1.1 Introduction to Cells

Understanding:- According to the cell theory, living organisms are

composed of cells- Organisms consisting of only one cell carry out all

functions of life in that cell- Surface area to volume ratio is important in the

limitation of size- Multicellular organisms have properties that

emerge from the interaction of their cellular components

- Specialised tissues can develop by cell differentiation in multicellular organisms

- Differentiation involves the expression of some genes and not others in a cells genome

- The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development. It also makes stem cells suitable for therapeutic uses

Applications:- Questioning the cell theory using atypical

examples- Investigation of functions of life in

Paramecium and one named photosynthetic unicellular organism

- Use of stem cells to treat Stargardt’s disease and one other named condition

- Ethics of the therapeutic use of stem cells

Skills:- Use of a light microscope to investigate the

structure of cells and tissues- Drawing cell structures as seen with the

light microscope- Calculation of the magnification of

drawings and the actual size of structures shown in drawings and micrographs

Nature of science:- Looking for trends and discrepancies:

although most organisms conform to cell theory, there are exceptions

- Ethical implication of research: research

Robert Hooke

Create a Facebook page for Robert Hooke

Include:- Profile picture- Cover photo- Date of birth- What he did- What happened to him- Relevant status updates

Cell theory principles

1. All organisms are made of one or more cells2. Cells are the smallest units of life3. One cell can perform all functions of life

Cells vary in shape and size but have some common features…

Cell common features

1. Every living cell is surrounded by a membrane, separating the cell contents from everything else

2. Cells contain genetic material – storing all instructions for cell activities

3. Enzymes inside cell catalyze reactions

4. Cells create their own energy

Nothing smaller than a cell can survive on it’s own

Misfits

Do not fit cell theory

- Striated muscle- Fungi hyphae- Giant algae

Misfits

Describe the 7 functions of life - what do cells need to do to be classed as ‘living’?

How do giant algae, fungi and striated muscle not fit into the cell theory?

MISFITS

Unicellular organisms

How do they carry out some of the functions of life?

ParameciumChlorella

Function of life Paramecium Chlorella

Reproduction Divides transversely Divides transversely

Metabolism Metabolic pathways happen in cytoplasm

Metabolic pathways happen in cytoplasm

Homeostasis Manages water content using vacuole

Manages water content using vacuole

Growth Ingests food, grows and divides Ingests food, grows and divides

Response Cilia moves in waves = movement

Cilia moves in waves = movement

Nutrition Cilia sweep food into cell ‘mouth’

Photosynthesis in cytoplasm provides foodAlso ingests

Excretion Expel water containing metabolic waste controlled by

membrane

Oxygen waste controlled by plasma membrane

Also metabolic waste

Draw a picture of an animal cell

Draw a simple animal cell

Rules when drawing cells

Correct or annotate onto your diagram:

1. Sharp pencil2. Draw single lines not sketches3. No shading4. Label each structure with a straight line 5. Include a title6. Include the magnification or scale

Light microscope

Resolution

Low MagnificationGood Resolution

High MagnificationPoor Resolution

Microscope’s ability to separate objects that are close together so more detail can be seen

MagnificationMagnification is the process of enlarging something

only in appearance, not in physical size.

Quantified by a calculated number

The ratio of the size of an image to the size of the

object

Microscopes

Create a table to describe the key differences between the three types of microscopes:

1. Light microscope2. Transmission electron microscope3. Scanning electron microscope

Light Microscopes

Thin specimens

Requires staining

Limited magnification

Most commonly used

Living or dead specimens

Light Microscopes

Transmission Electron Microscopes

Thin specimens

Beam of electrons

Far greater range of magnification with much improved resolution

Expensive, used mostly in research

Dead specimens

Transmission Electron Microscopes

Scanning Electron Microscope

Beam of electrons

3D image

Crystal clear resolution at high magnifications

Specimens coated in heavy gold ions

Expensive, used mainly in research and specialist labs

Dead specimens

Scanning Electron Microscopes

Working out Magnification

Either:

Magnification = Apparent size of image Real size of image

Or:

Calculated by multiplying the viewing lens magnification by that of the objective lens

E.g. you have a x10 eyepiece and x40 objective, the total magnification is x400

Measurements are expressed in

micrometers (um)1mm = 1000 um

Calculating magnification & actual size

um

um x

Calculating actual size:

Calculating magnification:

Calculating magnification & actual size:

Magnification

Magnification = Apparent size of image Real size of image

Green blobs always measure 0.01 mm

Remember to convert into um

first1mm = 1000 um

30mm

Magnification

0.01 mm x 1000 = 10 um30 mm x 1000 = 30,000 um

Magnification = 30,000/10

Magnification = x3000

Green blobs always measure 0.01 mm

30mm

Now work your way

through the calculation

sheet

Cell drawings

Look at the drawing of an onion cell

Use the tick list on the page – do you think the cell is well drawn?

Use this to help you draw your own later!

Magnification Practical

1. Collect microscope2. Follow instructions – find pre-prepared cells3. Follow instructions – create onion slide4. Follow instructions – find onion cells 5. Draw onion cell using drawing rules 6. Label diagram and include magnification