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Cell Structure and Function

Practical Biology Biol 101

Lab 3

Hail UniversityFaculty of Sciences

Department of Biology

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The cell is the structural and functional unit of all living organisms.

Researches had formulated the cell theory that has three principles:

Robert hooke was the first scientist who look at cells under a microscope by viewing and describing the box – like structures of cork.

All organisms are composed of one or more cells.

The cell is the basic functional unit of living organisms.

All cells arise by division of pre-existing cells

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All cells share four structural

features:

Plasma membraneDelineate the border of the cellFunction in regulate the passage of

materials into and out of the cell. 

Deoxyribonucleic acid (DNA)Function as the genetic instructions

for the cell. 

Plasma membrane

Genetic material

DNA

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Ribosomes Function as a site of

protein synthesis 

CytoplasmComponents

enclosed by the plasma membrane by which the rest of organelles are floating.

Genetic material

DNA

Plasma membrane

Ribosome

Cytoplasm

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Cells vary in: Size

Function

Organization

With respect to internal organization there are two major types of cells according to the presence of nucleus.

Nucleus is the spherical organelle within the cytoplasm, which contain the genetic materials (DNA) and controls cell metabolism and division.

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Prokaryotic (before the nucleus)

Eukaryotic (true nucleus)

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Prokaryotic EukaryoticUnicellular unicellular ex. Protists

multicellular ex. Animal, plants and fungi

Small cell size (0.5 – 5 µm) Large cell size (5 – 200 µm)Don’t have organized nucleus surrounded by nuclear membrane and the DNA found free in the cytoplasm

Have organized nucleus enclosed by a nuclear membrane, the DNA found within the nucleus

Don’t have membrane bound organelles

Have membrane bound organelles ex. mitochondria

In this lab. We will examine a prepared slides of different bacterial cell shapes

In this lab. We will examine and describe cells of humans (animals) and onions (plants)

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Basic shapes of bacterial cells

1. Spheres (cocci)

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2. Rods (bacilli)

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3. Spirals

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Human cheek epithelial

cellsThe cells that line the inner check (inside the mouth) called epithelial cells, easily removed by:

1. With a clean toothpick, gently scrape the inside of your cheek several times.

2. Roll the scraping into a drop of water on a clean microscope slide.

3. Add a small drop of methylene blue.

4. Cover with coverslip gently.

5. Discard the used toothpick.

6. Examine under microscope and notice:

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•The cells are flat

•The nucleus will be blue

•The cytoplasm will stain light blue

•The cell membrane

•The cell appear as pentagons

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Onion epidermal cells

Prepare a wet mount of onion epidermal tissue according to the steps

Cut an onion bulb into quarters. Remove one of the fleshy scale leaves

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Fold the leaf backward to produce a ragged piece of epidermis.

Peel back a small piece of epidermis.

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Observe under microscope and notice

Add a small drop of Lugol’s solution, gently cover it by cover slip to avoid air bubbles

Spread the epidermis in a drop of water on a slide

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•The shape of onion cells

•The nucleus

•Cytoplasm

•The cell wall

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Cell wallCell membrane

Cytoplasm

Mitochondrion

Ribosome

Large central vacuole

Chloroplast

Golgi apparatus

Nucleus

Rough ER

Smooth ER

Plant cell

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Cell membrane Cytoplasm

Mitochondrion

Ribosome

Golgi apparatus

Nucleus

Rough ER

Smooth ER

Lysosome

Animal cell

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Animal cells compared with plant cells

Plant cell Animal cell

Chloroplast -

Cell wall -

Central vacuole -

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Thank You