cells: topic 2

Why do you need thin sections of a specimen when using a light microscope?

So that light can pass through

Why do you stain some specimens?

Most structures are not coloured and require staining to be made visible

What is a micrograph?

A light micrograph is a photograph of an image taken through a light microscope

Why would a light micrograph include a scale bar or image magnification?

So you can calculate three actual size of the specimen

Name 4 advantages of a light microscope

• cheap, easy to use and portable

• Natural colour is maintained

• Samples are easy to prepare

• Specimens may be living or dead

Name the 2 types of microscope

• transmission electron microscope (TEM)

• Scanning electron microscope (SEM)

Explicable how a Transmission electron microscope works

• a beam of electrons is passed through the specimen and focused to produce an image

• The wavelength of electrons is shorter than visible light

How large can the magnification of a TEM be

X500000 (much greater than light microscopes)

Negatives of a TEM

• very thin sections

• A vacuum so can only view dead cells

• Specimen must be stained with heavy metal compounds

• Sample preparations require great skill and may introduce artefacts

• Expensive

Explain resolution

• the ability to distinguish between 2 separate points and depends upon the wavelength used

Units

1 meter= 1m=1m=1m in a meter

1 centimetre=1cm=0.01m=100cm in a meter

1 millimetre=1mm=0.001m=1000mm in 1m

1 micrometer=1um=0.000001m=1000000um in 1m

1 nanometer=1nm=0.000000001m=1000000000 in 1m

Describe the structure of the nucleus

• consisting of a nuclear envelope (a double membrane) with nuclear pores

• Nuclear envelope is attached to RER

• Contains the genetic material and nucleolus

Describe the function of the nucleus

• allows mRNA to travel to the cytoplasm through nuclear pores

• The nucleolus manufactures rRNA and assembles the ribosomes

Descirbe the structure of the rough endoplasmic reticulum

• sacs made of membrane called cisternae

• Covered in ribosomes, the sites of protein synthesis

Descirbe the functions of the rough endoplasmic reticulum

The site of aerobic respiration (ATP production)

Describe the structure of the smooth endoplasmic reticulum

• Sacs of membrane called cisternae which is not covered in ribosomes

• Has a smooth appearance

Describe the function of the smooth endoplasmic reticulum

Synthesises, stores and transports lipids and carbohydrates

Describe the structure of the Golgi body

• similar to SER

• Forms Golgi vesicles

Describe be the function of the Golgi body

• modification and packaging of proteins:

— adding carbohydrate of proteins to from glycoproteins

— producing secretory vesicles

— secrete carbohydrates

— transports, modify and stores lipids

— forms lysosomes

Describe the structure of the mitochondria

• double membrane, the inner membrane is highly folded to form cristal

• The fluid inside is called the matrix

• Contains a small amount of mitochondrial DNA and small ribosomes

• They are self-replicating

Describe the function of mitochondria

The site of aerobic respiration (ATP production)

Describe the structure of lysosomes

• formed from vesicles produced by the Golgi

• Contains hydrolytic enzymes

Describe the function of lysosomes

• hydrolysing cells and organelles

• Exocytosis to release enzymes outside of the cell

Describe the structure of ribosomes

• 80S are found in eukaryotic cells

• 70S are found in prokaryotic cells, mitochondria and chloroplasts

• Consists of 2 subunits, 1 large and 1 small

• Made from ribosomal RNA (rRNA) and protein

Describe the function of ribosomes

The site of protein synthesis

Describe the structure of chloroplasts

• consists of a double membrane and a fluid filled centre called the stroma

• Flattered sacs of membranes, called thylakoids, stacked to form grana

• Chlorophyll is found inside the thylakoids

• Contains a small amount of DNA, small ribosomes (70S) and starch grains

• They are self replicating

Describe the function of chloroplasts

Absorbs light for photosynthesis

Describe the structure of the cell wall

• foun din plant, algal and fungal cells

• Found outside of the cell surface membrane

• Cellulose in plant ells

• Chitin in fungal cells

Describe the function of the cell wall

• supports the cell and plants as a whole

• Withstanding osmotic pressure