Cell Types and Cell Structure

Overview of Cells

• Cells are the basic building blocks of life.

• Definition: Cells are the smallest unit of life that can replicate independently.

• Types of cells to be covered:

  • Eukaryotic cells (Animal and Plant)

  • Prokaryotic cells (Bacterial cells)

Types of Cells

Eukaryotic Cells

Animal Cells

• Animal cells are multicellular, meaning they contain many cells.

• When cells in animals divide, they typically grow or replace dead cells rather than forming new organisms.

Plant Cells

• Plant cells are also multicellular.

• Similar to animal cells in structure but have additional components.

Prokaryotic Cells

Bacterial Cells

• Bacteria are unicellular organisms and consist of a single prokaryotic cell.

• Each bacterial cell is a whole organism.

• Unlike eukaryotic cells, bacteria do not have a nucleus or membrane-bound organelles.

Cell Characteristics

Size and Composition

• An adult human is thought to contain over 40 trillion cells.

• Cells vary in type, with hundreds of different types identified in humans.

Structure of Cells

• Understanding cell structure includes examining their subcellular structures, often referred to as organelles.

Common Structures in Eukaryotic Cells

1. Cell Membrane

• Function: Regulates substance passage into and out of the cell.

• Selectively permeable; allows some substances in while keeping others out.

2. Nucleus

• Contains the cell's genetic material (DNA).

• Controls cell activities and functions.

3. Cytoplasm

• A gel-like substance in which organelles are suspended.

• Site of many chemical reactions; consistency akin to jelly.

4. Mitochondria

• Known as the powerhouse of the cell.

• Function: Provide energy through aerobic respiration, breaking down sugars like glucose.

• Energy released is vital for cellular functions.

5. Ribosomes

• Sites of protein synthesis (where proteins are made).

• Present in high quantities to facilitate the production of proteins.

Additional Structures in Plant Cells

1. Cell Wall

• Comprised of cellulose, provides structure and support to plant cells.

• Prevents cells from bursting due to excessive water intake.

2. Permanent Vacuole

• Large sac filled with cell sap (a mixture of sugars, salts, and water).

• Stores nutrients and helps maintain turgor pressure within the cell.

3. Chloroplasts

• Site of photosynthesis, enabling plants to convert sunlight into chemical energy (glucose).

• Contains chlorophyll which is the pigment that absorbs light energy for photosynthesis and give plants their green colour. It:

  • Absorbs light energy (mostly red and blue light).

  • Converts light energy into chemical energy during photosynthesis.

  • Allows plants to make glucose (food) from carbon dioxide and water.

  • Releases oxygen as a by-product.

• Chloroplasts are the “factories,” and chlorophyll is the “solar panel” inside them that absorbs light energy.

Structure of Bacterial Cells

Key Characteristics

• Bacterial cells have:

  • Cell membrane

  • Cell wall

  • Ribosomes

  • Cytoplasm

• Bacteria differ as they lack mitochondria and chloroplasts.

Genetic Material

• Instead of a nucleus, bacteria have a single circular strand of DNA that floats in the cytoplasm, known as the nucleoid or circular chromosome.

• May contain plasmids: small rings of additional DNA that can carry genes for antibiotic resistance.

Mobility

• Some bacteria have flagella, thread-like structures that enable movement by rotating and propelling the bacterium.

Conclusion

• Cells are an integral part of all living organisms with specific structures performing unique functions.

• Understanding the difference between eukaryotic and prokaryotic cells is key to understanding biology as a whole.