Cell Unit

Objectives:• Describe cell organelles and their functions.• Differentiate between prokaryotic and eukaryotic cells.• Compare and contrast plant and animal cells.• Identify scientists who were important to cell discovery and cell theory and discuss these findings.• Label cell structures.

Vocabulary: cell * unicellular * multicellular * Hooke * Virchow *

Leeuwenhoek * Schleiden * Schwann * cell theory * eukaryote * endosymbiosis * prokaryote * cell membrane * cytoplasm * nucleus * selectively or semi-permeable * cytoplasmic streaming * organelle * ribosome * rough & smooth endoplasmic reticulum * Golgi apparatus * Mitochondria * lysosomes * microtubules * microfilaments * spindle fibers * cilia * flagella * nucleoplasm * nucleolus * cell wall * vacuole * plastid * chloroplast * chromoplast * leukoplast * tissues * organ * organ system * osmosis * diffusion * hypertonic * isotonic * hypotonic * homeostasis * concentration gradient * equilibrium * turgor pressure * plasmolysis * cytolysis * contractile vacuoles * passive transport * active transport * facilitated diffusion * endocytosis * pinocytosis * phagocytosis * exocytosis

Robert Hooke was the first to see little box shaped structures in dead plant tissue. He called them “cells”.

Anton van Leeuwenhoek (a microscope maker) was the first to observe living cells.

How might the appearance of dead cells differ from living cells?

Botanist, Matthias Schleiden, discovered all plants are made of cells.

Theodor Schwann declared that all animals are made of cells.

Rudolf Virchow found that all cells come from pre-existing (already living) cells.

And so it became apparent that the cell is the basic unit of life.

Cell Theory:1. All living things are made of one or more cells.2. Cells are the basic unit of structure and function in

living things. 3. Cells are produced by existing cells. (Virchow)

Types of Cells:

Eukaryotes which contain a membrane bound nucleus and membrane bound organelles. (Ex: plant, animals, fungi, algae, etc.) Some scientists believe that eukaryotic cells evolved from prokaryotic cells through endosymbiosis.

Prokaryotes which lack a true nucleus and membrane bound organelles. (Ex: Bacteria)

Note: bacteria, and only bacteria, are prokaryotes.

Cell Structure

Nucleus - The nucleus is considered the control center of the cell. It directs all cell activities including cell division. The nucleus is filled with a gel-like fluid called nucleoplasm which contains chromatin (DNA and protein - the hereditary information) Chromatin condenses to form chromosomes when the cell is ready to divide. The genetic material in the nucleus codes for all of the proteins and other substances the body needs.

The nucleolus - is found in most cell nuclei and this is where the assembly of ribosomes occurs before being transported out of the nucleus to the cytoplasm.

The nuclear envelope is a double membrane made mostly of lipids but containing pores and protein channels to allow certain substances in and out.

Outside of the nucleus lie many organelles (“little organs” - each with a specific function) surrounded by the cytoplasm:

Cytoplasm - a protein rich, gel-like substance containing water and mineral salts. The cytoplasm flows around (and with) the organelles carrying nutrients, etc. to them and taking wastes away. The movement of the cytoplasm is called cytoplasmic streaming.

The cell membrane: - surrounds the cytoplasm, separating it from the

environment - gives shape to the cell- regulates what enters or leaves the cell. Since only

certain things may pass through, the membrane is called “semipermeable” or “selectively permeable”.

Insideof cell(cytoplasm)

Outsideof cell

Cellmembrane

Proteins

Proteinchannel

Lipid bilayer

Carbohydratechains

Figure 7-15 The Structure of the Cell Membrane

Analogy: In or Out?• How is a window screen similar to a cell membrane? Read on to find

out.

• 1. What are some things that can pass through a window screen?air, fine dust, and rainwater

• 2. What are some things that cannot pass through a window screen? Why is it important to keep these things from moving through the screen?

Insects, leaves, and other matter that may fall from trees. The screen keeps out annoying insects and objects that may bring dirt into the home.

• 3. The cell is surrounded by a cell membrane, which regulates what enters and leaves the cell. Why is it important to regulate what moves into and out of a cell?

