Cell structure and function

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Lesson notes

Cell Theory and Discovery

**Robert Hooke** discovered cells in 1665, naming them after their resemblance to monastery cells.
**Cell theory** (Schleiden & Schwann, 1839) states: all organisms are made of one or more cells; the cell is the basic unit of structure and function; all cells come from pre-existing cells.
Cells are the **basic structural and functional unit** of all life.
Most cells are microscopic; they contain a cell membrane, cytoplasm, and genetic material.

Two Major Cell Types: Prokaryotes vs. Eukaryotes

**Prokaryotes** (bacteria and archaea) lack a membrane-bound nucleus; their DNA is in a **nucleoid** region.
**Eukaryotes** (animals, plants, fungi, protists) have a **membrane-bound nucleus** and other organelles.
Prokaryotes are generally **smaller** (0.1–5.0 μm) and simpler than eukaryotes.
Eukaryotes can be **single-celled** (e.g., yeast) or **multicellular** (e.g., animals, plants).

Eukaryotic Cell Structure

**Cell membrane** – semipermeable barrier that controls what enters/leaves the cell.
**Nucleus** – contains DNA; controls cell activities.
**Cytoplasm** – jelly-like substance where organelles are suspended; site of many chemical reactions.
**Mitochondria** – produce energy (ATP) through cellular respiration.
**Ribosomes** – make proteins (found in both prokaryotes and eukaryotes).
**Endoplasmic reticulum (ER)** – rough ER (with ribosomes) processes proteins; smooth ER makes lipids.
**Golgi apparatus** – modifies, sorts, and packages proteins for transport.

Plant Cell vs. Animal Cell

Plant cells have a **cell wall** (made of cellulose) for support and protection.
Plant cells contain **chloroplasts** for photosynthesis (convert sunlight into sugars).
Plant cells have a large **central vacuole** that stores water and maintains turgor pressure.
Animal cells lack cell walls and chloroplasts; they have smaller vacuoles (if any).
Both plant and animal cells have a nucleus, mitochondria, ER, Golgi, and ribosomes.

Prokaryotic Cell Structure

Prokaryotes have a **plasma membrane** and a **cell wall** (peptidoglycan in bacteria).
DNA is a **single circular chromosome** located in the **nucleoid** region.
**Plasmids** – small circular DNA molecules that carry extra genes (e.g., antibiotic resistance).
**Ribosomes** are present but smaller than eukaryotic ribosomes.
Some prokaryotes have **flagella** for movement and **pili** for attachment or conjugation.

Organelle Functions Summary

**Nucleus** – stores genetic information (DNA).
**Mitochondria** – powerhouses of the cell; produce ATP.
**Chloroplasts** – sites of photosynthesis (plant cells only).
**Ribosomes** – protein synthesis.
**Cell membrane** – regulates transport; maintains homeostasis.
**Cell wall** – provides structural support (plants, bacteria).
**Vacuole** – storage and waste management; in plants, maintains turgor.

Animal cell with key organelles labelled.

Plant cell showing additional structures: cell wall, chloroplasts, and large vacuole.

Prokaryotic cell (bacterium) with key features: nucleoid, plasmids, ribosomes, cell wall, and flagellum.

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Practice questions

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1.What is the basic structural and functional unit of all living organisms?
Easy
- ACell
- BNucleus
- COrganelle
- DTissue
2.Which structure is found in plant cells but not in animal cells?
Easy
- ACell wall
- BNucleus
- CMitochondrion
- DCell membrane
3.Which organelle is responsible for providing energy to the cell through aerobic respiration?
Medium
- AMitochondrion
- BChloroplast
- CRibosome
- DNucleus
4.Prokaryotic cells lack which of the following structures?
Medium
- AMembrane-bound nucleus
- BCell membrane
- CRibosomes
- DCytoplasm
5.Which component of the cell envelope in bacteria provides rigidity and prevents bursting in a hypotonic environment?
Hard
- ACell wall
- BCell membrane
- CCapsule
- DPlasmid
6.In the diagram of a bacterium, which structure contains the genetic material?
Medium
- ANucleoid
- BNucleus
- CRibosome
- DPlasmid
7.What is the function of the cell membrane?
Easy
- ATo control what enters and leaves the cell
- BTo provide energy
- CTo store genetic material
- DTo make proteins
8.Which of the following is found in both plant and animal cells?
Medium
- AMitochondrion
- BChloroplast
- CCell wall
- DLarge central vacuole

