Science 8 Unit B Section 2.0 Cells play a vital role in living things.

Section Outcomes Students will be able to identify the parts of a microscope Students will be able to use a microscope and prepare slides Students will be able to explain the role of cells as a basic unit of life Students will be able to identify plant and animal cells

Section Outcomes Students will be able to identify the differences between one-celled and multicelled organisms Students will be able to explain osmosis and diffusion Students will recognize the roles of cells, tissues, and organs

2.1 – The Microscope The human eye is limited in how well it can see small objects The limit to human vision is objects that have a diameter of about 0.1 mm Humans cannot see individual objects that are less than this size Therefore, to observe smaller objects, we need a microscope

The Compound Light Microscope Compound light microscopes all use light passing through a specimen and then a number of lenses to magnify objects We’ll look at the microscope and identify its parts:

Parts of the Microscope Ocular Lens (Eyepiece) Coarse Adjustment Knob

Parts of the Microscope Fine Adjustment Knob Revolving Nosepiece

Parts of the Microscope Objective Lenses Stage

Parts of the Microscope Stage Clips Condenser Lens

Parts of the Microscope Diaphragm Lamp (Light Source)

Parts of the Microscope ArmBase

Using Microscopes Microscopes are precision instruments and are therefore fragile Keep the following pointers in mind when using them:

2.2 – The Cell is the Basic Unit of Life Cells are the smallest functioning unit of life Cells are visible using microscopes The internal structures in the cell may be visible depending on: 1.The type of microscope used 2.The power of the lenses 3.The quality of the prepared slides

Preparing Slides Not all specimens that you will study come on prepared slides Often scientists have to produce their own slides This is a delicate process – improper preparation of a specimen will produce a slide that is difficult to study

Preparing a Wet Mount 1.A clean slide, cover slip, eyedropper, tweezers, water and a specimen must be collected 2.Handle the slide only by the edges 3.Place a drop of water in the centre of the slide 4.Lay the specimen on the drop of water 5.Carefully place the cover slip over the specimen, trying not to trap air bubbles underneath

Plant Cells

Animal Cells

Structures in Cells NucleusMitochondria Cell Membrane

Structures in Cells VacuolesCytoplasm Cell Wall

Structures in Cells Chloroplasts

Identifying Plant and Animal Cells Plant cells can be identified by two structures that are not present in animal cells: 1.Cell wall 2.Chloroplasts

2.3 – Organisms Can be Single- Celled or Multicelled The smallest kind of organisms known are called mycoplasma These are so small that they need to be viewed under an electron microscope They are single-celled (unicellular) organisms

Unicellular Organisms There are a number of different unicellular organisms: 1.Diatoms 2.Bacteria 3.Protists

The Disadvantage of Unicellular Organisms Unicellular organisms have to carry out all of their processes within a single cell This means that they also must absorb all of their nutrients through their cell membrane Therefore, the cells must remain small otherwise they cannot absorb enough materials to stay alive

Multicellular Organisms Multicellular organisms have tissues These collections of cells allow a “division of labour” With the presence of tissues, organisms can become larger – cells can be specialized to a single task These specialized cells often are dependent on each other

2.4 – How Substances Move Into and Out of Cells Recall from the particle model of matter that all particles are always moving This also means that various particles move across cell membranes The movement of materials across a membrane can come in one of three forms:

Diffusion Diffusion: Diffusion occurs naturally as long as the particles are small enough to cross a membrane Therefore, it requires the cell to use no energy

Osmosis Osmosis: Cell membranes are selectively permeable – they only allow certain materials to pass though Therefore, osmosis can occur across cell membranes

The Effects of Osmosis on Cells Isotonic environment (identical solute concentrations) Hypotonic environment (lower solute level outside the cell than inside) Hypertonic environment (higher solute level outside the cell than inside)

Active Transport This process requires energy Often this process is used to collect nutrients from the environment around a cell

2.5 – Cells Combine to Form Tissues and Organs Unicellular organisms are limited in size Therefore, when they reach a certain size, they divide as shown below:

Multicellular Organisms & Specialized Cells Although our body cells are specialized, they do reproduce in the same manner as unicellular organisms Our specialized cells gather together to form tissues There are three main types of tissues in animals:

Animal Tissue Types 1.Connective Tissue 2.Epithelial Tissue

Animal Tissue Types 3.Nervous Tissue 4.Muscle Tissue

Plant Tissues 1.Photosynthetic Tissues 2.Protective Tissues 3.Transport Tissues