Materials such as oxygen and food that are needed by the cell have to be able to get inside the cell. At the same time, excess materials have to leave the cell.

The cytoskeleton is made of protein structures called microtubules and microfilaments. They are the cell’s framework, helping the cell maintain its shape. They also help organelles move.

Microfilaments just under the cell membrane help material move in cytoplasmic streaming.

Specialized microtubules, called spindle fibers, help the movement of chromosomes during cell division. Other specialized microtubules form the centrioles in animal cells from which the spindle fibers project toward the chromosomes.

Some microtubules form hair-like projections extending out from the cell membrane. Cilia (short projections) and flagella (longer projections) help certain cells move. (Sperm move using flagella. Euglena move using cilia. Cilia line the respiratory tract to help expel dust, mucus, etc.)

Cell membrane

Endoplasmicreticulum

Microtubule

Microfilament

RibosomesMichondrion

Cytoskeleton

Ribosomes - make protein (used in growth, repair, hormones, enzymes, etc.) If the ribosome is free in the cell, it will probably make a protein that will be used within that cell. If the ribosome is bound to a folded membrane extension coming off of the nuclear membrane, called the endoplasmic reticulum, the protein will probably be exported from the cell.

Endoplasmic Reticulum (ER) is a folded membrane network:

A) Rough ER - contains ribosomes and will modify the proteins made by the attached ribosome.

B) Smooth ER - is continuous with rough ER but has no ribosomes. Smooth ER can store proteins from rough ER, make lipids, help prepare proteins for transport to Golgi apparatus, etc.

Animal Cell

Centrioles

Nucleolus

Nucleus

Nuclearenvelope

Rough endoplasmic reticulum

Golgi apparatus

Smooth endoplasmicreticulum

Mitochondrian

CellMembrane

Ribosome(free)

Ribosome(attached)

Figure 7-5 Animal Cells

Golgi Apparatus - receives proteins made by ribosomes on the rough ER and may attach a lipid or carbohydrate to the protein. It then packages the protein in a membrane bound vesicle for transport out of the cell via exocytosis.

Mitochondria - These are scattered throughout the cytoplasm. This is where cellular respiration occurs. Nutrients from food are converted to ATP, the cellular energy currency. They are the cell’s power plants. Mitochondria are so important that they have their own DNA!! (This is inherited strictly from the mother!) Cells that require more energy (Ex: muscles, the brain), have more mitochondria.

Lysosomes - are small, spherical organelles, containing strong enzymes that can help break down lipids, carbs., proteins, worn out organelles, bacteria, etc. They are like the garbage disposal is many ways. They are also important to embryonic development. They selectively destroy tissue on the hand so fingers can form. (Not found in plant cells.)

Cell wall - plant cells, fungal cell, and some bacteria have cell walls. Plant cell walls are made of cellulose (a tough carbohydrate) and lignin. Wood is made of old plant cell walls. The cell wall supports and protects the cell. It prevents plant cells from bursting from excess pressure if too much water is taken in. Note: Animal cells do NOT have cell walls! Too much water will cause animal cells to burst. This is called cytolysis.

Vacuoles - are storage areas for water, certain nutrients, toxins, etc. Plants often have a single large vacuole. The water pressure in the vacuole can help plant cells stay firm. If a plant becomes dehydrated, the cell membrane may pull away from the tough, fibrous cell wall. This is called plasmolysis. If a plant’s vacuoles are filled with fluid and the plant stands erect, this is called turgor pressure. (Animal cells may have SMALL vacuoles.)

Plants also have specialized organelles called plastids.

Chloroplasts contain green chlorophyll and/or other secondary pigments that help absorb energy from sunlight to drive photosynthesis. Carbon dioxide from the air and water from the soil are combined to make sugar. Oxygen and water are “waste” products.

6 CO2 + 12 H2O C6H12O6 + 6 O2 + 6 H2O

Chromoplasts - manufacture pigments (the colors in plants)

Leukoplasts - store food, i.e. starch (Ex: potatoes)

See p. 183 for a comparison of cell types.

