Biology Cells Quiz

Study Notes

Cells are the Basic Unit of Life

Cells are the fundamental building blocks of all living organisms, whether single-celled (unicellular) or multicellular.
They are responsible for carrying out all the essential life processes.

Types of Cells

Prokaryotic cells: Lack a membrane-bound nucleus and other internal organelles.
- Examples include bacteria and archaea.
- Are the simplest and most ancient forms of life on Earth.
- Some prokaryotes, like cyanobacteria, are capable of photosynthesis.
- Many prokaryotes thrive in extreme environments, making them extremophiles.
Eukaryotic cells: Possess a true nucleus containing their genetic material (DNA) and other membrane-bound organelles.
- Include both single-celled organisms (like protists) and multicellular organisms (like plants, animals, and fungi).
- Evolved later than prokaryotic cells, approximately 1.7 to 1.9 billion years ago.

Major Parts of a Cell

Nucleus: The control center of the cell.
- Contains DNA, which carries the genetic instructions for the cell.
- Regulates gene expression, directing the synthesis of proteins.
Cell Membrane: A thin, double-layered barrier that surrounds the cell.
- Controls the movement of substances in and out of the cell, maintaining its internal environment.
Cytoplasm: The fluid that fills the cell, located between the cell membrane and the nucleus.
- Serves as the site for numerous metabolic reactions.
- Provides structural support to the cell.

Organelles: The "Little Organs" of the Cell

Organelles are specialized structures within a cell that perform specific functions.
- They contribute to the overall functioning of the cell.

Membrane-Bound Organelles

Nucleus: The largest organelle in the cell.
- Contains chromosomes, which are thread-like structures made up of DNA and proteins.
- Responsible for cell growth, reproduction, and protein synthesis.
Nucleolus: A smaller structure within the nucleus.
- Composed of RNA and proteins.
- Responsible for the production and assembly of ribosomes.
Nuclear Membrane: A double-layered membrane that encloses the nucleus.
- Separates the chromosomes from the cytoplasm.
- Provides structural support to the nucleus.
Endoplasmic Reticulum (ER): An extensive network of interconnected membranes in the cytoplasm.
- Smooth ER: Composed of tubules and lacks ribosomes.
  - Involved in the synthesis and storage of lipids and steroids.
- Rough ER: Covered with ribosomes.
  - Involved in protein synthesis.
Golgi Apparatus: A stack of flattened sacs found in both plant and animal cells.
- Responsible for processing, modifying, and packaging proteins and lipids that are received from the ER.
- Involved in transporting these molecules to other parts of the cell or to the cell's exterior.
Lysosomes: Spherical sacs containing digestive enzymes.
- Break down biomolecules, including carbohydrates, lipids, proteins, and nucleic acids.
- Involved in recycling food particles and destroying invading bacteria.
Mitochondria: Known as the "powerhouse of the cell."
- Responsible for aerobic respiration, a process that produces energy in the form of adenosine triphosphate (ATP).
- Essential for providing the energy required for cellular processes.
Chloroplasts: Found in plant cells.
- Site of photosynthesis, the process by which plants convert light energy into chemical energy (sugars).
Vacuoles: Storage structures that store water, nutrients, and waste products.
- Larger in plant cells than in animal cells.
- Play a role in maintaining cell turgor pressure, keeping cells rigid.
Peroxisomes: Organelles containing enzymes that oxidize organic substances like fats.
- Break down toxic materials and use oxygen to break down molecules.

Non-Membrane-Bound Organelles

Cell Wall: A rigid outer layer found in plant cells.
- Provides structural support and protection to the cell.
- Maintains cell shape and prevents the cell from bursting due to high internal pressure.
Centrioles: Organizing centers for microtubules, found in animal cells.
- Important for cell division (mitosis and meiosis).
- Form spindle fibers during cell division, which attach to chromosomes and help move them apart.
Ribosomes: Small organelles composed of RNA and proteins.
- Found in both plant and animal cells.
- Involved in protein synthesis, translating genetic information from mRNA into amino acid chains, which then fold into functional proteins.