Revision notes

## Cell Structure and Function - Quick Revision ### Key Concepts - **Cell**: basic structural and functional unit of all life. - **Cell Theory** (Schleiden & Schwann, 1839): 1. All organisms are composed of one or more cells. 2. Cells are the fundamental unit of structure and function. 3. All cells come from pre-existing cells. ### Two Main Cell Types - **Prokaryotes**: no nucleus, no membrane-bound organelles; single-celled (bacteria, archaea). - **Eukaryotes**: have a nucleus and membrane-bound organelles; can be single-celled or multicellular (animals, plants, fungi, protists). ### Eukaryotic Organelles (Focus for Middle School) - **Nucleus**: contains DNA; controls cell activities. - **Cell membrane**: semipermeable barrier; controls what enters/leaves. - **Cytoplasm**: jelly-like fluid; site of many chemical reactions. - **Mitochondria**: powerhouse; produce energy (ATP) for the cell. - **Chloroplasts** (plants only): site of photosynthesis; convert sunlight to sugar. - **Cell wall** (plants, bacteria, fungi): rigid outer layer; provides support and protection. - **Vacuole**: storage of water, nutrients, wastes; large in plant cells. - **Ribosomes**: make proteins; found in both prokaryotes and eukaryotes. ### Prokaryotic Features - No nucleus; DNA in **nucleoid** region. - Cell wall (peptidoglycan in bacteria). - May have **flagella** (movement), **pili** (attachment), **capsule** (protection). - Small (0.1–5.0 μm); simple structure. ### Cell Membrane - Semipermeable; made of phospholipid bilayer. - Protects cell, regulates transport. ### Comparison | Feature | Prokaryote | Eukaryote | |---------|------------|-----------| | Nucleus | Absent (nucleoid) | Present | | Membrane-bound organelles | Few/absent | Many | | Size | 0.1–5 μm | 10–100 μm | | Examples | Bacteria, archaea | Animals, plants, fungi | ### Key Facts - Cells discovered by Robert Hooke (1665). - First cells appeared ~4 billion years ago. - Most cells visible only under microscope.

Cell: The basic structural and functional unit of all living organisms.
Cell theory: All organisms are made of cells; cells are the basic unit of life; all cells come from pre-existing cells.
Prokaryote: A single-celled organism without a nucleus or membrane-bound organelles (e.g., bacteria, archaea).
Eukaryote: An organism whose cells have a nucleus and membrane-bound organelles; can be single-celled or multicellular.
Nucleus: Membrane-bound organelle that contains the cell's DNA and controls cell activities.
Cell membrane: Semipermeable barrier surrounding the cell that controls what enters and leaves.
Cytoplasm: Jelly-like substance inside the cell where chemical reactions occur.
Mitochondria: Organelles that produce energy (ATP) for the cell; the 'powerhouse'.
Chloroplast: Organelle in plant cells where photosynthesis occurs; converts light energy to sugar.
Cell wall: Rigid outer layer found in plants, bacteria, and fungi that provides support and protection.
Vacuole: Organelle that stores water, nutrients, and wastes; large in plant cells.
Ribosome: Organelle that makes proteins; found in both prokaryotes and eukaryotes.
Nucleoid: Region in prokaryotic cells where the circular DNA is located; not enclosed by a membrane.

Flashcards

What is the basic structural and functional unit of all living organisms?

The cell is the basic structural and functional unit of all forms of life.

What are the two main types of cells?

Prokaryotic cells (lack a nucleus) and eukaryotic cells (have a membrane-bound nucleus).

Which organelles are found in eukaryotic cells but not in prokaryotic cells?

Eukaryotic cells have membrane-bound organelles such as a nucleus, mitochondria, and chloroplasts (in plants).

What is the function of the cell membrane?

The cell membrane is a semipermeable barrier that controls what enters and leaves the cell.

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

The nucleus contains the cell's genetic material (DNA) and controls the cell's activities.

What is the function of mitochondria?

Mitochondria provide energy for the cell by converting nutrients into ATP through cellular respiration.

What is the function of chloroplasts?

Chloroplasts capture light energy and use it to produce sugars through photosynthesis.

What is the function of the cell wall?

The cell wall provides structural support and protection, and prevents the cell from bursting in hypotonic environments.

What is the function of ribosomes?

Ribosomes are the site of protein synthesis, where amino acids are assembled into proteins.

What is the function of the cytoplasm?

Cytoplasm is a jelly-like substance that fills the cell and holds organelles in place; many chemical reactions occur here.

What is the function of vacuoles?

Vacuoles store water, nutrients, and waste products; in plant cells, a large central vacuole maintains turgor pressure.

What are the three parts of cell theory?

1) All organisms are composed of one or more cells. 2) The cell is the basic unit of structure and function. 3) All cells come from pre-existing cells.

Who discovered cells and in what year?

Robert Hooke discovered cells in 1665.

What is the main difference between prokaryotic and eukaryotic cells?

Prokaryotic cells lack a membrane-bound nucleus and other membrane-bound organelles; eukaryotic cells have a nucleus and membrane-bound organelles.

What is the nucleoid?

The nucleoid is the region in a prokaryotic cell where the circular DNA is located, not enclosed by a membrane.

What are examples of prokaryotes?

Bacteria and archaea are prokaryotes.

What are examples of eukaryotes?

Animals, plants, fungi, and protists are eukaryotes.

What is the function of flagella?

Flagella are long, whip-like appendages that help cells move.

What is the function of pili?

Pili are hair-like structures on the surface of bacteria that help them attach to surfaces or other cells.

What is the cell wall of bacteria made of?

The bacterial cell wall is made of peptidoglycan.

What is the function of the bacterial capsule?

The capsule is a gelatinous layer that protects bacteria from drying out and from attack by white blood cells.

What is the function of plasmids?

Plasmids are small, circular DNA molecules that carry extra genes, such as antibiotic resistance genes.

What is the function of the cytoskeleton?

The cytoskeleton helps maintain cell shape, enables movement, and aids in cell division.

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