Cells

Discovery of the Cell

In 1665, Robert Hooke was one of the first people to see and identify cells.

• He used a microscope to look at thin slices of cork. The cork was made of thousands of tiny chambers.

• He called the chambers “cells” b/c they reminded him of a monastery’s tiny rooms, called cells.

Robert Hooke

The Cell Theory

Proposed by 3 scientists in the mid-1800’s

• All living things are made of cells.

• Cells are the basic unit of structure and function in living things.

• New cells are produced from existing cells.

The cell theory applies to ALL living things!

Prokaryotes and Eukaryotes

Prokaryote• Do not have a nucleus• Small and simple• Bacteria are prokaryotic

Eukaryotes• Have a nucleus • Larger and complex• Cells of protists, fungi,

plants, and animals are eukaryotic

Prokaryotes and Eukaryotes

Eukaryotic CellProkaryotic Cell

Cell Structure

Eukaryotic cells are divided into two major parts – the nucleus and the cytoplasm.

• The cytoplasm is the portion of the cell outside the nucleus, but inside the cell membrane.

Cell Structure

• Eukaryotic cells contain many structures, each with specialized functions. These specialized structures are called organelles.

Cell Structure - Nucleus• Contains almost all of the

cell’s DNA; the DNA contains genetic info and instructions for making proteins

• Controls the cell’s processes/activities

• The DNA exists as chromatin when the cell isn’t dividing. Chromatin consists of DNA and protein.

• Double membrane

Cell Structure - Nucleolus

• Inside the nucleus is a structure called the nucleolus.

• The nucleolus manufactures ribosomes.

Cell Structure - Ribosomes

• Ribosomes are tiny organelles that manufacture proteins.

• Ribosomes are located on rough endoplasmic reticulum and throughout the cytoplasm.

Cell Structure – Endoplasmic Reticulum

• ER transports substances throughout the cell.

• Rough ER has ribosomes on it, so it produces proteins.

• Smooth ER lacks ribosomes

Cell Structure – Golgi Apparatus • Closely-stacked

membranes• Modify, sort, and

package proteins and other materials from the endoplasmic reticulum for storage in the cell, or secretion outside the cell.

Cell Structure - Lysosomes

• Lysomes are small sacs filled with digestive enzymes.

• These enzymes break down macromolecules into small molecules .

• They also break down old, worn-out organelles. They “clean up” the cell.

Cell Structure - Vacuole

• Large sac-like organelle in plant cells

• Stores water, carbs, proteins, and salts

• Is usually the largest organelle in plant cells

Cell Structure - Mitochondria

• Convert the chemical energy stored in food into compounds that are more convenient for the cell to use.

• “Powerhouse” of the cell

• Double membrane

Cell Structure - Chloroplasts

• Not found in animal or fungi cells

• Capture energy from sunlight and convert it into chemical energy in a process called photosynthesis.

• Double membrane

Cell Structure - Cytoskeleton

• In all cells, the cytoskeleton maintains the shape of the cell

• Cilia and flagella (extensions of the cytoskeleton) help some cells swim through water.

Cell Structure - Cytoskeleton

Cilia• Numerous• Short and hair-like• Help unicellular organisms • Help multicellular

organisms rid organs of dust and move mucous

Flagella• Usually a cell only has one• Long and whip-like• Help unicellular organisms

swim in liquids

Cell Structure – cell membrane

• Regulates what enters and leaves the cell

• Double layer of phospholipids

• Fluid mosaic model (not rigid)

• Selectively permeable

Cell Structure – Cell Wall

• Not present on animal cells

• Rigid; made of cellulose and protein

• Support and protect the cell

Plant vs. Animal Cells

Plant cells• “boxy” • Often green• Contain chloroplasts,

vacuole, and cell wall

Animal Cells• Variety of shapes

depending on function• May contain structures for

movement (cilia and flagella)

Plant Cells

Animal Cells

Transport Across Cell Membrane

• Passive transport requires no energy input from cell (Ex. Osmosis, diffusion, facilitated diffusion)

• Active transport requires energy input to move molecules across the cell membrane

Moving Across the Cell Membrane(Passive)

Diffusion is the movement of particles (solutes) from an area of greater concentration to an area of lesser concentration.

When the concentration of solutes on both sides of the cell membrane is the same, equilibrium exists.

• When equilibrium is reached, solute particles still continue to move across the membrane in both directions.

Moving Across the Cell Membrane

Moving Across the Cell Membrane

Osmosis is the diffusion of water across a membrane.

• Isotonic if concentration of dissolved particles is the same outside of cell compared to inside

• Hypertonic if concentration of dissolved particles is higher outside of cell compared to inside•Hypotonic if

concentration of dissolved particles is lower outside of cell compared to inside

Moving Across the Cell Membrane

Osmotic Pressure• What would happen to a cell if it were placed

in an isotonic solution?• What would happen to a cell if it were placed

in a hypertonic solution?• What would happen to a cell if it were placed

in a hypotonic solution?

Moving Across the Cell Membrane

Movement Across the Cell Membrane

During facilitated diffusion, molecules that cannot cross the cell membrane by themselves b/c they are too big, get help from protein channels in the membrane.

Uses transport protein

Endocytosis and Exocytosis

• Endocytosis • Exocytosis

Movement Across the Cell MembraneSometimes, cells must

move substances in the opposite direction of diffusion against the concentration gradient To move substances from a low concentration to a higher concentration requires energy. This requires active transport.

Uses transport protein

Cell Diversity

Unicellular Organisms• Made of only one cell

Multicellular Organisms• Made of many cells

Cell Diversity

Multicellular organisms are made of many, many specialized cells. In cell specialization, the cells of a multicellular organism develop in different ways to perform different tasks in the organism.

Levels of Organization

In multicellular organisms, the levels of organization of the body are (from simplest to most complex):

• Cells• Tissues - a group of similar cells that perform a particular

function (ex: nervous, connective, epithelial, and muscle)

• Organs - a group of tissues working together to perform a specific function (ex: heart, pelvis, uterus)

• Organ systems – group of organs working together to perform a specific function (ex: cardiovascular system, reproductive system)`