Animal Cells Plant Cells

Lysosomes

Cell membraneRibosomesNucleusEndoplasmic reticulumGolgi apparatus VacuolesMitochondriaCytoskeleton

Cell Wall

Chloroplasts

Venn Diagram

Cells working together for a common purpose/function form tissues. (Ex: certain cell types work together to form the linings covering our organs) Tissues working toward a common function form organs. (Ex: the tissues covering our organs may work with contractile tissues and vascular tissues to form the heart) Organs working toward a common function form organ systems. (Ex: In the circulatory system, the heart works with arteries, veins, capillaries, etc. to deliver blood.)

Cells tissues organs organ systems

Improperly functioning cells can lead to illness or cancer.

Muscle cell Smooth muscle tissue Stomach Digestive system

Levels of Organization

Cell Homeostasis and Transport

Homeostasis - a balance that is maintained by regulating what gets in or out of the cell.

Diffusion - movement of molecules from an area of high concentration to low concentration. (Ex: when a sugar cube is put in hot tea and it breaks apart and spreads throughout the tea, sweetening it all.)

Concentration gradient - difference in concentration of a substance across space or across a membrane. (Ex: at first there are more sugar molecules close to the cube than in the rest of the tea)

Equilibrium - when molecules are evenly distributed throughout a substance or across a membrane.

Small molecules can sometimes move freely across a cell membrane by simple diffusion. When no ATP is needed to move a substance, it is called passive transport.

Water can diffuse freely across. When water diffuses across, it’s called osmosis.

But larger molecules may need special protein channels to allow them passage through the semi-permeable cell membrane. This is called facilitated diffusion. This is a type of passive transport.

Some substances cannot freely enter or leave the cell or they are being moved against the concentration gradient (from low to high concentration) These may require energy (ATP) and special protein gates for movement. This is called active transport. (Ex: the sodium-potassium pump concentrates K+ in the cell and Na+ outside)

HighConcentration

LowConcentration

CellMembrane

Glucosemolecules

Proteinchannel

Facilitated Diffusion

Single celled organisms often have a special organelle known as a contractile vacuole to regulate the amount of water or dissolved solutes within their cell. This prevents cell death. This too involves active transport.

Some substances cannot freely enter or leave the cell. These may require energy (ATP) and special protein gates for movement. This is called active transport.

If the solution surrounding a cell has more dissolved substances in it than the cell’s interior, the solution is hypertonic and water will try to leave the cell. In plant cells, the cell membrane may pull away from the cell wall, this is called plasmolysis - the plant wilts.

If the solution surrounding a cell has less dissolved substances in it than the cell’s interior, the solution is hypotonic and water will try to enter the cell. If the cell bursts, it’s called cytolysis.

A solution is isotonic if the concentration is equal on both sides.

Osmosis Cont.

• Hypertonic-more concentrated solution• Isotonic- same concentration solution• Hypotonic- less concentrated solution

Substances may also move in or out of the cell via vesicles.

When the cell draws substances in, it is called endocytosis To do this, the cell membrane indents and then surrounds a substance that has triggered a receptor site, creating a membrane encased vesicle..

If a liquid is drawn in this way, it’s called pinocytosis.

If a solid is drawn in this way, it’s called phagocytosis.

To export large substances or large amounts of a substance, the cell builds a membrane enclosed vesicle around the substance. Then the vesicle attaches to the cell membrane, fuses with it while opening up to the outside environment. This is called exocytosis.

Figure7-20 Active Transport

Endocytosis- cell membrane folds in to itself to take in particles

-Phagocytosis- type of endocytosis

Exocytosis- removal of large amounts of material from a cell

Cells

prokaryotic

Example

Which have no true…

Examples

Fungi & Protists

Organellesnot found in animal cells

Organelles found inplant & animal cells

Analogy: How is a factory like a cell?

nucleus

Main Office

Shipping Dept.

Golgi Body

Electricgenerator

ribosome

Cell membrane

Doors &Windows

mitochondria

cytoskeleton

walls

cafeteria

lysosome

Recycling center