Homeostasis, Cell Structure, and Function Flashcards
Homeostasis
The process of maintaining balance in an organism’s internal environment
One of the structures responsible for homeostasis is the plasma membrane.
The plasma membrane forms a thin, flexible boundary between a cell and its environment.
The plasma membrane is composed of phospholipid bilayer – two layers of phospholipids are arranged to allow the membrane to exist in a watery environment.
The phospholipid bilayer has polar heads facing outside and nonpolar tails facing inside the cell, allowing the membrane to keep the internal and external environments separate.
History of the Cell Theory
A cell is the basic structural and functional unit of all living organisms. Robert Hooke first used the term “cell.”
Cells are so small that their existence was unknown before the invention of microscopes.
The cell theory is one of the fundamental ideas of modern biology, and includes the following three principles:
The cell theory
- All living organisms are composed of one of more cells.
- Cells are the basic unit of structure and organization of all living organisms.
- Cells arise only from previously existing cells, with cells passing copies of their genetic material on to their daughter cells.
Eukaryotic cells contain a nucleus and other organelles.
Organelles are specialized structures that perform specific cell functions.
Eukaryotic cells contain a nucleus and other organelles.
The nucleus is the distinct central organelle that contains the cell’s genetic material.
Eukaryotic cells are generally much larger than prokaryotic cells.
Prokaryotic cells are cells without a nucleus or other membrane-bound organelles.
Smaller and simpler than eukaryotes
Believed to be similar to the first organisms that lived on earth
Eukaryotic cells likely evolved from prokaryotic cells.
The endosymbiont theory proposes that a symbiotic relationship formed between two prokaryotic cells, one of which lived inside the other.
Eventually the symbiotic relationship led to the two cells becoming one.
Origin of cell diversity
Because eukaryotic cells are larger and more complex, they developed specific functions.
These specific functions led to cell diversity, and thus organismal diversity.
Plasma membranes have selective permeability, meaning they allow some substances to pass through while keeping others out.
Control of how, when, and how much of various substances enter and leave a cell depends on the structure of the plasma membrane.
Structure of the Plasma Membrane
Polar substances dissolve in polar substances.
Non-polar substances dissolve in non-polar substances.
Small, uncharged molecules pass through the cell membrane easier than larger, charged molecules.
Other components of the plasma membrane
The plasma membrane also contains cholesterol, proteins, and carbohydrates.
Roles of proteins in the plasma membrane
Receptors: transmit signals to the inside of the cell.
Support: give membrane structure and strength.
Transport: form channels to move substances through the membrane.
Roles of cholesterol in plasma membrane
Cholesterol is non-polar; prevents the fatty acid tails of the phospholipid bilayer from sticking together.
Cholesterol contributes to the fluidity of the membrane.
Roles of carbohydrates
Carbohydrates define the cell’s characteristics
Help cells identify chemical signals
Roles of carbohydrates
Glycoproteins: carbohydrates (glycogen) attached to proteins
Glycolipids: carbohydrates attached to lipids
Other components of the plasma membrane
The fluid mosaic model describes the phospholipids in the bilayer as a “sea” in which other components can float and move around.
The different substances in the plasma membrane create a pattern or mosaic on the surface of the cell.
