Biology Chapter: What are Cells?

What are Cells?

• Cells are the smallest living units of an organism
• All cells share three common features: a cell membrane, cytoplasm, and DNA

Cell Membrane

• Separates the cell's interior from the external environment

Cytoplasm

• Gelatinous fluid within the cell

DNA

• The cell's genetic material

Types of Cells

Eukaryotic Cells

• More complex than prokaryotic cells
• Contain organelles, including the nucleus and other specialized structures
• Found in plants and animals

Prokaryotic Cells

• Lack a nucleus or membrane-bound organelles
• Genetic material is not enclosed within a nucleus
• Always single-celled organisms (unicellular), like bacteria

What are Organelles?

• “Small organs”
• Specialized parts of the cell with specific functions

Nucleus

• Control center of the cell
• Contains DNA
• Dictates cellular processes and function

Chromatin

• DNA in its interlinked and dispersed form within the nuclear membrane
• Condenses into chromosomes when the cell is about to divide

Nucleolus

• Structure within the nucleus responsible for ribosome production

Ribosomes

• Synthesize proteins
• Move freely within the cytoplasm or attach to the endoplasmic reticulum (ER)

Endoplasmic Reticulum (ER)

• Network of membranes that transport materials like proteins (synthesized by ribosomes)
• Two types:
  • Rough (granular) ER - ribosomes attached
  • Smooth (agranular) ER - no ribosomes

Golgi Apparatus

• Also called Golgi body
• Receives proteins and other materials from the ER
• Modifies proteins
• Packages them into usable forms for the cell
• Adds lipids or carbohydrates to proteins

Vacuoles

• Sac-like structures for storing various materials
• In plant cells, the central vacuole stores water

Lysosomes

• Waste disposal centers
• Contain enzymes to break down used or damaged parts of the cell

Mitochondria

• Powerhouses of both plant and animal cells
• Produce ATP molecules through cellular respiration, which provides energy for cellular processes
• Cells with higher energy requirements have more mitochondria

Cytoskeleton

• Supports and maintains the shape of the cell
• Contains:
  • Microfilaments: thin protein filaments
  • Microtubules: hollow tubes

Chloroplasts

• Found in plant cells
• Site of photosynthesis
• Green due to the pigment chlorophyll

Cell Wall

• Present in plant cells outside the cell membrane
• Provides shape, support, and protection

Cilia

• Tiny hair-like projections
• Found in cells lining the respiratory tract
• Wave-like movements help capture inhaled particles and expel them through coughing

Flagella

• Tail-like structures
• Found in some bacteria
• Allow the cell to move or propel itself forward
• The only human cell with a flagellum is the sperm

Summary

• Eukaryotic cells (plant and animal cells) have a nucleus and membrane-bound organelles
• Prokaryotic cells (unicellular organisms) lack these features
• All cells have a cell membrane, cytoplasm, and genetic material
• Only plant cells have chloroplasts, but both plant and animal cells have mitochondria