The cell would lose its rigid, boxy shape.

• The plant would no longer be able to stand upright.

• The movement of organelles and the process of cell division would be disrupted.

• The cell would lose its protection from external factors.

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Plant vs. Animal Cells

Similarities

• ​Both plant and animal cells are eukaryotic, meaning they have a true nucleus.

• ​​They share many common parts, including a cell membrane, cytoplasm, and mitochondria.

• ​Both also have ribosomes, an endoplasmic reticulum, and a Golgi apparatus inside them.

Key Differences

• ​Plant cells have a cell wall for support, and chloroplasts for making food.

• ​​They also feature a large central vacuole that stores water and maintains firmness.

• ​Animal cells often have lysosomes to break down waste, which plant cells don’t.

Multiple Choice

What is a fundamental characteristic that plant and animal cells share?

• They are both eukaryotic cells that have a true nucleus.

• They both contain chloroplasts to make their own food.

• They both have a cell wall to provide rigid support.

• They both feature a large central vacuole for storing water.

Multiple Choice

Which statement best explains the function of two structures that are unique to plant cells?

• The cell wall provides rigid support, while chloroplasts make food.

• The cell membrane breaks down waste, while lysosomes provide support.

• The cytoplasm makes food, while the mitochondria store water.

• The nucleus provides energy, while the cell wall allows for movement.

Multiple Choice

Based on the roles of a plant cell's structures, what would most likely happen if a plant does not get enough water?

• The plant would likely wilt because its cells lose firmness.

• The plant's cells would start producing more lysosomes to find water.

• The plant's cells would become more rigid to prevent water loss.

• The plant would be unaffected because the cell wall provides water.

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Common Misconceptions

Misconception	Correction
Plant cells have chloroplasts instead of mitochondria.	Plant cells have both to make and use energy.
The cell wall and cell membrane do the same job.	The membrane controls entry, while the wall provides support.
Mitochondria create energy from nothing.	Mitochondria convert food into usable energy for the cell (ATP).

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Summary

• The cell membrane acts as a gatekeeper, and the cytoskeleton provides internal support.

• The nucleus, ribosomes, ER, and Golgi apparatus work together to process proteins.

• Mitochondria provide usable energy, while chloroplasts in plant cells capture sunlight.

• Plant cells have a cell wall, chloroplasts, and a large central vacuole.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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