Chapter 7 Notes Cell Structure and Function
I. Cells and Cell Theory • Cell: the basic unit of all forms of life • History 1. Robert Hooke (1665) - described the empty chambers of cork as “cells”
2. Matthias Schleiden (1838) - all plants are made of cells 3. Theodor Schwann (1839) - all animals are made of cells 4. Rudolph Virchow (1855) - all cells come from preexisting cells ** before this, people believed in spontaneous generation
Cell Theory 1. All living things are composed of 1 or more cells 2. Cells are the basic units of life 3. All cells come from preexisting cells ** exception: viruses?
II. Prokaryotes and Eukaryotes • Prokaryotic cells do not have nuclei - example: all bacteria • Eukaryotic cells have nuclei and organelles - example: plants, animals, fungi
III. Cell Structures • Cytoplasm: everything between the membrane and nucleus 1. Structure a. Cytosol: jelly-like mixture consisting of water, proteins, carbohydrates, and other organic compounds
b. Organelles: structures that work like miniature organs, carrying out specific functions in the cell (suspended in the cytosol) 2. Function a. Biological reactions take place in the cytosol b. Organelles each have specific jobs within the cell
3. Analogy - like the body of a person organelles = organs cytosol = everything surrounding organs
IV. Cell Shape and Size • Maintenance of shape 1. In plants: cell wall 2. In animals: cytoskeleton • Cytoskeleton - consists of 2 types of structures 1. Microtubules: hollow tubes made of tubulin
a. Cilia: short, hair-like projections b. Flagella: long, whip-like projections
2. Microfilaments: NOT hollow – 2 twisted chains of proteins (like a rope) • Size of Cells - can vary from 1 micrometer (bacteria) to 1 meter (nerve cell)
V. Movement through the Membrane • The cell membrane is semipermeable - only certain molecules can get through • Passive transport: no energy required 1. Diffusion: the movement of molecules from a region of high concentration to a region of low concentration
- continues until equilibrium is reached (equal concentrations on both sides of membrane)
- temperature affects diffusion: higher = faster - size of particles affects diffusion: smaller = faster
97% water 100% water 2. Osmosis: the diffusion of water across a membrane from high water concentration to low water concentration Which way will the water move?
97% water 90% water Which way will the water move?
95% water 95% water 90% water 98% water This solution is hypertonic - water diffuses out of the cell This solution is hypotonic - water diffuses into the cell
95% water 95% water This solution is isotonic - no net change
3. Facilitated diffusion: uses protein channels to move molecules from high concentration to low concentration • Active Transport: energy required 1. Carrier proteins may act as pumps -example: sodium-potassium pump a. Cells continually pump potassium ions into the cell, and sodium ions out
Na+ • Important for muscle contraction and nerve impulse transmission K+
a. Pinocytosis: membrane encloses a fluid droplet and brings it inside the cell b. Phagocytosis: membrane encloses a large particle and brings it inside the cell
3. Exocytosis: materials move outside the cell - wastes and cell products may leave the cell this way