Cell StructureChpt. 7

Microscopes

Simple Microscope• uses single lens• max magnification x400• uses light

Compound Microscope• microscope used in our labs.• max magnification

x1000

Compound Microscope

• Has two magnifying lens:

- the Eyepiece Lens is the lens that you look through.

- the Objective lens is the lens that is immediately above the specimen.

Compound Microscope

The Objective Lens:

• There are three objective lenses:

- the scanning lens with the 4X label- the low power lens with the 10X label- the high power lens with the 40X label

Compound MicroscopeParts of the Microscope

Compound MicroscopeParts of the Microscope

Part Function

Lenses Magnification

Stage To place the slide on

Clips Hold the slide in place

Diaphragm To control the amount of light

Coarse Focus Knob

To focus the image

Fine Focus Knob To precisely focus the image

Light To supply light to the object

Compound MicroscopeMagnification

Total Magnification:

magnifying power of the eyepiece lens x

the magnifying power of the objective lens

Example:

Eyepiece lens = 10XObjective lens = 4X

Total magnification = 10 x 4= 40X

Cell Structure seen using the Light Microscope

Robert Hooke

Robert Hooke looked at thin slices of cork under a microscope.

He thought the spaces he saw reminded him of Monks Cells –

Hence the name cells

Cell Structure seen using the Light Microscope

Animal CellCytoplasm:• living material outside the nucleus.

• most reactions take place in cytoplasm.

Protoplasm:• comprises all the living parts of the cell e.g. Nucleus and surrounding cytoplasm.

Cell Structure seen using the Light Microscope

Plant CellCell Wall: - made of cellulose - function: supportCell Membrane: - pressed close to cell wallVacuoles: - contain cell sap - function:

strength shape

store materialsChloroplasts: - photosynthesis

Electron MicroscopeAllow cell structure to be seen in greater detail

- ultrastructure

Electron Microscope

•Uses Electrons instead of light

•Electrons have much lower wavelength than light – image is shown on a screen or as a photograph

•Resolution is much better

•Magnification is much greater

Images from Electron Microscope

Bacteria

Cytoplasm

Platelet

Electron Microscope

2 Types

Transmission Electron Microscope (TEM)• beam of electrons sent through thin section of the sample and shows

the INTERNAL structure

Scanning Electron Microscope (SEM)

• beam of electrons provides a surface view.

Cells

- All living things are composed of one or more cells.

- Cells are the basic units of structure and function

in an organism.

- Cells come only from reproduction of existing cells.

Organelles

• Cells contain a variety of internal structures called ORGANELLES.

• An organelle is a cell component that PERFORMS SPECIFIC FUNCTIONS FOR THE CELL

Organelles we need to know

•Cell membrane•Nucleus

•Mitochondria•Chloroplast•Ribosomes•DNA

•Cell Wall•Vacuole•Nucleolus

Animal Cells Animal Cells contain the following structures

Cell Membranes

Mitochondria

Nucleus

Cytoplasm

Only the cell membrane, the cytoplasm and the nucleus can be seen under the light microscope.

Cell (Plasma) Membrane

Cell Membrane: composed of phospholipids and proteins.

Cell (Plasma) Membrane

Phospholipids:• contain a water-loving phosphate group and a water-hating lipid group.

• arranged into double layers - bilayers

Phosphate(Water loving)

Lipid (Water Hating)

Cell (Plasma) Membrane

Proteins:• completely or partially embedded in phospholipid bilayer.

The phospholipids and proteins are in constant motion.

Therefore membranes are thought of as fluids

Functions of Cell Membrane

• Separate the cell organelles and cytoplasm from the outside. • Semi permeable – controls what enters and

leaves the cell.

• Membranes give some support to the cell. • Membranes recognise molecules that touch them.

Nucleus

• A large organelle near the center of the cell is the NUCLEUS. 

• It contains the cell's genetic information.

• It is the control centre of the cell.

Ultra Structure of the Nucleus

What’s in the Nucleus???Double Membrane: nucleus is surrounded by a double membrane with nuclear pores.

Nuclear Pores: allows the controlled entry and exit of molecules in and out of the nucleus e.g.

- allow a type of RNA called mRNA to pass

in and out of the nucleus.

Nucleolus:

• contains RNA, DNA and protein.

• is responsible for making ribosomes which

are made up of RNA (Ribonucleic acid).

What’s in the Nucleus???

Chromosomes:• nucleus contains strands of DNA which are arranged into structures called Chromosomes.

• genes are located randomly along chromosomes:

genes = units of inheritance

• when cell is not dividing the chromosomes form a mass of threads called chromatin.

Functions of Nucleus

• directs growth, development and activities of the cell.

• makes replicas of DNA for new cells

• carries out cell division

• instructs the formation of enzymes and hormones

Cytoplasm• liquid in a cell that surrounds the nucleus

• small bodies called organelles are suspended in the cytoplasm:

1. Mitochondria

2. Chloroplasts

3. Ribosomes

4. Vacuoles

Cytoplasm Organelles

Mitochondria

Cytoplasm OrganellesMitochondria

• Found in all cells except bacteria.

• Supply energy to the cell – sites of respiration:

Lots of mitochondria Lots of energy

Few mitochondria Less energy

• Consist of a smooth outer membrane and a folded inner membrane.

• It is on the inner membrane, especially the infoldings, that energy is released. Therefore the more infoldings the more energy produced.

Cytoplasm OrganellesMitochondria

Inactive mitochondria: - have a decrease in infoldings and as a result a decrease in the energy released.

Active mitochondria:- have a increase in infoldings and as a result an increase in the energy released.

Cytoplasm OrganellesChloroplasts (Plants Only)

• Found in plant cells only.• Green structures in which photosynthesis takes place.• Contain the green pigment chlorophyll.

Cytoplasm OrganellesUltrastructure of the Chloroplast

The thylakoids contain the chlorophyll which traps the sun’s energy

Cytoplasm OrganellesRibosomes

• Found in all cells

• Tiny, bead – like structures

• Made up of ribonucleic acid (RNA) and proteins.

• Function: - to make proteins by combining a sequence of amino acids.

Cytoplasm OrganellesVacuoles

• Vacuoles are membrane-bound sacs within the cytoplasm of a cell.

• Vacuoles provide structural support, as well as serving functions such as storage, waste disposal, protection, and growth.

• Plant cells have large vacuoles

Cell Wall

• Found in plant cells only

• Made of cellulose

• Very strong and contributes the following to the cell:

- strength- protection- shape

Ultra Structure of an Animal Cell

Ultra Structure of a Plant Cell

Differences between Plant and Animal Cells

Plant Cells Animal Cells

Have cell walls No cell walls

Contain chloroplasts Do not contain chloroplasts

Contain chlorophyll Do not contain chlorophyll

Have large vacuoles Have small (if any) vacuoles

Prokaryotic and Eukaryotic Cells

Living things can be placed into special categories depending on the complexity and

structure of their cells.

Prokaryotic Cells

Do not have a nucleus or membrane enclosed organelles.

• They are single celled organisms e.g. Bacteria

• Their DNA is found as circular loops found in the cytoplasm.

• Do not have mitochondria or chloroplasts.

• Respiration and photosynthesis is carried out on infolding of the plasma membrane.

Eukaryotic CellsHave a nucleus and cell organelles, all of

which are enclosed by membranes

• More advanced than prokaryotic cells.

• Larger than prokaryotic cells.

• Plant and animal cells are examples of eukaryotic cells.