Cell Structure and Function Chapter 7 Biology Miller • Levine

The Scientists… Robert Hooke (1665) Anton van Leeuwenhoek (1674) Viewed cork under a microscope Called the chambers he saw “cells” Anton van Leeuwenhoek (1674) First to see living organisms in a drop of water

The Scientists… Matthias Schleiden (1838) Theodor Schwann (1839) All plants are made of cells Theodor Schwann (1839) All animals are made of cells Rudolf Virchow (1855) All cells come from preexisting cells

The Cell Theory All living things are composed of cells Cells are the basic units of structure and function in living things New cells are produced from existing cells

Unicellular vs. Multicellular Unicellular – single-celled organism Multicellular – many-celled organism Cell specialization – cells are specialized to perform certain functions Cells → Tissues → Organs → Organ systems → Organism

Prokaryotes vs. Eukaryotes Have a cell membrane & cytoplasm, but do not have a nucleus Ex. Bacteria such as E.coli Eukaryotes Have a nucleus, cell membrane, cytoplasm & organelles Ex. Plants, Animals, Fungi

Prokaryotes vs. Eukaryotes

Basic Cell Structures Cell membrane – thin, flexible barrier around the cell; protects the cell Present in all cells Cytoplasm – material inside the cell membrane (not including the nucleus) Prokaryotes & Eukaryotes

Cell Wall Found in many organisms, including plants, algae, fungi and nearly all prokaryotes Not found in animal cells Lies outside the cell membrane Main function is to provide support & protection for the cell

Nucleus Almost all eukaryotic cells, including plants and animals have a nucleus Prokaryotes do not have a nucleus Controls most cell process and contains the DNA

Nucleolus and Nuclear Envelope Inside the nucleus Where ribosomes are made Nuclear Envelope: Double-membrane layer around the nucleus Allows material to move into and out of the nucleus

Nucleus

Cytoskeleton Found in all eukaryotic cells Not found in prokaryotes A network of protein filaments that helps the cell maintain its shape It also is involved in cell movement

Ribosomes Found in all cells Main function is to make proteins Can be found floating in the cytosol or attached to endoplasmic reticulum

Endoplasmic Reticulum (ER) Found only in eukaryotic cells Where components of the cell membrane are assembled Two kinds: Smooth ER & Rough ER Smooth ER: no ribosomes; makes lipids Rough ER: has ribosomes; involved in making proteins

Endoplasmic Reticulum

Golgi Apparatus Found only in eukaryotic cells Enzymes attach carbohydrates & lipids to proteins Send proteins to their final destination

Lysosomes Found in animal cells only Break down lipids, carbohydrates & proteins from food into particles that can be used by the cell Also break down “dead” organelles

Vacuoles Not found in prokaryotes Animal cells have small or no vacuoles Plant cells have a large central vacuole Store materials such as water, salts, proteins & carbohydrates

Chloroplasts Found in all plant cells Some prokaryotes have them, but most do not Use the energy from sunlight to make energy-rich food molecules during photosynthesis

Chloroplasts

Mitochondria Found in eukaryotic cells only Release energy from stored food molecules

Cell Membrane Regulates what enters and leaves the cell (selectively permeable) Provides protection and support Lipid bilayer – two layers of lipids Proteins run through the layers Carbohydrates are attached to some of the proteins Fluid Mosaic Model

Cell Membrane

Diffusion Molecules move from an area of high concentration to an area of low concentration Movement continues until equilibrium is reached Many substances move across the membrane by diffusion Does not require energy (passive transport)

Diffusion

Osmosis The diffusion of water No energy is required Isotonic – equal concentration Nothing happens Hypertonic – higher concentration Water moves out of the cell Hypotonic – lower concentration Water moves into the cell No energy is required

Effects of Osmosis on Cells

Osmotic Pressure In pure water, an animal cell would burst Plant cells are protected by their cell wall Some freshwater organism have special structures like contractile vacuoles to get rid of extra water

Facilitated Diffusion Some molecules cannot cross the membrane without help Some of the proteins in the membrane form protein channels Materials still move from higher to lower concentrations No energy is required

Facilitated Diffusion

Active Transport Materials move from lower concentration to higher concentration Requires an input of energy Works kind of like a pump

Transport of Large Amounts Endocytosis – movement into the cell Phagocytosis – “cell eating” – solid particles Pinocytosis – “cell drinking” – particles dissolved in water Exocytosis – movement out of the cell

Phagocytosis

Pinocytosis